Help with 375 Grain bullets & Retumbo

[jbs2014]

I am looking to do some load development for my 375 Cheytac with Retumbo powder. I have a Lawton Rifle with a 31" barrel. I was thinking of starting at 132 Grains of Retumbo and moving up. Is this a safe starting point for this cartridge?

Thank You for your time

 

[WeiserBucks]

Don't trust your safety on my response , but most 375 shooters seem to be using between 130-133 grains of Retumbo with the 350 SMK.

 

[Deleted member 46119]

I disassembled a CheyTac 350 SMK round.

The powder is Retumbo.
The charges is 132 grains.

I did not start at 132, I backed off from the factory rounds to 125 then worked back up. My loads duplicated factory at ... 132 grains. That is a slightly compressed load.

I wouldn't go much higher and your accuracy is like @WeiserBucks most likely to be in the 130-132 range.

 

[jbs2014]

Thanks for the info. I am using 375 grain Rocky Mountain Bullets have you shot those before? Any start load info?

I plan on trying those 350 SMKs. How far off the lands do you guys seat them?

 

[jbs2014]

Oh what velocity are you getting at those SMK loads you mentioned? My barrel is 31"

 

[Deleted member 46119]

I am using 375 grain Rocky Mountain Bullets have you shot those before? Any start load info?

Seating depth, seating depth and seating depth.

That is what will determine you charge weight, with either the SMK or Rocky Mountain. The only reference I can give you is the same, start at 125grains of Retumbo, maybe less is your seating depth is less than 4" for the RMB . Anything else would be IMO unsafe.

I have not used RMBullets. I have trouble finding their web site.

SMKs out of your 31" barrel could get you around 2900fps, +-100fps. I was loading and shooting a friends 375 CT and no longer remember the speeds from his 28" barrel. My loads matched his ballistics solver that came with the rifle.

Seating depth, seating depth and again seating depth.

If you have to seat your 375 RMBs deap you may have to switch to a slower powder than Retumbo.

 

[jbs2014]

I did some tests today with retumbo and H50BMG. 138 grains of H50BMG was a good load despite being a bit compressed. No pressure signs at all. Retumbo had a real decent load and others with pressure signs. I will post more on the retumbo later.

 

[jbs2014]

Would you all say that these are excessively high pressure signs or not

 

[jbs2014]

Seating depth, seating depth and seating depth.

That is what will determine you charge weight, with either the SMK or Rocky Mountain. The only reference I can give you is the same, start at 125grains of Retumbo, maybe less is your seating depth is less than 4" for the RMB . Anything else would be IMO unsafe.

I have not used RMBullets. I have trouble finding their web site.

SMKs out of your 31" barrel could get you around 2900fps, +-100fps. I was loading and shooting a friends 375 CT and no longer remember the speeds from his 28" barrel. My loads matched his ballistics solver that came with the rifle.

Seating depth, seating depth and again seating depth.

If you have to seat your 375 RMBs deap you may have to switch to a slower powder than Retumbo.

I have been seating them .035 from the ogive to the lands.

Quick question, how does pressure directly relate to seating depth? Is it the deeper the seating depth the greater the pressure or opposite?

Thanks for all the info you have provided

 

[Deleted member 46119]

the deeper the seating depth the greater the pressure

yup