Lockback check? How can I check for short stroking?
The lockback check is simple to perform.
-Insert empty magazine into the magwell. Pull back charging handle and make sure the mag will lock back the bolt.
-Remove the empty magazine from the rifle and load one round.
-Reinsert the magazine and load rifle.
-Fire the rifle.
The bolt should lock back. If it does not, it's short stroking. The lock back check is the first step you should take when trouble shooting any self loading rifle and will often save you time and trouble. Of course, it won't work with such rifles as the AK.
I'm uncertain what type of ejector the Ruger Mini uses. If the ejector is the plunger type like the AR uses, the empty will be ejected as soon as the case mouth clears the action, long before the bolt travels far enough to be able to pick up a fresh round from the magazine. As long as bolt travel is far enough to pull the case clear of the action, short stroking has little affect on ejection. A rifle with plunger ejector will stove pipe if there is a problem with the ejector itself. Sometimes it will be due to weak extraction.
If the Ruger uses a fixed position ejector like a Mauser 98 or a FAL, then the case won't be ejected until the bolt travels far enough for the case to hit the ejector. With a fixed ejector, the bolt also has to travel with enough velocity to ensure positive ejection. Short stroking will have a direct affect on ejection by causing weak ejection. One symptom of weak ejection with a fixed ejector is stove piping.
Stove piping in a self loading rifle with a plunger ejector is usually caused by a weak ejector spring or a worn ejector plunger. Sometimes it's caused by the extractor.
Stove piping in a self loading rifle with a fixed ejector can have several root causes. If the ejector pivots, it could have a weak spring or gunk hindering it's movement. The ejector face could be worn or broken and is now too short. Bolt speed could be too slow, either from fouling or short stroking and the case isn't hitting the ejector with enough force for positive ejection.
When trouble shooting your problem, keep in mind that the malfunction can have more than one root cause. For example, a stove pipe with a plunger ejector could be caused by a problem with the extractor as well as the ejector. With the fixed ejector, the problem could be the ejector, extractor or bolt speed or any combination of the three.