Yes...but there are exceptions. The Mauser Broomhandle springs to mind. It is grandfathered in if you are using an original shoulder stock. The reproduction models start edging into the grey...
Others can have stocks added if a 16" barrel is also used...Glocks and 1911s fall into that category. You have to install the longer barrel FIRST and then the stock. Same holds true for conversion units like the Roni; SBR unless you first add a 16" barrel.
Or you can use the MechTech CCU that CoRoMo noted above. It is a "replacement slide" with the 16" barrel and stock already installed so that you use only the grip frame assembly. Currently made for the Glock and 1911 (as illustrated) and I believe they were planning to offer it for the Sig also.
There may be others, but I am old and forget stuff.
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