Even if you don’t isolate out the reflective surfaces and use anechoic foam to reduce echo as much as possible (which is a best practice), you have a relevant test indoors from the basis of comparison of one can to another in the same position on the same equipment.

Out in the world where people shoot silencers they will sometimes be in a forrest full of reflective trees, or in the hallway of a building being cleared or in a parking lot of parked cars, or even inside the car doing training for vehicular ambushes, or in a hunting blind.

Looking around we see all the european companies making cans are testing them indoors.  We know AAC historically tested indoors and silencer co, and AB, and others.

This is because a silencer can be developed and improved indoors.

The outdoor test on the open field will be the most favorable to dosing for all suppressors, and for a suppressor that is projecting a loud sound forward, because less sound will reflect back.  

So there are ways for the open field to softball some of the cans and show less of the big environmental picture.

The ability for reflection to occur even on a minor level, in some minor ways is a more comprehensive (tougher) test and answers some of the criticisms of testing which explode into scientific nerds suggesting there should be an array of 8 or ten microphones getting far and near field measurements.

The problem with these arguments is that if we make testing require an hour drive and half a day settup, we reduce the amount of development happening by reducing the frequency of testing.  These recommendations have zero regard for the need for testing to be efficient in order for development to happen in a relevant period of time.

Thanks, its cool when people understand the concepts, as they are moderately complicated.

The environmental geometry causing reflection will reduce reported dosing limits (sound reflection at lower amplitude than peak will represent more DB per unit of time average leq/leaq) but most indoor settups render reflection incapable of effecting peak because reflections where applicable come back lower than the original peak amplitude. Pressure decays rapidly over short distance and through impact/reflection.

So the indoor test will have lower AHAAH weekly permissible exposure than the open field which is relatively absent reflections other than the ground itself.  This of course means the indoor test result is more conservative and less optimistic than the outdoor test for the average shooting scenario where open fields are less common.

The dosing effect will essentially be fairly applied to all cans in that same environment. So it could be considered a more conservative bias to the test results.

I've seen ratings with like 12 rounds or 15 rounds a week, and those are reaching a level where the can is safe to use without ear protection on something like a SWAT callout or for a lot of military missions, or some hunting use, and those are indoor testing numbers which would be a little higher if tested outdoor because AHAAH is dosing based off all the noise including all the reflected noise which will be reduced outdoor. We are making a bolt carrier presently that doubles the dosing of 5.56mm suppressors in indoor testing.  

I get your point of it won't be a good idea to fire 300 rounds with a can without ear pro, but it also wouldn't be a good idea by the same metric to fire the rifles with ear pro without a can where 40 rounds a week is an M16A2 outdoors with a pair of peltor com-tac ear protectors according to AHAAH dosing which is really harsh standard for sounds around or below 140DB A, and I would argue a much softer standard for sounds over ~153DB A.  Most laypeople would think it was safe to shoot 300 rounds with that combination, but it's not, so ear protection itself can provide a false sense of security, and a feeling of a wholistic solution to the problem.  

Looking at the test numbers, it's important not to get confused and think there is no protection being provided by the suppressor.  But I get your argument boils to what difference is it if 4 rounds a week or 14 rounds a week are safe.  Which somewhat captures the difference between not so great and great 5.56mm cans.   I think in that argument it's important to remember that AHAAH will sometimes say firing an unsuppressed .308 indoor is safe for 3 rounds a week, and then you have to remember Army brass probably leaned on that scale to provide the Army some liability protection for all the guns Uncle Sam doesn't give a damn about buying a can for, regardless of how many people are going to go deaf because of it.  I guess what I mean there is there is more distance between those two cans than AHAAH implies.

John from Silencer Research did a good deal of testing and he mentioned how 1474E testing gave him the impression that silencers could "cheat the test" by projecting sound forward instead of sideways.  I kind of see a little of his point in that.  I think one of the variables eliminated by testing in the free field is the concept of projecting pressure forward where none of the microphones are.  It isn't all that uncommon to see silencers that have a long funnel for a front cap, or a large lip around the outer edge that seems designed to catch and redirect pressure forward.  

The Sig SLX has like a megaphone for a front cap.  It is like 1.2" deep and aggressively conical in shape.  The sound indoor when firing it is loud as hell and then you walk to the pulse and see the numbers aren't all that terrible and it's fairly obvious what happened.  

In the first round flash you see the shape of the muzzle impulse and it's the shape of one of those hand held traffic directing light wand cones.  Pretty long and narrow and forward.  Pushing the peak forward reduces the peak reported at 1M left, but it doesn't make the silencer more quiet, so the issue there is that around objects in the environment the sound bounces back and it is hard to pretend it doesn't exist.

I think the cyclic increase metric requires full auto and the timing of at least a magazine vs without the can.  A lot of cans can behave differently for one round than for 28-30 in succession.  The auto ROF test gives realistic cyclic increase by allowing the can to backup with pressure if that's what's going to happen.

The buffer itself buffers differently for the first 5-7 rounds of a burst than for the rest of the burst due to rebound rates of the polyurethane material of the buffer bumper.  That by itself will cause variable bolt speed in the first ~7 rounds of the magazine.

There is a NATO method that puts an 8? mic array around the firer, and it is probably the more comprehensive test, but it is also very cumbersome and I'm not aware of anyone in the US using it.  It's probably used by military testing people.  I think the greater emphasis is on user ears and reducing liability, and injury to personnel, but I can't speak for the military.  To hazard a guess, I think they prefer systems that effect no changes to the rated use specifications of the systems they are attached to.  I've never met anyone who worked for the military who could speak for the military on the subject of what their objectives are for sound suppressors, and I've met a good deal of the people. Those people also don't speak on their own behalf because having a personal opinion appears to be seen as unprofessional.

It seems in the government the only way to get into trouble is to do something, or say something, or have an opinion.  So nobody has an opinion.  They for the most part don't do anything interactive like that, and it keeps them all employed and out of trouble.  It often seems the common objective is primarily to stay employed. There are a bunch of "for the warfighter" catch phrases and stuff, and I just don't see having no opinions, and providing zero feedback as being helpful to, or advocating for the warfighter whatsoever, so I call horseshit on that. I've asked a lot of people on that side what they are looking for, and there have never been any answers to those questions.  

So I only know what matters as a person who was in the military and who was a sniper in the military and I think protecting the users ears is important, and concealing their location is also important.  I know the doctrinal sniper community answer is that the silencer would be used to further conceal the position of the sniper, reduce tossed vegetation, reduce dust, sound, and flash signatures.  I know that with SF teams in a more typical short gun, door kicker type of mission set, the suppressor is used to protect hearing (often indoor) and enhance IFF and ability to communicate.  

The organizational procurement objectives, and the objectives of the military end users are most likely two or more, totally different sets of objectives.  I don't think the end users have nearly enough input on what they are issued.  I think if they were involved in procurement, there would be a lot more feedback, there would be a hell of a lot more passion and they would be getting things that work better for what they need them to accomplish.

At one of the events, an elite unit (who will obviously remain nameless) said we had an item that was hands down the best item of 8 vendors with said category item present, and other than as a positive statement, that was meaningless, because the elite unit has no particular representation in the procurement of their own gear.