Short stroke on new rifle

[SigLeader]

Hi, new here. I read other posts here, and white they were useful didn't fit my setup exactly. 

I am having an issue with short stroking. The bolt will not lock back after firing the last round, and will not consistently pick up a round. Picture of what happens (added more oil than is seen here later). Rounds do eject consistently.

I purchased a complete M5 upper and complete lower from aero precision. It is an 18" barrel with rifle length gas block. The gas port is on speck with the 0.089" size they say it should be. The gas block is lined up with the gas port. The BCG/bolt were well lubed before going to shoot. The bolt rings were set so they are not all in alignment. It is a rifle length gas tube with a carbine lower. 3.8oz buffer with aero precision 308 buffer spring. 

Any help would be greatly appreciated

Edited August 10, 2020 by SigLeader

[edgecrusher]

First thought out of the box is your recoil system is incorrect. The buffer weight is way to low. Can you give us some exact measurements of the buffer, spring relaxed with coil count and internal depth of receiver extension 

[SigLeader]

Internal depth of the buffer tube is 7", Spring is 12" with 25 coils, buffer is 2.5"

[98Z5V]

36 minutes ago, SigLeader said:

Internal depth of the buffer tube is 7", Spring is 12" with 25 coils, buffer is 2.5"

Buffer weighs 3.8oz, right?  Too light. The spring will suck, too.  Proper spring for an AR15 Carbine Receiver Extension (which is what you have) and the 2.500" buffers is the Sprinco Orange Spring.  You're borderline on the gas port diameter.  18" Rifle Gas is gonna need a little more than 0.089".  You need a 5.4oz buffer, or as close tothat as you can get, and the spring I mentioned.  I can give you a $20 option for the buffer situation, that will be way better than what you're running now. Requires a little work.

I know you say you lubed it up - but that thing is BONE DRY in that pic you provided, and that's never good for a large-frame AR.  They don't need "just a little lube" like an AR15 - they need to be borderline dripping with lube.  Heavy lube. 

First thing you need to try is to lube the hell out of it, and shoot it again.

Edited August 11, 2020 by 98Z5V

[SigLeader]

Ya that is a picture before trying it lubed up. I put oil that was dripping off and then it still did it. 

I am new to all of this, so excuse my ignorance. I thought that the larger weight and stiffer spring is for a over gassed set up, but you mention that the gas port is borderline small? Can you please explain the mechanism for what you think might be happening. So I can better understand. 

Aero precision today said that it might be under gassed for the spring since it is a rifle length gas tube with a carbine buffer tube. However, every thing I find says that should not be the problem. It seems like everyone (online) says that it will be an over gassed problem like what you are saying. 

I called springco and he wanted me to check the casing trajectory before he would recommend a spring. He didn't really think I had looked everything over in the gun. And was not convinced that the spring was the issue

So I stripped it again. Looking for gas leaks. There was a little leaking around the gas tube in the gas block, but the hole is lined up perfectly. The gas port is lined up perfectly. There is no leak around the gas key where it meets the bolt carrier, the BCG without bolt closes at less than 45 deg and the bolt will not go in the the BC with gravity. Without the spring the BCG sits clear of the bolt catch. 

 

Sorry for the long post, but I hope this helps explain where I am. (Lost)

[98Z5V]

9 minutes ago, SigLeader said:

 Can you please explain the mechanism for what you think might be happening. So I can better understand. 

Yeah, no problem - read this thread here:

 

[98Z5V]

17 minutes ago, SigLeader said:

It seems like everyone (online) says that it will be an over gassed problem like what you are saying. 

1st - I never said you were overgassed.  2nd - Everyone else (online) is incorrect, and probably don't know what they're talking about - not enough time on the system, to even understand it. 

You have two things going on - you're UNDERgassed and definitely UNDER-RECOILED.  You don't have enough buffer weight to control and Ass and Mass of a .308AR standard BCG, and your gas port is too small.  You're compounding problems with problems, here.

Read the thread I linked above.  Ask questions after you've read it.

Edited August 11, 2020 by 98Z5V

[98Z5V]

15 minutes ago, SigLeader said:

 Looking for gas leaks. There was a little leaking around the gas tube in the gas block, but the hole is lined up perfectly. The gas port is lined up perfectly. There is no leak around the gas key where it meets the bolt carrier,

You'll get carbon fouling on every single new AR that you build, no matter if it's AR15 or Large Frame.  That happens, every time. Until you build up enough carbone fouling to SEAL these parts - you'll have "gas leaks" - and it's no big deal.  Shoot the gun, create carbon fouling, seal your gas system.  That's part of the game.  Every one of them...

