.450 build not cycling

Talk about the AR15 style rifles chambered in 450 Bushmaster.

Moderator: MudBug

Re: .450 build not cycling

Postby Hoot » Fri Sep 21, 2018 5:31 pm

1: Different block though I doubt it will solve the problem. More of a "General Principle" thing.
2: Drill it out in increment.
3: Enjoy shooting for shooting's sake


P.S. Get a steel gas block. The melonited (black nitrided) SS ones are easier to clean.
In Theory, there is no difference between theory and practice. In Practice, there is.
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Re: .450 build not cycling

Postby plant_one » Fri Sep 21, 2018 10:33 pm

joegun53 wrote:I think I will try a different gas block. there's 4-5 thou. slop in the barrel (.748 barrel vs. .753 gas block) and 3 thou. on the tube vs. hole in block. Probably too much.

ok so your journal is 0.002 undersized and your block is 0.003 over... bad combo....

go to the gun store, take your calipers and find a block that ID's at .749 tops. 1-2 thou is ALL you need to get one to seat right and seal. shouldn't be hard to do. if you dont have a LGS - call BCA back and ask them to find you one at .748 or .749 so that it matches your gas block journal properly.

you should have to turn a block to seat it... if it slides on like stepping into a hoolahoop you're gonna have problems - every time. 0.005 varience might as well be a hoola-hoop. caliber be damned at that point. even a 5.56 with a hugely oversized gas port wouldnt run right with that poor of a fit.

do NOT put a drill bit to the gas port until you have a properly sized block installed.
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Re: .450 build not cycling

Postby joegun53 » Tue Oct 23, 2018 6:28 am

Hey Everybody,
Just wanted to give you all an update on my gun and thank all of you for your help. I ended up getting a new barrel from BCA but the gas journal was really no bigger than the original one (.7485). I still had the old barrel so I decided to do the gas hole enlarging on it before I sent it back. I figured it was used and they would probably junk it anyway. I drilled it out and it ended up being about .098-.099. I went out with 5 rounds of 35.5 Lil Gun and 3 rounds of 38 Lil gun. The 5 rounds cycled perfectly but it kicked pretty good, bolt locked fully open on the last round. I then tried the 3 38's and things got interesting. The first round fired(kicked like a mule) but it not even come out of the chamber and the next round tried to load which pushed the bullet down into the case. I got it cleared, tipped the muzzle up and the spent round fell out. I loaded the 3rd round and fired (probably not to smart on my part) the case ejected but the bolt stuck open, hit the bolt release and it stayed open. I tapped the butt with my hand and the bolt went shut. Obviously over gassed with the heavy loads and large hole. Sent that barrel back.My shoulder hurt like hell for a week, not bruised but like I pulled something. When I Cerakoted the new barrel I did not tape off the gas journal, just plugged the hole.Gas block fit better. I first shot the 35.5 loads and it did not cycle correctly. Drilled it out to .093, still had incomplete cycling on 2 out of 5 shots, Drilled it out to .096. Shot 5 rounds 35.5 and 5 rounds of 37.5 and the gun worked perfectly . I will now work up some different loads and try and find the most accurate. I hope this new barrel shoots as good as the old one did. Thanks again for everyone's help. Deer season is just 6 weeks away. Hoot, I should have done what you said back on Sept. 13th. your 1st post. Oh well, maybe all the other ideas posted will help someone else in the future.
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