Short stroking issues with my new build

[Apothus]

I just had my gunsmith put together my upper for me. It's an LAR Grizzly upper with their bolt carrier group and their bolt. The barrel is a 20" tube in 6.5Grendel from Sabre Defense with YHM gas block and a gas tube from Rainier Arms. While assembling the barrel, my 'smith had to tighten the barrel extension because it was finger loose. When it was properly tightened the gas port was no longer lined up straight to the feed ramps. I was very frustrated with that but I hoped everything would be ok.

Now, when my gunsmith went to test fire the gun for me, it short stroked with 2 different types of ammo. The bolt comes back to the shoulder of the next cartridge in the magazine and then stops. It does not extract the fired cartridge. My gunsmith also noted that the bolt carrier group is remarkably heavier then the standard carrier group. Here is my theory. The gas port is too small, and with the combination of a heavier than standard bolt carrier group, there isn't enough gas to cycle the gun.

Can you guys shed some light on why this would happen? If you agree with my theory of not enough gas flow, should I have him open up the port hole a little to allow more flow? If so, what measurement should the hole be opened up to?

 

[K_4c]

Re: Short stroking issues with my new build

possible...gas block may be misaligned with the gas port.

 

[jakhamr81]

Re: Short stroking issues with my new build

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Apothus</div><div class="ubbcode-body">While assembling the barrel, my 'smith had to tighten the barrel extension because it was finger loose. When it was properly tightened the gas port was no longer lined up straight to the feed ramps. </div></div>

I believe this is the main cause of your frustration.

 

[LSUbeatUby40]

Re: Short stroking issues with my new build

Nothing anyone in this thread hasn't told you, but the short stroking is because the gas port is not lined up correctly..

 

[M25BeastShooter]

Re: Short stroking issues with my new build

Send the barrel back the Barrel extension has to be torqued to the barrel and normally after that the gas port is drilled. If the extension is torqued after or loosened and re-tightened then its NOT going to line up 100%. If you're lucky they might be just off but it sounds like yours is WAY off.

 

[rcw3]

Re: Short stroking issues with my new build

One can jump to a lot of conclusions on the scenario you put forward, but the first thing I would say is normally whoever took responsibility of putting together the upper as a complete unit may not have done what was necessary in terms of the compiling and fitting of the parts together as a complete and functioning integral unit. Plain and simple the upper is a "Heinz 57" of parts from different makers and that's an issue right there. If you put an extra heavy bolt carrier group in with a barrel that is ported to function with a standard weight group, it may short stroke and you may need to change some things with the gas system to get it to function. If you purchased pre-made parts and upon torquing the extension on, it did not line up with the gas port correctly, then some work may need to have been done (and the operative word is "may") to make it so it did or the flow of gas is unimpaired (and who really knows where that stands with your upper - cannot determine that on this forum). What this all tells me is whoever put it together may not have known how to put an AR-15 together correctly. Anyone can just screw parts together but that's not what making an upper is all about. My advice, get someone who knows what they are doing with an AR-15 upper and have them give it a look over - that's what should have been done to it when it was put together in the first place. Bear in mind also, short stroking may have nothing to do with your upper too, as many times there are issues with lowers that can cause that. We build and test fire the uppers we make and sometimes you send them out and customers insist there is something wrong with the upper, and when you investigate further you find out they have a lower issues (i.e. they installed an extra heavy or extra light after market buffer or buffer spring, or used buffer parts that were not compatible dimensionally, etc.). Like I say, it's easy to jump to conclusions that may be wrong. An AR-15 is a total and integral functioning rifle and package, not just a mish mash of parts screwed together that in theory should work.

 

[Swift]

Re: Short stroking issues with my new build

You just need to take longer strokes and it will function 100% (most of the time)

 

[NoName2010]

Re: Short stroking issues with my new build

If the parts were mine, I would have sent the barrel, bolt, and whatever parts came with them back when the loose extension was discovered.

