Short Stroking Help

[NorCalFocus]

I have a new build that has a 16" barrel, carbine buffer spring, standard carbine buffer, and carbine gas system. I went out to test fire it today and had some issues.

-First 20 rounds were Federal XM193 and it shot a cycled fine. But on the last round it didn't lock the bolt back. (At first I thought it was a mag issue until I had the other issues)
-Next 20 was Tulammo 75g Steel Case. Bang, pull trigger and click, cycle bolt manually, eject, chambers into battery, bang. Repeat.
-Last 20 was hand loads that I've used in both my other AR's without any issue. Same as the Tulammo. Although I did have one of the 20 where it did cycle and chamber.

So I know enough to know its short stroking. I came home and checked the gas block and its aligned, the bast is a prefect circle around the barrel hole and the gas block hole. I also blew through it and fished wire through the gas tube to make sure it was clear from obstructions. I counted the coils on the spring, its 39 and it measures 10 3/4", so that checks out.

So where do I go from here? What are my options to fix this? Does a heavier buffer add more force to the spring to make it cycle? Can I drill a bigger hole in the barrel to give it more gas? Should I try a different spring?

Thanks.

[kevins750]

Is that gun lubed up real well?

[frahuang]

Check the spent casings, do they look shining or they have scratch or dull looking? Are the XM193 ones ejecting to 4 o'clock direction? May just need to polish the chamber, I assume it's a new build with new barrel.

[17+1]

[NorCalFocus]

I'll try lubing the hell out of it. It was a little dry. 3 different mags, all P-Mags. I was running a brass catcher so I don't know where they were ejecting.

Both the 193 and reload cases look normal. No scratches or anything. Maybe a bit dull.

[MrBlazito]

Try swapping buffer/spring from one of your other AR's

[BJames]

I have a mid length from Palmetto and was having short stroking problems. I played around trying everything people were recommending and it was still happening. Finally I threw a different bolt carrier group in there from another AR and it functioned perfectly. Luckily, Palmetto exchanged the problem Bolt Carrier group (nickel) and the replacement functions perfectly. Since you have multiple AR's, you may check this too.

[NorCalFocus]

So I went to lube my BCG up and found the gas key was loose. That's gotta be my problem. Leaking gas between the key and carrier.

Now that key shouldn't be coming loose. The key is staked but they didn't make contact with the bolt heads. I tightened the bolts back down for now. However can I put red lock tight on them? Or do I need the staked better?

[nate76239]

There are companies like Young manufacturing that don't stake their gas key screws

[NorCalFocus]

Short Stroking Help

Well I made a run out this morning before work and shot it again.

Tula Steel case still doesn't cycle all the time. My reloads worked pretty damn well. The mags still aren't locking open though. So it's either got to break in some more or I need to find a way to get more gas, less spring, or something.

[ar15barrels]

I have a new build that has a 16" barrel, carbine buffer spring, standard carbine buffer, and carbine gas system. I went out to test fire it today and had some issues.

-First 20 rounds were Federal XM193 and it shot a cycled fine. But on the last round it didn't lock the bolt back. (At first I thought it was a mag issue until I had the other issues)
-Next 20 was Tulammo 75g Steel Case. Bang, pull trigger and click, cycle bolt manually, eject, chambers into battery, bang. Repeat.
-Last 20 was hand loads that I've used in both my other AR's without any issue. Same as the Tulammo. Although I did have one of the 20 where it did cycle and chamber.

So I know enough to know its short stroking. I came home and checked the gas block and its aligned, the bast is a prefect circle around the barrel hole and the gas block hole. I also blew through it and fished wire through the gas tube to make sure it was clear from obstructions. I counted the coils on the spring, its 39 and it measures 10 3/4", so that checks out.

So where do I go from here? What are my options to fix this? Does a heavier buffer add more force to the spring to make it cycle? Can I drill a bigger hole in the barrel to give it more gas? Should I try a different spring?

Thanks.

Look at the top of the carrier where the gas key attaches.
Is there any gas leakage?
Lack of lube using "wonder parts" which claim not to need lube?
New PMAGS?
All new parts?

What is the gas port diameter in the barrel?

[NorCalFocus]

Look at the top of the carrier where the gas key attaches.
Is there any gas leakage?

No leakage. I did tighten the bolts down after finding they were loose last night. Can I lock tight them in place though?

Lack of lube using "wonder parts" which claim not to need lube?

No RF85 magic parts. I was little dry on the first run, but today it was well lubed.

New PMAGS?All new parts?

Pretty much all new parts. The upper had about 40-50 round on it with a different gas system, but other than that all new parts. Yes two brand new 30 round P-Mags and one lightly used 20 round P-Mag.

What is the gas port diameter in the barrel?

Just big enough for a 1/16" allen to fit inside. So maybe 3/32" of an inch at the most.


Like I said above, today it did do better. Hell the first single round of Tula locked the mag open. But after that it wouldn't cycle the Tula. Hand loads cycle okay, but I think I need another 1/4" of travel in the system to make it prefect.

[CoopsDad]

Are you absolutely sure the gas block is secure? Recoil can cause a seemingly tight gb to creep a bit, causing the port to be shrouded and restricting gas flow. Reposition the gb and make sure the set screws are in dimples to keep them in place.

[NorCalFocus]

Are you absolutely sure the gas block is secure? Recoil can cause a seemingly tight gb to creep a bit, causing the port to be shrouded and restricting gas flow. Reposition the gb and make sure the set screws are in dimples to keep them in place.

Yup I'm sure. Just took it off again to check the gas hole for Randal. Prefect circle, nice and alinged.



For $25 I'm thinking of trying this.

https://www.midwayusa.com/product/693755/tubb-speedlock-systems-flat-wire-buffer-spring-ar-15-rifle-stainless-steel

[ar15barrels]

No leakage. I did tighten the bolts down after finding they were loose last night. Can I lock tight them in place though?

Loctite won't help as the gas key can get well over 400 degrees in normal operation.
Torque and stake them.