I am putting together a suppressed TC contender in 44 magnum. The twist is 1-20. I tested the carbine with 310 grain bullets cast from a Lee mold with gas checks. I used a Lee factory sizer die to apply a heavy crimp. 8.2 grains of NM04 (like Bullseye) gave 1050 fps with a stdev of only 7fps.

At first things looked good. I went through about 50 rounds testing various loads and sighting in. As I expended more ammo I noticed that my groups were degrading. At the end of the day I was shooting 6 inch groups at 100 yards and greater than 2 feet at 200 yards.

When I got home I noticed that I had a good deal of lead built up on the first few inches of the barrel. This was surprising as I used subsonic hard cast bullet with gas checks and I do not get this leading when using the same bullet at 1200 fps in my Blackhawk revolver. I need to find a solution to the poor accuracy and the lead buildup. Is it possible that a lighter crimp can help? Maybe I am damaging the bullet with heavy crimp?

I do not think the twist rate is too slow, but I will try a lighter (shorter) bullet to see it if helps. Any suggestions? Thanks.

Ranb

Maybe you need a softer alloy so your bullet will bump up sooner at lower pressure and acceleration?

likely the low velocity keeps the bullet from obdurating fast enough to keep from leading. You might try melting a bit of beeswax in a saucepan half full of water and letting it cool to produce a sheet of wax about 1/8th inch thick. charge the case with powder, press the sheet over the casemouth, and then seat the bullet.

Rich

You should size you're bullet to the size of your throat. You may need (most likely) to lap your Lee sizer out to .431" to 432"..
Your twist rate should be ok if your bullets aren't showning tipping on the target at 200 yds.

I am getting better results with no crimp and WC820, a slower burning powder. I need to get a better lube.

Ranb