Reboring and rifling a barrel - tips?

[303Guy]

Hi folks!
I bought this old Long Tom 303 Brit for the specific purpose of boring out to 375/303. I have cut off a bit of the barrel leaving 20". I have given the off cut bit a trial run at boring out to 9mm. That went OK but the dril bit did bite a bit and is in any case not long enough for the final job. This barrel has five grooves and the drill bit two flutes. Any tips and suggestions?

The final barrel length is to be 18". This is supposed to be my short bush carbine and is intended for cast bullets at around 250gr to 300gr with a muzzle velocity of 1800fps. For simplicity, I am considering three narrow grooves but have doubts as to whether that would provide enough driving to avoid forming a gas leak on the trailing edge. (My No4 two-groove barrel does that so I don't use it for cast - that's OK because I have a five groove 303 Brit that works just fine with cast and it's a Long Tom with a No4 barrel so low pressure is good for it).

[StarMetal]

Hi folks!
I bought this old Long Tom 303 Brit for the specific purpose of boring out to 375/303. I have cut off a bit of the barrel leaving 20". I have given the off cut bit a trial run at boring out to 9mm. That went OK but the dril bit did bite a bit and is in any case not long enough for the final job. This barrel has five grooves and the drill bit two flutes. Any tips and suggestions?

The final barrel length is to be 18". This is supposed to be my short bush carbine and is intended for cast bullets at around 250gr to 300gr with a muzzle velocity of 1800fps. For simplicity, I am considering three narrow grooves but have doubts as to whether that would provide enough driving to avoid forming a gas leak on the trailing edge. (My No4 two-groove barrel does that so I don't use it for cast - that's OK because I have a five groove 303 Brit that works just fine with cast and it's a Long Tom with a No4 barrel so low pressure is good for it).

You would need a piloted drill to insure it followed the bore straight. A regular drill bit with an extension would wander off track. Then you'd have to ream it get a smoother finish. How are you intending to rifle it?

Joe

[Cap'n Morgan]

+What Joe says.

You can grind a pilot on an ordinary drill if you have access to the machinery, or just grind it down by hand, braze on a bushing and turn the bushing to size. Still, you need to ream to finished size.