Necking down from 7mm to 6mm - how much to neck-turn?

R

rifledeerhunter

Guest
I'm necking down RWS 7 x 57 brass to 6mm to make my .240 PSP brass. The unloaded outside neck diameter before I neck-turn is 0.279 inches after I neck down with the full-length .240 PSP sizing die with the expander ball in place. My chamber reamer drawing has three diameters for the neck, near the mouth the diameter is 0.2770, two thirds down the neck it shows as .27892 and at the neck/shoulder junction it shows as .2790 on the drawing. As this is for a hunting rifle, what outside neck diameter should I neck-turn to either without the 6mm projectile in the neck or with the projectile in the neck? Thanks for any advice.
 
At .277" you may (probably) not have to neck turn at all. I would use the smallest dimension for calculating clearance.

whoops- just re-read your post and see the .279" is after sizing. disregard the no turn required. :eek:
 
Last edited by a moderator:
If I turned to a loaded .274 with .0015 clearance either side and thus have a slightly thicker neck, what disadvantages might I have? Wouldn't the necks last longer (being thicker) than with the suggested .271 with .003 either side?
 
Last edited by a moderator:
rifledeerhunter said:
If I turned to a loaded .274 with .0015 clearance either side and thus have a slightly thicker neck, what disadvantages might I have? Wouldn't the necks last longer (being thicker) than with the suggested .271 with .003 either side?
Click to expand...

.0015" neck clearance is probably not a good idea in a hunting rifle. For one thing if the necks grew a little thicker when fired or you changed to a different bullet you might end up with an excess pressure situation. You are just asking for trouble when there is virtually nothing to be gained.
 
Clearance PER SIDE!

rifledeerhunter said:
If I turned to a loaded .274 with .0015 clearance either side and thus have a slightly thicker neck, what disadvantages might I have? Wouldn't the necks last longer (being thicker) than with the suggested .271 with .003 either side?
Click to expand...

.003 PER SIDE is a lot. Many shooters order reamers to cut a chamber neck with about .002 to .003 TOTAL clearance with un-turned cases. Shooters sometimes get into trouble if they make a mistake or don't know the actual neck diameter of the chamber, but .003 actual total clearance (.0015 PER SIDE) should be fine. As to whether they last longer; probably yes, as long as your size die is a good match to your chamber and doesn't work the brass more than necessary.
 
Any clearance is OK

But listen to those that know best. Determine the diameter of the bullets you'll use and turn your necks to suit the largest diameter. By that I mean turn your necks such that a loaded round will be a bit smaller than the chamber neck diameter- clearance if you will. Write that diameter down and note each (lot of) bullet you use is that diameter or less. Don't guess or use anything but actual measurements when doing this. Keep your chamber clean.

Get a die that doesn't use an expander mandrel, pick a neck bushing that works and you're all set for the best possible accuracy.
 
Cool - Make sure your chamber matches the drawing and you're all set. Measure new bullets to make sure you're not going over the line. It wouldn't be terrible to measure a few loaded case necks now and then just to make sure you have SOME clearance remaining.
 
You must log in or register to reply here.
Back
Top