Home Forums Lever Action Central Marlin 336 Lever Actions 336 Converted to .375

My hunting partner has acquired a 336 that has been converted to .375 Winchester. This is uncharted territory for either of us. First, is there any difference in strength between such a conversion and one originally chambered for .375? Secondly, he is looking for loads using the 200 grain Sierra, so any suggestions there would be appreciated. Thanks in advance.

Interesting post, was looking forward to some feedback on this.

So was I!

Have you asked this question over on the Marlin owners board? I think I read there that the Marlins in 375 had a beefier action where the barrel screws in and rifles that have been converted from something like 30-30 or 35 Rem. have experienced failures, due to the increased pressures and a thinner section left after the re-chamber.

Well worth some time surfing over there for info on all things Marlin.

I don't know whether there are any differences between a factory Marlin 375 action and a regular 336 action. However according to some, Marlin never made or released many in 307 due to pressure problems, so perhaps they didn't make any alterations. I think Marlins featuring the so called Vee thread barrels are those chambered in 450, 338ME and 308 ME.

The factory 375 Win chamber has a really long throat, similar in some respects to a 458 Win mag. This throat was designed for reducing pressure and help attain the velocities they did for such a modest case capacity (same as the 458). If it were me I would want know whether that rifle had the regular (ie long) throat for the 375 as this will affect whether you can use the max published loads safely.

Personally I would be cautious and load to the lower end of pressures. This cartridge works best with a very narrow band of powders and the best we have available here are Reloader 7 and H-4198. The good thing about these powders is that they are accurate over a wide range of pressures, so you can start low and work your way up for your rifle.

Its a nice cartridge and works best with heavier cast pills in my view (250-300 gr).

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The Marlin 336 is the same rifle inside and out in either the 30-30 or the 375. The only difference is the caliber. The 375 has only one chamber size. What JFE above, is referring to is that some of the gunsmiths who rebore are using the 38-55 chamber specs. rather than the 375 specs. As JFE noted, the 375 has a longer throat with a 2 degree approach to engagement.

Be sure your 'smith rebores to the 375 specs. with a .156 more free bore than the 38-55, and not the 38-55 chamber specs.

The 375 and the 38-55 are two distinctly different cartridges with two distinctly different chambers. Don't let anyone tell you otherwise. A chamber casting will tell you instantly which chamber you have.

Guys, thanks for the replies - I'll pass the information along.

The 308ME and 338ME use a triangular thread rather than square.It is supposed to be stronger.I have a 336 that was in 35 Rem.converted to 356,It has no problems.Lots of 336s are converted to 307 Win.

Mr Bledsoe gave you the real facts. Need I say more. Verify which chamber. Jack

The .375 is a great cartridge, I love mine. Hits with lots of authority without kicking the snot out of you. Probably the reason you bought it! I don't notice too much difference over the 30-30.

JES does many of these conversions and can tell you everything you need to know, but I think the posters above already did it. JES can be reached at http://www.35caliber.com/

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JES does good work. My only complaint with JES is that unless otherwise requested he will make a three groove barrel. Makes it very difficult to accurately slug the bore. I would want the four groove barrel if I were to order a rebore.

Bought a 375 big bore win when first came out took moose, deer and brown bear with it with the 250pp factory load. killed far better than it's paper ballistic's would suggets. Moved to 356 after win dropped the 250, wish had kept it, didn't know kodiak made a 250 that would have worked. Did some reloading for it with the 220 hornady, RL-7 worked the best. Ken Waters did a report on the 375 win available in his books. On a medium size brown bear, had bullet (250pp) go thru right front shoulder bone, stomach full of wet grass and lodge in rear of left hip at 25yds with a perfect mushroom. Good cartridge! Have heard of several marlins converted but no personal experience with that.