Walther P99 in 40 S&W - MIGHT/MIGHT be able to be converted to 357 SIG
AdamsQuailHunter
Member Posts: 2,022 ✭✭✭✭
"Spyman" the Walther P99 was produced in a 40 S&W chambering:
https://www.gunbroker.com/item/987889190
The parent case for the 357 SIG is the 40 S&W case.
Since I have a Browning Hi-Power in 9mm and a CZ-75 in 40 S&W - I got out my electronic digital calipers and did some cartridge measurements. The 9mm had a case diameter of .3845 inches - the rim diameter was .349 inches - and the overall length of the round was 1.150 inches.
The 40 S&W case diameter was .420 inches - rim diameter was .421 inches and the overall length of the round was 1.122 inches.
The 357 SIG is a necked down 40 S&W case and the Walther P99 was produced in a 40 S&W chambering. The dimensions on that slide model would be suitable for all of the 357 SIG dimensions.
Theoretically - it MIGHT/MIGHT be possible to rechamber a 9mm barrel for the 357 SIG case - providing the barrel diameters are the same on both "models". BUT/BUT - the diameter of the 357 SIG case is larger than the 9mm case and it is very likely that the feed ramp would have to be modified for that case diameter. This is something you might want to post up a "Paging Forgemonkey" on the "Ask The Experts" and/or "General Discussion" Forums.
Another - BUT/BUT to be considered is that the 357 SIG pressures are higher than the 40 S&W - according to the "Wikipedia" cartridge description.
You will need to ask the more experienced members if they know of a "smith" that could do the conversion work and maybe get a copy of the "Firearms News" and check the "smiths" section and inquire directly to the various ones with a listing.
Best Regards - AQH
Comments
I would ask Rocky. I know he is extremely knowledgeable, when it comes to reloading.
Why? Just buy a model that comes in .357 or has conversion bbls. You can’t just widen the chamber on a 9mm. Extraction and recoil to need the .40 slide assembly.
any pistol that comes in .40 could theoretically be converted to .357 sig with a bbl swap yes .357 sig uses a 9mm bore. your measurements are irrelevant
just buy a 9mm rated for +p and shoot hot 9mm. for no trouble.
if you want to spend as much as another pistol to make something that might not work and hurt resale value for no real benefit I don’t get it. No appreciable increase in performance.
I’d just look for a barrel in .357SIG and drop it in. There were 3 choices for them and you’re gonna have to scour the used market for them as they are discontinued. Walther made a very small amount of them. Bar Sto and Jarvis Custom did as well.
But as someone who owns a gun in the caliber and loves the .357SIG I can tell you feeding it is EXPENSIVE as hell. And most ammo companies have watered it down A LOT from the original load…124 grain bullet going 1450fps that equaled the similar.357 Mag load down to 1200fps. To get full power stuff you have to buy Buffalo Bore or Underwood or reload for it. IMO I’d stick with .40 and just find a fast 150-165ish grain load which Underwood has for reasonably cheap and gets very close to the original .357SIG speed without having to spend $200+ on a barrel.