Home Forums Hunting & Shooting Ask The Gunwriters SAAMI Pressure Specs and Reloading

Just wondering how cartridge pressure specs should be appropriately applied when reloading. This would be especially so with 'wildcats', which obviously do not have 'official' specs. For instance, the 30-06 SAAMI pressure spec is 60,000 psi, whereas the 270 Win in 65,000 psi. Now first, I assume that the components for a particular rifle, say a Ruger 77, won't be any 'weaker' in a cartridge with a lower SAAMI pressure spec. So, for instance, if I were to have a Ruger 77 in 30-06 and rebarrelled it to 270, I wouldn't expect any problem.

What about other components? For example, the SAAMI pressure for 7x57 is 51,000 psi, whereas for .257 Roberts +P it is 58,000 psi. If I were to neck down some 7x57 brass, would there be a possible problem loading them up to full .257 +P levels? Same question for necking down 30-06 brass and loading to 270 Win levels as well. Perhaps a more extreme example might be necking down parent .250 Savage cases and loading to 22-250 levels (45,000 cup vs. 65,000 psi).

Pressure limits are set for both cartridge and gun. Because the .30-06 and 7 Mauser are older than the .270 and .Roberts, it can be presumed that there are older rifles chambered for those rounds. Rifles don't get stronger with age, so SAAMI sets a lower pressure limit for older rounds. The newer the round, the more likely it is to have a higher pressure limit because there are no old rifles originally chambered for it.

From that, you can see that a new rifle can probably handle pressures beyond the official limit - but once you cross that line, you are jogging blindfolded in cliff country.

Lol ('blindfolded off a cliff'), ok thanks for your reply. It sometimes seems as though the pressure specs are 'out the window' when it comes to reloading, on the basis of the 'modern rifle and components' argument. So on the basis of that argument, with my 'modern bolt action' rifle in .250 Savage, I can neck up .22-250 brass and be 'secure' in loading well over the rather modest SAAMI spec of 45,000 cup (no psi spec, but translates to maybe just under 50,000 psi) - since the .22-250 spec is 65,000 psi?

There are two opposing arguments. The first says that your components and (I assume) modern bolt rifle can certainly take the same pressures as the .22-250. The second says that without pressure measuring gear, you are still on that cliffside jogging blindfolded because no tested data for the .250 Savage goes as high as its offspring. In short, how would you know when you are approaching your self-imposed pressure limit?

You could certainly use the three basic rules for reloading to calculate an approximate velocity based on the changes in bore diameter and bullet weight. But you'd never really know what pressures you were seeing.

OK, thanks once again for your reply. So basically 'someone' (typically a company intending to publish a loading manual) would have the facilities to pressure test and then reloaders would rely on the velocities given corresponding to 'max' loads - since a chrono is alot easier to manage than pressure testing. So in practice I assume even the 'max' loads shown in reloading manuals build in a signficant 'margin', given the pressure / velocity variations between individual rifles? Then the 'traditional' pressure warning signs are best considered 'dashboard idiot lights', i.e. you've already walked off the cliff and you're hanging by a branch?

Pretty much so. However, the data you see is in fact right up to the highest charge that stays below the SAAMI pressure limit. The "fudge factor" -if any- is in the SAAMI limit, not in the load data. The next higher load increment would exceed the limit.

Now, though that's true, there is some variation in how an individual lab defines "exceeds the limit" and also in how they set charge increments. Those variations and physical aspects such as component lots, individual test guns and other factors like weather are the main reason for differences in book loads.

Finally, pressure testing is no longer out of the reach of a serious hobbyist. Pressure testing gear is now available at prices comparable to a good chronograph. Not only is it available, but it is at least as accurate as lab gear, according to Dr. Ken Oehler and others who have done tests on it.

The max loads in reloading books do take into consideration the variation in pressure spikes that occur from round to round, but the published figures from manufacturers that provide pressure data are just what they are...they are observed findings under laboratory conditions.

The lab conditions and test gear are set by high industry standards. Factory rifles have looser tolerances, but because of the overall testing procedures, the published loads are considered to be safe maximums in all rifles, providing one observes the proper safety precaution to start with the "start" loads and carefully work up...just in case.

From a practical perspective, in a modern bolt action rifle, the same maximum pressure limit would apply to all calibers based on the same parent case...that's somewhere around 62k psi in the 30-06 family.

There is no necessity to load down to turn of the century pressure levels in a modern rifle using modern components, but there is nothing to be gained from exceeding the max limits for the parent case either.

