Need help fireforming brass

[moombaskier]

I have a 7mm-375Ruger and 200 hydro formed brass. I worked up a great load with the raw brass, but when I went to use the fire formed brass the load went south. I'm trying not to use up a bunch of H1000 and my 180VLD's just to get the brass final formed for my chamber. It appears that the brass needs to grow about .006" in length from rim to shoulder. What's the best way to do this?

 

[Stormrider]

If I understand your question properly, these methods will all work.

You can prime the case and put in about 15-20 grains of pistol powder and fill the rest of the case with cornmeal.

Or, you might be able to load the bullet long enough that it jams into the lands and holds the case to the rear of the chamber.

Expand the neck up one caliber and form a false shoulder in your resizing die that is in the right place for proper headspace.

 

[BountyHunter]

The cream of wheat or cornmeal method will fireform using fast burning pistol powder to the 95% point IF you carefully work the load up one at a time and test it before doing all of them. You want to use enough powder to get a clean sharp shoulder. Only way is to test and shoot one piece of brass until you get there and then test virgin piece to compare.

Be sure to use either wax or tissue paper in the end of the case.

If you have muzzle brake take it off!!!!

Second best method is the false shoulder method. Expand the necks up one caliber and then use a neck bushing to size just enough of the neck down that the bolt closes just a little tight and shoot them. Use the cheapest bullet around, and forget load testing but it puts 200 rds down the barrel which will be a lot in that case configuration. I would not use this method or the jamming into the lands.

Jamming into the lands burns the barrel the same as the false shoulder method and is inconsistent at times with ignition and final case forming.

Based on you having 200 cases to do, I would use the COW method above and try it to final fireform

BH

 

[Stormrider]

...
Be sure to use either wax or tissue paper in the end of the case.

If you have muzzle brake take it off!!!!...
BH

I forgot to mention that. Thanks BH.

 

[moombaskier]

I do have a 3 port brake on this beast. I really don't want to remove it cause I had it Cerakoted and there is no seam. What if I used cotton instead of paper or wax? Is that only used to keep the C.O.W. and powder from falling out, or to help increase pressure or both? So far the difference in case volume from the hydro formed and my fire formed is 1.5grs. of H1000 to achieve the same velocity and accuracy. I have already shot 100rds. and was looking for a shortcut.