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Pushing the Limits of the Marlin 336 (or, How my .30-30 Got the AX)

August 13, 2014

I got to wondering recently. Typically, if that goes on long enough, the ol’ measuring stick comes out, then unusual credit card charges begin to appear, and before you know it, there’s a fresh pile of chips on the mill table. Sometimes a small pile of discarded parts sacrifice themselves to the cause of science. Tragic, yes, but necessary, and not without ceremony, which mostly involves uttered incantations that would prevent the offending part from having a place in heaven. But let me assure you, dear reader, that no parts were harmed in this recent experiment.

 

The thing I got to wondering about was this: I was looking online at the .308 Marlin Express FTX bullet—you know, the one with that tantalizingly slender ogive, and the way it wears that cannelure…well, let’s just say it doesn’t leave much to the imagination. And that ballistic coefficient! Are you kidding? Fast and easy, just the way I like them. Kind of makes Hornady’s companion bullet, the .30-30 FTX, look a little stodgy. 

 

So I got to wondering, what if we could stuff that 308 Marlin Express FTX bullet into the .30-30 AI case, leaving more room for powder, and picking up higher velocity and BC in return? 

 

Some off-the-cuff calculations indicated that the cartridge overall length (COAL) would be at least 2.68”, which is a fair step up from the 2.55” to which the factory Marlin 336 action is limited. I also guestimated that I would have room for an extra 3 grains of powder in the case. 

 

Oh ho! I knew that I could stretch the action capacity of the 336 to accommodate such a cartridge, so all I had to do was hustle two blocks over to 10-Ring, our local purveyor of fine reloading supplies. Faster than I could say, “Marlin Express,” I had a box of the sleek .308ME bullets in hand, and the project was off and running.

 

If any of you have read my previous articles, you know that a short time back we reamed a Marlin 336 .30-30 to Ackley Improved (AI), and saw some major improvements, both in performance and accuracy. Since that rifle already had increased case capacity, I thought it would make the ideal subject, which, I reckoned, might end up rubbing elbows with the elegant 308ME itself. Or if not rubbing elbows, at least be admitted to the party.

 

The RPPMarlin 336 .30-30 AX 

I decided to call this stretch limo the .30-30 AX, as in Ackley eXpress, or eXtra, or eXtreme—whatever. You get the idea. It’s not a new cartridge—the rifle undergoes more changes than the case—but there needs to be some way of referring to it, so there you are.

 

With the AX-conversion to a Marlin 336 30-30 rifle, the idea was to duplicate the ballistics of the .308ME cartridge with the more common .30-30.

 

As it turned out, the 308ME bullet, seated to the cannelure, brought the new COAL to 2.71”, a stretch limo indeed, but certainly within the structural limitations of the 336 action. Furthermore, I found that the slender ogive of the new bullet did not necessitate cutting a longer leade in the chamber—in fact it would have a slightly longer jump to the lands than a factory loaded bullet! This meant that factory Marlin .30-30 cartridges could still be fired in the chamber with no loss in accuracy potential, a fact which pleased me, as it further broadened the potential of the modified rifle. This new .30-30 AX cartridge looked a lot less like an old Saturn rocket, and a lot more like, well, an entirely more modern boondoggle capable of launching sleeker projectiles into space.

 

Quite piqued now, I handed my test rifle over to the shop elves, who probably consulted with Gandalf or some such, worked their wizardry, and brought the gun back to me looking much the same, but with a new digestive tract capable of swallowing (and spitting out) .30-30 AXes by the handful. Sweet. You may find this hard to swallow, but believe me, there must be elves in the machine shop. The only other explanation is that my partner and I have found a way to actually be in two places at once. And if Occam’s razor means anything, that’s just silly talk. 

 

Hand loads and load testing

Meanwhile, I’d been at the reloading bench, filling fire-formed .30-30 AI cases with dangerously heavy charges of LEVERevolution® powder. It worked out that a charge of roughly 41gr of LVR powder would max out the capacity of the case, with the bullet resting on powder, cannelure at the case mouth. For comparison sake only, a factory Marlin .30-3.0 case, or a .30-30 AI case, when paired with the Hornady .30-30 FTX® bullet, will fit about 35 and 38gr respectively. For the substantially fatter 308 ME-FTX cartridge, Hornady lists a maximum charge of 42.6gr. with the 160gr FTX bullet. I’m no fool. I did not start my new loads at 41gr, nor did they end there. 

 

But I did get into the high 30s on my first run to the range. On a 95 degree Texas afternoon, I ran test loads up to 40 grains before encountering a sticky lever and unusual shot dispersion. The previous 39.5gr charge had given me a 5/8” group at 100yds. But I’d found the outer limit, and reversed course immediately. 