I much prefer the real world benefits of easy extraction, tight primer pockets and longer case life, regardless of caliber, and I have never seen any benefit from a bullet that may strike a target 50fps faster.

TC

If a SAAMI maximum pressure spec for a given cartridge is established at (say) 60,000 psi, and the pressure variability of a given load is great (high standard deviation or SD), the ammo companies will load that cartridge to a lower level to ensure that none exceed the 60,000 level.

If the SD is low and the pressure excursions not great, they will load to a higher pressure, but be certain the pressure of any individual cartridge does not exceed the 60,000 level.

The ammo companies also load with the expected climate in mind. The expected climate in Africa or Arizona calls for higher ambient temperatures and will give higher pressures for a given load as compared for the same cartridge fired in winter-time Alaska. The companies do not control where the cartridge will be fired, and therefore err on the side of caution.

Strain gage pressure measurements may be sensitive, but without
a method to calibrate the gage installation they are not as accurate. What is normally done is to compare readings with a
factory load (at what ever pressure it gives). The classic signs heavy bolt lift, loose primers, case head expansion ect. tell you that the brass has begun to yeild.
Good luck!

Thanks once again all for your replies. Having read up on the SAAMI pressure specs, it is my understanding that some variation is in fact incorporated into the specs themselves. What is commonly referred to as the 'maximum pressure' for a cartridge is in fact the maximum average pressure. The measure of variation is included as part of the spec.

Interesting comment regarding the 'parent case' limitation. Several of the .30-06 case based cartridges have signficantly higher max (average ) limits than .30-06 itself. In fact part of the reason I referred to .250 Savage and .22-250 specifically earlier is that that is one of the instances with a large difference between the specs (45,000 cup or approx. 50,000 psi for .250 vs. 65,000 psi for .22-250).

Thanks for the heads up regarding the pressure testing equipment, I hadn't realized that things had changed to the point where pressure testing equipment was so affordable.

I think the pressure differences for the 250 sav and the 22-250 have more to do with the rifles they were chambered at the time.
IE,the Savage model 99 and the rear bolt lock-up.

You're welcome.

They also take gun types into consideration. A couple of notable examples would be the .280 Rem and .250 Savage. The 280 was and is chambered in pump action rifles and the 250 in the classic Savage 99 - neither of them known for brute strength. So SAAMI holds pressure down. Some rounds like the .45-70 have such a wide range of rifle actions that loading companies develop up to three pressure levels of load data. Any of those rounds fired in a recently-made bolt rifle could safely be leaned on quite a bit - but how much is up to the individual.

We're all big boys now, and hopefully can make rational judgments. Unfortunately, many of us are still living through what I call the "magnosterone years" where more is always better. That is most decidedly not true, but the poor boogers in that age bracket can't be convinced of it. If they make it to gray hair, they'll learn.

And then Remington, Savage and Browning turn around and chamber those "weak" pumps and autoloaders in 243 @60,000 psi pressure, 308 @ 62,000, and 270 and 6mm Remington at 65,000! The current SAAMI pressure spec for 280 is 60,000, same as 243 and 30-06. (Here is where I found this data: http://www.leverguns.com/articles/saami_pressures.htm) Is somebody holding pressure down??

I can't explain that, either! Thanks for finding the current spec for the .280 Rem. I confess that I had not looked it up and it may well have changed - or what I'd been told about it was never true in the first place.

We might make the same observation about the Savage 99, which is now chambered in .308 Win. If it can take that (which it presumably does) then why was the 250 held down? If it isn't due to better metals technology for newer rifles, it beats me, brother.

Metallurgy changed during and after WWII, so the post-war Savages and similar rifles are stronger. My old smith did a lot of work on all varietites and ages of rifles, and noted a difference in pre-1930s and post-war guns. Also, I believe I read that the 99 was lengthened a skosh to accomodate the .308 family with its longer OAL.

The Remington 740 auto and 760 pump were post-war developments, and stuff they learned about military arms and ammo during war production may have influenced the new ways of doing things.

The 740 became the 742, the 7400, Model 4, and 750, and some design and materials improvements occurred along the way. I do understand that some gas system improvements were made from model to model.

From my experience handloading for my 740 in 30-06, I also wouldn't be surprised to find that it may not reload reliably with a slightly higher pressure cartridge like 270. For instance, it'll run all day long on 52 gr. of IMR 4064 with any 150 gr. bullet you care to load, but not with the slower IMR 4350, and any 4831 turns it into a single shot.