[SigLeader]

Thank you!  For your time and help! I think I found another problem. The spent casings stuck in the chamber. I put an unfired round in the chamber and it come out easily. So head space is good. Then I put a fired brass in and it stuck. Not just a little. I had to get a hammer to get it to budge. My buddy tried one of his spent brass in his chamber and it came out by hand. Mine had to be hammered out. 

 

 

 

[98Z5V]

If your buddy's brass wasn't fired from your gun, then that doesn't matter what his fired brass did in your gun.

Fired brass is expanded brass - that's why you have to resize it, before you reload it.  It's not uncommon for fired brass to NOT just slide right into a chamber.  Ammo differences, as well - so, your buddy fired his own brass, and then it was going into your chamber - was he firing the exact same ammo, loaded to the exact same pressures, as what you fired? And through the exact same barrel configuration, from the exact same barrel manufacturer?  Probably not.

You need to try to compare apples to apples, and not compare apples to hammers.  Doesn't work.

Don't try to invent tests for this stuff.  You'll only frustrate yourself, with findings that don't mean anything. Hope that makes sense.

Go drag yourself over to that thread link I posted, and get yourself ass-deep in it.  It'll help you understand.

Edited August 11, 2020 by 98Z5V

[SigLeader]

Actually the same type of factory ammo was shot in both guns. I barrowed some rounds from him to test with. To be clear the brass was tested in the rifle it was fired from in both cases. I normally reload and wanted to try a couple different rounds. 

Before picking up this rifle I did a lot of bolt action stuff. The only time I had an issue with brass sticking was when it was a super hot load or a problem with the chamber. While I do understand they are different worlds, Is it possible that there is an issue in the chamber that is causing it to stick and then that little loss in power causes a short stroke?

[98Z5V]

Go read the thread I linked in here... 

His chamber is not your chamber, his barrel is not YOUR barrel. 

Respond again once you've read that thread.  Until then, you're just searching, blindly, for information that we can't provide you.

Go get a grip on on the mechanics of this gun, recoil systems, gas systems... 

Go get your head around THAT information.  Then come back.

If you're gonna be lazy, and not take advantage of the information provided - I have nothing more to say. I'm done with this thread.  YOU go put the work in, now.  Or, whatever...  

Edited August 11, 2020 by 98Z5V

[edgecrusher]

11 hours ago, 98Z5V said:

Buffer weighs 3.8oz, right?  Too light. The spring will suck, too.  Proper spring for an AR15 Carbine Receiver Extension (which is what you have) and the 2.500" buffers is the Sprinco Orange Spring.  You're borderline on the gas port diameter.  18" Rifle Gas is gonna need a little more than 0.089".  You need a 5.4oz buffer, or as close tothat as you can get, and the spring I mentioned.  I can give you a $20 option for the buffer situation, that will be way better than what you're running now. Requires a little work.

I know you say you lubed it up - but that thing is BONE DRY in that pic you provided, and that's never good for a large-frame AR.  They don't need "just a little lube" like an AR15 - they need to be borderline dripping with lube.  Heavy lube. 

First thing you need to try is to lube the hell out of it, and shoot it again.

 

12 hours ago, SigLeader said:

Internal depth of the buffer tube is 7", Spring is 12" with 25 coils, buffer is 2.5"

This will need to be fixed even if the gas port is incorrect. Buffer is too light and spring is wrong. Having incorrect parts will only make matters worse. Manufacturers who are incorrectly drilling gas port size and then compensating for their mistake by using the wrong parts are a huge issue with large frame ar’s. 

[98Z5V]

11 hours ago, edgecrusher said:

Manufacturers who are incorrectly drilling gas port size and then compensating for their mistake by using the wrong parts are a huge issue with large frame ar’s. 

And the opposite is quite true - manufacturers that want to save money on a cheap, too-light buffer, whatever spring they throw in, and the compensate for that light buffer in this system by intentionally making a gas port smaller than it should be...

That's just cutting corners to save a buck, and hope most people won't notice.  That's what a company that sound like BS-Hay does... 

[Radioactive]

Think he’ll come back?

[SigLeader]

Sorry, rough day yesterday. I will have to order some parts and do some testing. I want to try a lower from a friend too as his works. However, he won't be back in town for another week. I will post my findings as I get more information. Thanks again for the help. 

[SigLeader]

So the issue ended up just being a dirty chamber. We thoroughly clean the chamber of all of the preservative they put on when it leaves the factory. I actually wasn't aware that that was there until I talked to my gunsmith. once we cleaned it out that problem I was having where the brass would stick after I put a fired brass back in completely went away the chamber was nice and shiny and everything worked well. Cycles perfectly will all the rounds I put through it. 

To help with recoil and to help extend the life of the weapon I will also change out the buffer spring and buffer when I get a chance.

[98Z5V]

This is good news, man.