*** Update ***
Today I went out with six different kinds of ammo and ten different magazines. All the ammo in all the magazines worked fine. When the stock was firmly on my shoulder, the bolt locked back every time.
When the stock was not resting on my shoulder, all six types of ammo, in all the different magazines failed to lock back.
I removed the Red LT spring and the T-2 Buffer and replaced them with the White spring and factory LT Buffer and repeated the process.
Results were the same.
I took a LT Stealth upper and put it on my tOBR upper (the one experiencing the problems) and did the same as above. No issues when the stock was firmly on my shoulder.
When I shot the different ammo and different magazines without the stock firmly behind my shoulder, the bolt locked back as it should on the last round.
I then placed the tOBR upper on two different LT Lowers and repeated the above steps over. Again, with the stock on my shoulder, it worked fine
When the stock was not on my shoulder, the bolt failed to lock back.
I put the tOBR upper back on the tOBR lower and changed the gas block to "suppressed" instead of "unsuppressed" The bolt would not cycle.
I put it back to non-suppressed and still experienced the bolt failing to lock back on the last round when the stock was not pressed against my shoulder.
Soooo, based on the different ammo, different magazines, and the same problem on three different lowers (when other uppers work on those lowers) this has to be a gas issue correct? What would you guys do at this point?
On the last round of the magazine, should the bolt lock open if there is nothing behind the butt stock (such as your shoulder)?
I noticed the bolt wasn't locking open when shooting from a sled type of rest a few weeks ago. Today, I had the chance to go and try to solve the issue. I had a lighter spring and a lighter buffer to try. Before changing anything, I discovered that when shooting the rilfe with my shoulder behind the butt stock, in a normal shooting stance, the bolt locks back just fine. Remembering I was shooting from a sled when experiencing problems, I held the rifle to the side of my shoulder (so there is nothing behind the butt stock) It will cycle rounds just fine, but when there is nothing behind the stock, the bolt will not lock back on the last round.
I didnt take any other AR's with me, and I didn't change out the spring or buffer. I was hoping someone would know what should be happening without some force behind the butt stock before I started changing things around.
Thanks guys!