Hunter Keith,
The Challengers are great pistols. You’ve probably seen the picture of my Challengers and Buckmark here on the forum. For the age of my Challengers I only use target velocity ammo.
The screw on the back of the slide/frame is to adjust the trigger pull.
You can tell the year of manufacture from the serial number. The “U” means it’s a Challenger. That U separates the serial number from the year it was made. From 1962-1968 Browning used a single digit before or after the U to show the year of manufacture. For instance a 2U12345 or 12345U2 is a Challenger made in 1962 with the s/n of 12345. In 1969 Browning went to two digits to indicate the year. Mine are a U7 and a U8, (‘67 and ‘68), after the s/n.
Original Browning Challenger magazines are harder than hens teeth to find. I think Browning only shipped them with one magazine. I have two original magazines and one aftermarket Triple K magazine, but it doesn’t fit well in the magazine well.
If you have access to a mill, Buckmark magazines can be made to work.
Bill