I am befuddled. Posted a response and it vanished into thin air. <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />
Walking down the exploration road myself but in more mundane ways, mostly concerned that I don't wind up re-cocking the lock from vented pressure and the attendant hazards of stuff splattering my face whilst shooting a slug gun and hoping to duplicate BPCR velocities, or as least come close in the .40-.45 bore with 500ish grain boolits.
Well, that said there is a fella named Sherman Bell published frequently in Double Gun Journal who uses Oehler equipment in good fashion with BP and low pressure Le Smoke loads in scatterguns...mostly. What he does is...
Have his loads tested in a piezo pressure gun and then uses them to calibrate his test equipment, and vice versa...sorta like two way verification. He uses a NEF break action 12 for his testing and I believe he has settled the issues related to differences in chamber dimensions and effects of chokes. He not only tests chamber pressure but has attached sensors in short interval to verify/examine the curve as the shot rambles down the tube. All in all the results are that he has developed nitro for black loads that he uses in damascus guns that actually give the same velocity at less pressure and with a similar curve. Point of consideration with the strain gauge system is that it is alleged to give poor results with thick walled chambers/barrels at low pressure levels. Apparently this is not an issue with shotgun barrels. I presume it would be easy enough to calculate a minimum safe wall thickness for a give rifle cartridge though that is only speculation. The NEF would be a dandy if that approach were taken...I'd use a block house or an empty range and a long string...
I have also read in several different sources that the Naval Ordnance Board used BP to generate pressures in excess of 100KPSI some years prior to WWII though I've not seen documentation to that effect.
I think you're right regarding the lack of info on BP pressures and have no inside info regarding that subject or forum boards where it may be discussed. That said it is obvious that there are thresholds not clearly defined by manufacturers and SAAMI. The scattering of different recommended BP loadings from gun builders in phenomenal, from 90 to 180 grains, using conicals or RBs. I've read of fella using 600 grain bullet with 180 grains as a working load in .58 caliber in Africa to no ill effect(except on the quarry).
My suggestion would be to contact Mr. Bell thru DGJ...if anybody knows he would, at least a source of some info or technology...something. A second possibility would be to contact the web master at
http://www.eskimo.com/~jbm/ . I've had a couple of email chats with him and seen him on a few boards over the last few years. He knew Robert McCoy personally and that would indicate more than passing knowledge of the issue of ballistics. My .02 worth on that matter.
I note that many if not most BP guns from days gone by have rather thin barrels, an exception being styles common to today's BPCR rifles and of course old double rifles. It says a lot about the pressures involved...or the fashion of the day.
