Post by triggersqueezer on Sept 18, 2014 19:02:34 GMT
i could be wrong but to controll neck tension you need a bushing die so you can buy different sizes.if you measure a sized round then a loaded on the difference should be a good indicator.what makes you want to change it?
You need neck bushing dies! my .260 Ack Imp has 2though neck tension i use a .284"thou bushing. with a .264 bullet and neck thickness of .11thou so a loaded round will measure across the neck of .286"thou
Following through a thread over on That other forum (apologies but I do look and post there also!) confirms my long-held understanding that an expander mandrel should leave enough neck tension to retain a bullet satisfactorily....but... I have used the K & M mandrels in 260 Rem (6.5mm) and 6mm with good results but when using a new 308 mandrel the other day to ease excessive neck tension on virgin Lapua brass the result was that the bullet slid right through the case with very little hand pressure ! Suitably bewildered I went on to use a neck sizing bushing die to correct matters. I measured the mandrel and it shows .308 to .3085 depending on my level of dexterity with the calipers. I would have expected enough spring-back after expansion to give me .001" or more of NT but clearly didn't get that result in this case. I am thinking that either the brass is not exhibiting the expected spring-back (batch problem?) or the mandrel actually IS that little bit over-sized OR I simply have misunderstood their usage all these years! Any thoughts or experiences very much appreciated.
Either way I will be neck-sizing as a precaution after using an expander in future as I was lucky to get away with the neck sizing operation having already charged the cases and had to take out the decapping assembly.
Yeah, I meant what is the diameter of the expander in the neck die. If you compare that to the diameter of the new mandrel, and the new mandrel is bigger then that is your problem. Doing it that way also cancels out any inaccuracies in whatever you are using to measure them with.