5,000 fps .308???

[IROC]

Originally Posted by pwd72s

Maybe in a particle collider?

Our projectiles travel at about 883,872,000 fps. In a vacuum. No tail wind.

[Jeff Higgins]

As much as I enjoy my 19th century arms, I have also done quite of bit of work at the higher end of the velocities attainable with modern centerfire arms. 4,000-ish fps seems to be about the ceiling right now, with some specific combinations getting maybe a couple hundred fps more than that. Anything higher starts running into some, as for now, pretty insurmountable obstacles, at least with the propellents currently available.

My platform for this has always been the .220 Swift. I bought a Ruger #1 so chambered way back in the early 1980's. It didn't take me long at all to blow the throat out of its first barrel. Or its second... I eventually learned how to play its game, however, and the current barrel (from Dan Lilja in Montana) has survived the last 20 years or so.

The problem with any chambering when pushing to these velocities is what P.O. Ackley referred to as "expansion ratio", the relationship of case capacity to bore capacity. Past a certain ratio, as case capacity increased, he would refer to a chambering as "over bore capacity". The .220 Swift lies firmly in this camp. At the other end of the scale, the .223 is about "ideal". By way of comparison, I'll use 40-45 grains of a slower burning powder like IMR4350 or Reloder 22 in the .220 Swift, whereas I'll use 23-25 grains of a faster powder, like IMR4895, in the .223 with the same bullets (50 to 60 grain). The "bore capacity" is the same, but the .220 Swift is burning almost twice as much powder.

Doing so results in very much accelerated barrel erosion, particularly in the throat, right ahead of the chamber. The only way to mitigate this in these "over bore" chamberings is to be very mindful of barrel heat - we simply cannot let them heat up. I ruined my first .220 Swift barrel in just one day on a prairie dog shoot, shooting much too quickly. Probably less than 200 rounds that day before it very dramatically fell off in accuracy. Lesson leaned...

This is why the military cannot utilize these kinds of chamberings. Both the 5.56 and 7.62 NATO are somewhat small capacity cases compared to their bore sizes. We can put a lot of rounds through those very quickly, getting them smoking hot, without the problems encountered with the .220 Swift (or the various .300 mags in .30 caliber).

This is all why a number of things jumped out at me at the mention of this "5,000 fps .308". It simply does not have the case capacity for one. Secondly, even if we used a case with enough capacity to achieve that, there remain other problems. Lastly, the military would have no practical use for such a round. The whole thing just didn't add up.

[deanp]

I don't know much about these topics, but did a google search on some of the terms in this thread. I found some dated info on DAG .308 Blue Plastic training rounds that are reported to have 4400 to 4700fps muzzle velocities.

[Jeff Higgins]

That must be what these guys were referring to, since they said it was "blue" and "German" and "practice" ammo.

So... a ten grain plastic bullet. The video says 3,500 fps, nowhere near 5,000 fps. What a cool idea, though - gotta hand it to those Germans. With very specific, very narrow requirements for cheap, safe ammunition for use in initial familiarization and specific training scenarios, it looks like they developed a wonderful solution. I'm impressed.

Edit: I found a source for this stuff (currently out of stock, though), who, lists muzzle velocity as only 1,150 fps. I wonder if it comes in several different specifications? Still just a ten grain bullet.

[deanp]

The video said the info they were given was 3500 fps but they didn't have equipment on hand to verify. A couple of older website forums said 4400-4700 fps, but I didn't see anything indicating that it was verified, just the general consensus that the velocity would drop very quickly since it was a very lightweight 10g bullet.

[deanp]

This video has a chronograph testing showing 4000 fps +

[deanp]

https://www.dansammo.com/ammo.asp

$99 for 500 rounds, $189.99 for 1000 rounds.

[Jeff Higgins]

There must be different specifications available. Here is one I found that lists 1,150 fps:

https://www.outdoorlimited.com/rifle-ammo/7-62x51mm-nato/dag-7-62x51mm-ammunition-srt-plastic-training-ammo-dm18a1b1-10-grain-plastic-projectile-case-of-1-000-rounds/

Regardless, it looks like it could be fun to play with. Doesn't matter how fast it goes for its intended purpose.

The conversation on the shooting forum was regarding the phenomena of lightweight, high velocity projectiles penetrating steel plate all out of proportion to their size. I've demonstrated, for example, my .220 Swift shooting through the web of a piece of railroad track that stopped every "big game" round we tried, up to and including the .375 H&H. Anyway, some fool participating in that exchange tried to argue that velocity wasn't the factor everyone else thought it was, and used this "5,000 fps .308" inability to do that as support. Well, now that I see this is actually a ten grain plastic bullet, it's pretty obvious why it wouldn't.

[deanp]

Yeah, did you see the section of the video above where he shot into a silicone ballistics gel and it penetrated about an inch and bouched back out? Velocity but no mass.

[Jim Bremner]

I have some. I was going to post them but was to late

[Bill Douglas]

Originally Posted by deanp

Yeah, did you see the section of the video above where he shot into a silicone ballistics gel and it penetrated about an inch and bouched back out? Velocity but no mass.

It's a bit like cops shooting people with rubber bullets out of a shotgun. Bowls them onto their arse but doesn't kill them. Lose an eye at worst.

[93nav]

Originally Posted by Jeff Higgins

who, lists muzzle velocity as only 1,150 fps.

I wonder if someone translated meters per second to fps?

1150 mps = 3773 fps. Getting close to 4000fps, but not there.

[Jeff Higgins]

Originally Posted by 93nav

I wonder if someone translated meters per second to fps?

1150 mps = 3773 fps. Getting close to 4000fps, but not there.

Good catch! I wouldn't be at all surprised if that is what happened. Here is a guy chronographing it:



I kind of had to laugh, though. This guy has no idea why some are "duds".

[Por_sha911]

Originally Posted by BReif61

My question is WHY would you want/need to fire a .308 that fast? Purely for bragging rights?

For the same reason that Excellence Magazine drones on about the new Porsche touted acceleration of 0-1 zillion in a zeptosecond. Absolutely worthless to an average Porsche owner other than for bragging rights at the country club.