Drawbacks of a carbine?

[Mauser98]

When similar styled bullets of the same SD are fired at the same pressure, they have the same velocity. Eg; a .30 caliber 165 gr bullet (SD .248) and a 130 gr .270 bullet when both bullets are loaded to 50,000 lbs pressure both bullets will have the same velocity, which for the sake of argument might be 2800 fps. Going to a bullet with a higher SD might result in a smaller drop in velocity from a short barrel because that bullet would be slower to start with so when the drop of velocity is viewed as a percentage, the actual velocity drop for the slower bullet would be less.

Well, I've stared long and hard at your statement and , after some cursory research, I'm going to have to respectively disagree. If the statement were accurate, then all bullets of similar SD and launched at the same pressure level then all these bullets would have the same velocity. eg. a 150 gr .270 bullet(SD=.279) launched at the same pressure as a 400 gr .458 bullet(SD=.272) will not have the same muzzle velocity. I have no proof of this but my gut tells me it is so.. Bullet weight, bullet basal area, powder capacity and expansion ration are some of the factors that should be looked at when we are discussing velocity loss from shortened barrels. IMO, SD is only a factor when the bullet hits the animal(theoretical penetration) and even then, it is of doubtful use.

Playing with powders of different burning rates will serve little purpose. If you get the best velocity in a 24" barrel with 4350, switching to 3031 for the same bullet in a 20" carbine will result in reaching excess pressure before you hit the velocity you expect, and as in the case with the long barrel, A very slow powder like Retumbo will bulk out before you get the velocity you want as it did in the long barrel. If 4350 gives you the best velocity with a 24" barrel, it will with a 20" barrel as well. The faster powders will be equally effected by the shorter barrel.

I agree.

The comments regarding powder and bullet type I made in my first post were meant to reflect some factors that might influence velocity loss per inch in a given rifle.

 

[Boomer]

OK, it took me a while to find it, and I didn't have it quite right, but I was on the right track.

Correctly put, "The same pressure, applied for the same length of time, to two bullets of the same sectional density, regardless of caliber, will result in the same acceleration and must attain the same velocity". PO Ackley

My head tells me that if two bullets of the same SD are compared, the bullet with the shorter bearing surface would attain higher velocity, but Mr. Ackley didn't say that, he said that the same pressure had to be applied for the same length of time, so perhaps that makes up for the length of the bearing surface.

Edited to add;

The only time that the sectional density is useful to determine the terminal effects a bullet might have on a target is when that bullet does not expand. As soon as a bullet expands SD as a means of determining penetration goes out the window. What is left is the bullets expanded diameter, it's mass, and it's velocity at the time of impact and the resulting momentum that drives the bullet through the target.

 

[jedimaster]

Well I can tell you from my army days that the stats on two identical bullets one with a boattail and one without. The boat tail will leave the muzzle slower but will bridge the speed gap at 100 yards and be faster further down range do to improved aerodynamics so it will lose speed less than a normal bullet. So I would think that the actual bullet will play a fair bit of a roll in how fast it flies.
As to if an identical bullet comming out of an 18" 1 in 10 twist barrel with x amount of powder, under the same exact conditions out of a 22 inch barrel will make it slower, I would think it would depend on the propellant and how much.
My understanding as well from being in the artillery for 8 years was that there is an ideal ammount of propellant, the ideal ammount is such that the volume is still expanding as the bullet is leaving the barrel. If it burns too fast or there is not enough to burn the bullet will be slowing down in the barrel. Too much and you ill lose accuracy as the mshockwave comming out of the barrel will affect trajectory. Granted this was theory based on a 105mm howitzer shooting many km's versus just a couple hundred yards. BUt I would think the principles are the same.
Longer barrel allows you to burn more powder through out the distance of the barrel.
For this comparision obviously there will be a perfect balance of round weight and fps versus ammount and type of powder but keeping all things equaly is about the only fair way to judge this.
I would think most rounds have more than enough powder to push a bullet through a 22" barrel and probably not so much that it would adversly affect the round in an 18" barrel.
One thing to note. A bullet starts to de celerate the instant it leave the muzzle.

