Supported Bolt Carrier Group Hype of Not?

Yondering

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There are tons of references in those legacy things people don't use any more called "Books."

There are a few other web sites you can sift through (try Brian Enos for three-gun, and nationalmatch for highpower rifle).

John Feamster (author of Black Magic and one the USAMU loaders in the Custom Ammo Shop) holds a few National Bench Rest Shooter Association (NBRSA) and International Benchrest Shooter (IBS) "Official Screamer" groups (five shots in .099 at 100, or ten shots in .199 inches; five in .250 at 200, or ten in .449 fired in verified, scored competition) using ARs 'smithed by Bill Wylde. Zediker, Tubb, Sweeny, and McKee all have good books your library can get you for free.

There are lots of things you can do -- like bedding uppers to lowers; truing upper receiver faces and bolt faces; using forcing bolts from the bottom; using split pins; heating uppers and force-fitting extensions into the upper, etc. Expensive to do (billable gunsmith-time wise) that may or may not give significant improvement for a team of four to sixteen guys to maintain across five uppers each.

My advice is good for exactly what you paid for it. Whether or not you use it is absolutely and completely up to you. More than a few on this site say I'm full of chicken feathers.
Fella, I don't know who you are or what you've done, so all I can go by is what you're posting here, and you'll have to count me in the group that thinks your full of chicken something. I'm not seeing any useful contribution here from you, I'm just seeing an arrogant guy with a chip on his shoulder against gunsmiths.

Your assumption that anyone who disagrees with you must not read books makes you sound like an arrogant fool. I read 2-3 books a week on average, but that has little or nothing to do with the topic. There is plenty of information in books that completely counters your assertions as well. There's also plenty of good info online, like the Accurate Shooter link above. If you prefer to disregard guys like that who're actually building accurate rifles, that's your issue, personally I'll choose to try their tricks and see what works for me.

Claiming that things like shimming/bonding or thermofitting a barrel to an upper doesn't improve accuracy is silly; it's easily provable that it can, to anyone willing to try it. Obviously that doesn't help on every rifle; if you start with one that's already tight, it won't give the same improvement as comparing to a common "mil spec" upper and barrel extension. That's just one example of many tricks that CAN improve a rifle that needs it.
 
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RyanScott

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Firstly, you misunderstood his posts.

Secondly, the person you are speaking to once commanded the AMU.
 

RyanScott

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He might be right or wrong on something but he did earn some respect. He also gave a list of things you can do to increase accuracy which he didn’t think were worth the investment, but some may.
 

lennyo3034

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Expensive to do (billable gunsmith-time wise) that may or may not give significant improvement for a team of four to sixteen guys to maintain across five uppers each.
This is where I believe most of the disconnect on this thread lies.

A guy building one accurate rifle for himself is going to be willing to spend much more time than someone paying for a gunsmith to work on possibly hundreds.

I personally bed my barrel extensions and true uppers, but I have a very methodical process to do it. I can’t imagine the cost of paying a gunsmith to do it across dozens or more uppers.

I shoot my gas guns in local PRS type matches as well as gas gun specific matches. Mag fed .223 to 800+ is not the same as single loaded to 600.

I’m all for innovation and testing to squeeze the best accuracy possible, and have done a lot of myself. However my situation is completely different from Sinister’s and can’t base my builds around what he did nor can I fault him for building a certain way.
 

Charger442

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Does he need you to speak for him?
Not really. Carrier tilt with piston guns is not about how hard the piston pushes, but where it pushes. In a DI gun, the bolt does the pushing, and is aligned with the carrier. On a piston gun, the force is applied above the carrier at what is normally the gas key. That causes tilt.

What's being discussed in this thread is a different thing, that is more about how a loosely fitting carrier sits in an upper.

so i dont really know who Sinister is (seems to be given some deference by others here) and i dont know who you are, but your above statement slid by a lot of people already on here, and even though it did, its very inaccurate.

in DI and piston guns, whether it be gasses directed at the gas key by the gas tube, or a metal rod acting on a point similar to the gas key, the carrier and bolt are both "pushed" back at the same point on the carrier. if someone is saying there is tilt induced by this, its done similarly by both DI and piston guns.

now, what you claimed would be accurate for 9mm ARs and 22lrs which are direct blow back operation. and not direct impingement, like traditional ARs.
 

Charger442

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The gas doesn’t push on the key it pushes against the gas rings. The forces are in line with the bore.
well, technically, yes, but the force of the gas has to be turned down in the key. so you have a force component that hits rearward at the gas key elbow.
 

whatsupdoc

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The gas is directed between the bolt and the bolt carrier causing both to want to move away from each other. The bolt gas rings only provide a seal between the two. The bolt cant move forward so the pressure drives the carrier rearward causing the carrier cam slot to push on the cam pin rotating and unlocking the bolt.
 
