7.62 NATO No4 barrels

[bigduke6]

Just wondering - do you know what the groove diameter in the 7.62 mm No 4 barrel is? How much under-size from a standard No 4 barrel is this?
reason I ask, is: I note in the UK that No 4 barrels in .303 cal are very scarce, but those chambered to 7.62mm Nato are available.
My question is this: Could the 7.62 barrel be reamed out to take the.303 case, and could the bore cope with a standard .311" ( = .303) bullet?
And, if not, would the neck or full length resizer in a standard reloading die allow a .308 bullet to be seated into a reloaded .303 case, making a rimmed .308?
And, if this conversion was done, would it pass Proof? And would the calibre still be .303?
Just wondering...

Rob, some good questions and was asked similar last year, the case neck can be resized using a .308 die, so that's not a problem, regarding proof house think something like this you can provide them with the cases etc, as its a wildcat round probably proofed as a .303/.308.

As regards to re chamber its a no go as the 7.62mm/.308 chamber is to fat for a .303 reamer, the solution would be to bore out the 7.62mm chamber and then make an insert in .303 I,m not sure if anyone has done this and if it would be any good?

As regards to the reamer you would need to get a .303 reamer reground on the neck to the same as .308

To be honest the easiest solution is to use the 7.62mm barrel as it is.

I took in a No4 Mk2 barrelled action some time back in 7.62mm (its one of the Belgian barrels that was in a recent thread) I had the woodwork but shelved the idea. Its only due to recent post from thunderbox that I,ve looked at rebuilding it plus I use a lot of downloaded ammo now, and with x amounts of unique powder and a 110 grn round nose .30 bullet produce excellent results.