Oxblood wrote:
I have a dpms LR-308 that I had the barrel chopped down to 20" on. (was 24 to start with).
Last time I took it to the range, it seemed to be short stroking- the bolt would not travel back far enough to engage the bolt catch on an empty magazine.
I was thinking that maybe shortening the barrel has something to do with this- since the bullet is leaving the barrel earlier, there's less time for the gas system to be pressurized.
Is my reasoning sound? What should I try to fix this?
Yes, shortening the barrel results in less gas getting to the bolt carrier (shorter dwell time). The fix is to have the gas port opened up to supply more gas. (Not an adjustable gas block, that is to restrict gas flow on an oversized gas port, opposite problem from what you have.) I do not recommend just attacking it at home with a drill press, although some guys do that. If you do, at least use a brand new sharp high quality drill bit; you'll need to measure the existing port and step up in small increments in drill bit size until the rifle cycles correctly.
If your rifle has a heavy buffer in it now, you could try going back to the standard carbine weight buffer, but I wouldn't go any lighter than that. Be aware there are two different size buffers your rifle could use (308 buffer or AR15 buffer) and it depends which buffer tube is on your rifle.