Diameter difference in RCBS .357 Sizers

[shooting on a shoestring]

I've been following the thread on case neck tension - good stuff. I got excited b/c I've got a NMBH in .357, 4&5/8 barrel that I've not got to group well. I haven't paid any attention to case neck tension on my .357s, so I decided it was time to investigate.

I have 2 sets of 38/357 RCBS dies. Both are carbide. I found one sized my Winchester cases to .355" inside diameter and the other to .354". Upon further inspection the smaller is marked "77" on the top of the die, the larger "79".

I wasn't aware there were different sizes of sizers to be had.

Incidently, the expanders from each set both measured .355" O.D.

After seating and pulling some Group Buy 175 gr KSWC cast air cooled WWs, I discovered the boolits were getting sized by roughly 0.002". The mould drops the boolits 0.359 @ 90 degrees to the parting and 0.357 at the parting. The boolits were run through a 0.359 die (which really measures 0.359) and lubed with Felix Lube, and they were not sized by the die. However after seating and pulling them, the diameters were 0.357 to 0.355, still out of round, but smaller. I didn't expect that.

The cases were sized with the smaller die w/o using the expander, a couple were sized with the larger die w/o expander, and then some were sized using the expander. All sized my boolts to .357 x .355.

Looks like its time to go to harder boolits, and perhaps I should lap the mould to improve roundness.

Perhaps my grouping problem is not the Blackhawk, but its fodder.

[HeavyMetal]

I don't think you need harder boolits I think you need an expander plug that mike's .357!

Seat boolits and roll crimp as needed to secure the boolit.

As for the RCBS dies, many people do not know that RCBS stamps the year of production on thier dies. In this case you have one sizer die made in 1977 and the other in 1979.

Leave the boolit alloy alone until you try the bigger expander plug!

[44man]

I don't think you need harder boolits I think you need an expander plug that mike's .357!

Seat boolits and roll crimp as needed to secure the boolit.

As for the RCBS dies, many people do not know that RCBS stamps the year of production on thier dies. In this case you have one sizer die made in 1977 and the other in 1979.

Leave the boolit alloy alone until you try the bigger expander plug!
Harder would be better. Reducing case tension will not improve accuracy. Not the way to go for revolvers.

[S.R.Custom]

SOS, You mention you're shooting air cooled WWs. Try dropping them straight from the mold into a five gallon bucket of water. (Water quenching.) That'll harden 'em up, and you won't have to change a thing.

BTW, you're not using a Lee factory crimp die, are you?

[shooting on a shoestring]

HeavyMetal, gee I learn something new everyday. Year of production - I wonder why that would be useful information on a die?

SuperMag - No Lee factory crimp die here, but thanks for the thought. I do water quench as needed, and this looks like its needed. I had these AC'd for .38s and didn't have time to cast another run. That'll come in a couple of weeks. Mean time, today I need to go empty some brass so I'll have room to work up some new loads. Got unload once in a while to be a reloader.

Yep I'll be working on harder boolits and more case neck tension in the next couple of weeks.

[cbrick]

shoestring,

HeavyMetal said (Leave the boolit alloy alone until you try the bigger expander plug!) and 44man said (Harder would be better) and are both right? How could that be?

You didn't mention what your load is or what velocity your trying to acheive, only bullet weight.

If your using a faster easy to ignite powder HeavyMetal is right, try a larger expander plug with the softer alloy. This will give you less case tension but this will be somewhat less important with smaller charges of an easy to ignite powder and your bullets won't get sized down. A good, solid crimp could help if needed.

If your using any of the slower (and harder to ignite) powders and especially the slower ball powders 44man is right. Case tension is everything to revolver consistency and accuracy and its not possible to compensate with crimp. Try an alloy that's just barely hard enough to prevent sizing down the bullet but keep in mind that too hard can be worse for leading and accuracy than too soft.

Rick

[GP100man]

time for a lyman M die.
i ran into the same thing especially with pmc brass because it`s thicker .
M die titened up groups & lessened throat leading .
it`s all on me now!!

GP100man:castmine: