Building an AR 450 Bushmaster

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Building an AR 450 Bushmaster

Postby Smithjdsr » Thu Jan 18, 2018 5:30 pm

I’m thinking of building an AR in 450 Bushmaster. I have successfully built AR’s in 5.56 and .223, but this would be my first big bore.

Background- this year Iowa changed its law to allow a number of straight-walled ‘pistol’ cartridges for deer hunting fired from a rifle. 450B is among the allowed chamberings. I have looked at the Ruger American Rifle, but the word is that its short barrel and flash hider make it extremely loud. At $500 or so, building an AR begins to look way more appealing- and fun.

Some questions, if I may?

My lowers will work, right?
Other parts are standard, like handguard, gas tube, gas block, barrel nut, stock, tube, spring... no need to get special parts for 450B, I think?
I have ‘full auto’ bolt carriers, so I guess I’ll just need to change the bolt itself for 450B.
Where can I get a parts list of the parts that have to be special for 450B?

About the upper receiver? I have a stripped upper. I guess I have to make some modifications? There’s no ejection port Cover, right? And I have to modify the size/shape of the ejection port? How do I do this? To what size and shape?

I don’t really even know what questions I need to be asking?
“Remember; No matter where you go, there you are.” -Buckaroo Banzai
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Re: Building an AR 450 Bushmaster

Postby Hoot » Thu Jan 18, 2018 9:01 pm

Smithjdsr wrote:I’m thinking of building an AR in 450 Bushmaster. I have successfully built AR’s in 5.56 and .223, but this would be my first big bore.

Background- this year Iowa changed its law to allow a number of straight-walled ‘pistol’ cartridges for deer hunting fired from a rifle. 450B is among the allowed chamberings. I have looked at the Ruger American Rifle, but the word is that its short barrel and flash hider make it extremely loud. At $500 or so, building an AR begins to look way more appealing- and fun.

Some questions, if I may?

My lowers will work, right?
Other parts are standard, like handguard, gas tube, gas block, barrel nut, stock, tube, spring... no need to get special parts for 450B, I think?
I have ‘full auto’ bolt carriers, so I guess I’ll just need to change the bolt itself for 450B.
Where can I get a parts list of the parts that have to be special for 450B?

About the upper receiver? I have a stripped upper. I guess I have to make some modifications? There’s no ejection port Cover, right? And I have to modify the size/shape of the ejection port? How do I do this? To what size and shape?

I don’t really even know what questions I need to be asking?


Welcome Aboard JD!

The only unique parts on the 450 bushmaster are the barrel and bolt. Many manufacturers sell them as a set. The upper receiver will need an ejection port sized to pass the fatter case however. Some upper receivers come already appropriately sized and many do not. Here's the dimensions that Bushmaster actually uses as measured on my first upper.

Image

Let me back up. You will need a magazine that will handle the single stacked fatter cartridges also. A few 556 mags have been reported to work without modification, you can mod an existing mag, or you can buy one specifically made for the 450b.

IIRC, there are how-to's online showing how to open up the ejection port to the appropriate size and not have it look "bubba'd".

Bushmaster uses a standard spring and rifle buffer in their uppers. There are equivalent ones for an M4 style, adjustable stock but I don't have any experience with them. Both my 450b rigs run a standard spring and rifle buffer. A medium size, black, slip-on SIMS Limbsaver recoil pad is a big plus if you do not intend to put a muzzle brake on your rig for reasons you already stated (loud). Without a muzzle brake, you may benefit from a 20" barrel as they get the noise a little further away and the added weight reduces the perceived recoil a little. I'm biased though. I like rifles to have rifle length barrels on them as I don't kick down doors or engage in CQB for a living. ;) Did I mention the additional 100+ fps from the same ammo?

Hoot
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Re: Building an AR 450 Bushmaster

Postby plant_one » Fri Jan 19, 2018 11:05 am

the only proprietary parts you *NEED* for a 450 bushmaster are going to be the bolt, and an upper with the proper ejection port dimensions. otherwise you're very much correct that its going to be like any other ar upper build you've done.

a standard lower will work just fine. if anything you may want to put a H2 or H3 buffer in the stock on a 6 position lower, but otherwise you wont need to do anything. It WILL run with a regular 3oz carbine buffer, but it may (or may not) be rough on your brass. not a concern if you're not gonna reload anyway. as an added bonus, in all but special circumstances (for example: a 300 blk, carbine gas, shooting subsonics, unsuppressed) a H2 or H3 buffer is going to be compatable with pretty much everything else, and will help with symptoms of overgassing in those uppers too.

perosnally i would order a stripped uppper with the proper ejection port in it. its worth the few extra bucks in my eyes for those of us who arent a machinist.


secondly and this is just personal preference, but i much prefer to have a complete BCG & charging handle for every upper i own. that way it just stays with the upper and there's no 'damn i forgot to grab my bolt carrier' things going down. Since you're buying a bolt anyway, adding a carrier doesnt jump the price that much - and as you noted a basic mil-spec "full auto" bcg will do once you swap the bolt. Bargin shop - you can pick one up for around $50 or less on sale. and then you have a spare 5.56 bolt laying around in your parts bin :)

hth and good luck with your build!




