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357 AMP handloading

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BEEMER1 View Drop Down
Callahan's Auto Mag
Callahan's Auto Mag

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Post Options Post Options   Thanks (0) Thanks(0)   Quote BEEMER1 Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jan 2019 at 12:33am
As far as 19 grains being as low as one should I guess that all depends on the gun.  I was told to start there and work up until I found a load that would lock the bolt back and met my accuracy expectations.  Both 19 and 20 did that in my gun so I stayed at 19.

The springs in my gun probably need changed and after putting in Wolff +10% springs I am sure I would need to go up.

good luck.

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Luc V. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Luc V. Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jan 2019 at 11:36am


The numbers on the supervel file are CUP (copper units pressure) to make it even more difficult there is also LUP (Lead units pressure). Those two terms were used back in the days, depending on the type of crushers used.

One remark about the conversion formule you found, I would not trust this much because there are to much different copper crushers used. With each new batch of proofed crushers you had to be recalculate the whole formule to get the correct pressure. Back then you could not just read the pressure from a clock on the test pressuregun. It had to be calculated from the measurements of the crushed piece of copper.


As far as your 19 grains of H110 it might work well. The reason the slow powders work OK on much lighter loads as usual is because you used it in a bottle necked case instead of a straightwall case. I'm pretty sure  a to light load would not work well in a straightwall case.

I have a similar result with my 357 Sig caliber.

Because you have to push all that volume of burning powder throug a smaller diameter the pressure will rise (due to the shoulder in the shell) before the bullet leave the shell, not the barrel. Difficult to explain in words, but try this to understand: take a waterhose and sqeeze it off to a smaller diameter you will see that it will spray water much further because of the rised pressure. If you sqeeze it even more tighter you might burst the hose (if enough water pressure to start with.) I hope this makes you understand somehow the way pressure works...


To get back to your 19 grains load, to make it work well and consistent, make sure you have a verry good grip of the bullet in the case. The use of a factory crimp die (I use Lee Presicion) is recomended. If the bullet has to little grip in the case the primer can have enough force to push the bullet foreward before a good ignition of the powder. Then you should find much unburned powder in the barrel. If it burn well and have a clean barrel, you a probably good to go. 

About a case not completely filled with slow burning powder, it fails because there is to much room (airspace) inside the case and primer has enough force to blow the powder foreward and the flame is to cold to short for good ignition. I doubt it it could happen in a 357AMP case with 19 grains H110. Thats why I said to use magnum primers.

In all my reloading experiments I had that happen once with a very light load in 45-70 Gvt cartridge. I worked well when I switched to magnum primers.

It all sound difficult, but its just logic....








I would suggest to load 20 or 30 rounds and try them but also look good for accuracy, if they are consistent and good groups, it will work fine. If you have fliers all over the target the pressure (ignition) is not reliable you should adjust the load.








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paul v. View Drop Down
International Auto Mag
International Auto Mag

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Post Options Post Options   Thanks (0) Thanks(0)   Quote paul v. Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 2019 at 6:40am
This may help.
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