Before I start, I purchased the rifle in question long before I undertood the differences between makers. So any responses to this effect is unecessary. This carbine has been relegated to a loaner rifle and will not ever be used for SHTF or formal training.
Many years ago I purchased a mid-length carbine for a song. As it turns out there is a reason for the low price. It’s a 14.5" CMMG with a permanenetly attached “long” Flash Hider on a Bushmaster Lower.
It short strokes when I shoot anything but “hot” ammo (ie: 5.56 pressure rounds). I’ve already checked the Gas Key and replaced the Gas Rings. I don’t see any leaks around the pinned Gas Block.
What happens is even with crappy 55-grain Wolf WPA it cycles fine but will not lock back on the lasst round. I’ve tried different magazines with the same results. Like I said, hotter rounds do fine. I have also tried dfferent BCGs, buffer weights (upt to H3) and a new spring.
I was thinking of replacing the Gas Tube next. Any other suggestions? Thanks in advanced.
Is the gas block pinned or clamped to the bbl? The reason I ask is that I recently picked up a used AR with similar issues. Turns out that it had sustained an impact to the clamped front sight/gas block, causing a slight misalignment. No evidence of gas leakage around the block/bbl interface.
Removed the gas block & cleaned everything thoroughly. Reinstalled, using a bubble level to make sure gas block was level with upper receiver. It now runs with everything I put through it.
My brother had problems with an AR like this before. He changed the buffer to something lighter, sorry can’t remember the weight or brand. It fixed his problem and is cheaper than most fixes.
Are you the same Carlos from down around Vancouver, WA?
I’ve only run across a gas tube with an undersize bore once in 20 years, lots of other gas tube problems though. Too bad you have the PF, it helps to look up inside the front sight base and make sure the hole in the FSB lines up with the hole in the gas tube and that the hole is clear and the proper size.
I’ve got a 14.5 middy that’s running similar. I pulled the gas tube out of it yesterday and found that the end that goes into the key is about .005" smaller than a used gas tube I had on my bench.
It looks like the existing gas tube never had the bulb end on the tip of the tube where it goes into the key. And there’s a lot of carbon fouling on the 3" of tube forward of the key.
I have a new tube showing up today. So I’ll get to shoot the gun pretty soon. I’m not sure if that .005" is leaking so much gas that it’s causing the light cycling or not…
