Accuracy and Upper Receivers.

Potss

Full Member
Feb 16, 2017
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#1
So in Lowlight's most recent interview with Glen Seekins, Glen claims that on a normal AR upper loading the handguard with a bipod/sling/barricade can throw off POI by as much as "a couple inches at 100y" (at 2:50 in video). Frank seems to heartily agree with this sentiment. The claim seem to be corroborated by testing that was done some time ago on upper receiver flex under heat/stress throwing off POI by as much as .3-.5moa, not to mention by Robert Whitley.

So the claim is that while a normal upper will not generally decrease precision it can decrease accuracy because of POI shift as the upper flexes due to force on the handguard. While a noticeable POI shift would likely not occur off the bench, it may in competition or similar circumstances where significant force and/or heat are present. The secondary claim being that thick walled uppers and especially mono or polylithic designs mitigate this problem. Two questions for fellow hide members on these claims:

1.) Has anyone else experienced POI shifts like the ones mentioned by Glen and others above?

2.) Does anyone have experience with the Seekins IMRT uppers, or Aero M4E1 uppers, or the Vltor MUR uppers which claim to mitigate said POI shift?

Very interested for folks experience here.
 
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hlee

Sergeant
Jul 14, 2012
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#3
I load the bipod pretty hard and have never seen this. Not saying it can't happen, but I've not seen it. Maybe I don't load as much as I think...
 
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redneckbmxer24

Gunny Sergeant
Jan 15, 2005
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#4
I've had this happen in some rifles but certainly not the norm. Both of my two current precision AR15's are built on standard receivers and they shoot the same POI regardless of how the forend is supported or how hard I load the bipod.

I had one BCM upper that was BAD about this. Really bad.
 
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Potss

Full Member
Feb 16, 2017
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#5
Very interesting, this is what I hear and have seen personally as well. Seems very hit and miss. Maybe something like a MUR-A1 just makes it even less likely?

Anyone else have thoughts/experience please post up!
 

Blazin

Sergeant
Aug 6, 2008
368
3
18
Maryland
#6
I just watched the Seekins video a day or two ago and have been kicking this around in my head too. All of my precision builds use either Vltor or BCM uppers and I've been trying to think of an experiment to do to test the POI shift.

In the video Glen also poo-pooed the thermal upper/barrel fit which kind of surprised me.
 

hlee

Sergeant
Jul 14, 2012
938
158
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#7
I just watched the Seekins video a day or two ago and have been kicking this around in my head too. All of my precision builds use either Vltor or BCM uppers and I've been trying to think of an experiment to do to test the POI shift.

In the video Glen also poo-pooed the thermal upper/barrel fit which kind of surprised me.
Seekins has a product to sell...
 
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bigjake83

Golden Shellback
May 19, 2013
2,462
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Southern Idaho
#8
So in Lowlight's most recent interview with Glen Seekins, Glen claims that on a normal AR upper loading the handguard with a bipod/sling/barricade can throw off POI by as much as "a couple inches at 100y" (at 2:50 in video). Frank seems to heartily agree with this sentiment. The claim seem to be corroborated by testing that was done some time ago on upper receiver flex under heat/stress throwing off POI by as much as .3-.5moa, not to mention by Robert Whitley.

So the claim is that while a normal upper will not generally decrease precision it can decrease accuracy because of POI shift as the upper flexes due to force on the handguard. While a noticeable POI shift would likely not occur off the bench, it may in competition or similar circumstances where significant force and/or heat are present. The secondary claim being that thick walled uppers and especially mono or polylithic designs mitigate this problem. Two questions for fellow hide members on these claims:

1.) Has anyone else experienced POI shifts like the ones mentioned by Glen and others above?

2.) Does anyone have experience with the Seekins IMRT uppers, or Aero M4E1 uppers, or the Vltor MUR uppers which claim to mitigate said POI shift?

Very interested for folks experience here.

Potts.... I think you have seen enough of my builds and Range reports to know I've been on a Quest for the .25 MOA all day AR for a long time, and my last build was largely a success.

I don't know how many of you have paid attention to the tips and little trade secrets I've learned, but if you look back several years, you will see I talk about "Receiver Flex" long before it was ever talked about with Glen.

