Neck resizing question

[rnhunter]

My gunsmith recommended that I do neck resizing only to help with accuracy. I did buy a neck resizing die and followed the instructions on the RCBS sizing die. For some reason I can't get the resized shells to chamber in my rifle. My gunsmith has said that he runs his chambers pretty close to specs. Any idea what is going on? Im just not experienced enough with neck sizing only as I have done FLS. Also, I have heard that neck sizing can increase pressures, is this true and why would that be. Thanks gentleman.

[azslim]

did you check and trim case length?

[rnhunter]

Yes, I was under SAMMI specs.

[112coues]

Is the brass already fire formed to your chamber? If its not you probably should full length it first

[STOMP442]

Sounds to me like you need to bump the shoulder. Only need to move it .002 to chamber properly. Neck sizing can be done with a full length die as well just back it out a half turn. Most of the time you can get away with just neck sizing for a few firings before having to bump the shoulder but if you are running a stiff load it may require bumping each time. By bumping it a couple thousandths you are not over working brass as you would be with full length sizing.

[rnhunter]

Yes, the brass has been fire formed in my rifle. How do you "bump" the shoulder? I have reloaded doing the basics for most of my life but have to admit I'm not sure how to bump the shoulder.

[WampusCat]

Neck sizing only does not guarantee better accuracy.

 

You will need a comparator style gauge from sinclair or hornady to use with your dial caliper to measure the fired case from the base to the shoulder datum. This will give you a base line and allow you to adjust a full length or body die to achieve only a .002" resize or "bump". I neck sized only for a while but went back to full length bushing style dies several years ago and continue to have better results.

 

What case are you sizing?

[rnhunter]

7 Mag. I really can't complain about the accuracy it has been fantastic but always looking for that little extra. I'll look more into the neck sizing but if it doesn't necessarily produce noticeable improvements in accuracy I probably don't really need it. Thanks for all the input!

[WampusCat]

I would recommend full length sizing with a bushing die that will let you control neck tension. A whole new set of variables in your search for consistency.

 

Edit: I should have added that an accurate minimum "bump" is especially important on a belted magnum like your 7 Rem or a 300 Win allowing the case to headspace off the shoulder instead of the old school belt. When done correctly your case life will increase and you'll likely see improved accuracy.

[L Cazador]

Your 7mm case has stretched beyond the dimensions of your chamber, that is why it will not fit your chamber now. You'll need to restore the case to minimum dimensions by using a full length die. Careful die set up will help reduce any further stretching. You'll need a Hornady or Sinclair headspace guage to set the sizing die up properly. Measure the headspace as it is now and then bump the shoulder in 2 thousands intervals till it fits the chamber. Make a notation of this measurement for future reloading of this brass for this rifle. Once you've done this you will have a minimum of brass stretching or "brass movement" which is conducive to good accuracy. Use of a bushing die with a set of competition shell holders is the simplest way to go! Competition shell holders are in 2 thousands increments.