450Bushmaster.net

Well this is the 2nd 450 I've built. The 1st one was perfect the 2nd not so much.

Bolt and barrel are budget buys from Davidson's defense.

16", carbine length barrel, surplus GI mags. Nothing fancy.

Hand cycles perfectly

With mag inserted, bolt doesn't cycle back, at all after its fired. Hand cycle to clear the chamber and strip the next round

Insert mag, charge the handle then drop the mag, bolt cycles and ejects.

What I forgot, old man brain fart, was to test with empty mag to see if bolt catches after the single round cycles

Not sure if this is a gas issue, mag issue or combo of the two

Is it hard to manually cycle the carrier?
You most likely have a gas issue. You will have to pulle the gas block (with gas tube attached) and check to see if you're properly aligned. Also check to see if there is a blockage at the port for the gas block and barrel. Also measure the gas port.

Hand cycles very smoothly. This is the 2nd run to the range. I tweaked the gas block alignment before I went out today.

did you test it with a known good mag - one that works in your other gun?