Deathbydanish - I doubt that the 417 will be compatible with a M4-style outer barrel since the real steel models have specialty barrels; knowing VFC, it'll be almost identical to the actual firearm.
But a longer barrel, or extension, will be nice. I personally like the 20" barrels used on the DM rifles.
![](http://www.eliteukforces.info/images/sas/hk417.jpg)
-Gunner0331