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.
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