Marlin Guide Gun barrel specs

[Westerman]

The Marlin web site says the 45-70 Guide Gun features a "deep-cut Ballard-type rifling (6 groove)" barrel.

I'm thinking of a bore ride cast bullet with front band same length as throat.

Anyone here have land and groove diameters?

Throat length?

Thoughts?

Thanks

[BABore]

I just went through whole thing on a new barrel for my 450 Marlin GG. First off I would slug the bore. An egg sinker inserted in the muzzle just below flush measured 0.4852". One driven all the way through measured 0.4573". You could feel the constrictions under every dovetail cut and roll marking. If I had started shooting cast right away my bullet would have been 0.0009 undersize by the time it went through the last bit of barrel. I ended up using a Beartooth lapping kit to straighten things out. Group size went from 1 1/4 to 1 1/2" to practically one hole at 100 yds.

I then did a cerrosafe casting of the chamber in preparation of getting a custom mould. All of this data and discussion is on Mnt. Moulds forum. My final, and most critical work was on nose configuration and length. Using my throat dimensions I thought I had it all figured out. Then I tried some similar designs seated to approximate my wishes. They would not load through the magazine loading port. You are dealing with a 2.55" COAL. This length doesn't take front band size and length, and meplat dia. into consideration. I had to make some sacrifices to get things to work out. Desiring a 75% meplat, I had to go with a 0.425 long nose at my land dia. of 0.452". Bigger would have been better but with the limited camming action of a lever I went the safe way. Most all lever action bullets, that are commercially cast, have a similar nose diameter and a length of 0.400 to 0.450". The length is dependent on the meplat size. There are ways and smiths available to alter the Marlin action to feed longer rounds. I was seriously eyeing my Dremel for a few moments.

[Dutch4122]

My Marlin 1895GS throat measured at .091" with a jacketed slug seated backwards in the case; and the barrels grooves slugged at .4575" with a Meister Bullets bore slugging kit.

Best to slug your own bore and check the throat length as well on your own rifle as your mileage may vary.

Hope this helps, :)