I use Hodgdon's powders for reloading. 308 and 358 Winchester ammunitions are based upon the same case that yields the same case head area for determining back thrust on locking bolt system. Yet Hodgdon's reports 308 safe handloads for nearly all handloads for both cartridges as being about 10,000 CUP higher. This number is a 20 percent difference.

Why?

Check the numbers again. The higher numbers for the .308 are for those loads with pressure measured by PSI. All of the .358 loads have the pressure measured in CUP. At this performance level, PSI values are typically about 10,000 higher than CUP values. For example, look at the loads for the 7mm STW in CUP compared to those for the 28 Nosler in PSI.

Cheers, Al

Yet another of my AHA! moments. Many thanks for your reply.

quote:

Originally posted by ClassicAl:
Check the numbers again. The higher numbers for the .308 are for those loads with pressure measured by PSI. All of the .358 loads have the pressure measured in CUP. At this performance level, PSI values are typically about 10,000 higher than CUP values. For example, look at the loads for the 7mm STW in CUP compared to those for the 28 Nosler in PSI.

Cheers, Al

Al's observation about CUP vs. PSI is an accurate one in this instance.

However, there are numerous cartridges which share the same case but, somewhat ironically, have different pressure maximums assigned by SAAMI (Sporting Arms and Ammunition Manufacturer Institue), the standardizing "authority" in the U.S.

Examples are the .222 & .222 Magnum, which are both assigned lower pressures than the .223, despite there being no physical reason for this related to the case itself. (In this instance, Armalite needed a tad more velocity to meet military specifications the .223 so they just upped the pressure enough to get the velocity they needed.)

Another odd divergence is the .270 Winchester, with its somewhat higher pressure and the .280 Remington, despite the latter being a quarter of a century or so newer. (The apparent reasoning for the lower .280 pressure limit was that it was to be chambered in the Rem 760 pump and 740 auto -- but the same guns were chambered for the .270, so how did that make sense?)

The .257 Roberts and 7mm Mauser, both simply necked down 8x57 cases, have lower pressure standards than the .244 (6mm) Remington which is based on the same case. Apparently SAAMI thinks that there are old and questionable 7x57 military rifles out there which don't need to digest heavy loads, but the .257 Roberts? Makes no sense.

So, generally, loading manuals feel obligated to keep their tested loads within the limits set by SAAMI. An exception is when they list "+P" ("plus pressure") loads specific to stronger rifle actions such as .45-70 loads for the Marlin and Ruger, or +P loads for the Roberts.

The standardizing authority in Europe, CIP, (which I believe has some actual legal standing, unlike SAAMI in the U.S.) often has different pressure standards, some higher and some lower.

The loading books were published by idiots..I't bugs the hell out of me when they print CUP and PSI in a list of loads and mix them all together, makes it a pain...I would also appreciate it if they would all list pressures for every load...Mostly they just copy each other from one degree to another and that sucks...Then you have the peronoid companys that only print mild loads and claim max, then some are just the opposite and must be intent on blowing primers or worse..

If you read the specific load for any caliber in a dozen reloading manuals, I assure you if your a newbie at reloading, you will be completely dumbfounded and righteously so..

You guessed it Im anti reloading manuals although I have a dozen or so that I rummaged thru a lot when working up loads, but in the end I work up my own loads the old fashion way, by shooting the gun and looking for pressure signs..and I have become well accomplished at that over the years, now if I could just remember how I did it last time..No wonder Jack O'Connor shot factory ammo in his senior years. Anybody want to buy all my handloading stuff at a bargain, I would sell and shoot factory the remainder of my time on this earth. Reloading saves money? That's BS in most cases, we reach a point when we have loaded a 1000 or more rounds for every caliber we own, it becomes a addiction, an expensive habit..If we shot factory, we would buy two boxes of ammo a year like dad did his whole life, sometimes just one box..