So basically the short answer to your question is Yes, but it's the Barrel that dictates the style of receiver needed. If you want a varmint style rifle with a 24" bull barrel I would strongly suggest a thick walled upper receiver from JP or a cheaper one from Mega. If you're running a lighter Slimmer profile Barrel like a Recon, you will be fine with a quality forged upper receiver.

When moving to a 18" barrel especially a medium Varmint Contour or a heavy H-Bar style Barrels I will use the VLTOR Upper Receivers.

Me personally I just run VLTOR Uppers regardless of barrel Contour or length all the way up to 20"and that just gives me a lot of Peace of Mind, mostly because I am very familiar with their consistent quality, and even though I send all my upper receivers away to have the face trude, none of my VLTOR AR uppers have actually needed it, they've always been true and tight from the factory.

There is more to the seekins upper receivers then most people know.

seekins-precision-irmt3-billet-upper-black-223-0010900011-by-seekins-precision-3df.jpg

Not only are they beefier like the VLTOR uppers, they have a huge amount of increased surface area surrounding the barrel extension that eliminates receiver Flex, and he also uses a true free-floating Barrel design where the handguard is not mated directly to the Barrel Nut but to the receiver, also eliminating POI shift upon applying torque to the handguard when shooting off a barricade or what have you.

The only flaw that I can find in his design is that he utilizes a steel external barrel nut. Due to the barrel nut surrounding the chamber area it's going to receive the majority of the Heat during long stages of sustained firing. The heat will pass through the barrel into the barrel nut and eventually dissipate through the aluminum upper receiver, causing a inconsistency to Cooling and essentially insulating the chamber area, but if he used a 7075 Barrel Nut, heat would pass through and bleed off consistently.

See Fourier's law.
 

flyer

Sergeant of the Hide
Apr 25, 2018
496
165
43
#10
I don't believe barrel weight has anything to do with POI shift because loading the bipod or slinging up puts far more stress on the barrel nut than the force of gravity.

Either way, the standard AR upper receiver barrel threads are puny so improving that is a really good idea. Once you beef that up by inverting the threads, I don't think the rest of the receiver needs much strengthening.

In terms of heat disapation, the standard barrel threads are puny leaving only a small path for heat conduction away from the barrel extension, the rest is surrounded by air which is an insulator so a steel reversed barrel nut is a small price to pay for the much bigger heat transfer pathway between the barrel extension and the enlarged snout.

I like the Aero enhanced uppers. I would be surprised if you need any more than that to eliminate the POI shift.

The stiffness of a tube is dominated by the O.D., not the wall thickness so as long as the exterior dimensions are similar, you don't need it to be heavy wall.

The other receiver/rail combos probably do it as well or better but anything is so much better than standard barrel threads that the differences hardly matter.
 

bigjake83

Golden Shellback
May 19, 2013
2,462
107
63
Southern Idaho
#11
I don't believe barrel weight has anything to do with POI shift because loading the bipod or slinging up puts far more stress on the barrel nut than the force of gravity.

Either way, the standard AR upper receiver barrel threads are puny so improving that is a really good idea. Once you beef that up by inverting the threads, I don't think the rest of the receiver needs much strengthening.

In terms of heat disapation, the standard barrel threads are puny leaving only a small path for heat conduction away from the barrel extension, the rest is surrounded by air which is an insulator so a steel reversed barrel nut is a small price to pay for the much bigger heat transfer pathway between the barrel extension and the enlarged snout.

I like the Aero enhanced uppers. I would be surprised if you need any more than that to eliminate the POI shift.

The stiffness of a tube is dominated by the O.D., not the wall thickness so as long as the exterior dimensions are similar, you don't need it to be heavy wall.

The other receiver/rail combos probably do it as well or better but anything is so much better than standard barrel threads that the differences hardly matter.
Puny, Snout, dominated ????

Is English even your first language?? because your Grammar is just as fucked as your understanding of basic physics.

Here I'll dumb it down for you.....

Take a Medium Heavy to a Heavy Varmint contoured Barrel and hold it straight out in front of you with just using your fingertips holding onto the barrel extension, then do that same exercise with a Recon barrel. The light should come on.. God willing, and you will understand about Receiver Flex, Barrel whip, Barrel harmonics, metal conductivity and expansion. The sheer amount of torque that is put onto the upper receiver due to the weight and leverage of a heavier Barrel.

