I've got a .44 Magnum barrel that I bought a few years ago from the Gardner MA facility. It has 12 each shallow grooves and lands. I don't know if it fits the technical definition of "microgroove" but I've had the idea that it does. Because of the CAS situation and how most of those shooters feel about microgroove, I don't know if Marlin is still making .44's using that design rifling. When they were, they had the 12 grooves and lands as my Handi barrel has. What I don't know is, if the lands in my Handi barrel have the same geometric profile as a technically microgroove barrel. What I do know for sure is that it's oversize, more below.
I don't shoot this barrel very often; in fact, I only bought it because I have a revolver in the same caliber. I haven't taken shooting it very seriously, and when I have fired it, it's been with jacketed bullets that have given me so-so accuracy at 100 yards. But then again, I'm shooting it with the original open sights with 58-year-old eyes. The last time I had it out, I peppered a pretty good 10 inch shotgun pattern at 100 yards.
Well now, jacketed .44 bullets have gotten rather expensive lately so I decided a while back to cast some up for use in this barrel. Having the benefit of reading posts on this site, I was aware of the .44 Magnum barrel oversize bore issue. For that reason, I slugged the bore in my .44 Handi barrel and sure enough, it measures .432 across the grooves and .427 across the lands.
Before I forget, here's a link to a fairly well thought-out post on another site re. the microgroove barrel situation:
http://www.leverguns.com/articles/fryxell/microgrove-barrels.htm If you read through that article, you'll see that the author suggests that there isn't anything inherently wrong with shooting lead bullets in Marlin microgroove barrels, so long as you get the bullet size matched to the size of the bore.
So starts the problem. Nobody makes a .432 or .433 sizer/lube die as a regular item; special orders are a possibility at high cost. A lee push-through sizing die can be custom ordered for, what, $30 or thereabouts, but that commits you to use liquid alox lube that isn't necessarily compatible with the design of your cast bullet. You can always use your bullets in their as-cast size if they come out oversized to approximately what you need, but then you are going to have to pan-lube them and that's not my first choice.
My mould is a Lyman 245 gr. Elmer Keith bullet, and I already had a Lyman sizing/lube die in .429 and .430. The .429 sizing/lube die I probably wouldn't use as it is undersize for any use I might anticipate.
The bullets cast in my Lyman 4-gang mould block drop out at .433, just about a perfect size for my .432 presumambly Marlin-made barrel. My solution for lubing these was to take my .429 lube/sizing (Lyman calls them an "H&I die") and hone it out to .4325. I did this carefully on my drill press. I took a piece of dowel slightly over 3/8 inch, cut a kerf in one end, and inserted a small strip of Emery cloth which I wrapped around the dowel. Carefully, I honed out the H&I die making sure to rotate it around while honing to ensure uniform concentricity (as much as I could Mickey-Mousing it around such as I was). I used cast bullets to check it for size periodically while honing, and after not too long, I got it opened up to .4325. I made a quick pass with some 320 sandpaper to finish it off .
Basically, the idea in this case is to use the H&I die for lubing only. I want the bullet in its as-cast size, but want to use the H&I die to perform the lubing process.
Part of the H&I die set is the metal rod that goes in the cylinder. The bullet sits on this rod (or round) inside the actual die while it is being sized and lubed and this metal rod is exactly sized to fit closely without friction inside the die. When you hone out the die, the bore size is greater than it ought to be in relation to the metal rod that fits inside it. The extra clearance between the die and the rod allows some sizing lube to leak out into the area underneath the bullet. When this happens, as you lube bullets you have to clean this out every pass or two, which is a pain in the neck. The H&I die has rows of holes along the sides to allow the sizing lube to flow into the lube groove on the bullet. Since my .44 bullets only have one groove, I only needed two holes open on the sides of the die, opposite each other spaced at 180 degrees. These holes are 1/8 inch diameter. I took 1/8th inch diameter roll solder and plugged all of the holes except the two that were needed to lube my bullets. This was pretty easy; I just left the metal rod inside the die, then stuffed the solder into the holes one at a time and cut them off. With the stubs of solder in place, I seated them by pounding with a copper hammer. Then I put the die in a padded vice and filed the excess solder off with a non-ferrous metal file. Finally, I gave the inside of the die a quick dress-down with #320 sand paper. With these excess holes plugged, the lube only goes through the two that I want and very little excess gets between the rod and the bore of the die.
You'd think that a .44 is a .44, but it ain't necessarily so. I have a knack for encountering goofy challenges in the calibers I reload, so this one doesn't surprise me.
I read that this overbore problem has been sorted out by now, so that's a good thing. I don't recall exactly what year I bought my .44 barrel but it might have been before 2006. I've also read that Marlin corrected the problem circa 2006; but Marlin may have been making some barrels for NEF before purchasing the company. Marlin has made barrels for many other companies over the years including the M-1 rifle.
