Old recipe, different brass. Best way.

P

Pond James Pond

New member
All my existing loads that I have developed have used Norma cases as these were what I had.

I've not found any source of Norma brass save buying fresh Norma cartridges which is not cheap. The Norma brass I have is starting to show signs of fatigue and has gone through one annealing already.

So I'd like to use different brass of which I have access to a decent supply.

None of the loads I have worked up are in the hotter range. It seems with my rifle or I (probably the latter) prefer loads that are a little lower down the velocity range so I think that pressure spikes are less of a risk.

However, I'd still like to pick TFL brains: what would be the best way to check or match my existing optimal charge weight to this new brass in a safe but efficient way?

By efficient, I mean the least consumption of bullets, powder and primers.
 
All of my loads will perform about the same regardless of case, or primers. I test them as individuals and typically I can find a charge weight that works well with all other variables of primers, and brass. It keeps me from having to fiddle with things so much if I have to substitute something.
 
A rule-of-thumb but not an absolute. Assuming your existing Norma brass is the control, a heavier case means slightly higher pressure & a lighter case slightly lower. You could compensate with a charge weight change accordingly. In this case a chronograph would really help duplicate your original load in the new case.

FWIW....
 
Over the years I've reduced loads when changing brass, but I always wind up at the same load anyway. So, now I just don't worry about it, and change brass when needed and leave the load the same. No problems so far in 223, 220, 260, 270, and 308.

If, however, my load was on the upper edge of maximum, I'd reduce loads and work up with new brass.
 
Different commercial brass doesn't make enough difference to matter. Just load whatever brand you can get and you'll be fine.
Not much consolation, but Norma everything is higher priced than other brands everywhere.
"...has gone through one annealing already..." The only part that another annealing won't fix is if the primer pockets are getting too big. That you can measure with a Vernier calipre. The link will help with that. Otherwise, anneal 'em again, IF you're getting cracked case mouths.
https://ballistictools.com/articles/primer-pocket-depth-and-diameter.php
 
Well, judging from the responses it does seem like I could do a straight swap.

Here are the bullet weights along with my optimal charge weight as well as the min and max charge weights used in the ladders for each. All are .308

AMAX 155gn (N135)
Chosen load 40.6gn. Min-Max=40.1-41.9gn

Lockbase 170gn (N140)
Chosen load 44gn. Min-Max=43.7-45.5gn

Norma Oryx 165gn (N140)
Chosen load 44.5gn (0.8MOA, 4-shot group! :D). Min-Max=44.5-46.3gn

So in the case of all three, the chosen loads are quite low down in terms of charge weight and so I'd have said that the risk of a change of case causing bigger pressure than the max loads listed above is pretty slim.
 
Not that familiar with weight of Norma brass, but if on the heavier side, Remingtons are also heavier and could be a good substitute. Federals are also heavier but have the reputation of being softer which can result in premature loosening of primer pockets. Try Remingtons if you have those available.
 
The rule of thumb is to divide the difference in water capacity by -1.87 to get the difference in charge weight change that will match pressure fairly exactly. Wm. C. Davis, Jr. worked it out long ago.

Whether or not that will be enough to affect your load performance depends on how charge-weight immune the load was in the first place. It's common to notice no difference, though in both 308 Win and 300 Win Mag, there can be substantial differences in case weights between brands. Much more than most other cartridges. Some South African 308 brass has proven to be 194 grains, which is what most 30-06 cases weigh, while, at the other extreme, the 92 Palma Match brass made by Winchester weighed around 150 grains. That's enough difference that if the exterior dimensions were identical and the case alloys were identical, you'd expect to need 2.7 or 2.8 grains less powder in the South African cases to reach the same peak pressure. You would not, however, expect as much velocity as the smaller case capacity raises the expansion ratio causing muzzle pressure to be lower, so late in bore travel the bullet would experience less acceleration. The formula is only about achieving matching peak pressure, not velocity, which would take a higher peak pressure to do in the South African case.
 
Going from Win 308 case to SA 80 or 81 case, am using .5 grain less 748 for same velocity (different primers also). Same as going from Win 308 to Fed or older military cases (same primer). About .2 or .3 grains less from Win to Rem. Never used any Norma.
 
Given that all my loads are close to the lower end of the ladder (the very end in some cases) I think I will load 5 shots of the starting load, 5 of the original and then 5 just over (0.3-0.5gn).

15 bullets per recipe to find the equivalent accuracy is not too bad.
 
Just keep in mind that matching velocities matches average pressures down the total lengths of the bore, not including any friction discrepancies. It does not match the peak pressures. A combination of higher peak and lower muzzle pressure can produce that same velocity, and this is what you get when you use the same powder to match velocity in a smaller capacity case.
 
OK, but given where my loads are in the ranges I've so far safely worked with, wouldn't you agree that the chances of excessive peak pressure is unlikely?
 
About the only thing I could say with certainty is the make of 308 brass can and does matter in upper end loads, and the only way most of us have in estimating smaller pressure increases is measuring velocity with a chronograph.

Have seen much larger differences between Fed and Wby 270 wby brass, and it was very significant.

Am not willing to test rifle loads without a chrono, and comparing velocitys/charge weight to manuals.
 
Never used Norma brass. Was going through the same situation, started with Remington brass 308 cal. A shooting buddy that doesn't reload gave me his FC Federal 308 cases. I also fire listed medium range loads IMR 4064 41.5 gr. under a Sierra 168gr.HBT bullet. Found the federal brass much thicker then Remington cases. Lowered to 40.5 grouped just as tight no pressure problems, moved up to 41.5 just as good 1/2" groups at 200 yards. as long as the weather is 65+ colder weather 40.5 shoots 1" lower. I like the Federal cases better, change in some cases is a good thing. No pun intended.
 
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