My Griswold and Gunnison and Spiller and Burr shoot about the same as the other .36 caliber reproductions.
The Spiller and Burr pistol was a brass framed pistol very similar to the 1851 Colt Navy except for it's round barrel. Most folks don't notice it has a different barrel.
The Griswold and Gunnison was supposed to also be a brass framed gun similar to the 1851 Colt Navy but somehow it was copied from the .36 caliber Whitney. Most folks think it is a very poor attempt to make a brass framed Remington.
The only thing I don't like on my Griswold and Gunnison is the loading lever/cylinder pin retention system.
Like the Whitney, it consists of a thumbscrew which is retained by a small screw on the opposite side.
With the thumbscrew head in a horizontal position, the shank engages the cylinder pin to keep it in place. Rotated 180 degrees, the thumbscrews notch clears the cylinder pin to permit its removal. There is no way to determine which way the thumbscrew is installed without trying to remove the loading lever/cylinder pin.
If anything accedently rotates the thumbscrew, the loading lever/cylinder pin can fall out.
The loading levers attachment to the cylinder pin is IMO, rather weak although I haven't had any problems with mine.
If you get either of these guns, remember that most of the folks around you will be thinking "He's got one of those cheap brass framed Colts (or Remingtons in the case of the Spiller and Burr).
Very few people are familure with these guns.
Because they are brass framed, I would suggest a powder load of 12-15 grains of FFFg to keep the stresses from firing them low.