The 209 adapter is the most trouble free ignition system choice available. If you use the #11 caps or the musket caps there is a significant amount of blow back through firing pin hole into receiver. Ultimately you have to use what your state law allows. For only one shot or two while hunting it isn't an issue. I use mine for target practice firing up to 40 shots in a session. I use Mr. Hubbards 209 nipple and I add a small 0-ring, #60 and this makes a perfect seal allowing no blowback. Another advantage to the 209 is if you use the vari-flame converters by Precession Rifle you can use small pistol and small rifle and their variants for ignition. This allows you to use Triple Seven without the ring deposit left in the barrel.
With the .58 you will need only the 209 to give you ignition to the 70 grains of Triple Seven. Vari-flame not needed unless you shoot allot. That's my load, 70 grains under a patched round ball and the only thing I found to shoot accurately, a clover leaf out to 75 yds. This load will ignite with the #11 cap or the musket cap, it's just dirty. You have to decide, based on your use, which is best for you.
