Supressor lowering Power!?

I have always experienced POI changes after installing suppressors on my air rifles. In fact, when I purchased my Wildcat from UA, the sales representative told me to expect a shift in POI when the suppressor -- which was mailed from a different location than the rifle -- was installed.

I have never tested for velocity changes when using a suppressor vs without the suppressor.

P.S. Occasionally, I have experienced pellet-clipping after installing an aftermarket suppressor. This condition can cause erratic POI.

I recently purchased Sumo moderators from DonnyFL. He had me purchase one size larger than the calibers of each of my rifles. They work fabulously. No noticeable POI occurred. The sound level was reduced dramatically. AND service was terrific.

Suppressors can change your barrel harmonics and POI. 

If you are unable to chrono your gun without the suppressor, allow a foot or two of space between the muzzle and the first screen. Muzzle/Air blast can give error messages.

Just a comment about not being able to get a reading with the suppressor removed. How much separation do you have between the muzzle and chronograph? If it’s at least 1ft, the chronograph should be able to read it unless it’s one known to be persnickety in the first place. Otherwise it’s an indicator that it is wasting air and you may want to try backing off the hammer spring until the velocity tapers off to about 95 - 97% of the maximum. 

The chrono he is using is a chrono attached at the end of the suppressor. So it's 1/4 inch from end of suppressor, I have one myself. Works fine but without the suppressor the air burst makes chrono give "bad" reading and doesn't work. When attached if also makes pellets fly all over the place. Definitely a poi shift. Regarding the velocity shift, I wouldnt be surprised if that's the case. But by how much fps is hard to tell with such a chrono. If he wants to test it he needs one that isn't attached to the suppressor..

I have seen poi shifts with suppressors too also accuracy issues. My Impact is more accurate with donnyfl Tanto than the factory caps and a little quieter.

Just a quick qualitative result here I observed when testing basically all the major airgun suppressor manufacturers back to back: POI shift tended to be downward, and seemed to be mostly dependent on the weight of the suppressor. This makes me think that bending of the barrel under the weight of the suppressor is the more significant cause of the POI shift than velocity loss. Some suppressors have no POI shift at all, at least none I observed at 100 yards. Your mileage may vary. I hope that is helpful.  

If you don't have an alternative chrono, and don't want to buy one, you might consider shooting groups at a series of different ranges with and without your suppressor. From there you can compare (or use a ballistic truing app) to do a diagnostic split between velocity loss and barrel flex. 

I hope that helps.  

The weight of the suppressor can cause a drop in poi if the barrel is an unsupported or supported barrel if it has some flex from the added weight. A change of harmonics due to adding weight to the end of the barrel can also cause the poi to change even if the barrel does not droop under the weight of the suppressor. Firearms will either keep the same velocity or have a slight gain in velocity with suppressors not a loss of velocity and I have never had an airgun lose velocity from the suppressor and never noticed my airguns increase velocity either.

I've never noticed any issues using a suppressor. The Sumo is my suppressor of choice and I have no problems with accuracy or power.

The loss of velocity with suppressor use is normal. In my experience the amount of speed attenuation is a product of effectiveness, where the more noise suppression the more velocity loss. However, speed loss is usually not more than 5%. STO is also correct that barrel droop due to suppressor weight is the primary reason for POI change, which by itself is not a reason for accuracy loss. If there is accuracy loss, assuming no pellet clipping, is primarily caused by baffle design inside the suppressor.

I would think that suppressors vary quite a bit. Considering even the weight added to the front of a long skinny barrel and it's affects on harmonics. Sure is nice to keep it quiet though. Some years ago Ruger and maybe others made a barrel tuning device that was little more than a muzze brake that screwed in and out. It made a huge difference having that weight moved around on the end of a long barrel.