The Broxa won't last long shooting that hot, 350fps tops. Anything over that will eventually break the mechbox and you won't be able to utilize the fps for range with such a short barrel anyhow. The MP5 platform isn't a long range gun. Be better to get it to shoot accurately for the 100' or so range it has. A tightbore is the first order of business, matched with a decent hopup sleeve & bucking. What's the fps now?
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