A question for you firearms aficionados...

[mmadsen]

[Color=Yellow][b]Velocity(fps) / muzzle / 100yds / 200yds / 300yds / 400yds / 500yds[/b]
(---sabot) / 3770 / 3215 / 2726 / 2286 / 1888 / 1541
(standard) / 2700 / 2497 / 2303 / 2117 / 1941 / 1773[/Color]

Interesting. Why would a sabot lose velocity more quickly than a thicker projectile?

[Color=Yellow][b]Ft-Pounds / muzzle / 100yds / 200yds / 300yds / 400yds / 500yds[/b]
(---sabot) / 1735 / 1262 /  907 /  638 /  435 /  290
(standard) / 2670 / 2284 / 1942 / 1642 / 1379 / 1152[/Color]

That's a lot less energy -- even right out of the barrel.

 

[Mr. Draco]

I think it's because the Sabot round has less momentum because of it's lesser mass.

 

[Ace]

Hi again!


Hmm, so they were. Muzzle velocity is given as 3400 fps, comparable to a very hot .223 load. So that one is "about the same" as a .223. I'd take a good close look at such a round before stuffing it into a lever-action's tubular magazine, though.



The old stovepipe can certainly come in handy, and is fairly low-profile - most rural authorities would hardly give it a second glance. But don't forget that automatic weapons are still legal in the 1920's in the United States (though restricted in some localities). Both the Thompson SMG and the Browning Automatic Rifle are sold commercially (the BAR as the "Colt Monitor"), and could do a lot to get a pack of intrepid monster hunters out of a jam. And they're really fun when the party member holding one loses just a little too much Sanity...

Hope this helps!

Good points both

The Sabots are Remington ammo and I have never heard of any problems with them. IIRC the bullet is well back in the case and the exposed sabot has a safe flat surface.

Oh and you can't go wrong with a tommygun in Call of Cuthulu

 

[Tratyn Runewind]

Hello again!

Posted by mmadsen:
Interesting. Why would a sabot lose velocity more quickly than a thicker projectile?

Posted by Mr. Draco:
I think it's because the Sabot round has less momentum because of it's lesser mass.

Pretty much. There are 2 factors at work here:

1) the smaller projectile is facing more air resistance, because it is moving faster (the way the resistance scales with speed will overcome the advantages of smaller cross-section past a certain velocity), and

2) it loses more of its velocity to overcome a given force of air resistance because of its smaller mass.

You can see the dynamics of this in the tables posted - as velocity gets lower, the slugs lose less and less velocity after each succeeding 100 yards, as air resistance lessens at their new, lower speeds.

The smaller bullets just don't "buck the wind" as well as the heavier ones. I seem to recall stories of competition shooters in DCM (now CMP) matches finding out just how true this was when they finally shifted from the M-14/M-1A to the M-16A2/AR-15A2 in their "service rifle" matches a few years back.

Posted by Ace:
Oh and you can't go wrong with a tommygun in Call of Cuthulu

Yes, it may not bother a Great Old One much, but it should do nicely against your average demented cultist, or lesser minions like Deep Ones.

Hope this helps!

 

[mmadsen]

1) the smaller projectile is facing more air resistance, because it is moving faster (the way the resistance scales with speed will overcome the advantages of smaller cross-section past a certain velocity), and...

In fact, air resistance is roughly proportional to cross-section and to velocity squared.

2) it loses more of its velocity to overcome a given force of air resistance because of its smaller mass....The smaller bullets just don't "buck the wind" as well as the heavier ones.

But the sabot rounds are smaller in all three dimensions, are they? They have a smaller cross-section, but I thought they were roughly as long as a regular round, giving them the same ratio of mass (and thus momentum for a given velocity) to cross-section as a larger round.

 

[Tratyn Runewind]

Hello again!

Posted by mmadsen:
In fact, air resistance is roughly proportional to cross-section and to velocity squared.

Yes, that was pretty much my point. Double the velocity of a bullet, and you'll quadruple the air resistance. Halve the cross-sectional area, and you'll only halve the air resistance. You can see how this would bode ill for energy retention of small, high-velocity bullets.

Cross-sectional area of the sabot bullet we've been discussing here is just slightly over half that of the regular bullet. Velocity is about 1.4 times that of the larger slug, using the figures for the .308 round. (Air resistance for full-diameter slug) x 0.5 x (1.4 squared, or about 2) = pretty much the same resistance for both rounds - that load is right about at the break-even point, the "certain velocity" I mentioned earlier.

The bullets overcome the force of that resistance with the kinetic energy of their movement. And because that energy is equal to the slug's mass times its velocity, you can see that the light slug will lose more velocity than the heavy one when they lose the same amount of energy to overcome the same force of air resistance.

Then, because the smaller bullet is losing velocity faster, it will fairly quickly get into the range where it is facing less resistance than the bigger bullet. At 300 yards, their velocity is pretty even, meaning that the smaller bullet is facing about half the air resistance of the larger. But it still has only a third of the mass, so it is still losing velocity 50% faster than the larger slug, despite facing less resistance. A glance at the last columns of the table will show how this ends up - the sabot round will be slower despite both its large initial speed edge and its smaller cross-section.

Posted by mmadsen:
But the sabot rounds are smaller in all three dimensions, are they? They have a smaller cross-section, but I thought they were roughly as long as a regular round, giving them the same ratio of mass (and thus momentum for a given velocity) to cross-section as a larger round.

If the sabot rounds were the same length as the standard rounds, then the mass difference would be directly proportional to cross-sectional area difference (edit: assuming same materials for same density, and assuming similar tapering; they're not perfect cylinders) - they'd be half the mass of the .308 slugs. But they're actually a third or less of the mass; the .308 slugs range from about 150 to 180 grains, compared to the 55 of the sabot slug.

The sabot bullets are .224 inches in diameter and 55 grains. M-193 military ball .223 ammo bullets were .223 inches in diameter and 55 grains - virtually identical. That's typical for civilian .223 loads too, though the military's moved to a heavier load in the M-16A2 that requires very fast rifling to stabilize. And .223 bullets I've seen were certainly not as long as .308 slugs.

Again, hope this helps, and hope the other readers are having as much fun with the physics and aero stuff as we are...