Looking to build a 450 bushmaster

1.Does it require a larger ejection port upper receiver or will a standard one fit?

2. What Collapsable stock system works the best?
   a. Is the "self-collapsing" stock an issue with these.
   b. Buffer weight or buffer and spring combo?
   c. Extra power spring good for these?

3. Anything else one needs to know before building one of these?

Thanks!

Did you mean 450 Bushmaster? Or 350 Legend?

The 450 does require a larger ejection port, but, it should work fine with a standard carbine or rifle buffer assembly provided the gas port is sized correctly.

Get ready to pay a pretty penny for ammo.

Oops. Thanks for catching that. I fixed it. A 450 Bushmaster.

Yes, you need an enlarged ejection port.
Go TROMIX for your barrel and bolt.
TROMIX has uppers with enlarged ports but if you have your own or one you especially want to use, Paladin Machine Shop Service, tp555(at)windstream.net, will open it up and get it back to you in a week, two max, and not charge very much either.  He can also lathe true the front of the receiver for a little extra.  Contact him for exact pricing and return shipping.  Probably both done for about $30 plus shipping and insurance.

IMO, start with standard buffer and spring.  That's my recommendation for .458 SOCOM but the .450 does operate at higher pressures.  Still, you cannot go wrong starting with the standard weights and adjust if needed.

I use Magpul stocks, CTR is my favorite, on my .458s and .458 cats and have never had a problem.  The ACE M4 SOCOM needs to be fixed into position or it can collapse.  Mine did but it was a first generation and I have no new information about the current models.  IMO stay away from CAR or M4 stocks military grade stocks and stick with anything Magpul or a maker that will stand behind their product.  Most aftermarket stocks will be OK probably but I only have experience with the two, ACE and Magpuls.   If in doubt, call them or email them and ask if they will warranty it for use on the .450 BM.

I built mine using a Satern upper receiver and barrel.  I know you said collapsible stock, but I threw this a1 on mine.  Adjustable gas block as well.  Once I got the gas block set, it’s ran flawlessly.

Attached File

What about the flash hider? Does it take the same one that is used on the .308 or something larger?

Yes, you'll need the port enlarged. A decent smith can open up the ejection port for you, or you can buy one already to go. Tromix, Satern, Anderson, and Aero have them in this configuration.

You can run them on a rifle buffer, or a standard carbine system. Tromix, IIRC, advertises their barrels as ready to go with either... but don't quote me on that.

Your muzzle device will usually be threaded at 3/4" by 24 or 11/64 by 28. The inner bores of them are nominally .480". No way you can put a .30 cal device on there by accident.

I built mine using a Satern barrel, Tromix compensater, Odinworks hand guard, Anderson upper, Spikes' lower, and carbine receiver extension with a MagPul SLS stock. Runs perfectly fine, no issues. The Satern barrel has a heavy, bull barrel profile with a .875" gas block journal. I didn't want the lighter profile that other manufactures offer. In order to get around the large barrel and the gas block, I used the Odin Handguard because it has a 1.5" inner diameter. The larger ID handguards are more than ok too, like Seekins, Spikes, and Aero Enhanced... just not the look I was going for. I'm not a fan of overly fat handguards.

Which bolt?  If you don't mind?

No, mine was 3/4x24.  Idk about others.

Thanks for the info guys I really appreciate it. I wanted to make sure I did it right and get some tips along the way.

My 18" mid weight Tromix would not run on either one. I sent Tony an email after trying everything I could think of - short of drilling the gas port larger - and he sent me one of his carbine spring & buffer sets. It now runs factory ammo reliably, but my plinker reloads are hit or miss. I am going to drill the port to match my (11) BCA barrels which all ran perfectly(yes, really!). I can always throw an adjustable gas block on to tame it, if needed. I'll be able to go back to my rifle buffer then too.

There is one other thing I'm not thrilled about with my Tromix barrel - the lack of a shoulder at the muzzle threads. If you buy this profile, you're forced to use a locknut for your chosen device. I prefer to lock a device up to a shoulder 1), for security and 2), it's easier to blend the device to the barrel for a nice clean look.

Is 450 Bushmaster the most common big bore?

Or is it just preference?

Get good magazines.. I also got a new follower for 223 mags and it has worked as well  .

Probably as far as factory ammo availability goes.  Personally, I'm a self admitted 458 socom fanboi since it uses regular GI mags to full capacity fine (though I run almost exclusively unmodified lancers for 11+1, or 13+1 w the extended basepad) and the bullet selection is great w/ .458 diameter bullets.  But, some states only allow for straight wall cartridges for hunting so that factors into why a lot of people choose that.

When you weight out the pros and cons of 450 vs the 458 and 50 Beo, it comes out ahead for a few key reasons:

- factory ammo availability
- factory ammo cost
- straight wall for hunting in states that don't allow bottleneck type
- cost and ease of reloading (can use 45acp bullets, loads like a pistol cartridge due to straight wall design)
- cost of reloading components (more factory brass available, 45acp bullets again, load with cheaper shotgun powder)

For most people, that is enough to sway them to the 450 unless they are set on having the biggest (50Beo) or already reload for 45 Colt or another caliber that uses .458" bullets.

45 Colt uses .452" bullets, same as the 450.  That is what swayed me to the 450 as I already loaded 45 Colt and have a pile of projectiles.  Also the magnum powders that I alrready used in 45 Colt work well in the 450.  The only "bad" thing about the 450 is it uses small primers, which I am not flush in like large primers.

I think he just left out a comma,”or already reload for 45 Colt or other caliber that uses .458" bullets.” Should have read, “...or already reload for 45 Colt, or  other caliber (such as .45-70) that uses .458" bullets.”

Commas are important and can really change the meaning.  Like the old school example of “let’s eat grandma” and “let’s eat, grandma.”

Never mind.  Guess I assumed wrongly.  He did mean .45C was .458.

I bet if I owned a 45 Colt, I would have known that... not sure why I thought they used the larger .458" bullets. I stand corrected!

But yeah, component commonality is nice especially in these times of lesser availability. I have plenty of SRP, but I load my 450bm witb CCI450s and do wish I had a few more of them than I currently do. I'm using Lil Gun for powder and loading the same 230gr fmj's I load in my 45acp rounds for 450 plinkers.