.450 Bushmaster velocity test 12" vs 16"

[MCMXI]

I've had a .450 Bushmaster for five years or so. It came with a 20" barrel but last year I SBR'd the lower and cut the barrel down to 12" with the idea of using it suppressed. Last week I received a 16" Faxon barrel so figured I'd shoot a couple of factory loads to see how much of a difference 4" makes. I want to buy the SilencerCo Hybrid to use on this rifle as well as a Marlin 1895 SBL in .45-70 Govt. so was curious if 12" was a really bad idea. Here are the results and a couple of photos of the rifle. I installed a Superlative Arms adjustable gas block and straight gas tube with the Faxon barrel.

 

[BigBore44]

So around 100-150 FPS. Not much of a difference. I wonder what kind of difference handloading can make as you’re only measuring factory loads. But that doesn’t discount the experiment in any way as that’s what your intention was. 2000fps in a pistol bullet is zipping and slowing it down some may actually improve bullet performance.

 

[someguy2800]

wow, not much difference at all

 

[mcb]

Nice data, thanks for sharing.

Maker Bullets has a 425 gr bullet designed for subsonic use in 450 BM. I have not got to play with it yet but have had great performance from their 220 gr 300 BO bullets. I do have a subsonic load worked up for a 405gr bullet, but I don't have a 45 suppressor yet.

 

[MCMXI]

Maker Bullets has a 425 gr bullet designed for subsonic use in 450 BM. I have not got to play with it yet but have had great performance from their 220 gr 300 BO bullets. I do have a subsonic load worked up for a 405gr bullet, but I don't have a 45 suppressor yet.

I have a bunch of Remington .458 cal 405gr JSP bullets and bought swaging dies to size them to .451". I'm planning on working up a subsonic load with those bullets. Do your subsonic loads produce enough gas to cycle the bolt?

I was using an AAC Ti-RANT 45 on the 12" barrel shooting only subsonic loads but didn't get far enough along to say anything meaningful.

 

[mcb]

I was using the the same bullet and had sized them down with Lee sizing dies. They will not cycle my 20-inch or a friend's 16-inch without a suppressor; they occasionally eject but never got the bolt back far enough to strip a new round. But both cycled well and would lock back on the last round using his silencerco hybrid suppressor.

 

[MCMXI]

I was using the the same bullet and had sized them down with Lee sizing dies. They will not cycle my 20-inch or a friend's 16-inch without a suppressor; they occasionally eject but never got the bolt back far enough to strip a new round. But both cycled well and would lock back on the last round using his silencerco hybrid suppressor.

Good to know ... thanks.

 

[Goosey]

wow, not much difference at all

It doesn't lose much, but it loses about as much as I expected.

For example, you might have a 308 that looks like this when you chop the tube:

16" barrel = 2660
12" barrel = 2422
(numbers based on rifleshooter.com test)

But that 12" 308 gives 91.1% of the 16" 308 velocity.


In the OP's test, from the 12" barrel, the Hornady and Remington, respectively, gave 93.7% and 93.9% of the 16" barrel's velocity.

And 93.8% vs 91.1% sounds a lot closer than 132 fps vs 238 fps.

It's 59.5 fps/inch vs 33 fps/inch, but only 2.2%/inch vs 1.6%/inch (both round to 2% )




A lot of cartridges have much more similar gains or losses, ratio-wise, when chopping the barrels, than people think.

 

[MachIVshooter]

A lot of cartridges have much more similar gains or losses, ratio-wise, when chopping the barrels, than people think.

True of smaller capacity cartridges, but doesn't hold when you get into bigger magnums burning 70+ grs. of slow powders. Start cutting .300 win mag and larger to less than 20", you see very dramatic reduction in velocity, with commensurately large fireballs.

 

[Goosey]

True of smaller capacity cartridges, but doesn't hold when you get into bigger magnums burning 70+ grs. of slow powders. Start cutting .300 win mag and larger to less than 20", you see very dramatic reduction in velocity, with commensurately large fireballs.

I can give these examples from the same rifleshooter.com tests:

243 WINCHESTER
24" barrel: 2826
16" barrel: 2488

p = 88.0%

308 WINCHESTER
24" barrel: 2932
16" barrel: 2660 (interpolated)

p = 90.7%

300 WIN MAG
24.25" barrel: 2892
16.25" barrel: 2575

p = 89.0%

338 LAPUA MAG
25" barrel: 2848
17" barrel: 2547

p = 89.4%


Indeed some cartridges can be quite noticeably more "efficient" than others... for example, the 7.62x39. But a whole lot of them are closer than people expect. For example, you will hear many people will say that a .25-06 "needs" a 24-inch (or even a 26-inch) barrel. But in fact, with most powders cutting a twenty-six inch .25-06 to 24, 22 or even 20 inches is going to scrub only about the same proportion of the velocity as a 26-inch 308 would lose, being cut down to the same length.

