Every winter I seem to get involved in one of these wildcat or conversion projects. Last winter, it happened to be a 22 Spitfire. The difference between the 5.7 Johnson and the Spitfire is the shoulder angle. The 5.7 has a 23 degree and the Spitfire has a 26 degree. 4-dproducts.com has reamers to rent for the Spitfire version. I used Redding forming dies and 2 dies are required as it is done in 2 stages. I want to explain something about the dies before I go any farther with this. I called the company who supplies Midway with their chamber reamers and discovered that there was a difference between the two. They were the folks who told me about the different shoulder angles. I then called Bruce Merkur at Redding and he didn't know there was a difference. After checking their blueprints, they found they were stamping their dies 5.7 Johnson but the shoulder was 26 degree for the Spitfire. I used the Redding 2 piece die set. Form die #1 is #90401. Form die #2 is 83401. This 2nd form die also requires an extended shell holder. Any questions on this can be directed to Bruce Merkur at Redding, 607-753-331-31.
I based my rifle on a CZ-USA 527 American in 22 Hornet. I had the barrel set back 1 1/2 turns and rechambered. The magazine isn't hard to modify. My rifle doesn't throw the cases out reliably like it should, but I think that is more of a gunsmith screw-up issue. I use it for ground squirrels and shoot it as a single shot so it doesn't bother me. I really like this cartridge and it performs great on squirrels. I'm using Winchester brass, CCI BR-2 primes, 13.1 grains of Lil'Gun and the Sierra 40 grain Blitzking and getting 3248 FPS. I tried using loading data for the 218 Bee as case capacity of water is almost identical, but it seems that data for the K-Hornet is better. This is also what Cartridges of the World
recomended.
