Well, after several fits and starts, challenges with supplies, and about six months of effort ... I feel like I've got a solid result that maps to my current stock of reloading supplies. Given component shortages, I've been working two batches in parallel to try and get optimum reference loads for both setups. The rifle is a Barrett MRAD (MK22) with the 300-PRC barrel conversion kit. My range trip this week was to shoot 5 rounds for a group at 100 yards for each set of components ... that my past data said should be pretty friggin' close to perfect.
Darn happy with the results and figured I'd share the data and the load details.
Setup #1 ... Lapua 1x brass - Accurate MagPro 77.8gr - Berger 220 LRHT - Neck Mandrel .3055 - Seat Depth .80 (Mag-limited)
Result: Avg 2859 ft/sec - SD 2.6 - ES 6 - Group .75 MOA
YES ... a Standard Deviation of 2.6 ... I audibly gasped when I saw that on the LabRadar summary screen. It's the lowest I've ever seen ... by a bunch.
Setup #2 ... Lapua 1x Brass - Hodgdon Retumbo 77.4gr - Hornady 225 ELDM - Neck Mandrel .3055 - Seat Depth .80 (Mag-limited)
Result: Avg 2907 ft/sec - SD 5.3 - ES 14 - Group .60 MOA
No pressure signs either felt or visible in either setup.
I've got a ton of Accurate MagPro and less Retumbo, so I'll start the competition season with that Setup #1 recipe, and see how I do.
I've also got a bunch of Hornady 225's and fewer Berger 220's ... so my next test is a try with the MagPro powder behind the Hornady 225's ... and see if I can get that to provide similarly low SD's.
BTW ... I zero'd in on both these charge weights using flat spots in ladder tests ... I know many don't believe in that, but it worked for me, and was actually reproducible.
I'm happy to answer any questions about how I got here, and the equipment I used along the way. I see a lot of 300-PRC load development questions, hence the share here hoping somebody can benefit from all the supplies I wasted to finally get a good result.
Darn happy with the results and figured I'd share the data and the load details.
Setup #1 ... Lapua 1x brass - Accurate MagPro 77.8gr - Berger 220 LRHT - Neck Mandrel .3055 - Seat Depth .80 (Mag-limited)
Result: Avg 2859 ft/sec - SD 2.6 - ES 6 - Group .75 MOA
YES ... a Standard Deviation of 2.6 ... I audibly gasped when I saw that on the LabRadar summary screen. It's the lowest I've ever seen ... by a bunch.
Setup #2 ... Lapua 1x Brass - Hodgdon Retumbo 77.4gr - Hornady 225 ELDM - Neck Mandrel .3055 - Seat Depth .80 (Mag-limited)
Result: Avg 2907 ft/sec - SD 5.3 - ES 14 - Group .60 MOA
No pressure signs either felt or visible in either setup.
I've got a ton of Accurate MagPro and less Retumbo, so I'll start the competition season with that Setup #1 recipe, and see how I do.
I've also got a bunch of Hornady 225's and fewer Berger 220's ... so my next test is a try with the MagPro powder behind the Hornady 225's ... and see if I can get that to provide similarly low SD's.
BTW ... I zero'd in on both these charge weights using flat spots in ladder tests ... I know many don't believe in that, but it worked for me, and was actually reproducible.
I'm happy to answer any questions about how I got here, and the equipment I used along the way. I see a lot of 300-PRC load development questions, hence the share here hoping somebody can benefit from all the supplies I wasted to finally get a good result.