I LIKE the squareback trigger guard!
I just bought a Pietta 1851 Navy .36 at Christmas for $199. I like it a lot, but it has the rounded trigger guard.
I might get on Uberti's site and see if I can buy that guard as a part and fit it to my Pietta.
It has been said that Uberti 1851 Navies have a short arbor, which can lead to problems down the road with the wedge and cylinder gap. My Pietta has a good arbor fit with only .001" barrel/cyl gap. I have had to sand the wedge on both sides to get the wedge spring to protrude through the barrel flat, and then re-blue. It has also been said that Uberti has a better hand/spring fit, whereas the Pietta does not.
I have some .pdf files insofar as tuning Pietta (read first) and Uberti (read second) 1851 pistols but the author modifies the pistols using a Ruger Old Army plunger (and variants) for the hand/cylinder stop with frame mods. Very good info but I'm not willing to modify that far.
PM me and send your email address: I'll send you the .pdf manuals (6 ea. files). Make sure your mailbox is empty and I will respond as promptly as I can.
I'm a noob with BP but am learning quickly about 1851 pistols and will pass on any info I have.
Jim