How important is grain/caliber for range work?
Here's the situation:
I currently have a .40 Glock 22 and 23. These are my primary carry guns. I have used 180 gr. JHP for carry ammo and 180 gr. FMJ for practice at the range. I have a limited amount of money I can shell out for ammo each month. I would like to get to the range at least twice a month, although weekly would be better.
My short term goal is to maximize the time/rounds vs money spent honing my marksmanship and familiarizing myself with the grip and trigger pull of the Glock. Long term, I would like to spend more time in tactical training.
Here are the questions:
1) Is it better to shoot the same grain you carry (180 vs 165) every time or is going with a lower grain for more ammo (165 seems to be cheaper than 180) on occasion a fair trade off?
2) Is dropping to a lower caliber in the same style gun (thinking of picking up a G17 and G19) acceptable for some target shooting in order to provide more shots per month (9mm ammo is substantially cheaper than .40)?
3) What is the minimum amount of shooting per month (rounds/range visits) you would be comfortable with to hone/maintain your skill with a gun?
4) Is it better to shoot 50 or a 100 rounds on a weekly basis or will one or two range visits firing 200 rounds accomplish the same thing?
Thank you in advance for any feedback. I've been around guns my whole life but am starting to get serious about mastering them and want to make efficient use of my available resources.