Accurizing the Marlin Lever Action Rifle

I’m joking, of course. But I’m also illustrating a point. Or two points, to be precise. The first is that rifle accuracy is treated, even now, with a lot of superstition, some of which has been immortalized on paper. Unfortunately, gunsmiths as a group are just as susceptible to the pull of myth as society at large. Too often, we draw conclusions from limited test samples, or simply swallow whole what has been passed on to us by others “in the know.”

The second point is that rifles, like people and most other critters, are most comfortable with consistency. The shooter’s choice of skivvies probably does not concern the gun, but plenty of other factors do. I won’t attempt to relate an entire body of knowledge here, or set myself up as The Expert. For those who have a deep curiosity about the subject, I suggest reading  Harold Vaughn’s Rifle Accuracy Facts. Mr. Vaughn, an actual rocket scientist, is a real life myth buster. He went to the trouble of performing an extensive series of carefully controlled and well documented experiments to determine what makes a rifle accurate. Most other published theories are conjecture or based on very limited results and/or understanding.

Vaughn’s treatise was entirely focused on the bolt action rifle. So while his conclusions could be applied to other platforms, we did have to come up with our own methods of applying them to lever action rifles. Marlins and other tube fed rifles present a special set of challenges to the builder and ‘smith. Years ago, when I was still on a very steep learning curve in this profession, I bought a book written by a noted gunsmith, because it had a chapter devoted to accurizing tube fed lever actions. His methodology proved so arcane and convoluted I had trouble following it, and I read on an eighth grade level, or I did in the fourth grade anyway--who knows what damage college might have done. After experimenting with his techniques for a while, I decided they lacked merit, or at least clarity, and pursued my own ideas.

The techniques I currently use to accurize Marlins are based on one simple and verifiable fact: a gun’s accuracy is determined overwhelmingly by the barrel’s ability to consistently point at the same spot in relation to its sighting device. If this seems like kind of a “duh” statement, maybe it is, but it is more encompassing than one might think.

Look at it this way: to build the ultimate rifle you could start with a match grade, bull barrel of modest length and screw it into a fifty pound cylinder of solid steel. Instead of a bolt use a precisely machined breech plug, through which passes your spring loaded firing pin. Weld some heavy steel scope rings to the top of the cylinder, lap them, and mount the best optic you can buy. Then bolt the whole contraption to a heavy concrete bench. You have now eliminated most, but not all, of the factors that can have a detrimental effect on accuracy, and you will probably have one of the world’s most precise (if impractical) rifles.

I noted before that tube fed rifles present special challenges. The reason for this is all the junk hanging on the barrel. All that junk—the forend, magazine tube, barrel bands, bullets—has a tendency to shift around and exert varying tensions on the barrel from shot to shot, moving it slightly from its previous aiming point in relation to the scope.

What happens under the hood of a Marlin lever gun is fairly complex. Forward of the receiver, you have a wood (known to expand and contract with temperature and moisture levels) forearm that is in full contact—give or take a bit—with the barrel along its channel. Securing the forend to the barrel, you have a fixture (a rear barrel band or forend cap) which may or may not place the forend into tension with the barreled receiver.

Under the barrel you have a magazine tube that may or may not contact the barrel in one or more places inside the forend. Often, but not always, the tube will contact the rear barrel band cross pin. In the case of a forend cap, sometimes one or the other screw will contact the mag tube, depending on assembly. But the magazine tube will contact the barrel, indirectly at least, at its forward mounting point (band or tenon), and sometimes (with barrel bands) once again even closer to the muzzle. If that’s not enough, the weight of the mag tube will vary with rounds loaded, thereby altering the harmonics of the barrel from shot to shot.

Oh, and I almost forgot, all those cross pin slots and dovetails cut into the barrel to hang this junk create little tight spots in the bore. To muddy things just a bit more, mass produced, sporter weight barrels have a tendency to deform a bit as they heat up during shot strings. From the standpoint of someone looking for consistency, it’s a chaotic mess.

Outside the crazy love triangle of forend + barrel + mag there are still other factors that influence accuracy. But the fact is, outside of an untroubled barrel and quality ammo, most of the other factors don’t amount to a hill of beans unless something is grossly out of whack.

Given all this, it’s a wonder Marlin lever action rifles can shoot well at all, but they do, often times delivering 3-shot, MOA accuracy out of the box. This is plenty good for their intended hunting role.

As a side note here, I have to say that I am amused by the MOA guarantees issued by some high-end bolt action rifle makers. Typically this guarantee stipulates 3 shots with high quality ammo. This amuses me because, given modern metallurgy and manufacturing techniques, if your bolt action rifle will not put three match rounds inside an inch, you got ripped off at any price. You can’t blame the rifle makers for capitalizing on our lust for accuracy. But I won’t pay a premium for an MOA guarantee on a bolt gun. I have a rack of inexpensive Savages that will better that easy feat. But I digress.

If many factory Marlins will put 3 in 1 inch at a hundred yards, why bother with all the fuss over “accurizing?” The first reason is that we’re just accuracy freaks, and if you’re reading this, you probably are too. Regardless of their hunting adequacy, we still spend a lot of time with Marlins on the bench, and it’s gratifying to stretch their capabilities. By which I mean how about 5 or 6 shots in an inch instead of just 3? Or how about sub-MOA accuracy at 200 or even 300 yds? We do it because we can. And it’s fun.

The second reason is that often, when we build customs, we have shortened barrels and mag tubes, repositioning barrel bands and changing harmonics. We are starting over. And if you’re going to start over, why not do it better than before?

The attentive reader may have surmised by now that when it comes to accurizing a Marlin, any successful modus will have at its core the goal of controlling and/or eliminating the various forces at play on the rifle’s barrel. It is not practical to “free float” a Marlin barrel in the true sense. We work with what we have, which is a lot of junk that must hang from the barrel or fall off the gun. The forend must contact the barrel at least twice in order to be stable. The magazine, too, must contact the barrel at least once—though we’ve found twice is preferable.

So we minimize, condense, and control these contact points as much as possible. For example, we eliminate any contact between mag tube and barrel that does not coincide with a point of contact created by a necessary fixture (i.e. barrel band). Same goes for the forend. We also want the relationship of these contact points to remain constant, so we use epoxy bedding where necessary to minimize wood influence and to fix the radial position of the mag tube.

As to minimizing cartridge count harmonic influence, we find it useful to create a deliberate and fixed tension between barrel and mag tube. This tension will result in a noticeable shift in point of impact, drawing the barrel slightly downward, but also influencing barrel harmonics. Some experience and experimentation is required to determine how much tension is optimal. And since harmonics are affected, the same amount of tension may not be optimal for every load. Of course, favoritism is in the nature of every barrel, regardless.

Lastly, in the matter of those pesky tight spots in the bore, there are limited options. Fire lapping is the most promising. We have experimented with Beartooth Bullets’ lapping kits, with promising results; however, the process is quite labor intensive. Unless you are determined to improve a poor barrel or squeeze the last bit of accuracy from a good one, the investment may not make much sense. Fortunately, we find that most Marlins will deliver more than acceptable accuracy without lapping.

What kind of accuracy do we consider acceptable? Well, for starters, one inch or better at 100yds with three shots. That’s a benchmark that our custom builds are required to attain before they ship, with the caveat that the base rifle (if provided by the customer) came with an acceptable barrel. What we prefer to see, and often achieve, is 5 shots under an inch, with the first 3 very tight. If a rifle is a poor shooter (2-3” groups) out of the gate, it probably isn’t destined for greatness. But we have been able to coax a number of losers into performing surprisingly well.