AR being uncooperative

[gmar]

My neighbor is having the same issue with a brand new Combat Shooters rifle. I contacted who I thought owned the company but he sold it a year ago and now they're out of business. However, he said he thinks the barrel might be over tightened. He suggested taking off the barrel and torque it to 40 lbs.

 

[Perplexed]

Well, I went back to the range this morning with the hand guard off the AR so I could futz with the gas block in between shots. After a couple adjustments, I got it where it would cycle Wolf Gold 55 grain .223, but it still would not cycle Champion 62 grain 5.56 ammo. I adjusted the block back and forth, and left and right, but to no avail. I tried a different bcg, even though the first one looked fine and had a tight gas key, with no luck. After an hour, I got tired of the whole thing and started shooting a pinned/welded 14.5" AR. Had zero issues with that as usual, so I may just remove the 18" barrel on the problematic AR and install a p/w 13.7" barrel with Flaming Pig. If that works, I'll leave it alone.

 

[rc508pir]

My neighbor is having the same issue with a brand new Combat Shooters rifle. I contacted who I thought owned the company but he sold it a year ago and now they're out of business. However, he said he thinks the barrel might be over tightened. He suggested taking off the barrel and torque it to 40 lbs.

99% of milspec ARs are torqued to around 55lb so I doubt that would be the issue. Cant see that being the issue for short stroking in anycase

 

[rc508pir]

Well, I went back to the range this morning with the hand guard off the AR so I could futz with the gas block in between shots. After a couple adjustments, I got it where it would cycle Wolf Gold 55 grain .223, but it still would not cycle Champion 62 grain 5.56 ammo. I adjusted the block back and forth, and left and right, but to no avail. I tried a different bcg, even though the first one looked fine and had a tight gas key, with no luck. After an hour, I got tired of the whole thing and started shooting a pinned/welded 14.5" AR. Had zero issues with that as usual, so I may just remove the 18" barrel on the problematic AR and install a p/w 13.7" barrel with Flaming Pig. If that works, I'll leave it alone.

I'm betting that your rifle is under gassed for that 62gr Champion stuff. Dissapator rifles have that problem a lot. The gas port is to close to the muzzle. Once the bullet leaves the barrel the gas pressure is dropping off enough to cause the short stroking. The gas port is most likely just wide enough to push the 55gr bullet through but not quite enough to push the 62gr through. That gas port should be in the .08 to .09 size range to operate heavier rounds with a normal weight BCG. Take it to a smith and find out what the port size is.

I'm betting the gas port just needs to be opened up some to function with heavier bullets. The smith will cost you less than getting a new low mass BCG

 

[Perplexed]

I was thinking the Champion 5.56 ammo had a higher pressure than the Wolf Gold .223 ammo? According to the Net, the Champion runs at 3020 fps with a MV of 1332 ft. lbs, while the Wolf comes in with 3250 fps and 1290 ft. lbs. Isn't the MV the indicator of the amount of back pressure?

 

[dennishoddy]

Isn't the MV the indicator of the amount of back pressure?

Not really. Your powder burn rate, weight of bullet, all contribute to chamber pressure.

 

[rc508pir]

I was thinking the Champion 5.56 ammo had a higher pressure than the Wolf Gold .223 ammo? According to the Net, the Champion runs at 3020 fps with a MV of 1332 ft. lbs, while the Wolf comes in with 3250 fps and 1290 ft. lbs. Isn't the MV the indicator of the amount of back pressure?

No, Using the same powder and the same amount of powder, the pressure is the same. It just pushes the lighter bullet faster.

 

[Perplexed]

Thanks for the input. I'll take it to FBT and have them check the gas port size.

 

[rc508pir]

Thanks for the input. I'll take it to FBT and have them check the gas port size.

Just checked some notes I made a few years ago. Gas port size for a 18incher with Rifle gas is .89 to .108. A probable happy medium would be .099

 

[gmar]

99% of milspec ARs are torqued to around 55lb so I doubt that would be the issue. Cant see that being the issue for short stroking in anycase

Yeah, it's the first time I've ever heard of that but that's what he said about my neighbor's rifle that wasn't cycling and ejecting rounds.