When it comes to non-light bearing IWB holsters, we always recommend a holster made for the fullsize version of a gun for use with a compact gun (assuming the frame/slide profile is the same) as the extra length aids in concealment. If the holster is made for the shorter compact version of a gun, the grip of the gun above the belt line tends to tilt out away from your body which makes the gun print more when concealed. The additional length of a fullsize holster helps to counteract the gun from tilting out above the belt line. In most cases the extra length also allows a comfort puck to be mounted to the back of the holster which further counteracts the tilting.
A 3.9" Staccato C2 in a holster for a 4.25" 2011 Commander
A CZ P-07 in a holster for a CZ P-09
A Glock 19 in a holster for a Glock 17
With subcompact guns like the Glock 43 or Sig P365, we will use the longer version of the gun as the mold (i.e. Glock 48 or Sig P365XL), and then simply trim down the end of the holster to reduce the overall length but still keep the holster around 1/2" longer than the gun's frame/slide profile.
If a longer version of a subcompact gun doesn't exist (i.e. Springfield Hellcat), then we will artificially add an extra 1/2" inch to the slide/frame profile of the mold.
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