Re: Once zero'd can a CAN cause POI shifts?
Well, I would have to say then a couple of items to look at and consider:
1. depending on the can design, you have heard of first round pop, well that noise is not all that is an ill effect, volume, temp and suppression can create some weird momentary issues, not consistent either! Have seen this over the many years and testing.
2. are we shooting reloads or factory? you know where I am going with this, quality of reloads basically could be questionable.
3. no matter if its an AI or X-brand, if the suppressor is maintained on the weapon constantly, never off you could still find a POI shift. when determining and checking for POI shift, I have found, taking the rifle out and performing the following will and has directly assisted me in many years:
1. rifle zero'd @ 100yds, I use the same ammo/lot for the entire run
2. cold bore with x2 follow ups
3. wait 10 minutes, with x3 rounds, suppressor attached, fire x3 rd group, determine initial POI shift.
4. now single load x1 rd (safety first here!) unsuppressed, fire, next attach suppressor load x1 rd fire, repeat this for a total of x6 rds, x3 suppressed and x3 unsuppressed, but the can on and off after each rounds. this will determine if the mounting device and suppressor are reliable and repeatable. this completes the 100yd testing and determines what you have in POI shift and repeatability. if all looks good here, you have your correction data, plot and lets go to next step.
5. 200yds, here I will perform the x3 rds unsuppressed, x3 rds suppressed for a quick verification, no corrections made, simple checking the repeatable/predictability of setup.
6. 300yds, here we make corrections, determined from 100yds and 200yds groups. fire x3 unsuppressed, make POI correction, x3 suppressed, and repeat this sequence x4 times each, making a group total grouping of x24rds. This will consist of x4 3rd groups unsuppressed and x4 3rd groups suppressed.
With all this being done, what you have completed is a true break in of the suppressor and muzzle attachment, reliability, repeatability checks and most of all SELF ASSURED confidence in the setup you call YOURS! One note, most always ask me, is what do you find to be the outcome. If I can do the 300yd grouping at the end, cover the group with the palm of my hand, you have something to work with. On some suppressors, I have found even with the POI corrections, the end results here could and have demonstrated as much as a 4MOA end result. Single flyers, from can off to on and so on will create this. No matter what, the proof is there, you have to work it, determine it and deal with it at this point.
End note, I don't understand why someone would leave a suppressor on all the time, especially a precision rifle. This tends to be more problematic than less corrections and issues in the end.