Sherman Wildcats pressure limits?
- Thread starter RevJim
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bigngreen
Well-Known Member
Don't know where min would be, never been there.
MagnumManiac
Well-Known Member
I run a pressure trace, I have tested the so called thrust being less theory by using 'plasti-gauge' across the case head on 22-250 and 22-250AI, both came out almost identical.
I know this is not a definitive test on pressure, but it is a comparason that can be repeated. The difference is less than .0001" in width between the 2.
Cheers.
I know this is not a definitive test on pressure, but it is a comparason that can be repeated. The difference is less than .0001" in width between the 2.
Cheers.
It would be nice to see some numbers as far as pressure goes. I have a 6.5 Sherman and am in the process of building a 6SST and a 7SST. I've had guys on other forums bash the Sherman and say how over pressure I am. I tell them that the speeds I get are verified with drops and I see no signs of pressure on my brass or heavy bolt lift. 5-6 firings on Nosler brass tells me that my load can't be that hot.
bigngreen
Well-Known Member
Who cares about the pressure your running, over pressure is based on the cases ability, the Sammi numbers are just a base line they mean nothing practical, there is brass out there that will really struggled at Sammi to be reloadable some not even effected. If your relaoding a rifle from the turn of the century then you need to be aware but even then your just hoping your rifle runs to the same pressure as the book load is at. Modern actions will handle anything the brass will, if you pounding brass your pounding your action.
I totally agree. I just get tired of guys saying that there's no way the Sherman can make these speeds without being way over pressure. Doesn't happen on here much but on some Canadian sites I frequent, it happens all the time. At least there is a few Sherman guys up here who come to my defence.
adam32
Well-Known Member
Except those guys are completely true...they are running over SAAMI of the parent case...FACT!
There's no magic pixie dust making the bullet go faster...
bigngreen
Well-Known Member
If a case head yeilds and primer pockets loosen on a parent case you can bet it will at the same pressure of the wildcat, it is what it is. Pressure is not the only component, time or pressure under the curve is important and the time to peak also make a difference. If you watch a pressure trace using like, H1000, Retumbo and R33 you can run them to the same pressure but the effects are different, you'll see time to peak and pressure under the curve making the difference not peak pressure.
Rich Coyle
Well-Known Member
Bob Nosler told me, "Peak pressure destroys guns. Average pressure imparts velocity."
MagnumManiac
Well-Known Member
If a cartridge is blown out and the capacity changed, even by 5%, velocity is going to increase.
How do you know that the Sherman's are being run above SAAMI max pressure?
Do you know that around 2013 SAAMI changed their Maximum Pressure testing to be ABSOLUTE, rather than AVERAGE maximum pressure?
I run 222 cases to 58,000psi AVERAGE maximum pressure.
I run my 22-250AI to 60,000psi, my 375 Weatherby is run at 65,000psi, just as the factory loads I have tested were, albeit some were well above 70,000psi in my 270 Weatherby, which I found surprising.
It all depends on the brass, nothing more.
Cheers.
Predator 22
Well-Known Member
"FACT!" Is only fact if you have PROOF! If you do I would genuinely like to see it.
Rhovee
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I do not believe that velocity is the best indication of pressure. Look at any reloading manual and you can see that velocity and pressure change with different powders. Perfect example of peak pressure and average pressure. I ran a 30/28 Nosler with Nosler brass and got 3 reloads before pockets were toast. Was this over 65K? Most likely. Dangerous, i don't think so. Shot thousands and just burned out barrels and brass.
adam32
Well-Known Member
bigngreen
Well-Known Member
Measure the case head on a Sherman case after firing, simplest number out there. I ran my 6.5 SS hard with 140's 3200+ and my first 20 brass went over 20 firings and had barely expaned the head.
I've built in the same week a 7SAUM and 7 SS and used the same brass and shot them in and showing the same pressure signs the SS was 100 fps faster. None of use really have better to go on.
Both dad and I looked for the pressure traces on his Sherman but the computer is long dead and after shooting it enough we learned that it just was saying what the case head was and we never used it any more. If I recall a normal Sherman load at that time was running 62,500 give or take about 2000 psi depending on powder and how fast it hit peak pressure when we could see we we're nearing top.
