No.4 Mk1 Barrel and receiver machinist drawings

[tbonesmith]

Plan "B" is to build a .30-.303, a chambering /barrel combo that has been around for several decades. .300 / .308 1:10" twist, just like a .30-06 barrel, BUT with a .303 chamber, cut using a reamer with a .299" pilot for the smaller bore. This actually works with the more abundant (and cheaper) .308" bullets out there. With a little creative carpentry, you can stuff a very chubby barrel under the woodwork of a No4 or even a No1. Naturally, the usual fun and games finding the "magic" load will ensue. Unless the reamer is custom-ground for a tight neck and throat (leade) this will NOT be a "bench-rest" chambering job, but it WILL function safely with .303 ball in a pinch. If you plan to ONLY EVER shoot .308" bullets no longer than the 168 SMK, you will probably get away with the even more common 1:12" twist barrel in your choice of Moly or stainless. If you are not doing virtually all this work yourself, carefully check the hourly rates at your local gun-plumber.

I got a reamer custom ground for this a few years ago and built a rifle up for a guy. I ran a new heavy sporter 1:12" twist barrel and set it up in L42 style wood. I tested it with 155gn sierra SMKs and it was just magic. With the vast array of 30 cal projectiles available and the reliability of the feeding and function of the .303 round in the action I'm surprised it's not done more.