Aluminum has a thermal conductivity of 237 (W/m.k)

And thermal expansion of 23,5 10E-6(k-1) from 0 to 100°C

Stainless Steel starts at 15!!! (W/m.k)

I suppose a stainless steel radiator in a vehicle would make sense to you as well right??

No one here cares about what you Think you know, and unless you can support your opinions with actual facts, keep them to your fucking self

It's because of people like you, and the blatant ignorance that spills out onto the Net that ruins this sport for most people, causing the uninformed to make poor decisions.
 

flyer

Sergeant of the Hide
Apr 25, 2018
496
165
43
#12
Yes, English is in fact my first language.

Puny means small.

If you have ever studied mechanical engineering, you would know that the stiffness of a tube is dominated by the O.D. as in the O.D. has much more effect on stiffness than the wall thickness.

If you've ever studied thermomechanics, you would probably know the difference between conduction, convection and radiation. You would know the heat transfer coefficients of aluminum, steel and air too.

When you suggest things that don't make sense, don't be surprised when you get called on it. When you can't understand the grammar used, that might be a clue that you've waded out beyond your depth.
 

redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
83
VA
#13
I just shot 4x 5 shot groups at 100 yards with my 224 Valkyrie which has a Craddock barrel with Seekins SP3R rail on a standard Aero receiver. I shot 5 shots at one dot controlling the load on the bipod as I normally do, 5 shots at another dot pushing into the rifle more each shot and then repeated the test for a second round. The two groups controlling the load shot as they normally do just making one hole a little bigger each shot. The two groups deliberately loading the bipod differently each shot had significant vertical stringing about 1-1.25" and one threw a shot out right more that didn't feel like I pulled.

I've got a Seekins IRMT-3 receiver and am ordering a VLTOR MUR right now. Once the MUR gets here I'll test this same barrel in all three receivers on the same day.
 

redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
83
VA
#15
The VLTOR MUR is ordered from Midway and shows it will ship tomorrow. There were really no discounts anywhere but Midway is running a $20 off $200 promo which was nice.

My Seekins IRMT-3 will hopefully be back from Seekins at the end of next week (minor issue with the index pin channel) and I'll get to testing them.

Tomorrow I'll be ordering a 11.5" 223 Wylde Bartlein barrel from Craddock for a pistol build that will probably find a permanent home in the VLTOR MUR receiver but I'll test it the same way with the Aero receiver as well. I won't be testing it on the IRMT-3 however since the only hand guard I have for it is 15".
 
Jun 1, 2017
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#16
This is very interesting. I have never really thought about this possible issue. I have always loaded the bipod on my ar’s relatively light because of the light recoil but this is something i will play around with when im punching paper with my 5.56 again... im not so much worried about this with my 8” 300blk sbr.. all it has to do is hit a coyote out to 250 yards and im happy lol
 

bigjake83

Golden Shellback
May 19, 2013
2,462
107
63
Southern Idaho
#18
You gonna have
The VLTOR MUR is ordered from Midway and shows it will ship tomorrow. There were really no discounts anywhere but Midway is running a $20 off $200 promo which was nice.

My Seekins IRMT-3 will hopefully be back from Seekins at the end of next week (minor issue with the index pin channel) and I'll get to testing them.

Tomorrow I'll be ordering a 11.5" 223 Wylde Bartlein barrel from Craddock for a pistol build that will probably find a permanent home in the VLTOR MUR receiver but I'll test it the same way with the Aero receiver as well. I won't be testing it on the IRMT-3 however since the only hand guard I have for it is 15".
The VLTOR will definitely make you happy happy happy.
 

Red_SC

Redheaded Stepchild
Nov 26, 2003
1,920
14
38
Florence, SC
#19
I just watched the Seekins video a day or two ago and have been kicking this around in my head too. All of my precision builds use either Vltor or BCM uppers and I've been trying to think of an experiment to do to test the POI shift.
@Blazin an easy test is to put a laser boresighter in the barrel, and watch the dot through your scope while loading your bipod. If the receiver is flexing, you will see the dot wander.

I use Aero sets in most of my builds, I feel it helps. I've also used Seekins and Mega with similar success.
 

Blazin

Sergeant
Aug 6, 2008
368
3
18
Maryland
#20
@Blazin an easy test is to put a laser boresighter in the barrel, and watch the dot through your scope while loading your bipod. If the receiver is flexing, you will see the dot wander.

