Accuracy and Upper Receivers.

bigjake83

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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.
Yes it is critical to have proper fitment with the barrel Extension and Receiver. If you don't want to spend the extra $60 for a oversized barrel extension, then use High Temp Red Loctite. If we are talking about a Precision Rig then don't Half Ass it! Polishe the Barrel extension to a mirror finish, true your Receiver Face (by a Professional) and Bed or Thermal Fit the Barrel, make sure to season the receiver theads and apply some Anti Seize, and lastly don't over torque the barrel nut, 50-65 FTLBs is ideal.
 

natdscott

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...and lastly don't over torque the barrel nut, 50-65 FTLBs is ideal.
My opinion has always been that..for the price of a lot of barrel nuts, when you reach proper torque, just cut out anything that's in the way of the gas tube. I know that isn't always an option, but if it is, it makes sense.

They are a HUGE increase in cost over a mil-spec M4, but the "comp" extensions aren't $60.

The proprietary 20TPI from Holliger is $42: https://www.whiteoakarmament.com/competition-barrel-extension-m4.html I used one on my 1,000 yard upper. Works fine. Probably entirely unnecessary, but man it checks a box for the ticky, and I do think the finer threads are a good idea.

BAT Machine's is only $31, and is standard dimensions, albeit a little larger shank, depending on which you roder, 1.000" or 0.999". I cannot for the life of me figure out why a guy spec'ing out an accuracy AR would NOT call BAT and get one of these. Given the rest of BAT's work, the extensions are probably dimensionally perfect.

https://www.batmachine.com/batactions/ar-15/

I DON"T have a BAT extension to prove that to myself, but if you've never seen a lathe-built Remington 700 action screw, man their's are truly a work of art.

Pair a 0.999" BAT with a BCM tight receiver, and there wouldn't BE any bedding. I don't think you'd get a 1.000" in without turning some material off the shank, or nitrogen fitting.

-Nate
 

whatsupdoc

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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.


What is the issue with the Seekins upper?
 

padom

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My opinion has always been that..for the price of a lot of barrel nuts, when you reach proper torque, just cut out anything that's in the way of the gas tube. I know that isn't always an option, but if it is, it makes sense.

They are a HUGE increase in cost over a mil-spec M4, but the "comp" extensions aren't $60.

The proprietary 20TPI from Holliger is $42: https://www.whiteoakarmament.com/competition-barrel-extension-m4.html I used one on my 1,000 yard upper. Works fine. Probably entirely unnecessary, but man it checks a box for the ticky, and I do think the finer threads are a good idea.

BAT Machine's is only $31, and is standard dimensions, albeit a little larger shank, depending on which you roder, 1.000" or 0.999". I cannot for the life of me figure out why a guy spec'ing out an accuracy AR would NOT call BAT and get one of these. Given the rest of BAT's work, the extensions are probably dimensionally perfect.

https://www.batmachine.com/batactions/ar-15/

I DON"T have a BAT extension to prove that to myself, but if you've never seen a lathe-built Remington 700 action screw, man their's are truly a work of art.

Pair a 0.999" BAT with a BCM tight receiver, and there wouldn't BE any bedding. I don't think you'd get a 1.000" in without turning some material off the shank, or nitrogen fitting.

-Nate

I dont use BAT extensions anymore because of how sharp the back side of the lugs are. Just takes nasty chunks of brass out of the cases on extraction. Now you can take a Dremel 520-02 Impregnated wheel and polish the back sides (as suggested by JP) to smooth them out which I have done and works. Pain in the ass when the extension is already on the barrel and make sure you flush everything thoroughly.

I now use JP extensions only. They are already polished and coated and are smooth as butter. Yes, they are more expensive but the best extensions I have handled.
 

padom

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I just put my 20" Keystone Kreiger 1:7 .223 Wylde in a MEGA SBU Billet upper and lower with a YHM 15" TJ Competition handguard. Talk about a tight fitting upper/lower and a beefy upper. Thats an understatement. I honestly though the upper/lower didnt fit together till I got it perfectly straight up and down and pressed it into the lower. Ive built a lot of AR's from all kinds of forged and billet receivers but this is by far the tightest set EVER.

On sale at JSE Surplus right now. Hard to beat this price for one beefy, tight fitting setup.


Regular MEGA SBU Upper

http://www.jsesurplus.com/AR-15SBUBilletUpperwithoutSideChargingHandleSlotJSEEXCLUSIVE.aspx

Side Charging MEGA SBU Upper

http://www.jsesurplus.com/AR-15SBUBilletUpperwithSideChargingHandleSlotM0300JSEEXCLUSIVE.aspx

MEGA Billet Lower

http://www.jsesurplus.com/megaarms-4-1-1.aspx
 

natdscott

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I dont use BAT extensions anymore because of how sharp the back side of the lugs are. Just takes nasty chunks of brass out of the cases on extraction. Now you can take a Dremel 520-02 Impregnated wheel and polish the back sides (as suggested by JP) to smooth them out which I have done and works. Pain in the ass when the extension is already on the barrel and make sure you flush everything thoroughly.

