450Bushmaster.net

The bolt won't lock back after the last round. This is a 20" upper. I've tried 3 mags.The lower is a YHM with a arfx stock and it locks back with my 6.5 grendel upper on it. Any idea's why? Paul

Have you tried holding the bolt back with the charging handle to see what looks different (where it contacts the bolt catch) compared to the 6.5g mag followers? I'm sure someone around the electronic campfire has run into this before...

commander faschisto wrote:Have you tried holding the bolt back with the charging handle to see what looks different compared to the 6.5g mag followers? I'm sure someone around the electronic campfire has run into this before...

CF is right. There is a cycling malfunction referred to as "short stroking". If you were shooting factory loads and the gun was relatively clean, it shouldn't short stroke on you. Any other particulars, like make and model of magazine, shooting from the hip, reloads, hasn't been cleaned in a coon's age, etc?

Hoot

So is it the 450 carrier not allowing the bolt to lock back or is it the 450 Mags not engaging the the bolt catch ? Have you modified the mags?

This is what a new bolt catch assembly should look like.
Note the small pin that the magazine follower presses up on
after the last shot. This pushes up on the bolt catch.


Also note there is a spring and detent that should
give pressure to the bolt catch to disengage it when there
is no magazine installed or a fully loaded clip installed.

Here is a short video on how to. This guy does it backwards from the way
I learned to do it. I drive the roll pin in from the rearward ear towards the front ear.
And that tool is nice. Wished I had one. Hmm Christmas list..Yeah.
Anyway....
http://www.youtube.com/watch?v=-2HDVE1ql_c
Bolt Catch

Scroll down picture for the Lower Receiver.
Part #s 11,12,13,14

I hope this helps.

This is a new bm upper and 1 mag is factory ,2 are colt with fulton blue followers. I'm using hornady ammo. It seems to me to be short stroking. Ejection is at 1 o'clock with some emptys landing on the shooting bench and others go 4-5 feet. If you pull the charging hanle back on the empty mag,it will lock back. hope this helps some. thanks Paul

livelyxp100 wrote:This is a new bm upper and 1 mag is factory ,2 are colt with fulton blue followers. I'm using hornady ammo. It seems to me to be short stroking. Ejection is at 1 o'clock with some emptys landing on the shooting bench and others go 4-5 feet. If you pull the charging hanle back on the empty mag,it will lock back. hope this helps some. thanks Paul

Consider removing the faux gas block. It's like tits on a boar anyway. Then look inside the handguard with a bright flashight to see if the real gas block looks like it is rotationally centered and if possible look for soot around it which might imply it's leaking some of the gas out each shot. I seem to recall someone reporting getting their 450b recently with the gas block a little off center, which might be obscuring the gas port alignment. Just tossing up what you may or nay not have already checked. Lastly, when they're new, these babies can be a little stiff running until they are run in. Mine was not that way, but it never hurts to mention these things. Does it seem unduly resistive when you pull back on the charging handle, say compared to the Grendel?

Hoot

Hoot has a good point. Focus on your gas system and your carrier key then the buffer system. BTW if you remove your fake Gas Block, SAVE IT! It's just an inactive Gas block, and can be used if needed to replace a worn gas block.

Texas Sheepdawg wrote:Hoot has a good point. Focus on your gas system and your carrier key then the buffer system. BTW if you remove your fake Gas Block, SAVE IT! It's just an inactive Gas block, and can be used if needed to replace a worn gas block.

TS has a prudent point. It's not actually fake, just window dressing. When I built up my 6.5 Grendel from parts, it saved me having to buy a gas block for the project.

Hoot

Hoot wrote:

Texas Sheepdawg wrote:Hoot has a good point. Focus on your gas system and your carrier key then the buffer system. BTW if you remove your fake Gas Block, SAVE IT! It's just an inactive Gas block, and can be used if needed to replace a worn gas block.

TS has a prudent point. It's not actually fake, just window dressing. When I built up my 6.5 Grendel from parts, it saved me having to buy a gas block for the project.

Hoot

Dittos to what Hoot said. I did the same thing for my 6.5 Grendel build. It fit perfect.