The only time I try to roughly guess how many rounds I've shot in any given gun, is when I've got one for sale, and I'm asked "how many rounds"? If it's a relatively new gun, and I figure it's been to the range once or twice, I figure a hundred rounds each trip, so my answer is often, I'll guess two hundred rounds. And guns that I have had longer, a round count is difficult..
Not being a round counter should not be natural to me. As an Ordnanceman, we had to keep track of how many rounds have been thru a given barrel on many of our weapons. I don't even remember how we recorded the count. :?
I often see in firearms classifieds in different sites, and then the question, "how many rounds"? And I'm surprised how many people do have an answer. It's got 3,268 rounds down the tube. Really? How do people keep such a count?
Lastly, when I buy a gun, I never ask how many rounds fired. I might ask how old it is, but that's usually volunteered by the seller in the beginning. I do look very closely at the condition, and certain wear patterns and cleaning patterns give me an idea of how much it's been used or carried, but round count is not an issue.
I have owned multiple SR9's and/or SR40's. My use pattern is, when a gun is new, I shoot it fairly often, a hundred rounds or more at a time, until I'm comfortable it'll operate when it's expected to do so. When it becomes a trusted carry piece, I find I shoot them much less often, other than to rotate ammo thru the magazines while I'm at the range ringing out other guns.
So, in spite of the multiple SR pistols I've owned, I'll bet the average is 500 to a thousand rounds per gun before I sell them and move on. Not a good answer, and it does not speak at all to longevity. And this would be a pretty standard answer for most of the plastic pistols I've owned over the years.
Now if you were to ask how many rounds I've shot thru any given all steel and/or aluminum (shooter) pistol or revolver, my answer could be
thousands. And if you looked at the bores and the guns in general, they will still look very nice. It's then, that if I was unscrupulous, I could say it's only had a couple boxes thru any of them, and it could be believable. Exactly the reason I don't ask for a round count.
I have bought similar condition guns that sellers tell me they've also shot thousands of rounds. It all boils down to condition.