[Jack19]

Can someone help me get my brain around this? Seems that longer barrels help many calibers but seemingly not the 9mm and a few others. Using small words, I don't reload, can someone tell me why?

[mete]

Small case capacity for one. You could increase the gain by using a slower burning powder.

[AJ Dual]

My Kel-Tec Sub9 carbine manual shows that 115gr ball standard loading gets about a 20% boost from the Sub9's 16' bbl.

I suppose that if it's a fast powder and burns in the length of a normal handgun barrel length, a 16" carbine barrel won't be of any benifit from a velocity standpoint, but it might still help that a shoulder fired carbine will be more accurate because of the stock or the longer sight radius than a pistol.

So a carbine length barrel can give a velocity boost, or it might not, depending on the round and the speed of the powder.

Powder grains have different surface area to volume ratio, where a powder like a ball will be slow since it has the least burnable surface area to it's volume, a rod powder has more, and a flat disk like flake powder has the most surface area for it's volume.

The more surface area a powder has, the faster it burns, which makes it more efficient in a short barrel. If the powder is to slow, it will still be burning when the bullet is long gone, and is wasted. However, faster burning powders create higher pressures if the bullet is still there being pushed down the bore. So developing a load is a balancing act between the desired velocity, the length of the barrel you're using, the weight of the bullet etc.

However, factory ammunition can only make educated guesses about the type of gun a given ammo will be used in, plus they have to keep it safe for all guns it's likely to be used in. Some can handle high pressures and some can't. It would be impractical and way too expensive to make 100 different kinds of 9mm for each bullet weight, and barrel length it would be used in.

So that's why some calibers benifit and some don't from longer barrels. It's also one of the reasons hand loading and reloading are so popular since an individual can taylor his loads to a particualr firearm, and save money over factory ammo.

[bdhawk]

GREAT QUESTION!!
just like mete said, 9mm normally uses fast burning powders in a small case. frequently the powder is consumed and the pressure is decreasing towards the end of a longer 9mm barrel. depending on the powder and bullet weight the powder may be consumed in 5-6 inches. i have never seen a study done on 9mm, but elmer keith did one on .44 mag and found 5 inches the optimum length, and .44 magnum normally uses somewhat slower burning powders. keith also factored in sight radius, carry ease and personal preference. in fact, in the faster burning powders, you may actually have a "slowing of the bullet" due to the extra friction from pushing the bullet down a longer barrel.

mostly rifles with slowburning powders in bottlenecked cases do you get a real velocity advantage with longer barrels.

this is not all that bad. you still have the extra stability of the rifle platform and the longer sight radius. the fps drop or lack of fps increase in negligable.

i have a 9mm carbine with a red dot sight. it is loads of fun.

[45+]

Good posts, guys. Also, in some other threads discussing the difference between a 9MM and a 38/357 in a snub, it is often pointed out that the 9MM loses less in a snub than the 38/357 due to the short barrel. The 9MM is loaded to optimize performance in a "short" barrel. The same is true with the 45ACP. It does not gain much from the carbine barrel length with commercial ammo. The 38/357 commercial stuff is loaded to benefit from a "long" barrel, so it gains more velocity when used as a round.

Safe packin'

[Jack19]

Thanks guys!! Excellent answers! I get it now. I wish there was a smilie face with a light bulb coming on over it's head. lol

:D

[Redlg155]

The 9mm carbine also lets you make use of +P and +P+ rounds more efficiently. My 14.5" AR has almost zero muzzle blast in low light conditions. The same load in a small Glock 26 has a healthy blast.

I don't have any velocity comparisons, but hopefully I'll have a chronograph in the very neat future to test some loads.

Good Shooting
Red

[clubsoda22]

all i know is 9mm aguila iq rips out at nearly 2000fps from a carbine.

[CaesarI]

well I've seen gains of 100fps with regular over the counter 9mm loads in a 9" barrel vs a 4" barrel. In general though, the reasons given are good ones. 9mm was designed at the turn of the century for use is pistols. To get the most out of a long barrel use the heaviest bullet and the slowest powder if you reload.

-Morgan

[FireInTheHole]

Better pressure curves with slow burning powder in a carbine. If you get it right, you can have a relativly quiet round as the bullet exits the barrel.

Does anybody know what types of powder are used in Corbon +P and +P+?

[Grayrider]

clubsoda22,

How is that Aguila IQ in terms of accuracy and function? That might be just the ticket in my CX4 Storm when it gets here.

GR

[000Buck]

On the flip side, does a shotguns projectile(s) reach full velocity very early on in the barrel, around 8" or less? I would think so since it is a fast burning powder, same as pistol....but I dont know for sure. Is that true?