Fire forming 7mm TCU from .223/5.56 brass

Danny Ross

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A TC Contender I got recently came with a 7mm TCU barrel. Checking online, I found that most videos showed using 7mm TCU dies to expand the .223/5.56 brass to 7mm, then fire forming the result in the barrel that will be using by firing a loaded cartridge. This process seemed unnecessarily complicated, not to mention expensive as it uses a 7mm projectile, of which there seem to be a shortage here anyway.

Being a congenital cheapskate, and lazy to boot, I decided there had to be an easier way.

I had read about fire forming without a projectile by loading Unique, topped by a small wad of toilet paper to hold the powder next to the primer, topped by cream of wheat, and the whole topped by a wad of wax. Being a southern guy, I substituted grits for the cream of wheat, and a small square of aluminum foil for the wax. I annealed the brass before loading it. I started with 4 grains of Unique, which did not expand the neck to 7mm, and quit at 8 grains, which sometimes expanded totally and sometimes did not.

Next I substituted Bullseye for Unique, and found that 5 grains always fire formed the brass perfectly to the chamber. I did this with 20 cases and did not have any neck cracking, even though I did not anneal 5 of the cases.

My next step will be to test accuracy, but that will have to wait until I can cast some projectiles. I will add to this post when I do so.
 

swampratt

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Excellent!
I love that you were thinking outside the box and saved on projectiles.
Welcome! from a late post and 2019 join date. I hope you continue to post things like the above.
 

TheDoubleD

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Back a long time ago to make 7 TCU brass I just fired .223 cartridges. Necks and shoulder blew right out. After forming I annealed by holding the brass with thumb and forefinger and rolled the neck over the flame of cigarette lighter. When I felt the heat in my fingers I dropped the case in cold water to quench.
 
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