It is particularly significant that even though the .500 S&W Magnum cartridge tops out at more than a ton and a quarter of muzzle energy, all the loads operate under 50,000 psi, which, incidentally, is significantly less than the 60,000 psi SAAMI-limit MAP for the smaller caliber .454 Casull.
From Hodgdons 2006 Annual Manual..for the 450 Marlin...pg.#110
COL 2.510"
Nosler 300 grain Partition
H4198 Start..43.0 grains 2116fps..33,900 psi...Max ..53.0 grains 2331fps 42,200 psi
Sure your loading longer...so that would offset the pressure somewhat..but..how much I am very unsure of...So I'm glad you would approach the max loadings cautiously...H4198 will quickly raise pressure expotintially with small incriments...I've found this out with my 45-70 Marlins..and Handi...so please be cautious...
All of the loading data has been lower than 50k for the round I've looked at...even Cor-Bon themselves reduced the pressures on it...and Hornady never did come out with their high pressure offering that I've seen from the introduction...So...extrapolating bolt thrust amongst the various cartridges...while fun to some of us ( We all can dream)...trying to make it a reality is another matter...The Handi frame is not a Ruger or Browning frame...and making some of these cartridges would most likely end at best in frustration..a stretched frame..or worse..an injury..
The 45-70 Hornady 300 gr load I worked up for my NEF BC is rated at 51k CUP by "Load Disk", I won't hazard a guess on the Kpsi and I haven't seen any evidence of pressure problems with the load and that case has a 0.608" case head,
...Since we are talking about big bores...Hodgdon list it's Max Ruger load at 63 grains of H4198 at 2532 fps and 50,000 cup...and this is using the Sierra 300 grain hollowpoint...which has the shortest bearing surface and the thinnest jacket of
any of the 45-70 300 gr. jacketed bullets...This loading isn't for...nor never designed for the Buff Classic...or any Handi rifle....Straight walled cases don't show pressure signs as readily as bottle neck cartridges...this is a well known fact...and while you haven't been visited by Mr. D Murphey while shooting them...I would be real hesitant to say you won't be at 1 time or another...before too much longer...
My 45-70 loads are considered hot by some folks standards...Using the 300 grain Nosler Partition and H4198 they are well in the 40,000 cup range...but these are very mild... compared to what you say you are loading and shooting out of that Buff Classic without
any incident...While your "given loads" and results are most impressive to say the least...they certainly aren't within the specs of the rifle's tolerances...and cannot be considered "safe" to publish...without some type of stearn warnings attatched to them...so please...bear that in mind for future reference
If the Handi's receiver was forged from a single billet of high grade steel...I wouldn't worry so much...but...it isn't...and hence the reason for my concern for the safety of me...and everyone else attempting to duplicate your "feats"...and also in lusting after one of those awsome .375's and wanting to convert one...I forget this sad fact from time to time when I start wondering
"what if"...but....then reality sets in...and I know it won't happen..
You can place your trust in Load from a disc if you so desire...I prefere a much more reliable approach...one most folks here can duplicate for free....I much rather talk with all my friends at the powder companies...bullet companies...and even rifle companies...and get precise,detailed, accurate information straight from them,the ones who do this day in and out for a living......These folks I trust and have great respect for...all else remains questionable data...wither coming from an individual who elects to post it...or..from a computer program dealing in "approximations".I don't have a problem using a computer program to get in the ball park...we do have to have a starting point...and if it is available..then by all means use what you got...BUT...I will not qoute from it as a definative absolute source...
because it is not...It is after all an approximation of what could be...not a definate what it really is...The best rule to follow in this regard is to check all current manufactures published data first....Then go from there...
If I had the time and money and a disposable reciever...I would certainly try for one of the 375's discussed(non-belted ofcourse)...just to see for myself...but....I don't..and truthfully we really shouldn't be recommending that others try it...not without atleast giving them fair warnings of the dangers they can and most likely will encounter if they elect to undertake a simalar project..Speaking with persons familiar with the Handi's strenghts and also it's weakness who have done actual big bore conversions is still the best bet..Most good smiths I know personally won't recommend doing this type of a conversion...and fewer yet will actually do it for you....They know the limatations of the action very well from previous conversions..and are very hesitant to get into a liability issue down the road with their work...
Mac