I removed the grips from the 539 to see how the mags insert.
https://imgur.com/GdWotyx
At this point is where much more force is required with the 639 mags.
https://imgur.com/ZEhYqZZ
There doesn't seem to be any obstructions or the slot being too narrow, which is good.
Thanks for all the replies. The mags between the guns are normally compatible (my question answered), but something is slightly off with my 539, since all three 639 mags have the same resistance to smoothly insert into my 539.
I don't have the instrument to make a fine measurement. I will just...
Images of the 539 and 639
These are the links to my images that are not displaying. The links are wrapped in the img tags. There is a second set of links below this box with the img tags. They are just not visible for some reason.
https://imgur.com/dqXoHvq
https://imgur.com/7VtpTwh...
That's what I figure, but the force required makes me concerned that I will damage something in the 539. The mags insert smooth in their respective guns, and the 539 mag fits smooth in the 639.
I picked up a 639 and a 539 (nickel plated). The 639 came with 3 mags. The 639 mags look the same as the 539 mag. I can insert the 539 mag in the 639, but none of the 639 mags want to insert into the 539, without a good amount of force.
Are mags for a 639 compatible with a 539?
Thanks