The Walker used the same loading lever latch as the Patterson, but the largest Patterson caliber was 36. The Walker with its bodacious powder charge had too much recoil for the latch.
The Walker also had serious cylinder strength problems with the 60 grain powder charge, and were known to blow up. The steel quality in the late 1840s was not that great.
Weight was also an issue, and the barrel, lug and cylinder were cut down to reduce weight and reduce the powder charge.
The Dragoon was still a Horse pistol even after the weight reduction.