303 brit

J

J10archer

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Kingston, Ontario
so I'm getting ready to do a bunch of "plinking" 303 British. I'm planning on making them fit the many guns my friends and I have. My nicest pice, no 4 mki. I noticed the bore is measuring at .308 and the factory Winchester rounds are .308 as well. I ordered .311 am I missing something? What and/where should I look or measure/test more? Any help is much appreciated
 
Maybe want to confirm the terms that you used?? The "bore" is the hole drilled down the barrel. You say it measures .308". The bullets need to seal tight to the bottom of the grooves - in a No. 4 the grooves are typically .004" deep - so grooves on each side, that ".308" bore" barrel is asking for .308" plus .004" plus .004" equals .316" bullets. So the barrel sounds like a .308" bore and .316" groove barrel. That would be well worn, about .005" over original spec, but not unusual to find, at all! Unless you have pulled the Winchester factory bullets out of the cartridge case, you are not likely measuring at the bullet's widest diameter.

You can use a pure or soft lead "slug" and slug your barrel - take a ball of soft lead about .325" or so and gently tap into the muzzle, and perhaps a few inches into the barrel. Then use a cleaning rod to tap it back out. Your "slug" will now have reverse impressions of the grooves. You can measure them with a calliper - unless you have a five groove barrel!!! Accurately measuring a diameter from 5 grooves takes some fancy math and some special tooling that few of us have.
 
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Thanks. I was looking at this late last night after the little one went to bed. You are making sense. It is a 5 groove barrel. I will slug it, i will do it for fun an interest. Thanks Potashminer
 
Buy bullets made for the 303. They are typically 311 to 312.

I suggest full length sizing the brass, if it will be used in a number of rifles, but back the sizer out 1 rev from touching the shell holder. This will reduce the working of the brass and it will last longer.

Also, for the same reason, load the Start load. easier on the brass and the shoulder.
 
Snider shooter said:
Five groove or any barrels with odd number of grooves is impossible to measure without special tools. Use the 0.311 or 0.312 bullets and you should be fine. The only problem I had was one of my rifles didn’t like boat tails.
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measuring them by turning the slug works that's what martini henry shooters do with that 7 groove henry rifling. my Lee Enfield mle measures out at .316" at the muzzle
 
Thanks gentlemen. Snider shooter.ganderite.Potashminer. over thinking it while trying to raise my little monster. I will pull one of the Winchester bullets. I do have .311 and .312 on the way.
 
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