doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pressure vs. Velocity

Great thread! I'm learning a lot.

Drew;
I have seen those feathered edges on plastic shells which were fired in correct chambers so the hull did not even enter the cone, much less the bore.
I read Bell's report at the time but don't recall how many shells he actually fired, in my "Opinion", not hear enough.
The greatest work which has ben done on this question was done by the British with the introduction of the pie/fold crimp shells in the late thirties. It was delayed a bit by a "Little Domestic Spat" going on known as WWII, but was completed shortly thereafter. This was all of course done with paper hulls loaded with card & felt wadding.
What Bell truly did was to confirm that what had been common practise across the pond for nigh onto a half century would work on this side, even with plastics.

Just doing a quick review of the article, looks like Bell tested about 15 different loads, including a couple each 3" shells and round ball rifle loads.

Something we've failed to mention here is that you can get yourself into trouble if you're shooting an older gun--almost always 19th century I think--that has a forcing cone that's more like a "step" than a taper. Charles Fergus reported on that in an article he did for Shooting Sportsman. He was getting a loud report and blown ends on British 67MM shells which, according to the information on the box, are approved for 2 1/2" guns. Those same shells worked fine in a 1930's vintage 2 1/2" British double. But he had to use true 65MM/2 1/2" shells in that older gun with the "step" style forcing cones to avoid problems. In those guns, it's pretty obvious that you would not want to use reloaded 2 3/4" hulls.

I have mentioned this before, in a thread about pressures, but I know a guy who had a cheap imported 12 ga. double gun, with 2 3/4" chambers. He thought it was great fun to get his likkered up buddies to shoot two 3" magnum loads in it at the same time. This took place numerous times, until he got rid of the gun (for kicking too hard? ). The gun never exhibited any symptoms of extreme recoil or chamber pressure overload.

Aside from the obvious stupidity involved here, the amazing thing is that the gun is still in one piece, on face, with tight wood. Modern steels are unbelievably tough. It was a Boito, IIRC.

SRH

I was thinking about what Drew is attempting to do, and I don't think a bit of boilerplate can be cleanly written that can be repeated all across the ether to useful effect.

I'd say something like, "If your gun was made before WWII, read the cartridge box, and use the lightest possible load you can make work (pressure and payload), so as to avoid injury, or premature decay of your firearm."
Then the SAAMI people could be pressured to make manufacturers print their pressures on their boxes. Like a cigarette package. Without the judgement.

A slight tangent:

On the 'feathering' that Drew mentions, I think that much more an effect of the skiving done to the mouth of one brand plastic hull vs. another even though there are many slight known length variations in plastic hulls, inclusive of some from the same manufacturer. Too, there are different plastics being used from one type hull to another or even the same type ammo in some cases where a manufacturer has decided to affect a change.

Lest that statement be confusing in ref. to lengths, I am speaking about different 'runs' of ammunition and different loadings using what at first appears to be the same hull, NOT hulls from the same box. The same could be said of paper hulls. There never was a 'standard' length for the un-loaded hull, per se.

Also, in the FWIW, dept. not all modern paper hulls are created equal either, some will 'pin-hole' [burn through] on the first firing. I attribute that to thinner walls, less substantive paper and lack or absence of wax. Just my take on it, no science.

Federal paper hulls remain the best, IMHO & there are many good published low pressure recipes available using them. They also use a wound paper base wad that many other paper hulls do not, using plastic for said purpose instead. I find Federal paper hulls good for about two loadings before they start to pin-hole.

TW,
You brought up paper shells. In the Bell article, he tests for pressure change with paper shells.

I have heard many times that bulky 2-3/4" paper shells would have a greater pressure increase in 2-1/2" chambers than plastic. His testing indicates that the increase was actually less than with plastic.

Bill

Also probably good to remember, while we're discussing pressure, that the SAAMI service pressure standard is the same for both 2 3/4" and 3" 12ga loads: 11,500 psi. The difference comes in recoil, because of the heavier shot charge that can be stuffed into a 3" hull.

There is no such thing as a "SAAMI service pressure standard." The 11,500 PSI figure given is the SAAMI "Maximum Average Pressure" (MAP), is one of the three reference pressures the SAAMI performance standards uses to describe the testing of ammunition subsequent to its manufacture, and is a number that has meaning only within that testing environment.

Anyone interested can go to the SAAMI site and download a set of the SAAMI manufacturing standards. Bring your statistics books with you :-)

SAAMI:

http://www.saami.org/