.008 shoulder Bump?

[slikmrc]

You could take a fired, deprimed case and put a piece of scotch tape on the base. Chamber it and feel if there is any resistance on bolt close. This works best with a stripped bolt, at least pull the firing pin. If you do feel resistance you can adjust your FL die until the round just chambers. Depending on the chamber/die difference the shoulder may push forward before the case is fully inserted in the die. I generally back the die off from the shell holder a half turn and go from there.

 

[Alex Wheeler]

I spun a few cases on the comparator and the shiny spot is appearing at the base of the shoulder where it meets the body of the case, the angle of the case and comparator seem to be different.

Get your hands on a different comparator. Sinclair makes some that are decent. You do not need the one they recommend. You can even use one with the wrong shoulder angle, the main thing is that it contacts the shoulder more towards the middle.

 

[TXTrained]

I would get a neck die, either a Lee Collet for a cheap way to try it out or a bushing die if you want to go full bore. Neck size a batch and check your groups, my bet is they will be as good or better than your over Full Length sized ones.
Why mess with a case that chambers easily, fits the gun well, and does not have excess headspace. Only thing you are sizing for is to get enough neck tension to hold the bullet. (I am well aware that neck sizing has gone out of fashion and not looking to start that argument, but for belted mags and many other hunting applications it is still a real good option.)

I agree with you 100%npn those Belted Magnums.. Why resize the whole case that does not need it totally resized.

 

[slikmrc]

You can also use a 40 cal pistol case as a gauge in a pinch. A little tricky but if you inside chamfer the case mouth it works pretty good

 

[philipbrousseau]

Trying to neck size with a full length sizer can cause the case to bulge. Like squeezing a water balloon .squeeze top of case the lower part unsupported by the die expands. Try just bumping the shoulder and see if your cases fit.

 

[ajkellerusmc]

I spun a few cases on the comparator and the shiny spot is appearing at the base of the shoulder where it meets the body of the case, the angle of the case and comparator seem to be different.

Alex Wheeler, I was sizing some 6.5 PRC today and spun a case on the comparator and noted where the comparator sits on the shoulder of the PRC case. It is much different on the 308 case. I am going to cut the 308 comparator down on my Lathe to get the contact to the center of the shoulder as in the pictures and I think my problem will go away resizing the 308's.

What say You?

Thanks for your input on this subject.

Resizing the PRC is easy to bump .002".

 

[misterc01]

Yes - the comparator on the .308 is off - it should be more in the midline like the PRC case. Whose comparators are you using? None of mine have a bevel - the flat edge sits at the midline (center of the shoulder) like the PRC to measure the headspace.

 

[slikmrc]

I haven't used the Sinclair bump gauges but I don't see how that is giving you a false reading. With that gauge bottoming on the shoulder before the shoulder/ body junction it should be giving a good reading I would think.

 

[ajkellerusmc]

Yes - the comparator on the .308 is off - it should be more in the midline like the PRC case. Whose comparators are you using? None of mine have a bevel - the flat edge sits at the midline (center of the shoulder) like the PRC to measure the headspace.

I'm pretty sure these are from Sinclair.

 

[misterc01]

Looking closer at an expanded image, I see where the .308 is sitting lower, just not at the midline. The PRC is just sitting higher. My Sinclari .308 does not have a bevel as you can see, and it sits higher.

 

[ajkellerusmc]

Looking closer at an expanded image, I see where the .308 is sitting lower, just not at the midline. The PRC is just sitting higher. My Sinclari .308 does not have a bevel as you can see, and it sits higher.

What is the part number on your insert mine is a #20, Maybe I'm using the wrong insert????

 

[misterc01]

We may have solved your mystery. Mine is a #30.


749-000-931WS
30 Caliber (0.308") Comparator Insert
Mfr Part: 090308

 

[slikmrc]

According to Sinclair web site the .308 insert is a bullet ogive comparator where the #20 insert is a bump comparator for a 20 degree shoulder up to 30 cal case.

 

[Alex Wheeler]

If the comparator contacts near the neck or shoulder junction a diameter reduction will read as a "bump".