 

Having proofed the concept with promising powder charge weights and accuracy results, the next step was to get out to our private range, where we could set up a chronograph to get some useful data, and then crack a couple of brews and discuss the results. This my partner and I did a couple of weeks later. And the results were worth discussing.

 

First, I should point out that our load testing has been far from exhaustive, and that any hand-loader should approach recommended maximums with caution. We loaded in Hornady cases, which are some of the heavier ones available, and did our shooting on a very hot day, so the loads mentioned should be safe, but individual discretion is a must in this sport. 

 

In a nutshell, we stopped testing the 160gr (ME-FTX) load with 38.5gr of LVR powder (after backing away from a high of 40gr.) This load yielded an average muzzle velocity of 2530fps out of our 20” factory test barrel, a speed within 100fps of the 308ME out of a 22” test barrel, according to Hornady’s handbook. If one subtracts the usual 50fps per inch of barrel, then the two are practically identical. Another .5gr of powder might be perfectly safe, but I feel that 38.5 is a safe place to stop, and gives all that should be expected of the .30-30 AI case. 

Given the potential flexibility of this improved platform, I wanted to experiment with at least one other bullet. I chose Speer’s 130gr Varmint HP, thinking that it would be outstanding on predators at longer ranges. I was not disappointed with its performance. Accuracy was spectacular, with the first 3 shot group clovering tightly at 100yds, pushed by 39.6gr of LVR. Velocities averaged about 2675. Later, running out of time and prepped cases, I grabbed a few of random weight, and fired a five shot group of the same powder charge at 200yds. The rounds printed in a perfect vertical string of 2.5”, which wouldn’t be worth mentioning, except that the impact point of each round correlated precisely with its clocked muzzle velocity. This leads me to suspect that weight sorted and carefully prepped cases would print easy sub-MOA groups at 200yds and beyond. A better barrel than the one on our test rifle might halve that. 

 

NOTE: the 130gr Speer Varmint HP has special needs in a tubular magazine. While its gaping hollow point poses no danger of igniting primers, the crisp edges of the meplat tend to cause feed jams because the bullet noses don’t like to lift out of the slightly recessed primer pocket of the succeeding cartridge. I found that imparting a shallow chamfer at the primer pocket rims alleviated jamming. An extra step in case prep, but worth it for the bullet’s performance. Otherwise, feeding and ejection were flawless in our test rifle.

 

At this point, our testing has been limited to just a couple of bullet and powder combinations. But some useful and interesting data has been collected on the way. We know that the .30-30 AX loads are capable of fine accuracy without modifying the chamber or leade in a manner that precludes accurate shooting with factory .30-30 loads as well. We also know that maximum charge weights of LVR powder do not fill the case entirely, so there is room in there to play with potentially more temperature stable extruded powders, like Hodgdon Varget and the like. And finally, we know that the AX loads are, for all intents and purposes, a ballistic copy of the 308 Marlin Express.

 

Why not just buy a new 308 Marlin Express Rifle?

The answer is there are no compelling reasons not to. If you have the spare cash for another rifle, and don’t mind getting into another caliber, the MarlinMX is a fine platform, with a well sorted cartridge. But, while it may have been well received, only time will tell if the combination has any longevity in the marketplace. The .30-30 on the other hand, has been around the block a few times, and despite a steady onslaught of newer, better, faster hunting cartridges, the popularity of the original shows no sign of abating. You probably have at least one in your safe right now.

 

And therein lays the advantage of the .30-30 AX improvement. If you reload, then these straightforward modifications may be the most economical (and satisfying) way to bring more power and range to your lever gun hunting grounds. Keep the 336 rifle you have, and expand its flexibility to 308. Whether you want to drill coyotes and varmints across a field, take deer at distance, or bust boars close up, your old friend will have fresh, virile blood in its veins. You may see a different rifle breathing with a deep, steady confidence under that care worn varnish.  And you will have a recipe book full of options (not to mention heat-and-serve dinners) when feeding time comes around.  

 

Marlin 336 .30-30 AX rifle modifications

So now, to nuts and bolts. The required modifications to various parts, including the receiver itself, are irreversible. However, as previously mentioned, they are completely backwards compatible, and not especially evident to the casual observer. Our AX-converted rifle will feed, fire, and/or eject all factory .30-30 cartridges, as well as cartridges fire formed and handloaded in .30-30 Ackley improved brass. Reloads may use any .30-30 bullet in addition to bullets with longer ogives/seated lengths, like the one Hornady sells for use in the 308 Marlin Express cartridge, as well as a number of others, as long as they have tips that are safe for use in tubular magazines. You may not fire factory 308 Marlin Express cartridges in the AX improved rifle.

 

Think about that. Look at the options. Look at the ballistic coefficients. If you find them too tantalizing to resist (as I did), then contact us.

 

May the sun be at your back, and the breeze upon your face. Happy hunting. 

 

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Best,

Adam Devine

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