[TXplt]

Notice that from this data you have a 60 fps drop between 8" and 6", and a 90 FPS drop (i.e. half again) between 6" and 4". The rate of velocity loss is going up with the shorter barrel as more unburned powder and accelerating gases go out the front (the web link you have addresses this concept as well if you take a good look at it). This tends to support exactly what I was talking about--I'll bet this increases dramatically as you go from 4" to 2" (with 3" obviously being somewhere in-between). It's going to be even worse with slower burning powder or cartridges designed for rifle barrels.

Quote:       Originally Posted by Taurus Fan

It looks like it proved your point exactly to me too. Numbers from the article were almost precisely what you predicted they'd be.

Thanks -- Guess we'll see if someone ambitious looks at rifle cartridges in shorter bbl. pistols. The .327 also starts at a greater diameter, so it won't have to expand quite as much to be effective.

[samuel]

I dont care "who,s" right,just "whats"right.

[Ron AKA]

I don't often read the handgun discussions, but on a review of the thread, I think I get the gist of it. This may not be a perfect calculation, but I think the general trend of it is likely in the ballpark. I used the method described in this link:

Effect of Barrel Shortening

I assumed the following:

- 357 Mag
- Initial barrel length of 10", including the length of the cartridge
- Cartridge length 1.29"
- Case volume of 27 grains of water
- 10" muzzle velocity of 1500 fps
- No change in the load for the different lengths

I got the following muzzle velocity reductions in fps:

10-9" - 28
9-8" - 33
8-7" - 40
7-6" - 49
6-5" - 64
5-4" - 89
4-3" - 137

Not sure what effect there would be in a revolver, as this formula was developed for rifle cartridges. Gas loss in the revolver would be another complication that is not reflected in these numbers. However, I would think the trend would be the same. The other complication not reflected is that I suspect you can do things by changing the powder type and amount as the barrel length is reduced, to potentially offset some of the velocity loss. In other words the pressure may go down as your reduce the barrel length so you can afford more powder or faster poweder. Don't have any experience with loading handgun cartridges so just guessing on that one...

Hope that helps some,

Ron

[TXplt]

That looks about right--if you'd continue the trend to 2 it looks pretty close to the vel drop for the difference in the .357 out of the 340 PD vice a 4" bbl .357.

Thanks

[Ron AKA]

Quote:       Originally Posted by TXplt

That looks about right--if you'd continue the trend to 2 it looks pretty close to the vel drop for the difference in the .357 out of the 340 PD vice a 4" bbl .357. Thanks

The 2" total barrel length does not make much sense. The actual barrel left after the cartridge would only be about 0.7" long.

Ron

[TXplt]

bbl length on 340PD is 1 7/8" (after flash gap); vel. loss of .357 ammo vice 4" bbl revolver .357 is approx. 300 fps (+/- depending on ammo.)

[Taurus Fan]

Quote:       Originally Posted by TXplt

bbl length on 340PD is 1 7/8" (after flash gap); vel. loss of .357 ammo vice 4" bbl revolver .357 is approx. 300 fps (+/- depending on ammo.)

Yeah the figures are interesting, I believe the velocity loss with a revolver's flash gap included would make the numbers a bit larger in the shorter barrel ranges ...or maybe even much larger. Just a gut feeling, I could be wrong.

[Ron AKA]

Quote:       Originally Posted by Taurus Fan

Yeah the figures are interesting, I believe the velocity loss with a revolver's flash gap included would make the numbers a bit larger in the shorter barrel ranges ...or maybe even much larger. Just a gut feeling, I could be wrong.

This is just my gut feeling, but my strong suspicion would be that the effect of a revolver flash gap would be to reduce the loss per inch of barrel length. If you compare a non flash gap gun with a revolver and measure from the back rim of the case in both cases, you have to end up with less starting velocity -- due to the energy loss through the gap. With that effect alone, the loss will be lower when the initial velocity is lower.