I use Aero sets in most of my builds, I feel it helps. I've also used Seekins and Mega with similar success.
That’s so simple yet effective, thanks, will try that!
 

redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
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#22
The VLTOR MUR showed up this morning. I've known about these uppers for a while but have never had one in hand. Comparing it to a standard receiver it's definitely much heavier in the walls. Will be interesting to see how much of a difference there is.

At this point I'm just waiting on my IRMT-3 or a replacement to come back from Seekins. I'm hoping it shows up soon so that I can conduct this test before starting load development for the Valkyrie. I'd like to eliminate this potential variable before hand.

I also have a LMT MLR rifle in 224 Valkyrie on order. I obviously won't be able to do a direct comparison with the same barrels since it has a proprietary receiver extension but I'll conduct the same very unscientific test with it. I already know what the result will be since I've had several LMT MRP's and MWS's and they administer zero flex ever.
 
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Potss

Full Member
Feb 16, 2017
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#23
redneckbmxer24 still very excited for your results.

If anyone else on this board has experience with POI shift issues or wants to do a quick test to see if they can get their upper+handguard combo to shift, that would be excellent. The more data we can gather the better.
 

flyer

Sergeant of the Hide
Apr 25, 2018
496
165
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#24
I was just thinking about that and had my new Aero M4E1 enhanced upper out to bend a little.

I was specifically looking to see if I could spot any deflection behind the handguard interface section when bending left and right.

That's the area where the MUR and Seekins might have more meat than the Aero. It's the new "weak spot" due to the open bottom and ejection port cut. The old weak spot was the receiver threads because it was a thin aluminum tube and all of the handguard bending stress was loaded in to it through the barrel nut.

The result of my non-scientific bend test was very little deflection, not enough to localize in any one place.

I don't have a bipod or scope on it to see any deflection with a laser bore sight but in my hands it feels quite solid.

Once I have a bipod and scope, I'll try with a laser.
 
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redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
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#25
redneckbmxer24 still very excited for your results.

If anyone else on this board has experience with POI shift issues or wants to do a quick test to see if they can get their upper+handguard combo to shift, that would be excellent. The more data we can gather the better.
I'm still waiting on my Seekins receiver to come back but I decided I don't want to wait any longer. The tests won't be on the same day but they should be the same result regardless. I went ahead and tested the standard Aero mil spec receiver today that shoots great with a consistent load on it. Varying the load and really loading into it the results were pretty terrible. I tried to hold different loads and shot groups in different places. I used an Atlas bipod so that I could pan it side to side and see the effect and it pushed the shots sideways too. I'll post pics up a little later. I'll pull my barrel tonight or tomorrow morning and put it in the VLTOR.
 

redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
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#27
My Seekins IRMT hasn't gotten back yet but I've completed my unscientific testing of the standard Aero mil spec upper and the VLTOR MUR, and even factoring in some error the results speak for themselves. This was all done with the same 224 Valkyrie rifle and same optic, the only difference being the receivers

Please pardon my horrible handwriting and even worse arts and crafts skills.

In the pic you will see the two top targets labeled mil spec receiver. I didn't include a baseline/control for this as I've been using this receiver for several months and with a consistent load the rifle is sub 1/2 minute, sometimes sub 1/4 as you will see if you look up my load testing in the 224 Valkyrie thread... Yes, I just said sub 1/2 and 1/4 minute AR.

The left target was varying more and less load each shot for 15 shots, nothing consistently. Pretty much all shots broke clean but seeing as this was the first of all the tests I wondered how much of this could have been my error, I'll let you be the judged based on the ones with the VLTOR. I know there's some error but I don't think it's much. The strange thing here to me was how much the shift was left in addition to the accuracy opening up.

The right target was shot on another that had a few rounds on it already to I dialed .5mil low and shot 10 shots. For this I tried to load it far more than I normally do and fire 5 shots at a consistent load and then load it even more holding it and fire another 5. You can pretty clearly make out two different POI's aside from the 3 that are out a little. Once again POI shifted left more than anything but trying to hold a consistent load for 5 shots at a time I was able to maintain decent accuracy for most of the shots.



The lower row are all with the VLTOR MUR receiver. The receiver made a huge difference without a doubt. Everything was far more consistent but it still exhibited some shift which is to be expected. The shift was all vertical except for the two that I panned the Atlas each direction as well.

