SBR Bolt Action - 450 Bushmaster or .308?

[westford86]

I’m looking for advice and to generally discuss the topic of an SBR bolt-gun build.

Backstory: I have a Remington 700 that’s a registered SBR. It currently has a 12.5″ .45 Raptor barrel on it, but it’s just awful. Even for a short .45, the accuracy is totally unacceptable. The best I have ever gotten it to shoot is 3 MOA, and I know the problem isn’t me because I have gotten my 12.5″ .450 Bushmaster AR to group nearly 1 MOA. So I am going to rebarrel it, but this time I am going to skip the wildcat-cartridge route in favor of something commercially available; I simply don’t have the bandwidth for reloading like I used to.

My original intent with this build was to have a lightweight, compact hunting rifle for medium game. I have a Christensen Arms MPR chassis I’ll be chopping down the forearm on and dropping it into, so the whole package will be pretty light and compact and easy to stow away when hiking out from a hunt. Up here in AK, caribou are pretty damn easy to shoot, and most people don’t take a shot over 100 yards if they don’t need to, so I am not worried about the lack of effective range. I also wanted it for the novelty of having an SBR bolt-gun with a heavy-hitting big-bore round.

Why .450 Bushmaster or .308? .450 Bushmaster is an 80% solution compared to the .45 Raptor, but still meets my intent of the original build without the headache of having to reload. I already have a .45 rifle can, which I have no use for other than this build (I am scrapping my aforementioned .450 Bushmaster AR upper because of feeding-reliability issues), and now there are factory subsonic rounds for .450 BM, which would be a fun novelty for range days. However, I am also thinking .308 because it will be more accurate than .450 BM and still deliver plenty of punch out of a 12.5″ barrel for something like a caribou at 100 yards. There is an abundance of factory ammo options, and some manufacturers like Fiocchi are making SBR-specific ammo now. With a short barrel, I don’t think there is any advantage to using a more modern cartridge like the 6.5 Creedmoor, or anything with greater powder capacity.

I am not interested in going the .223 or .300 Blackout route, but I am open to suggestions on other cartridges. If anyone has experience with SBR bolt guns, I’d like to hear what you have to say.

 

[Old Man with Gun]

I'd go 450BM, big bores are far more efficient in short tubes and a real subsonic option.

 

[Niles Coyote]

450 Bushmaster, but I'm biased.

 

[tekmann2377]

If significantly improved accuracy is an important criteria, I would go 308, and consider a slightly longer barrel (13.5-14) if that is not an issue.

I have a bolt 450 BM and while it provides decent accuracy, it doesn't seem to measure up to what I can easily achieve from bottleneck cartridges. Subsonics also don't shoot that well either, mainly due to vertical dispersion.

If you are looking for maximum terminal effectiveness with subsonic then a big bore is the only way to go.

A shorter 308 with the right bullets (IE 125-135 gr bullets pushed fast) has a much better effective range than a big bore if you are looking to do any shooting past 200 yards.

 

[westford86]

450 Bushmaster, but I'm biased.
View attachment 8783287

Nice looking build. What barrel did you use? I am thinking about getting a blank from Preferred.

 

[westford86]

If significantly improved accuracy is an important criteria, I would go 308, and consider a slightly longer barrel (13.5-14) if that is not an issue.

I have a bolt 450 BM and while it provides decent accuracy, it doesn't seem to measure up to what I can easily achieve from bottleneck cartridges. Subsonics also don't shoot that well either, mainly due to vertical dispersion.

If you are looking for maximum terminal effectiveness with subsonic then a big bore is the only way to go.

A shorter 308 with the right bullets (IE 125-135 gr bullets pushed fast) has a much better effective range than a big bore if you are looking to do any shooting past 200 yards.

I am not expecting much when it comes to accuracy, if the gun shoots 1.5MOA I'd be content. After all, it is a straight wall cartridge pushing out a big fat slug. I really wish 458 SOCOM wasn't so expensive to shoot, from my experience it's better than 450 BM in every way except price and the reduced mag capacity. If I really want to be accurate or do any hunting beyond 200 yards I'll just reach for something else in the safe.

What are the details of your 450 BM bolt gun? I am curious how other people decided to spec their rifles.

 

[Niles Coyote]

Nice looking build. What barrel did you use? I am thinking about getting a blank from Preferred.

16 twist Green Mountain m24 contour. It's a heavy setup but has shot many good groups with handloads and both Hornady 250ftx and subsonic 395s

 

[tekmann2377]

My rifle is not a custom rifle. It is a Ruger Gunsite Scout with a 1/16 twist and 16" barrel. It shoots pretty well with loads using the 250 FTX. It did not shoot as well with the XTP Mag and 395 SubX. The 250 FTX seems to both feed well and shoot the best of the bullets I have tried. It would meet your accuracy standards but just barely.

I would be satisfied with the velocity and accuracy for deer size game with the 250 FTX and my combo for <200 yards.

My suggestion regarding 308 instead of a 450 BM is that I think the terminal effects, ballistics, and trajectory are better shooting something like a 308 with a 125 Accubond than the typical 450 BM load.

 

[bohem]

Ive built a number of barrels and converted regular 308 actions to 450 bushy in the past few years for guys hunting straightwall regs.

Factory Hornady Black ammo in 250gr shoots 3 under MOA out to 400 fairly consistently for me in these guns. Hand loaded SML bullets like the 275 XLD Arrowheads and similar typically run tighter than that til about 600.

