Friday, March 13, 2020

Addressing the Minimum COL Limit for the Marlin 1894 Action

As is typical of the remainder of this blog, I am writing this following an experience with a problem about which I found frustratingly little clear information online.  That is not to say that I found little information; rather, I found a great wealth of conflicting, inaccurate, or at least confusing information obfuscating simple, but perhaps nonobvious truths. 

Let's start where the experience starts -- a rifle owner buys some new boxes of 44 Special (240gr LSWC) ammunition to use in his ca. 1971 Marlin 1894 chambered for 44 magnum.  While the first few rounds worked, the rims eventually start jamming between the lifter and the mouth of the magazine tube.  This was unexpected; all the prior boxes of old 246gr LRN 44 Special ammunition worked fine, and still do.  Why is the rifle jamming with the new ammunition?  My eyes see an obvious suspect, but let's get a second opinion.

HSM 44SPL (240gr LSWC), Winchester 44SPL (246gr LRN), Winchester 44MAG (240gr JSP)

If one immediately googles a relevant query, forums across the web will authoritatively dispense the answer with certainty. It's the "dreaded Marlin Jam", which is variously described as:
There are grains of truth spread nonuniformly throughout those discussions, but there are also a lot of misunderstandings and conflations going on as well.  It's easy to see how that happens.  The 1894 action is definitely susceptible to feeding problems, whether it is a consequence of the lack of controlled feed or the weaknesses of the simple mechanical logic going on inside.  It's also frustratingly difficult to visualize what exactly is going on inside.  There isn't a good way to see or measure the part clearances and timing as the action cycles, and the critical limits of those hidden details are fairly subtle.  It's easy to presume the causes incorrectly.

To narrow the subject, I am not talking about misfeeds caused by holding the rifle at an extreme angle or on its side, resulting in jams involving the bolt, breech, or ejector.  Those are a consequence of gravity and the uncontrolled feed.  I'm not talking about double-feeds caused by short-stroking or similar incomplete cycling motions. That's just a consequence of the fact that magazine interruption mechanism is reversible, while the feeding of the current round is not.  What I am talking about is the minimum reliable cartridge length for the 1894 action and jams caused by short cartridges in otherwise unworn rifles.

The Existence and Specifics of the Minimum COL Limit

But wait, the lifter automatically acts as a magazine interrupter.  Does the 1894 even have a minimum COL limitation?  Well, if you ask around, you will amusingly find people who will tell you that the design of the mechanism cleverly ensures it does not.  This is incorrect.  There most definitely is a minimum COL limitation. If you would like a quick proof that a lower bound exists, load a full magazine with empty cases (easier said than done) and see if you can get the action to lift a round without jamming on the next.

What that length is depends on the cartridge.  While the lessons of this study should also apply to other chamberings, 44 Remington magnum provides an illustrative complication as its chamber can also accept 44 S&W special. The SAAMI COL spec for 44 Magnum is 1.535-1.610 inches. On the other hand, the spec for 44 special is 1.415-1.615 inches. It's conceivable that a firearm designed around the magnum cartridge spec might not accomodate the wider spectrum of 44 special cartridge lengths.  Certainly, the first page of the manual for the Marlin 1894 states the acceptable range of cartridge OAL echoing the SAAMI spec for 44 magnum.  The case with 357 magnum and 38 special is similar.  These new boxes of ammunition are approximately 1.475" long -- well outside the limits recommended by the manual.

While the spec on paper is merely an assertion, it is the design of the mechanism and the particulars of its geometry which ultimately determine the actual practical range of cartridge lengths. When the lever is closed, the current round is captured at an angle between the loading gate, the right-hand face of the lever arm, and the next round in the magazine.  As the lever is opened, its arm clears the rim of the current round, allowing it to slip off the front edge of the loading gate.  At this point, the cartridge is captured between the forward face of the lever arm and the subsequent cartridge.  The cam surface on the lever begins to raise the lifter, shearing the stack of cartridges as they follow the motion of the lever rearward. In order to function correctly, the lifter must rise high enough to block the next cartridge before its rim clears the mouth of the magazine tube.  If the cam-lifter timing is retarded by some defect, or if the cartridges are too short, the lifter will not be in a position to fully block the next round before its rim clears the magazine mouth and a jam will occur.  It is this geometry of the lever arm and cam surfaces, as well as the lifter and magazine mouth which determine minimum cartridge length. 

Lever closed; cartridge offset and held on loading gate
Lever open; cartridges following lever arm
Magazine interrupted; cartridge uncontrolled

You should now be experiencing a creeping doubt regarding the invariability of the effective minimum COL requirement.  Not only is it an issue of timing between moving surfaces, the mechanical advantage of the cam/lifter system means that feed reliability is going to be significantly sensitive to small geometry changes caused by wear or receiver alignment.  There's enough tolerance in the screw holes that reassembling the rifle in a slightly different manner may significantly change its reliability with marginal-length ammunition.  If the receiver halves are tightly-fitted, the front screw may not pull them together completely with reasonable torque; a few taps with a hammer may be necessary to seat them completely. It's easy to think it's assembled correctly, and still have a 0.005" change in alignment make the reliability go from 95% down to 10%.  The same can happen if there are burrs or any debris between the receiver halves near the front screw.  The "Marlin jam" fixes addressing seemingly miniscule lifter peening should now start to make sense.