 

[MachIVshooter]

with most powders cutting a twenty-six inch .25-06 to 24, 22 or even 20 inches is going to scrub only about the same proportion of the velocity as a 26-inch 308 would lose, being cut down to the same length.

The change is more dramatic with the more overbore cartridges, and the .25-06 is actually slightly more overbore than the .300 WM (1,292 grs. per square inch vs. 1,267).

The change in .308 velocity from 24" to 20" is 4%, while it's 5% for .300 WM. Drop from 20" to 16", the .308 loses 5% while the .300 WM is 7.5%. That trend continues in both directions, the .300 mag losing proportionately more with ever shorter barrels, the .308 gaining proportionately less from longer ones. The .25-06 will follow a very similar curve to the .300 WM.

As well, the percentage change is relatively meaningless when the actual change results in a massive MPBR loss.

These higher velocity rounds, of course, have little to do with a short barreled thumper as is the subject of the thread. His velocity loss of 30 FPS per inch from 16" to 12" is about what I'd expect of a lower pressure round with such a high powder capacity to bore ratio (262 grs. per square inch). Going the other direction with it, from 16" to 24", I'd expect a mean increase of less than 20 FPS per inch.

 

[Gtscotty]

When you chopped my .30-06 from 22" to 18.5", original velocity decreased 3.25% (95 fps) with my 165gr load and 2.93% (82 fps) with my 180gr load. Just another same barrel reduction data point.

 

[mcb]

But OP is also going sub-sonic. The short barrel is an advantage as you can run loads with more gas volume to get a higher port pressure without going super sonic.

 

[Gtscotty]

I meant to ask, what dies and process are y'all using to size jacketed .458 bullets down to .452? Do you have to use multiple steps? Is there a specific die set folks use for this?

 

[mcb]

I bought regular Lee sizing dies, .454, .452, .451. I ended up using just the .454 and .451 dies. I did it in two steps to reduce the required effort. I used a good closed arch RCBS press and lots of liquid Alox. Pre-lub the dies the first time too. I pushed a batch of bullets through the .454 die then re-lubbed the bullets and then through the .451 die. They sprang back a touch and my batches mic'd .4515 - 4522.

 

[MachIVshooter]

When you chopped my .30-06 from 22" to 18.5", original velocity decreased 3.25% (95 fps) with my 165gr load and 2.93% (82 fps) with my 180gr load. Just another same barrel reduction data point.

Your loads actually did a little better than I would have expected, but not too far out of the ballpark for rounds with that 800-1000 grs. per square inch powder capacity to bore area ratio. I would have estimated 30-35 FPS per inch for a net loss of about 100-120 FPS going from 22" to 18.5.

I compiled this chart to help illustrate the ratio that gives us an indicator of how barrel length will affect velocity. Of course there are other variables like powder burn rate, and a few of these rounds are not in the typical 55-65 KSI range of high velocity rifle rounds, but it gives some perspective on which rounds perform better as barrel length is reduced. In general, the higher the ratio, the more velocity loss you'll see as barrels get shorter, especially into SBR territory.

I had to pull case capacities from a number of sources, and some may be slightly different than what you'd find in your own google search, but close enough for these "quick & dirty" purposes. Capacities rounded to nearest integer, ratio to nearest 5. Sorry for the loss of formatting in my C&P

