RCBS Full Length Resizing Die Modifications

[jepp2]

That lapping compound should work for you. Yes, I insert the lap from the cartridge end of the die. Just don't touch the lap (compound) to the side of the die, or the tape will serve as a lap. If you do, just remove it and wipe all the compound off the die body. Check your progress often until you get a feel for how long it takes to remove a 0.001".

 

[RonAKA]

Gesswein is another source for professional quality stones and other abrasives.
People that make plastic injection molds use Gesswein tools and abrasives.
http://www.gesswein.com/?gclid=CjwK...jDHtMBpNyQmYxidU3_spyHUXWQeCs5UBQOhoCnFrw_wcB

Yes, I found that site. However I was trying to find a site where I could buy both the through-hole lap and the lapping compound to save a few $'s on shipping and minimum order. But, I couldn't find the through-hole laps at the Gesswein site.

 

[RonAKA]

Well, I have received my through hole lap and lapping compound, and need to make an almost final decision on the diameter of the neck in the FL sizer die. I have seated bullets in five dummy loads. Here is my thinking:

The minimum diameter of the neck in the dummy loads with a 0.264" bullet is 0.2947"
The diameter of a neck without a bullet to get 0.002" tension would then be 0.2927"
If I wish the expander ball to bring the neck up the last 0.001" then prior to that I need 0.2917"
With a 0.001 spring back that means I need a neck bushing ID of 0.2907"

Does that make sense?

I sized down 5 cases with the existing unmodified die and got very consistent 0.2845", which with an assumed spring back of 0.001, the existing neck must be about 0.2835". Or I have about 0.0072 to lap out.

I'm thinking of targeting an even 0.2900" to give a little margin for safety. I can lap larger after I load a bunch more of the stuff, but not smaller!

 

[ireload2]

You might be a little more conservative and try .289 to get a feel for the process. Then load a few rounds for grins.
I would test it at regular increments to enable you to sneak up on the final dimension. There is not much to lose by lapping it and leaving it small until you have given it a through test. The amount of spring back may fool you because it will vary with the work hardening of the brass.
Fresh anneal cases may not spring back any.

You also may need an extra .001 to enable you do deal with thinner brass. I don't remember if you are controlling the thickness by turning or using unturned brass. Factory brass can vary so if you get a thin lot of factory brass you might have to lap another die to make the new lot work.

Before I bought a set of gauge pins I checked die necks with a small hole gauge and by sizing junk brass. I found that the .001 spring back was often nothing but a myth. If I sized a case multiple times and rotated it between sizings I found that it only took 2 or 3 sizings to make the OD of the case neck match the measurement of the die.

I eventually had about 100 dies that I had checked with brass and the small hole gauges. When I got my gauge pin set I double checked most of those dies and found that my small hole gauge measurements were very close to right on. Using gauge pins you can check the neck for taper and they will often be larger or smaller on one end of the neck. The small hole gauges could detect that and also the necks that were a little larger in the middle than on either end.

My first neck bushing die was a 6X47 Remington die made by Neil Jones. With my unturned brass it produced about .0015 to .0017 interference. At the time I thought the grip was a little wimpy. I contacted Neil Jones and found he could provide bushings in .0005 increments. So I was able to get exactly the bushing I needed and never had to fool with that die again.

You're right. The put it back on technology is lagging the take it off technology.

Well, I have received my through hole lap and lapping compound, and need to make an almost final decision on the diameter of the neck in the FL sizer die. I have seated bullets in five dummy loads. Here is my thinking:

The minimum diameter of the neck in the dummy loads with a 0.264" bullet is 0.2947"
The diameter of a neck without a bullet to get 0.002" tension would then be 0.2927"
If I wish the expander ball to bring the neck up the last 0.001" then prior to that I need 0.2917"
With a 0.001 spring back that means I need a neck bushing ID of 0.2907"

Does that make sense?

I sized down 5 cases with the existing unmodified die and got very consistent 0.2845", which with an assumed spring back of 0.001, the existing neck must be about 0.2835". Or I have about 0.0072 to lap out.

I'm thinking of targeting an even 0.2900" to give a little margin for safety. I can lap larger after I load a bunch more of the stuff, but not smaller!

 

[RonAKA]

0.289 is it then. Thanks for the detailed response. My only issue now will be remembering how to do it, when I decide down the road that the neck in the die is still too tight!

You might be a little more conservative and try .289 to get a feel for the process. Then load a few rounds for grins.
I would test it at regular increments to enable you to sneak up on the final dimension. There is not much to lose by lapping it and leaving it small until you have given it a through test. The amount of spring back may fool you because it will vary with the work hardening of the brass.
Fresh anneal cases may not spring back any.

