doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Low Pressure Question

Thanks guys now that makes sense.

An example of hoop pressure. Obviously no obstructions. This does show the importance of wall thickness.


The DuPont chart Miller is referring to:


What the DuPont booklet goes on to say:


Pete

Back to my original post...

The Reloading Bench Burn Rate Chart

28. 700X (IMR)
40. SR-7625 (IMR)

700x is FASTER than SR-7625

This is true.

If you load the two powders to the same chamber pressure, the slower powder will provide more total velocity.

The pressure curve will drop off more slowly with the slower powder, resulting in more total area under the curve.

Thus, the loads aren't "the same". Peak chamber pressure is just one data point on the curve.

I keep a bottle of Unique for cast bullets for years. Will try some for my LP loads.

I've never paid much attention to Burn Rate Charts relying on published recipe data.

Thanks all for setting me straight!!!

Was shooting pitted laminated twist 10ga with 10-12ga chamber reducer yesterday. Used 7625 with 1oz and 800x with 1 1/16oz. Clays with 7/8oz wouldn't seal in the very over bored 12 (poor pattern)I think 7625 and 800x hold pressure longer to seal wad in very over bored 12. Black also holds pressure longer (see chart C above). I use real FF or F with 1 1/8 when hunting. PSI in load data is only one thing to look at. Also if you haven't read Sherman Bell's "Finding Out For Myself" articles in the Double Gun Journal, they are very interesting, concerning shooting damascus and twist barrels.

I've shot damascus barreled SxS's for ten years - have tried to keep my loads under 7000psi. IMHO it doesn't matter what powder is used - 7000psi is 7000psi be it BP or any nitro. My BP load is 70grs of 3F and 1oz of shot - fiber wads. If my gun hasn't blown up in a 130 years, it isn't gonna now with 6 or 7000psi loads. Any American made double of years past was built plenty stout [ not like those skinny British guns ] and should be safe with any pressure curve if it's under 7000psi. Paul

An 850 bar gun has a service pressure standard (NOT proof pressure) of almost 11,000 psi--not far under the SAAMI 12ga service pressure standard of 11,500 psi.

There used to be an old wives' tale that black had a much different pressure curve than smokeless. Yes, different--but not much different. As established by both the Dupont chart above and by the tests Sherman Bell ran and reported on in Double Gun Journal. If a gun is safe at pressure X with black powder, then you're not risking it shooting smokeless loads at the same pressure.

I read that Unique burns in a similar manner as black. I am not sure about using slow burn powders with light shot charges in Damascus barrels. Many old quality guns had their barrels "swamped" in a severe manner. That means they got thin quick! A powder like Red Dot will propel a 1 oz charge below 7000 psi and it will be consumed before the wall thins. 7625 will hold pressure out a foot or so.

bill

Another chart of interest comparing FFFG and 7625


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