This article by By Mustafa Curtess of Austwell, TX, was published in the May/June #229 issue of The Fouling Shot.
I have come to agree with Ed Harris that Micro-Groove barrels can shoot cast bullets extremely well, but I only discovered this by accident.I have a M336 made for Sears, Roebuck. It had a 6-groove barrel marked J.C. Higgins M45 that was completelyshot out, although the barrel looked decent at thegun show. Never mind that, the price was too cheap to walk away from, and otherwise it was in nice condition. It would shoot the first three to five CB rounds from a clean barrel into sub-two-inch groups with the biggest CB that would chamber, so I carried it in my pickup for years.
Gun Parts, Inc. advertised original barrels for Sears M45 for something like $25 and wording implied that they would be exact replacements.
When it arrived, there was no doubt it was factory new, but deeply stamped Sears. Even so, it had the same catalog number that was on the J. C. Higgins version. But my heart sank when I looked through it, Micro-Groove! I was so disappointed I didnt even bother to swap barrels for two to three years, expecting the usual removal and installation problems and having no tools for a levergun. Also, it was a clearance item that could not be returned.
Eventually I did take it to the farm shop, clamped the frame with a shop towel wrapped around it in the bench vise and attacked the barrel with a big pipe wrench. Surprise! It broke loose without even marking anything. The new barrel I clamped in the vise between two onepound wheel weight ingots and screwed the frame onto it, this time with a 24 Crescent wrench padded with the shop towel. The index marks lined up with very reasonable torque, and everything else aligned perfectly (the notch at the front, forward of the sight blade for the barrel band screw, sight notches, etc). That was all just too quick and easy. I remounted the scope, cleaned the oil and residue out of the bore, and chambered a 30-30 round for another M336 (a 4-groove K prefix) stepped out the door and dropped the hammer at a steel target about 75 yards away, mainly just to see if it would fire at all. It hit dead-on the point of aim! What were the chances, after a barrel change and a scope dismount and remount? The entire thing had been just too good to be true. I figured it couldnt last, but it did.
To this day I havent slugged that barrel; I have only miked a bore-ride CB that fits the muzzle lands nicely (.301).
The ammo was my standard for the 4-groove M336; SAECO 315 lubed in a .310 die over 12 grains of SR4759, and accuracy held up for about 1/2 of a box of 50.
The usual bore cleaning didnt produce anything on the patches except the usual black carbon (or whatever) but it didnt restore accuracy either, although it was still sub-3 at 100 yards (still good enough for a truck gun, at least).
Then on a whim, and to see what a new fired case would look like, I shot three factory rounds through it, which looked fine except for the typical primer flattening I like to avoid in my own loads. One solvent and one dry patch, and I was back to 1-1/4 to 1-3/4 5-shot groups with the 4-groove ammo.
Early on I had two Micro-Groove rifles I got rid of because they simply would not shoot CBs, regardless of diameter, alloy, load, lube, or anything else. But, that was before I read that shooting a couple of jacketed bullets would remove alloy deposits too little to be seen or felt, and could only be removed with mercury.
I never bothered to write a report on this, because just one instance doesnt prove anything, and the entire thing may have been a fluke.
But it does occur to me that just maybe a truly alloy free barrel is a key to CB accuracy in a Micro-Groove barrel. (The leading has more places to hide?)
Soon after that experience, I discovered mica, and then PVC wads (which fit 30-30 case necks under 170-180 grain CBs wonderfully) and Ive never needed to shoot another jacketed bullet through that barrel. The factory rounds did kick the finger lever down palpably, so I knew that whatever ammo wore the original barrel out also wore the bolt and locking lug a bit. A few experimental loads with powders in the IMR3031 class will kick the lever down as well, so I keep loads down below 1500 f.p.s., which meets all my requirements perfectly.
The forearm stock and magazine tube design of that Sears M336 doesnt lend itself to any relieving, so longer strings heat things up enough to cause scope zero to wander a bit, but when allowed to cool down a bit, itreturns, so it is still a 5-round lever gun, but no cleaning is required.
Ive been tempted to buy a decent-looking Micro-Groove Marlin used, just to follow-up on the clean barrel theory, but at todays prices? (Not to mention that seven 30-30s hanging on the wall is more than enough, with most requiring individualized CB ammo.)
