The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

meles meles wrote:Hmmm, the brass will have gone thick at the neck, thus will hold the bullet too tight and give an increased pressure? So we needs to shave a fraction off the neck to compensate?

No, if the brass is too thick, you risk exceeding the maximum allowed O/D. In a tightly chambered barrel, there may then be insufficient clearance between case neck walls and the chamber hampering bullet release and seeing pressures rise substantially.

As an example, PT&G's chamber drawing for its 6.5X47 Lapua CIP Chamber reamer specifies 0.292" plus or minus one thou'. Typical Lapua 47L brass has neck walls 0.0125-0.0130" thick and Lapua / CIP specify a maximum neck wall thickness of 0.345mm = 0.0136". So if you had a box of cases all at the maximum and a chamber at PT&G's minimum tolerance with the usual a little over the nominal 0.264" bullet diameter - say 0.2644-inch, you get a cartridge neck O/D of:

0.2644 + 0.0136 + 0.0136 = 0.2916" against a minimum chamber neck diameter of 0.2910". So, on paper with this cartridge, if the tolerances run the wrong way, you have nil clearance and potentially serious over-pressure problems.

Even with everything at nominal dimensions, the round has an O/D of 0.290 v a chamber of 0.292", only 1 thou' clearance at any single point around the neck. Make the brass up by reforming 308 and it'll likely have neck thickness values well above Lapua's maximum and in in this case the resulting rounds (perhaps fortunately for the user) probably won't chamber. (There is always Murphy though with a strong right arm and failing that a mallet to make things go where they'd rather not!)

There is nothing wrong with reforming 308 for lots of cartridges, although I'd baulk at doing it with 243 with so much good and affordable brass around for the cartridge from very competent manufacturers. It is essential though to measure the wall thickness of necked-down cases either on the walls themselves with a tubing or case-neck micrometer, or by seating a bullet and measuring the O/D.

Hahaha... Badger, and you laughed at me when I tried to explain my simplistic approach to reloading last year..!

I make my 6mm Musgrave (a .243" as near as damn it) brass from sized down .303 brass and they all need neck turning inside (to get the right neck tension on the bullet) and out (to get them to chamber).

I certainly wouldn't bother with .243" for the reasons already stated, life is too short for some things.

Hmmmm, life might get very short....

Thanks for the explanation Laurie, we'll order a bag of proper .243 brass instead.

Well, we have some proper .243" brass now, so back to the subject: what powder should we be contemplating ? Our bullets are 90 grains, and we have both cast (gas checked) and copper jacketed to try... The barrel is 1 in 8 twist and 16" long.