I am really confused....starting to feel like I’ve begun to forget what I thought I once knew.

For those that have read my recent posts you know I’m working on a load for my son’s .300 Win Mag.

We bought 100 brand new Hornady brass and all have been fired once now. In an effort to make his brass last as long as possible and potentially produce marginally more accurate ammunition I decided to set his die up to PFLR. I have the old Stoney Point headspace tool and my comparator body and measured a few cases and got a “base to datum line” measurement of 4.276” (this isn’t absolute as I don’t zero the calipers), so knew that to get a .002-.003 bump my new base to datum line measurement would need to be 4.273-4.274”

As I set out to do this I screwed my die out from the cam over setting to FLR and started sizing. The brass elongated to 4.280+\- pretty quick and stayed there for most of the adjustment.....right up to the end. When I finally got down to where it was supposed to be my die was camming over significantly...in essence what appeared to be FLRing.

Out of curiosity I decided to see what one of the cases that measured 4.280” would do in the chamber and in my opinion it had the nice snug fit I’m actually looking for.

I know that it can’t be right....no way I elongated it .004 and have it fit.

What am I missing? What did I do wrong?

Brass can come out of the chamber shorter/smaller than the chamber.

Size by feel in that case...hence the longer measurements to get a snug fit?

After reading a bit more on the subject and taking Mathman’s comments I’m wondering if the measurement on the fired cases, before running through a die are actually where it needs to be...if 4.280” is a slight crush fit then .002-.003” setback would put it right back at fired case dimensions.

Am I thinking correctly or off my rocker?

Maybe you're over thinking it. The only length I am concerned about is over all length. I'll trim if necessary.

I often will not touch the shoulder with a full length sizing die. But if the re-sized case enters the chamber with more force than I like I'll bump the shoulder. I barely bump the should, turning the die down about an 1/8 of a turn until the case enters the chamber easier.

I think I'd go by feel as well. If you think it feels too snug, you can then bump it back a touch.

I'm sure that you know this, but we're talking about half the thickness of a sheet of paper here to get to 0.002", three quarters to get to 0.003". Tiny fractions.

Smoke a case neck and with the die set out so the die doesn't contact the shell holder start screwing the die in until the soot is wiped off the neck just at the neck shoulder junction and lock the ring there.

I think you are over thinking it. Belted case's sometime's come with rifles with sloppy chamber's. That's where partial sizing really come's in handy. First reload just neck size staying above the shoulder. Second, if the fired case will chamber, do the same thing. That case probably won't chamber on the third loading. BTW, you can see how far down the neck your sizing without soot on the neck. When you have reached that point, start setting the die down a bit at a time feeling for the shoulder to rub. It will be distinct rubbing. Keep going down till the shoulder no longer rubs in the chamber. At that point the case fit's your chamber. Some claim what has actually happened is you moved the headspace to the shoulder. But, that belt is still there and now it should headspace on the belt and the case will fit the chamber. Don't be confused, all your actually doing is making the case fit the chamber of that rifle if, the chamber was sloppy to begin with. I learned it on a 7mm Rem Mag years ago. After a couple firing's I could see the ring around the case head the indicate's head separation is on the way. And in doing that with that 7mm mag, I went to doing it on all my cartridge's. Just an example of different chamber's, I have two 243's. Only tie in my life I've ever had two rifle's in the same cartridge. Both rifles have their own FL die set so that both can be adjust to the rifle with a deticated die that once set, I never move. Reloads for one of the rifle's will fit in both rifles but reloads from the other will not chamber in the first! Simply the difference made from min and max chamber size's and both could be loaded with simple die adjusting instruction that came with the die.Does one way out shoot another? Not really a clue about that. Both rifles shoot pretty consistent 1/2" groups at 100yds using different bullet's in each. Only way I'd know if it improved the larger chamber rifle would be to reset the die and start load development all over again, I'm not going to do that, think I'll simply live with what I have!

I have never had tool's to measure chamber's with and not even for seating bullet's. Never has been even a remote need for me. I think the deeper we get into measuring this and that the more we get into the science of it and few are actually trained to actually understand what all that means.

That method can lead to hard chambering.

How so?

The body section of the die can squeeze the case in such a way that the shoulder, and hence the shoulder/neck junction, moves forward. So when the length of the neck is sized and the mark stops at the junction the shoulder is forward of its best position.

I have a number of FL size dies for 308 Winchester. The Hornady sizes the body the most, reducing the diameter and imparting more taper to the body section of the case. I've used it to lengthen the head to shoulder distance of some brass to better fit a deeper chamber. If I used the smoke and stop method with this die in the original rifle the brass would chamber hard for sure.

Thank you for your reply. I have done what I posted for a few rifles but I checked the brass for ease of chambering. Doing what I posted and checking the brass in the chamber and turning the die down if necessary would work wouldn't it?

It should.

Make sure you know how to adjust your dies if you decide to bump your shoulders.

The first time you “over bump” ... and get around 10 thousands to far - you will get light prime strikes ... click with no bang = no joy.

You won’t forget doing it wrong though...

Seems to me that anyone fiddling around to this extent is kinda looking for hard chambering.

Not sure I understand this. Bump the shoulder to far and get light primer strike's? You can only bump the shoulder so far and you return the case to SAMMI min spec! You get light primer strike's there and I'd guess your chamber has excessive head space. Then either get it fixed or learn to size the case to fit your chamber. That get's back to partial sizing, aka bumping the shoulder.

If you are using a redding body die you can compress the shoulder below SAAMI, then the short cartridge will move forward when the trigger is pulled, and you get what seems like light primer strikes, but it’s really you have too much headspace and the brass is moving forward.

I’ve seen brass 10 thousands too short cause this personally.

I use a Wilson adjustable headspace gauge for my belted cases. No measurements are needed.

Take a 1x fired case (or a 2x fired case if it still chambers easily after neck sizing only) and drop it into the gauge and adjust it so it fits. The case will be headspaced on the shoulder. Tighten up the adjustment screw.

Now you have a template of your chamber (Close enough because of spring back).

Adjust your body die by testing brass fit in the Wilson gauge that you adjusted so the brass headspace on the shoulder.

I NK size then FL size in that order. I anneal after 3 firings. Belted brass will last as non belted this way.