I was experiencing 1 to 2 failure to extract jams per mag on my 357 DE. After cleaning, use new brass, load experimenting and online research I suspected either slide springs and/or extractor spring was the likely cause. Unknown how many rounds through the DE but likely significantly more than Magnum Research recommend to install kit to correct spring tension loss. Completely stripped and cleaned DE then reassembled with kit. Appears to have solved the problem as no jam in 4 mags so far. Note: Re-installing the extractor is very challenging as the pin is a very tight fit and the extractor has to be inserted correctly to be temporarily retained with a punch before driving in the pin (need 3 hands). Note: I understand each kit (357, 44 & 50AE) are exactly the same except for the mag spring. Note: The kit pricing (and all other DE parts) is a rip-off at $141/$161 or more than double the US price of $70 (US$49) as appears only available from distributor Herron. I wish Safari, Cleavers, Magnum Sport or some other dealer would bring in some parts more reasonably priced!!!