Rebarelling the No.4 action to bigbore.

PoFF

PoFF

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Last time I went shooting in my hometown, the gunsmith that owns the range show me his latest work, he took a Lee-Enfield No4Mk1 action, and fitted a custom 18 inches .458" barrel with a 450 Marlin chamber. He lightly tweaked the extractor to fit the slightly bigger rim and modified the magazine to hold 5 cartridges in a single stack position.

This package seemed to be a nice option for a light and powerful woods repeating carbine, but I was wondering if the No.4 action was strong enough to handle the power of the 450 cartridge on the long run.

Any comments on this?
 
Not sure how the Marlin 450 operating pressures compare with the 45-70, but I know the .303 Enfield conversion to 45-70 is a fairly common one.
 
From my informations, factory 45/70 has a SAMMI rating of 28000 psi, while 450 Marlin is operating at 43500 psi.
 
SAAMI pressure for the .303 is 49000 psi but the "thrust area" is slightly smaller than the .450 Marlin. The bolt thrust from the .450 should be comparable to the .303 but I haven't actually calculated it, I'm just basing that in the realtive sizes of the case head.
I have been thinking about this conversion for a while but haven't had time to do anything about it.
What I don't know is if there is enough metal surrounding the chamber of the450 cartridge. When I get the chance, I will measure the chamber wall thickness on my Marlin 45/70.
At first glance, it looks like it should be OK.
 
In a word "yep" no time soon but definetley some day. There was a .40 cal barrel on the board cheap but I missed it. I am currently patiently waiting for my 45-70 mauser to come from the gunsmith. could be another 6 months but patience is my strong point. That project , stocking, load developemt, sight regulation will keep my big bore interests satiated for a while but once that is done I am on to the maynard project.
 
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