Why is this in the sidearms/knives section??
(Just giving you a little grief...not like there is a leverguns section and not really much of any better place to put it).
In any event...I have a couple leverguns that I have upgraded, as well as a Marlin 1895SBL that came prettymuch outfitted from the factory aside from a Burris Scout scope (2.75x) I mounted on it and some trigger/action work done by yours truly.
It all comes down to what you want to do, your budget and what you are expecting at the end of it all as to whether it will ultimately be a worthwhile project for you. There are plenty of levergun smithies that can help you out. You can go with a cut-down barrel to match up the length of the magazine tube, or you can go with an extended/modified mag tube depending on your barrel length and how short/handy you want the overall rifle to be and how much mg capacity you want/need. I like the XS sights a great deal and would suggest you stick with that idea. You can go with the straight add-on sights fore and aft, or you can go to the XS lever rail setup with the rear sight included and then just get the front sight to match. I'm not a huge fan of the Ramline stocks as they are pretty cheap and not all that beefy, but your other options for stocks that are synthetic and strong are FAR from cheap (i.e. - the MPI stocks for example).
The other consideration you need to think about is whether to hack up a perfectly good old levergun or if you just want to think about buying something like a newer 336BL (extended tube, shorter barrel, etc.) and adding the scout rail/sight and optic to it, etc.
You should also check out the Marlin forums for ideas, instruction, advice, etc. Lots of great info over there...see here:
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