Neck sizing question

[M113A3]

Just starting out and have the Redding Competition Die set. In setting up the neck sizing die per the instructions it does the full neck although I have read some folks find doing less has been better for their rifle. Should I just start out and do the full neck and only adjust if needed?

Additionally what might be some of the reasons to do less of the neck? Something to due with the neck tension and seating depth. I guess this might impact velocity although this is only a guess.

BTW I am reloading .308 using once fired Federal brass and will start out loading 175 SMKs.

Thanks,
John

 

[spife7980]

I would start out doing the whole neck if only for the sake of uniformity. Once you get a load dialed down you can start to vary it and see if the corresponding changes in bullet grip make it better or worse.

Sizing less of the neck will lessen the amount of bullet grip/bullet hold that the brass is imparting on the bullet. Yes, it might impact velocity but only to a minor extent, most of a bullets velocity is developed once its sealed off in the barrel with the expanding gases behind the bullet driving it forward. The changes in amounts of neck sizing corresponds to increasing or delaying the departure of the bullet and thus bullet timing, much in the way that seating depth does. If you need to delay the bullets arrival at the muzzle to get it in a more preferable area of the harmonics you can seat it deeper or you can hold it tighter which will delay when the case releases the bullet. Its a bit of give and take.

Theres no pre written prescription for any of this, its just trial and error and controlling your variables.

 

[M113A3]

Thanks for the reply. I will hold off on the fine tuning of the neck sizing and bullet seating depth until I work up a load I think will be a good starting point for my rifle.

Cheers!

 

[Diver160651]

John,

The adjustment is more more not crimping the neck/shoulder junction or creating doughnuts in your brass than “how much of the neck” you size, but ya, that also could be used to over think the process.

Jim

 

[Greg Langelius *]

I'm one of those who only resize the neck partway down. I'm hand loading the .260, and making up my .260 brass by necking down 7-08. I do this by simply running the 7-08 through my 260 F/L die using the sizer ball, and adjusting the die so the case only enters far enough to resize the last 1/2 of the length of the neck. the diameter difference is only .5mm, and this does not appear to be an excessive deviation. These cases will still chamber without any appreciable additional bolt drag, and fire conventionally in regular use.

Why? Just some hunches of mine.

I think the interference fit between neck and chamber more positively centers the cartridge's forward portion relative to the bore axis, working toward using the chamber itself as a concentricity aid.

I also think the shorter resized portion of the neck produces a lighter overall neck tension, which is something my testing from well over a decade back suggested aids better accuracy. By doing this with a F/L die axially instead of diametrically with a bushing die, I believe I can 'manage" neck tension more economically, and maybe also more precisely.

I have also noticed a very clear difference in the carbon staining on the forward case area. Conventionally sized case have carbon reaching down below the shoulder. My cases have no carbon below the flare in the case neck. I interpret this to mean that my method results in more positive and definite case sealing under firing pressures.

I don't run peak pressures in my ,260 loads, preferring to use a 28" barrel to get my velocities, rather than using bore destroying hot loads. Consequently, I am not encountering shoulder growth to any significant extent, as should be the situation with hotter loads.

For me, the strategy appear to work without issues. YMMV.

Greg