Great variance in groups with different guns

[zacman]

I initially qualified for CCW with a Ruger SP101 .357 revolver and despite very limited experience beforehand I shot really well - trainer said "awesome shooting". Later I bought a Ruger LC9 and qualified with it as well, and again, despite having only put about 50 rounds through it beforehand, I shot very, very well.
Later, at my home range, shooting from 21 yards I shot very well with the LC9 but shot fairly poorly with the SP101. A couple of days later, again shot very well with the LC9 but not so well with the SP101.
I am trying to figure out if there is a reason for this. Could this be somehow a result of learning to shoot a bit differently with the pistol, or is it common to score differently when shooting such different guns, or is it just that I need more practice, or. . . ?. I plan to carry the LC9 and keep the SP101 at the ready for home defense.

[durandal]

triggers have different characteristics. also ergonomics may play a factor. you need to do dry fire practice on different firearms to be able to jump between different types of handguns comfortably (single action revolver, double action automatic, striker fire auto, etc)

even firearms with apparently similar mechanisms can have extremely different triggers (kahr and glock for example)

[postal]

Exactly^^^^^

And.... different guns have different accuracy... and the same gun has different accuracy with different brands of ammo/weights/etc...

But it mostly boils down to what Durandal said.

[IeatPi]

Could it be possible that while you were qualifying with the SP101 the first time, you were under pressure to do well, so you paid more attention to the details of shooting, and on subsequent times out you paid less attention so did more poorly? I also get into a worm where I now expect to do badly with a certain gun, and that puts me into a mental rut and I am pretty sure I only perform badly because I am thinking about it negatively.

[zacman]

All good points and I will use the advice to improve.
Also, re the SP101 the first time - yes - I really did pay attention to every detail - very carefully to all the instructor was saying - and followed his advice completely - so that could also be a factor. At the range I built at home, it is just me and likely I am not paying as much attention. Next time out I will think back to the advice given and see how I do. Thanks for the posts guys.