Micro-Groove for Patched Bullets?

[Bent Ramrod]

Of course, the conversation has gone round and round about the suitability or otherwise of Marlin's Micro-Groove rifling for cast bullets, and this design seems to have caused enough people enough annoyance that Marlin offers the option of Ballard rifling for CAS and other cast lead shooters in their more traditional rifle designs.

However, the semi-old literature often made the claim that the reason paper patched bullets didn't work in current (1920'-1930's) rifles was that the old barrels were shallowly rifled especially for paper-patch bullets and the newer, deeper rifling did enough damage to same to make the accuracy not worth bothering about.

Modern experimenters have proven that claim untrue, but what about the older, paper patched rifling? Would a Micro-Groove barrel show better accuracy with paper-patched bullets than it would with grease groove ones? Has anybody tried this and noticed anything?

Just a random thought in the AM as the coffee finally kicks in.

[felix]

BR, your "thought conclusions" are correct. The purpose of any kind of jacket is to increase friction to enable the projectile to have more accurate tracking with the lands. The jacket material must be able to withstand the friction, by percentage enough to maintain desired accuracy. So, what you pick as the jacket material, for operating in a given land configuration, is the challenge. ... felix

[longbow]

Bent Ramrod:

So far I have had pretty good results with paper patch boolits in an 1894 Marlin .44 mag with 1:38 microgroove rifling.

The boolits I have used are 0.421" so undersized for the 0.425" bore. I patch them up to about 0.432". The main reason I started was to try a heavier boolit of around 300 gr. so I made a mould that produces a smooth sided slug and tried paper patching. It went pretty good and patches weren't burned but accuracy wasn't good past about 75 yards. Out to 50 accuracy was much better than with the Lyman 429421 but I don't find it shoots well in my gun. Beyond 75 accuracy fell apart.

In the end I decided the problem was the slow 1:38 twist with the heavy boolits as I get good accuracy out to 100 yards with both grease groove and paper patch boolits up to about 265/270 gr. which results in the length the Greenhills formula says is max for 1:38 - coincidence? Others seem to do better than I with heavy boolits. Maybe better boolit design?

Anyway, back to the question, yes I have gotten good accuracy with paper patch in microgoove rifling.

I will be doing some testing for no34570 with some knurled boolits to bring diameter up to about 0.434". I will be recording boolit diameter, patched diameter and accuracy. I just have to get in gear and get it done. I'll post results good or bad.

Longbow

[pdawg_shooter]

M.G. rifling tends to displace more paper than standard rifling. This requires a tougher patch. I found that sizing to bore dia. and patching with 16lb, 100% cotton fiber paper works well. I tried 9lb, and 12lb and the patch just wouldnt stand up to the trip down the barrel. Accuracy was bad and there was some leading. With the heavier paper, and better paper, the accuracy is as good as my Ballard rifled barrels.

[Bent Ramrod]

Thanks for the information, pdawg. Maybe the paper patch is the fix for those microgroove guns that don't like cast boolits.