I had this exact same issue with a different rail. Bought a Spikes rail that should have been 1/2" short of the end of the barrel. Instead, it was 1/2" over the end of the barrel. I sold the 12" version and bought the 10" version.
When I read the thread title, I just knew it was going to be about the KMR. It got me too... KX-5 on a 7.5" barrel and a (supposedly) 9" barrel. For the record, when the KMR first came out BCM did not indicate that it was actually longer than the stated length.
Jagee, I have to agree, phylo's toy will obviously have issues with the disproportionate wave harmonics generated by the extended 'shroud'. I think he should donate it to the INGO committee on barrel harmonics for further study.
Bad bad phylo. Just to show compassion, I'll help you dispose of the SB-PDW brace.