compression die

[Beekeeper]

Would someone please explain a compression die in plain english!
Was getting ready to buy one and hit a wall.
What I see on the web sites is a pin of some sort with a 7/8-14 thread head on it.
In the description they say nothing on how it is used.
On a post here someone wrote about it fitting a sizing die?
Everyone states they compress 120 to 200 thousanths.
How do you know as there is no micrometer dial or head on any of the ones I saw?
Do you only need one or one for each caliber and boolit?



Jim

[montana_charlie]

Would someone please explain a compression die in plain english!

Try this...

A die set intended for a straight-walled case will have three dies, and one of those is the expander die.
You can buy custom plugs for the expander die...which enables you to manipulate the case mouth for an exact amount of neck tension on the bullet.

You can also buy a plug which is not intended to expand the case neck.
Instead, it is a very close fit to the inner diameter of the mouth, and is cut square on the end to provide a flat pressure on a powder charge...or over powder wad...when compressing the charge.

In the RCBS and Lyman dies, the plugs (expander and compression types) have a 9/16-18 thread...and cost about $18 at BACO.

If you use the expander die for expanding necks (I don't because I shoot fireformed brass), then it's nice to have two expander dies...one equipped with an expander and one set up for compression. Then you don't to have to keep switching plugs during the reloading process.
You can get an extra (expander) 'die body' and equip it with the plug of your choice. That item (being a die which screws into your press) would have a 7/8-14 thread.
(Because each plug has a stop collar which can be locked where you need it, it is not unreasonable to switch plugs in the expander die. It's just more convenient not to.)


Adjustment of the compression plug for a certain depth can be figured out in a variety of ways. I have a fireformed, stretched and trimmed case with a moveable slug inside which can be set to a given depth...then used as a gauge for setting the compression plug.

Then, there are the various trial and error methods which work you into the setting you need.
The problem arises when you decide to change something in the stack...or switch to a different bullet style with different requirements.

I use my gauge to set the compression plug for the absolute deepest seating depth I will ever use. Then I place shims between the top of the die and the bottom of the stop collar on the plug. The shims mesure from .001" to .125", and I use the number and sizes which get my plug to the desired depth...then check it with my adjustable gauge.
To change the seating depth for a particular combination, I add or remove shims. That's how I get around the absence of a micrometer adjustment on the slug.

Do you only need one or one for each caliber and boolit?

You need one per caliber, at least.
If you change loads a lot (within a given caliber) you might want to have compression slugs pre-adjusted for each load...or separate compression dies (if you can stand the expense).

Did I leave anything out?

CM

[Dan Cash]

Would someone please explain a compression die in plain english!

It is a die with an adjustable stem that just fits inside the case mouth to compress the powder. A case expansion die can be used in lieu of a dedicated die but is not the best solution.

Was getting ready to buy one and hit a wall.
What I see on the web sites is a pin of some sort with a 7/8-14 thread head on it.
In the description they say nothing on how it is used.
On a post here someone wrote about it fitting a sizing die?
Everyone states they compress 120 to 200 thousanths.
How do you know as there is no micrometer dial or head on any of the ones I saw?

Trickle/drop tube your charge in the cartridge case and place a wad on top. With the compression die installed in the press and the stem screwed up so that it does not contact the powder charge and wad, raise the cartrige on the press ram to the top of the stroke. Screw the stem in until it contacts the wad in the case. Lower the ram and screw the stem in approximately enough to compress the powder charge enough to allow the bullet to be seated the desired depth. Raise the ram with charged case to top of stroke, compressing the charge. Remove the case from the press and measure the depth from case mouth to compressed wad and compare it to the desired seating depth for the bullet being used. Continue to compress and measure until desired depth is achieved. Lock the die.

Do you only need one or one for each caliber and boolit?
Yes. The compression plug is caliber specific.

Jim

I hope this helps. I too was confused when I first started and compressed with my bullet. That does not work.

Dan

[EDK]

Money versus aggravation, get an extra die body from Buffalo Arms and the appropriate size compression plug.

I measure the depth to the over powder wad with a dial caliper...it's what I have. Gently set the over powder wad on top of the drop tubed charge and measure; then adjust the compression die to what you want...with the proper seating depth of your booolit...and measure again. A checking device can be made with a length of dowel and a sharpie marker.

Mike Venturino's book SHOOTING BUFFALO RIFLES OF THE OLD WEST is one of the best; Randolph Wright's LOADING AND SHOOTING PAPER PATCH BULLETS, A BEGINNER'S GUIDE has a lot of good information that also applies to grease groove bullets. The little library of Paul Matthews books from Wolfe Publishing is good reading too.

Go over to shilohrifle.com/forums and do some searches and a lot of reading.

[Beekeeper]

Thanks Charlie,
That is one of the best explanations I have seen and explains most everything I needed to know.

One more question if I may!
Thought of it as I was posting the other time and decided to wait to see what answer I got.

I am going to be loading bottle neck cases,71/84 Mauser (43 Mausers) 577/450 and depending how I do maybe for my 577 snider and a 45/70 Handi rifle.
Met a guy that told me if I ever shot black I would never go back to smokeless so am trying to get as much data as I can to help me decide if it comes to that.

Thanks to everyone for your answers .


Jim

[Beekeeper]

Geez,
I went through all that and still didn't ask the question.See what happens when you get old and senile.
All of the data I have seen talks about the straight walled cases(ie: 45/70) does it still hold for the bottleneck cases (43 Mauser and 577/450) as well or is their some other tool for them?

Thanks again,

Jim

[montana_charlie]

When I typed that explanation, I edited it several times to make it more clear. I also edited it once to specify that it applied to die sets for straight-walled cases.

Frankly, you will have to get Kurt, or martinibelgian, or 'somebody' to talk to you about the bottlenecks. I have some impression of how they would be handled, but it's based on presumptions...not anything concrete.

CM

[Lead pot]

Beekeeper

My .44-90 BN's does not do well with compression over .200" and the over the powder wad must be in the case neck.
I compressed loads while developing a load from zero compression to .400. The zero to .100 is my best load.

Kurt

[Beekeeper]

Thanks Charlie, Leadpot,
I think I now have enough info to at least partally understand compression.
When I get to the point of trying to develop loads (if) I will get or have Buckshot make me a compression die for each caliber.
Thanks again for taking the time to answer.


Jim

[Tom-ADC]

One reason I switched to Swiss is because it doesn't take as much compression.

[martinibelgian]

577-450 - no need to compress at all. The case already is so big that you'll not even succeed in filling it to the level of the bullet base, and still have a reasonable load (i.e. less than 85grs of powder). FWIW, loading 577-450 is an art in itself, requiring special techniques, different from 'normal' BP reloading.
In general, for all BN cases, zero compression or very little will work fine. They don't 'work' like the straight cases, don't even try to load them the same way, it will just get you frustration and mediocre accuracy - and a sore shoulder, I might add....