Been a long time since I posted on this site. I haven't used my 450 for a long time. BUT I recently purchased a custom barrel with a 1/16 twist. I wanted to revisit shooting resized 400 grain bullets. I disassembled my Bushmaster upper and installed the new barrel. Reusing the bolt (it was head spaced to the barrel extension) and gas block/gas tube. Went out and shot some factory ammo and some 405 Remington resized 405's. The action would not eject. I shot a few rounds of factory and the reloads (single shot), and the groups were better than what I had with the Bushmaster barrel. Especially with the 405's.
So I set my phone up in slow motion video and low and behold the bolt never moved. I looked into the action and no gas tub was protruding. DUH!. The barrel is a mid-length and I put carbine line gas tube in. Dumb move, but I just assumed it would have been made with a carbine system (I use a full length rifle hand guard). I purchased a mid-length gas tube and tried it again. It ejects, but will not lock back on an empty magazine. It actually locks in-between the bolt carrier and bolt head. It will not pick up a round from the magazine. The gas hole was way smaller than the standard 0.090 in the bushmaster carbine system. I opened up to hole to 0.089, but still it will not lock back. I opened the hole up to 0.0925 and will try it again this weekend. BUT I am curious if anyone else has run mid-length systems and what gas hole diameter works?! FYI I am using a standard carbine spring and buffer (3 oz).
This thing has to work at 20 below. If not it goes back to the barrel maker.