Dan;
Thank you for your response.
When I was performing those notorious 4Fg tests, I was measuring muzzle velocity, not pressure. That led to some nice equations for estimating BP muzzle velocities. Now I'm interested in pressure, a different animal. The first step in investigating BPCR pressure is to see what others have published.
Unfortunately, there has been relatively little information published about the pressures generated by BP cartridges. Perhaps this is because no one much cares. After all, modern breech loading rifles of strong design are much stronger than needed for the relatively low pressures generated by BP, so there's no particular safety problem to investigate. While smokeless powder can potentially generate pressure spikes in excess of 200,000 psi, BP is limited to a maximum pressure of about 86,000 psi. This maximum pressure of 86,000 psi was determined by British captains Noble and Able using a pressure vessel which did not release any of the BP combustion gases.
Modern breech loading rifles of strong design should be able to withstand pressures well in excess of 86,000 psi. A proof load typically produces a pressure that is 30% over a cartridge's normal maximum pressure. Some modern smokeless cartridges can generate peak pressures of 65,000 to 70,000 psi in their normal loadings, which translates into about 55,000 cup. That means the rifles firing these cartridges must be able to withstand a proof load of 90,000 psi.
Since these strong, modern rifles are routinely operating at pressures near the maximum that can possibly be generated with BP, it seems like nobody particularly cares how much pressure a BP cartridge could generate because they expect it will probably be within a modern rifle's margin of safety. Of course, we've all heard of rifles that have blown up for one reason or another. Bore obstructions are a major culprit, also defects in the barrel steel, loading the wrong cartridge in the rifle, etc., etc.
I'm interested in BP pressure because of the way it affects bullet design. If a bullet's unsupported nose is too long, or the alloy is too soft, or the base pressure is too high, the nose may slump and bend the bullet out of shape, causing yawing and inaccuracy. If I can estimate the pressure that will be generated by a particular load of BP, it will help in the bullet design process. Right now, I just want to work up some pressure estimating equations that I can include in my bullet design spreadsheet.
You wrote, "It sounds as if you're looking to create something akin to a BP Powley Computer, if not in the same form, at least for the same general purpose. If that is so I'm sure that somebody somewhere has already been there. Perhaps the folks at Aberdeen could point you in the right direction ...or Goex/ KiK/ etc., etc. If that is the case why would you want data on something you don't recommend yourself?"
A Powley computer for BP? A great idea, but probably beyond my skills. If there is something like that out there, I haven't been able to find it. I've talked to a few folks associated with Aberdeen, and they say they haven't got any information on this topic or, if their lab does have it somewhere, they don't know anything about it and cannot find it. My reason for posting on the GOEX board was in hopes that someone associated with GOEX would step forward with lab tested pressure data, but that hasn't happened yet. Does KIK have a similar board where inquiries could be made?
I don't recommend the use of 4Fg in BPCR rifles for several reasons. Number 1, nobody I know has done any pressure measurements to prove it is actually safe. Theory says it may be, but theory and reality are two different things, and I am not going to recommend anything that I think may be questionable or unproven. Number 2, the powder manufacturers do not recommend it, and their lawyers must know something. Number 3, 4Fg does not give a particularly useful increase in muzzle velocity or a decrease in fouling as compared to 3Fg. Number 4, increased pressure beats the heck out of bullets and forces you to use high drag blunt nosed bullets to prevent nose slumping . Number 5, this is an open forum, and inexperienced shooters could possibly read this stuff and get themselves into trouble. Hence I do not recommend the use of 4Fg powder in BP cartridges. This chronicle of my researches is presented for informational purposes only.
You asked about the sharing of pressure data. I haven't done any pressure measurements myself, other than examining primers for signs of overpressure. Therefore I haven't any pressure data to share.
Regarding the gathering of pressure data with strain gauge equipment, there are some problems associated with the potential accuracy of home style pressure measuring equipment This was discussed earlier on the GOEX board. Oehler makes, or used to make, a fine hobbyist rig for measuring barrel strain. Others make some similar but less sophisticated strain measuring equipment. However, none of this strain gauge equipment is as accurate as a calibrated piezoelectric transducer setup on a pressure gun. Oehler specifically says its hobbyist unit can not be relied upon to generate absolute psi values.
Hobbyist strain gauge equipment can compare loads fired at a given range session but, even for cartridges for which standardized SAAMI pressure test ammo is available, there are too many variables involved to make any claims for true pressure calibration. Regardless, there is no standardized SAAMI pressure test ammo available for BP cartridges.
Oehler says you have to glue the strain gauges to the barrel and that means, at a minimum, removing the bluing over the chamber, and maybe hogging out the stock to fit the gauge. Now, someone else might want to jump right in and do this and spend $500 or more, but I'd like to start out by inquiring whether or not someone else has already done it, and would be willing to share their results.
You said you had read some of my verbiage about the 40-82 by Googling some earlier posts on other sites, but you still had questions. Also you said I did not have to quote earlier posts because you guys had good short term memory. I quoted some of the preceding posts in this string so that anyone else who might Google up this topic or my responses would get a full picture and would see that I was not making this stuff up.
You asked if I was pissed off. No, I am not pissed off, just disappointed that an honest effort to further our understanding of BPCR performance has been misunderstood and/or misrepresented by some.
You wrote, "Case trim is as basic as it gets when reloading and if you're looking for data (reliable) you need to embrace the concept of perfect mastery of details or it's garbage in/garbage out."
Absolutely agreed.
So, it's real simple. I'm looking for lab tested data on pressure generated by BP cartridge rifles. Can anyone help with this search?
All the best,
Dick Gunn