Assumming you have enough propelant to push a given round for 22 inches you assume the bullet will be accelerating for all 22inches or the casing would be under powered. If you then cut off 4 inches of acceleration time than it only stands to reason that some acceleration is lost.
As for how much? I don't know. But there almost has to be a loss in FPS at the muzzle end assuming you had enough juice to begin with.
I would certainly not think your going to lose 18 percent(ammount of barrel lost with 4 inches, but that would be the theoretical maximum loss.

With a 3000 fps round at 22 inches that is a total theoretical loss of 540 fps or 135 fps per inch.

I know for a fact that the acceleration of a round inside a barrel is a curve eg, it gains the most speed at the breach end of the barrel. What that actual curve is its hard to tell.
What that curve looks like I would think would depend on the propelant, the bullet characterisitcs, the chamber, ammount of friction, the actual fit of that individual round etc...
I would however think that the acceleration is some sort of decreasing exponential curve though.

Is what I am saying sound correct or just full of horse ####.

 

[barktwid]

That was awsome!!!!

 

[Boomer]

Jedimaster, your statement concerning the difference in velocity between the plain base and boattail bullet is intriguing. Perhaps an explanation is thus . . . the two bullets are the same weight and construction, so the the SD is equal. The boat-tailed bullet due to it's shorter bearing surface, would have less resistance to movement, so it would exit the barrel at a lower velocity because it spent less time at the same pressure than the plain base bullet with the longer bearing surface that required more pressure, or the same pressure for a longer time to overcome it's resistance to movement, in the same barrel over the identical powder charge.

The size of the powder column is relevant when we consider the effect of a shorter barrel on velocity, but the type of powder, not so much because the burning rate is more significant to bullet weight than it is to barrel length. Consider the .30/06. A 220 gr bullet has the best velocity from a powder with a burning rate consistent with H-4831, bullets from 150-180 grs do best with H-4350, and a 110 gr bullet does well with burn rate consistent with IMR-3031. A medium burning rate powder like 3031 requires a smaller powder column than a slow burning powder like 4831, but the effect of reducing the barrel length will reduce velocities in either case. The maximum load for 3031 with a 220 gr bullet is 200 fps slower than the maximum charge of 4831. The 3031/220 load is already 200 fps behind, and it will also loose velocity in a shorter barrel, albeit to a lesser amount, so unless you anticipate a barrel so short as to loose well over 200 fps, little is gained by moving to the faster powder in a carbine.

I tend to agree a with you with respect to the velocity curve inside a barrel. It would follow that there is a greater velocity increase in the first 12 inches of barrel than in the second, and as you say what the curve looks like is dependent on many variables, and is unlikely to be identical even between very similar barrels.

The A-Square Manual has load data for the 105, probably to show what applies in one case also applies in another.

 

[jedimaster]

If I was reallly motivated I could use some of my graphing tools at work and plug in velocity and barrel lengths to create a curve of best fit for acceleration. However. I firmly believe that the highest acceleration rate is almost instantainious.
I think to be most accurate you would eed to start the graph with no barrel. eg a bullet in a vise whacked with a hammer and use that as the 0" baseline. If you get that fps for a give round, then shoot that same same at 3 or 4 lengths I think you would get a pretty accurate measurement as to what the curve would look like.

I honestly don't believe that the actual barrel length plays a massive role in the acceleration rate and the final velocity of a bullet.

I have always believed that that barrel lenght provides the ability to stabilize the bullet during that acceleration.

For example if Bullet X with X amount of powder to burn can accelrate Bullet X for say 20 inches of barrel lenght before the preasure is no longer growing enough to accelerating the bullet than it does not good what so ever to have a barrel of 24 inches. In fact the bullet will leave slower in some instances.
Of course the more powder you have the greater the initial preasure and initial acceleration burst..ths why we have magnums. However there come a point lke I said where the shockwave as the bullet leaves the barrel will actually server to de-stabilize the spin rate of the bullet as it leaves the barrel, the barrel will flex too much, etc.. etc... In fact I would think if you really really overpowered a given round the round would tumble.
Now I think I am just saying what I already said.

I think the most basic thing to understand are.

