I'm looking for the base diameter of 243 Winchester brand brass. Not the rim but the largest diameter of the body.

After reading about forming 22-250AI brass from 243 brass on Varmint Al'sweb site I thought I would give it a try. I formed my cases from Lapua brass and found it would not chamber in my gun. The base diameter is .469 which is about .004 too large for my chamber. Fire formed 22-250 cases from my gun show a base diameter of .4645.

Al responded to my e-mail saying Winchester brand brass worked for him. I don't have any to measure.

xp-guy:; my win. new brass in 243 measures
.2661"

22-250 new win. brass measures .2638"
I measured 10 in each caliber with + - .0002"

243 chamber should be .4714"
22-250 chamber should be .4681"
I wonder how varmint al formed his brass?

for my 243 AI i full length resize then fire form . the die i use was cut from the same reamer that was used to ream the chamber.

hope this helps ..

You will find that new brass will vary a few thousandths, from lot to lot, and manufacturer, Lapua 243 brass is "big" compared to most US brass, which is mostly undersized, according to sami specs. The best thing to do is take your caliphers shopping with you, and measure before you buy.