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Old July 27, 2021, 11:01 PM   #1
corbanzo
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Making the 450 bushmaster work

After owning my .450 bushmaster for over a year, I am finally getting to the point of it being reliable... and not because the action has worn in, so I thought I would make a write up of my science project.

First of all, if you are considering getting into a bigbore AR-15, let me highly recommend you go with the 458 SOCOM, as it is actually designed to work in a semi-auto. I understand that the 450 bushmaster being a straight-walled cartridge makes it, according to certain state laws, the only option. This is not the case in Alaska where I live, but it's the route I took, cause you know, more power!

The 450 bushmaster is a pain in the ass, but it does pack a wallop if you can make it work correctly. Mine is a bear creek pistol. It is gassed and sprung correctly, so the action works as it should, but the two major problems facing the .450 bushmaster are the magazines and the magazines.

The first problem with the gun is the straight-wall cartridge has to load at quite and angle out of the magazine making it stick in the chamber at angle, either stopping the action or slowing it down enough so it won't close completely.

There are three fixes to this issue, the first I did to mine but I don't really recommend: "Glock" the chamber. By adding a little bit of chamfer to the mouth of the chamber and smoothing it out as much as possible it doesn't give quite as much edge for the the case to stick on. This does remove a little bit of support for the case expansion so if you take too much it will allow the case to expand to the point of being unsafe. This by itself will not get rid of the problem but will help a bit. I ground down my feed ramp and shined it up slick as well. I have not noticed any large deformations in the web of the brass.



The second fix for this is bullet selection and seating. Anything to keep the case length to a minimum will help make the case not stick while loading. I have used pistol bullets like the 300 grain Hornady XTP. and seated to the recommended COAL under hornady, the bullet projects from the casing enough that the shoulder of the bullet will make it stick in the chamber. Barnes TSX bullets have the opposite problem, with their long nose, the nose will stick it in the chamber, at recommended COAL's the TSX sticks worse than the XTP. The hornady FTX with its rounded nose that starts directly after the crimp ring is less likely to stick than the other two.



The third fix is to cut back the feed lips on the magazine. This allows the base of the bullet to pop up sooner and the cartridge to feed into the chamber straighter. On a standard magazine, this involves cutting the feed lips to about 75% of their original length. This creates another problem: the front part of the cartridge pushing up at an angle and the bolt catching on this cartridge which I will get into later. You have to make sure either way you have a quality magazine with strong feed lips. Plastic magazines with plastic lips just don't work with the .450.



If you are having problems with the rifle cycling, it could be a problem with the gas system, and in such case an adjustable gas block could fix your problem, or a change in buffer weight, but I'm going to get into the mechanical problem which is pressure from the magazine on the bottom of the bolt. With the large cases sliding over each other, it creates resistance that slows down the slide and also pushes the next case in the magazine forward in the magazine, and pushes the nose of that next bullet down which makes it catch in the magazine.

This first change is to use the proper follower - and I don't mean the single stack follower that manufacturers are making for these magazines - those are junk. They make a huge resistance that messes up the last cartridge feeding, the ones I have seen are tall which reduces capacity, and they are not anti-tilt which doesn't push the cartridge up as it should. You can see in this picture the brass left behind on the follower when the cartridge is fed.



What I found is that using a standard anti-tilt follower and just grinding down the double stack nub and adding a little slot in the center to center the bullet performs the best. It gets rid of some of the feeding resistance, and allows you to easily remove some of the material around the edges to have to follower come all the way to the top of the feed lips to push the case up further and feed straighter.



These large cartridges, especially if you cut the feed lips back, can push out on the feed lips and cause more problems. To solve this, and to help with the resistance between the cartridges, remove the spring and bend it towards itself on the edges along the spring to shorten it, and to lower the total spring weight. Don't got too far or the last round wont have enough power to pop it up out of the magazine. High capacity magazines with any sort of bend in them don't work. Also, play with how the spring sits on the bottom of the follower to keep the front of the follower up, without shoving the nose of the cartridge up too far.

So far, the tromix lancer magazines are the best I've seen. Their single stack followers are crap and allow a lot of tilt and only allow it to hold three without forcing it in the rifle. Their double stack follower is the best I've seen, modified as above is best. The duramag magazines are better than standard, but they have much too powerful springs, as well as followers that tilt and stick. Remove some of the sides of the follower and squish the spring and it works ok. Either way don't over load any magazine, the 7 round duramag holds 6 extremely well.

I had to make all of these changes before I could actually go through a pile of mags without any failures. Before it was every 2-3 rounds I would have a failure.



