300NMI 245 Berger Loads

[RustyB]

I recently acquired a 300 Norma Mag Improved and was looking for some load data on the 245 Berger EOL. Any info is greatly appreciated.

 

[ISS]

Mine is almost finished, at least the metalwork (FCH) portion. We will proof five rounds with the Sierra 245's and reload those five cases as dummy rounds so it can go to Alex Sitman for final fit and then to Bc'z for clear coat.

Rumors abound that a good place to start is 88gr of N570 or about that much Retumbo.

 

[shoot4fun]

Reloading Data Center – Hodgdon Reloading Data Center

hodgdonreloading.com

Retumbo is a favorite of mine for the big stuff. I would suggest you take Hodgdon's data for the 245EOL in 300NM and work up from there.
It seems there are a couple different version of the improved but either Ryan's or @Alex Wheeler (what I have) version is 35˚ and accuracy is pretty dang amazing.
If your experience with the 300NMI is as good as mine has been you won't stop smiling.

 

[FeMan]

Retumbo is a good place to start. One of mine is a 30-inch Bartlein and likes the 245s jumped about 0.075" with 88.2 grains of Retumbo. Itll shoot 0.4 moa 5-shot groups reliably. The other is a 32" Brux and doesn't shoot Retumbo as well but its best load is 245s jammed about 0.015" with 85.5 grains of (0.75 moa 5-shot groups) .

I am in the middle of load workups with N568 and N570. The 32" Brux loves a very heavy dose of N568 at a Jam of 0.010". So far it is shooting this under 0.2 moa at 3100 fps. I plan to do a 900 yard powder ladder with both rifles and N568 and N570 next week. That should tell me more. I'll fine tune seating depth and then neck tension after that and be ready for ELR season.

 

[ISS]

thanks, I hope to be sitting there next to you watching as you proof my 300NMI.

Rich

 

[4xforfun]

Question on the Retumbo thing....I read a few posts like you, but they were 10 or more years old, and there were concerns about DANGEROUS PSI spikes at COLD temps. Is that still a thing. I steered away from my 8 pounder of Retumbo and went with RL33 for my 1st tests.

Not a 300 NM, but a 300 rum with HEAVY bullets.

Tod

 

[FeMan]

I have shot my 300 NMI Retumbo loads in temps down into the teens with no issues. Brian Litz told me a few years ago that in his testing, Retumbo was the most temp insensitive powder he had ever tested, to the point he called it virtually temperature immune.

I have read that about N570 but never heard that about Retumbo.