[HT/LT] Sawed-Off Smoothbore Longarms

[Sam Cade]

Originally Posted by evileeyore

Did you somehow miss the thread title?

No.
I was explaining how rifling works in relation to accuracy to better illustrate how barrel length is meaningless in the context of smoothbore firearm accuracy

[Anthony]

Originally Posted by Varyon

I was working under the assumption that a longer barrel could serve to stabilize any sort of "wobble" the bullet might have going down the barrel

Normally barrels are a tight enough fit that wobbling is a non-issue. The exception to this is shot, but for shot there doesn't seem to be evidence for anything but the choke mattering much.

[Sam Cade]

Originally Posted by Anthony

Normally barrels are a tight enough fit that wobbling is a non-issue.

That is what the patch is for. The ball is undersized for the bore.

Originally Posted by Anthony

The exception to this is shot, but for shot there doesn't seem to be evidence for anything but the choke mattering much.

No.
The wad is equally important. The tightest patterning factory shotgun shells use FliteControl wads and work best absent a choke.

[Anthony]

Originally Posted by Sam Cade

No.
The wad is equally important. The tightest patterning factory shotgun shells use FliteControl wads and work best absent a choke.

Well, okay, but in any case barrel length doesn't seem to be relevant.

[Sam Cade]

Originally Posted by Anthony

Well, okay, but in any case barrel length doesn't seem to be relevant.

Correct. It matters not.

[Jack Sawyer]

from what I understand about ballistics, whether or not a barrel is actually useful for more velocity depends on the propellant (slow vs fast burn) and you really want to tailor the propellant to barrel length (slow burning propellant in too short a barrel leaves unburnt propellant which creates problems. This was an issue with the M855, which is one reason they went with the M855A1 which is a fast-burn propellant and works better in shorter barrels but can also work with longer ones.)

If I remember rightly the wrong combo of powder and barrel length could actually create a situation where the bullet 'slows' down because the resistance of the barrel is greater than the push of the propellant, so you can actually have too long a barrel where you get little or no benefit.

[Rupert]

Originally Posted by Jack Sawyer

from what I understand about ballistics, whether or not a barrel is actually useful for more velocity depends on the propellant (slow vs fast burn) and you really want to tailor the propellant to barrel length (slow burning propellant in too short a barrel leaves unburnt propellant which creates problems. This was an issue with the M855, which is one reason they went with the M855A1 which is a fast-burn propellant and works better in shorter barrels but can also work with longer ones.)

If I remember rightly the wrong combo of powder and barrel length could actually create a situation where the bullet 'slows' down because the resistance of the barrel is greater than the push of the propellant, so you can actually have too long a barrel where you get little or no benefit.

That is all correct. This is why powerful 'magnum' hunting rounds and wildcat designs tend to be used in rifles with long (26" long or so) barrels, so they can use slow burning powders that are, if they have a sufficiently long barrel, more efficient than fast burning powders, and which allow the use of more powder for the same peak pressure.

[Sam Cade]

Originally Posted by Jack Sawyer

M855A1 which is a fast-burn propellant and works better in shorter barrels but can also work with longer ones.)

It is 842 from St.Marks. It isn't a fast powder but is very fast for a rifle powder. Fast enough that folks were blowing up pretty regular a few years ago once it started to dribble into the surplus market absent any published load data. Personally, I'm a little afraid of it.

[Jack Sawyer]

Originally Posted by Sam Cade

It is 842 from St.Marks. It isn't a fast powder but is very fast for a rifle powder. Fast enough that folks were blowing up pretty regular a few years ago once it started to dribble into the surplus market absent any published load data. Personally, I'm a little afraid of it.

Well it was a somewhat higher pressure, somewhat more energetic propellant. It caused some problems when it was initially introduced (I think they dropped the pressure a few thousand PSI because of it) but you could also use a slightly lower propellant charge (and if I remember the DTIC entries I read, possibly condensed charges.)

And you're right, its not the fastest (tanks used higher pressure propellant right up until NGSW became a thing.. now they're aiming for rifles that run at tank gun pressures, which make St Marks look positively tame.)

I also know about a decade back that Knox Engineering Company had promoted a novel 'enhanced' propellant design that offered a higher force constant for 5.56 NATO without a higher flame temp (suggesting it was some novel sort of low molecular weight propellant, I think.) The gimmick was that they used a straight cartridge with no shoulder and half the propellant of M855 which resulted in something like a 30% weight savings. Although from what I've read they also blew up a ton of test barrels which is probably why it never went beyond the experimental stage.