Real-caps?
 

Want to run M-series with strictly real-caps with 30 round capacity ONLY. No lo-caps, no med-caps. What brand am I looking for that is *generally* compatible with different brands?

you Could take mid caps and just fill them with 30 shots... just saying...would be simple enough I imagine.

or pin them to 30

I do 30 loads now, pain in the ass with the loader, time consuming, and generally imprecise. Didn't know you could pin airsoft mags. Explain process?

take the guts out of the mag, load the mag to 30 rounds, then drill and insert a pin to prevent the follower from going any lower (just make sure you don't pin the spring in position)
Alternatively, remove the spring and backfill the back so the spring is fully compressed when you load 30 rounds

You could also use a loading tube instead of a speed loader, that's how I load all my PTW mags to 50 rounds precisely. I agree it's very difficult to do with a speed loader

Similar process as pining real magazine but I'm pretty sure it's going to be pain to do. Airsoft lowcap/midcap also has spring with follower, similar to r/s mags. You'd have to open each mag and pin it to 33/35 rounds. I use something different. I have shortened AEG loading rod, which is cut to hold 70 rounds, half (35rd) is marked with electrical tape. Rod is not too long and fits fine inside vest pouches. I use it in the field and can load a mag in about 30 seconds without spilling a single bb. Open the bag, close top end of loading rod with your finger and keep pocking inside of the bag. Rod will fill up in couple of seconds.