Problems with fireforming 303 Brass for .410 shells

[44 minimum]

Here's a question for you guys out there that have been through this before.  What am I doing wrong?  I was trying to fire formed this Brass so that I can make 410 shells.  Here is what I was using -New Winchester Brass that was annealed, Remington large rifle primers, six grains bull's eye powder, filled to the top with cream of wheat.  I'm going to try to add a picture here so that you can see the results.  In the picture, on the left is a case that bulged, in the middle a new 303 case, on the right a case that had the base wrapped with two turns of masking tape and filled with powder and cream of wheat and fired.  Both of these cases are very difficult to extract, had to use pliers.  I've not ever fire formed anything before so I could use some guidance here.  A 444 Marlin loaded with powder and shot extracts easily and I might just have to use them for my project.  I will have to purchase them but I'd rather use the 50 new pieces of 303 Brass that I have.  Anybody have any ideas?

[John Traveler]

Nothing wrong with either your fireforming load or procedures.  The tapered .303 case lies down in the chamber and causes that bulging.  Trimmiing and a first firing with .410 will get rid of it.

Try holding your shotgun vertically when firing the fireforming loads.  The idea is to get the case to center in the chamber.  The masking tape trick works too.

Don't worry about the stiff extraction.  The freshly annealed case mouth and the cream of wheat filler makes the case cling to the chamber....the purpose of the fireforming to begin with.  Your loads sounds good too.  I usually use 5 to 7 grains Red Dot, Bullseye, or WW231 to fireform, and increase 1/2 grain at a time toget full case fillout.  That COW filler is what pushes the case neck out...and at safe pressures.

[John Traveler]

Oh yeah.  The scuff marks on the case from difficult extraction can be avoided by oiling or waxing the cases before firing.  No problem with lubricated cases in fireforming, unlike with bulleted ammo, where it can unsafely increase breech thrust.

Using a carbide pistol sizing die with also straighten out the bulged case no problem.  Try a .44 Magnum size, or if that doesn't work, a .41 Magnum.

[BIG Dog454]

Why  not just order some brass 410 shells from Midway?  Saves a lot of problems and not too expensive. midwayusa.com

[44 minimum]

thanks john

i've got 50 303 cases now i'd like to use, brass .410 shells to begin with wouldn't be any fun or challenge now, would it?

[quickdtoo]

Why  not just order some brass 410 shells from Midway?  Saves a lot of problems and not too expensive. midwayusa.com

Let's see, $20 plus $10 shipping plus $3 min order charge, vs free 303 brass, some time shooting and powder/primers, not much of a decision there.

Try the lube JT mentioned on the cases, it works, I've used TC Borebutter cuz I had it handi, smells good too!!

Tim