Neck sizing vs full length

[RDHNTR]

I recently tried neck sizing with my Lee collet neck sizer on a proven load in my Mini 14. Versis the same load with the cases full length sized. Feeding was not a problem but accuracy was. The neck sized cases grouped approx .250 larger than the full length sized cases.Im not sure I understand it but would like anyones input on the subject.

[Bill_in_TX]

I recently tried neck sizing with my Lee collet neck sizer on a proven load in my Mini 14. Versis the same load with the cases full length sized. Feeding was not a problem but accuracy was. The neck sized cases grouped approx .250 larger than the full length sized cases.Im not sure I understand it but would like anyones input on the subject.This is just my guess (WAG if I want to be accurate). I'm guessing that the collet resizer does absolutely just the neck and doesn't touch the shoulder. I'm also going to guess that there's a (very) little slack in the bolt lock-up that allows the shoulder of the cartridge to expand forward upon firing.

Since the cartridge indexes on the shoulder, when you just resize the neck it's effectively increasing the freebore a hair. The bullet is destabilizing a bit more before hitting the rifling. Conceptually, I think it might be doing something similar to what happens in cases of throat erosion that you sometimes encounter with old military rifles.

Again, it's just a guess. It was brought to mind by a similar issue I'm having in a little pocket pistol. In my case the designer built in 0.25" extra freebore to keep chamber pressure down. That, however, has really caused some ammo selection issues. It's a 9mm and some 124 grainers are so bad that they keyhole out the barrel.

[kwg020]

I do an "almost" full length resize. Just enough to squeeze the shoulder down to ensure the round feeds well and I also neck resize. I have not checked for accuracy but I'm more concerned about reusing my cases, feeding into the chamber and the bullet staying in place in the case, especially if I load a large magazine. kwg

[steve4102]

When a round is fired in a bolt action the brass expands to the exact chamber dimensions, it then springs back just a bit to allow for easy extraction. This brass will be very consistent in size from round to round. You can neck size this brass a few times until the brass has expanded to the exact chamber dimensions. At this point the round will be difficult or stiff to chamber. It is now time to FL your neck sized brass to shrink the case body and bump the shoulder back.

In an auto-loader things are a little bit different. A round fired in an auto-loader expands to fit the chamber just like the bolt action. However, the brass is usually still under a tiny bit of pressure when the round is extracted. This extraction under pressure will cause the brass to become somewhat distorted. By distorted, I mean not an exact replica of the chamber, usually the head to shoulder measurements are affected the most and each piece of brass may measure completely different than the next. Especially, if you are mixing spent brass from different powders and loads. Consistency is the key to accuracy. If your neck sized brass is not all of the same dimensions from "head to shoulder" and case bodies chances are your accuracy will suffer.

Get a Stoney Point Gauge, FL size your brass and be consistant.

[Marlin 45 carbine]

I have 2 single presses in tandem. first one I have the full-length die set to size with die off the shell holder 1&1/2 turn then into neck size die. about every 4th loading I screw the full length down tight then check OAL and trim if needed (usually is) and chamfer. then neck size and load.

[Bill_in_TX]

"first one I have the full-length die set to size with die off the shell holder 1&1/2 turn then into neck size die."

That sounds like you're using the full-length die to just bump the shoulder back into position, which is what I was trying to say might be missing above in my long-winded guess.

[Alaskaman]

I recently tried neck sizing with my Lee collet neck sizer on a proven load in my Mini 14. Versis the same load with the cases full length sized. Feeding was not a problem but accuracy was. The neck sized cases grouped approx .250 larger than the full length sized cases.Im not sure I understand it but would like anyones input on the subject.

Hi,

in my opinion less neck tension is the problem. Add a Lee factory crimp !

Regards

Alaskaman

[cajungeo]

Some good ideas here. With my retiring and moving 3 times I haven't got my reloader out in a couple of years. This thread makes me want to dig it out of storage and start working the brass!:)

[totalloser]

I like Steve's answer. I couldn't have even guessed why the accuracy would suffer. I would have guessed it would be better. My advice to you is to FL size every time. Not worth the headache of a stuck case in the chamber. It's generally considered kind of a no-no to not fl size with autoloaders. My suspicion is that your brass would last longer anyhow as the fl sizer partly sizing combined with neck sizing seperately will work the brass more than just fl sizing. All my brass failures in .223 have been from split necks, so the neck I think may be the part you don't want to overwork.

My experience with loading for the mini has been that the most important accuracy issue is bullet weight, second charge weight (I have good luck with large charges of slow powder) and lastly, a crimp. Mini's, I believe have kind of a long throat, so a crimp can make a pretty big difference. Not ALWAYS true, but often.