No you can not interchange them. The hole beneath the muzzle is larger on the Gen4 to accomodate the larger RSA.
Gen3 on left and Gen4 on right.
Gen3 on left and Gen4 on right.

Interesting! Glocks are the best, there are so many accessories and modifications they take.chuckds said:You can use a Gen 3 in a Gen 4 if you use an adapter "washer".
Thank you for your help!Argyle_Armoring said:That's why I have my business. To help Glock shooters have an even more enjoyable experience. I love the Gen4's and prefer them over the Gen 3 Glocks.