• Sizing Die Setup and Shoulder Bump

    Whether your brand new to reloading or a seasoned veteran, you're probably already heard, read or watched something pertaining to sizing die setup to get the proper amount of shoulder bump and not overworking your brass. Most every reloading manual on the market explains how to do this, as do the instructions for every sizing die on the market, but some of those methods and instructions can be rather wordy and confusing. There are also a plethora of specialty measuring tools and devices on the market that are advertised to simplify this process - some of them work well, some aren't worth a hill of beans. With all that in mind, today I'm going to share with you my simple and easy process of adjusting my sizing dies so I get exactly 0.002" of shoulder bump when resizing my brass.

    First up, lets cover what equipment and tools you will need to do this...

    • Reloading Press
    • Proper Shell Holder for Cartridge
    • Full Length Sizing Die
    • Fired Cases (5-10 is enough)
    • 6" Caliper
    • Feeler Gauges
    • Sinclair Hex Bullet Comparator

    Note: Due to the Hex Bullet Comparator's only being offered for bullet diameters up to .338 caliber, this will only work with cases that have an outsize neck diameter of roughly .320" or less.

    First thing you will want to do is to setup the sizing die as directed by the instructions that came with it which typically entails adjusting it down until it contacts the shell holder when the ram is at the top of it's stroke. Remember a little cam-over is always recommended here.

    Using the Sinclair Hex Bullet Comparator, find a caliber hole in the Hex that your fired (not yet resized) case neck will fit into where the sharp edge of the hole will stop somewhere in the middle of the shoulder (effective the datum line). For the sake of this article I'm using .250 Savage AI brass for which the .30 caliber hole is perfect. Insert your case neck into the appropriate hole in the Hex and then measure the overall length of the case and Hex with your caliper and write down the measurement. I recommend measuring at least 3-5 cases, and if there's a little variation between them use an average.

    The next step is to go ahead and resize those same pieces of fired brass you just measured. Once resized, measure them again with the Hex using the same method as outlined above and jot those measurements down as well.

    From here it's simply a matter of subtracting the second (resized) measurement from the first (fired) measurement for each piece of brass to determine how much the shoulder has been bumped. In my case with the .250 Savage AI brass I had a fired measurement of 2.600" and a resized measurement of 2.590" which tells me my die is bumping the shoulder 0.010".

    We know that we only want to bump the shoulder two to three thousandths of an inch to maximize the life of our brass by not overworking it. So in my case where my die is bumping the shoulder 0.010" I know I need to adjust my die up/out around 0.008" or so to get that ideal 0.002" shoulder bump.

    Using a feeler gauge of the approximate thickness, I loosen up the lock ring on the sizing die and unscrew it a little so that I can fit the feeler between the bottom of the die and the shell holder when the ram is at the top of it's stroke. Screw the die back in and adjust as necessary until you have the proper cam-over with the feeler gauge in place, then screw down the lock ring and tighten the set screw to lock in the height.

    Repeat the whole process again with 3-5 more pieces of fired brass to verify you are getting the amount of shoulder bump you desire with the new die setting. Continue making adjustments as needed until you get it right.

    Since we are measuring off the datum line on the angled shoulder of the case our adjustments won't translate to a 1:1 effect on shoulder bump, thus the need to make additional small adjustments after the first one. Once you do it a few times with a few different dies you will start to get a feel of how many thousands you need to add for a given shoulder angle to get closer to your desired movement on the first adjustment.

    For those shooting .30 caliber and above that won't fit in either of the Sinclair Hex Comparators, you can accomplish the same thing by simply boring an appropriately sized hole through a sufficiently sized hex nut from your local hardware store. Just don't get a Grade 8 nut - they're a little hard on drill bits.

    Comments 5 Comments
    1. Robinhood's Avatar
      Robinhood -
      Nice Article Jim.
    1. mike21's Avatar
      mike21 -
      Agree with Robinhood, excellent article. The Sinclair comparator is on my shopping list. Never felt real warm and fuzzy with the lock n load thing of three parts stuck together for measurements (KISS). Thanks for your efforts, well done.
    1. J.Baker's Avatar
      J.Baker -
      Thanks. The Sinclair Comparator is basically a 1" hex nut, but on the one I have it's not exactly 1" on all three measurements. One's dead nuts 1", ones 0.997", and the other is 0.998" IIRC. Mainly it's designed for measuring/checking ogive consistency on bullets.
    1. imartin's Avatar
      imartin -

      Nice article. To add my .02, I use Redding Comp Shell Holder sets. For those who aren't familiar, the sets include shell holders of different thickness (.010 - .002 IRCC). You start with the thickest shell holder, run the brass through your sizer to see if you are getting .002 bump. With my 25-06 for example, the .010 and .008 shell holders don't bump the shoulder back at all, but the .006 provides the .002 of bump I'm looking for. Either way it involves some trial and error along with measurements to see what's giving you the results you want. In this case, you aren't moving your sizing die up and down, but rather the brass via the thicker or thinner shell holder. For me, it gives me the confidence that my die is tightened down in the press without any play to keep concentricity issues to a minimum. At least in my head, that's what gives me confidence and has worked for me. Always happy to learn about different ways of doing things. Thanks again for the good info.

    1. J.Baker's Avatar
      J.Baker -
      I have one of those Redding sets for .222/.223 sized cases - only because I got a set of .222 Rem dies that were something like 0.135" short. Given what a set costs I'm not about to buy one for every size shellholder I use. Both my presses are turret presses so once the dies are set they stay put and I just change out turret wheels when changing calibers.