So if you are making your way into the .450 bushmaster in a semi-auto, good luck.

Last edited by corbanzo; July 28, 2021 at 12:00 AM.
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Old July 28, 2021, 04:56 AM   #2
stagpanther
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I went with 458 socom when trying to decide between the two, given a choice between tromix/Teppu Jitsu and Alexander--I'd go with Tromix. Nice you figured it out, I've never had any issues with the socom using tromix's single stack follower installed. I like having a shoulder too. There's always the 350 legend for the straight-wall crowd.
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Old July 28, 2021, 12:40 PM   #3
berettaprofessor
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I have a 16" Bear Creek complete 450 Bush upper. Ran flawless with the only adjustment being adding an H2 buffer (hickuped occasionally with a carbine buffer). Runs on any factory ammo or reloads, except for some "subsonic" commercial 450 that I bought which makes it a single shot. My reloads were always Hornady FTX's with IMR 4227 powder. And I use Magpul mags with 3-D printed followers purchased on EBay and one ARStoner 450 mag without issue.

Only concession I made was buying a thicker butt-pad for the rifle For perspective, my 308 load in an AR10 calculates to 9.7 ft-lbs free recoil energy; the 458 was 17!

I would disagree with OP's recommendation for a 458 SOCOM; 450 Bushmaster has a broader choice of bullets and the straight-wall design is more applicable to other states, even if yours doesn't require it. Easier resale.
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Last edited by berettaprofessor; July 28, 2021 at 01:13 PM.
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Old July 28, 2021, 06:58 PM   #4
bfoosh006
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Very helpful ! Thanks for sharing.

If I may, I would also suggest , making sure the front of the bolt face , where the cartridges rim / case head slides across... is polished smooth.

That helps the cartridge feed better, just by eliminating any unwanted "friction" between the bolt face and case head.
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Old July 28, 2021, 07:04 PM   #5
jmr40
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Quote:
The 450 bushmaster is a pain in the ass, but it does pack a wallop
I don't understand the "packs a wallop" comment. At best the 450 BM will ALMOST equal 45 caliber black powder muzzle loader performance. For the guys who previously were limited to muzzle loaders only I can see why they might like to get similar performance from a cartridge fired weapon. It is a very good option for states with limited options for deer hunting.

But nobody ever claimed a 45 caliber muzzle loader packed a wallop. In fact it is the legal minimum for deer in most places and not considered powerful enough for larger game such as elk.
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Old July 28, 2021, 07:40 PM   #6
stagpanther
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Quote:
But nobody ever claimed a 45 caliber muzzle loader packed a wallop.
My CVA 45 paramount does--accurate too.
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Old July 28, 2021, 07:58 PM   #7
4V50 Gary
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Excellent thread.
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Old July 29, 2021, 08:24 AM   #8
MarkCO
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I had two .450BMs and knew many others with them. The OPs issues appear to be related to a specific firearm and in no way is it the cartridge itself that is the problem. Like most AR15s, the .450BM the OP has, based on the specs I looked up, would be over gassed by a good margin. Over gassed incorrectly seen as a magazine problem is a common issue for AR15s in all calibers.
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Old July 29, 2021, 08:31 AM   #9
9x19
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My only .450 Bushmaster was a 12" carbine gassed model and I didn't have any magazine issues with it. I used 20rd aluminum mags with a .450 follower (both dedicated and a tray that fit over the 5.56 follower).

Recoil was significant, and my arthritic shoulder thanked me when I sold it.
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Old July 29, 2021, 08:36 AM   #10
stagpanther
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Quote:
I would disagree with OP's recommendation for a 458 SOCOM; 450 Bushmaster has a broader choice of bullets and the straight-wall design is more applicable to other states, even if yours doesn't require it. Easier resale.
And I disagree with this...the .458 has better made-for-rifle bullets and the slight shoulder is better for more reliable headspacing IMO. Unless I lived in a straightwall state I'd take the socom in a heartbeat over the bushmaster. It appears the OP was most likely having issues with magazine conversion from double-stack to single stack. Tromix got ya covered with their single stack follower conversion and Lancer magazines. Never an issue feeding anything--rifle or pistol bullet, but the bushmaster is slightly narrower so who knows.
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Last edited by stagpanther; July 29, 2021 at 08:43 AM.
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Old August 2, 2021, 07:38 PM   #11
Rembrandt
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Dittos on the Tromix followers and Lancer magazines.....built (5) 450 BM's for family to hunt with, we're all using Lancer/Tromix. No more feeding issues.
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