Best way in my opinion to upgrade your M4(I like mine as a DMR), start with the inner barrel, 6.03 for starters, 6.01s require proper care, but 6.03s are just as good and cheaper. Add a suitable strong bucking, scs spacer, extend the outer barrel, either with a suppressor, or outer barrel and suppressor. To determine what inner barrel length you'd prefer measure from the hop up to the end of your barrel, convert the inches into millimeters, google it and it will pop up. You can add accessories and change the hop up if the stock version breaks for whatever reason, but start with those things if you want to see a change in your accuracy for cheap. ROF mods, will require new motor, battery, reinforced parts, if not stock already. Deans are high performance connectors increasing your efficiency and possibly a higher power output and ROF. You have to buy deans connectors for your gun, and you have to find, or make a connector so you can charge your battery. But totally worth it in the end. Lipos also do the trick, bust cost for a new charger and the possibility of burning your house down must be factored in.
