If you have a FS and a Compact, put your Compact slide on your FS frame and let me know how it works for you. As far as binding, why would there be if you’re using the correct guide rod for the slide installed... hence compact slide with compact guide rod.
I did. I posted it out in post #4. That's the problem. With the Compact frame and Full Size slide no problems. With the Compact slide on the Full Size frame there is serious resistance at full slide back. It doesn't feel or sound right and I perceive it as coil bind. When I get back from shooting today I am going to measure the guide rods and count coils. I'm thinking the shorter guide rod in the compact slide is going fully compressed. The Compact slide on the Full size frame just doesn't feel or sound right at say the last 1/8" before full slide back. The guide rod that's in the the Full Size slide is noticeably longer and hence has more space before full compression but I haven't measured it.
In the link from this forum that posted post #5 states "buddy of mine said the full-size 2.0 and compact recoil springs have the same number of coils and spring thickness ,haven't checked for my self but mine just broke after about 600 rounds so i guess ill either get a replacement from S&W or check out the full size spring,both have blue paint"
Both of mine have orange paint but I doubt paint color has anything to do with it. The .40 and 9mm should have the same springs. The Full Size and Compact do not, the spring is longer on the Full Size and before you ask, yes I'm sure the proper spring are in their guns. The slides easily interchange back and forth but there is binding or some other interference at the very end of pulling the Compact slide back on the Full Size frame.
I have never considered changing slides between the two but in marathon cleaning sessions I have put the wrong slide on the wrong gun. That was quickly noticed and changed. There is a variable here that you are missing and tonight I will try and see how much travel each guide rod has. If my assumptions are correct there is more with the longer guide rod.
Your statement that both frame sizes are the same size is incorrect, the Full Size frame is approximately 3/16" of an inch longer on the .40 Full Size then on the Compact. Plus it's a blanket statement, the frame on the 3.6 Compact has a Overall Length of 6.8 and is definitely shorter.
I think you can easily do the swap but will have to change guide rods. I had both guns side by side yesterday and measured. I came up with a 3/16" difference. IMO you are either going to have to put the longer guide rod in your conversion or you are going to break the shorter one because it fully compresses at the very end of slide travel. Under fire it may work for a while (600 rounds as in post #5 above) but somethings going to give. Hopefully it's just the guide rod and not the slide. I would go back to the LGS and check it out. I misread your post, yes "The FS slide on the compact frame seems to work" as I wrote in post #4 but "the compact slide on the FS frame seems to have what I interpret as coil bind". They seem to swap but at the very rearward of travel something is happening.
I misread your intentions and thought you were good to go. Yes it seems to work that way - FS slide on compact. I would go to the LGS and put the Compact slide on the Full size. Pull the slide ALL the way back. You will feel it get really hard at the most rearward travel and hear somethings amiss. I'm pretty sure it doesn't work that way or wont for long. If S&W would post part numbers you will see the guide rods for the 4" and 4.25" are different. Galloway shows this as fitting the 4" compact. If it fit the Full Size, don't you think they would state that?
https://gallowayprecision.com/smith...led-guide-rod-for-m-and-p-m2-compact-pistols/
Alright I'm off to the range, I'll post my findings after I tear them down and clean them. That will probably be tomorrow some time. I'm bringing five guns and will have a lot cleaning to do.