Upper receiver question

[BrokenGrunt]

I've slowly been collecting pieces for a 450 BM build. I finally have my barrel inbound and have a question about upper receivers.

Will a standard AR15 upper work or am I better off spending the money for one of the XL type receivers with the larger ejection port?

Thanks!

[Hoot]

I've slowly been collecting pieces for a 450 BM build. I finally have my barrel inbound and have a question about upper receivers.

Will a standard AR15 upper work or am I better off spending the money for one of the XL type receivers with the larger ejection port?

Thanks!

Welcome Aboard Grunt;
Its hard to say. Time was, most AR upper receivers were only sized for 5.56 but that was before other larger calibers became more prolific. These days, many AR upper receivers are coming out with their ejection port already large enough. You have to approach it on a case by case basis. If you can't touch it before buying it, I would advise inquiring with the manufacturer. Not that it's hard to mod the ejection port. About the only down side is you wind up breaking through the anodizing where you relieve it. As long as you clean it from time to time, enough lubricant will remain on the exposed aluminum to keep it from oxidizing. Well, that and the obvious visual reminder. As you already mentioned, you can buy a receiver with its port already enlarged before anodizing and be done with it, but the price of the project goes up.
All the work that I've done with this caliber over the past 13 years was done using a 20" AR platform. So, I know the "gazintas and the gazoutas" pretty well. If you have any questions, fire away. There are plenty of helpful minds here.

Hoot

[Al in Mi]

You'll need the bigger port. Many have done it with a dremel, but check with Tony at Tromix, he usually has something ready to ship.

[Texas Sheepdawg]

2A4C226D-E001-416B-8268-20DEAE82C171.jpeg (73.61 KiB) Viewed 10669 times

This image is purposefully arranged with the A.R. 15 upside down, where the cover detent is towards you, and the muzzle end of the firearm is pointing to your left. If you want to modify your own port, here’s the specs.
I think Timothy LeGendre was the one who sent me this pic but he got it from a member here. (HOOT)

[Hoot]

I think Timothy LeGendre was the one who sent me this pic but he got it from a member here.

Its my 20" factory bushy. Everything was covered in a coating of Dow Corning MolyKote G-n, hence the gray color

Hoot

[Texas Sheepdawg]

I think Timothy LeGendre was the one who sent me this pic but he got it from a member here.

Its my 20" factory bushy. Everything was covered in a coating of Dow Corning MolyKote G-n, hence the gray color

Hoot

It’s been so long since I got that picture. I just know that I have it in my archives of stuff that have to do with a 450Bushmaster. There’s a lot of stuff in there from Tim too.

[BrokenGrunt]

Thanks everyone. I ordered an upper with the larger port.

I assembled my 450 BM today. I need to get a heavier buffer. I thought I had an H3 laying around but I can't find it. So I need to order one.

I bought the black mag followers off of eBay, hoping they will work with Pmags. I ordered a steel tanker style muzzle device from eBay...yeah I'm cheap. I'm a 100% disabled Veteran unable to work so funds are somewhat limited. I've been piecing this 450 together for over a year.

I think I have my bases covered. I've got a .223 Wylde, .300 BO, 6.5 Grendel, and now my 450 BM. I love building and tinkering with the AR15 platform.

I also reload and cast my own bullets. Not sure if I'm going to try and run cast through the 450 or not. My Ruger PCC eats cast bullets like a fat kid does Skittles.

I scored some 450 BM once fired brass from a local range so I'm almost set. I just need to either pick up a couple boxes of ammo, or some bullets to reload.

Again...thanks!

[Texas Sheepdawg]

Why do you need a heavier buffer?

[Hoot]

Why do you need a heavier buffer?

Translation: Why do you think that you need a heavier buffer? The 450b was designed to work with a conventional rifle buffer, whether it be in an A2 stock or Carbine stock. There are standard weight buffers for each. New builds typically take a while to "run in" because everything is new and rough as a rule of thumb. A heavier buffer would exacerbate that stiffness. If, once it is broken in and cycling gets smoother, you find that its swiping your brass, then you can entertain perhaps needing a heavier buffer. Ditto on the buffer spring. My original rig was a Bushmaster 20" with A2 stock, standard buffer and spring and it ran like a Swiss watch.I made a weight for the bolt carrier to delay unlocking a little to make life easier on my brass, since I reload all my calibers.

IMHO. the biggest mistake you can make is getting a barrel with too long of a gas system. That can make for a finicky to tune rig. Also in my opinion, if you're running a 16" barrel, stick with a cabine length gas system and if its a 20", then you can go out to a mid-length gas system. I do not recommend a rifle length gas system. Been there, regretted that.

Hoot

[Texas Sheepdawg]

I was going to go into details about the buffer system, but I decided to just sit back and see if maybe he had a genuine concern or a reason to get a heavier buffer. But my response would’ve been the same as what you see Hoot explaining above. Timothy designed this cartridge to run on A.R. 15 platform with mil, spec, parts, (mil spec bolt carrier, mil spec buffer, and mil spec spring, be it a A2 or a carbine.)
I wanted to do the same thing to my AR platform for my 450 bushmaster. I wanted to beef it up. But Timothy convince me that it just wasn’t necessary. The only thing I did was get a custom “RecoiLess” A2 stock by John Noonan. I don’t think he makes them anymore but if you can get in touch with him you could ask. Speaking of which, has anybody heard from Gunnut lately?