The bottom left is a 10 shot control group that I shot after firing a few rounds at another target to zero the new receiver.

The next target over is a 10 shot group fired loading more into the bipod each shot. The shots consistently tracked lower the more I pushed into it. It was very consistent and I was pushing into the bipod very hard towards the end, far more than anyone ever would in any scenario.

The two targets on the bottom right are with the Atlas bipod fully panned in each direction and loading very hard and varying the load. Like clockwork the POI was pushed left and right and vertical stringing was present just like the previous test.


For a non laboratory test I'm very satisfied with the results. At this point I doubt I will ever build a precision AR with a standard receiver again. I should be able to finalize this with the Seekins IRMT some time next week.



 
Feb 10, 2017
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Tuscaloosa, AL
#28
Looks like I’ll be building off a Vltor MUR if I end up building an SPR. So I’m guessing the lower reciver fot to the upper did not vary your shot consistency? I ask because I have a stripped Aero Gen2 lower that would be used. @redneckbmxer24

Looking forward to seeing results from the Seekins.
 

redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
83
VA
#30
Looks like I’ll be building off a Vltor MUR if I end up building an SPR. So I’m guessing the lower reciver fot to the upper did not vary your shot consistency? I ask because I have a stripped Aero Gen2 lower that would be used. @redneckbmxer24

Looking forward to seeing results from the Seekins.
I don't believe upper/lower fit makes as much of a difference as some do. In some positions I believe it can make some but prone with a little load on the bipod I believe it makes little if any difference. IMO the accuwedges or tension screws that only put upward pressure on the rear and do nothing for the slack in the front or the slop side to side are a gimmick. I do see some validity to bedding the receivers though, it certainly will not hurt anything.

The lower that I've been running for this rifle is one of my ole faithful LMT lowers that has had the stock 2 stage trigger swapped for a Geissele SD-E and the sopmod stock swapped for the Magpul ACS. It has a nice fit with my receivers but not tight, there's some play but it's minimal. Once I get the Seekins back and do the test with it I'll be bedding it to a Seekins billet lower that I also got for this build.
 
Feb 10, 2017
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24
Tuscaloosa, AL
#31
I appreciate the response. The testing is pretty eye-opening for me. Was considering a full WOA A4 upper build, but these results make me consider building an upper.

Kinda ironic as WOA is a known winner for High Power/XTC rifles. I guess their accuracy requirements and a scoped rifle requirements are different enough to notice a difference.

Any one here have a WOA upper that can shed light on this?
 

flyer

Sergeant of the Hide
Apr 25, 2018
496
165
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#32
Upper to lower slop might not be a big deal but a set of oversized takedown and pivot pins with reamed pin holes is the best way to get a zero stop upper to lower fit.

On a LR308 the pins are big enough to use an adjustable reamer. An AR15 probably needs a plain reamer.
 

SLG

Gunny Sergeant
Sep 2, 2009
515
133
43
#33
I have a MUR 6.5G upper that was built by MSTN about 5 years ago. It is a laser, and exhibits no real shift under various circumstances. I shoot it slung up, as well as off a bipod, and rested on a bag as well. No shift. With my Colt's, there is a shift.

With my KAC, there doesn't seem to be a shift, but the jury is still out on it.
 

redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
83
VA
#34
Upper to lower slop might not be a big deal but a set of oversized takedown and pivot pins with reamed pin holes is the best way to get a zero stop upper to lower fit.

On a LR308 the pins are big enough to use an adjustable reamer. An AR15 probably needs a plain reamer.
I'd rather have the wider and longer footprint of bedded receivers personally, I suppose fit pins and holes wouldn't hurt too but one of the other I'll take the bedding. The pins and points of the receivers around the pins will also be taking all of the stress from firing if there's a gap between the receivers. The pins are going to take a lot of stress regardless but at least with looser pins and bedding or no bedding some of that will be shared with the receiver surfaces.

Receiver fit is one of the last aspects of accurizing that I'm concerned with, IMO it's about the least important.
 

flyer

Sergeant of the Hide
Apr 25, 2018
496
165
43
#35
I clamped my receivers together while I was reaming and reamed very slowly with my tiny adjustable reamer until I had a very tight slip fit on the pins.

Now my upper can only pin in when it is in tight contact with the lower.

One grain of sand would probably keep it from pinning together, luckily it is very easy to wipe off the mating surfaces while the receiver is open.

