the .57 BMG Idea

[The6thMessenger]

First, i wanted to open up with the .50 BMG.

It comes for different barrels right, M2/HB usually has 45-inch of barrel, standard M107 has 29-inch, QC version has 20-inch, MICOR Leader 50 has 24-inch, and the way i heard it there are 16, 18, and 22-inch barrels for the .50 BMG.

But i also heard that the optimal barrel length for anti-materiel rifles are 29-inch, as it has the least velocity drop from the 45-inch barrel length.

Now my question is, wouldn't anything below 29-inches would make the .50 BMG a bit more inefficient?

Here is an idea, the Russian 14.5x114mm, or the .57 cal is a bit common, just as the .50 BMG albeit not NATO standard ammunition. Supposed that the .50 BMG would be necked up to accept 14.5mm bullets, with the very same amount of propellant, but 1050-grain bullet.

Would a larger diameter bullet would have better effects on a shorter barrel than the original .50 BMG?

Effect being it's muzzle energy would be higher against the .50 BMG with the same short barrel?

Supposed that the .50 BMG is fired at these barrel lengths; 16,20,24 inches, would the hypothetical ".57 BMG" have a better performance against the original .50 BMG upon a shorter barrel. Lastly, what is the optimal barrel length; being the shortest, like 29-inches for the .50 BMG.

 

[50 Shooter]

Your pushing a heavier bullet with the same amount of powder, you're already behind. Then you add a shorter barrel and losing velocity. So, no it won't really be an improvement over the 50 BMG. Another thing you'll need to do is have a faster twist barrel for the heavier bullet. Standard is 1:15, for that heavy you'd have to go with a 1:9.5 twist. That will bring your cost up also on a project like this.

Have you looked at the 14.5mm JDJ round?

 

[ihctractor]

The other problem is that your new .57 cal rifle would be considered a "destructive device" under the ATF and have to be registered, taxes paid etc.
Lot of messing around for 0 gain over the .50.

 

[50 Shooter]

The .57 would be exempt just like the JDJ round, using a .50 case as the parent. 20mm rifles have an exemption also, so that's the least to worry about.

 

[The6thMessenger]

Huh, didn't know about the 14.5 JDJ. Thanks anyways.

Wikipedia don't have a lot of info about it too xD.

 

[MachIVshooter]

The .57 would be exempt just like the JDJ round, using a .50 case as the parent. 20mm rifles have an exemption also, so that's the least to worry about.

The developer would have to submit it to ATF FTB and hope they give it the sporting exemption. There is no guarantee; totally up to ATF whether or not they consider a weapon or cartridge "particularly suitable for sporting purposes".

20mm weapons most certainly are not DD exempt. Inert 20mm ammunition is not a DD, nor is any other artillery round, so long as there is less than 1/4 oz of explosive compound within (hence the Raufoss being legal)

 

[HankB]

NFA issues aside, from a purely ballistic standpoint, there might be some marginal benefit to necking up the .50 BMG, just as there is to necking the .30/06 up to .338, .35, or .375. Heavier bullet, more impact at closer ranges. It would no doubt take a lot of development - projectiles, powder, barrel twist, etc. - to reach the level of refinement of current .50 BMG ammo.

BUT - what for? The .50 as it is has a BIG surplus of power for the biggest of animals at close range, and in rifles is mostly well regarded as a VERY long range target or sniping round; necking it up would sacrifice it's long range capability for more close range power, which is superfluous.

And for "anti-materiel" purposes, there probably wouldn't be enough of a gain to make it worthwhile, at least while 20mm rifles are around. (I believe that was what killed the experimental .60 machine gun round which was briefly considered for aircraft use - although that used a larger case than the .50)

 

[WestKentucky]

Necking up eliminates part of the bottleneck which amplifies the effect of the cartridge, much more so than diameter would indicate. Area of a circle or area of bullet base being pushed is pi*r^2 so the area of a .50 bullet is .785 Inches. Take that up to .577 and you get an area of 1.04 inches with a given charge you are getting about 23% more push due to smaller base. Going the other direction to a 45 caliber you would see gains over the 50 in velocity As you would get to a .66 surface with all that pressure funneled into a smaller tube. If you want to improve over .50bmg you neck down, not up. Necking up gets you nowhere on game, nowhere on velocity, nowhere on energy...it's equivalent to moving from a 30-30 to a 32win. No net gain.

