Long means good range and accuracy
Check out SVD version of Smersh system made by SSO. System is modular and pretty comfortable to wear. It has tons of different pouches available and is being used by real soldiers for long, long time now. Smersh can also be easily modified to be used with AK's, RPK's, PKM's without buying whole new setup. It's not cheap but totally worth it and will probably last your entire airsoft carrier.