I just worked up a new load for a 338LM after my Reloader 33 dried up. The problem is that the cases are now for shit and the other headstamp I have on hand is 31 grains lighter. PPU vs. Hornady. I'm not typically super anal about case weight but 31 grains seems like a big enough difference to change things up. Does anyone have practical experience with this kind of thing? What was the outcome? I will be ordering more cases, but I still want to be able to shoot what I got too. Thanks in advance
Effects of case volume
- Thread starter jambau
- Start date
Lighter case means more space inside, once its fire formed at least. Usually lower pressure than a heavier, so thicker case with the same powder charge. Either way, start with a lower powder charge and work up, monitoring pressure. The best way is by tracking velocity. Changing powder and brass means you need to restart the whole process of building a safe accurate load for that rifle.
31 grs difference is a very very large difference, even for a 338LM. It's not unusual to have some difference from one headstamp to another or even from one lot to another of the same headstamp. I've not got any experience with any 338's, but it's like with my .308 when comparing PPU brass I have weighing 175 grs to Winchester brass weighing 157 grs. That difference in weight translates into a substantial difference in case volume (volumes for fired cases) requiring very different loads. With different loads required, one had to do a new load development. . .especially when a new/different powder is involved.
Here is data from Peterson Cartridge Co. for some .338 cases they produce and you can see how case weights and volumes can be different:
What about water volume of the brass, what is the difference there?
The water volume will tell you what, indirectly, you are seeing in brass weight differences and resultant estimates on wall thickness etc.
You could then use Gordon's Reloading Tool -- take your known good load, piece by piece, and enter its data in GRT. Include the water volume of the brass used in that known good load.
Now take the new brass volume in water, and change that variable in GRT. It will tell you what you want to know about powder charge suitability.
The water volume will tell you what, indirectly, you are seeing in brass weight differences and resultant estimates on wall thickness etc.
You could then use Gordon's Reloading Tool -- take your known good load, piece by piece, and enter its data in GRT. Include the water volume of the brass used in that known good load.
Now take the new brass volume in water, and change that variable in GRT. It will tell you what you want to know about powder charge suitability.
