I’m new to ARs. Got 2 7.5" AR15 Pistols within the last 30 days. Bought one used and the other new. Both supposedly had 200 rounds through them. They both will only shoot 5.56 without any problems. I get FTEs after the first round of .223s are fired. I load only 25rds in 30rds Magpul G2&G3s. Cleaned & lubed per recommendations given by numerous YouTube experts. I did a Google search and didn’t find similar problems. Could this be a buffer spring issue.
As mentioned above, what weight buffers are in them? Are they using standard carbine springs or some aftermarket ones?
Replace buffers and springs with standard carbine ones. Increase carbine buffer weight until you experience problems with the weakest ammo you plan to shoot (magazine using standard carbine 3oz. weight, if it functions as it should, repeat with fresh magazine and H1 3.8oz. buffer next, etc.)
Speaking of magazines, are you 100% postive the magazines you are using are gtg?
After you find what the heaviest buffer each one likes is, then you can worry about upgrading the carbine springs in each (Sprinco) if you further desire to mess with them to further tame recoil/fine tune cycling.
Gaijin/ColtSeavers, thanks for advice. The pistol shoots. 223s well when I use the T2 buffer from my Spike’s rifle. So, I’ll be shooting 5.56 until the new T2 arrives.
Yes, I originally started with a standard weight buffer. Also, the STT2 experiment failed after 100 rds. I’m going to try the Bootleg adjustable BCG next.
Check your gas key screws and the tightness/position of your gas block. I had an AR that was not locking back on last round with only Wolf ammo. Cycled fine though, and all 5.56 ammo was locking back properly. My gas block screws were still tight but it had shifted forward a fraction. Repositioned it and it worked great again. I promptly dimpled the barrel for the GB and it’s been great since.
Spent casing isn’t ejecting. Appears gun isn’t cycling. I’m thinking it’s a underage problem.? Gas block seems to be in over barrel hole. Gas line seems clear of obstruction.
I meant undergassed, not underage, in my earlier post. One round locked worked intermittently. .223 ammo included new Sig, AE, Remington and reman from AmmoValle and Octane. Tried different buffers: carbine, H2, H3, STT2.
Latest status is 1 rd lock doesn’t work and gun doesn’t cycling. One thing I haven’t really check was the gas block & line. That’s next when time allows.
Honestly, this has been fun experience troubleshooting this problem. And thanks for all of the help.
Problem is fixed. I need to increase my attention to detail. The pin holding the gas tube to the gas block was slightly broken causing the tube to slip just enough to cause an undergas situation. Thanks for the responses.
