I have acquired a spare stainless steel 21" factory tapered T/C Contender carbine barrel and I am trying to decide what to do with it.

Up here in Canada it is very difficult to find Contender carbine components so to sell this barrel would be a tough call but I do not need it in 22LR due to already having another 22LR barrel.

So I'm wondering if it is possible to just rechamber the barrel to 22 mag or a .223" bullet diameter 22 Hornet or does .001" not make a big enough difference and I can go to a .224" 22 Hornet or K-Hornet?

Depending on the twist which I would assume would be slow like 1:16 I'd say your best bet would be .22mag But if the twist is high enough I'd go with a .22 hornet. That is one hot little round.
Don't know about the bullet diameter but on something that small .001" might be a big difference

years back it was quite common to rechamber 22's to hornets. in fact there are bullets in 222 available yet (for the old rem jet) but having one of these old pieces i find 223 bullets work just fine, and actually 224 bullets work fine too, however i stick to the 223's

I've owned and shot several .22 Hornets and K-Hornets which were built on various single shot and bolt actions, using Model 416 Stevens .22 LR barrels, which used to be available forty years ago from Numerich Arms for a short song.

There was no discernable difference during actual use between them and any of my .224-barreled Hornets. They were just as accurate, used the same loads, and lasted just as long before showing significant wear.

Maybe that shouldn't be, based on logic alone, but in actual practice it is the way it has worked so far for me.

If it was my barrel, I think I might get it chambered in AI Hornet, work up loads it likes, and then just enjoy it.

I fully concur with Alberta. Your barrel is likely a 1-16" twist which will work fine with Hornet bullets that are typically 45 grains and less. It will probably work fine with 50 grainers, for that matter. You'll never know the difference between shooting .222", .223", or .224" bullets.

Thanks for the replies they are a great I'm definitely thinking 22 Hornet of some kind now.

I called T/C this morning they told me their 22LR barrels are all 1 - 15" twist rate.

I havea martini 12/15 rechambered to 22 k-hornet shoots great.