AR short stroking

aric84

aric84

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Ok, first off I am new to the ar platform so bear with me.

I recently assembled a Stag upper and lower for my first rifle, the upper is a 20" heavy barrel and the lower is a plain jane stag. Both were used so I have no idea of their history.

I was shooting some AE 223 and was having trouble with the rifle occasionally short stroking causing a jam, and on the last shot, the bolt catch would grab the carrier rather than the bolt face.

I checked the buffer and it was stamped HH, so I am guessing it is a heavier one than standard. I swaped it out to a standard one from another butt stock I had around. I have not tried it since but am wondering if there are any other causes I should be looking for?
 
Having just been through this this is the gas port requirements for the Ar platform
* 10.5" - .093
* 11.5" - .081
* 14.5" - .063
* 16" - .063
These are All Car Length Gas ports but with a 20 inch I've seen different sizes do some google work check what size the gas port is on the barrel make sure you are using Good ammo etc and use the same mag
 
BattleRife said:
Is it a fixed stock or collapsible?

Check to ensure your gas key screws are tight, if loose the key can leak.
Click to expand...

It's a collapsible stock. I'll look at the screws tomorrow, thanks for the tip. Failing this I might have to check the port diameter somehow. I may change the gas block since it is a low profile and I'd like to put a standard or railed one on to have a front sight.
 
If it's not a pinned low profile gas block make sure it is aligned propperly. If it is not aligned perfectly over the barrel port it could be cutting off some of the gas.
Also since you say it is all used stuff check that the gas tube is clear.
Lube the bolt and carrier with oil not grease for winter months and make sure the gas rings are installed. You should be able to stand the bolt and carrier assembly on the bolt face with it extended and the bolt should not slip into the carrier. If it does change your gas rings.
Other than that ensure you have a carbine length spring and buffer in your carbine length tube.

Good luck
 
The C7A2 uses an HH buffer and it's a 20" barrel so I think your ok there. If I took a guess it's either a loose gas block or a problem with your Bolt or carrier (gas rings, loose gas key)
 
Well, everything looks good on the bolt and the gas block looks like it is pinned straight.

I think the culprit is the buffer spring itself. I had a spare carbine stock and buffer around so I changed out the spring and now the bolt seems to go back further than before when pulling the charging handle. Upon closer inspection, with the old spring in, the bolt face would just clear the bolt catch enough for it to engage. With the new spring the bolt face has about 5mm between the face and the catch when pulled fully back. I'm guessing the the old spring was maxing out and bouncing the bolt back prematurely, causing the short stroking.

I'll try it out with the shorter spring this weekend and post back, hopefully with a success story!

Thanks for all the help guys.
 
Looks like that may be the case, it was longer than the other one that I grabbed out of the other carbine stock I had. My lower looks to be a bitster(buttstock looks to be a ruger one), so it may have never been tested before I bought it. Hopefully the shorter spring will sort the issue out.
 
The gaps on the gas rings on the bolt have to be misaligned. I never quite realized how important they are for proper functioning until I saw an animated *.gif of the M16/AR15. The gas from the gas tube expands inside the bolt carrier against those rings, and which act like the gas chamber on an FN C1A1 (just to date myself). No one really explained it thoroughly enough.

Secondly, I find service guns work well when the bolts are heavily lubed. You can always wipe off what splatters out, but you can't put oil where it never was. I know this from a particular military range qualification when we drew rack rifles and bolts, then had stoppages up and down the firing line. Someone found a little squeeze bottle of CLP and we used it up on all the bolts. No more problems.
 
northmedic2075 said:
Having just been through this this is the gas port requirements for the Ar platform
* 10.5" - .093
* 11.5" - .081
* 14.5" - .063
* 16" - .063
These are All Car Length Gas ports but with a 20 inch I've seen different sizes do some google work check what size the gas port is on the barrel make sure you are using Good ammo etc and use the same mag
Click to expand...

No need to measure a Stag Arms gas port. ;)
 
dangertree said:
A2 Rifle Stock Action Springs and Carbine Action Springs are a different length. Using the correct spring will solve this.
Click to expand...

A2 Rifle receiver extension: return spring 12.5" nom free length
Carbine receiver extension: return spring 10.7" nom free length

Ref: C-71-295-000/MY-000 (C7-C8 PARTS CFTO)
 
Well, tried it out again over the weekend and it was still short stroking, but got better toward the end of the session. I lubed the bolt a bit more and it seemed to help. I'm wondering if it may also be the magazines(LAR 15 mags). Going to try and source some regular mags but not sure who has some good reliable ones in stock.
 
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