doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Tom Roster SSM article re low vs high pressure

He'll reply tomorrow morning about 7 to 7:30, Miller. He ain't done yet, I'll bet'cha.

SRH

Well Stan . . . speaking of being done . . . I'm still waiting to hear about a shotgun that was sleeved using Whitworth tubes. Or maybe you're done on that one.

And then there's your contention about big shoots and how there will always be more top level shooters than average shooters. Results of this year's Wisconsin Ironman, with 290 shooters: Total of 91 in Master, AA, and A Classes combined. Outnumbered by the 96 shooters in Hunter Class.

So Miller, you haven't yet attempted to explain to the great unwashed masses here exactly how it is one goes about determining the average TOTAL pressure produced by a particular load. And why it's important for us to bother. Obviously, since we know there's only one peak pressure per load after which the pressure drops, it clearly doesn't remain the same from the breech to the muzzle. And we all know that pressure drops faster in some loads than in others. But what the heck is the whole "total pressure" thing about? I've sent quite a few reloads (and some factory loads) to Tom Armbrust to have them tested for pressure and velocity. Very valuable information. He gives me an average pressure for each load. But he doesn't tell me anything about total pressure.

What's it about? Awe c'mon Larry, why is there always discussion here about "low pressure" loads? Are you saying that if I were looking to end up at a particular velocity, all else equal, that two different "average" pressures can end up with the same velocity?

I have no idea, how many of the same load might Tom A. recommend be tested to come up with an 'average' what have you data for the particular load?

I don't know what total pressure is. Are you integrating under the pressure, time curve? If so, I'm not sure what that is, but probably not total pressure.

If I was looking for the ragged edge of an upper safe load limit, I would qarn well want to know what the variance is, in addition to the average peak (max) pressure.

Larry;
IF you could simply understand what you read then you really would not have had to ask such a question. It all started from the knowledge that, yes max pressure falls off fast. However, it still takes the same amount of total force to get that oz of shot out the end of the barrel at 1200 fps, or any other load you desire to make a comparison with.

The whole point was if you have a gun with thin barrels near the muzzle, even if you drop the peak pressure from 10K to 5K, you have not lowered the total force applied, just redistributed it. You thus have not truly done that gun with thin walls near the muzzle a favor by lowering the peak pressure, you have actually slightly increased the pressure down under the thin spot.

As Force = Pressure times Area this also explains the comparison of firing the same load to the same velocity from guns of different gauges. Area of a gun's bore is proportional to the square of their diameters, thus the pressure is also proportional to the area.

Using nominal bore diameters (.729/.615) = 1.405. For brevity, I simply called it a 40% increase in area for the 12 over the 20. Therefore if you fire the same 1oz of shot to 1200 fps from both gauges TOTAL Average Pressure for the length of the barrel will be 40% higher in the 20 gauge.

Once again this has absolutely NOTHING at all to do with Max Peak Pressure regardless of how many shells were tested to list the AVERAGE. This all based upon "Proven" Scientific Facts & actually applies to many fields other than just guns where pressure is involved, including internal combustion engines, hydraulics, etc.

Until some time as you get it through your head that there is a lot involved in shotgun ballistics than JUST the Max Peak Pressure then I suppose you will never come to an understanding of this. In the meantime, if you so desire just go on with your non-related blurbs which mostly gives the appearance you have little understanding of mathematical principles. Personally, I think, Perhaps, the appearance is not deceiving.

PM sent.

Miller: Since Force equals pressure times area and recoil is a force, then why do we hear on this forum over and over that pressure has nothing to do with recoil? I�m confused on that. Thx.

The issue here, it seems to me, is really how low one should go in terms of PEAK pressure where vintage gun X is concerned. I've never been a real low pressure Nazi. I know some guys liked their PB loads at 5,000 psi or so . . . but I was never one of them. At some point, someone here stated that if you have a gun that can't handle peak pressure somewhere around 8,000 psi (might even have been you, Miller), then it's probably not a good idea to shoot it. I'm pretty much in the same camp. Given what we've learned about vintage loads going way back, they weren't lower pressure than that. Never mind the fact that if you live where I live (serious cold country) and shoot when it's below freezing, you'll often get pretty poor performance from very low pressure loads. I've heard very weak sounding Winchester low noise/low recoil loads in cold weather (far weaker than when it's 70 or so). Reloading manuals used to give us hints along those lines. Like "not a good cold weather load".

But given the fact that pressure only goes one way (down!) after its peak, it seems to me you'd need a pretty darned thin spot down close to the muzzle if you were going to blow the barrel there. Has anyone ever heard of a gun that's blown out near the muzzle as a result of a very low pressure load? I can't recall anything here. And that's an unusual location for a catastrophic barrel failure anyhow, unless maybe there's a muzzle obstruction.

Well, I missed the time by a few minutes. But, you're predictable if nothing else.

Funny you would bring up two past discussions where you clearly lost the debate both times. One more time, that ain't a big shoot. Spread your wings Lar'. Get out a little more. It'll do your perspective good.

Larry Brown ............... not necessarily right, but never in doubt.

SRH