The problem with coatings is straightforward. If you put a coat on, you must account for the thickness of the coating when milling the bcg. Many manufacturers produce bcg's that are barely to spec as is. Add a coating and now you have problems. Some manufacturers mill undersized in an effort to control this. Sometimes with subpar results. My advise here is to stay with well know-name brand bcg's. Yes they cost more, but most of the time you get what you pay for.
When cleaning, especially in the tail and seal areas, be careful. Hard pressure can ruin the bcg. Then you have folks scraping all the crud off with hard tools and ruining the coating and causing more pressure seal issues. Not to mention scraping so hard that you litterly undersize the critical seal areas.
Dont forget the ar15 bcg should be run somewhat wet. Some folks will disagree on this. It wont hurt the gun at all and may actually help you with cleaning chores.
Another problem is gas rings. The standard for checking ar15 bcg gas rings is to stand the bcg on the tail and see that it does not collapse. This only works with the 3 ring sets, not one piece rings. There is no mil spec for ar15 one piece rings. Also, with large frame ar308 type guns you can't do this test. The bcg is heavier and invalidates the test. There are no mil specs for the large frame ar308. One of the problems with that platform. The best way to ensure that your bcg is what it is supposed to be is the measure it. Again, costly since several pin gages and a few other specific tools are required. You can do this yourself if you download and read the M16/M4 manual. This has all the spec info contained therein. The gages necessary are not all that expensive, but that is to each person to decide. If you need or suspect your bcg is having issues, consult a qualified gunsmith that will test and measure it out for you. You may be surprised what you find out. And it will save you time and frustration.
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