Very short COL resulting in jam on cartridge body
Marginal COL resulting in jam on rim

The form of the jam may vary depending on the scenario, leading people to mistakenly assume that the causes are necessarily different, perhaps misattributing them to other causes which produce identical end-conditions.  In the case of a very short cartridge, the next round is entirely trapped between the magazine mouth and the top face of the lifter.  In the case of a marginally-short cartridge, the rim of the next round may protrude only far enough to hook edge of the magazine mouth, becoming wedged against the front face of the lifter nose.  Bear in mind that the front edge of the lifter is not always close to the magazine mouth; neither is it moving in a straight line.  It moves in an arc, and presents a considerable gap when it is only beginning to interrupt the magazine. The exact contouring of the front edge of the lifter nose, caused by wear or intent otherwise, may further contribute to inconsistent behavior in marginal conditions.

Of course, this is just my insight from having spent a few hours trying to get a single rifle to run with two boxes of a specific brand and loading of cartridge.  I don't own 50 Marlin rifles.  I haven't fired 1E5 rounds of every kind of ammunition ever made without a single jam.  I haven't shot Marlins professionally for the last 90 years, uphill both ways in the snow.  I don't even hang out on the forums with all the people who assuredly did, so what do I know?

Toward a Remedy

While this particular case is an issue of short ammunition, the effect is the same as the lifter wear with which other owners contend.  As mentioned, I'm not the first person to try solving the problem; there are plenty of proposed fixes.  The bottom surface of the lifter which mates with the cam may be built up by welding or using an epoxy-bonded shim.  The lifter itself could be bent slightly. Generally, these solutions amount to a timing advance to shift the range of allowable COL down.  I don't know whether it's possible to effectively reduce the maximum COL by doing this; that limitation may be determined elsewhere in the mechanism (distance from magazine to cartridge stop surface) or loading cycle (chance of stumping on the breech face).  I'm not worried about overly-long cartridges at the moment.

The cam surface on this lifter is different than that of other (newer?) rifles I've seen.  Its curvature precludes the easy use of spring steel shims.  I simply elected to shape a brass shim from 0.015" shim stock and adhere it with JB-Weld.  This may prove to have a relatively short longevity, but it is more than adequate for this application.  With only a 0.015" shim, the lifter nose is advanced roughly 0.030", and the interruption occurs about 0.150" earlier (depending on where you assume the cartridge contacts the lever arm at that moment).  Again, the point is that small changes in the cam interface cause a large change in the effective minimum COL.

For my own purposes, I am content with the potentially temporary shim.  I don't want to weld or bend anything permanent; the shim can easily be removed without harm.  All it needs to do is allow the rifle to function with this particular lot of ammunition -- which it does excellently.  Once they are consumed, the rifle can simply be fed with a more appropriate choice of ammunition.  The long-term solution is merely an applied understanding of the mechanical nuance -- and/or perhaps some handloading.

Afterthoughts and a Helpful Gesture

It might just be me, but these 240gr SWC bullets almost look more at home in 44 magnum brass.  They would produce a good COL in that combination.  It might simply be an issue of the difference in demand between the cartridges and a desire to consolidate production components.  If everyone likes their Keith-style SWC's in the magnum cartridge, why not just stick the same bullets in the 44 special offerings too?  After all, 1.475" is well within the SAAMI spec for 44 special, and it's probably a fair assumption that most of them wind up in revolvers anyway. 

As for those who want to run lighter loads in their 44 magnum 1894's without dealing with tweaking the rifle, there are probably some factory loads available with more appropriate COL.  Of course, nobody states that metric on the box or the web.  I guess you can always bring your calipers to the store or do some approximation from image analysis.  The alternative is to handload.  Again, SWC bullets with high cannelures seem to be the most popular.  It may simply be easiest to use those with magnum brass to get a more reliable COL, loading down to 44 special ballistics.  At least at Brownell's, the price is identical for magnum or special brass -- for both Starline and Winchester.  That's probably of little comfort if you're sitting on a pile of special brass.  I suppose if casting is desired or acceptable, the Lyman Cast Bullet Handbook linked below lists the COL for cartridges assembled with various bullets from Lyman molds.  For example, a comfortable 1.571" COL can be achieved with a 245gr bullet from the #429421 mold.  There are always plenty of other recommendations around the web.

Toward that end, these pdfs may be useful.  Sometimes the older books are actually favorable if you have stock of discontinued powders, or if you want pressure data for legacy loads as a reference for comparison.  If you want newer editions, just hit up Amazon or AbeBooks, or the relevant manufacturer's site. 

Lyman Cast Bullet Handbook - 3rd Edition - 1980
Lyman Reloading Handbook - 48th Edition - 2002
Modern Reloading - Richard Lee - First Edition - 2000
Hornady Handbook of Cartridge Reloading - 3rd Edition - 1980
Hornady Handbook of Cartridge Reloading - 4th Edition - Part 1 - 1996
Hornady Handbook of Cartridge Reloading - 4th Edition - Part 2 - 1996
Cartridges of the World - Barnes - 8th Edition - 1997
ABC's of Reloading - RCBS - Dean Grennell - 1985
The Gun Digest Book of Handgun Reloading - Dean A Grennell - 1987
Gun Digest - Shooter's Guide to Reloading - Philip P. Massaro - 2014
Precision Handloading - John Withers - 1985
Introduction to BPCR Loading - Chuck Raithel 2001
A Cast Bullet Guide for Handgunners - Fryxell - Applegate
The American Rifle - Whelen - 1918
Complete Guide to Handloading - Sharpe - 1937
Handloaders Manual - Earl Naramore - 1943
Alliant Reloaders Guide - 2009
Hodgdon Basic Reloading Manual - 2015
Winchester Reloaders Manual - 15th Edition - 1997
Western Load Guide - 6.0 - 2016
Powder Bulk Density Chart - 2007

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