Obviously if the feedramps lined up with the barrel extension not torqued properly, they were never going to be aligned properly when the extension was tightened.

At this point, I'd say that the barrel and barrel extension still need to be returned to the Seller or Manufacturer. Otherwise, that barrel is never going to index correctly on the upper, with the front site base correctly positioned. The question of whether the gas port is correctly drilled the right size, and in the correct place can be visited at the same time.

 

[rcw3]

Re: Short stroking issues with my new build

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NoName911</div><div class="ubbcode-body">If the parts were mine, I would have sent the barrel, bolt, and whatever parts came with them back when the loose extension was discovered.

Obviously if the feedramps lined up with the barrel extension not torqued properly, they were never going to be aligned properly when the extension was tightened.

At this point, I'd say that the barrel and barrel extension still need to be returned to the Seller or Manufacturer. Otherwise, that barrel is never going to index correctly on the upper, with the front site base correctly positioned. The question of whether the gas port is correctly drilled the right size, and in the correct place can be visited at the same time. </div></div>

We do not know how much the extension overshoots the port, it may be very minor and of no consequence and resolvable if one just takes a chamfering tool and puts a small chamfer on the gas port as it exits the barrel (been there, done that, works great, should be done anyway as "insurance" to guarantee an unimpeded gas flow).

I know from putting on barrel extensions, you can put one on and torque it up, then drill the port, but if you take the extension back off then re-torque it to the exact torque setting as before you will typically overshoot the port by a small margin, but that does not make anything defective and it can many times be worked around.

 

[BOLTRIPPER]

Re: Short stroking issues with my new build

the brain trust is over at ar15dotcom



i would look for another gunplumber too

 

[rcw3]

Re: Short stroking issues with my new build

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BOLTRIPPER</div><div class="ubbcode-body">the brain trust is over at ar15dotcom

. . . </div></div>

Shucks - this is the forum for the dummies? Oh well, I guess we're at least in good company amongst ourselves.

In any case, considering how many potential items can cause short stroking in an AR-15 (and there are quite a few of them) I wish the guy good luck with his AR.

 

[SELPHB]

Re: Short stroking issues with my new build

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Apothus</div><div class="ubbcode-body">I just had my gunsmith put together my upper for me. It's an LAR Grizzly upper with their bolt carrier group and their bolt. The barrel is a 20" tube in 6.5Grendel from Sabre Defense with YHM gas block and a gas tube from Rainier Arms. While assembling the barrel, my 'smith had to tighten the barrel extension because it was finger loose. When it was properly tightened the gas port was no longer lined up straight to the feed ramps. I was very frustrated with that but I hoped everything would be ok.

Now, when my gunsmith went to test fire the gun for me, it short stroked with 2 different types of ammo. The bolt comes back to the shoulder of the next cartridge in the magazine and then stops. It does not extract the fired cartridge. My gunsmith also noted that the bolt carrier group is remarkably heavier then the standard carrier group. Here is my theory. The gas port is too small, and with the combination of a heavier than standard bolt carrier group, there isn't enough gas to cycle the gun.

Can you guys shed some light on why this would happen? If you agree with my theory of not enough gas flow, should I have him open up the port hole a little to allow more flow? If so, what measurement should the hole be opened up to? </div></div>

I would highly recommend not shooting the gun and send it back to the company you got the barrel from…..

Your head spacing is going to be way off and possibly dangerous creating way too much pressure. I would also not take anything back to the smith that did the work especially since it sounds like he didn’t even check for proper head space.

If you need any help let me know since Sabre Defense is no longer in business; the last I heard ATF shut them down for illegal sales of gun parts to foreign countries.

