Any one good at firearms ballistics?

[Kenne]

case in point.
M1 carbine round.
110grain bullet 1900fps muzzle vel.
slo for rifle, fast for pistol.

question.
if you reduce the bullet weight from 110gr to 55gr, reduction by 50%,
would you see and increase in MV by that same percentage?

all other factors the same, primer, powder, barrel lenght etc.

[curry1]

case in point.
M1 carbine round.
110grain bullet 1900fps muzzle vel.
slo for rifle, fast for pistol.

question.
if you reduce the bullet weight from 110gr to 55gr, reduction by 50%,
would you see and increase in MV by that same percentage?

all other factors the same, primer, powder, barrel lenght etc.

Not exactly because it would spend less time in the barrel to have the acceleration.  But yes assuming it was the same force applied in a vacuum instantaneously to a bullet half the weight it should go twice as fast.

[smoe]

Not exactly because it would spend less time in the barrel to have the acceleration.  

This sentence above somewhat contradicts itself. If the bullet spends less time in the barrel, then yes it probably means it is traveling faster.  

[Triton28]

I doubt you'd see a uniform increase.   Some powders are better for lighter bullets.   I would bet you'd want to change powders for that light of a bullet.

[SmokinLoon]

The US M1 Carbine is a fine tuned machine.  It was designed with everything in mind from the get go as a self defense carbine for non-riflemen.  The size and weight of the carbine itself is directly related to the capabilities of the cartridge.  I suggest you not bother with all the fancy trajectory mumbo jumbo and stop and think about your capabilities as a shooter and the capabilities of the carbine you're inquiring about.

First, I'm not even looking up the ballistics.  There is no need to.  I can tell you this though: the "improvement" you may think you have between 1 and 100 yards will diminish big time between 100 and 300.  You as a shooter are not going to be able to tell the difference with this carbine and with this caliber, regardless of bullet weight.  Your eyes are not that of an eagle, and you simply do not have the finesse to make an M1 Carbine shine as a tac driver.  Buy or reload the standard ammo and enjoy.  Besides, the lighter the bullet weight the more variables that can and will effect it.  You're better off using the standard 110 gr round nose it was designed to use for stability.

Now, if you were asking about a 7.62 NATO chambered rifle and wanted to get in to the specifics of powders, primer types, bullets weights and designs, ranges, optics, barrel lengths, triggers, etc, then we're talking about a different story.  There is a whole realm of things to consider, adjust, tweak, and test.  But the M1 Carbine.... nah, just go shoot it and have fun.    

[Masherbrum]

case in point.
M1 carbine round.
110grain bullet 1900fps muzzle vel.
slo for rifle, fast for pistol.

question.
if you reduce the bullet weight from 110gr to 55gr, reduction by 50%,
would you see and increase in MV by that same percentage?

all other factors the same, primer, powder, barrel lenght etc.

The muzzle velocity is actually 1990fps for Ball Ammo.    Considering the small cartridge size, the energy is around 965ft-lb of energy.   As for the added velocity, I don't see it helping much.  

[smoe]

I looked into a m1 carbine and decided it is fun to shoot, but limited for practical use. It only shoots ball ammo reliably, hollow point ammo doesn't seem to feed too well. I would recommend something like a 9mm carbine instead. A 9mm Hi-point carbine shoots +P stuff pretty close to the speed of a m1 and feeds almost everything.

[Vulcan]

Just get a .243

[Oldman731]

question.
if you reduce the bullet weight from 110gr to 55gr, reduction by 50%,
would you see and increase in MV by that same percentage?

55-grain .308 diameter is going to be pretty close to a round ball.

The answer to your question, though, is a high school physics topic. It's just been a long while since I had that course.  Velocity will always go up as bullet weight decreases, except in very short barrels, but I suspect the proportions may not be as related as you suggest.

- oldman

[Gman]

Old is right, velocity will increase, up until a certain point.  The 2nd poster said something to the effect that 1/2 the bullet weight would be 2x the velocity in the M1 carbine.  Well, I'm pretty certain it would be extremely difficult to develop the pressure needed to launch a 55 grain bullet at 3800 feet per second from an M1.  So it isn't just a simple formula/answer for the OP's question, there are many variables and factors.

Anything from a rifle moving at 3000fps requires tremendous pressure to achieve, and rounds moving close to 4000 fps are REALLY moving, and are typically specialized calibers, the WSSM's, magnums, bench rest rifle calibers - that sort of thing.  As you close in on that 4000fps velocity bullets start behaving differently as well, there is mucho stuff on google if you want to read about it.  An example: The .408 caliber, pretty much the gold standard for long range shooting, that or the 416, both move at around 3500 FPS with a 300 gr bullet.  It takes over 65,000 PSI to get it to that 3500fps velocity, which is a crazy amount of pressure going off right next to your head.  This bullet is still supersonic at 2000 meters, but much of this is due to bullet composition and tech, as well as the weight/velocity etc.

[-ammo-]

I agree with old man and Gman.

Velocity isn't everything.  Muzzle energy retained throughout the effective flight of the projectile is what you want.

I played around with a 125 grain bullet for my 30-06 several years ago and did achieve some interesting results.  I wanted to work up an effective load for coyotes.  I don't have my reloading notes with me, but I remember getting over 3500 FPS at the muzzle.  I killed a few coyotes, deer, and one big hog.  I was worried about the hog.  That little bullet can't be expected to penetrate and hold together on its thick hide and all that fat and muscle.  I did kill it, but I was lucky.  When I dressed the hog I found the bullet just made it to the vitals.

[curry1]

This sentence above somewhat contradicts itself. If the bullet spends less time in the barrel, then yes it probably means it is traveling faster.  

Exactly it will be moving faster than the bullet with twice the mass and therefore it won't have as much time to accelerate in the barrel.  It won't get the full acceleration to double the speed.  However this is true of any gun obviously some of the energy is always wasted.

[ToeTag]

Buy a reloading manual before you blow something up.  There are so many variables that can go wrong.  No! I'm not going to list them for you.   Do it right or donate some fingers where so many have before!

Oh...and when you create your FLESH EATING MONSTER get a chrony to test it so you know that you have it under control.

[mtnman]

Exactly it will be moving faster than the bullet with twice the mass and therefore it won't have as much time to accelerate in the barrel.  It won't get the full acceleration to double the speed.  However this is true of any gun obviously some of the energy is always wasted.

If it's accelerating faster, it doesn't NEED as much time to accelerate.

Side note- that lighter bullet will also decelerate quicker.  Long-range, it may not fly as flat of a trajectory as the heavier bullet would.

And, as oldman pointed out, that 55gr bullet will be a much less efficient shape.  I think what you'll get is a bullet combination that has an unnoticeable "edge" at close range, but performs worse at all other ranges when compared to a standard load.

[Kenne]

thanks so much for the replies.

the classic 'what if' follows:

Iv always studied Stoners Ar15, and marveled that 556 brass is VERY similar to M1 carb brass. Save the 556 is a lil longer and the extractor groove isn't as deep. And iv found that blanks made for the M1 carb are sometimes made from 556 brass.

that got me to wondering, if instead of Stoner starting from scratch, cood he have just install nu barrels (20" of course) on the M1 carb, necked down the brass, and have the same 300m max range rifle?

also, would the factory carbine gas system (short stroke piston) still work for this 'necked' cartridge?

TIA