Quote:
Originally Posted by STORMINORMAN
I'm really confused! 357 SIG MAX loads of Longshot for 124gr XTPs per Hodgdons data is 9.3 gr @ 1,429 with a 4.00" barrel: pressure is listed as 37,900 PSI.
Their START for 357 Magnum with Longshot and a 125gr XTP is 8.2 gr @ 1,529 and their MAX is 9.7 gr @ 1,647 in a 10.00" barrel: pressure shown as 42,000 CUP.
Nonwithstanding the different way pressure is expressed, doesn't the 357 Magnum case have a significantly greater volume (26.2) than the 357 SIG (19.5)? Especially when using what are basically the same size bullets? There's the lack of a cannelure on the .355, but the profiles are really not that different...
I'm not trying to argue apples vs. oranges here, but shouldn't a case THAT MUCH smaller (as in 25+%) in volume generate significantly higher pressures were the powder loads to be equal... Say, using 9.2 gr which is halfway between the Magnum's START and MAX? Wouldn't the smaller case pressure be higher?
We get routinely concerned with an unintentional increase in pressure when bullets are loaded deeper by relatively minute amounts (typically measured in thousandths, even hundredths of an inch?), nothing that would ever result in a 25% decrease in case volume?
P.S. From what I can determine that MAX Magnum load pressure of 42,000 CPU × 1.516 - 17,902 = 45,770 PSI (approximately?)
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Difference is the barrel length. Lee also has the 9.3 grain charge with a 124 grain bullet for 357 Sig but their test barrel is an actual pistol barrel. I have no idea why Hodgdon publishes a 10 inch barrel in their PISTOL section. They should have two difference clocks for 357 mag, one for pistol and carbine.
With a short barrel like 4 inch, you will need on average much more powder to get an equivalent fps because the short barrel evacuates pressure much more quickly, because it is short. Also, that 9.3 grain longshot charge for Sig is underclocked. It says 1,429 fps but i got an average of 1,469 in a 3.9 inch barrel, and a high of 1,513.
Don't pay attention to CUP pressure ratings, you'll give yourself a panic attack. Just get a chrono, and then watch both your fps and felt recoil. That is a better, faster indication of danger. If Lee says 9.3 grains of longshot will give you 1,429 with a 9mm round nose bullet, which it won't, best start on the low end at 8.5 and then do a chronograph to see where you really are, and then go for there
Same with the weird 10 inch 357 mag data. Me personally, i took my 4 inch and started on the highest charge in that situation because i knew the 10 inch barrel velocity and pressure was far beyond mine and were overstated. It was, and then i increased the charge from there until i got what i wanted. At that point felt recoil was dimilar to factory 357, a bit sharper since Longshot burns faster, and the velocity for 180s was in the same vicinity of stated factory 180 grain loads. I inspected the brass, which looked fine, deduced that i was safe, and stopped pushing the charge. I could probably go higher but i am fine with 540 ft/lb 180 grain loads, not much will walk away from that.