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B.P. Air Gap?

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Guns Garrett:
Being fairly new to black powder cartridge shooting, I have come across mention in some of my reading that seems to fly in the face of what I thought I knew of loading.  Most loading data for black powder doesn't specify a grain weight for powder, other than an approximation, and states how important it is to have a FULL case, whether it be all powder, or having the addition of wads or fillers, and to ensure there is NO air gap between the base of the bullet and the charge.  Otherwise, pressures spike and you end up with a broken gun, or worse.

Now - how did the old Scheutzen shooters manage to shoot straight black powder or duplex loads, and do this with the bullet seated anywhere from 1/32" to 1/8" in front of the chamber throat?  Most state that a pasteboard, cork, or fiber wad was placed in the neck of the case only to keep the powder from spilling out, or to keep the charge in the rear of the case near the primer.  Some didn't use any kind of wad or filler, just kept the muzzle elevated during loading.  Was there another trick they knew about?  Or did they just NOT know.  I'm not planning on doing this myself, it just came up in a conversation the other day and got me thinkin'.

Fox Creek Kid:
This is a topic to be treated with kid gloves. Remember, there are many neophytes here who know very little and as such may blow themselves up. There are many myths around BP. Yes, Schueten shooters loaded like this as well some FACTORY BP loads in the late 19th & early 20th century. HOWEVER, this is not for the untrained to duplicate as the penalty may be life ending. I would never recommend this type of loading to anyone as it's an unexplored area in regards to pressure spikes, stress coefficients, etc. Due warning.

Delmonico:
When breech-seating with these old arms the wad was at the top, not on the powder charge.  This way the air gap is between the powder and the wad, not between the wad and bullet.  Air pressure is the problem, just like sticking a wad in the barrel of a shotgun.

klw:
Really interesting, and maybe very dangerous, subject.  This was debated at GREAT length and with some really heated opinions elsewhere a year or so ago.  My understanding is as follows.

Filling a blackpowder cartridge case absolutely full so as to get a little compression when the bullet is seated IS NOT KNOWN to cause any pressure problems.  If you want a lower charge then fill the case with the charge you want and then use something like oatmeal to fill up any air gap.  I've never heard anyone suggest that filling up a case with an inert substance causes any pressure problems.

Air voids?!  Well some people think that they are ok.  That leaving a significant air gap is not going to cause you any problems.  More than that there are folks who get VERY nasty to anyone who suggests that this practice isn't safe.

But there is a problem, I think, with this logic.  If they are right, if leaving an air gap causes no problems, so what?  What does that buy you?  But if they are wrong.  If, eventually, a cartridge with an air gap is going to generate high pressures, then doing this could kill you. 

So to my way of thinking there is no advantage in using an air gap and there is a REAL risk.  Don't do it.

El Paso Pete:
Like most of the pards that have replied, you can put me in the no air gap column.

Don't matter if there is 1/4" between the bullet and the powder or 18".  Both meet the definition of an obstructed barrel. 
http://www.brimstonepistoleros.com/Articles/squib.html  Here is page by Dr. Stephen Wardlaw of the Brimstone Pistoleros.

I have never found a reason to need an air gap.  If I ever did, I'd use grits to fill the space.  It's real hard to get in trouble if your always in the fail safe mode, not impossible, just real hard to.

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