Will powder charge change, changing brass?
- Thread starter DngBat7
- Start date
I normally shoot .308 Palma brass necked down to 6.5 for my .260A.I.s. However, I wanted to try Peterson S/R primer brass so I would not have to go thru the entire gamut of case forming from Palma to .260. I found out that Peterson brass, at least in the .260 cases, has right at 2 grains LESS case capacity! I does not ill effect the velocity, however, if you did not know that, you could send pressures into the stratosphere!
Ledd Slinger
Silver $$ Contributor
Depends on how forgiving your accuracy node is, but often times yes you will have to tweak your load.
Dusty Stevens
Shiner
Your powder charge has already changed since you shot last so yes its going to be different.
This is somewhat relevant. A while back I loaded a lot of rounds for load development with mixed brass on accident and didn't catch it until later. Well I had 4 each per charge weight per batch. I made sure to take note when shooting. Example would be 3 Winchester brass shot back to back and the last one Hornady and I'd just annotate it. The brass was somewhat weight sorted at that time. What I saw on more then a few occasions (shot the last from that reload session last night) was that I'd put 3 Winchesters side by side all touching and then the Hornady would be down a tad or visa versa. I honestly wouldn't expect to see accuracy or poi implications from brass with same internal capacity at 100 yards but I did. It could be a fluke or something, maybe my shooting, but it happened enough to make me wonder.
I won't mention the time I ran out of ccibr2 primers and had some fed210 in the batch...
I won't mention the time I ran out of ccibr2 primers and had some fed210 in the batch...
MikeMcCasland
Team Texas F-T/R
As others have posted, yes you will probably need to back your load down and work back up. The internal capacities of brass from different manufactures will vary, even for the same round. For example, recently I was running 45gr of H4350 in Lapua brass and achieving ~2800FPS. When switching over to necked down Lake City it only took 43.7gr of H4350 to achieve the same velocity.
Switching from Hornady to Peterson probably won't require as much deviation in your powder charge, but it's strongly advised that you back your load off and work back up.
Switching from Hornady to Peterson probably won't require as much deviation in your powder charge, but it's strongly advised that you back your load off and work back up.
Ned Ludd
Silver $$ Contributor
Different brands of brass have different neck, casewall, and webbing thicknesses. Because the outer case dimensions are necessarily fixed for a given cartridge/chambering, that means the usable internal case volume varies with different brands of brass, in some instances by a significant amount. If the internal volume varies with different brass, then the pressures generated will also vary for a given charge weight. If the pressure changes, so will the velocity of a given bullet, and so on, and so forth.
It all boils down to how much the effective internal case volume changes between brands. If the difference is very small, you may not see a marked change in the load (i.e. velocity). However, depending on the brand of brass you switch to, it is more likely that the internal volumes are different enough that you will observe a change in pressure/velocity. As long as it's in the same chamber/barrel, you can probably get very close to where the original load was in the old brass by reproducing that same velocity with the new brass. It the new brass has greater effective case volume than the old, it will require a greater charge weight; if it is less, you'll need to back off on the original charge. As has been noted, it's always better to assume higher pressure and back off a bit in the initial load workup in the new brass.
It all boils down to how much the effective internal case volume changes between brands. If the difference is very small, you may not see a marked change in the load (i.e. velocity). However, depending on the brand of brass you switch to, it is more likely that the internal volumes are different enough that you will observe a change in pressure/velocity. As long as it's in the same chamber/barrel, you can probably get very close to where the original load was in the old brass by reproducing that same velocity with the new brass. It the new brass has greater effective case volume than the old, it will require a greater charge weight; if it is less, you'll need to back off on the original charge. As has been noted, it's always better to assume higher pressure and back off a bit in the initial load workup in the new brass.
Measure the capacity and see how close they are, then you'll know.
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