How to compress powder loads?

[44Blam]

I recently started loading for .357 sig and I found that a slightly compressed load of AA9 was really accurate.
I also saw that some people push the loads almost 1.5 grain past the top load I shot.
I loaded an Accurate mold 125-YG (my boolits drop right around 127.5 grain) and my "max" load was 13 grain of AA9 with a COL of 1.140".
At 12.5 grain, there was no (or very little) compression and the boolit set perfectly at 1.140. But at 13 grain, the initial seating set the boolit at 1.142". So, with 357 sig, it seems like you don't get good neck tension until you crimp the case...
What I want to know is, if I increase my charge to maybe 13.2 or maybe work up to something like 14 grn, what is the best way to compress the charge to ensure that I can still seat at 1.140" COL?

[NWPilgrim]

It gets compressed by seating it. I have seated bullets when the powder is to the mouth of the neck. There is quite a bit of airspace between powder kernels so when you compress there is a lot of air to be displaced.

If you can’t fit all the powder in, then you need to get a longer drop tube from the measure to the case (measure is off the press of course in this situation). The longer drop helps compress the powder a bit so you can get more into the case.

[tsubaki]

Use a drop tube, the same one used in black powder cartridge reloading.
You may also poke the powder with a narrow rod or wire as you are filling the brass, this is too tedious to be productive.
Trail Boss may be safely compressed this way but recent data updates from Hodgdon does not support some compressed Trail Boss loads.

[greenjoytj]

You could buy a steel powder compression plug to screw into an expander die body.
The 357 Sig not being a parallel sided case may not have an expander die in the set but maybe a 38 Special expander body with a compression plug. See the Buffalo Arms (BACO) web site for the compression plug or Track of the Wolf for a 38 special die body and compression plug kit.

[popper]

You will probably find a good crimp is needed to keep the boolit seated right. You can use a long drop tube to get better fill without compression.

[44Blam]

I loaded about 150 of these the other day (and shot all but 14)... They shoot pretty well and even after 136, my barrel was pretty clean.
Ended up loading 12.5 grain so there was no real compression. They certainly still bark pretty loudly so I would assume that it is super sonic but I have not chrono'd them yet.

[David2011]

Sorry; my first thought was to just put too much powder in the cases. Please have mercy on my sense of humor.

I had to pull some j-words the other day and found powder stuck to the bottoms of the bullets. The manual didn't list it as a compressed load but when I dumped the powder it was clearly compressed into the cases.

[fredj338]

Compressing a powder charge is just that, there is no way to do it better or more safely with ball powders. Stick or flake powders will benefit from a drop tube. Just understand that all powder can not be compresses in all calibers/cartridges. AA#9 is really slow, so even 110% compression in the 357sig will not likely show pressure signs. As always the bullet is the deciding factor but you are already loading near max with a lead bullet so going hotter, it will vary with the individual gun/bbl. Without a chrono, you are flying blind just adding more powder.

[beagle]

How about placing against a vibrating tumbler before seating. May settle it a bit. I'm loading some 20 guage dove loads right now (got to get ready early) and I find that I get better crimps if I tap the shell with shot loaded before crimping. Settles the shot a bit and makes a difference between just dropped and crimped loads and loads that have been tapped. I'm with the train of thought to use a BP type extended drop tube. Worked with black for a black powder shooting partner I had./beagle

[scotner]

I loaded about 150 of these the other day (and shot all but 14)... They shoot pretty well and even after 136, my barrel was pretty clean.
Ended up loading 12.5 grain so there was no real compression. They certainly still bark pretty loudly so I would assume that it is super sonic but I have not chrono'd them yet.

Here is the chrono reading for my 35-125Y (no GC) with 13.0 #9. It is only a 5 round group so take it for what it is worth but the velocity is pretty consistent at about 1300 fps with an sd of 6. And yes, I think it is safe to say that 12.5 grains is supersonic.

[44Blam]

Here is the chrono reading for my 35-125Y (no GC) with 13.0 #9. It is only a 5 round group so take it for what it is worth but the velocity is pretty consistent at about 1300 fps with an sd of 6. And yes, I think it is safe to say that 12.5 grains is supersonic.

Nice!!! I think I'll be able to get out to the range that I can chrono this weekend. Hopefully.