The operative question when determining whether a particular model is dangerous is to not only test whether the primer particles are leaving the receiver area or not, but whether those particles could potentially cause injury.
I personally try not to ever fire a muzzle loader without wearing eye protection even when hunting.
If eye protection is what is required then that is clearly an important warning for folks to be aware of.
If it's discovered that one particular model allows particles to actually cause injury, then I don't think that automatically means that all plunger rifles are unsafe across the board. They all have slightly different designs that may affect the degree of potential injury such as the size of the receiver opening, the strength of the plunger spring, the size of the flash channel, how tight the primer hole is, whether having a scope mounted blocks injury causing particles etc...ad nauseum.
I have several plunger guns including a Marlin .54, a Lyman Cougar .54, a Traditions 12 ga. shotgun which all utilize #11 nipples and I recently bought an older unfired Knight Bighorn .50 with a triple ignition system.
I have a TC weather cover to enclose the action that secures with Velcro to help keep the scope finish from getting damaged by the hot gases and which I think would help to contain any flying particles.
If that wasn't used then I think that the scope and rings might block any particles if the spring weren't strong enough to keep the plunger closed.
The #11 nipple contains many of the gases too. The Bighorn uses the full plastic jackets but there's the optional breech plug for using bare 209's, and Traditions also offers a similar conversion breech plug.
I've never found a need to use 209's but then I generally don't load with over 100 grains of powder. 100 grains of ffg is equal to about 90 fffg, and installing the conversion breech plug doesn't increase the recommended powder capacity of the rifle, even though the larger bore sizes might allow them a higher rating.
And loose 777 powder is suppose to be reduced by 15% according to Hodgdon anyway, so if these were .50's they would only be rated for 85 grains of 777 and not 100 grains of loose 777.
I realize that the newer magnum plunger version by Traditions is rated for 150 grains of pellets, and I don't know whether that's dangerous enough to cause injury or not. Or if it did what is the practical prevention for it without affecting performance.
Wearing safety glasses, or using a weather cover, or having a scope mounted over the top of the open receiver, or having a better made and improved breech plug, or a stronger plunger spring? I don't know.
But let's not condemn across the board without evidence for each and every individual plunger gun without some kind of proof that an injury can actually be possible.
To warn about a model based on facts is good. To warn about all plunger models based on conjecture could be worthy if it's based on bona fide evidence.
But simply flying particles by themselves are not necessarily evidence of a potentially serious degree of injury any more than any other muzzle loaders.
The warning needs to be commensurate to the degree of injury possible verses all other muzzle loaders.
It was Cayugad who was hit with a flying piece of musket cap flange in the forehead not too long ago when shooting one of his TC sidelocks. He posted a photo of the blood and flange. The angle of the hammer may have prevented it from being able to strike his eye directly at all, I'm not sure.
But possbily worse damage to the eye can be done by a scope not having enough eye relief, or if it's mounted or held to close to the eye during firing.
That doesn't necessarily mean that all scopes are dangerous when mounted on any and every muzzle loader. But we all know the potential for receiving scope eye by mounting a scope on any recoiling rifle.
And we don't categorize all sidelocks as dangerous as a result of one cut from a musket cap flange. And how many people have complained about CCI discontinuing their 6 flange caps in favor or only producing their 4 flange reenactor musket caps?
CCI thought it's important enough to discontinue the use of 6 flange caps over the potential, yet some reenactors still prefer the 6 flange type.
Sure, muzzle loading has a lot potential for injury in many different ways. For example, using real black powder is more dangerous to load than substitute powders are because it has a lower ignition temperature which can lead to the increased potential for cook offs. But we generally don't announce it far and wide that loading with real black powder should be avoided in favor of substitute powders because that would discourage flintlock shooting as being more inherently dangerous. That would be offensive to all of the people who load with black powder and do so safely.
Flintlocks can spew a lot of particles too from the flint, the frizzen, the pan and the vent.
So let's keep everything in perspective and not over hype it and make a mountain out of a mole hill.
This could be something that folks should be aware of so that they can deal with it accordingly.
But if safety glasses are the practical solution, then wearing them should already be a part of everyone's muzzle loading safety regimen.
If safety glasses aren't enough then how much worse could the injury be?
Are these particles any worse than having a cook off during loading and not knowing enough to keep one's head away from being bent over the muzzle during ramming?
Of course these small particles won't blow a person's head off.
Since cook offs during ramming are deadly & dangerous too, should we proclaim far and wide that all muzzle loading is deadly & dangerous?
Well folks it can be deadly & dangerous.
But we try to educate folks about how to deal with the dangers and put the odds in perspective.
In real terms, what are the odds of being injured, what could the nature of the injuries be and what are the practical solutions?
To never load over a certain amount of powder, to always wear safety glasses, to find ways to block the particles, to identify the particular guns that can be proven to actually cause injury or what?
All of the guns are capable of causing injury if the shooter doesn't practice safe methods.
But in order to blame some guns as being inherently more dangerous needs to be put into
perspective verses all of the other BP guns and all of the other BP hazards of which there are a multitude.
It can be easily shown how particles coming from a flintlock can injure people's eyes too if they don't wear safety glasses. And I suspect that the same kind of prevention is what's required to deal with any potential particles coming from these magnum 209 plunger guns too.
So it makes sense to continue to inform people about how all of the basic safety rules of muzzle loading
are important for all folks to follow at all times when they are participating in the sport.