Depends partially on the brand of MP5. A G&G MP5 would be better then no name MP5. I like the MP5 for indoor and CQB environments. I do see people use them outdoors though. In terms of modifying it to shoot further (and more consistintley) it depends on the type of MP5 it is. Ive seen some nicely upgraded MP5's that people used outdoors and had good accuracy and range. Some brands have a wider range of parts available and are able to be take being upgraded better. Cheaper and low quality brands arn't usually compatible with most of the parts out their and are probably gonna break quicker.