[30Caliber]

I don't know that your results are right--I think you're setting the shoulder back by pounding the case into the chamber.


To find the length to the lands, take a properly sized and loaded case and stuff it into the chamber with your thumb. If it drops out just by tipping the muzzle up, then the bullet is not in contact with the lands. So what you do is seat a bullet long, then check it; keep seating deeper until the case drops out on its own. This is a lot easier and more repeatable than say the RCBS precision case mic. It also makes it easy to set the jump since the seating die is now set to jump=0.

 

[30Caliber]

Yeah but jump = 0 = higher pressure, from what I've read. I just read the Speer manual, says .060.

But if we go back to my OP, has anybody else had high pressure signs from short jumps? Signs that went away with deeper seating? What is the optimum jump in an M14? How much is too much, before pressure rise due to lower case volume, like raising the compression ratio in an engine? I know 'pinging' is bad...

I wasn't saying you'd want 0 jump. You can measure the ctg OAL at that point and then dial the seating die down to get the exact jump you want. The standard match bullets work fine with 0.020" jump.

I get flattened primers (WLR and Rem) at nominal velocities with 0.020" jump.

 

[30Caliber]

The SMKs are fairly insensitive to bullet jump. You might gain a little by moving them out.