Curious about rechamber

[BCall]

I know some of you guys are alot more knowledgeable about the math than I am, so I was hoping if someone could help me out with a rechambering question. It seemd that the WSM calibers and most new magnum cartridges are unsafe as rechamber options, because of the increased head diameter coupled with higher pressures are too much for the tip-up action of the Handi-rifle. But how about an older magnum cartridge such as the 300 H&H? My manual lists the 30-06 and 35 whelen calibers as having a maximum working pressure of anywhere between 57-60,000 psi. The 300 H&H is listed with a maximum of 54,000 psi with many max loads around the 52,000 mark. Would these possibly be considered safe, or does the .05 larger case head require still lower pressures? Just curious really, as I don't really know how to calculate it myself. Thanks, Billy

[LaOtto222]

I think you would be pushing the edge of the frame's pressure range. Head diameter for a 300 WSM is .535" for the H&H Magnum it is .532" there is only .003" difference. Sure the old H&H does not have as much pressure as a 300 WSM, but the 30-06 will come with in 100 fps of the H&H with the same weight bullets. There really is not much of an advantage for the 300 H&H Magnum over the 30-06, so little I can not see any real advantage. Cases would be more expensive and harder to get. Loaded ammo - much harder to get and more expensive when you do. If you load down the H&H to make sure pressure limits are safe in a Handi; it's small advantage over a 30-06 would be wiped out. There is a theory that a slopping shoulder and body (like an old H&H) causes more pressure on the breech than a straighter body and sharper shoulder. IMHO - there is no reason to have a .308 caliber bored out to a 300 H&H when you can get a 30-06 as a standard chamber. Good Luck and Good Shooting

[BCall]

I guess I kinda phrased my question wrong, it was late, sorry. I was really more curious about at what level is the larger case head safe? Would it have to be loaded to 450 marlin levels at 42,000, or even lower because of the tapered case? In all reality, I was not considering rechambering for 300 H&H, I realize gains would be minimal, I was more curious about what the math said the pressure levels would be safe, the 300 H&H was just the first case I saw that was operating at lower pressures than a standard caliber when I was up late last night. Like I said, just curious really, sometime being alone late at night here makes me curious about odd things. Thanks, Billy

And as an aside, it had me thinking about the 500 S&W, which can supposedly be loaded to 60,000, but as I understand it the rimmed case has less internal area to produce thrust, and it is straight walled as well, so I do not know how much that affects it, but do most guys keep it loaded to lower levels to avoid any trouble that some seem to have had? Thanks

[quickdtoo]

300H&H pressure isn't 54kpsi, it's 54kcup which is close to 64kpsi, take a look at the 300 WinMag on the conversion chart below.

Tim

http://kwk.us/pressures.html

http://www.leverguns.com/articles/saami_pressures.htm

[BCall]

Thanks Tim, the link didn't work for me, but you made me realize something about the manual I have on hand. The only one I have here is a Lee manual, and I saw PSI listings for pressure, but not paying close enough attention, I assumed the H&H was also PSI. I guess I shouldn't read when I'm tired because they list the H&H in CUP. After a quick scan, the Lee manual lists pressures in PSI, CUP, and some even list CIP. Wish they just would have used one pressure rating, listing several different ones can confuse someone like me. Thanks, Billy

The pressure list showed fine, that I appreciate greatly, been looking for that for awhile. Thanks

[quickdtoo]

I've tried a 300WSM barrel on a late model SB2 frame, I had hoped to achieve 30-06AI velocities with reduced loads using specific powders that would keep the pressure down, but that never happened, I couldn't even equal 150gr 30-06 velocities without action flex, so the $17.50 barrel(got it for the cost of shipping) became a donor stub for my 6.5x55, the .555 case head is just too much for it.

Tim

[LaOtto222]

I hate to beat this to death, but you mentioning the 500 S&W got me to thinking too. IMHO the 500 S&W is pushing the outer limits of the Handi frame components and barrel lug. While I do not have one, I seems to me that I have read here that there are several people that have had issues with theirs. Issues like shooting loose or just plain breaking a lot. I am sure that if I have some wrong thinking on this; I will be corrected.

[coyotejoe]

The Lee manual contains no original data. By that I mean they didn't load and test fire anything, it is all just gleaned from other published sources. That is my least used manual because one really can't tell anything about how the data was compiled, in some cases you can't even tell if the round was fired from a rifle or a handgun, much less what sort of rifle or handgun, what barrel length, how pressure was measured, etc.

[quickdtoo]

LaOtto,

While there have been some 500S&W barrels that shot loose and a couple members that had problems with theirs, there have been a whole lot more that have had no problems with them, myself included. If you look at data for the 500S&W, maximum operating pressures are about 52kpsi, the 500S&W has a .526" case head, and as Billy mentioned, is a straight walled case, the saving grace IMO as compared to bottlenecked cartridges which create more bolt trust effect due to the shoulder, even with max loads, I've never had problems with action flex with Ruger loads in the 45-70 or max loads in the 500S&W. 

FYI, the 300H&H has a .513" case head, not .532",  rim diameter isn't a factor for calculating bolt thrust(breech thrust in our case), bolt thrust is a product of internal case head diameter and pressure.

Tim

http://stevespages.com/page8d.htm

http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm

Bolt Thrust

Bolt thrust is easy to calculate. Only two inputs are required. They are peak chamber pressure in PSI and as mentioned, the inside area of the case head that the gas pressure can work on. The formula then is:

THRUST=AREA*CPSI Where:

AREA=3.1416*(HS/2)^2

HS=the diameter of the inside of the case head.