5,56 to 7 TCU

[kr54]

Several posters have mentioned just firing the 5.56 cartridge in a 7mm TCU firearm to form cases. My Contender just dents the primer. Is there any trick to getting 5.56 cartridges to fire in a TC 7mm TCU?

Thanks.

[dannyd]

I always used 223 remington brass because the 5.56 didn't work for me. I made and reloaded about 650 rounds shooting silhouette. Even in 300 blackout I find 223 brass works better to.

[Greg Mercurio]

kr54: No tricks required. You need to size the case until it JUST allows the action to close with a healthy snap. This keeps the case from moving forward with the firing pin and extends case life. Keep adjusting the sizing die down until you achieve the above. I fireform with a minimum published load and 140 grain bullets. I'm too lazy to anneal, so I lose some to split necks but I have thousands of donor cases so a few lost every once in a while is acceptable. There were a bunch of articles written by Bob Milek and Steve Herrett regarding the case sizing/fireforming process during their development of the .30 and .357 Herrett. Worth researching for scanned or PDF copies. I've used that process on just about every case I've reformed.

[kr54]

Not formed as 7mm, these are loaded 5.56 cartridges. They just won't fire. Sized primed 223's will fire the primers, but the 5.56, don't.

[45_Colt]

Could be that the hammer spring is on the light side or weak. Military cartridges generally use a harder primer to prevent slam fires. They may fire on a second attempt.

45_Colt