Matching a reamer to my FL Die - advice please

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RAG2

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Probably going to have a reamer made up for a 20 Tac I'm going to put on my BAT varmint rig. Have dies, brass and bullets. I took some multiple fired .223 brass and ran it through my Redding 20 TAC Type S bushing die...the brass was squeezed down to .3743 at the base and .3573 at the shoulder. So I was thinking a reamer with base of .375 and .359 at the shoulder would be about right. But I don't know. I forget how much bump I get from my Harrels dies, but they always seem to work out so well.

The neck is easy...I'm not going to turn, and loaded rounds (Dakota/Lapua brass) range from .230 to .231 (with most right around .2305), so I'm going to go with the "standard" .233 neck (or I could go with .2325 if I want to split hairs, giving and average clearance of .002 and no less than .0015).

Thanks!!!
 
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I just took some of my 10x fired 223AI brass and ran it through the reamer...now it measured .3735 at the base and .3575 at the shoulder...a bit different. I suppose I should get my hands on some actual Dakota 20 Tactical brass that has been fired-formed, and then size it. But even then, I'm not sure how much under to set the reamer dimensions...I recall hearing .002 at the base and .001 at the shoulder works well...anyone?
 

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I think you would getter a better result by measuring the interior of the die. I use Starrett small hole gages or telescoping gages (depending on case size) to measure the die at the shoulder and .075" in from the base of the die for the base measurement. Most reamer base measurements are set .200" from the boltface/bottom of casehead and shell holder is .125" thick so that leaves .075" up in the die as the .200" measurement from the bottom of the casehead. I've used +.002" on shoulder, +.003" on base (.200" point on reamer). Those dimesions have worked well on larger cases and maybe someone else will have a better suggestion for 223 cases.
 
When you sized the cases from the chamber with the die that you measured, how did the cases compare with the reamer drawing? The reason that I measure cases is that they spring back to larger dimensions than the die's. I use well used, work hardened cases as a worst case (pardon the pun) situation. I think that this tends to eliminate guessing about spring back, and is therefore more precise.
 
For having the reamer larger by ".002 on the shoulder and .003 at the base" rule of thumb...is this when compared to a fire-formed case or the actual dimensions of the sizing die...guessing the latter. If so, when comparing to sized brass, maybe .0015 at the shoulder and .0025 at the base?

By the way, even though I trust the information because I have heard it so much more, for me it seems counter-intuitive that you would size the base more than the shoulder...I don't know...I guess I always assumed the base stretched less and had less spring-back.
 
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RAG2 said:
For having the reamer larger by ".002 on the shoulder and .003 at the base" rule of thumb...is this when compared to a fire-formed case or the actual dimensions of the sizing die...guessing the latter.
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Actual dimensions of the die. If you don't have the measuring tools to measure the interior of the die you could use Cerrosafe and measure it that way.
 
I was wondering about using Cerrosafe. Just getting back into things and I can't seem to find my cerrosafe...I was thinking it would just re-melt some of my chamber castings. Oh well, I'll order more. Thanks.
 
RAG2 said:
By the way, even though I trust the information because I have heard it so much more, for me it seems counter-intuitive that you would size the base more than the shoulder...I don't know...I guess I always assumed the base stretched less and had less spring-back.
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It does sound counter-intuitive, but the reality is that the base end of the case is thicker and harder than the opposite end and expands less. Consequently, the size die needs to be tighter near the base in order to size it at all. If the numbers are exactly .002 at the junction of the body and shoulder and .003 at the .200 datum, the sized case will come out about .001 smaller near the shoulder and less, maybe .005 or so nearer the base.

It works.

Scott
 
Wow, it's nice to be able to put some numbers to it. So .001 at the shoulder and .0005 at the base is the magic number. Thanks.

SGS said:
It does sound counter-intuitive, but the reality is that the base end of the case is thicker and harder than the opposite end and expands less. Consequently, the size die needs to be tighter near the base in order to size it at all. If the numbers are exactly .002 at the junction of the body and shoulder and .003 at the .200 datum, the sized case will come out about .001 smaller near the shoulder and less, maybe .005 or so nearer the base.

It works.

Scott
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You have one more zero in front of the five than the post that you quoted, and I might add that evidently you all missed the point that guessing about spring back isn't needed if you simply use the intended die to size a case, and measure the case to see what the die actually produces. Then, you can dimension the reamer for whatever fit you desire. Die castings and direct measurement of a die still leave you guessing about brass spring back. Why guess if you don't have to?
 
I realize I'm over-thinking the hell out of this project, but it's still a great learning experience for me.

I'm pretty sure he meant to say .0005 and not .005 (in regards to how much the fired cases will be sized at the datum lin if the die and reamer and chamber/reamer dimensions are .003 apart), right?

Also, Boyd...I like what you are saying that that's what I originally tried to do. I sized some 223 and some heavily used 223AI brass in my 20TAC with the die, and got slightly different measurements (possibly due to different spring-back) from each case...which is why I thought I' double-check the math by taking some measurements from a cerro-safe casting. So, if you size the brass, would you want to set the reamer to .001 larger at the shoulder and .002 larger at the base .200 datum line (adjusting by about .001 for springback)...to ensure the brass don't develop bolt click after 20 or 30 firings?

And...I'm thinking I will error on the large side with the reamer dimensions, as I can always hone the factory die a tad. At least I think ;)

Boyd Allen said:
You have one more zero in front of the five than the post that you quoted, and I might add that evidently you all missed the point that guessing about spring back isn't needed if you simply use the intended die to size a case, and measure the case to see what the die actually produces. Then, you can dimension the reamer for whatever fit you desire. Die castings and direct measurement of a die still leave you guessing about brass spring back. Why guess if you don't have to?
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RAG2 said:
I realize I'm over-thinking the hell out of this project, but it's still a great learning experience for me.

I'm pretty sure he meant to say .0005 and not .005 ...............................?
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Are you just wanting to guess your way to a solution or find a for real solution?

If you have the Redding die you are planning on using then get PTG to grind you a reamer. Kiff has all the Redding die drawings....geesh!!
 
For all of the projects that I have worked on, where we measured sized cases, they were fired in a factory chamber the same caliber chamber that we were building, so the spring back was more manageable than you would get, reforming a case. Also, we selected brass that was likely to give the most spring back, because it had been fired and FL sized a lot, and was work hardened well beyond what new brass would be. If I were doing a project where I did not have well used brass, I would probably go on line and see if someone would sell me some that had been shot a lot. A few cases, preferably shot with warm loads, that were toward the end of their life cycles would be all that would be needed.
 
RAG2 said:
Wow, it's nice to be able to put some numbers to it. So .001 at the shoulder and .0005 at the base is the magic number. Thanks.
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I did indeed mean .0005 at the base. Not magic numbers, just a general estimate. Your mileage may vary.

Scott
 
I sent an email request, but haven't heard back yet. I'll call during the week if I don't get a reply in a few days. So that was a great idea. Thank you!
JerrySharrett said:
Are you just wanting to guess your way to a solution or find a for real solution?

If you have the Redding die you are planning on using then get PTG to grind you a reamer. Kiff has all the Redding die drawings....geesh!!
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Bummer. PTG didn't make the 20 TAC reamer for Redding, they got it elsewhere apparently. So that means I'll make the cerrosafe casting, but I recall the Cerrosafe "moves" some after cooling and you have to account for that. Anybody know anything about this?

WSnyder said:
Actual dimensions of the die. If you don't have the measuring tools to measure the interior of the die you could use Cerrosafe and measure it that way.
Click to expand...
 
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