Building an AR 450 Bushmaster

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Re: Building an AR 450 Bushmaster

Postby plant_one » Wed May 02, 2018 9:42 am

Hoot wrote:I would never loctite a barrel nut. Quite the contrary. I put copper bearing anti-seize on them and use the tighten/loosen, repeat, to get them to >30 <80 ft lbs, depending upon where the gas tube hole aligns. Never had one come loose and that included my 300 WSSM AR 15 upper. That thing made a 450b seem like a 6.5 Grendel by comparison. Great for clearing out the shooting benches on either side of me. :o

Hoot


im with hoot - i'd never loctite a barrel nut on. they can be SOB enough to remove without it sometimes. save the loctite for places its needed - like scope ring screws :mrgreen:
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Re: Building an AR 450 Bushmaster

Postby Smithjdsr » Wed May 02, 2018 7:34 pm

I got some anti-seize and I’ll be ready to build as soon as the gas tube and block show up!

Next dilemma: do I buy the BCG I can afford now or do I save a little more for the Fail Zero? I know, I know, you say Fail Zero... but I’ll build another one soon, won’t I? I WANT TO SHOOT THIS THING!!
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Re: Building an AR 450 Bushmaster

Postby Hoot » Wed May 02, 2018 8:57 pm

Smithjdsr wrote:I got some anti-seize and I’ll be ready to build as soon as the gas tube and block show up!

Next dilemma: do I buy the BCG I can afford now or do I save a little more for the Fail Zero? I know, I know, you say Fail Zero... but I’ll build another one soon, won’t I? I WANT TO SHOOT THIS THING!!


With an attitude like that, you'll be right at home here. ;)
I got along just fine with phosphated BCG's the first 6 years or so. Just lube 'em good. Mine mostly ran with a coating of Dow Corning MolyKote Gn paste, brushed on with a flux brush. Less inclined to have grime stick to it and almost as slick when the oil carrier began to evaporate as when it was first put on. It gets into the generous pores in the phosphate and stays put.

I have ordered tubes of it over the years only to recently find it cheaper, ordered by the 2 oz tub off of Ebay. Got half the guys in the lab where I work, hooked on it. A million uses. Image

Hoot

PS: put a little of that anti seize under the gas block. Once tightened up, the layer of grease adds to the seal and you're less likely to skin up the finish on the barrel or gas block when you move it around.
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Re: Building an AR 450 Bushmaster

Postby Bmt85 » Thu May 03, 2018 1:32 pm

I'm with Hoot, it's not needed. They do run super smooth and are easier to clean, but I have a Bushmaster factory upper with a phosphate carrier and haven't had an issue. Another option could be to pick up a Melonite carrier or complete BCG and pop in a 450 bolt. I have a couple like that and they run fine. They don't seem to hold lube too well, but it hasn't affected anything for me during break in, after that I strip em, spray em with break cleaner, then run a light coat of Hornady One Shot HD-Extreme. It's a dry lube that has shown to be one of the best in protecting, and it's super slick. I run it in all my BCG's after break in, although it doesn't seem as effective (slick) on phosphate BCG's, but hasn't caused any issues, so I still run it on them.
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Re: Building an AR 450 Bushmaster

Postby Smithjdsr » Sun May 06, 2018 10:08 pm

I have some questions (background is that I’ve always bought complete uppers before)

My handguard came with some shims. These don’t go on unless I can’t get it lined up, right?

Also, about torquing the barrel nut. I can’t torque it yet. The barrel nut is about a 28 mm and the 1 1/4 crowfoot I have just barely catches the corners. I’m not sure it will take very much torque and I don’t want it to slip. Does it HAVE to be torqued just to shoot it a few times while I try to find a proper size crowfoot?
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Re: Building an AR 450 Bushmaster

Postby Hoot » Mon May 07, 2018 4:51 am

Smithjdsr wrote:I have some questions (background is that I’ve always bought complete uppers before)

My handguard came with some shims. These don’t go on unless I can’t get it lined up, right?

Also, about torquing the barrel nut. I can’t torque it yet. The barrel nut is about a 28 mm and the 1 1/4 crowfoot I have just barely catches the corners. I’m not sure it will take very much torque and I don’t want it to slip. Does it HAVE to be torqued just to shoot it a few times while I try to find a proper size crowfoot?


