.450 cycling problems

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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.450 cycling problems

Postby amac_26 » Sun Nov 09, 2014 5:11 pm

Hi, I'm having some troubles with my .450 bushmaster cycling. Today was the first time I shot it and won't cycle after the first round. I have an 18" barrel and a mid length gas block on it with a carbine stock. I made sure the gas block was lined up right. My dad was watching me shoot to see if it would eject the shell but he said it looked like the bolt was coming back but only half way. Any suggestions?
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Re: .450 cycling problems

Postby wildcatter » Sun Nov 09, 2014 9:04 pm

amac_26 wrote:Hi, I'm having some troubles with my .450 bushmaster cycling. Today was the first time I shot it and won't cycle after the first round. I have an 18" barrel and a mid length gas block on it with a carbine stock. I made sure the gas block was lined up right. My dad was watching me shoot to see if it would eject the shell but he said it looked like the bolt was coming back but only half way. Any suggestions?


Shore, do you have allot of aftermarket DO-Dads on that 18 incher??

..t
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Re: .450 cycling problems

Postby Hoot » Sun Nov 09, 2014 9:07 pm

Welcome aboard Amac. Load a round into the chamber, then remove the magazine and see if the problem persists. If it goes away, make certsin the bolt is not dragging on the top of the magazine. Also, pass along other details regarding the carbine length system such as regular or enhanced spring? Regular or heavy buffer? Those could impact bolt travel. It could just be that it needs more breaking in. Running them wet the first couple of boxes, while cleaning out any displaced phosphating sluffy and re-lubing will ensure it polishes its way in. Never saw a 450b with a mid-length gas system. IMHO, it makes more sense than a rifle length system and am surprised we don't see more of them. I assume you were shooting factory loads?

Hoot

EDIT: was typing when WC replied before me...
In Theory, there is no difference between theory and practice. In Practice, there is.
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Re: .450 cycling problems

Postby OldManLee » Mon Jun 15, 2020 12:48 am

Hi All,
I know this thread is old, but I too have cycling issues. I assembled my own AR-15 16” in .450. I’ve had 80 rounds of Hornady ftx 250g go through it. I’ve lubed it good. It has a carbine length gas block, I replaced the buffer with an H3 and am not sure what to do next. The brass gets stuck and won’t eject out half the time. When the brass does eject it goes out about 3 o’clock. If brass ejects the next round gets stuck on its way into chamber. I have an ASC 5 round mag and I got a lancer 5.56 mag that I replaced the follower with a tromix follower for the .450. Any suggestions?

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Re: .450 cycling problems

Postby thsoccer3 » Thu Sep 17, 2020 5:26 pm

I built my first stripped lower and just returned from the range. I need expert advice.

My 450 Bushmaster 18" complete upper from Bear Creek Arsenal is short cycling. Shooting Hornady 250grn FTX, the casing ejects, but the next ammunition will not load. I have had this upper for a few years and used to shoot it on an M&P15 without modifications to the buffer or spring.

To troubleshoot, I put the 450 BM upper onto my Black Rain Ordinance lower, and the next ammunition loaded and action cycled correctly. I then put the 5.56 Black Rain Ordinance onto my built lower, and the 5.56 also cycled correctly.

Because of this, I am assuming my carbine buffer and spring in my built lower (adjustable buttstock) is not adequate for the 450 BM action. I do not see any markings on the buffer or spring. Do I need to replace the buffer (heavier?), spring (stiffer?), or both? I am also up for any other recommendations or ideas.

Thanks in advance.
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Re: .450 cycling problems

Postby plant_one » Fri Sep 18, 2020 9:39 am

what weight buffer do you have in your B.R.O. lower?

carbine is generally speaking a bit light... so you could be getting some bolt bounce.
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Re: .450 cycling problems

Postby Hoot » Fri Sep 18, 2020 10:09 am

I sprinkle some HBN powder down in my receiver extensions to keep everything moving as smooth as possible. MoS2, WS2 and good old Graphite will do just as well. Might help. Might not. Easy enough to try.

To narrow down the culprit, try swapping either the buffer or spring out from the lower unit that does work, assuming it is a carbine type as well. Needless to say, only swap one part at a time.

I'm a slow typist and tend to double with other responders.

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Re: .450 cycling problems

Postby plant_one » Fri Sep 18, 2020 12:04 pm

Hoot wrote: Needless to say, only swap one part at a time.



Hoot



^^^ SO MUCH THIS!

very critical. one change at a time is the key to diagnostics!
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Re: .450 cycling problems

Postby thsoccer3 » Sat Sep 19, 2020 11:53 am

plant_one wrote:what weight buffer do you have in your B.R.O. lower?

carbine is generally speaking a bit light... so you could be getting some bolt bounce.


Both lowers have a 2.9oz buffer. I did notice the spring in the built lower was 1/2" longer than the spring in the BRO. It is also a bit stiffer, so I cut it to the same length as the BRO spring. I will give that a try Monday at the range.
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Re: .450 cycling problems

Postby plant_one » Sat Sep 19, 2020 1:15 pm

you would have probably been better served to try a spring swap before doing something like cutting coils off... but too late now i guess.


carbine gas springs are supposed to have 37-39 coils and be at least 10" long and the rifle spring is supposed to have 41-43 coils and be at least 12" long


that extra ½" you just chopped could well have destroyed the functionality of it. more importantly - cutting a spring like you did will only - possibly - take away the symptom, not fix the actual problem.

suffice to say... with this big ole caliber... too much spring pressure isnt very likely to give you any grief, especially with a standard carbine buffer weight in there.



for example, i've got a 4oz slug in my bolt carrier (thanks hoot) and am running a 5.3oz H3 buffer. admittedly its a 20" barrel, but still.... we've got a couple 18" midgas between friends and family and those run on h3's as well just to tame them down.
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