Cartridge Case Capacity Bore Area Grs/sq.in. bore area

.17 Rem 27 .023235 1170

.204 Ruger 33 .032685 1010

.22 Hornet 14 .039408 355

.223 Rem 31 .039408 790

.22-250 Rem 43 .039408 1090

.220 Swift 48 .039408 1220

.223 WSSM 53 .039408 1345

.243 Win & WSSM 54 .046759 1155

6mm Rem 55 .046759 1175

.257 Roberts 56 .051875 1080

.25-06 Rem 66 .051875 1275

6.5 Creedmoor 53 .054739 970

6.5x55 Swede 57 .054739 1040

6.5 Rem Mag 68 .054739 1240

6.5-284 68 .054739 1240

.270 Win 68 .060263 1130

7mm-08 Rem 56 .063347 885

7x57 Mauser 59 .063347 930

.280 Rem 68 .063347 1075

7mm Rem Mag 84 .063347 1320

7mm RUM 108 .063347 1705

.30-30 45 .074506 605

.308 Win 56 .074506 750

.30-06 Sprg 69 .074506 925

.300 Win Mag 94 .074506 1260

.300 RUM 111 .074506 1490

8x57 Mauser 62 .081940 755

8mm Rem Mag 98 .081940 1195

.325 WSM 83 .081940 1010

.338-06 70 .089727 780

.338 Win Mag 86 .089727 960

.338 RUM 112 .089727 1250

.338 Lapua 114 .089727 1270

.35 Rem 51 .100660 505

.35 Whelen 71 .100660 705

.350 Rem Mag 73 .100660 725

.375 H&H Mag 95 .110450 860

.375 RUM 114 .110450 1032

.378 Wthby 133 .110450 1205

.404 Jeffrey 113 .139870 810

.416 Rem Mag 107 .135920 785

.416 Rigby 129 .135920 950

.444 Marlin 69 .144550 475

.45-70 Govt. 79 .164750 480

.458 Win Mag 93 .164750 565

.460 Wthby. 140 .164750 850

.50 BMG 293 .204280 1435

 

[MCMXI]

I meant to ask, what dies and process are y'all using to size jacketed .458 bullets down to .452? Do you have to use multiple steps? Is there a specific die set folks use for this?

Good thing that @mcb answered this. I stole his idea a few months back and only bought .454" and .451" based on previous comments but I haven't sized a single bullet yet. Regardless, kind of makes that ".458 SOCOM has better bullet choices" kind of moot.

Had I planned things better I would have tested velocity at 20", 16" and 12" using the same Bushmaster barrel but in my haste I chopped the barrel to 12". The test results are interesting but it's quite possible that the Faxon barrel and Bushmaster barrels would give different velocities for the same load and same length.

But OP is also going sub-sonic. The short barrel is an advantage as you can run loads with more gas volume to get a higher port pressure without going super sonic.

Yep, I want a good all-around barrel length for the three combinations that I plan on running i.e. suppressed subonic, suppressed supersonic and unsuppressed supersonic. 12" is a good length but if I were doing it again I would cut the Bushmaster to 13" or 14". I'm not going to cut the Faxon down.

 

[Gtscotty]

I was using an AAC Ti-RANT 45 on the 12" barrel shooting only subsonic loads but didn't get far enough along to say anything meaningful.

How did the .450 subs sound suppressed with your .45 can? I have an Obsidian .45 in jail, so if I go .450, i'd be running a similar setup.

I was using the the same bullet and had sized them down with Lee sizing dies. They will not cycle my 20-inch or a friend's 16-inch without a suppressor; they occasionally eject but never got the bolt back far enough to strip a new round. But both cycled well and would lock back on the last round using his silencerco hybrid suppressor.

What powders are y'all using for these loads? There isn't much out there in the way of reloading data for .450 subs. It seems like most people are using Trail Boss, which supposedly tops out at about 900 fps with 405gr and doesn't usually reliable cycle ARs (at least from what I've read). I guess VV Tin Star is supposed to work a little better, but I don't think I've actually ever seen any in person.

 

[someguy2800]

How did the .450 subs sound suppressed with your .45 can? I have an Obsidian .45 in jail, so if I go .450, i'd be running a similar setup.



What powders are y'all using for these loads? There isn't much out there in the way of reloading data for .450 subs. It seems like most people are using Trail Boss, which supposedly tops out at about 900 fps with 405gr and doesn't usually reliable cycle ARs (at least from what I've read). I guess VV Tin Star is supposed to work a little better, but I don't think I've actually ever seen any in person.

Coming from literally no experience, I would expect trail boss to work well in a bolt or single shot but I don't think it would have enough gas volume in an AR15 since its a very fast burn rate. I would bet that something like 2400, CFE BLK, or 1680 to work better.

 

[mcb]

I started with Trailboss and it topped out at about 908fps in my 20-inch 450 Bushmaster pushing the 405 gr bullet. I simply ran out of case volume. I switch to Vihtavuori N32C Tin Star. It is a competitor to Hodgdon/IMR Trailboss but has a higher bulk density so you can get a bit more in the case and I managed to get to 1050fps with the 405gr bullet. That said I suspect my load is a touch over SAAMI MAP for 450 BM according to my Quickload analysis. Not much but a 1000 psi or so, and I can't know for sure without a instrumented test barrel.

 

[MCMXI]

How did the .450 subs sound suppressed with your .45 can? I have an Obsidian .45 in jail, so if I go .450, i'd be running a similar setup.

They were quiet as far as I remember. I was using 12.8gr of Trailboss and a 300gr lead bullet from Oregon Trail getting velocities of 1,120 fps to 1,130 fps but that load wouldn't cycle the bolt.