feather,
You bring up very good points, none of which I can really argue with. But, there are some points you are overlooking.
Looking up some fuel for the fire
there was only one source I could find that described what a gas check was. Interesting. Everybody seems to know what a gas check is, so guess it's one of those generic terms it's expected that you will know. Lyman's 46th Reloading manual was the only quick description I could find, and here's what they say.
Gas Checks: A gilding metal cup which is used to protect the base of a cast lead alloy bulllet from the effects of burning powder gases.
Lets take that apart. An LDPE wad definitely isn't a metal cup. But, it does protect the base of a Leads bullet from the powder gases.
Now it has always been my impression that all the wads we use, of various materials, does exactly the same thing. So..... Are they gas checks to? Would seem so, and if it's the case then they should be outlawed to. From what I can see your objection to the LDPE material is that it protects the bullet base better than the other materials.
So, lets look at this "better" a little closer. Isn't "better" what we look for when we get a new mould to try out? Better BC, better velocity retention over long distances, etc. Isn't "better" what we look for when testing different alloys and lubes? Isn't "better" why we try different powder brands? To find the most efficient, cleanest burning, and most accurate?
The list goes on and on. But the whole idea is we are constantly trying..... within the rules... to find a better way of getting the best we can out of our rifles. To reject a material that doesn't meet the definition of gas check just because it does a better job than any other material just puts us on a slippery slope.
If we reject the LDPE wad, because it is more efficient than other materials that do the same job within the rules, then we can also make the case for outlawing the currently used .40/65, the .32 Miller short, and several other calibers because they are more efficient than others. The .40/65 especially comes to mind. It only resembles in name only it's original description as to bore size, twist rate, and bullet wgt.s used. But, it's a more efficient cartridge now. Same for the ,45/70, the .38/55, the .32/40, and many others. All have been changed from their original spec.'s to one extent or another yet I don't see anyone wanting to outlaw them. Why not? The same reasoning can be used for them as for the LDPE wad.
PETE