 

[Inebriated]

I'd rather a 5.7 BMG...

 

[barnbwt]

There's a reason the 14.5x114 is about twice the power of a 50BMG, and not just a necked up 12.7x108. If doing a DD, why go as small as a BMG case?

TCB

 

[Thermactor]

I'd rather a 5.7 BMG...

That's the eargesplittenloudenboomer IIRC
(edit: no it's not.. that one is a 378 weatherby magnum necked down to 224... close enough!)
Maybe the closest thing is the 6.5-50BMG

Whispers of 6000fps echo through the halls of Valhalla

 

[docsleepy]

Has the original poster ever fired a 50 BMG? I would not worry about the barrel length. As long as you're not aiming at an Abrams tank, whatever you hit is going to cease to exist in any meaningful fashion.

 

[jmorris]

Things don't disappear after being hit with them, they just get lighter.




If I were going the route of the DD stamp, I would step up to the 20mm myself.

Although these guys also offer the 14.5mm too.

http://www.anzioironworks.com/MAG-FED-20MM-RIFLE.htm

 

[Jim Watson]

Maybe you could build a 16mm Vega.
As I understand it, it was a project to fire a worthwhile explosive shell from a .50 BMG size gun. I always thought it was a straight neck up of the .50 but they may have messed with it.

 

[50 Shooter]

The 16 mm Vega was going to be an auto cannon based on a necked up .50 case. It didn't work out and they went back to using a regular .50 BMG gun. The 16mm was going to be used on a modified P38 Lightning, would've been a nasty set up.

The rounds had a bigger explosive payload and would've destroyed targets with less rounds then the 50 BMG was ever capable of.

 

[MachIVshooter]

The rounds had a bigger explosive payload and would've destroyed targets with less rounds then the 50 BMG was ever capable of.

One word: Raufoss.

It didn't exist at that time, but the Mk211 mod 0 round is devastating in an anti material role.

 

[50 Shooter]

Raufoss is an amazing round against armor and other flammable objects but for a light show M1 incendiary rounds (blue tip) are the best. If 16mm Vega rounds were more common to find and a gun to shoot them out of, would be interesting to see which would preform better.

Do a search on military cartridge relationships and you should see different up size and down sized rounds using the 50 BMG case as the parent. You can see how much bigger the 16mm is from a standard 50 BMG round.

 

[MachIVshooter]

Do a search on military cartridge relationships and you should see different up size and down sized rounds using the 50 BMG case as the parent. You can see how much bigger the 16mm is from a standard 50 BMG round.

I'm fairly familiar with the documented ones, from .338-50 Talbot to .950 JDJ. They all compromise one attribute to gain something else. It really does seem that the original round is the best balanced (although the .416 Barret is impressive in it's own right).

 

[HankB]

I'm fairly familiar with the documented ones, from .338-50 Talbot to .950 JDJ. They all compromise one attribute to gain something else. It really does seem that the original round is the best balanced (although the .416 Barret is impressive in it's own right).

The .950 JDJ is based on a 20mm x 102mm Vulcan case.

As for the .50 being best balanced . . . notice that the proportions are pretty close to those of a scaled-up .30/06. Given suitable propellants, necking the case up or down would probably give gains or losses proportional to necking the .30/06 up or down.

 

[barnbwt]

The 14.5x114 is also similarly proportioned to a smaller bottleneck rifle cartridge. The 20mm, however, starts looking once again like the ye olde round nose cartridges like 30-40Krag with their enormous bullet points. Fluid mechanics, especially hypersonic fluid mechanics (and especially especially when involving reacting flows) does not necessarily scale well, however, so I wouldn't read tons into these observations. For instance, if you hold the ratios steady and go down too far (4.6x30) you start having great inefficiency getting the gas atoms to march down the narrow neck, single file (Reynolds number effects)

The biggest problem with 14.5mm is barrels; not exactly just laying around. In fact, there's a live KPV barrel for sale online, for like 5000$. That's why, when I get around to getting a tax stamp to undertake my semi-auto KPV rifle, I'll be stitching together two demilled barrel sections into something functional (with lots of engineering/analysis in the process). The other wrinkle, at least for x114, is getting barrel long enough (5.5ft). Now, a necked up 50BMG will drop its pressures faster due to the larger bore volume, so you'd run out of gas over less barrel for sure; not sure if the additional bullet surface area would bring velocity up fast enough to compensate (increased perimeter means more friction and blow by)

TCB