I know this has been covered before, but the archives are inaccessible so I have to ask.

I have a Bushmaster that I had cut from 16" down to 14.5", FH installed and also put on a CAR 6-pos aluminum buttstock. The buffer and spring came with the new telestock. Before doing this, with an A2 buttstock and 16" barrel the gun ran great and digested all ammo great.

Now, when shooting Wolf or some commercial, it wants to short stroke. I did test it with 1 round in the mag and sometimes it won't hold open. It will eject the round, but not strip another. With hotter ammo, it runs fine (XM-193 or my reloads which are similar spec as 193).

So, from what I know about this, I have two real possibilities.

1, there isn't enough gas. The port was not opened up when the barrel was cut AFAIK. This makes sense to me, but since it's not an easy fix, I hesitate to assume OR...

2, the buttstock/buffer/spring is wrong and I'm speeding up the action and need a heavier buffer or stiffer spring.

Am I on the right track here? And, what would be the best way to figure out what I need to do. I've gone over all the obvious checks. The gas tube isn't dented, bent or installed wrong. The key is tight, the gun is lubricated correctly, and the chamber is clean. What now?

Port size should be .070 to .086.  

With the barrel shortened, it should be closer to the .086 range, with the 16" barrel port around the .070 range.

Either check the port (this means pulling the FSB), or get the smith on the phone that shortened the barrel and ask him what size he openned up the port to.

P.S. The reason that there is a range for the port size depends on how tight the chamber is.  The looser the chamber, the less pressure needed to cycle the action (read pry the spent case off the sidewalls).

Craig, if you dont figure it out by saturday we'll pull off the FSB and see what size the port is. I'll bring tools to open it up if we need to.

Quoted: Craig, if you dont figure it out by saturday we'll pull off the FSB and see what size the port is. I'll bring tools to open it up if we need to.

Cool, thanks!