A friend of a friend is having Remington's custom shop make him a Safari grade rifle in .375 RUM.He asked me for loading info for this caliber using the bullet weights of 250,270,and 300 grs.I have no idea how to respond except to refer to my four loading manuals.The guy wants to use Hogdon Retumbo powder in his load developement.Could anybody shed any light on prospective loads?I am sure he would want powder charges,type of bullet and velocities,etc.I can go to the manuals,but would,also,like to provide him with some real world practical advice.
Thanks for any and all help.
Jim

Go to the Favorite loads forum and you will see what I have for 250gr and 260gr bullets. I was using RL22 and H-4350 though. The reason why I used RL22 is cause I had some layin around from my 7mm, and I started using H-4350 cause I realized real fast that 1# of powder disappeared quick. Went to a faster burn rate to use less powder. I now get around 80 cartridges out of 1# of powder. On a side note, I am going to purchase Accurate Data 86 since the stuff is like $60 for 8#, and has a burn rate similar to H-4831. Gonna use it for practice rounds, and the "good stuff" for my hunting rounds. If he plans on practicing a lot, he should look into that stuff, and work up a seperate load with the Retumbo. Others say practice with what youre gonna hunt with, but man, that can get expensive.

I am in the process of working some 300gr bullets.

You are probably not getting much response to your question because of safety concerns.Many of us reload but do not like to offer loads that are not published. We don't want anyone to get hurt using the data incorrectly.Guns vary, components vary, temperature varies,and reloaders themselves vary.Some guys will list non- published loads,but do so with lots of warnings.I don't think you are just being ignored. You might want to do a search on 375 Rum data, also look at the reloading pages. Good luck.

Of course going along what Longshots is sayin, use my data as a reference. If he does try to work up to one of my loads, make sure it is just that. Working up to it. FYI those loads are not max in my rifle.

I will start this off with a bit of a disclaimer and say that I am not currently reloading for the 375 RUM but I am in the process of having one built so I have researched load data until I am blue in the face. From what I have seen I think Retumbo may be a little on the slow side for the 375 RUM. The slowest powders I have seen listed in any manual were H1000 and RL 19 & RL22 and those were with the 300 gr. bullets. I used Retumbo extensively in my 300 Ultra with excellent results, although I much preferred RL-25. I think Retumbo was designed for the "truly overbored" cases like the 7 & 300 Ultra's, 30-378 Wby, and the Lapua's. Those are just my observations.

I figured gixxer would be able to help here. He has good info there.

Retumbo is way too slow and bulky for anything except maybe 350 grainers or heavier bullets. It may be great in the smaller bore .300 RUM, but the expansion ratio requires a faster powder in the bigger bore .375 RUM.

H4350 is tops for 270 grainers, and H4831SC is great for 300 grainers. I follow the Hodgdon data and get very similar results.

Other good powders for the 300 grainers would be Norma MRP, RL-22, VVN165, IMR 7828.

You might want to look at Saeed's .375/.404 data. It should be interchangeable with the .375 RUM.

You could also look at my .375 WBY data in the Reloading pages too, and work up from there. Since those days I am a convert to Hodgdon H4350 and H4831SC Extreme powders.

Actual chronographed data in a 26" Remington M700 LSS factory rifle barrel for the .375 RUM:

300 grain Swift (crimped at cannelure)//RP brass//Rem9-1/2M(primer)//93.0 grains of IMR7828//2803 fps//74 degreesF//sub-MOA (duplicates Factory Load)

300 grain GSC FN (crimped at 3.545" COL)//RP brass//GM215M primer//90.0 grains H4350 Extreme//2705 fps//76 degrees F//sub-MOA (heavier dose of H4831SC might be better)

270 grain GSC FN (crimped at 3.545" COL)//RP brass//GM215M primer//95.0 grains H4350 Extreme//2921 fps//76 degrees F//sub-MOA (excellent max load for 270 grain GSC HV or FN work up to cautiously with other bullets)

Those are some "best loads" to be worked up to from 5 grains below, with the usual precautions.

96 grains of H4831SC was getting the Sierra 300 grain GameKing up to about 2750 fps, preliminary ... and groups were "sub-MOA."

Those Remington factory rifles are amazingly accurate.

RIP is right about the Retumbo being on the slow side. You can use it, but you would run out of space before you start to see good speeds. This should put it into perspective<let me get out the trusty Swift manual>.

250gr A frame
H-4350 89.3gr Max 96.0gr
H-4831 99.0gr Max 106.5gr(98% load density)

RL19 93.0gr Max 100.0gr
RL22 98.1 Max 105.5gr(97% load density)

IMR-4831 91.1 to 98.0
IMR-7828 95.8 to 103.0(95% load density)

270 A frame
H 4350 88.4 to 95.0
H-4831 98.6 to 106.0(101%)

RL19 91.1 to 98.0
RL22 97.7 to 105.0(100%)

IMR-4831 90.2 to 97.0
IMR-7828 95.8 to 103.0(98%)

300gr A frame
H-4350 82.8 to 89.0
H-4831 92.1 to 99.0(96%)

RL19 86.0 to 92.5
RL22 90.2 to 97.0(94%)

IMR-4831 83.7 to 90.0
IMR-7828 88.4 to 95.0(92%)

From the load densities I posted above, you can see that even with H-4350 you are getting some load densities @ or over 90%! H-4350 is miles away(I.E. faster) from Retumbo on the burn rate chart.

Part of the reason why you use faster powders is cause of the bigger bore than the 300, you are pushing hot gases down a larger diameter hole, the exit of gases is less restricted. Maybe RIP could explain that in a more scientific way than what I just said.

The reason why I have a Swift manual, and no actual load data is cause I used it for my 7mm Sciroccos, and just used the loads posted above as a ballpark for the 250 NF's and 260gr Accubonds.

I have settled on using a powder that I can get good speeds regardless of bullet weight with less than 100gr of powder. RL22 doesnt count cause I had it layin around, but the H 4350 fits the bill. I also feel that after shooting a load with RL22 and H-4350 SxS, I feel the faster powder imparts less perceived recoil on the shooter(me). 260gr Accubonds over 95gr of H-4350 feels "nicer" than 98.2gr of RL22 under a 250gr NF. Wierd. Lighter bullet too.

How deep he plans on seating his bullets does play a part in load density, but that is a whole other conversation. Did I leave anything out?

Thanks to all for your responses.
Jim