I've bought two .50 A&H rocklock Mountain Rifles, one in 1:28 twist & the other in 1:66 - and have virtually instant ignition from both. 
 
I used the same Goex FFFg Holy Black as both the main & the priming charge in both rifles - but different charges for the conical rifle vs the PRB rifle.
I NEVER put even as much as a 1/2 pan full of powder in the pan.    FLASH - BOOM !
The owner/shooter DOES, however, need to tend to his flints, ensuring a square hit with a good spark shower.
 
AFAIK, all A&H Mountain Rifle barrels were made in Spain, with the guns assembled in Provo, UT - until about 2 years ago, when Traditions bought out all the old A&H NOS/warehouse material, and sold the same rifles in caplock or rocklock, but stamped "Traditions".
 
The early guns were available (new) with either "standard" or "Deluxe" (Tiger) Maple stocks.
 
I adjusted the powder charges so that the rifles zero when using the full buckhorn rear sight as a peep sight - which makes them both very accurate for me.  YMMV, of course.
 
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