Reloading .303 British : Case Neck Concentricity

The cases had been neck sized several times and with these moderately high power .308 loads, a fired case shows just a bit of resistance when chambering in the last 1/16 inch of bolt travel (space between bolt handle and receiver wrist). I could have necked sized these cases again, but wanted to try out the new die.

I did not “full length size” the cases per se, but set the die position in the press such that the case shoulder was pushed back by .002 inches as compared to the fired case.  I did this with the use of a Hornady Case Headspace Gauge, setting the case headspace to 1.626 inches (fired cases measured 1.628 inches).  I confirmed by chambering the “partial length sized cases” that the bolt fully locked with only the slightest hint of very light resistance just before the bolt handle touched the receiver.  That way, the case head is seated against the bolt head on firing and will minimize case stretch. 

Checking fired and sized case neck runout on the RCBS Casemaster gauge showed fired case neck runout < 0.001 and sized case neck runout < 0.002, and I’m quite happy with that. 

I like having the complete control to set neck tension.  I sized the first 5 cases using a .334 inch diameter bushing, checked the neck ID with a pin gage and it was a bit small at .3035+, I think that’s more neck interference than desirable with a .308 bullet.  The .335 bushing gave me a neck ID of .3050- with that size pin gage, giving a .003 inch interference with the bullet, about just right. 

Next step is to load these cases up with 168 grain TMKs using the Wilson In-Line Bullet Seater, measuring the force needed to seat the bullets then measure bullet runout.   

I’m not really expecting these loads to shoot any better than the previous loads with cases neck sized in the Lee Collet Die, but will be happy if they perform equally as well at Long Range. 

Now, I’m not suggesting you guys need to go run out and get these dies, I did this to satisfy my own curiosity and to fix a significant bullet runout problem that was costing me points with my .223 Rem 600 yard load using the 80 grain SMK.  That naturally made me curious if it might improve my 800 and 1000 yard results with the 168 and 175 TMKs in the No. 4 7.62 DCRA.