Marlin 450

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mtngun
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Marlin 450

Postby mtngun » Thu Feb 21, 2008 7:50 pm

from the old forum, perhaps posted by BAbore ??? :

I finally got my 1895M 450 Marlin rebarreled, lapped, and a chamber cast done. Now it's time to get serious on a mould. Here's what I got.

Image

I also saved my AutoCAD drawing as a bitmap if you can't see this well enough. Don't quite know how to post that though.

Before I fire lapped the bore it had constrictions of 0.001". A full push through sinker was 0.4571". A muzzle slug measured 0.4581. The bore was extremely rough prior to lapping. A full push through slug now measures at 0.4583". Group size went from 1 1/4"-1 1/2" at 100 yards to basically one hole. My first ten bore conditioning shots went into 7/8" at 75 yards with five complete cleanings. So now I'm ready.

Looking to design a 420 gr OFP bullet with a 73% meplat, Hornady step shank and most likely two driving bands with a 0.8 or 0.9 ratio. The nose length and front driving band are what I would like some help on. The chamber cast looks to have an extra 0.137" in length before going into the leade and throat. I also have to contend with the 2.55" OAL. Any good suggestions.

I forgot to mention. The 0.4595 dimension, on the chamber cast drawing, is just where the throat ends. not farther out.
Image

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mtngun
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Joined: Fri Feb 01, 2008 5:45 pm
Location: Where the Salmon joins the Snake

Re: Marlin 450

Postby mtngun » Thu Feb 21, 2008 7:52 pm

OK, you're saying the throat has a gentle 1.3° angle? Beautiful !!!!! The freebore diameter is oversize, or at least it is now that it has been firelapped. Oh, well.

If I understand you and the drawing correctly, you have 0.187" freebore as measured from the case mouth. Ahead of the freebore, there is a gently tapered section that has some rifling but is still oversize. That gently tapered section is about 0.250" long, correct???

My advice, for what little it is worth: a full diameter tangential ogive would probably chamber fine, maybe even with a 0.150" long front band. It is impossible to predict with certainty if such a nose would engrave at all -- probably not -- or if does engrave, how hard. Considering this is a lever action and a hunting rifle, I would err on the side of reliablity. The nice thing about your gentle throat is that it will help guide the nose in straight even if the nose doesn't engrave when it chambers.

Regarding the nose length, whatever feeds best. A 420 grainer is not going to be hurting for powder space, so if a 0.425" feeds better than 0.450", go for it.

Thanks again for the invaluable throat information.


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