Question

[Twotone]

Hi all,
I am loading .357, 158gn bullet. I am changing from a copper bullet to a lead rnfp. If I crimp the lead bullet where it is supposed to be crimped, just behind the shoulder i lose about .020" COAL compared to the copper bullet. At the same time I lose 1.39% of case volume.
This will then obviously increase pressure, i am just asking if this increase will be substantial or not? Using 12.5 gns of 2400 in the copper bullet has proved a great load and I am unsure where my start point would be using the lead with the decreased case volume. Althoug the load manual says start 12.2 gns with a lead bullet it does not say the type of bullet I am using. Any help would be greatly appreciated.

[clovishound]

First, comparing COAL between two different bullets to determine case volume is an exercise in futility, unless they have identical profiles.

This is especially true if you are comparing a round nose bullet to a flat point. Where the rubber meets the road is the amount of bullet that is actually in the case. I have found that most of the bullets of the same weight that I use have very similar distances between the canelure and the base. I normally just crimp in the canelure, begin with the start loads and work my way up.

The other issue is that .357 magnum was designed as a variant of a black powder cartridge, so it has lots and lots of room in the case when loading with smokeless powder. Yes, one must still factor in case volume, but it is far less of a worry than something like 9mm, that has a small case volume in comparison. Using faster powders, I can fit 3 or 4 loads of powder in those tall cases and still have plenty of room to cram a bullet on top.

I can't comment on 2400, but if you look at the data on Hogdgon's website, Most of the data for lead in .357 magnum maxes out on velocity long before it maxes on pressure. They don't list data for lead loads using their slow powders, like h110 and h4227. The pressures they list for medium to fast powders is well below max SAMMI specs.

My suggestion would be to use a different powder for lead in .357. Choose something a little faster than 2400. Unless you use something like Trailboss, you must be careful that you double check each and every powder drop, since a full load of powder in that big case is a fraction of the volume available.

Hope that's not too much info.

[ditto1958]

OP, I think clovishound is correct, and you would be best off using something different for lead bullets. Alliant does not list a load for 2400 for your bullets. My Lee guide doesn’t list one either. Lyman does have data for lead bullets and 2400, but their data is for bullets cast using their molds.

[Twotone]

Thanks guys, its such an intersting subject and so much to learn. I do have a tub of unique which i can play around with but never had much success before. The .358 copper plated bullet with 12 gns of 2400 I tried tonight was giving amazing accuracy, i was just wanting to switch to lead for cost reasons, shot around a hundred tonight and it gets a bit expensive with UK prices ! Thaanks so much for your help, really appreciate it, I did see those loads in my Lyman book but as you say , not for my bullet.