Redding Bushing die size math for 6cm (and other reloading Qs)

[Senor_Barney]

I reload 6.5cm and I want to begin 6cm. I have a few quick clarification question that hopefully the seasoned reloaders here can answer.

Question 1: Please grade my math -- is that how I calculate neck tension?

• I use Redding's competition die set with the neck bushings and want to confirm what size bushing to use.
• I've had really strong results with my current 6.5 load. The die set I bought used on PX came with a 0.288 neck bushing. Currently, my loaded cartridge neck diameter using Berger 140gr Hybrids (0.264) and Hornady brass (0.0145) comes out to 0.292 average of 5 rounds.
• Neck tension of 0.292 - 0.288 = 0.004

Question 2: If I want to start with this same neck tension, how do I know what size bushing to get for 6cm -- component list below?

• Hornady brass 0.0145
• SMK 107gr 0.243
• Implied cartridge neck diameter 0.272 = 0.243 + 0.0145 + 0.0145
• My guess for bushing with 0.004 neck tension = 0.268??

Question 3: Can I use my 6.5cm Redding full-length sizing die to FL size 6cm -- I don't yet have the components in to try first hand?



Question 4: Anyone care to share a starting load and CBTO seating depth for 6cm using the component I plan to run

• Hornady 1x brass
• SMKs 107
• H4350
• CCI 200 LRP

 

[spife7980]

Quesiton 1: not so easy to answer correctly in regards to actual tension. Damn near impossible. But for just the interference fit measurements, you have it down well enough.
Loaded round diameter minus sized round diameter leaves you the interference fit of the case and bullet.

You are being redirected...

2) if you want 4 thouh of interference fit then you did it right. Well as right as can be done via book learning. Really you have to experiment because the bushings arent that great at actually being what they are called and spring back changes it even more. Itll be serviceable though and its really all I ever do.


3) You can use a 6.5 bushing die with a smaller 6mm bushing just fine, not the other way around usually.
I dont because generally the chambers arent a perfect match so Id always be fiddling with it right off the bat in each session to set it up and dies are (can be) cheap enough that its worth just getting one set up per chamber.

4) https://www.wheeleraccuracy.com/videos go to the vide called finding your lands. Thats how I do it.

 

[CK1.0]

I reload 6.5cm and I want to begin 6cm. I have a few quick clarification question that hopefully the seasoned reloaders here can answer.

Question 1: Please grade my math -- is that how I calculate neck tension?

• I use Redding's competition die set with the neck bushings and want to confirm what size bushing to use.
• I've had really strong results with my current 6.5 load. The die set I bought used on PX came with a 0.288 neck bushing. Currently, my loaded cartridge neck diameter using Berger 140gr Hybrids (0.264) and Hornady brass (0.0145) comes out to 0.292 average of 5 rounds.
• Neck tension of 0.292 - 0.288 = 0.004

Question 2: If I want to start with this same neck tension, how do I know what size bushing to get for 6cm -- component list below?

• Hornady brass 0.0145
• SMK 107gr 0.243
• Implied cartridge neck diameter 0.272 = 0.243 + 0.0145 + 0.0145
• My guess for bushing with 0.004 neck tension = 0.268??

Question 3: Can I use my 6.5cm Redding full-length sizing die to FL size 6cm -- I don't yet have the components in to try first hand?



Question 4: Anyone care to share a starting load and CBTO seating depth for 6cm using the component I plan to run

• Hornady 1x brass
• SMKs 107
• H4350
• CCI 200 LRP

1. Your math is fine. Yes, if the bushing you like is .004 less than the OD of one of your loaded necks, that's commonly referred to as ".004 neck tension", that said, remember that's just what you're calling it, it's not a measurement of actual tension, I'm not sure what the actual neck tension you're getting from your combo of brass and bushing unless you fully nerd out and get some gauge pins, but you get the idea...

2. If you've calculated your loaded neck OD will be .272" for the 6, then yes, starting with a .268" bushing as your baseline/reference should work for you. Doesn't mean you won't end up buying/trying .267", .269", etc

3. Yes, 6.5CM and 6CM are the same from the neck down, just swap out the bushing and pull out any expander if you haven't already.

4. A safe one to start with using those components IMO would be:

First, make a long ass dummy round to help you find out what your CBTO for jam is in your barrel (google Erik Corina and Jam videos if you need to)

If you have to size the brass first, I'd just barely touch the shell plate with the FL die so you're not smashing the shoulder back too much further than you have to until you know what it is (-.002" shoulder bump after you fire and measure it), and primer depth ~.005-.006"

39 grains of H4350 is safe and should get you in the neighborhood of ~2850-2900fps, depending on what you get when you chrono it you should be able to figure out what to do from there (if anything)

subtract .100" from your jam number and seat at that CBTO, that'll be a pretty healthy bullet-jump of .100" and will tell you whether you want to experiment with more jump or a little less depending on what you see downrange. Even if you're weary of bullet-jump, IMO if you would like your barrel to last longer than 1500rds, I wouldn't even bother seating any closer to jam than .040". Seating close to the lands in 6CM is awesome for like ~100rds until it changes and possibly turns into dogshit. More jump = more forgiving of seating depth, and with 6CM your goal post is moving, so if you don't want to have to constantly adjust your load, jumping is the way IMO...

Good luck!

 

[Senor_Barney]

1. Your math is fine. Yes, if the bushing you like is .004 less than the OD of one of your loaded necks, that's commonly referred to as ".004 neck tension", that said, remember that's just what you're calling it, it's not a measurement of actual tension, I'm not sure what the actual neck tension you're getting from your combo of brass and bushing unless you fully nerd out and get some gauge pins, but you get the idea...

2. If you've calculated your loaded neck OD will be .272" for the 6, then yes, starting with a .268" bushing as your baseline/reference should work for you. Doesn't mean you won't end up buying/trying .267", .269", etc

3. Yes, 6.5CM and 6CM are the same from the neck down, just swap out the bushing and pull out any expander if you haven't already.

4. A safe one to start with using those components IMO would be:

First, make a long ass dummy round to help you find out what your CBTO for jam is in your barrel (google Erik Corina and Jam videos if you need to)

If you have to size the brass first, I'd just barely touch the shell plate with the FL die so you're not smashing the shoulder back too much further than you have to until you know what it is (-.002" shoulder bump after you fire and measure it), and primer depth ~.005-.006"

39 grains of H4350 is safe and should get you in the neighborhood of ~2850-2900fps, depending on what you get when you chrono it you should be able to figure out what to do from there (if anything)

subtract .100" from your jam number and seat at that CBTO, that'll be a pretty healthy bullet-jump of .100" and will tell you whether you want to experiment with more jump or a little less depending on what you see downrange. Even if you're weary of bullet-jump, IMO if you would like your barrel to last longer than 1500rds, I wouldn't even bother seating any closer to jam than .040". Seating close to the lands in 6CM is awesome for like ~100rds until it changes and possibly turns into dogshit. More jump = more forgiving of seating depth, and with 6CM your goal post is moving, so if you don't want to have to constantly adjust your load, jumping is the way IMO...

Good luck!

Wow, my mind just blew up! Need to sit down and digest all this knowledge. Appreciated!

Below is my comp die set from Redding in 6.5cm.

• Middle with the yellow arrow (i dont know the actual term) is the dies that sizes the case
• Left die deprime and resize the neck (via bushing).
• Right is bullet seater

For clarification, the middle die in 6.5cm is compatible with 6cm? I already have it set it the holder at the proper depth for my 6.5cm, will i need to back it off / play with it first for 6cm?

 

[CK1.0]

Wow, my mind just blew up! Need to sit down and digest all this knowledge. Appreciated!

Below is my comp die set from Redding in 6.5cm.

• Middle with the yellow arrow (i dont know the actual term) is the dies that sizes the case
• Left die deprime and resize the neck (via bushing).
• Right is bullet seater

For clarification, the middle die in 6.5cm is compatible with 6cm? I already have it set it the holder at the proper depth for my 6.5cm, will i need to back it off / play with it first for 6cm?
View attachment 7682439

In that set: the middle die is the Body Sizing Die, it sizes the body-only (includes the shoulder), so yes, it's good to go with the 6mm as well as the 6.5.

The Neck Size die only sizes the neck so yeah, swap out the bushing and you'll be good to go. Just don't forget about changing out the expander too if that's what you use to deprime and expand your necks and you want to keep your process the same as you're used to (if it's a OEM 6.5 die the expander's OD is going to be something ~.263", you'll need ~.242" for the smaller bullet, just like changing the bushing).

Or, I'd recommend removing the expander thingy all together and opening up the necks in a separate step with a mandrel die, but if you're going to go there, then, I'd say you might as well get a new 1-step FL die purposely for 6CM...

Here's the thing: with what guys know now as far as collective reloading knowledge, it's pretty widely accepted and decided that neck-only sizing is wrong/dumb/bad/ignorant, whatever word you want to use, they all apply. That Redding set was state-of-the-art 20 years ago specifically because it allowed one to neck-size only most of the time, and then only size the body every now and again when it needed it because the rounds stopped fitting in the gun... guys thought it was better, it wasn't, old-thinking, all wrong. You need to fully resize a case every time, which means body size AND neck-size every firing if you want the best consistency/accuracy.

In your case it would save you a step, and if you got a Redding FL bushing die it'd still work with what you've already got for the 6.5 and provide you the smaller expander you need for 6 too, so you don't have to do it, but might as well sooner rather than later because you'll probably end up there (just saying). But, if you want to keep using the dies you've already got, that's fine too, it's just a second step every time because you should use both the body and neck die every single time.


Beyond all that, yes, you'll have to readjust your Body Die because the chamber may be slightly different (unless you're lucky as hell or if the two chambers are within a couple thou of each other which in that case, you wouldn't have to sweat it really if it was way more convenient for you to just leave the die set up).

 

[Mike Casselton]

You could also get a set of the Redding competition shell holders and once you figure out which shell holders to use, then it's just a matter of using it instead of moving the die.

I load for two 6.5 CM and use a shell holder that's .002 shorter for my Bartlein.