How do rifle suppressors affect muzzle velocity?

There seems to be some debate as to the effect of a suppressor on a rifle’s muzzle velocity. Some say it doesn’t affect the muzzle velocity, while other contend that a suppressor will increase your MV, effectively lengthening your barrel. I’ve been gathering data on the same loads in the same guns with and without a suppressor trying to determine if any meaningful conclusions can be reached. While I’m in a never ending data gathering process, I decided to share some of the information I’ve gathered so far to add to the conversation.

First up, let’s take a look at a Ruger Precision Rifle in 6.5 Creedmoor:

In the test shown here, I am comparing 5 different 142 gr SMK loads in the same rifle, both with and without a Q LLC suppressor.

You’ll note that in 3 out of the 5 loads, the non suppressed rifle has a higher muzzle velocity, while in 2 out of 5 loads, the rifle equipped with a suppressor has a higher muzzle velocity.

What about on a rimfire?

In this case, let’s take a look at my Lithgow with a Q can.