I now use JP extensions only. They are already polished and coated and are smooth as butter. Yes, they are more expensive but the best extensions I have handled.
I do exactly what you quote.

Ordering John Holliger's 20TPI extension a few weeks before the barrel blank arrives, I, uh "work on it" to deburr and polish everything I see that needs it, with the obvious exception of load bearing surfaces, threads, etc.

It also gives me a chance to test fit in the upper, and to hand-fit the M4 extensions to the receiver to create one 'seamless' polished ramp.

Works.

My most recent one is on my 1,000 yard upper, and that brass needs all the integrity-help it can get!

-Nate
 

Potss

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Feb 16, 2017
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Excellent replies so far folks, thanks. Still hoping more people will actually get out there and do some testing, and maybe post pics. That would really lend some more credibility to these claims.

Quick side note, what are people's thoughts on lightweight uppers? Surely going in the opposite direction of the Vltor or DPMS (who make the walls thicker) would exacerbate the POI shift? For example, the 2a Armament Balios lite is quite light, and I wonder if it is more vulnerable to said POI shift.
 

flyer

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If you make the upper too light, it will try to bend between the takedown pins and curl the Picatinny rail slightly.

It would probably be less of an issue than bending at the barrel nut but both will be factors and on an upper like the Aero M4E1 enhanced, it's probably the only thing that changes POI when loaded.
 

redneckbmxer24

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Figured I’d post this here. SKD is doing a 24hr flash sale on the VLTOR MUR receivers for 20% off and then already have about the lowest prices on them.

Link here.

Add to cart for the sale price. The forward assist version is $143.97. The non forward assist should be a bit less.
 
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Mike_in_FL

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It seems like I've encountered this issue with a .300 BO recently. I could get no consistency and POI seemed to move around. There was nothing lose, no bad scope, yada yada. I ended up replacing the barrel with the same results and installed an AGB more in an effort to preserve brass.

What I did notice was that in using a Badger 22 moa base it extends out onto the rail over the barrel nut. The rail on this upper attaches like the MI do, you have two bolts on the bottom that clamp over the barrel nut. As it turns out when you install an AGB on a pistol length gas system and have a 13" rail you can't reach the torx on the front of an SLR.

So I wanted to remove the rail at the range to adjust the AGB. And it wouldn't simply slide off removing the two clamping bolts. I ended up hitting the top of the rail with a file to provide a little clearance and my groups have improved substantially. I can only guess that the downward pressure of the Badger base on the rail directly above the barrel nut was the culprit.
 

