Got to know "when"
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To the OP..
At first, after the first 50 - 100 rounds, things (muscle memory) start going down hill as what you're feeling are all the new motor muscles coming on-line that you've never used before.
Think: stance/back, then head, arms/shoulders, grip-hands - wrists/fingers
All these tiny and, some, larger, motor muscles are being used and the_balance of all of them starts to fade, to fail, at some higher round count and on - per session.
I'd say - look at (first 50 - 100 rounds i.e accuracy and close (16ft - 18ft) and what you feel a month from now if you're going 1-3 times a month and your gun/s should start to feel lighter (even when loaded) easier to point to aim and your overall shooting should be improving (now at 20ft - 25ft) etc., along with staying power - i.e more good rounds as compared to however many guns and rounds you are shooting per week/visits - as of your/this post.
As mentioned, the only bad thing about shooting a lot of rounds, and 3 different guns, is the second and last gun you pick up to shoot are not gonna shoot as good, or long, as, say, if you started shooting with the last gun first.
Seems, of late, I take 3 guns: Sig P229n/r 40, Beretta Px4 40, and one of my Sig's 228/nr 9mm (but rare, low round count) or my main HD/SD 229R CT 9mm or SA EMP SAO 1911 9mm
Each gun goes thru, max, 50 rounds and sometimes, many times, I come home with 25 rounds left of 40cal and 20 rounds of 9mm just because the "rush phase" has been gone for a long time, IIRC, after the first year and now into my 4th yr - it's all about "quality time" and not rushing, rather, what I call "staying current" with my main guns of HD/SD, and type shooting I think will be needed, being aimed shots, point and aim shots w/double taps, and always a mag's worth of DA pulls with any of my DA/SA guns and 5 - 6 rounds with one hand only.
It's, as mentioned, too many rounds (early on) just makes for possible bad habits to form and the shotgun pattern effect shows it vs look carefully at your first 50 rounds, then the next 50 rounds (with another gun), etc. Not to mention why your hands are talking so much i.e hurting long after the session/s.
You should see your best shots in that first 50 - 100 rounds.. After that - until your motor muscle skills come on-line, permanently, with min once a week real time at the range and, as I said, the very same guns will feel much lighter, including trigger pulls as the trigger finger even gets stronger and, at the same time, the gun/s start to break in more and more, spring/strenght/felt-wise becomes less/lighter/easier/smoother the more you shoot them or practice (safe) dry-firing at home.
Try and learn to "limit" yourself vs the urge to shoot it all, in that, if you come with 400 rounds, try and only shoot 200 of it, for example, and work yourself down until you find what works (round count wise) with any of the 2 or 3 guns you take each time.
When it's all there, by not wasting ammo, and finding the_zone of quality time that is the positive-effect one wants, to walk away, knowing that one "is current" with whatever gun or guns one has for HD/SD needs..
Bottom line - In a Nutshell: when "frustration" enters, first starts, while at the range shooting or one has/feels when leaving, accept/learn when it "first starts" to set-in (being felt).. STOP, load-up, (unload) and "head home" and make mental note of round count.
"Less is more" (in staying current) not more is better - without need to undue the "shoot it all, high round counts" ending in frustration and bad habits - i.e the shotgun pattern effect vs what your see around you with the more seasoned shooters targets shooting far less ammo, for the very most part.
Most important:
Knowing that IF the day ever comes for a real HD/SD need and use of any gun you are current with will be, only, the first mags cold shots (otherwise, "a very low, cold, round count usage) and it's done/over.
OMMV,
Ls
Ps.. outstanding inner discussion on lubrication and that link provided along with a great saying: "If it slides - grease - If it rolls - oil "
(just kiddin)
