Getting down to the bottom of this -
...
So, we're talking about the trigger take-up and ease of break of his 228's SA break vs your 220's take-up but much harder/stiffer SA break..?
I wonder IF it could be in the trigger itself as I, too, bought a NIB 228/9mm not long ago and I'm thinking like mine, his came with the SRT, short reach trigger, vs the standard trigger (thicker, heavier) as seen below, possibly..?
Standard and SRT
As said, mine came with the SRT trigger which I didn't like, as it pinched my finger with each shot and my accuracy was way off so I changed it out to the bigger, standard, trigger and solved my problems, trigger comfort/feel and accuracy.
My 220R DA/SA has the standard trigger as well so the question is which trigger does your 220 have and IF his is the same or different as seen above than yours.
If that's it, then you might want to change to the same trigger he has and if not, then it's a simple fix via going with a lighter mainspring and using some kind of thinner lubricant down the face of the hammer face sear and on the sear itself that will stay and not attract dirt, spent powder, like gun oil will.
I've had great success with all my guns trigger actions using a synthetic dry lube called Eezox.
I'm sure it's not about quality control as, IIRC, his 228 and mine where produced in 2009 and my 220 was produced in 2005.
With your 4 first serial numbers, like mine is G382xxx I can tell you when your 220 was made a/o with your buddys 228's if you want to know. But -
I could be wrong, (i.e trigger size or feel) not "feeling" the SA action/pull/break of your gun but I've had 2 of my Sigs triggers that sucked in both DA and SA and both were easily fixed by changing out the factory mainsprings and treating the trigger action with Eezox, every now and then, as it last, works, for long periods of time in-between cleanings and re-treatments, being that Eezox is a cleaner/lubricator in one product I've been using with great results over the last 6yrs with all my guns.
And, both my 220 and 228 have the original mainsprings and both are "smooth" even/easy DA pulls with predictable SA take-up and clean SA breaks with no need of mainspring change fyi. But both have been treated, trigger works as mentioned, with Eezox which makes any metal on metal contact slippery. Whereas, my one 229/40's DA pull felt like pulling a boat anchor across a patch of tiny rocks and on the other the SA break had a lot of "creep", after taking up the slack, before the actual SA break, and that, too, was made right with lighter mainspring and treatmeant with Eezox but -
Let's start with what trigger, standard or SRT you have and your buddy's size trigger..
Ls