20 rounds in one session is too much for my old bones.. 40 is an absolute non starter..
Typically I get in 3-4 sets of 3 shot groups (9-12 rounds total) in a single range session.. and thats all I want for a day shooting 300gr .375 H&H..
Thats off the bench though.. If I were shooting exclusively off sticks I might would go to 20 rounds.. but I think that would be about my limit..
I know there are a lot of folk here that dont care for lead sleds.. but for initial zero, and annual confirmation of zero that I do on all of my rifles, I LOVE my lead sled solo...
I just did 12 rounds of 375 (new scope needed to get dialed in), 18 rounds of .35 whelen (toying around with different loads to see what works well with the gun), 6 rounds of .308 (confirm zero), and 6 rounds of .22lr (confirm zero) this past weekend... and I didnt feel a thing at the end of the bench session