make it an MP5K, it'll be the easiest and cleanest. And with a proper barrel, it will work for all ranges, plus it's a great looking rifle to mod after.

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"For the sake of historical truth I must verify that only the Greeks, of all the adversaries that confronted us, fought with bold courage and highest disregard of death." -Adolf Hitler (From speech he delivered to Reich on May 4, 1941)
^^^true story