1) Any powder that burns after the bullet leaves the barrel donothing but add a flame effect

2) A massive ammount of the actual acceleration that takes place does so at a 0" barrel length

3) If powder is not burning for the full duration of the bullet in the barrel the round is under powered(now weather or not a given barrel, breach or shoulder can handle the maximum amount of powder is not known to me, perhaps you could still accelerate effectivly a .223 with 2 pounds of powder.

4) The more powder you need the longer it takes to burn thus you would need a longer barrel to allow for that complete powder burn.


These are just my somewhat logical assumptions based on not much fact but it makes sense to me.

It helps to think of it in terns of extremes for example a 7mm win mag shot out of a 0 inch barrel, a 1 inch barrel and an 80 foot long barrel.
In the 0 inch barrel the bullet would still be going damn fast, but not spinning and the bullet would not fly very straight
the 1 inch barrel the bullet would atleast spin a bit but probably not be very stable in that it has only spun about 1/10th of a turn and would probably stop spinning at some point. The preasure would be increased and the bullet would go faster.
In the 80 foot long barrel the bullet would likely not leave the barrel and at some point in that 80 feet it wold stop accelerating and would start to decelerate. That would be the ideal barrel lenght in my eyes. How long that distance is would depend on the ammount of powder and the bullet characteristics(boat tail, bullet length, fit of the bullet in the barrel smoothness of the bullet and barrel, no different than a piston in a car engine)
Everything is atrade off right? How much force can your shoulder take, how much preasure can the barrel take without distorting too much to affect trajectory, What is the ideal spin rate of the bullet and how long does it take to accheve that spin rate with engough momentum to maintain that spin rate down range...

The way to really get an idea of this whole topic of velocity in relation to barrel length is to like I said cronograph a bullet with no barrel.
Than shoot the same setup through a 22 inch barrel a 20 inch barrel and an 18 inch barrel then that should be enough to get a good estimatation of the accleration curve.

My guess?
Ok here goes.
I am guessing that in a round that shoots at 3000fps out of a 22 inch barrel. I would think that the same round would go at least 2/3 that speed if shot with no barrel at all.
So that leaves 1000 feet per second of acceleration over 22 inches. So that would be an overal average acceleration rate of 45 fps per inch of barrel.
However I still think that the barrel provides greater efficiency down at teh breach end.

But I think my numbers are pretty close.....anyone feeling crazy with a vice and a crono..haha just kidding I would not recomend doing this it could be very dangerous. Better leave this one to myth busters.

 

[Boomer]

It could be an interesting experiment, the old time gunfighters did alright with the barrels removed from their Colt SA's at across the table ranges.

In a modern bottle neck cartridge though things might be a little different. The primer is much more powerful than the cowboy's revolver, so when the primer ignites, the powder column is compressed against the base of the bullet, and the bullet is driven into the lead of the barrel prior to any powder being ignited. An unconfined bullet would likely drop out of the case and there would be a big plume of burning powder in the air behind it, but velocity would be 32 fps/ps on the way to the ground.

 

[Calum]

I dont think the moose would notice the difference

Also when I use my carbines I seldom notice the muzzle flash in daylight, but anyone standing next to me sure does.
Case in point the M44 carbine.

http://www.youtube.com/watch?v=BlRG-AfaDac

About the only drawback I see to a carbine is that they are fun, and practical, and this makes them more likely to get worn out.

 

[manbearpig]

Also when I use my carbines I seldom notice the muzzle flash in daylight, but anyone standing next to me sure does.
Case in point the M44 carbine.

some of the commo-block ammo produces significantly more muzzle flash. i was getting massive muzzle flash from cheap Chinese .223 FMJ, but barely any in the same gun with US Winchester & Remington ammo.
same goes for my M44s, some of the Yugo or Hungarian steel-cased FMJ produces quite an impressive muzzle flash, but then i get a lot less with hunting ammo, even Igman softpoints which are from the same country.

perhaps its the different powder they use in the older surplus stuff.

 

[jedimaster]

Older ammo has slower burning powder so it would stnd to reason that alot of it would be spit out of the muzzle after the bullet is long gone.