Sabot Rounds

For those of you not up to spec on the metric system, that equates to:

4134 FPS for a 95.7gr bullet.

Thats actually phenominal for a .308 case..... I'm hoping to get 4000 with a 69 gr.

MEL

Nek,

With the new ammo, were your PSG-90's rebarreled? Is the rate of twist still 1:10" (1 in 254mm)? I wondering about stabilization issues of .224 bullets in 60+ grains out of a .308 barrel.

MEL

Mel:

No, our rifles were not rebarreled to handle the new ammo. Also, it doesn't seem to cause any wear out of the ordinary. I recently had my barrel x-rayed etc to check for wear and tear, and the wear was par for the course for having had around 7000 rounds put through it, and it has at least a couple of thousand rounds more in it.

interesting... I think I'm going to have problems stablizing a 69gr .224 bullet with a 1:10 twist .308 barrel. I may have to back down to below 60gr.... tests will tell

MEL

Nekekami:

I am ignorant of your sniper round; what caliber is the projectile? is it a 224 or smaller, bigger?

Max338:

The dimension is 4.81mm

Mel:

Your talking about stability problems made me ponder... How about trying to use a longer bullet than a normal .22?

Nekekami,

Projectile diameter is 4.81mm? That would put it roughly at about .18 caliber, if I'm not mistaken. Are these bullets custom casted for the Swede sniper teams, or is this a caliber size in Europe that just hasn't made it to the US? I have never heard of a bullet this size. Is it available as a chambering in European sporting rifles, not as a sabot round but as a factory-loaded .18 caliber bullet? Although it does sound roughly like whats in our .17 remington centerfire rifles, although an admittedly unpopular and slightly obscure caliber in its own right.

Somewhat arbitrary, but is "sabot" pronounced sah-bot or say-bot? I've heard conflicting things from many fellow riflemen.

Jake:
Sabot is french for shoe so i would think the "t" is silent... im no french expert... so i may be wrong...

Jake:

The current projectiles are currently casted in Sweden, but the original projectiles, in the Winchester SLAP, are casted in the US.

They are specially made for use in sabots, and I wouldn't want to try and make a conventional round out of it. It's a tungsten penetrator, pure and simple... Except for the lack of fins, it's a scaled down version of the tungsten penetrators that tanks use in their anti-tank ammo.

As for the pronounciation, here's one example for how it's pronounciated in english:

\Sa`bot"\

Oh, I didn't think that the actual sabot would be used as a sporting caliber, just wondered if the bore diameter was. But I had forgotten that it was the same diameter as the projectile in the Win SLAP.

And thanks all for the pronunciation!

Nek,

Yes, a longer then average .224 bullet "might help" but when you make them longer, they gain weight which then goes right back into needing an even faster rate of twist. I'm hoping for the right sweet spot bullet to show up in my research

MEL

Mel:

Uhm, wouldn't it be the other way around, really? The lighter the bullet is, the faster the rate of twist must be? I mean, looking at 5.56x45 and its 1 in 7 to 1 in 9 twist, compared to 7.62x51 and its 1 in 10 to 1 in 12, and so on.

And, as I mentioned, our current round is somewhat more accurate than the SLAP round, because it uses a heavier projectile than the original SLAP. Higher weight for its diameter makes it less susceptible to wind, doesn't lose velocity as quickly. But you won't get the same muzzle velocity as with the lighter projectile. A trade-off that might be worth considering.

Well, actually, the required rate of twist is caliber and weight dependent. You must compare bullet weights in the same caliber. The reason most all the new crop of .223 rifles are at LEAST 1:9 is because the bullet weights have gone up. For the same given caliber, the required rate of twist to stablize a bullet must increase as the weight of the projectile goes up. There is actually a formula out there that computes this for you. I believe the length of the bullet comes into play also. I know to stablize the 69gr .224 bullet, you need at least 1:9 twist, if you go to 75+ you need 1:8, etc. Just like .308, 175 is very marginal for 1:12 twist barrels, 1:11 is ideal, 1:10 gets you to the 180's +.

MEL

Mel:

Yes, but, since you're using a sabot, have you taken the weight and caliber of the sabot into account for the calculations? It's a pretty major part that you must take into account.

Well, since the sabot seperates from the bullet once it leaves the barrel, it does not have an impact on the stabilization of the bullet. In order for the bullet to become stable it needs to achieve a certain RPM, now, I am NOT certain if the extra velocity of the bullet (if its up around 4000fps) would effect the required rate of twist, everything I've read seems to indicate that it doesn't. BUT, I need to fully state that I am NO expert in this. I just know what is required normally to stabilize a bullet, and the ROT of a .308 rifle probably will not be enough for the heavier .224 bullets. Of course, the ROT for what you are shooting is completely different, as that bullet must be EXTREMELY long. 95gr in about a .18 cal. YIKES! I'd really like to know the BC of that projectile.... and how I can get some

MEL

Mel:

It's not very long. It's just quite heavy. Tungsten-Carbide of that grade usually is. As for the BC, it's roughly 0.52.

But, for internal ballistics, you _have_ to include the sabot in the calculations. The rate of twist is lower, but you have a higher velocity that reduces the flight time and gives you a flatter trajectory.

.52 !!! :shock:

Holy freak. Thats awesome. Guess I need to invest in some tungsten.

Yes, less time of flight is great, but if the bullet is not stabilized (not enough rpm) it will lose accuracy, and in a bad case, even tumble (as is evenent with trying to shoot new NATO 5.56 (SS109?) in old M16A1's with 1:12 twist). I've literally have seen perfect SIDE profile holes of bullet passing through a target TUMBLING. This was from old M16A1's. Thats not good for accuracy!! This is purely external ballistics.... is it spinning fast enough when in flight.

Anyway, I wont know until I test them.... I do appreciate your info

MEL