Interesting. That's a big difference in velocity. I'm assuming 300blk?
A five round sample size probably isn't enough to make a determination solely on the silencer affecting velocity. For instance:
* Was the bbl warm for one string and cold for another?
* Indoors or outdoors? Environmental changes?
* Did you clean your bbl between strings?
* Confidence in the repeatability of your reloads? Randomly mixed batches, etc?
170fps spread is a lot. Almost like adding/subtracting 2-3in of bbl length.
I don't have enough experience testing velocities suppressed vs unsurpressed, so I'm not disagreeing with you. I just think other variables might need to be looked at before making a decision.
ETA: I'm also not sure where that extra velocity would be coming from. Once the tail of that bullet crosses the crown, suppressor on or not, aren't we done pushing that bullet out?