Well they used to load factory Weatherby ammo with Hornady's with NPT's as increased price upgrade. I never shot any Weatherby ammo as I thought it was too expensive. So when I got the chance to buy some Eldorado (PMC) factory stuff marked way down that featured original Barnes X 130gr for my 270 Weatherby mag I thought I'd give them a try and wallah copper fouled bad in 6 rds same as your experience. Next I tried the 6mm 85gr Xlc ( blue coated ones) in the 240 Weatherby actually got 3 3 shot groups this time before fouling out. I DON'T USE Barnes X bullets anymore in anything period.150 Hornady SP flatbase and a max dose of IMR 7828 gives me 3150 out of a 24" Mk 5 270 Weatherby mag AND GREAT GROUPS,as well as exit holes on every deer I shot with it. 100 gr Hornady SP flatbase worked well in the 240 ,243 and 6 mm with exit holes all ways. Weatherby thought Hornady's were the right bullets so maybe you should try them. I'm talking about their flatbase Spire Point Interlock line not their hp or any of the plastic pointed blow up tips they make. The old 120 gr hp interlock didn't expand well for me with 3100 fps 25-06 loads on antelope but maybe they would be fine on deer if you can find some good luck.MB
The 120gn Hornady HPBT was designed for elk which is why you found it a tough bullet on light game. It was designed by Joyce Hornady and he has been gone since the late 70's.