It's good enough for me and less mess.
 

lennyo3034

Gunny Sergeant
Apr 18, 2010
1,644
82
48
33
Southern MD
#36
I'd rather have the wider and longer footprint of bedded receivers personally, I suppose fit pins and holes wouldn't hurt too but one of the other I'll take the bedding. The pins and points of the receivers around the pins will also be taking all of the stress from firing if there's a gap between the receivers. The pins are going to take a lot of stress regardless but at least with looser pins and bedding or no bedding some of that will be shared with the receiver surfaces.

Receiver fit is one of the last aspects of accurizing that I'm concerned with, IMO it's about the least important.
I'm no sure if this actually has an impact, but out of curiosity: what bipod were you using for this test? And what surface were you shooting off of?
 

redneckbmxer24

Gunny Sergeant
Jan 15, 2005
5,565
479
83
VA
#37
Concrete patio with bipod feet over hanging into the dirt to get grip. Atlas PSR bipod with Hawk Hill feet. I tested the bipod panned each direction as well, those rounds are on the bottom right targets.
 
Feb 16, 2017
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#40
Great results so far redneckbmxer24 I hope Seekins gets you your upper soon! It might be interesting to try a free floated bolt gun too as a control in the same test and see what the results are.

Anyone else is still welcome to share their experiences with POI shift on ARs.
 
Jan 15, 2005
5,565
479
83
VA
#41
Unfortunately the Seekins test isn't going to happen because I'm now 0-2 in getting them to deliver me a usable receiver. My Valkyrie barrel has been bedded back into the VLTOR receiver and will be staying in it and the Seekins going back for a refund.

I've got several bolt guns and have had a ton more, almost all free floated in chassis or bedded stocks and I've never experienced any shift. The only time you're going to have any change on a bolt gun is if there's something wonky with the action to stock fitment. They're steel receivers with a lot of meat on them, they aren't going to flex enough under any normal or extreme use to see any change.
 

bigjake83

Golden Shellback
May 19, 2013
2,462
107
63
Southern Idaho
#42
I clamped my receivers together while I was reaming and reamed very slowly with my tiny adjustable reamer until I had a very tight slip fit on the pins.

Now my upper can only pin in when it is in tight contact with the lower.

One grain of sand would probably keep it from pinning together, luckily it is very easy to wipe off the mating surfaces while the receiver is open.

It's good enough for me and less mess.
JP already makes custom Fit take down pins for this exact reason.

https://www.jprifles.com/1.5.1.7_small_tp.php
 
Nov 5, 2013
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#43
Great results so far redneckbmxer24 I hope Seekins gets you your upper soon! It might be interesting to try a free floated bolt gun too as a control in the same test and see what the results are.

Anyone else is still welcome to share their experiences with POI shift on ARs.
i found out the hard way in a match with my large frame...its a gibbz side charge upper, lower is an aero i believe, but it has a set screw in the lower to remove play between upper/lower

anyways...after having some misses on an EASY barricade stage that werent explainable (target was on a t post in a tall grass field so misses gave 0 feedback, but position/distance/target size were simple as it gets), i went to the range the next day at 100 yds and found that...

from atlas bipod on concrete/wood with my normal load (as much as the rubber feet allow)


using a bag under the rail on a barricade and loading into the magwell hard, my POI shifted .3-.5 low depending on how hard


using the same bag and backing the magwell off slightly, there was no percievable shift


removing the bag and just loading into the magwell, no perceivable shift...it was only present with the bag wedged

after verifying that a couple times back and forth i went up .1 and right .1


then fired these 2 groups...top is rail resting on the bag/barricade with little to no load into the magwell again...bottom is loading magwell into the bag/barricade...all aimed at the center dot


just for good measure i changed dots and went 3 more with a hard load into the bag/barricade aimed at the black dot


in my case, it seems pretty clear that the bag being wedged into the rail/lower magwell area cause a decent shift...this doesnt happen in my multiple bolt guns regardless of hard/soft load
 
Jun 13, 2008
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#44
And yet... I have shot my uppers in competition all over the Midwest, in everything from 25 degrees to over 128-degree mat temperature...

...and sling prone (egads!), where I sling in with probably twice the force any of you can put on a bipod without breaking it...

...but I never have more thatn 1/2 MOA shift in zeroes due to anything but wind.


