Introducing the .36 RPP - Big Brother to the .35 Rem and .356 Win (Marlin 336 Rifle Conversion)
Some of you may have noticed that I haven’t emerged from my rabbit hole much lately. It’s been a busy, busy year, and it’s only speeding up as the fall hunting season looms on the horizon. To that end, my efforts lately have been focused on developing some exciting new hunting cartridges for Marlins. We’ve had incredible success with our 1894 pistol caliber short stroke conversions, but that success—and our preoccupation with filling orders—has left me with the feeling that the 336 platform wasn’t getting the love it deserved.
Quite a few of you noticed and commented on my thread regarding development of a couple of 6.5 caliber offerings. They are still in the works, being driven perhaps more by my passion than an expectation of huge commercial success. But in a simultaneous—and more secretive—endeavor I have been working on a new medium bore cartridge, this one inspired by our own @JackTW on MarlinOwners.com.
Jack has always admired our .30-30 AX project, but he is a really big fan of .35 REMs, so rather than commission a .30-30 AX, he started pestering me to work out a .35 REM AX, or something along those lines. I like the .35 REM, but I’ve always wished it could offer more, so I was all too happy to indulge Jack. However, as I began studying the .35 REM more closely, I realized that it had too many limitations, and I was going to have to come up with an entirely new cartridge if there was to be anything worth getting excited about.
So I did, and so it is. It wasn’t in the mission parameters, but I ended up designing one of the most powerful cartridges that can be stuffed into a Marlin lever gun. Oops. Blame it on JackTW.
We’re calling this new cartridge the .36 RPP. Why .36? Well, for one thing it seems silly, given the performance of this thing, to round .358” down to .35 rather than up to .36. For another, there is some Texas Ranger heritage entwined with the .36, and we like that. And, more recently there is a phenomenally good Texas small batch bourbon from Ranger Creek Brewing & Distillery that bears the .36 moniker, so this will make a triumvirate.
To address the inevitable question: “if I want a more powerful .35, why wouldn’t I just go to a .356 Win?“ Well, you could, and plenty have, and it is a fine cartridge. But it is severely hobbled by scarcity of brass and ammo. And there are many who feel squeamish about the .356’s chamber pressure of 52kpsi. I was one, but through study and first hand experimentation I’ve become convinced that, while some safety margin may be eroded, the 336 still has adequate safety at those pressures.
Having said that, one nifty aspect of our new .36 RPP is that it can deliver .356 Win performance while operating at comparatively tame .30-30 pressures. But what it can do at 50,000 psi is truly impressive.
Without further ado, here’s the skinny:
First, the juicy performance figures. From our test rifle’s 22.5” bbl, safe, accurate loads have achieved the following: 1) with Speer’s 180gr FP, a MV of 2800fps (3133 ft/lbs of energy); 2) with Speer’s 220gr FP, a MV of 2500fps (3052 ft/lbs energy); with Hornady’s 200gr FTX, a MV of 2635fps (3083 ft/lbs energy). Note that we believe the terminal performance of the 200 FTX will likely be compromised by these high velocities.
In short, the .36 RPP can add nearly 400fps to commercial .35 Rem loadings, and well over 100fps to .356 Win loads.
Accuracy in our test rifle’s match-grade Douglas barrel was stellar, with nearly all test loads shooting sub-MOA before the barrel was even broken in. Some loads shot closer to ½ MOA.
Parent case to the .36 RPP is the .35 Whelen. Not ubiquitous by any means, but readily available. Hornady makes quality brass for the palatable price of $.75/ea.
.36 RPP brass is formed by trimming and full sizing Whelen brass. No fire forming, reaming, or neck turning is necessary.
Max COAL is 2.72”. Case volume is 62gr H2O.
Dies are inexpensive and readily available .356/.358 win
Appropriate bullets are shared with the .35 Rem
Offers more power than any commercial lever gun cartridge except the .450 Marlin. Yes, this includes the mighty .444 and .45-70, as well as the .338 ME and its bolt action analog, the venerable .30-06.
Offers more range than any commercial lever gun cartridge except the .338 ME
* Donor rifles are Marlin 336s chambered in .35 REM—readily and cheaply available both new and used.
* Conversions require action stretching, but for the budget minded the factory barrel may be retained, and for those who want the ultimate in range and accuracy a longer match-grade Douglas barrel may be fitted.
I’ve kept JackTW in the development loop, since this is kind of his spawn in a way, and without speaking too much for him, it’s safe to say he’s very excited about this cartridge. I am too. I can already envision it becoming my favorite, for despite the impressive top-end figures, it promises a high degree of flexibility and usefulness on a wide range of game. For those of us who don’t live in grizzly country or feel the need to bring a keg-size bullet to the party, a medium bore like this makes a lot of sense. Like the excellent but virtually unobtainable .338MX, the .36 RPP can bring the lever action out of the woods, and into fields and mountain ranges. It will certainly give you the element of surprise—and probably some braggin’ rights—among your bolt action buddies.