Could be related to the stock trigger bar and sear cage. One of our newest gunsmiths ("Big John") made an amazing discovery this month on the DA pull.
If the trigger bar goes rearward just a few thousands to much at the very end of the DA travel, the DA can stack at the end of the pull and really push the weight up in DA.
Big John also figured out the solution. We observed one test CZ go from a "stacky" 8lb. 6 oz. DA down to an amazing 6 lbs. 14 oz., with a linear DA using his fix.
I too have noticed some variance in DA pull feel amongst very small differences in sear-cage-to-frame fit. Like.....if there's more movement of the sear cage, there is a bit more stack at the end, but if there's less the DA pull resistance seems to 'fall off'a bit earlier. I actually prefer the former a bit more in my two shadows as the DA feels a bit more 'linear' on quick pulls, whereas with the latter sometimes there's a little more chance of gun movement right before the hammer falls.
Also, I replaced the trigger bar in my Accu Shadow with a stock unit to get a little more trigger reach as the area where it engages the sear was different by around .009".
In my SP01 that I converted to SAO and mated with a TS Long Slide, there was a lot of clop between the sear cage and frame. Obviously no DA pull, but in SA you could notice a fair amount of camming even with a competition hammer and see the movement in etc manual safeties. So I did the 'stabilizing pin' mod on that and put made the SA break nice and crisp.
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