300-PRC Load Development Results ...

[rustyinbend]

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.

 

[Feniks Technologies]

You have repeatable flat spots with enough rounds to actually have confidence (approx. 30 round strings)?

That would seriously be amazing data to produce.

 

[rustyinbend]

You have repeatable flat spots with enough rounds to actually have confidence (approx. 30 round strings)?

That would seriously be amazing data to produce.

I used 10-string tests at .2gr increments and with MagPro and 300-PRC ... got two ladder tests with 2-round flat spots at or near my OCW noted above. Maybe coincidence ... I can acknowledge that ... but using it for group tests seems to have worked out.

 

[Cascade Hemi]

Sometimes luck is on your side. I'd like to see some more data and probably deeper seating to tighten up the groups.

 

[rustyinbend]

Sometimes luck is on your side. I'd like to see some more data and probably deeper seating to tighten up the groups.

Honestly ... with "perfect ammo" ... those groups are about as tight as I'd ever shoot with my advanced years, crappy eyes, floaters, and early stage Parkinson's. When I can get sub-MOA, I declare victory and go find a beer.