Marlin Conversion .356 Win. 20" bbl/scope mount

[Mike D.]

I don't believe that a Marlin 336 will stand up to prolonged use of .356 W. standard loads. 52,000 CUP will eventually destroy the single underbolt locking system.

[AJMD429]

I don't believe that a Marlin 336 will stand up to prolonged use of .356 W. standard loads. 52,000 CUP will eventually destroy the single underbolt locking system.

I'd have figured the .338 Marlin Express would be similar-pressured, both putting out 200 grain bullets around 2500 fps; maybe the .338 Marlin round is lots lower pressure?

[Hobie]

Many years ago on another forum/board, we had a long discussion about what happened to over stressed 336 actions. Much as made by a couple of the posters of the peening of the locking surfaces in .35 Remington and .45-70 (1895) guns. As often as I asked, nobody ever came up with photos of the peened locking surfaces so I can't comment on the veracity (one way or the other) of the posters. I don't have that in my 336s but so long as I've had them I haven't abused them.

A lot of this discussion also concerned the tendency of the TC Contender action (not the G-2 which didn't exist at the time) to stretch under those loads. Unfortunately, that does happen and it is all too easy to load the larger diameter cartridges (the larger dia the easier) to the point that the frame will stretch and the gun no longer function. This is one reason the G-2 frame was developed as TC had a lifetime guarantee and they were replacing, free, many stretched frames every year.

However, to get back to the .356 converted 336s. The .356 gun is supposedly more closely fit than the .30 and .35 Rem guns. This supposedly is why they will work. 336s (and 1895s and 444s etc) don't fail in the locking lug they seem to all fail where the barrel screws into the frame.

My personal opinion is that while the .356 and .307 Winchester conversions are inadvisable they are doable but the .358 and .308 Winchester conversions are just plain begging for trouble down the road for any number of reasons including their functional incompatibility with many factory loads and the probable ignorance of later owners.

[Blaine]

I still have that 336 that was reamed to .358.....Frankly, it worries me more than a little bit. If I shoot it, it will be with loaded down .358...A nice .35 ++P perhaps.

[Hobie]

The thing is, unless I'm missing something, is that it is all in the bolt head. Put a .30-30 bolt in that thing and it IS a .356 Winchester. REASONABLE loads should be both safe AND effective. It is how the thing is MARKED that's the real problem down the road. Sooner or later some goober will load a red-lined .308 Win round in there, likely fussing that he's had to load directly into the chamber rather than through the loading gate ("what WERE they thinking" is what he will be thinking) and then... I would hate to be sitting around heaven having a chat with all and sundry when the big guy calls me to judgement... "Do you remember when you re-chambered that .30-30 Marlin to .308 Winchester? I'd like you to meet Joe Putz. Now, please go to the elevator (down only...)." Why take a chance of inflicting that on anyone? If yours is marked .358 just restamp to .356.

[NFG]

Here is something to consider...

A 450 Marlin at 42,500 CUP with a case head area of .222 sq in(Area equal Pi times radius squared) has about 9435 lbs of pressure on the breech bolt face which is then transfered to the locking lugs two faces.

A 45-70 loaded to 40,000 CUP(straight out of Hodgdons manual and the WW 457 Mag conversion goes to 44,000 CUP) with a case head area of .290 sq in has about 11,615 lbs(12,760 lbs in the 457 Mag conversion) of pressure on the breech bolt face...

A 444 M at 44,000 CUP with a case head area of .207 sq in has about 9130 lbs of pressure on the breech bolt face...

A 356 Win at 52,000 CUP with a case head area of .175 sq in has about 9100 lbs of pressure on the breech bolt face...

AND a 308 MX at 55200 CUP with a cas head area of .175 sq in has about 9660 lbs of pressure on the breech bolt...

The 356 has LESS pressure on the breech bolt than the others and no one seems concerned about them causing problems...

Most people have little or no understanding of the actual pressure dynamics going on with the Marlin OR any other rifle for that matter, the strength of the bolt, locking lugs, barrel steel etc. and only see the SAAMI pressure number. I would worry more about the area below the chamber at the mag tube cutout and the thinness of the square threads of the barrel than with the locking lugs...BUT

I have no problem with my 356 Win Marlin 336 in loading it to a MAP of 52KCUP any more than loading my 45-70 switch barrel chambered to 458 American x 2.20" to 450 Marlin pressures, or the 444 M switch barrel loaded to 444 M pressures...OR loading the 45-70 case to 42,000 CUP for that matter.

I DON'T as a matter of course load ANY of my rifles to max SAAMI pressures as I value accuracy more than velocity, but the highest accuracy usually come near the top of the range.

One thing I learned early on was that dropping the pressure 10% only lost 5% in velocity and usually resulted in 100% better accuracy.

Simple solution is to load WHATEVER caliber or rifle to the pressure you feel comfortable with and call it good.

Hobie is right about the bolt...the 35 Rem had a smaller case head and uses a different breech bolt than for a .473 or .506 case and. My 336 was originally a 30-30 so the conversion to 356 W was simply a rebore/rechamber, but I have to install a 450 M/45-70 breech bolt and carrier for those larger calibers and cartridges.

MAP for the 338 MX is 46000 PSI...approx 42000CUP.

Luck