 

[Apothus]

Re: Short stroking issues with my new build

First i'd like to thank everyone for taking the time to reply to my question. i want to apologize for not explaining everything properly because i misunderstood what was happening and translated it wrong here. i assure you hes very competent and knows what he is doing. He made double sure to check and re-check the headspacing, which is correct.

we have decided to open up the gas port a little more to allow more gas to flow through. would anyone be able to provide me with a measurement number to aim for with the hole diameter? thanks again for the help, and sorry for crappy punctuation and capital letters, posting on my phone at work on lunch

 

[rcw3]

Re: Short stroking issues with my new build

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Apothus</div><div class="ubbcode-body"> . . .

we have decided to open up the gas port a little more to allow more gas to flow through. would anyone be able to provide me with a measurement number to aim for with the hole diameter? . . . </div></div>

20" barrel with std length gas tube and gas system = .093" port. Some go up to .098", but if you are not functioning with an .098" port, there's something else going on, don't just keep going bigger, or you will just wreck your barrel.

Before you do that, check to make sure the gas key is tight on your bolt carrier. One time I had a gas key that was loose due to someone over torquing one of the screws (broke the screw) and it cause an otherwise correctly ported rifle to short stroke. I would also check anything and everything you can think of that might be causing and interference with the carrier coming back to make sure it's not something dragging on the carrier assembly and causing a short stroking when the gas system is fine.

It's the "measure twice, cut once" principle, once you drill it bigger, it's bigger, and that's that. It's a little too late if you then find out the issue had nothing to do with the port in the first place.

Robert

 

[223Rem]

Re: Short stroking issues with my new build

Toss the barrel, that is where the issue lies, period! It sucked ass from the git go.

Take care of the obvious.

 

[pawprint]

Re: Short stroking issues with my new build

Your smith noted that your bcg was very heavy, this could be the cause of your problem. As this was noted during the build, I'd look right there first. Do you have another carrier? One you could swap bolts with and give it a try? Also, there are some bolt carriers that are made with extra weight-les baer makes one his, "National Match bolt carrier". Many shooter are using the "heavy" match bullets, the extra weight is a plus. Have you tried any 69gr loads? If the 69s work, and you already know your carrier is "heavy", you should be able to make a trade with someone carrier-carrier, as the heavy match carriers usually run around $50-100 more than a mil spec carrier. Go after the known problems first-you know your carrier is heavy, and your problem sounds as if your carrier isn't getting enough push, you may not have a big problem, just too light a load!

 

[Sniperhandle]

Re: Short stroking issues with my new build

Pull the gas block off, The carbon etc. should have left marks. My Friend had an Ar-10 that was short stroking and it turned out the gas block was not properly aligned. When we pulled the gas block off the carbon showed it was clamped on exactly a 1/2 hole off effectively reducing the size of the gas port by 1/2. My friend tried all kinds of things, like lopping off buffer spring coils one at a time, switching bolts etc, until he pulled off the gas block to discover the misalignment. its worth a look.

 

[kevin_j]

Re: Short stroking issues with my new build

I'd have to agree with a lot of the suggestions already brought up. But I just wanted to add one thing. What I see the most in this situation really doesn't have much to do with extension timing when both the ramps and the gas block don't align to 12' O'Clock with the receiver. That is usually because someone torqued the hell out of the flash suppressor which forced the extension pin under or into the extension pin receiver slot. That can cause gas leaks, but mostly ends up ruining the gas tube mushroom over time because the gas key is forced to move the tube when going into battery. This can also add to the amount of force necessary to unlock and move the carrier during the firing sequence.

I think the number one point of advice your going to find is to either send the whole upper back to the manufacturer or find a smith that specializes in the AR. It's really hard to diagnose issues without seeing the whole picture

It sounds to me like there might actually be more than one issue.

I suspect that if the ramps are leaning to the right as you look through the back of the receiver, when you pull the barrel, you'll find the Gas port and extension pin are actually aligned, but that the extension pin slot in the upper receiver is damaged on the right side as you look at the receiver from the front.

Let me know if I can be of any help!

--Kevin