I don't buy it, WE don't buy it, and it just isn't seen as often as the internet would say. The AR is not as easy to shoot well as a bolt gun, but witha float tube and some technique, it can really surprise the hell out of some people.

I'm not saying the impact shifts don't happen, I'm saying it isn't because of receiver flex or upper/lower fit. Bullshit. And believe it or not, I have an open mind about it.

-Nate
 

Potss

Full Member
Feb 16, 2017
527
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#45
natdscott I was hoping highpower folks would show up, because you do this all the time. This thread isn't about upper/lower flex, but about handguard putting pressure on upper at the threads which changes POI of barrel. The video and posts in the OP go into greater detail on this.

As you say though, a lot of highpower folks put a ton of sling pressure on the handguard and it doesn't seem to effect much. However, I'm not 100% sure where you attach your sling? Also the force put onto the upper with a sling vs. with a bipod might be a bit different due to the leverage points. But again, I just do not know.

I too have an open mind on this subject as it seems like I see evidence for POI shift in some cases and not others. Hence why I started this thread. The more data we can gather the better.

And morganlamprecht thanks for the post, that is interesting that the leverage of the bag seems to be causing it.
 

bigjake83

Golden Shellback
May 19, 2013
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#46
Potts...

I think this thread as been largely a success, whether it's the Barrell stressing the receiver or the handguard stressing the receiver, its pretty clear the the type of Receiver/Handguard Combo is a critical aspect.

A few years back we had some highly knowledgeable people on the Hide ( Semi Auto Guys), ALL of them have left the Hide now, and for good reason. There is too much shit information being regurgitated here and the uninformed are paying the price.
 
Jun 13, 2008
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#47
Potts, I'm not sure what you mean by "...[highpower folks]...do this all the time"...

My handguard float tube puts about as much torque on a receiver thread as is possible without causing issue with either my shoulder joint, or the rifle.

Our slings (Service) attach at the front of an A2 handguard (or at least the same distance). We apply both torsion AND "yaw"...X, Y, and Z axes. I can't tell you how much force it is, I just know that it will break the welds on sling attachment points, sling frogs, slings, sling keepers, etc.

I also know that, as long as I am on a Service Rifle, that tension is what gets me under 0.8 Minute hold. So I put up with it.

There is NO way a bipod is applying that much force on that many axes. Now I have no doubt that they BOUNCE (having shot them before some), and I have no doubt that loading them is of some use (having shot them before), and I have no doubt that it is easier for ME to shoot an AR well from a bag rather than a bipod, if I have no other choice.

I also know that a tighter upper/lower fit can help out the SHOOTER between their ears, and even slightly in repeatability of position in 3P stuff for kids who are not extremely consistent in their movements.

But same as it is with trick bolt carriers, the rifles don't care as much as the internet says.

It is very important with the AR to apply all the same forces from shot to shot, because the entire rifle lacks the "density" of a bolt gun, and the whole thing vibrates on firing enough that even gas-tubeless single-shot conversions have to be run very carefully.

It's a 2" gun that we try to make do 1/2". Some get that done, and some don't, but it ain't receiver thread flex that is making the difference.


-Nate
 
Likes: Rstrick0352
Jun 13, 2008
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#48
I wonder how much effect our use of glue, and/or oversized extensions/tighter receivers has on the whole thing?

Jake?

Some are nearly an interference fit, and the ones that are not almost universally get glued.
 
Nov 5, 2013
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#49
It is very important with the AR to apply all the same forces from shot to shot, because the entire rifle lacks the "density" of a bolt gun, and the whole thing vibrates on firing enough that even gas-tubeless single-shot conversions have to be run very carefully.
this is the issue...its nearly impossible to control all the forces and keep them the same on a rifle when shooting from prone/bag/barricade/rope/etc
 
Jun 13, 2008
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#50
this is the issue...its nearly impossible to control all the forces and keep them the same on a rifle when shooting from prone/bag/barricade/rope/etc
Bolt guns sure are easier.

But I just don't find that a good AR provides that many excuses either. I just don't miss enough more than I do with a bolt gun to evidence that idea.

Granted, I don't shoot off of roof tops or from barricades. But I sure have shot a lot off of logs, the sides of trees, lighting rod wires, piles of stone, hay bales, window frames, vehicle hoods, and just plain holding the rifles.

Best of luck to ya'll.

-Nate
 
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