Checking SD with Brand New Brass, or Once Fired???

[RaptorAddict]

Building a new PRS rifle and for load development, I am curious if I should start checking my SD's with brand new brass, or wait till it's once fired. Wasn't sure if it made a difference. In case wondered, the rifle is a Kelbly's Prometheus 700 clone action, Kreiger heavy varmint stainless barrel in 6XC. Using Peterson SRP brass with 115gr DTAC bullets with H4350 powder.

 

[NHPiper]

I have been doing a lot of load dev on virgin brass, ADG, Starline, etc. I check the SD on those expecting it will get better after I have some brass sized toy chamber. It shouldn't be hard to do load dev with a quality barrel and brass and get single digit SDs with virgin brass or no higher than 10-11.

 

[spife7980]

Develop for the manner in which it will be shot.
If you have enough virgin to shoot a match like that then develop it.
If you won’t then develop it in once fired.
I either case I would pay more attention to what it actually shoots like on target rather than what excel tells you it’s doing.

 

[diggler1833]

I've had some ridiculously low SDs across pretty wide powder ranges in different cartridges on quality virgin brass. When the brass went to once fired I saw almost no change.

I may have had to tweak the load 1% (and seen a ~1% velocity change) when going to once fired and subsequently fired brass. IMO you'll see more velocity change from when a new barrel speeds up than you will going from virgin to once fired brass.

In the case of your 6XC, I'm not sure how many new cases you bought, but assuming 2 - 300, you should have more than enough to figure out a load and run a match - so I'd mess with "checking" SDs for sure...just make sure you do it again once you've fired everything and reloaded it.

 

[RaptorAddict]

I've had some ridiculously low SDs across pretty wide powder ranges in different cartridges on quality virgin brass. When the brass went to once fired I saw almost no change.

I may have had to tweak the load 1% (and seen a ~1% velocity change) when going to once fired and subsequently fired brass. IMO you'll see more velocity change from when a new barrel speeds up than you will going from virgin to once fired brass.

In the case of your 6XC, I'm not sure how many new cases you bought, but assuming 2 - 300, you should have more than enough to figure out a load and run a match - so I'd mess with "checking" SDs for sure...just make sure you do it again once you've fired everything and reloaded it.

This is what I’ve been toying with in my head and was planning just that. Was hoping to hear this.

 

[diggler1833]

This is what I’ve been toying with in my head and was planning just that. Was hoping to hear this.

This was me just checking small seating depth and charge weight changes from an initial load that showed promise. This was all done on virgin brass.

 

[918v]

If you take your new unfired case and expand it with a bullet diameter mandrel and then size it back down to get your desired neck tension you’ll harden it a little and that will improve SD like in a 1x case.