This my be a stupid question,but seeing that it is a rimmed cartridge has there been many wildcats in TC based of this round? You got to remember guys i've spent most all of my time loading for wheelguns. So don't be to hard on me if your thinking where's this guy been for the last 30 years.

That's another that is on the edge of the envelope for the 'Tender. If you don't push it hard it will be safe, but not for factory fodder.

I wouldn't shoot it in the Condenter either. Maybe the old cordite rounds are okay, but why take the chance? I shoot 303 alot and it falls between the 3030 and 308 winchester, but it does shoot a nice heavy slug.

The original .338 JDJ was based on the .303 British case, and was chambered in some Contenders. However, after a time, JD noticed that pressures could become erratic and quickly escalate with some loads, so the round was dropped. Shortly thereafter, the .338 JDJ No. 2 was developed off the .444 Marlin case, like the .309, .358, 9.3, .375, and .416 JDJ's. The .338 No.2 is outstanding.
The original .338 JDJ is the only wildcat I'm aware of off the .303 case that has been put in Contenders, but there certainly may be others. Incidentally, in the book "Big Bore Rifles and Cartidges", Ken Waters reported that he also developed a .338/ .303 British Improved cartridge for use in reboring a shot-out Rigby rifle. I have no idea how closely his cartidge and JD's compare.

The 303 case has been wildcatted extensively in Europe and Australia for rifles. It's like our 30-30/308 over there.

WOW great info. guys, thank you. I knew if i asked about this old round you guy's would be able to give me the scoop. Sounds like if one was to wildcat off this round you had best stick with the encore frame.

Back in the day, I made .445 SuperMag cases from .303 British

Interesting.

Now since we're on this topic, several people have cut their .35 Rem. Contender barrels to allow for a rim, and subsequently formed ".35 Remington Rimmed" brass from .303 British and .30-40 Krag cases. I don't have all the stuff necessary for measurements etc. handy here, but could some of you who have done so, enlighten me on what all needs to be done in addition to necking the case up- trimming? fire forming? special dies, whatever. Thanks.

Maybe a tapered expander, a little trimming and fireforming...I can't see anything special really needed. I've not done it...my supply of the standard .35 Rem brass is too plentiful.

a 35rem trim die to cut the 303 to it's new length, size in regular 35rem dies, and fireform to shape. i like it.
as long as your factory chamber is not too deep to start with, it would not be 100% necessary. mine did misfire with some factory ammo, plus i just wanted to do it "because", plus a rim is kinnda nice to hang on to.

I made some 445 brass last summer from 303.No special reason I just came up with some 303 brass ( about 300 pieces) and gave it a try.