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AR15.COM
9/28/2016 12:38:06 AM EDT
Took out a new rifle that I just finished. It's an 18" barrel with a rifle gas setup. Everything in the rifle is new, barrel and Bcg are aero precision/ballistic advantage. I'm using a carbine buffer/spring, stock, and tube. I shot Black Hills 77gr and 55 gt xm193.  I loaded it up, fired the first round, which ejected fine. I pulled the trigger and just "click".  Checked the chamber and it was empty. I loaded it again and same thing happened. After five rounds of this, it did lock back on the final round.  I first tried the 77gr and then the 55gr, it did the same with both. Should I try a heavier buffer? Unde gassed? Over gassed?
9/28/2016 1:01:07 AM EDT
[#1]
Carbine buffers and springs were never designed to work with rifle length gas systems.  

Sometimes they do, but then sometimes demons pop up.  

What weight buffer are you using?
9/28/2016 1:08:26 AM EDT
[#2]
3.0 oz
9/28/2016 5:16:51 AM EDT
[#3]
It sounds like the bolt is not traveling far enough to strip the next round.  Have you tried another mag to make sure it isn't a feeding issue?

Have you tried swapping the upper onto another lower?
9/28/2016 6:42:10 AM EDT
[#4]
Sounds like its not getting enough gas. The fix for that is more gas or a lighter carrier/spring/buffer. But before you buy anything, make sure your bolt and carrier have plenty of oil, not just a light coat. They should be wet, especially while the rifle is new and parts are wearing in. Check gas block alignment also. If its not aligned with the gas port hole it may be restricting the amount of gas going back to the carrier.

I have found that 18" rifle gas barrels on carbine lowers tend to take a little break in before they run well with some ammo. I think its a combo of parts breaking in and smoothing up as well as letting carbon and crud seal off any leaks around the gas block and tube.
9/28/2016 8:22:11 AM EDT
[#5]
Will the bolt lock back on the empty mag reliably when a single round in the mag is fired? If not - it is undergassed. Check gas hole alignment with the gas block using a borescope.
9/28/2016 10:03:48 AM EDT
[#6]
Sounds like low gas.  What block are you using?  If it happens with a different magazine, swapping the block might an easy test followed by checking the port of the barrel.

I also have a 18", rifle gas, carbine buffer/tube, self-assembled AR and it shoots great using standard parts from AIM, Mega, PSA.
9/28/2016 11:54:33 AM EDT
[#7]
Quote History
Quoted:
Will the bolt lock back on the empty mag reliably when a single round in the mag is fired? If not - it is undergassed. Check gas hole alignment with the gas block using a borescope.
View Quote


Yes it will
9/28/2016 12:03:47 PM EDT
[#8]
If it will lock back on the last round reliably, but not feed the following round, its got to be a bad magazine. Try with a different quality mag and see if that helps.

If not, your buffer is probably too light or recoil spring is too strong and causing the bolt to outrun the magazine.
9/28/2016 12:07:13 PM EDT
[#9]
Quote History
Quoted:
If it will lock back on the last round reliably but not feed the following round its got to be a bad magazine. Try with a different quality mag and see if that helps.

If not, your buffer is probably too light or recoil spring is too strong and causing the bolt to outrun the magazine.
View Quote


I tried the same mag and ammo with another rifle and it worked fine.  I did not however swap uppers around.