Hello fellow members,

I was wondering why the 375H&H has a maximum safe operating pressure of 62000 PSI while the 375 REM Ultra Mag has a safe operating pressure of 65000 PSI...? Brass in either cartridge should have the same tensile strength. I imagine it has nothing to do with the action used... So what is the difference then? Why can one be loaded hotter? Even the 375 Weatherby operates at higher pressures...

Feel free to help me figure that one out.

Regards,

Maurice

There are many cartridges that can be used at much greater pressures than their SAAMI spec.

7mm Mauser for one.....the SAAMI spec is derived for the weakest gun known to be chambered for it at the time the spec was initiated and it's almost never changed after it is instituted.

Modern day cartridges typically are spec'd for higher pressure as the guns they are introduced in are extremely strong.

You are correct when you say the brass is the weak link....."the fuse" but this isn't true for such rounds chambered for the winchester M-94, the Savage 99, and a host of early guns and in the eyes of SAAMI the pre '98 Mausers.

If you have a M-70 or 700 Rem. (or other modern alloy steel bolt rifle) in .375 H&H you can load it to 75,000 if you want.....the actions will hold them!

I truly don't advise this however but it's done mostly by folks that have no pressure measuring equipment.

Thanks vapodog for your reply. Trust me, I have not plans in loading up to 75000PSI I will stick to my manuals

If you talk to some of the folks that have used the .375 H&H On dangerous game, they will tell you that they think it will penetrate somewhat better at a bit less velocity.

I'd far rather listen to them than Remington or Weatherby that is trying to sell me quite a bit more.

Just something to take into consideration when loading for the old H&H!

Different cases have different thickness of the brass at the web. This is often the limiting factor of chamber pressure. Back in the day when pressures were limited to black powder maximums it didn't matter and there were a lot of "balloon-head" cases with uniform thickness from mouth to rim. Today, case web thickness has the most to do with safe working pressure as almost all modern firearms designed for today's smokeless powders are engineered with safety factors far in excess of sane max pressures. Older designs and their ctgs have stayed conservative because of the older guns still in service, like the Model 94 Winchester and many military guns. Hence, rounds like the 30-30, 9.3 x 57, 22 Hornet and others are so thin that modern pressures are outof the question, even if the firearm can take them.

Tiggertate,

If web thickness is the limiting factor, you can only load a 375H&H to 62000 PSI, but fireform it in a 375 Wby chamber and now you can load as hot as 650000 PSI...

enigma,
For all intents and purposes 62 K PSI is the same as 65 K PSI.....the extra 3 K PSI can be achieved by a single grain of powder.

Consider them equivalent and get on with reloading. Pressures just might vary more than that with a given load.

the new ultra super mags are much less tapered, thus not wedging back as much upon firing, thus less bolt thrust. also factor in base diameter, that affects bolt thrust too.

there are many variables.

Also remember this round has been available for many years, the rate the round for the oldest guns chambered not the modern ones. There are pro bably some doubles and rifles where the steel is less stron than todays. So, loads will have to be safe for all.

quote:

Originally posted by vapodog:
enigma,
For all intents and purposes 62 K PSI is the same as 65 K PSI.....the extra 3 K PSI can be achieved by a single grain of powder.

Consider them equivalent and get on with reloading. Pressures just might vary more than that with a given load.

thanks...

IMHO, SALES! Remington wants the uninformed to think, "GHEE! I can load my new, hot rifle 'alot' hotter than some old duffer with a mere .375 H&H, ... -- a whole 3,000 psi!!!" As said, the difference can be one grain of powder, more or less, and the brass is being worked to its limit... Case life will not be good in either gun at these pressures... Then the engineer might have some explaination (I read them but don't pretend to comprehend) about the exact shape of this case means... Dan Pawlauck came up with the 30 degree shoulder for the PPC not too long before he blew himself up making Pyrodex... PPC has stood the test of time and with Hodgdon's help, Pyrodex survives... But I begin with Barnums" "one born every minute..." and recall my friends who say "Shoots good, goes bang..." luck.

why?
because 62382 psi is the same as 55,000 CUP.. and there is little practical difference between 65,000 and that is an easy enough to remember number.

no kidding, who wants to remember all the "wee" insignificant digits past the 62, and 65 is easier still.

and, yeah, 1 or 1.5 grains will drive you 3% higher, in some cases and cases

jeffe