Die setup for .300 Tommy questions..

Jake in NC

Well-Known Member
Oct 25, 2002
.. Hey guys.. I've been in the basement goofin' around with the new goodies and checkin' some things out.. I'd like to set these dies to where they size the neck and just bump the shoulder.. I took measurements before and after sizing.. What I gathered in this brief little experiment was that the die sized the neck from .343 (fireformed) to .334 (sized).. The way I had the die set it was sizing about 7/8 of the way down the neck..(Can I assume I wasn't touching the shoulder.?) I pulled the bolt guts (but not the ejector) to try and get a better feel for proper sizing.. Even with unsized cases (still FF'd) I didn't get any noticable resistance.. Eeenteresting.. I'm still not sure what the best way to check this shoulder is..
.. It seems that the neck size is pretty stout.. I'll be looking forward to trying out a set of collet dies on this puppy.. Any reason not to.? I got great results with them on everything else.. Most of the time the "improved" cases will work in the "standard" collets with no problems..
.. Any suggestions on die setup.? My first instinct is that since the dies and the chamber are made to spec then just bottom it out on the shellholder.. But I thought I'd tinker and see what came of it.. Whatchyathink.?? d:^) JiNC

PS- Ya gotta love that Winny bolt.!! Look Ma.! No tools..!!

Darryl Cassel

Well-Known Member
May 7, 2001

Bottom it (die) out or set the die so you have to overcam when sizing the case. This will bump the shoulder for sure. Don't overcam to far though, just enough to feel the die bottom out with the press handle and then a firmness can be felt as the handle goes down and then it has a release as the handle bottoms out.

We call this procedure overcaming to size further down the case and bump the shoulder..
I'm not sure you gain anything by bumping the shoulder though.

Once the new case is fireformed to the chamber, I usually just full length size the case after about five firings. Up to that point, I normally just neck size about 3/4 of the neck after each firing up to five.
Personal preferance I guess.



Well-Known Member
Jun 12, 2001
Palmer, Alaska
I try to do like Darryl, FL size only when really needed if things are getting too tight to chamber easily, extraction starts to get a little stiffer than normal with a known safe load. Keeping headspace to a bear minimum helps center the bullet better to the bore, especially if neck clearance is large like most factory always are, still it never hurts.

You can use a Stoney Point Headspace guage on a caliper like I do, it measures off the datum line on the shoulder so you know when the shoulder starts to move back as you very minutely screw the die down lower and lower. If you don't move the die down about a 1/32nd to a 1/16th turn at a time checking all the way for signs of movement, the shoulder will bump back alot real quick, often exceeding .005-.007" shoulder setback in one little adjustment! That's way more than's needed too.

Check your "average" group sizes over several groups when FL sizing verses just NK sizing them, you'll find the FL sizing opens them up noticably more than likely. My Ultra went from just over .5 moa to a solid .9 moa with just FL sizing. Not a conclusive test yet but, not one group went better than .8 moa. Compare that to some that were all the way down in the .3's and .4's.

Something else to consider when FL sizing is when the shoulder is bumped back, it will often bulge the case just below the shoulder and you'll need to go further if it does just to bring it back in enough to chamber smoothly. This will be noticed escpecially whn you get close to bumping the shoulder back as you try to chamber the case while progressing moe and more. The case will get increasingly more difficult to chamber and then finally it will get real easy all at once. The shoulder may have been moved back plenty far, just that the body of the die is not small enough to control the body dia until the case is up in it **** near all the way. The body being sized down will first move the shoulder forward causing most of the tightness closing the bolt when you start moving the die down to get it set up. Monitoring the datum point length will tell you where the tightness is coming from along the way as you are setting the die up.

If you are bumping the shoulder and sizing the neck at the same time, I'm assuming you don't have a neck die for it and just want to "Partial FL Size" them. Screwing the die down just far enough to move the datum point on the shoulder back a couple thou should get you there.

One more thing, If you don't have a headspace guage of some sort yet, just find a piece of pipe, tube or something like that fits over the neck and is flat and square on both ends with a hole in it the diameter that about equals the diameter of the middle of the shoulder on the case in question. Slip this onto the shoulder and use a dial caliper to measure the base to the top of the pipe or whatever you're using to indicate off the shoulders datum line to monitor any bump in the shoulder when you are sizing. You could make a fixture to hold a washer you could slip into or onto it and you're in buisness for a number of inside diameters you can drill the washers out to.

Good luck!


Well-Known Member
Jun 13, 2007
Wilmington NC
FL sizing with shoulder bump is easy to do, but first you have to know where you are starting from.

Take a stoney point set that has the inserts for measuring off the datum line or have your gunsmith take a barrel stub and make a shoulder bump guage. Measure virgin brass and once fired brass and record data. At some point (depends on cases and chamber) you will start getting cases that are hard to close. At this point take 2-3 hard to close cases and take a candle and smoke neck and shoulder. Measure datum line measurement before smoking. This will tell you how far your case datum line is moving.

Turn die up couple turns, size and see how far comes down the neck. Adjust die down a little, resmoke and repeat. Once comes down to just bumping shoulder and datum line. Clean case, measure and see where you are at. You want .002 bump back, no more. Repeat and adjust to get no more than .002. You can now record this measurement and lock die down to this point. That gives you FL size with shoulder bump each time. Less work on brass.

Another point that has been discussed. If you just routinely lock dies down at the "camover point" you could be getting .004-.008 shoulder/datum line movement. Ideal is .002 no more.

Second it is possible to cam over too much and move datum line back to point that they will not chamber. Been there done that.

Key is to record datum line measurements from virgin, once fired and point where they are hard to close. That way you know what you are dealing with.



LRH Assistant
Here are some related products that LRH members are talking about. Clicking on a product will take you to LRH’s partner, Primary, where you can find links to LRH discussions about these products.