In humid Hawaii, I had nothing but Pyrodex for many years. Corrosion City, and the only thing I ever found to prevent it was cleaning X 2 a few days apart plus the use of a non-petroleum lube/rust preventive like 1000-Plus. "Seasoning" the barrel with this DOES seem to help.

Pyrodex is hard to ignite, and via trial with two identical .54 T/C Renegade rifles, I determined that the most reliable nipple is the Spitfire made by Mountain States Muzzleloading, now a part of Caines Outdoors. This nipple is also available in .005" graduations up to .275 X 28 which is a great boon in fitting a nipple in old MLs. The Spitfire has a hollowed-out base just like the old-time nipples I have removed from old guns, and according to Hodgdon, maker of Pyrodex, it likes a good spray of white-hot cap ignition fragments - just what you would get from such a nipple design. ALL my muzzleloaders, old and new, now carry Spitfire nipples.

Guns with heavy charges of BP may like a basic, non-magnum cap, and my Pedersoli Mortimer long range rifle gives better accuracy using 104 gr. of 1.5F Swiss if I use a standard CCI cap rather than a magnum. Ditto for gentler primers, even pistol primers, for BPE loads and the like.

Now on using a musket nipple, I think you will find it unnecessary if you:
1) discontinue using ANY petroleum-based oil or lube in your gun.
2) use a Spitfire nipple ( standard 1/4-28 is likely to do it in your Pedersoli). I've never had any problems switching from the longer Pedersoli nipples to Spitfires.
3) Give a few whacks on the side of your gun near the breech after loading your powder, especially Pyrodex, to bring a few grains very near the spray of particles from cap explosion.

If you do use a Musket nipple and cap, you will have more blast than you need for BP, and the heat and power is equal to that of a No. 209 primer (!). It will likely solve any problem with Pyrodex, but so will the Spitfire nipples. Use the suggested nipple cups with a regular-sized nipple if you like but if you are having a lot of blowback from firing and that is what worries you, it is likely due to an overlarge nipple orifice. The Spitfire nipple has a good orifice size of .039" to best of my recall.

You'll get a lot more pressure increase from going to Triple 7 or Swiss (and likely Goex Express too) than from a musket cap. It is quite true that you can use about 15% less of either of these powders and equal the velocity of Goex or Scheutzen BP. Pyrodex used to have more pressure with some loads than Goex, but that may no longer be the case with today's improved Goex. See the Lyman Black Powder Handbook for a great many eye-opening pressure tests.

One important point is that the larger the bore, the harder it is to build pressure. At .72 you are not developing a lot of pressure with, say, 4 drams (110 gr.) of ordinary BP. If going up from there, follow manufacturer's recommendations, keeping in mind their conservative nature (read, Italy has lawyers too). Pedersoli, unfortunately, put out Pyrodex loading info in GRAINS, not the volumetric measuring we know in the US.. This is highly confusing to shooters used to seeing Pyrodex loads by volume. I don't know whether they have corrected this, but did write to them some time ago about the problem.

For fascinating info on shooting slow-twist, high velocity rifling and round balls in guns from about 14 ga. up, read Lt. Forsyth's small 1862 book, "The Sporting Rifle and its Projectiles".

Aloha, Ka'imiloa