Tj or lothar Walther help

You may be mentioning two different things. The barrel profile you want may come from experienced shooter recommendations. The machine work might come from a tech who knows nothing of the best barrel specs, but is an expert machinist.

For what gun?

This list a few years old. Call for current prices.

On the TJ list it shows for .177 and others that the groove size is the same as the caliber everyone commonly refers to. However for .22 cal the groove size is .214, can someone explain this? Like for slugs in that barrel, the best slugs to go in it are .214? Also, some pellets come in 5.51mm, which is .217. Wouldn't that really constrict or even deform the pellet? Sorry Im not contributing to OPs question, just trying to learn something.

All airgun slugs that are 216 to 218 size and are produced from larger manufactures are based on a Choked Lothar Walther barrel.
Why you ask? It’s all about the money. These are production barrels for more higher in guns and there’s a lot more out there in the world over anything from Todd.
Kind of sad isn’t it? FX can Knurl out any twist and land size they want to compensate for the industry. Even Jorg from H&N will admit to this as well as Nick from NSA, JSB ect. I’ve been trying to change this way of thinking for years but neither manufacturers will get on track.
Still trying to corner of the market of shooting a slug out of a pellet barrel, crazy!

I would hit up @BillG to get your barrel machined. He has been machining FX barrels for AGN members recently.

Here’s a more updated price list from TJs.