Help with Short stroking rifle

Balzer94 · Mar 24, 2020

I have an Ar-15 that is short stroking 1 to 2 times per magazine with the occasional failure to look open on an empty magazine.

With factory ammo I had not noticed any problems. I tried making some reloads and am currently at the high end of the powder range and still having issues. (Note these reloads worked well in my other rifles).

I checked the easiest thing first, the gas rings look fine. I took off the hand guards and see quite bit of what looks like carbon, coming from the gas block, on the barrel. I pulled apart one of the other rifles that was working and there is absolutely no carbon on the barrel coming from the gas block.

This rifles is a bcm upper. 14.5’ barrel,Mid length gas system, with an A2 front site base gas block, and a spikes tactical T1 buffer(weight is 2.99 ounces).

Thoughts on things to check? Should I replace that gas block? The rifles had probably somewhere between 500-1000 rounds through it.

Balzer94 · Mar 24, 2020

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tallen702 · Mar 24, 2020

What powder, primer, and projectiles are you using in the reloads?

Balzer94 · Mar 24, 2020

tallen702 said:
What powder, primer, and projectiles are you using in the reloads?

19.5 grains of hodgdon h4198, federal Small rifle primers, 55gr fmjbt w/ cannelure. Rounds are crimped

danb · Mar 24, 2020

if you had no problems with factory ammo, then its probably not the rifle. i think you have to look at the powered, projectiles, etc.

Balzer94 · Mar 24, 2020

danb said:
if you had no problems with factory ammo, then its probably not the rifle. i think you have to look at the powered, projectiles, etc.

Could the leaking from the gas block not be a problem?

danb · Mar 24, 2020

Balzer94 said:
Could the leaking from the gas block not be a problem?

Why would that affect your reloads and not factory ammo?

danb · Mar 24, 2020

also, did you chrono your loads?

SKIP · Mar 24, 2020

Balzer94 said:
19.5 grains of hodgdon h4198, federal Small rifle primers, 55gr fmjbt w/ cannelure. Rounds are crimped

I had the same problem using 4198. I would say it's the powder.
The remaining rounds I used in slow fire. Never in rapid fire stages for fear of the problems you described.

Balzer94 · Mar 24, 2020

danb said:
Why would that affect your reloads and not factory ammo?

Was just concerned with the leaking. Didn’t know if it is something to be concerned with.

I do not have access to a chronograph

Balzer94 · Mar 24, 2020

SKIP said:
I had the same problem using 4198. I would say it's the powder.
The remaining rounds I used in slow fire. Never in rapid fire stages for fear of the problems you described.

I don’t like that response haha. I’ve got two pounds I’m trying to burn through. Suppose I could use it in a different caliber but was hoping to make 223

SKIP · Mar 24, 2020

Balzer94 said:
19.5 grains of hodgdon h4198, federal Small rifle primers, 55gr fmjbt w/ cannelure. Rounds are crimped

I had the same problem using 4198 in my AR-15A1.
I would say it's the powder.
The remaining rounds I used in slow fire. Never in rapid fire stages for fear of the problems you described.

Uncle Duke · Mar 24, 2020

Balzer94 said:
19.5 grains of hodgdon h4198, federal Small rifle primers, 55gr fmjbt w/ cannelure. Rounds are crimped

OP, I'm pretty sure that the problem is with your load.

I have done a considerable amount of load testing in .223 since the last powder shortage in 2013, with the idea of finding load alternatives in the event of the next powder shortage.

Long story made short, 4198 is a very fast rifle powder. I had nothing but the trouble you describe with lower and mid level loadings of 4198. I concluded in my notes that this powder was suitable (and indeed fairly accurate) with 55 grain in my bolt rifles. But it proved to be a poor choice for my gas guns.

I would definitely try another (and slower) powder. I think you will find as I did that many choices will prove to be better choices.

SKIP · Mar 24, 2020

Balzer94 said:
I don’t like that response haha. I’ve got two pounds I’m trying to burn through. Suppose I could use it in a different caliber but was hoping to make 223

Works well in 7.62X39.

outrider58 · Mar 24, 2020

Could be a buncha things. Is this a new upper/gun? 14.5 mid length doesn't give much dwell time. Could be under gassed. The carbon leaking around the GB will be normal if it is indeed a new gun/upper. That carbon will help seal the GB to the barrel, so let it happen. Once the GB properly seals, problem might fix its self.

Couple things I'd recommend;

Take note of where the brass lands. That can indicate gas problems.

Other rifles, unless set up the same way, will be no indicator and an unreliable comparison.

Have you checked the torque in the gas key screws? If they loosen at 35 Inch/lbs, they'll need to be replaced and torqued to 50 in/lbs and the gas key properly sealed.(a poorly sealed/torqued gas key will cause loss of gas pressure). You should try a reliable BCG in the gun to see if this is the problem.

Another solution, if it is under gassed, would be to open up the gas port. That would require gas block removal.

You could address the powder aspect, but most ARs are built to be over gassed, and seeing how you are already high on your reloading scale, it's likely you are losing gas somewhere.

Then there's the chance you are over gassed. That brings us back to the question of where is your spent brass landing? Pics of the spent brass could help too.

Balzer94 · Mar 24, 2020

outrider58 said:
Could be a buncha things. Is this a new upper/gun? 14.5 mid length doesn't give much dwell time. Could be under gassed. The carbon leaking around the GB will be normal if it is indeed a new gun/upper. That carbon will help seal the GB to the barrel, so let it happen. Once the GB properly seals, problem might fix its self.

Couple things I'd recommend;

Take note of where the brass lands. That can indicate gas problems.

Other rifles, unless set up the same way, will be no indicator and an unreliable comparison.

Have you checked the torque in the gas key screws? If they loosen at 35 Inch/lbs, they'll need to be replaced and torqued to 50 in/lbs and the gas key properly sealed.(a poorly sealed/torqued gas key will cause loss of gas pressure). You should try a reliable BCG in the gun to see if this is the problem.

Another solution, if it is under gassed, would be to open up the gas port. That would require gas block removal.

You could address the powder aspect, but most ARs are built to be over gassed, and seeing how you are already high on your reloading scale, it's likely you are losing gas somewhere.

Then there's the chance you are over gassed. That brings us back to the question of where is your spent brass landing? Pics of the spent brass could help too.

I will see if I can make it to a range to answer some of your questions and gets some pictures of the brass.

CrazySanMan · Mar 24, 2020

Sometimes if you move your hips just right you can make the short strokes longer...

John from MD · Mar 24, 2020

Midgas plus short barrel is a poor match with 4198. Not enough gas volume. Get some CFE 223.

outrider58 · Mar 24, 2020

Just a note on powders and loads; You can overcome or at least compensate for underlying problems by catering loads to specific guns, but that's Viagra. You really want an AR that will work with any load you put in it. Reliability. Find the problem instead of masking it. MHO

Vile Shadow · Mar 29, 2020

SKIP said:
I had the same problem using 4198 in my AR-15A1.
I would say it's the powder.
The remaining rounds I used in slow fire. Never in rapid fire stages for fear of the problems you described.

Where Im scratchin my head though is how come its only 1 round per mag or so, instead of a lot more often than that

Help with Short stroking rifle

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