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Old 08-21-2009, 10:31 AM
Skip Sackett Skip Sackett is offline
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Lightbulb Yes, someone did pay for lab results, it just wasn't me!

Quote:
Originally Posted by pinkymingeo View Post
Every now and then I see claims that 4756, when loaded above current specs, gives high velocities at lower pressures. Where does the pressure data come from? Not from current loading tables, certainly. Has somebody paid for lab tests? I sometimes wonder about published data. Hodgdon, for instance, publishes data for LilGun indicating impressive velocities at remarkably low pressures. My chronograph tells me, however, that their velocity figures are materially overstated. If I loaded to published velocities would LilGun still provide very low pressures? I doubt it.
pinky,
To answer some of your questions honestly, I don't know. I do know that someone did in fact test SR4756 on two different occasions when we were talking about "THE LOAD" with differing results. One stated that the pressure was tested well above 30,000cup while the other was well under that. More in-line with 25,000cup. Well above current data, no doubt and outside of SAAMI standards for even the most serious of +P ammo.

While this is being discussed, you raise a good question. If I load to the Hodgdon's website data, say for 357mag with 158gr LSWC and I get "XXXX" fps velocity, which is 300fps below what they list, what pressure did I develop to get that velocity?

I think you are of the persuasion, and nothing wrong with taking that line of reasoning, that you had the listed pressure without the listed velocity. Is that right?

I am of the other persuasion, if I didn't get the listed velocity then I didn't have the listed pressure either. Apples to apples for me. I can get within 20fps of what they do when I load for the 40S&W and the same weight bullet within their data. That doesn't hold true when I go to revolver rounds. 38spl or 357mag.

It can be blamed on cylinder gap but in my experience with the 45ACP in both revolver and the 1911 platform it just doesn't hold true. Case in point: 230gr Ranier TMJ with 8.0gr HS-6.
M625JM**********************PT1911
Low 775fps ******************Low 772fps
High 827fps *****************High 833fps
Avg 806fps ******************Avg 796 FPS
ES 52fps ********************ES 60fps
SD 22.24fps *****************SD 17fps

As you can see from that data, I must have had one round in the PT1911 that went a little high while the rest of the rounds seemed to settle in at 790fps or so. I didn't keep a list of each round fired. What you can see though is that the cylinder gap didn't seem to affect the results at all. With a shorter barrel I got the same velocity (basically) from each platform.

It is from tests like this that I have derived my thought process, faulty as it may be!

I hope this helps you to understand my position. Not trying to sway you or anything like that, just to get you to understand, that's all. I think both points are valid, yours and mine. We both have used deductive reasoning to arrive at our conclusions.

If I have a closed system like a bolt action or single shot rifle to test out of I will stay with published data pretty much. I feel I am shooting on the same platform as the data was tested in. When we go to pistol/revolver rounds though, I don't have any single shot firearms to test my loads out of, therefore I go by velocity, within reason!

Again, I hope this helps you understand, not agree, but understand my position.

'Preciate your knowledge and participation on the forum.

Best to you!
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