Keyholing Marlin 30-30

[greer]

I've got a Marlin 336 (microgroove) 30-30 in the shop that at 30 yds  keyholes the bullets through the target. Everything looks fine as far as the bore and the spent cases. Something I did notice is that on the barrel it says" R.C. 30-30" right where the cartridge should be listed and it all looks very factory. I can't remember if I've seen the "R.C. "on other Marlin 336's. The ammo was factory Win. 150 gr. I need to talk to the owner who has not shot the rifle and got it from his father, also check the twist . I just wondered if I was missing something obvious. I was sure cussing my boresighter when at 50 yds I couldn't hit a poster size target.
                                                                               Thanks. greer

[Iowegan]

Marlin Micro-Groove barrels don't like lead bullets at all. If the previous owner fired lead bullets, there could be enough corruption in the barrel to prevent a jacketed bullet from spinning. Spin is what keeps the bullet stable down range so whatever is wrong, it has to be related to the bore. In extreme cases, I have seen a bad crown cause bullets to loose stability too.

[greer]

Thanks Iowegan,
 I'll check for that. I hope to talk to the fellow tonight. I'm still wondering about the"R.C. 30-30 "on the barrel. Could it mean rimmed cartridge? It looks like the factory stamped it.              Thanks again.  greer

[longgun]

The RC stands for regular carbine,  I read that somewhere.   don

[greer]

Thanks, Don.  Doug

[jed]

Check for bulge ring within an inch of crown,  Could have been fired with snow in muzzle causing ring.

[gunnut69]

I've not seen the 'RC' stamp before. All of the above can cause stabiklity problems. Bad crown, bulged bore, excessive leading and a custom twist rate. I would also check the bore diameter. I've seen rifles suddenly turn sour that you could feel the diameter variations in bore diameter. Best explanation I've heard is the rifle was fired with oil in the bore. The result is a 'stretched' bore. A tight patch on a jag will be difficult to push then easy. Usually this alternates for the whole length of the barrel. As you might guess accuracy after massaging the bullet like that then allowing the pressure to expand it to fit the normal bore again is NOT condusive to great accuracy..