I feel the other effect is the "spongy" response of a gap. The velocity loss formula is based on the difference in the expansion ratio of the original and shortened barrel. My thoughts are that the flash gap increases the expansion ratio of both the longer and shorter barrel, so overall the cartridge sees them both as longer barrels, and the differential is less. Think of it like this. The difference on a proportional basis between 99 and 100 is a lot less than 9 and 10, even though the absolute differential is the same.

Could be totally off track, but that is my gut feel as to the effect.

Ron

[TXplt]

Ron, you got your #'s by chopping the bbl from 10 to 3 " ?

Just curious; losses on 340 PD higher.....better w/lower press ammo though. A little over 300 with the tac sb .357 load from Buffalo Bore; mid 200's otherwise with .357 4" vs. 2" (1 7/8 if you want to get technical) in most cases. Wish it wasn't the case, though.

I do get asked "what you shooting?" at the range alot due to the noise and blast a fair bit. But I don't shoot alot of the full house loads just due to the pretty intense recoil and it hurts..... Just enough to verify POA and convince myself me and the gun can still shoot them. The BB do OK, but did have the cor-bon 140's exhibit some inertia pulling as well--locked up the cylinder once.

[Ron AKA]

Quote:       Originally Posted by TXplt

Ron, you got your #'s by chopping the bbl from 10 to 3 " ? Just curious; losses on 340 PD higher.....better w/lower press ammo though. A little over 300 with the tac sb .357 load from Buffalo Bore; mid 200's otherwise with .357 4" vs. 2" (1 7/8 if you want to get technical) in most cases. Wish it wasn't the case, though.

Yes, the numbers represent the inch by inch velocity loss going from 10" down to 3". At each step the starting velocity is reduced by the previous step.

Sorry, but I don't understand enough of the handgun lingo to understand your second comment... About the only thing I clearly understand about handguns is how not to hold a revolver with two hands! As a result I do clearly understand the gap issue however!

Ron

[samuel]

I have done my best to get the facts on this subject and believe we have gotten pretty close on paper.However in the real world,whereas we can come up with a fairly good formula for pistols by using closed chamber math,we will never be able to make it work with revolvers because of the varrying flashgap and the fact that even if you used only one revolver to formulate the readings,still,after multiple rounds,especially max rounds,we would find our readings altogather different.I have decided the only way to go is take any given revolver and accept whatever it does and not to ever find any other revolver that does exactly the same.I thank all of you for the hard work and research you have invested in this subject.There are just too many variables to conclude this matter anyplace but on the range while actually shooting through a chronagraph.Again,thank you. sam.

[TXplt]

Sorry, Ron, what I meant to say is that the losses in practice are between the mid 200's and low 300's between a 4" and 2" revolver, with .357 loads, and that it appears alot of pressure and powder in the higher pressure .357 is going out the muzzle in the form of blast and noise energy. They're not fun to shoot. In the case of the higher weight cor-bon ammunition, the bullets (due to the light weight of the revolver and fairly extreme muzzle flip) start to exhibit inertia pulling of the bullets. A heavier steel revolver wouldn't have this happen as much.

Also, for what it's worth, like a hole in a pipe, , I think the loss across the flash gap, in terms of energy and velocity, would go up as the pressure went up. It's basically just a leak of sorts, the magnitude of which is minimized by the low amount of time that the bullet is in the barrel compared to the pressure leak.

Thanks again and have a good one

[Ron AKA]

Quote:       Originally Posted by TXplt

Also, for what it's worth, like a hole in a pipe, , I think the loss across the flash gap, in terms of energy and velocity, would go up as the pressure went up. It's basically just a leak of sorts, the magnitude of which is minimized by the low amount of time that the bullet is in the barrel compared to the pressure leak.

I would agree. It would also seem that the longer the barrel the more time the bullet is in the barrel, and the longer the pressure loss due to the leak. As you shorten the barrel the time available for leakage is reduced and the relative effect of the loss is less. So it seems to me that a short barrel may be less affected by the leakage compared to a long one? And if we took this to a silly extreme, where there is a cylinder but no barrel, the gap has no affect at all...

Ron