K31 Reloading help again! Bullets are too big?

[Patrick Chadwick]

The cartridge OAL means nothing to me at all.

Well it will if you can't get the cartridge into the magazine

Seriously, neither Uncle Ray's Q&D method not my SbP method will give the answer to the last thou, and I have seen myself how meplats vary. I already pointed out that even with the excellent Lapua Scenars the OAL varies with a spread of about 4 thou - for that very reason - the RCBS competition seater is indeed indexing on the ogive, as do most (I'm not going to bet on all ) top punches (odd name, one doesn't punch with it). However, we all refer to OAL, and you are right to point out that that is not what we really mean (or ought to mean?).

But these methods put you quite close for a good first approximation. When I have made such a measurement, I seat the very same bullet in an empty case with the top punch screwed right out, and then by trial and error screw down the top punch and re-seat it until the OAL is about 20 thou longer than the SbP measurement. I then "paint" a black ring around the bullet with a felt marker pen, let it dry, and then reload the case in the rifle. When the cartridge is removed, the forcing cone, lead, transition, throat or whatever you like to call it will have made tiny marks at the contact points. Again, reseat a couple of thou deeper, paint and repeat, until no marks are produced. At this point the seating of THAT bullet is such that it is just off the lands.

As already remarked, since every mechanical item has tolerances, I like to take that setting and back off 8-10 thou (.2 - .25mm) for the final setting. For BPCRs I make that 20 thou, because of the fouling that builds up in a competition where you cannot thoroughly clean the rifle between shots.

If you like, you can go for 5 thou or even less. It depends how much confidence you have in your equipment. But on simple mechanical considerations, a seating clearance that varies from say 8 to 12 thou is going to cause less shot-to-shot pressure variation than one that varies from +2 (i.e. just free) to -2 (i.e. cammed into the lands).

Patrick