There are actually 4 colors/grades of polytetrafluoroethylene (teflon) tape available:
white - single density for small diameter thread joints (best on joints under 3/8" IPS)
pink - double density for large diameter thread joints (best on 1/2" - 2" IPS)
yellow - for gas lines (even a bit more dense & thick)
green - for oxygen lines (oil free)
I carry white, pink, and yellow on my truck (I'm a plumber, but also install black iron gas lines).
I have one inline (a Traditions) that the breech plug will seize if I use grease only. First time I took it to the range (anti-seize lube only) I actually had to remove the breech plug with an impact wrench. The plug allows so much blowback (the dirt gets so far back in the threads) that it will break loose fairly easily, then seize after about 1/4 to 1/2 turn out.
I found the yellow tape would work on the breech plug the fit is so bad.
With the yellow tape it's "hard to put in - hard to take out" for the breech plug, but at least it will come out.
I'd say the pink tape would be a good one to start with on most breech plugs. It's similar to white in thickness, but much denser (for comparison think of a tight weave fabric - a lot more material in the same area).
BTW - I use tape
and "dope" on all my pipe joints and have had no problems with leaks in the past 10+ years since I started using both. I do the same with the breech plug.
