shotgun "bullistics" question!

[Milkmaster]

I know a shotgun pellet is not a bullet, so don't go all twisted over my use of terminology here within my questions. Stay with me while I build a little background for my question...

I know that when rifle/pistol ammo is developed, it has an optimum barrel length for which the round is designed. shorter barrels do not allow the ammo propellant to expend all of its energy before the bullet leaves the weapon thereby reducing speed etc.

Recently I saw a question posted about shotgun barrel length not making a difference in effectiveness.


Question... So why does barrel length not make a difference in shotguns when it makes a great deal of difference in rifle or pistol ammo? Is it because of the larger bore and lower pressures?

I ask because I see the same unburned powder flash exit the muzzle of a short shotgun that I do not see on say a 26"-28" model.

Splain it to me please!

[sm]

Just because, now would go back to your room and finish your homework and quit driving me nuts? *wink*

[Jeff F]

I'm not a expert on this but I understand what your talking about. If a shotgun was just firing slugs a short barrel like a 14 inch would most likely get less velocity then a longer barrel just like with rifles. There will be an optimum length to get max velocity. Shooing shot shells you are looking for pattern density. this is governed by choke at the end of the barrel, the load you are firing and a couple of other things like forcing cone and whatnot. Short barrels can and do throw tight patterns just like long barrels, and long barrels with open chokes can and do throw open patterns. Probably with a little more velocity.

[romeo212000]

The reason is because all of the powder is burned up well before it reaches the end of even an 18 inch barrle. It makes a difference with pistols because you are talking about the difference between a 3 and five inch barrel. If your pistol barrels were 26 inches long it wouldnt matter either.

[RyanM]

http://www.thehighroad.org/showpost.php?p=4178027&postcount=54

Looks like a slug, at least, gains most of its velocity in the first 12", then a little bit more in the next 12"

[boilingleadbath]

Why?

Because the pressure curve (http://www.claytargettesting.com/study2/Study2.3.pdf) of a shotshell is very narrow.

A velocity v. distance curve derived from the first pressure trace of that PDF:
21 fps - .02"
82 - .12
235 - .44
465 - 1.14
678 - 2.3
838 - 3.8
944 - 5.6
1021 - 7.6
1081 - 9.6
1127 -11.9
1166 - 14
1196 - 16.5
1218 - 19
1237 - 21
1252 - 24
1265 - 26
1277 - 29
1286 - 31
1294 - 34
1302 - 36
1308 - 39

Now note: those barrel lengths don't include the chamber; the performance listed for the 14" barrel would probably be achieved in a 15.5" barrel or something like that. Further, I'm just guessing that it's a 12ga x 1.25oz load - these assumptions won't change the nature of the curve, but they will change the precise velocity figures listed.

Edited to add: those values also ignore friction, which while fairly low in a shotgun, will tend to decrease the advantage of a longer barrel.

Altogether, it's not a surprising chart for what is essentially a large-bore pistol cartridge: yeah, beyond a few inches of barrel, who cares what the barrel length is.

[Pete409]

I ask because I see the same unburned powder flash exit the muzzle of a short shotgun that I do not see on say a 26"-28" model.

Splain it to me please!

The reason you see that "unburned powder flash" from a short barreled shotgun is because all the powder hasn't burned prior to exiting the muzzle end of the barrel.

If you look closely, you can see a little unburned powder flash even from a 28" barrel, but it's not nearly as much as from a short barrel.

Some powders are worse than others for muzzle flash. If you want to see (and hear) a muzzle flash and loud muzzle boom, listen to some shells loaded with Longshot powder. It's an extremely slow burning powder (for 12 gauge) and consequently a good portion of it burns after it hits the atmosphere. This creates the flash and loud boom.