You also may need an extra .001 to enable you do deal with thinner brass. I don't remember if you are controlling the thickness by turning or using unturned brass. Factory brass can vary so if you get a thin lot of factory brass you might have to lap another die to make the new lot work.

Before I bought a set of gauge pins I checked die necks with a small hole gauge and by sizing junk brass. I found that the .001 spring back was often nothing but a myth. If I sized a case multiple times and rotated it between sizings I found that it only took 2 or 3 sizings to make the OD of the case neck match the measurement of the die.

I eventually had about 100 dies that I had checked with brass and the small hole gauges. When I got my gauge pin set I double checked most of those dies and found that my small hole gauge measurements were very close to right on. Using gauge pins you can check the neck for taper and they will often be larger or smaller on one end of the neck. The small hole gauges could detect that and also the necks that were a little larger in the middle than on either end.

My first neck bushing die was a 6X47 Remington die made by Neil Jones. With my unturned brass it produced about .0015 to .0017 interference. At the time I thought the grip was a little wimpy. I contacted Neil Jones and found he could provide bushings in .0005 increments. So I was able to get exactly the bushing I needed and never had to fool with that die again.

You're right. The put it back on technology is lagging the take it off technology.

 

[savagedasher]

0.289 is it then. Thanks for the detailed response. My only issue now will be remembering how to do it, when I decide down the road that the neck in the die is still too tight!

Just find a friendly tool grind shop in your area the can give you what ever you want .
Larry

 

[RonAKA]

Just find a friendly tool grind shop in your area the can give you what ever you want .
Larry

Too far down the DIY road for that now. I did consider it though.

 

[RonAKA]

So the job is done, and I now have a neck in the die that is very close to 0.289". I sized some of the brass and it comes out at about 0.2898, when it starts at about 0.294 or so. So all looks good for now. Thank you for all the help on this. The only issue is that the finish of the neck is not as great as I expected with the diamond lap compound. I also used a guide I made from about 3/4" of the head end of a 7mm RM case. I drilled out the primer hole to fit the shaft of the lap. Worked great except that I got a little careless and it got some lapping compound on it, and didn't stay fixed to the die, and spun on me a couple of times - scuffing up the body finish too.

Any suggestions on how to polish the body of the die and the neck. I have automotive lapping compounds an a Solvol polish that works very good on metal. However, what do you use to put the polish on with? This lap seems to have the diamond stuff embedded in it, and I don't think I can use it to polish now. And of course it is too small to do the body of the die.

 

[ireload2]

If you have a lathe or a mandrel, that you can spin the die body with, it is easy to polish it with 320 to 600 grit silicon carbide paper and a split wood dowel. I have polished maybe a hundred dies this way. I usually use a .250 wood dowel split about 3/4" with a coping saw. Put a strip of the silicon carbide paper in the dowel and wrap it to a good fit in the neck. Wet it with light oil or WD 40 and spin the die at about 300 to 600 rpm.
Polish by feel moving the dowel enough that you do not polish a ring into the die. It will take practice - about 2 or 3 dies to produce a better than factory finish in about 5 minutes. Too easy.

 

[RonAKA]

If you have a lathe or a mandrel, that you can spin the die body with, it is easy to polish it with 320 to 600 grit silicon carbide paper and a split wood dowel. I have polished maybe a hundred dies this way. I usually use a .250 wood dowel split about 3/4" with a coping saw. Put a strip of the silicon carbide paper in the dowel and wrap it to a good fit in the neck. Wet it with light oil or WD 40 and spin the die at about 300 to 600 rpm.
Polish by feel moving the dowel enough that you do not polish a ring into the die. It will take practice - about 2 or 3 dies to produce a better than factory finish in about 5 minutes. Too easy.

Thanks for the suggestion. I will try it. I have been buffing with a Dremel felt tool, but it keeps coming apart. For the neck I think I am good. I used a .22 cal nylon brush wrapped with patch material with compound on it.

 

[ireload2]

I think you will be happier polishing with the rigid stick. You do not need a mirror surface. A felt bob can wash out and leave an uneven surface.
All you need to to do is knock off the high points of the existing surface texture.
You only need that fine line grain finish that you see on old stainless steel machinist scales and micrometer thimbles.
Since spinning to polish a cylindrical shape puts texture line around the die cavity the first cases that you size will scuff up that finish a little.

Thanks for the suggestion. I will try it. I have been buffing with a Dremel felt tool, but it keeps coming apart. For the neck I think I am good. I used a .22 cal nylon brush wrapped with patch material with compound on it.