Our control load was a 500 gr Woodleigh RN Soft. Considered safe by most everyone. This was also the bullet used to confirm data on the second day of test work.
After testing some of the more common bullets used in double rifles it looked like our theories were being proven, and it appeared that the system was in fact working as we had hoped it would. We did test the Copper BBW #13 and it in fact gave very low readings of barrel strain, exactly as we thought it should. Other bullets fell right in line with was has been considered either good or not so good for double rifle barrels in the past.
Chamber pressures were up and down, depending on the bullet, and matched velocity and other measurements.
One mention is that the CEB Copper BBW#13 gave the lowest chamber pressure of any bullet tested, however it did not sacrifice velocity, which was actually better than most all the other bullets, with some exceptions of bullets at much higher pressures than allowed for this cartridge. What this is telling us is that we can have our "Cake & Eat it Too". Low pressure, high velocity, and low barrel strain, extreme penetration and performance, I don't see a downside to any of that.
Other bullets that performed well was the North Fork FPS giving a lower barrel strain than even the Woodleigh Soft. This was expected. Giving the very highest barrel strain reading of all solid bullets tested was an Old Style, Round Nose Barnes Solid, no bands. Again, this bullet has a reputation of being hard on double rifles, and it appears the data proves that as fact.
During our third run of barrel strain tests we discovered that cast bullets in double rifles might not be the best idea! In two tests done, one with a cast gas check bullet, the other a soft cast bullet with no gas check, these two bullets now have the highest barrel strain of any bullets we have tested. This came as a total surprise to both Sam and I. We actually figured the cast bullets would be the lowest of all bullet tested, certainly not the highest numbers we have recorded to date! It is our contention that the softer hard cast and cast bullet is actually slugging up in the barrel as it goes down the bore.
Neither Sam nor I proclaim that what we have done is "absolute", and that a particular bullet is safe, and another bullet is not safe. This would be impossible to do with the large variety of double rifles built in the last 100 years. Old, or modern, this will have to be decided by each individual owner of his rifle, only the owner can make such a decision as to what may or may not be safe in their rifle. It is our hope that this can be used as a guide, and to give you a better understanding of what a particular bullet may be doing inside the barrel as it passes a particular point, nothing more. Every rifle is different, so the information is here for you, but you have to make the decisions on what to use and what not to use, and what you consider safe or not safe.
Below is a spreadsheet I made up, pdf format, with all the test work.