450 bushmaster cycling issues

buckthumper

buckthumper

New member
I'm having major cycling problems with my 450 bushmaster and was wondering if anyone else has experienced issues with this cartridge in a AR.
It isn't feeding the next round and I have to pull the charging handle after firing every round. I tried the lower with a 5.56 and it worked just fine. From what I'm reading though it seems they have mag issues with some saying they had to modify their mags.
It's a BCA upper, ASC 7 round mag and hornady Black ammo.
 
Sounds like it isn't getting enough gas or your gas tube is too long for the pressure curve. Had the same problem with a wildcat I made. I put a rifle length plus 2 inches gas tube on it. It would short stroke in the offhand. Had to drill out the gas hole in the barrel to allow more gas. Went from 60 to 80 thou. works most of the time in offhand now. Always works in sitting and prone. Going to cut it down and plug the gas hole, then drill another one at rifle or mid area.
 
first things first... do you have a dedicated 450 mag? generally speaking a standard 223/556 mag doenst work right with the big bores.

a standard 450 mag has a cutout of the front to prevent jams from hooking up on the lip of the cartridge, and a large single shot style follower. see image below

(pic from the web)
mag-450-Bushmaster.jpg



tell us more about the lower? standard carbine spring? what buffer?


450's tend to be overgassed and will often outrun the mag spring if you're getting bolt bounce. its as common as short stroking is if your'e running on a carbine length gas system. the bushmaster 20" uppers are famous for it.


also which BCA upper do you have? the 16" or the 18"
 
I do have a dedicated 450 bushmaster asc 7 round mag and it acts the same whether there's 2 rounds or 7 in it.
It is a 16" upper, standard carbine buffer spring, 3 oz. Buffer and carbine length gas system.
The gas block couldn't haves moved because it did this on the very first shot
 
It sounds under gassed to me. I would double check that the gas block is in the proper position and make sure the gas tube doesn't have a sloppy fit in the gas block. I I've got the Bear Creek 18 inch version and it runs fine with Hornady black ammo in a 5.55/223 mag that I ground the follower on.
 
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Originally Posted By: buckthumperI do have a dedicated 450 bushmaster asc 7 round mag and it acts the same whether there's 2 rounds or 7 in it.
It is a 16" upper, standard carbine buffer spring, 3 oz. Buffer and carbine length gas system.
The gas block couldn't haves moved because it did this on the very first shot

ok... so you're at two likely options right now

You're overgassed and the carrier speed is exceeding the mag springs ability to move the round up to be stripped forward by the bolt

or the gas block is mis-aligned from the factory and you're not getting enough gas to get back far enough to pickup the round.



you can test which it is by putting a single round in the magazine, and shooting the gun. if it locks back on an empty magazine - you dont have an gas blockage issue.

If that is the case you're going to have two choices - use a heavier buffer (like a H3) or install an adjustable gas block.
 
Originally Posted By: varminter .223It sounds under gassed to me. I would double check that the gas block is in the proper position and make sure the gas tube doesn't have a sloppy fit in the gas block. I I've got the Bear Creek 18 inch version and it runs fine with Hornady black ammo in a 5.55/223 mag that I ground the follower on.

buddy of mine has the 18" BCA upper as well - runs like a swiss watch with hornady black, hornady custom & handloads.
 
I talked to BCA and they believe that the gas block is misaligned as well so they want me to send it back to check.

What kind of magazines was he using in that 18" upper?


 
I used ASC mags and they work. But I installed an adjustable gas block. Usually the gas block has enough coverage over the gas port that it will tolerate some misalignment. Uf it's locking back on a single round you probably have enough gas. Make sure your bolt goes back about a 1/4 in beyond the bolt catch. If not then something is causing it to short stroke lije a binding spring.
 
Originally Posted By: SnowmanMoI used ASC mags and they work. But I installed an adjustable gas block. Usually the gas block has enough coverage over the gas port that it will tolerate some misalignment. Uf it's locking back on a single round you probably have enough gas. Make sure your bolt goes back about a 1/4 in beyond the bolt catch. If not then something is causing it to short stroke lije a binding spring.

i beleive the OP said he tested the lower with another upper (5.56/223) and it ran fine.. so i that pretty much eliminates a buffer spring binding up on him.


on review - he is getting lock back with single loading, but failing to eject about 25% of the time. ( i missed that earlier).








personally i have a couple bushmaster mags and a couple AR-SToner mags i modified before the released their 450 bushmaster specific mags (pre cut groove, different follower), but my upper is a BM 20" carbine gas.

my friend who has the 18" bca upper is running the ar-stoner 450 bushmaster specific mags.
 
Originally Posted By: buckthumperIt fails to eject one out of every 4 shots and it never picks up the next round.
It does lock the bolt back when I single load it

does it leave the round in the chamber completely? or somewhere above the mag - ie: it extracts from the chamber but it "stovepipes"



edit: last round bolt hold open + failure to feed still leads me to believe you have a carrier speed issue due to overgassing, but i'm wondering if there's not an extractor and/or ejector problem with the bolt as well.
 
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