Sorry for the redirect but wanted to get the word out about this. It's a big bore "medium" in the tradition of the original Express rounds optimized for the Ruger No. 1 and other single shot rifles, done up by my friend Roger Renner.

My single shot rifle post here


Or just go straight to the RJ Renner website here

Jim, you startled me there for a moment.....thought I read .375 “Jenner”. That would have been “blasphemy “! 😁. memtb

Jim: Is there a case drawing for the Renner cartridge? Any loading data? The renner website is vague.

I really don't know the answers to those. Roger and I communicate now and then and he mentioned that he had developed this so I figured to spread the word. You'd have to contact him for more specific info. You can call him at 775-453-9355 up to around 4:30 PM PT on weekdays, he's always willing to chat.

Hi Jim,

This is very interesting. I went to RJ's home back in November to personally deliver a rifle for him to work his magic on. He did, and, as usual it was great! My 3rd rifle to him. While there I mentioned that I really like the 375 H&H, but I said I thought it was too much for most of North America (but I do hunt Alaska). He pulled out a project he was working on with the 375 caliber. It was not the 45/90 case, but was based on (I hope I'm not spilling any beans here) the 240 Weatherby case expanded to 375 and to be used in a No. 1. I brought a case home that he gave me and expanded it to 375 through a series of steps and measured a load of the same powder I use in my 375's (Re 15). It held approximately 53 - 55 grains with a bullet a little lighter than I normally use in my own 375's - 250-270 gr vs. 300). I thought I might be seeing that show up somewhere, but I guess it's now official for this case.

As he mentions, one of the distinct advantages of the H&H case is the taper for smooth insert and extraction, and I personally like a rimmed case for the No. 1. Boy-o-boy, if he is doing this on a 1S or similar configuration I may be looking for another No.1. He did work on a 450/400 N.E.(1H) for me and it's very nice, but I previously owned a 9.3x74R (1S) that I thought was the absolute best balanced rifle I ever owned. As far as I'm concerned Roger does to M77's and No. 1's what Ruger should be doing - I can HIGHLY recommend his work.

Terry

Thanks for your post. You're in luck! Or not, depending on the state of your checkbook. I emailed him to ask what contour he uses and it is the 1S contour, 1H being too heavy for his vision of how it should handle and 1A of course being too light for a .375 caliber.

Double ditto.

I may be in trouble! Guess I'm going to have to keep my eyes open for a donor rifle. Don't tell the wife! Terry

I like the way Renner thinks and his energy and integrity when he's got a new bone in his teeth on a run. Years ago when he was Dr. underhammer I jumped in and after several fascinating phone conversations ( prior to email for me anyway ) and after discussions on the underhammer design features and Forsythe rifling I ordered a 20 bore Zephyr. After taking one moose with both shoulders shattered and two cow Elk I'm convinced the round ball is a real performer within its inherent limitations. But if it hadn't been for Renner who'd a thunk it.

I love rimmed straight wall cartridges and and the 375 bore so give me something built on a good case between the H&H and the 375 Win and I'll certainly walk up to the edge and look over, maybe even jump.

Good to hear Idaho

The cartridge looks like the smith might have used a 375 H&H reamer but only reamed the chamber to 2.4", i.e. 45/90 length. I recall someone doing something similar but using an 8x57 case as the basis for their wildcat. Assuming this is the case, you could then easily modify 375 H&H dies to suit.

Sounds like similar capacity to a 375 Whelen

Not quite sure how the Renner beats a 375 H&H Flanged Nitro, guess some may be afraid of short stroking a falling block.
(But I do understand how a 375 Ruger beats a 375 H&H Mag in some applications.)

Why not use a 375 JDJ (or a 375/444 to avoid offending J.D. Jones) loaded to appropriate pressures for a Ruger #1?

From his website:

The .375 Renner is a cartridge designed specifically for the Ruger No.1 and hunting North American big game. It provides generous taper of the case, a gentle shoulder, and robust rim, while having capacity to hold 60 grains of IMR powders under the bullet. It easily duplicates ballistics of the .375 Whelen, or the more recent .375 Hawk/Scovill...

While patterned after the classic English singleshot cartridges of yesteryear, the .375 Renner is a brand new design and is based upon the .45-90 Winchester case. The .45-90 case is simply necked down within an appropriately shortened .375 H&H sizing die. It’s that simple. The result is an amazingly flexible cartridge capable of taking anything from marmots to moose and it will do it all with less stress than produced by the big .375 magnums.

Although the .375 Renner is a wildcat cartridge, it’s simple to make and load and even the novice hand loader will master it quickly. Yet, it offers new horizons of ballistic exploration for the most advanced hand loader - and we haven't even started exploring the potential of blackpowder in this case.

I see he has added a link with a cartridge drawing and loading notes, also some Quickload calcs.
Load notes

Quoting from that page:

The loads listed are intended for the .375 Renner English Stalking Rifle in consideration of its 7-pound weight. Heavier rifles can be loaded to higher levels of performance, but beware that recoil increases significantly, too.
For the most fun and economy with your .375 Renner English Stalking Rifle, keep bullet velocities below 2200 feet-per-second and save your shoulder for serious hunting loads over 2200 fps - IF needed.

A summary of QL loads shows:
Sierra 200 FP at 2418 fps (moderate load to not over stress this bullet)
Speer 235 at 2400+ fps
Speer 270 at 2267 fps
Hornady 300 RN FMJ at 2136 fps.