Anyone who has ever built up a new rig understands being anxious to get it to the range. All the barrel nuts I've done require an AR 15 Armorer's Tool to tighten. I've never seen one that you can get a crows foot wrench on but there's always a first time I guess. The point I'm getting to is If you can't torque it properly, don't shoot it! The handguard is a different horse. I have hand torqued one to try it out and by hand torqued I mean, As hard as I could turn it with my not weak hands. If you have a 3/8 drive torque, I can loan you my Armorer's Wrench. We're a trusting community here. I'm assuming your handguard is a different assembly than your barrel nut.

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Re: Building an AR 450 Bushmaster

Postby Bmt85 » Mon May 07, 2018 1:19 pm

Who makes the handguard and what do they recommend?
It almost looks to me like it has a proprietary barrel nut because of the mounting screws. can't tell enough if it needs a special wrench or tool.
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Re: Building an AR 450 Bushmaster

Postby Hoot » Mon May 07, 2018 2:13 pm

Sorry for the confusion (all mine) about the wrench you need. I had never looked at that particular handguard and now realize you do need a 1 3/16 crowsfoot. I'll see what I have when I get home from work.

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Re: Building an AR 450 Bushmaster

Postby Smithjdsr » Mon May 07, 2018 4:56 pm

Ahh! Ya big meanie! I knew you were gonna say it has to be torqued!

I already have a 1/2” torque wrench and a 1 3/16 crowfoot is on the way- by tomorrow or Wednesday. I’ll be punching .45 caliber holes in paper by Saturday!! (Your offer to borrow is very generous- thank you.) <sigh> Complete uppers don’t have this issue- you just push the pins and go shooting.

(No paperwork came with the handguard. They just said, “Ask someone who knows”). The handguard is proprietary. I thought I was going a little insane, so I went back and put my armorer’s wrench on the nut- no dice! It is way too small- and the wrong shape. I need that crowfoot. So, those shims, I start without them and only add them one at a time if it won’t line up between 60-80 ft-lbs? How many times to I torque it and remove before shooting it? Do you go all the way up to 80 on the first run, or start at 40, remove, go to 60... like that? Do I clean the threads and re-apply the anti-cease between runs?
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Re: Building an AR 450 Bushmaster

Postby Hoot » Mon May 07, 2018 5:30 pm

Smithjdsr wrote:Ahh! Ya big meanie! I knew you were gonna say it has to be torqued!

I already have a 1/2” torque wrench and a 1 3/16 crowfoot is on the way- by tomorrow or Wednesday. I’ll be punching .45 caliber holes in paper by Saturday!! (Your offer to borrow is very generous- thank you.) <sigh> Complete uppers don’t have this issue- you just push the pins and go shooting.

(No paperwork came with the handguard. They just said, “Ask someone who knows”). The handguard is proprietary. I thought I was going a little insane, so I went back and put my armorer’s wrench on the nut- no dice! It is way too small- and the wrong shape. I need that crowfoot. So, those shims, I start without them and only add them one at a time if it won’t line up between 60-80 ft-lbs? How many times to I torque it and remove before shooting it? Do you go all the way up to 80 on the first run, or start at 40, remove, go to 60... like that? Do I clean the threads and re-apply the anti-cease between runs?


The main reason for doing the back and forth with the nut is because most barrel nuts don't come with shim washers to get it to easily index on a gas tube hole in the range of acceptable torque. With shim washers, I'd only run it in and out a couple of times until it feels smooth. As for the exact torque, that too is a function of how easily you can get a hole to line up. I'd say if you hit index with however many shims it takes, go like 30 then 40 then 50 ft lbs and call it good. You may hit the sweet spot on the first try. Its far likelier that after each sub-torque, you may have to add a shim as it works in. To be honest, I've never had the benefit of barrel nut shims in my builds so the back and forth was a lot more important. I take that back. I had one PITA build where the nut went barely past one hole and no way it was going far enough to hit the next one. Had to shop around and buy shims for it. Point being, they were a corrective action, not standard procedure. The reason mil spec offers such a wide torque spec range is because most builds don't have the benefit of shims.

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