Its primarily "fit" and technique ...but there is a part of this that is affected by the quality of the trigger as well. Its hard to overstate how well you can shoot with a trigger that has very little slack, no creep and breaks like glass. Even if your technique ( like your grip isn't perfect ) - that trigger - and maybe the sights will make up for a lot. Recoil is a factor too ...
But you can compare the trigger in that Buckmark --- to any number of other guns .... a single action trigger in a double action revolver like a S&W, a good trigger in a well tuned 1911, a modified trigger in a number of the DA/SA guns ...and I think you'll find, its first and foremost "fit" / and then the Trigger - and then your technique ( grip, smooth action of trigger finger, follow-thru, etc ...
At least for me, my "mental" game ...is a factor as well. If I tell myself, I hate this gun, the trigger sucks ... then my groups are pretty bad. If I really like the gun - like the trigger - and know I can shoot it well ---and I push myself to perform ---then I can shoot up to my ability. If I'm just sending lead downrange with no goals ...no focus ...then my groups will show the result. Maybe with this Buckmark - you just told yourself - hey, I like it ...and you were really focused on doing your best ...
As I enter my 60's ....I'm constantly reminded --- my eyes are not very good, there is a little arthritis, some orthopedic issues ...and if I want to shoot up to my best potential, I really have to practice effectively and I have to want to shoot well. Picking the right equipment makes a difference - partly so those negative thoughts don't creep in there ---but I have to want it !
I talked to a buddy once - and he played a game with himself. Slow fire, with a revolver in .45acp - and at 10 yards - he had to put 100 shots into a
3" circle. For any shot outside of the 3" circle - he had to go home and put $10 into a jar ...and he hated putting that $10 in the jar .... He hated it even more, because it was $10 that his wife got to spend on her hobbies ...so it came out of his "shooting" budget. My recollection of the story might have the details off -- maybe it was $ 5, but the point is, he had to perform - or there was a penalty. Its easy to "yank" 1 or 2 rounds out of a 3" circle, even at 10 yds, out of 100 shots. It takes discipline and focus ....good equipment ...and good fundamentals.
Another trick I heard --- shoot the best 6 shot group you can at 10 yds. The goal is to shoot a 1" group ( so all shots are covered by a quarter ). Shoot one 6 shot group when you start your practice. Shoot another at the end of your practice .......if you can't do it ...go home and put the quarter in the Jar. ( the jar in my house, makes a lot of money ...) ....but I'm not letting it win !