buffalo hump

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Apr 14, 2019
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A preface: I am a new member and have never replied to any of several forums that I have perused over the past several years but this thread while becoming somewhat old is as relevant going forward as ever given the evolving nature of the ar platform. So, I figured I would give it a go. I spent many years learning and developing my shooting and technical rifle knowledge in pursuit of the lowly ground hog beginning in my college days in the early 80's prior to invasion of canis latrans who saw to the demise of the furry favorite and in doing so elevated himself to the position of numero uno in the local rifleman's target aspirations. Back in the day we turned brass, weighed cases, bedded rifles, spent obscene amounts of nearly 100.00 for aftermarket triggers in order to score long distance hits on marmota monax. In other words we wasted a lot of time cutting bait and not fishing but it was fun. Now to the subject at hand, we learned accuracy technicalities and how to progress in that endeavor from benchresters who were on the cutting edge of the sport. Back then as now it was known that action stiffness was everything. It was determined that even the venerable remington 700 after being blueprinted was lacking in that parameter when competition got tough hence the receiver sleeve. This gave rise to an entire industry of over built and geometrically redesigned actions to improve the aforementioned weaknesses of barrel deflection, barrel harmonic disorders and ultimately translating to improved accuracy (read as match wins and bragging rights). These incremental successes were measured in 1000's on the target. Fast forward 10 years when someone got the idea to chop the handle off an ar, replace it with a weaver compatible pic rail and mount a scope alas a hunting rifle! And to beat all they shot phenomenally. My first colt hbar with military trigger would go 3/8" with handloads leaving us all mouths agape and scratching heads. So, we fast forward to today after light speed refinement of the platform and to a point in time where people are starting to look at this rifle in the same light a benchresters were the turn bolt in the 60's and 70's. Yes Virginia, action stiffness is everthing! The ar was a late 50's design if I recall which came to fruition in the early 60's. Given the inexperience of working with aluminum for such a purpose as a firearm and the limited (by todays cad standards) machining capabilities its ultimate success is astounding. But the platform was engineered to carry a lightweight barrel of 18 to 20 inches or so and its accuracy requirements for a battle rifle was laughable by todays standards. We are now hanging longer heavier barrels in addition to cantilevering floating handguards on an action whose design team never fathomed such things. And all of these exorbitant forces come to bare on the lowly trunion at the face of the receiver. To exacerbate the issue the handle has been removed which gave significant support in terms of resisting receiver flex. Don't agree with this, just ask any Detroit auto engineer the challenges of body flex after chopping off the top to make a convertible. As an owner of a mil supplier aka mil spec receiver unit by defunct sabre denfence I can attest to the poi shift gremlin first hand. The unit I am referring to wears a 24" heavy fluted match barrel capable of veeeerrrry good accuracy. But depending on how it is bagged (I never shoot for group size with a bipod) poi shift can be an issue. Any bench'er will tell you that a rifle which is split into two pieces in the middle, joined by hinge pins, most often rattles at the juncture between the two halves, and when trigger is pulled undergoes what one old shooter friend termed an "eternity of monkey motion before primer strike" is the worst of all evils to shoot small groups with. But lets stick with the receiver and trunion issue. To bring this diatribe or novella to an end may I say that being semi retired and self employed, being blessed with living in open country and no close neighbors I have the luxury of shooting every day if I choose. I have at my disposal many of the top brands, phenomenal optics (which brings another fly into the ointment of accuracy in how people now a days never question their OPTICs ability to shoot small groups but that is for another day) and ultimate add on accessories to eliminate human error. Of everything I have shot and studied there are three manufacturers that come to mind and who appear to be addressing this receiver weakness issue and move the platform into truely a 21st century ar and away from the 20th century mil-spec weaknesses. Oops I am running out of space..... to be continued
 
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buffalo hump

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Apr 14, 2019
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this wrap up will be short and sweet, I laud the engineering inventiveness of seekins in their irmt 3 upper along with aero prec'n and their enhanced upper unit. In addition, pof and their critical examination of the weakness of the mil spec design and their engineering improvements to overcome those have greatly impressed me. I have several of the aforementioned and can whole heartedly attest to their success. In closing may I refer everone to a brilliant gentleman who goes by the name "varmint al". All should go to an peruse his eclectic website. He is a retired engineer from Sandia National Research Labs and a experienced shooter and coyote hunter. He has put together what amounts to a library of informative and entertaining information the likes of which will never be seen again and can only be likened to the Library of Alexandria of ancient lore only this dealing with rifles and shooting. It is here you will find countless data backed by scientific testing on action stiffness, barrel deflection as a result of length, mass, and diameter along with new data that really explains the gremlin of barrel harmonics. In college my biochem prof said "you can't be expected to remember everything so just know where to go to find it" (pre computer and google days). Thanks to Varmint Al for all your hard work you would make my physics and biochem professors proud. AAAhhh the effort to shoot small groups Carry on.
 
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buffalo hump

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flyer you are so right, my technical writing teacher is turning in his grave. Please excuse but this is my first attempt at popular casual prose after spending an entire career of ocd laced technical/scientific writing. And honestly, it feels good to violate the laws of of proper penmanship. Just hope this might help somewhat since we are all in this for fun. I promise to do better should I post in the future. God Bless.
 
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Almonz

Sergeant of the Hide
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Seems like you'd have to be putting an incredible amount of force on a bipod to have any measurable POI shift. I don't buy it until I see hard evidence in more than one case.
 

Back Spin

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It doesn’t take much pressure to change POI depending on the upper. On a couple of standard uppers, when I use sling support (not even super tight) I definitely see a low hit compared to the called shot (about 1.5 MOA low).
 

Potss

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Thanks for the the introduction to Varmint Al buffalo hump.

Almonz, that is what this thread is all about. Trying to get some actual data on this effect. It is clear shifting happens under load, and effects both POI and accuracy. What isn't clear is to what extent, how much load is needed, and how much solutions like thick walled uppers/mono/polylithic uppers like Aero M4E1, Seekins, POF, and Vltor actually mitigate it. My own experience says the load doesn't need to be THAT significant on a normal upper. If I had the time and the budget I'd just buy them all and get to work, but I personally don't so think of this thread as crowd-sourcing data of which we've already had two good tests on the first page.

So open invitation to anyone who has an AR, shoot a control 5x5 and then put some load on the handguard and shoot another 5x5 and show the results, lets see what the data shows.
 
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