sluged bore on 303B now?

**MIKE P** · November 16th, 2009, 05:02 PM

i slugged the bore on my 303 brit it measured .3125-.313 in the groves
& .311 on the bore
my bullets measured .311 copper jacket sierras
so im wondering if the .002 difference betwene the groves & boolits dia. is my problem with inconsisentcy at the target

i read were one needs to slug the bore to see what you got but cant find what to do with the info or how to use the measurements

**Dave in PA** · November 16th, 2009, 06:15 PM

Yeah, ideally, your bullet will generally be the same as the bore diameter, not the groove diameter. That will ensure a good gas seal and positive engagement in the rifling.

**knight0334** · November 16th, 2009, 07:17 PM

Originally Posted by Dave in PA

Yeah, ideally, your bullet will generally be the same as the bore diameter, not the groove diameter. That will ensure a good gas seal and positive engagement in the rifling.

Ideally you want a bullet to be the groove diameter, not the bore diameter. The rifling then swages the bullet to to engage spinning. Examples would be: a .308" bullet in a 30-06. The bore is .300" and the groove is .308". Or the 45-70 with .458" bullets - .450" bore and .458" grooves.

**Brick** · November 16th, 2009, 07:35 PM

Simple, if you load cast lead bullets or if you cast your own, get them sized to the groove diameter of .313". If you load jacketed bullets purchase those closest in size to the land diameter .311".

Simple rule to remember, cast and swaged lead (and the copper plated lead bullets) are sized for GROOVE diameter. Jacketed bullets are sized for LAND diameter.

Refer to Lyman or Lee reloading manuals.

**MIKE P** · November 17th, 2009, 09:04 AM

so are you saying the winchester store bought factory ammo that measures .311 would be accurate in this barrel ?
even though there's .002 air gap in the rifling groves????

**hornady** · November 17th, 2009, 09:19 AM

It may just be me but I never heard of slugging a barrel for Jacketed bullets, Unless you suspect the barrel is shot out. The 303 Brit. Is an old War horse. And most were accurate for there intended purpose. But these rifle are getting old. And being Mil-surplus. God only knows how many rounds have been through them. The 303 shoots a standard .311 jacketed bullet. Now if you intend on loading cast bullets. Yes you shoot a slightly over sized bullet.

**Tim Ault** · November 17th, 2009, 06:57 PM

More than likely the .311 dia. will shoot fine . More importantly is the condition of the muzzle/barrel crown .If its worn from improper cleaning its a crap shoot .

Tim

**MIKE P** · November 18th, 2009, 08:32 PM

well im sending the barrel to be recrowned by my sons boss a professional
will try that first thanks for the info
this rifle shot fine (i been useing it every year science 1992) before i used bore cleaner to remove all the lead & copper & a lot came out