That will only work on the pistol. You'll have to use the standard dimension that HK world quotes for a barrel length if you have the rifle... for now. Unless one of these guys can help you out. I cut mine myself so it's 9". I think the one on the gun is something like 8.85" long.You can measuring the barrel length yourself, just drop in a cleaning rod, so it rest against the bolt face, mark it at the muzzle, take it out and measure.