300 PRC resized to 375 Ruger

[HenryBowman]

Since 375 Ruger brass is tough to find, here is what has worked for me when converting 300PRC to 375 Ruger. Your results may vary.

Fire formed-
I started with the cheapest 300PRC loaded ammo I could find. Then I pulled the bullets and powder, poured in about 2cc of red dot powder and filled the air gap up to the shoulder with grits and packed it down with TP. Fire forming was performed in the same rifle I was loading for.

Manual Resizing-
Tumbled and annealed once fired 300PRC Hornady brass, sized up to 340Wby (340 arbor in a 375R resizing die) go slow and use case lube in the neck. Once upsized, put the 375R arbor back in the die and repeat with the same case.


Notes-
1. After resizing, I've had a few that cases that resulted in short necks, I loaded and fired them with no issue.
2. A few cases have had necks that lengthened on one side only after firing. I resized, trimmed to length and reloaded these with no issues.
3. So far, I have not seen a noticeable difference in accuracy between resized 300P and normal 375R cases. I've only shot my rifle out to 125y, no idea what it will do beyond that.
4. I'm about 1 in 8 cases for damaging them with manual resizing, most of these were when I started the process.
5. I use RCBS die/arbor and RC press for the upsizing of the 300PRC brass, but I use Lee dies in a Lee turret press for loading. It's just how I have my system setup.

 

[LeonardC]

Thank you!

 

[Daveintheburbs]

Just mined this up. Thanks for posting. I have been wondering how that process would work. Got a good supply of 375 but dont like not having s supply available.
I have never fire formed a case. I was unaware you could stretch the neck that far with a TP projectile. Could you give some more comments on the process?

 

[HenryBowman]

Just mined this up. Thanks for posting. I have been wondering how that process would work. Got a good supply of 375 but dont like not having s supply available.
I have never fire formed a case. I was unaware you could stretch the neck that far with a TP projectile. Could you give some more comments on the process?

Basically the TP provides enough resistance to blow the neck out. Just make sure the TP is packed down in the case fairly tight, or you will not get a uniform or full blown out neck. I've fired the 300PRC rounds in my 375 with no issue, just like firing 06 ammo in a 35 Whelen. YMMV

 

[Daveintheburbs]

Havent tried that either, but compared to reforming the necks by die, fire forming sounds interesting.

 

[HenryBowman]

Havent tried that either, but compared to reforming the necks by die, fire forming sounds interesting.

Fire forming is quicker and easier, but it will waste a primer.

 

[HenryBowman]

Working on some 375R load development and figured I would update this post with some visual aides.
L to R-New Hdy 375 Ruger, once fired Hdy 375 Ruger, once fired 300PRC brass die resized to 375 Ruger , once fired 300PRC brass die resized to 375 Ruger and fired in a 375 Ruger.

Note the shoulder and neck differences in the die resized brass. These were middle of the data loads, nothing hot or crazy. As is, they are about 2 MOA with the garbage 300gn RN I'm using for plinking ammo.

 

[LeonardC]

Thanks for the update and visual aides.