On April 16th, 2016 I took the "plunge" and proposed a third "Mildcat" cartridge for inclusion in the "Ammoguide Cartridge Master Data Base".
On June 1st, 2016 this Design was PUBLISHED in the "Master Cartridge Data Base" of "Ammoiguide Interactive" website as Case Number 971
This one is intended as a Larger diameter and harder hitting Center Fire Alternative for the .22WMR for use in Firearms converted to Center fire that were previously chambered for the .22WMR. it is shorter than the ".25 Stevens (Long) Rim Fire" of similar diameters.
It WILL require Barrel revisions / replacement as the proposed cartridge uses .250"-.251" diameter bullets.
Case length is trimmed to 1.024" Nominal with 1.056" maximum case length and they are Resized down to .276" diameter. Rims are specified as .050"-.045" thick and .314" diameter maximum, with the Extractor Clearance Cut similar to the 5.7x28MM Cartridge.
Overall Length is specified as 1.260" to match .22WMR overall length. This should simplify firearm conversions.
A 65 grain Round flat Nose bullet is intended but lighter and heavier Bullets are possible within the Maximum Cartridge length. Twist rate is stated as 1 turn in 9.8 inches to match the Available "Lothar Walther" (LW) .25ACP/6.35 Browning Barrel Blank specifications.
The LW Blank is specified as .243" Bore with .250" Grooves (tolerance is .001" on inner diameters), 1.024" outside diameter and about 23.82" Long so a rifle could be made from them. These Blanks are Made with 6 grooves and a one turn in 9.8 inches Twist to the rifling LW uses Button rifling in both Cr-Mo Alloy Steel and Stainless Steel Blanks.
LW says their blanks can be made into barrels with only about .050" trimmed from the ends compared to others barrels that need 3/4" to 1" trimmed off.
For converted Revolvers and 'blow-back' semi-auto Pistols the loaded MAP probably should be limited to around the same as the .22WMR, or about 24,000psi or slightly higher, perhaps 25,000psi.
for "Locked Breech" actions perhaps the limit may be the 40,000psi of parent .22 hornet, or the 50,000psi of the parent 5.7x28mm Cartridges. Careful Development is Indicated.
I already have a Converted Ruger "Convertible Single Six" in the works that is set up for Center Fire and use of Reproduction 8 shot Replacement cylinders. I have three, now four, cylinders being reworked for it at the moment, one is in ".25ACP", a second is being chambered for ".250ALRM" (a 1.250" case length 'Mildcat' development project) which will also accommodate my "6.35x32mmSR when loaded to a Overall Length of 1.400" or slightly less, and a third that will be chambered for my "6.35x28.6mmSR" 'Mildcat' of 1.125" Case length which will accommodate this new length cartridge also.
My reamers are all products of "Pacific Tool and Gauge" (PTG) and have the drawing on file with them. PT&G Reamers have Taper to the Chamber Bore for ease of ejection. A separate Series of reamers By JGS Precision (JGS) Have Tight Straight parallel wall chamber Bodies of about .2795" diameter.Talk to Dave Kitt at PTG if you are interested in getting one of the Chamber reamers made.
Best Regards,
Chev. William