Couple of points here... First of all, NEVER use a filter that has been unsealed/exposed to the atmosphere. Most filter have a useful life of a matter of days when unsealed, hours if used. Second, give the nod to masks that are compatible with NATO-style thread-on attachment. Easy and quick replacement when needed. U.S. M17 series is a good mask, but changing out its unique cheek filters is a BITCH. Third, opt for a mask that is equipped with a voice-emmitter, and a drinking tube that will attach to US canteens with drinking port in cap. Lastly, if you wear glasses, consider switching to contacts, because unless you have the hard-to-find eyeglass lens insert for your mask, your sight will be impaired. Try www.google.com search engine, and search for gasmask, and see what happens, Good luck, and safe shooting