Not counting shotguns(don't really shoot them except when camping) or .22lr (I could burn through 500-1000 rounds of that a week), I used to shoot 500 rounds a month on average (quite a bit more weather permitting, not quite that much in the winter - didn't like paying range fees when I had a perfectly good backyard)
500 rds/month X 12 months/year = 6000 rds/year
I'm only 22 now and hope to keep shooting for another 45-50 years, so:
6000 rds/year X 50 years = 300,000 rds
Now, when we factor in that I only have one pistol that fits into my above caliber restrictions, and I hope in the future to be able to buy many more guns in 5 other calibers we have:
300,000 rds/caliber X 6 calibers = 1,800,000 rounds
Of course, I will probably have neither the time nor money to be able to shoot 500 rds a month in all 6 calibers, so for fairness' sake, let's divide my total round count by half the number of calibers:
1,800,000 rds = 600,000 rds
So my final answer is 600,000 rounds. This total is not counting .22lr or shotguns as I previously mentioned.
Sadly, I just realized that I have put more thought into answering this one question than I have into three years of college.
I have a mild interest in guns. Actually, I think the clinical term is "obsession," but that makes me sound like some kind of gun-nut. Which is fair, since I am.
Wastin' away my future children's inheritance one box of ammo, range fee, and bottle of Hoppe's #9 at a time.