.450 build not cycling

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Re: .450 build not cycling

Postby plant_one » Sat Sep 15, 2018 8:32 am

Talon_ wrote:I would put that upper on one of your other lowers before drilling the gas port just to see if it would work.


^^ this


drilling your gas port should be the absolute last thing you do.

theres a ton of other things to sort thru first.

slap that baby on a lower that you know functions well and see if you can get it to run.
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Re: .450 build not cycling

Postby Hopalong » Sat Sep 15, 2018 8:41 am

Hoot wrote:
I wouldn't use anything wet as air is getting sucked into and blown out of the tube, increasing the risk of dust sticking to a wet surface.

Hoot


It's a dry lube/cleaner, only wet in the sense that it comes out of the aerosol can suspended in hexane. The MSDS doesn't specify what the lubricant is, but it dries almost instantly. Seems to work well for getting into places and leaving the lube behind.

https://www.midwayusa.com/product/170954/hornady-one-shot-gun-cleaner-with-dyna-glide-plus-10-oz-aerosol
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Re: .450 build not cycling

Postby joegun53 » Sun Sep 16, 2018 5:20 am

Thanks all,
I'm not sure what putting the .450 upper on my other lower would prove?? The RR has the same setup, A2 stock with a 5.3 oz. buffer just like I have and the other 2 are carbine buffers with adjustable stocks. I don't want an adjustable stock on the .450. I have ordered a set of numbered drill bits (been wanting some anyway) and I have made 3 aluminum slugs to replace the tungsten ones in the buffer. I can reduce the weight from 5.3 to around 4.6, 4.2 or 3.8 by replacing 1,2 or 3 of the tungsten weights with aluminum ones. Not sure what I'm going to try first??
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Re: .450 build not cycling

Postby joegun53 » Mon Sep 17, 2018 12:28 pm

I went out to the range today and shot 17 rounds changing out the tungsten weights with aluminum ones. I started with just 1 aluminum weight which reduced the weight from 5.3 to 4.6 oz. The gun fired 3 rounds and completely cycled all of them. The bolt did not completely lock open on empty, it locked on the carrier which it has done since day 1. I then switched to 2 aluminum and 3 aluminum weights firing 3 rounds with each, same result. I think with 3 aluminum it's down to about 3.6 oz. I then started to have some cycling problems, It might have been a switch to another mag, not sure but it started to jam with the new round stuck at an angle pointing up to the feed ramp. I went back to only 1 aluminum weight but the problem persisted. Not loading a fresh round and not locking completely back on the last round. My drill bits will be here sometime today. I guess I will drill the gas hole out to .096 and see what happens. On my way to Scheels to buy dies, bullets and powder. Looks like this might take awhile to solve. By the way, my last 5 shot blew one hole on the paper, very happy with that for a budget barrel.
Thanks again everybody for your help, I'll keep you posted on my progress.
Joe
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Re: .450 build not cycling

Postby Hoot » Mon Sep 17, 2018 1:44 pm

I understand you don't want to use the 450b upper on your other lowers on a permanent basis but there's nothing to lose trying the upper on them for a few shots. If the problem persists, it would cement your concern that this is a gas system issue. If it doesn't persist, then you know better than to try and drill your way out of the problem. I get confused with my suggestions as there is a similar thread going on.

Did you look at the upper screw that holds your butt plate to your stock, to make sure it has a hole through it into the interior of your receiver extension? it allows pressure built up in it to escape when the bolt pushes the buffer back. I'm a big stainless steel socket cap head screw fan and had mistakenly replaced my vented screw with one. The result was almost identical to what you're experiencing right down to the BHO locking on the carrier instead of the bolt. Swapping lowers is an easily reversed troubleshooting tactic. Once a hole is drilled, you're stuck with it. I've drilled barrels to get them to cycle. Once I did that in error when the real problem was the chamber was tighter than the SAAMI specification. Wound up buying an adjustable gas block to undo what I had done.

Just sayin'...

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
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Re: .450 build not cycling

Postby joegun53 » Mon Sep 17, 2018 3:46 pm

Thanks for the reply Hoot,
I guess I should have taken my RR .223 lower out and tried it. It has the identical buffer but is a rifle length gas system. I'm prepping cases now, ready to start reloading my own. I'll have some loaded up tomorrow. The vented stock screw is still in place, so we can rule that out. I'm not so sure that my problems this morning were not mag related, except for the bolt not locking open. I'm going to do some more work on the lips to reduce scratching and drag. This has been a real adventure but I enjoy working through stuff like this. Another note, I really didn't notice much difference in recoil with the different buffer weights.
Thanks again,
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Re: .450 build not cycling

Postby Gtek » Tue Sep 18, 2018 8:02 pm

Just asking- you say it (gas block) is aligned correctly. Do you have access to a Hawkeye or bore scope that can confirm this? I have put enough of these together and have come to the conclusion of not taking anything for granted anymore and everything meets measuring devices. So many sources for parts it has become second nature to measure port dimensions and locations on barrel and block in relation to shoulder and rear edge for confirmation of orifice centers. The ferrule thickness allowance cut into some and some not usually between .027" and .030" into shoulder. This sometimes can cause a situation where 30-40% restriction is placed in circuit with rotational alignment correct but fore and aft not so much. Also there seems to be no standard in the gas block orifice so unless checked who knows.
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Re: .450 build not cycling

Postby joegun53 » Wed Sep 19, 2018 6:01 pm

Hey all,
Went out today with fresh reloads, 250 gr. FTX, 35.5 gr. Lil Gun, 2.250 with a taper crimp of .475. Wish I could give you a better report but I shot 5 rounds each with my Sota .450 lower, my R.R. .223 lower with a rifle buffer and another Sota lower with an adjustable stock and carbine buffer. I actually had worse results than with the factory rounds. I think I only had 4 rounds actually fully eject from the chamber. The rest were stuck with a half open chamber. I will re -check the gas block but I'm about ready to drill the gas hole to .96 thou. If it doesn't work I might trash the Bear Creek barrel and gas block and opt for a better one. Don't know what else to try?? A good friend competition shooter I work with suggested I add some weight to the carrier. I don't know if that will help or make it worse??
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Re: .450 build not cycling

Postby Hopalong » Wed Sep 19, 2018 6:24 pm

Your brass looks okay? Is the chamber not in spec or perhaps rough? Is your extractor up to spec? Sorry if this has been brought up, but with all the changing on the lowers and ammo, it begins to sound like something dragging or not functioning correctly during case extraction.
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Re: .450 build not cycling

Postby Al in Mi » Thu Sep 20, 2018 4:11 am

might want to bump that load up to about 3gr, 38-39gr seems to be a sweet spot for most guys plus it will get you some extra gas.
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