ps: yes - we expect pics when you're all said and done too! :mrgreen: :mrgreen:
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Re: Building an AR 450 Bushmaster

Postby Smithjdsr » Sat Jan 20, 2018 3:50 pm

Thank you. Good, sensible recommendations. I’m not MOA shooter, so I don’t really need ultimate precision. My longest deer shot to date is 150 yards (with a .50 muzzleloader), so I don’t claim to be a long-range shooter. I’m leaning toward the 20” barrel to push the noise a little further away and to squeeze a skosh more velocity out of it. If I had a reliable 200 yard rifle I’d be happy.

The barrels I’ve seen seem to be $199 - $300. Does that seem right? Honestly, I might have to do this on a shoestring (you may have heard sixth grade teachers aren’t excessively well compensated) but would one of these kinds of modestly priced barrels do the trick?
https://www.franklinarmory.com/products ... ide-barrel
http://www.selwayarmory.com/glfa-ar15-4 ... tride.html
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Re: Building an AR 450 Bushmaster

Postby Bmt85 » Sun Jan 21, 2018 4:42 pm

That Franklin barrel has a rifle length gas port. Which really isn't needed, especially if you don't reload.
That GLFA is a good price because it also comes with the bolt. GLFA has been brought up a few times recently, and from what I can tell, they seem good. It doesn't say if it comes with a carbine length or midlength gas system. I personally would prefer a midlength, but carbine shouldn't really be a deal breaker.
There are other options out there if you choose not to go with those. Also take a look at Gryphon Trading and Tromix, they make 18" midlength barrels, they run $300 for barrel and bolt
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Re: Building an AR 450 Bushmaster

Postby Smithjdsr » Tue Apr 10, 2018 4:28 pm

I know the old addage “You get what you pay for.” I also know the old addage, “Public school teachers get paid diddly-squat.”

So, I’ll be brief. Is a Bear Creek Arsenal barrel worth having?

Saving for a barrel after building a new lower is proving... challenging. I dont need MOA. I’m not that good. I’m a deer hunter who’s looking for better 100 yard accuracy than my 12 ga slugs will do and, once in a while, the ability to reach out further to deer-lung-size targets at 150-200 yards. 3” groups at 200 yards might be scandalously poor for some of you, but that’s well inside of a target the size of a deer lung. I don’t shoot running deer and I avoid heavily quartering shots. I’m not looking to challenge Quigley Down Under, just want to harvest some venison. Is a sub- $200 barrel going to work?

https://www.bearcreekarsenal.com/barrel ... aliber=150
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Re: Building an AR 450 Bushmaster

Postby Al in Mi » Tue Apr 10, 2018 5:49 pm

Cheap enough to try.

http://www.primaryarms.com/search?keywords=450

Buddy has built a few uppers with their barrels in other calibers, all have shot pretty good.
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Re: Building an AR 450 Bushmaster

Postby Bmt85 » Tue Apr 10, 2018 5:55 pm

I have no experience with BCA, except a side charging upper receiver.
I haven’t seen anyone talk about stellar accuracy from anything BCA barrels. Will it be enough for your needs, maybe, but couldn’t tell you. I do know that many have reported not so great finishing from BCA. Very rough, and a lot of machining marks. But you can’t expect a lot from prices like that. If the bore is rough, you could try lapping it, but you have to be extremely careful because it’s a straight wall cartridge that headspacea off the mouth, not a bottle neck that headspaces off the shoulder.

Honestly it’s going to take at least $500 to build a complete upper. That’s using a good barrel (the ones mentioned previously) which are actually really good deals at around $300-350 for barrel and bolt. After that you can with some cheaper parts, but your still in the $500+ region.

Now I know you mentioned looking at the Ruger bolt rifles, but don’t like the 16” barrels. Well Ruger is coming out with a camo’d version that has a 22” barrel. I believe they will be selling for around $500. Look into it.
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Re: Building an AR 450 Bushmaster

Postby Smithjdsr » Tue Apr 10, 2018 7:44 pm

Yeah. Thanks. I saw that 22” barrel in the bolt action section. Looks nice. I’d wonder if I’m doing the right thing, but I still really want an AR Bushy.
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Re: Building an AR 450 Bushmaster

Postby gemoose23 » Tue Apr 10, 2018 8:05 pm

Also an Iowa resident, I am back on the 450 bushmaster train as I've been interested in 450 Bushmaster for a while... just life got in the way never built or acquired a 450 Bushmaster rifle.

As an alternative... Brownells now has released recently their own barrel set: comes with barrel, bolt and muzzle break: https://www.brownells.com/rifle-parts/b ... 13649.aspx

I am thinking of building my rifle off of this, it would give me a reason to visit the new Brownells show room as well.
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