Alright, I just did some science.
1 nickel = 5g
Blank Leo = purchased new by me from EK in Feb 2014, serial #944Key 1: held 11 nickels, 12th collapsed the dome
Key 2: held 11 nickels, 12th collapsed the dome
Key 3: held 10 nickels, 11th collapsed the dome
Key 4: held 10 nickels, 11th collapsed the dome
Key 5: held 10 nickels, 11th collapsed the dome
Average force required to collapse domes: 57gPrinted Leo = I purchased used, but it was part of first production run, serial #419Key 1: held 9 nickels, 10th collapsed the dome
Key 2: held 9 nickels, 10th collapsed the dome
Key 3: held 10 nickels, 11th collapsed the dome
Key 4: held 10 nickels, 11th collapsed the dome
Key 5: held 9 nickels, 10th collapsed the dome
Average force required to collapse domes: 52gI did multiple trials on each key, until I was satisfied that the results were consistent.
So, it seems there is, on average, a 5g difference between the two models. Of course this is not statistically significant, but these two Leos are absolutely different.
Sadly, I don't have my 55g RF handy to use as a control.
If you want to post your serial number and test results, it would be interesting to see.