20 Practical sizing weirdness

[Cuando]

I recently put together a Bighorn/Criterion in 20 Practical. I'm using once fired Rem brass I had previously sized for an AR and trimmed on a Giraud. I can size them in one pass using a .228 bushing and no expander ball (necks measure .230 with seated bullet) and all is well. When I resize the brass with the .228 bushing there is no longer adequate neck tension and the bullet will fall in the case. Same with a .227 bushing.

So, I annealed all the cases and now, there is so much neck tension when I neck them down with the .228 bushing I have to pull an expander ball through it so it doesn't crush a ring with the seater. Necks measure .228 with a seated bullet now.

After the first firing with the annealed brass, sizing with a .227 bushing has barely any tension. Makes sense as it's only one thou.

Anyone else run into this?

 

[nmkid]

I use unturned Lapua brass and use 2 steps to get it formed. My fired cases are at .233. Loaded they come in at .2315. I resize with a .230 Don't understand why they would create more tension after you anneal them. Have you tried sizing with either a .225-.226? I haven't had any coffee this morning so I can't get my feeble brain working on what's going on. LOL. I have done several wildcats and of all of them the .20 P was the most simple.

 

[Prose]

I saw this on some necked down Vartarg brass. Turned out my necks were thinner than I thought. The difference between loadings was that the expander mandrel didn't allow the case dimensions to fully expand vs. when it's fired in the chamber. Not sure if that's a good explanation.

 

[jepp2]

(necks measure .230 with seated bullet

vs. necks measure .228 with seated bullets. When I size down in one step, it leaves a slightly wider flare at the mouth of the case. So I think the .230 you saw was this slight flare, not the true neck OD. The .228 is about what I see for Rem necks loaded. And I size them with a .226 diameter neck of my CH4D sizing die.

I would expect your neck tension to increase after annealing IF you were getting a lot of spring back in the brass.

I take my 20P brass down in 3 steps, to .243 using a FL 223 die with no expander, to .236" using a bushing, to .226 using my 20P die.

 

[searcher]

Assuming walls .013" thick and .002" reduction wanted for tension in a bolt gun - that puts you right at the .228" bushing you tried. If you check your neck thickness with a ball micrometer and it is .013" or more (likely), the bushings should work. I'm pretty certain your problem is your expander ball is opening the neck back up as it exits the case and for the same reason - your smaller bushing does nothing more. Measure your expander ball at the widest point. it HAS to be UNDER .202" wide at the widest point, otherwise it will interfere with what you are trying to achieve with neck tension. I would turn it down to .200". That is easily achieved by taking your decap assembly out of the die and chucking it into a portable drill or drill press and using a diamond file or emery cloth or what have you to take it don in size as it spins. Check the measurement frequently with your dial calipers so you don't take too much off, though a little is o.k.

the alternative is to decap using a decap die that will accept your .20 caliber necks - then resize your brass without the expander ball.

Either of these same methods wok for A/R application, though you will want a bushing that provides .004" tension.

So - do a quick test by taking one of your sized cases that won't hold a round, then run it through your sizing die without the expander ball. That will show you if the sizer ball is the problem, if not greatly contributing to it. Either it reduced the neck or not. If not, you need a smaller bushing.

I will tell you that my first batch of brass I worked up for my A/R in .20 practical was also Remington. I put a lot of work into it with turnhing the necks, etc. and it was a large quantity. If I were you, I'd not use it. Go out and get some Lake City brass as it does not stretch like the soft Remington does. You will likely need to trim the Remington brass twice as often and case life will be shorter. I also found that if you don't address that expander ball if it is the problem - your necks will also prematurely crack from overwork and you will be annealing them all the time otherwise.
Good Luck!

 

[jds holler]

I stumbled onto a trick that us 20 cal guys can use.

I happened to notice that the decapper shaft in the Lee Universal Decapping Die measures on the shy side of .204".

I now do my sizing in a bushing die with no expander ball, and then de-cap with the Lee die. Kind of a mandrel effect. Spring-back from the .204 shaft has been leaving good neck tension, and all is well. jd

 

[jepp2]

I stumbled onto a trick that us 20 cal guys can use.

Well, that is a different take. I knew the Lee decapping die rod will fit in the 20 cal fired neck. I use it to deprime my brass. The Lyman decapping die rod will not fit.

But I have used the Lee Collet die mandrels to run through the case necks on new brass that are out of round. Just never thought of using them as an expander.

 

[searcher]

I would guess that would leave you with about .001" neck tension. You must be running a bolt gun. Another thing I have noticed is that is is so damn hard to keep those decapping assemblies arrow-straight, concentric necks are always going to be a problem. That is the reason I don't want the expander button even touching the neck for the final sizing and recommend going .002" under bushing size. Those little necks get tweaked really bad. I use a Redding Full-length "S" bushing die with the decap assembly removed for final sizing.

 

[jds holler]

With my decapper/mandril, I get a very good feel for neck tension. If I get a case that "feels" too loose or too tight, I just set it aside for either a fouler, or discard. My run-out isn't too bad considering these are brass that have been used an indeterminate number of times as 222 shells then necked down to .20. At any rate, these are squirrel shells, and I'm getting .3 - .4" groups with them. My belief is that I get much more consistent neck tension with the inner expansion than I would with outer neck compression on these cases which haven't been neck turned. jd

 

[Ledd Slinger]

I would guess that would leave you with about .001" neck tension. You must be running a bolt gun. Another thing I have noticed is that is is so damn hard to keep those decapping assemblies arrow-straight, concentric necks are always going to be a problem. That is the reason I don't want the expander button even touching the neck for the final sizing and recommend going .002" under bushing size. Those little necks get tweaked really bad. I use a Redding Full-length "S" bushing die with the decap assembly removed for final sizing.

True. Decapping rods are never perfectly straight. But expander balls on a decapping rod are fine so long as you "float" them in the die. I use expander balls on many of my cases and have less than .001" runout across the board. I always back my decapping rod lock nuts off at least a 1/4 turn to make sure they float in alignment with the neck where the sizing die left it.

I never decap with the rods in my sizing dies either. I always use a universal decapping die for knocking out primers. This ensures I'm not bending or warping the decapping rod in the FL die that my expander ball sits on.

 

[Ledd Slinger]

I use expander balls with the same concept as bushings. We float a bushing in the die to allow proper neck alignment and avoid binding right? Then we should do the same with an expander ball.

 

[nmkid]

True. Decapping rods are never perfectly straight.

Never really thought about that until about 2 years ago. Pick a sizing die, turn it upside down and screw the de-capping rod in or out. First time I saw the wobble I couldn't believe my eyes.

 

[Ledd Slinger]

Never really thought about that until about 2 years ago. Pick a sizing die, turn it upside down and screw the de-capping rod in or out. First time I saw the wobble I couldn't believe my eyes.

Yeah that's why I fully float them in the die. If they get too bad, they need to be changed out. They will usually remain pretty straight as long as you don't use them for decapping. I know it kind of defeats one of the purposes for which they are designed, but I'd rather use another universal die for decapping and keep the sizer die decapping rod as straight as possible.