Okay, Heard from Cory at Lane Suppressors LLC. He said using a 6.8 with 8.5" barrel on one of their Titanium Scorpions would not be a problem. They use a 7.5" 556 full auto all the time and have for some time now. No problems whatsoever.
He also sent me some data comparing 2 Suppressors. The owner of Coastal Suppressors sent him one of their 458s. So they did some DB testing. Here are the results, Cory ok'd me posting these.
458 SOCOM 450 GRAIN LEAD BULLETS 20 GRAIN IMR 4227 TRAVELING 1020.
UNSUPPRESSED
1 161
2 162
3 161
4 161.5
5 160.5
AVERAGE 161
COASTAL MODEL X
1 145.5
2 143.5
3 144.5
4 144.5
5 145
AVERAGE:144.6
REDUCTION: 16.6
LANE SCORPION 458
1 132.4
2 132
3 134
4 136
5 135
AVERAGE 133.9
REDUCTION: 27.3
Impressive numbers. Glad I went with the Lane.. Now I just need to work up some sub loads. Man I wish I had more time. Spent the whole day in the shop. Not even close to being finished there and won't be for a month.