It's not a bottleneck round but it also will hold minute of deer vitals at 400+ which is WAY beyond the needs of 99%+ of people hunting the straightwall regs.

At 400 yards it's still got more schwack left than a 45acp at the muzzle. It's closer to a 44 mag at the muzzle by that distance.

 

[MO Fugga]

I am not expecting much when it comes to accuracy, if the gun shoots 1.5MOA I'd be content. After all, it is a straight wall cartridge pushing out a big fat slug. I really wish 458 SOCOM wasn't so expensive to shoot, from my experience it's better than 450 BM in every way except price and the reduced mag capacity. If I really want to be accurate or do any hunting beyond 200 yards I'll just reach for something else in the safe.

What are the details of your 450 BM bolt gun? I am curious how other people decided to spec their rifles.

As far as expenses, the beauty of. 458S is the brass life. It does not stretch. I have brass that has been fired 15+ times without annealing or trimming. Primer pockets still tight enough. Not to mention bullet selection is the most versatile. 450 is at home in straight wall hunting states only, IMO.

It'll never be SAAMI approved, and factory ammo is expensive, but worth it.

 

[bohem]

As far as expenses, the beauty of. 458S is the brass life. It does not stretch. I have brass that has been fired 15+ times without annealing or trimming. Primer pockets still tight enough. Not to mention bullet selection is the most versatile. 450 is at home in straight wall hunting states only, IMO.

It'll never be SAAMI approved, and factory ammo is expensive, but worth it.

450BM won't be SAAMI approved? Or did you mean the 458 SOCOM?
Page 156 in the SAAMI spec

There are a couple of things I like about the 450 BM over the 458 Socom; the first is the brass construction. The parent case of the bushmaster is the 284 Win cut down at the shoulder whereas the 458S is a necked down pistol case, the 50 AE as I recall. The max pressure the brass on the 50 AE handles is about 35ksi-38ksi. However the Bushmaster retains the hardness spec and case web dimensions of the parent 284 Win brass. So it can be loaded to 60ksi

For AR15 use that's a wash because the gun design tops out around 36ksi for both of them (it's slightly better for the BM but not enough to really argue about). In a bolt action though, you can load the Bushmaster HOOOOOOT. For someone hunting in a straightwall area or just trying to prove a point the effective range of the 450BM is significatnly improved over the 458 Socom due to this.

In bolt guns the other nod to the Bushy that I see is the mag feeding. I regularly take a 308 action that is already mag fed and we stick a 450 barrel on it, tweak the mag lips a tiny bit and send it to the owner who can now run a 4 round mag wtih 1 in the chamber in pretty much any straight wall state in the country. The 458 doesn't like to feed as readily from AICS mags with the heavily rebated rim.

 

[Old Man with Gun]

As far as expenses, the beauty of. 458S is the brass life. It does not stretch. I have brass that has been fired 15+ times without annealing or trimming. Primer pockets still tight enough. Not to mention bullet selection is the most versatile. 450 is at home in straight wall hunting states only, IMO.

It'll never be SAAMI approved, and factory ammo is expensive, but worth it.

I really like my AR-458. Even Berry 350g plated round nose @1635 hit hogs hard and are cheap to load.

 

[MO Fugga]

450BM won't be SAAMI approved? Or did you mean the 458 SOCOM?
Page 156 in the SAAMI spec

There are a couple of things I like about the 450 BM over the 458 Socom; the first is the brass construction. The parent case of the bushmaster is the 284 Win cut down at the shoulder whereas the 458S is a necked down pistol case, the 50 AE as I recall. The max pressure the brass on the 50 AE handles is about 35ksi-38ksi. However the Bushmaster retains the hardness spec and case web dimensions of the parent 284 Win brass. So it can be loaded to 60ksi

For AR15 use that's a wash because the gun design tops out around 36ksi for both of them (it's slightly better for the BM but not enough to really argue about). In a bolt action though, you can load the Bushmaster HOOOOOOT. For someone hunting in a straightwall area or just trying to prove a point the effective range of the 450BM is significatnly improved over the 458 Socom due to this.

In bolt guns the other nod to the Bushy that I see is the mag feeding. I regularly take a 308 action that is already mag fed and we stick a 450 barrel on it, tweak the mag lips a tiny bit and send it to the owner who can now run a 4 round mag wtih 1 in the chamber in pretty much any straight wall state in the country. The 458 doesn't like to feed as readily from AICS mags with the heavily rebated rim.

Yes I meant SOCOM for not being approved. .450 definitely wins in that case. And you can buy it at Walmart.

 

[Bakwa]

My rifle is not a custom rifle. It is a Ruger Gunsite Scout with a 1/16 twist and 16" barrel. It shoots pretty well with loads using the 250 FTX. It did not shoot as well with the XTP Mag and 395 SubX. The 250 FTX seems to both feed well and shoot the best of the bullets I have tried. It would meet your accuracy standards but just barely.

I would be satisfied with the velocity and accuracy for deer size game with the 250 FTX and my combo for <200 yards.

My suggestion regarding 308 instead of a 450 BM is that I think the terminal effects, ballistics, and trajectory are better shooting something like a 308 with a 125 Accubond than the typical 450 BM load.

Have you tried any other subsonic rounds?
How bad was the XTP and SubX?

 

[bohem]

Have you tried any other subsonic rounds?
How bad was the XTP and SubX?

If you swab an oiled patch through the bore prior to the first shot the First Round Drop goes away with the SubX. I don't think I'd worry about any of them shooting past 100 yards for more than target practice but if you need head shots inside 75yd the oil trick does make a big difference.