Breech Seating and Airspace?

[RPRNY]

So, I breech seat bullets, .456" paper patched 380 grs in my 454 Casull Handi and .431" cast in my 444 Handi, over cases filled with black powder and a card wad, creating air space in the chamber of between 1/6" and 1/8th". This is by no means uncommon.

Why is this not a problem when we are manic about having no airspace in BP cartridges?

 

[25cschaefer]

I was wondering the same thing shooting 4v50gary's beer can mortar, with about 150gr of powder, there was about a half cup of air betwixt the butt of the can and the powder charge.

 

[Jim Watson]

I wonder the same thing, breech seated or breech-muzzle loaded scheutzen rifles pretty much have an "air space" built in.
I remember an old gunzine article about the .41 Swiss Federal muzzle loader with the Wild System ramrod, having a step to stop seating the bullet .1" above the standard powder charge.
Yet we are continually warned against it in either fixed ammunition or muzzle loader.

Do scheutzen shooters have rings in their chambers and just not notice or care because it is not where it affects bullet travel or case extraction?

 

[Jim K]

I think there has been some confusion between two conditions. One is air space between a powder charge and a single bullet; the other is air space between a fully seated bullet or one in a cartridge and another lodged in the barrel ahead of it. If there is a bullet (or any other solid obstruction) in the barrel and a bullet is fired into it, the heat dump from the kinetic energy will weaken the barrel and the pressure will bulge or burst it.

I have seen repeated warnings that an air space in a muzzle loader will cause a burst barrel, but I was never able to get it to happen; I think those burst barrels were the result of a barrel obstruction ahead of the bullet, not air space.

If the two (or more) bullets are touching one another, the result is like a single very heavy bullet; pressure may increase, but the barrel probably won't bulge or burst.

Jim

 

[Jim Watson]

No confusion here, I am not talking about screwups leading to barrel obstruction, the conventional wisdom is that black powder be loaded with no airspace between a suitable powder charge and a single standard bullet.

The scheutzens get away with it with breech seated bullets, somehow; but nobody I know or know of loads fixed BPCR ammunition with anything but a compressed charge. Reduced loads are accomodated with filler wads or granular filler like grits or Cream of Wheat. Or by substitution of a coarser granulation. Fg seems the answer to centerfire plinking with cases longer than 2.1".

 

[RPRNY]

Yes, my query is about airspace when breech seating not barrel obstructions.

And to further queer the pitch, how is it the scheutzen old timers breech seated and reused the same case, decapping, scraping it out, repriming, and filling with powder without compressing the charge? In Ned Roberts' book on the scheutzen rifle, there is mention of "tapping down" the powder and covering it with a "blotting paper" wad but nothing about compressing the load.

So how do we have some of the most accurate shooting ever done with A) the dread airspace and B) uncompressed powder?

 

[shunka]

This topic was discussed at length over on the now defunct open range
start here -
http://www.theopenrange.net/forum/index.php?topic=2078.0

then here
http://www.theopenrange.net/forum/index.php?topic=6128.0

then the 5 page discussion
http://www.theopenrange.net/forum/index.php?topic=2098.0

hope this helps
yhs
shunka

 

[Crawdad1]

Here is a good discussion on the differant powders and level of polishing used.

http://www.thehighroad.org/showthread.php?t=714163&highlight=swiss+powder

 

[Jim Watson]

Well, from all that, I conclude that airspace over black powder is not the problem that it is made out to be... except when it is.

 

[RPRNY]

Well, from all that, I conclude that airspace over black powder is not the problem that it is made out to be... except when it is.

Yes. Absolutely. Clear as mud then. ;-)

 

[CANNONMAN]

Don't know if this will make sense but... There is a geometric progression of pressure that forms with "air space." 0 -1 "units" of air space = known pressure of BP being used. But that is basically where it stops. 2 -3 "units" 10X more pressure. 3 - 4 100X. Too simplistic? Yeah, I know. But it's how thing blow up. Air space allows pressure to build, very quickly. Everything else is a variable of some sort making the amount of allowable airspace to be difficult to determine. Your variables are not the same as the next readers variables. The old M-80 was a little flash powder in a cardboard tube that was mostly air space. If this tube had been completely filled the results would have actually diminished. A little air space and you can have "improved" pressure. Case-in-point, helping the 45-70 push that big ol' bullet. Polish improves rate and consistence of burn. Therefor more sensitive to air space. Hence, best rule of thumb, No air space. If you are able to control ALL other variables. Air space may be challenged. I would hardheartedly suggest not doing this. Recall that those who have were VERY dedicated and seasoned in both the art and science of BP. "Chance favors the prepared mind. Here, I wouldn't take the chance." CANNONMAN

 

[shunka]

What CANNONMAN said.... additionally -
- in general the effect is more readily seen in artillary
- in general having a vent reduces the effect, thus it is reduced in revolvers, & flintlocks
complicated, nicht wahr?
yhs
shunka

 

[zimmerstutzen]

Odd
I breech seat my 32-40 Stevens but there is no gap. As I place the case full of powder, I can feel the seal over the case mouth give way and as the case is pushed, I can feel the powder crunch as the case reaches full depth.

No air gap

 

[RPRNY]

Odd
I breech seat my 32-40 Stevens but there is no gap. As I place the case full of powder, I can feel the seal over the case mouth give way and as the case is pushed, I can feel the powder crunch as the case reaches full depth.

No air gap

One method. But another is to seat the bullet approximately 1/16 to 1/8" ahead of the case mouth. So it appears that a small gap is okay whereas a large gap will create rebounding pressure waves.

 

[BCRider]

What Cannonman posted above about air gaps seems to make sense. Few things in life are either completely black or white or absolute. So a sliding range of response to an air gap makes a lot more sense.

I'd also suggest that those schutzen shooters that seats the bullet or ball then load a powder charge behind the bullet or ball is still very likely placing the powder retention wad card up against the rear of the projectile or very close to it. So the conditions are likely in that 0-1 "unit" range for the air gap.

A fellow I ran into at the range one day was testing for the cold and damp conditions with his BPCR. He was breech seating paper patched bullets by loading them long in loose necked casings which would let the bullet slide back when loading.

This would make his method similar to zimmerstutzen's method above I'm guessing.

 

[J-Bar]

Here's my take:

Imagine the cartridge in it's customary firing position; roughly horizontal. If there is enough powder in the case to cover the flash hole then when the primer is fired powder will burn progressively from the back of the charge towards the front. In that first instant of ignition, pressure would increase near the flash hole, pushing and compressing the unburned powder against the base of the bullet. No problem.

Now imagine that there is not enough powder in the case to cover the flash hole. When the primer ignites, the fire flashes over the whole horizontal surface of the exposed powder. The powder charge burns more rapidly because more powder is exposed to the primer flash, pressure increases faster than it should, and is directed sideways instead of towards the barrel. Maybe a problem??

So a little air gap is ok, but not one big enough to expose the flash hole.

This may not be the explanation, but it's fun to use one's imagination!