Why are the operating pressures between the two common shapes of cartridges considered different?

This question relates to Handi Rifles. For example, there is a factory 500SW offering. This is a .532 bodied case that operates at 60K PSI. Why then would a 300RCM with the same .532 body be considered a potential grenade?

Is there a lever effect from the neck working against the chamber? What about modern-ish, minimum body taper cartridges?

Just wondering, thanks all.

I don't own a Handi Rifle - but I believe it has to do with the pressure that it is designed to handle.

The 300 RCM has a PMap of 65000psi as do all RCM, all WSM, and all SAUM cartridges.

I'm sure Handi Rifle expert.

The basic rifle is chambered for the 22-250 and 25-06 both list max pressure in the 65,000 range.

Who is calling the 300Rcm a grenade?

Could it be the shape of the case and the amount of steel left around the chamber? It seems to me the factory 300Rcm and its short magnum cousin are loaded closer to the max then say the 25-06. No real testing on that.

If both cases have the same INSIDE diameter, and operate at the same pressure, the back thrust is the same. Do not try to calculate back thrust from a case OD and certainly not using a rim OD; it don't work that way in pressure vessel pressure calculations.

There is a lot of hog wash and a lot of good information regarding the Handi Rifle and what size case/pressure it can handle.

Most of the problems and BS revolves around people that don't really understand or know how pressure works.

The Handi has one VERY glaring problem in it's lockup mechanism and anyone who wants to muck around with wildcatting the Handi better take a very close look at it.

If it has been adjusted for maximum/equal contact on the locking bolt and the barrel frame gap is in the 0.002" range it will handle all the pressure for the SAAMI spec of the FACTORY cartridges...if not, you will have problems.

I ran into verbal problems on Graybeard's NEF forum when asking/talking about doing Stub barrels using the non-cast frame for doing larger cases like the belted mag and RUM size cases...DIRE consequences was about de rigueur for the course...NO ONE has any actual stress analysis data or done any actual stress test analysis as far as I know.

I have built several stub barrels in different cals from 17 to 50 cal and I have NO problem running pressures in the 50KPSI plus range with cases in the .473, 308-30-06 etc, .513-.532 base size range, belted mag and 500 SW, and 40KPSI plus for those in the .550, RUM and I have a couple of .590, Rigby size wildcats I might do someday.

Back thrust is one of the problems, but then again I have read that back thrust just isn't real and if you do your calculations right, back thrust is a very small amount for the area of the frame face...HIGHLY ARGUMENTATIVE and something I won't discuss...I have no way to actually pressure test so any discussion is moot.

The other side of this story is the discussion of whether a straight walled case has more "grip" on the side walls of the chamber and bottlenecked cases tend to "slip" due to forces from the tapered section. I don't even want to get into all that "stuff"

One last aside...I just built a 50-90 stub barrel for one of my Handi's and have loaded it to over 45KPSI calculated by QL...SLOWLY CREEPING UP...so far there has been no signs of pressure, no frame locking due to "back thrust", and the cases have fallen out with only a small amount of sizing needed at the very base. I've done the same with a 45-70 32" barrel Buffalo Classic, rechambered to 45-120 and when I posted the early relatively low pressure results on Graybeard I got the same old happy horsesh**...which is why I don't usually post MY load or pressure data unless it is also posted/available somewhere else like QL or reloading manuals.

The Handi will usually pop open when the pressures get up in the 45-50KPSI rang due to the week lockup, recoil forces and/or longer barrel flip.

NONE OF THIS IS IN ANY WAY A RECOMMENDATION OR AND INVITATION FOR SOMEONE WITHOUT MY LONG YEARS OF WILDCATTING AND OTHER "EXPERTISE" TO DO SOMETHING STUPID...there are just TOO many variables you have to account for when doing ANY wildcat and using pressure data in a simplistic way can get you into tons of trouble.

If you really want to know something about wildcatting the Handi then goto Graybeard's NEF forum for information and take a course in ballistics/stress analysis, etc.

Good Luck