I am trying to identify my Ballard. Maybe someone out there can help me out. Rifle has #6 1/2 stocks " small schutezen 
buttplate, flat on bottom of buttstock, checkered. Forestock
is checkered as well with dovetailed bone insert at tip.
Serial #'s match #4242 with exception of extractor #6107&
barrel #30389. The bbl. cal. #'s  38-55 have the funny looking 
#5's which leads me to beleive the bbl. was replaced at the 
factory. Frame is not engraved. Rifle has early dbl. set triggers and 2nd. type 1st. hammer.
  On top of the nickle plated buttplate is engraved H. MERCKLE . It also has the dbl. trigger ring lever & rebated frame. If someone has any ideas it would be appreciated.  I got all my info. from the books by James Grant.

A #6 was a pistol grip frame, but not a pistol grip stock. It also had a ring and spur lever, and DST triggers, so very distinctive vs. a #6 that was a PG frame with a ring lever and single trigger.
Both had large swiss buttplates and were checkered on forearm and buttstock.
A picture would really help determine what it is. If you're not familiar with Ballards the pistol grip frame is hard to detect when it's straight stocked.
Very few Ballards have the caliber marked on the barrel, and if it were a factory replacement it most likely would have matching serial number stamped on it to coincide with the gun's serial number, and the extractor would be blank, or match also.

More likely the barrel that is on the gun now was a donor barrel from a later gun when the original was removed. I could only guess as to the reason it was changed, but considering how common certain Ballard weights are and the fact the oct. and half oct. barrels use the same forearm shape, it's not surprising it fits. Also not surprising that the caliber would be marked on a barrel with a serial number that high. Marlin was much more likely to stamp calibers on their late guns, and that number puts the barrel late in production, around 1889-90 period.
The horn inlay in the forearm was dropped in mid production, and the low serial number of your frame would coincide with early production. If the frame is marked "JM Marlin" (most likely) and not Marlin Firearms Co. then it's probably built prior to around 1882.
Ballards are probably more often modified and reworked more than many other guns of the period. Finding an original unmodified #6 is very unusual, as most were shooter's guns and they got a lot of use and personalized modification. My #6 has been converted to .22 short, full octagon barrel, and most I see have some sort of change in one way or another.
Can't tell you anything on H Merckle.