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Charger442

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You're still wrong.
anyone know what a free body diagram is? The force from the gas impulse is not entirely parallel with the bore.

you cant have the force from the gas tube parallel to the centerline of the BCG, hitting into the gas key, which is above the line of the bore, and say that all the force is only acting along the center of the BCG.
 

Charger442

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It’s insignificant. Or does your exhaust manifold push your car into the ground?
well, we are discussing carrier tilt in a system using gas from an explosion. If someone is worrying about carrier tilt, and its significant enough to have "tilt", then the forces acting on it must not be insignificant.

and the answer is yes, exhaust would "push" your car into the ground, but it is insignificant and cannot be notice when compared to the force that gravity enacts on a vehicle whose mass is several orders of magnitude higher than a BCG.
 

Charger442

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It’s insignificant. Or does your exhaust manifold push your car into the ground?
and how can you call the gas force insignificant, when its the only force acting on the system, ignoring the spring force propelling the firing pin, and he force of the propellant at the bolt face when the lugs are locked.
 

srt-4_uk

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Are you taking into account the gas going through the bend in the gas tube? That should also give it a downward push since the tube bends slightly upward to go through the receiver.
 

sinister

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There are a few ways to center the bolt carrier group in the center of the upper with the firing pin hole coaxial with the center of the bore. Make a carrier with a large flange at the back end, bush the front end, and conically face the carrier to fit the end of the extension (a la LMT).

The carrier can't lock up so tight it prevents reciprocation to function.

You have three force vectors that change with every shot: the action spring pushing from the rear; the force of the magazine spring from the bottom (which varies at every shot from 30 to empty); and the force of the hammer as it hits not only the firing pin but pushes the carrier group into final battery.

Each and every mod can incrementally add to consistent lock-up.

The self-centering flange on the front end of an LMT enhanced carrier which mates into the receiver extension recess (M16):




AR-10/SR-25:
1576081172359.png

You can get anti-tilt buffers designed to help reduce tilting off-axis (advertised for piston rifles but can be used on direct-gas carriers, they fit into the rear of your carrier):

1576088982495.png


If I were to do anything else, I'd buy an LMT switch-barrel upper. You get the advantage of a long, heavy barrel shank secured to the upper over a longer distance at the cost of weight. Turn the barrel down in the front to compensate and you get a little more sinoidal whip.

The President's Match shoot-off at 600 yards at Camp Perry, fired with a sling, no sighters, 4.5X scope:

1576449806570.png
 
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Mike_in_FL

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Wow, just wow.
It is no surprise that the world is going to hell with the way we talk to each other, when we're supposed to be on the SAME side. I often wonder what would happen if certain groups showed up at a range together and realized who each other is, lol.
 

redneckbmxer24

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It is no surprise that the world is going to hell with the way we talk to each other, when we're supposed to be on the SAME side. I often wonder what would happen if certain groups showed up at a range together and realized who each other is, lol.
I'm near Tampa myself. Want to get a beer, smile, and call each other assholes?
 
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Mike_in_FL

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I'm near Tampa myself. Want to get a beer, smile, and call each other assholes?

LMAO, I know you live near me, I'm the one who told you to bring lube for Grandma in your infamous thread. A beer would be awesome although thanks to my ex-wives alienating everyone near them, I've learned to do quite well without any friends :).
 

Bball8703

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There are a few ways to center the bolt carrier group in the center of the upper with the firing pin hole coaxial with the center of the bore. Make a carrier with a large flange at the back end, bush the front end, and conically face the carrier to fit the end of the extension (a la LMT).

The carrier can't lock up so tight it prevents reciprocation to function.

You have three force vectors that change with every shot: the action spring pushing from the rear; the force of the magazine spring from the bottom (which varies at every shot from 30 to empty); and the force of the hammer as it hits not only the firing pin but pushes the carrier group into final battery.

Each and every mod can incrementally add to consistent lock-up.

The flange on the front end of an LMT enhanced carrier which mates into the receiver extension recess (M16):



AR-10/SR-25:
View attachment 7200148

You can get anti-tilt buffers designed to help reduce tilting off-axis (advertised for piston rifles but can be used on direct-gas carriers, they fit into the rear of your carrier):

View attachment 7200224


If I were to do anything else, I'd buy an LMT switch-barrel upper. You get the advantage of a long, heavy barrel shank secured to the upper over a longer distance at the cost of weight. Turn the barrel down in the front to compensate and you get a little more sinoidal whip.
Thanks Sinister, I appreciate your explainations. This thread has been informational and entertaining to say the least.
 

MontanaMan

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Well, I'm still scratchin' my head waiting for someone to post up some targets from the same gun with different BCG's that show any measureable improvement, or no improvement at all.

Cause so far, I haven't heard anything definitive one way or the other.

Trends, maybe; some "ought to's" but no data.

MM