I bought new brass for my .270 wsm and sized and trimmed to book specs. I loaded and fired about 20, sized and trimmed again and loaded the cases the same. I fired 10 rounds of new brass and 10 rounds of the once fired through a crono and I noticed the once fired were about 100 fps faster. Just wondering if you guys have had the same experience or did I screw up on the second loading? Thanks.
Once Fired Cases
- Thread starter hunt24/7
- Start date
- Nov 4, 2004
- 25,188
- 8,468
The fire formed cases will have a higher velocity because new brass uses some of the energy to fire form the case to your chamber.
Neck sizing or partial full sizing will reduce this and also extend the case life.
JD338
Neck sizing or partial full sizing will reduce this and also extend the case life.
JD338
JD is correct and I've seen things like this happen in other cartridges.
It's a bit funny cause we are always trained and told that cases with more capacity will have LESS PRESSURE and the opposite quite often happens after fireforming with the first firing. If I'm working with new brass and stumble onto a good load right away I usually reduce it by 1/2 grain on the next firing hoping to duplicate what happened on that virgin case.
(Although I do have to admit 100 fps is perhaps more change than I would guess in the wsm).
It's a bit funny cause we are always trained and told that cases with more capacity will have LESS PRESSURE and the opposite quite often happens after fireforming with the first firing. If I'm working with new brass and stumble onto a good load right away I usually reduce it by 1/2 grain on the next firing hoping to duplicate what happened on that virgin case.
(Although I do have to admit 100 fps is perhaps more change than I would guess in the wsm).
DrMike
Ballistician
- Nov 8, 2006
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- 5,997
JD and Kraky,
Do you have some data to share on this? I've not observed this. A priori reasoning would lead me to believe that the differential in pressure due to energy transfer to the outward expansion of the case would be negligible. Thus, there would be an essentially unmeasurable velocity differential between loads developed with virgin brass and with fire-formed brass. The possibility is sufficiently interesting that I will be looking at some experiments this winter.
Do you have some data to share on this? I've not observed this. A priori reasoning would lead me to believe that the differential in pressure due to energy transfer to the outward expansion of the case would be negligible. Thus, there would be an essentially unmeasurable velocity differential between loads developed with virgin brass and with fire-formed brass. The possibility is sufficiently interesting that I will be looking at some experiments this winter.
rick smith
Handloader
- Apr 6, 2005
- 1,249
- 0
I have chronographed a lot of rifles with new then once fired brass and have never seen that. If the pressure needed to expand a new piece dropped the velocity then the now larger case capacity would decrease the velocity by basically the same amount. Can't see how a larger case capacity with the same load would increase velocity.Rick.
