Re: Law Enforcement Suppressor Question
My thoughts. Point of Impact (POI) change and to a lesser extent First Round Pop (FRP) is experienced, to some degree, with every make of can.
I think it would help us all if you told us the first round POI location (as opposed to the following grouping).
It is important to remember that POI can be caused by a number of issues and those same issues can "stack." In other words, multiple reasons can come into play.
In a general way:
1. The weight of the suppressor. The addition of anything to the barrel, whether from the pressure of a fore-end (non float), the addition of a muzzle brake, flash hider, etc. will effect accuracy to some degree. It is for that very reason that adding the weight of a suppressor to the very end of a barrel causes Point of Impact (POI) changes. Heavier the can the more the barrel will be effected and is the reason some go with more expensive lighter materials in their suppressors. This would effect every round fired, and as such, appears not to be your problem.
2. The baffle stack. There are numerous configurations and designs found within cans. They all can have great consequences to accuracy and repeatability of POI. Depending on make and model, one can see huge differences between "monocore" (single monolithic machined cores) and more traditional cone baffles. Even within each of those catagories, whether the designer makes his stack asymmetrical, uniform and balanced at each baffle or uses a series of off axis gas paths can make a huge difference. Precision cans, the very best ones, that I have seen all have the same characteristics, they use fully formed and concentric conical baffles, not monocores. This can effect cans as they heat up as well, making it a possible contributor to your problem.
3. Chambers, size and "timing". From the design of the blast chamber, to the size of each post baffle chamber, it all matters for real accuracy and FRP suppression. Here is where we can see the effects of blast chamber design and First Round Pop. Too much oxygen early in the stack and the probability of signifcant FRP is almost assured. This is most likely your problem.
4. QD or screw on. This can matter, but not always. In my experience it has to do with the design of the brake itself, the manner the brake's ports are "cut off" and the resulting dwell and heat sink surrounding the captured jet effects. This also can develop with heat effect, possibly your problem, but I think not.
5. Any manufacturer can produce a can with little or no POI shift. It is fast, cheap and easy to do. Just overbore the can until it all goes away. Some do and, as expected, their cans are loud. The trick, the skill is to produce as high a tolerance bore stack as you can to increase suppression and maintain accuracy. Very few people I speak with recognize that the highest performance suppressor will always provide "boost", that means a perfect 12 oclock rise as the can itself generates additional velocity. Few cans are that good, and fewer people want anything other than as little POI shift as they can get. So we see suppression gladly traded for lack of shift at this ultra high end of the suppressor spectrum.
What to do?
You appear to have both FRP and POI shift, and for the time being you should try the following.
1. Make sure your round has as little unburnt powder entering the can as possible. You did not mention barrel length, in your case it might matter to know. Overcharged loads, allowing for propellant to burn in the blast/primary, will set off FRP in just about any suppressor. You did not mention sub sonic performance or requirement. That leads me to wonder what about FRP is driving your requirement to suppress it. Significant FRP as it relates to revealing position is a study all unto itself and if that is your concern, I would tell you that those that have this as a priority include it on their list right below accuracy and blast suppression (the point being accuracy is first.)
2. Try introducing an artificial gas environment prior to the first round being fired. Rather than to spell this out, ask your armorer to pursue this. There are a number of ways to do this. Remembering that this is an extra step that some will employ that involves charging the can with gas, it requires thoughtful attention if the technique you will use requires the bolt be closed on a chambered round. I would note that ablatives (oils, even the lightest of oils) may not help in the least and can cause considerable issues in centerfire rifle cartridges. Equally unhelpful is charging the can and sealing the end cap with anything that is expected to be removed by the projectile.
Lastly, it is true that some cans are First Round Pop offenders. They cannot really be "fixed" as the designs and tolerances held in those cans simply make them a poor choice in this regard.
