What's the reason for

gnmontey

gnmontey

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never leaving an air space between a BP charge and the projectile?

I have been shooting a cap lock and BP cartridges for more than a few years now and the rule of thumb has always been to tap the projectile down firmly upon the charge or use a compressed charge or a filler with cartridges.

Why does an air pocket cause an over pressure situation?

Thanks,

M
 
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I'm not a fluid dynamics expert or demolition contractor or anything. My understanding is that the wavefront or the unburnt powder at the front of the charge acts as a solid projectile which accelerates in the available space then slams into the bullet that's now acting as an obstruction. This can be enough to ring barrels or chamber by stretching the steel.

Black powder is a true explosive and acts differently than smokeless powder which is a propellant. I don't know exactly what the details are that make them different. It seems a little counter intuitive that smokeless can deliver more energy.
 
There are two school of thought on the matter.
One is, as you have stated, do not leave empty space between the BP charge and the projectile.
The other is that an air space is OK, so long as at least 75% (as I recall) of the available space is filled.
I have been shooting BP muzzleloaders for North of 40 years and always make certain the ball is firmly seated on the charge. However, I have been shooting BP cartridge (577-450 and 45-70) for a couple of years now and do not completely fill the cartridge - the 577-450 in particular. I put a good tuft of cattail down on top of the charge and seat the wad, cookie and bullet, which leaves some airspace. I have seen no ill effects and no signs of excess pressure.
 
vagrantviking said:
Black powder is a true explosive and acts differently than smokeless powder which is a propellant.
Click to expand...

Regardless of how it may be classed, black powder does not detonate as some people believe. The basis for saying that is that I tried breach seating bullets in a BP cartridge rifle with two different cartridges and two different rifles. I used a near case full of 3 F powder, lightly compressed then about 1/4" of compressible felt and the bullet seated in the bore with the base of the bullet at the mouth of the case. In both cases (no pun intended) I had case separations about 1/2 way up the cartridge and the front portion of the case jammed into the beginning of the rifling. The only way that I can explain that result is that the powder next to the primer ignited first and the powder progressively burned forward but without the inertia of the slug to hold the powder near the mouth of the case to ignite, the compressed plug of powder gripped the case walls and dragged the front half forward. If black powder detonated, the whole charge would go off almost instantaneously and would not drag the front of the case forward. I did not get that result when I used a more or less incompressible wad (wonder wad) between the bullet and the powder. In smokeless cartridges at least, case separation from excessive head space, occur just ahead of the web of the base of the cartridge. I don't recall having any similar case separations with black powder, maybe because they indexed on the rim

cheers mooncoon
 
Small airgaps are not a problem at all. I have shot many breech seated loads with black powder and use air gaps of up to 1/8" with no problems. This was a pretty standard thing to do in the old days with target rifles.

With gaps of several inches I have heard of bulged barrels in muzzleloaders though, so there may be limits :)

Chris.
 
Steve Garbe published a US Army study in the Black Powder Cartridge News where tests were conducted leaving air gaps between the bullet and the powder charge. Test vehicle was the issue Trapdoor Springfield 45-70 rifle.

Bottom line - no damage to the rifle but there was a significant variation in muzzle velocity, as might be expected.

I think this is one of those "... everyone knows ...." myths that has become "fact" over the years. Every one "knows" or "has heard of" such an incident, but not many have experienced it first hand.
 
Sharps '74 said:
I think this is one of those "... everyone knows ...." myths that has become "fact" over the years. Every one "knows" or "has heard of" such an incident, but not many have experienced it first hand.
Click to expand...

To some degree I agree but I also have a few guns with ringed barrels and have seen many more. It certainly happens somehow.
Is there a better explanation out there?
 
mooncoon said:
Regardless of how it may be classed, black powder does not detonate as some people believe. The basis for saying that is that I tried breach seating bullets in a BP cartridge rifle with two different cartridges and two different rifles. I used a near case full of 3 F powder, lightly compressed then about 1/4" of compressible felt and the bullet seated in the bore with the base of the bullet at the mouth of the case. In both cases (no pun intended) I had case separations about 1/2 way up the cartridge and the front portion of the case jammed into the beginning of the rifling. The only way that I can explain that result is that the powder next to the primer ignited first and the powder progressively burned forward but without the inertia of the slug to hold the powder near the mouth of the case to ignite, the compressed plug of powder gripped the case walls and dragged the front half forward. If black powder detonated, the whole charge would go off almost instantaneously and would not drag the front of the case forward. I did not get that result when I used a more or less incompressible wad (wonder wad) between the bullet and the powder. In smokeless cartridges at least, case separation from excessive head space, occur just ahead of the web of the base of the cartridge. I don't recall having any similar case separations with black powder, maybe because they indexed on the rim

cheers mooncoon
Click to expand...

A couple things could have contributed to the case separation, wet chamber, or long cases.
 
vagrantviking said:
To some degree I agree but I also have a few guns with ringed barrels and have seen many more. It certainly happens somehow.
Is there a better explanation out there?
Click to expand...

There is sufficient evidence that a lot of ringed barrels are caused by using wads (kapok, Puff-Lon, etc.) in large BPCR cases to hold a reduced smokeless load over the primer.
 
As I understand it, bottleneck cases and some fillers, cornmeal for example, are a bad combination because the filler can form a plug as it compresses to pass through the case neck.
 
Nothing mentioned in the Lyman Black Powder Handbook other than to seat the projectile on the charge.

M
 
Sharps '74 said:
There is sufficient evidence that a lot of ringed barrels are caused by using wads (kapok, Puff-Lon, etc.) in large BPCR cases to hold a reduced smokeless load over the primer.
Click to expand...

It's understandable that these kinds of fillers might contribute to ringed chambers but I don't see how these materials would be left anywhere in the rest of the bore with the gases from the powder charge coming behind.

One of the rifles with a ring in my safe is a muzzleloader which I presume hasn't seen smokeless or fillers. I acquired it with the bulge so can't say for certain but can only see it being caused by a ball not having been seated firmly on the charge.
 
The only person I know of that has done a detailed study of barrel ringing was Charlie Dell. You can read it in his book "The Modern Schuetzen Rifle". His experiments were quite interesting. As part of his work he built a brass chamber for testing as it will "ring" more easily than steel. In the end he was able to generate rings on demand.

Chris.
 
Embarrassed to admit a few years ago I fired a nice 34 cal original after short-starting the ball and busy talking to others forgot to seat the ball on the powder. Fired OK and hit the target but found on cleaning the piece later a slight bulge made evident by using my usual tight cleaning patch which found a "soft" spot on the down stroke. The bulge was about .005 thou which ruined my day for sure-good thing I was only using 35 grains of powder. ALWAYS seat the ball firmly!!!
 
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