The answer by Liam is great, though I think we can at least give a guideline about what constitutes a "The Great Outdoors" activity and what does not.
This is a theoretical "Let's apply the same logic across the board and see what happens" answer, and that is exactly how I believe that any "Is this on topic?" question should be answered. So my answer works for pistols, and it works for everything else too as a side effect. It demonstrates that pistols, how to use them, the differences between them, and similar questions are all on topic. It also goes into some examples of where these things go too far and become off topic.
This answer runs through the logic necessary to decide what is on or off topic, covering definitely on, definitely off, edge cases, some in between - analyzed with a core logical guideline; you really just need to go with the flow of the logic. So this answer is necessarily long.
What is the root of The Great Outdoors? What is at its core?
As has been said before, an activity does not become a TGO (The Great Outdoors) activity simply by being done outdoors. Similarly, just because an activity is done indoors does not immediately disqualify it from being a TGO activity. That is, questions about football rules or golf rules do not fit well here. And questions about indoor rock climbing do fit well here.
Huh? Why is that? Golf is outdoors and indoor rock climbing is, obviously, indoors. That doesn't make sense!?
This Stack Exchange is not called "Questions about activities which are performed outdoors." It is called "The Great Outdoors." The basic activities which you should have in mind to compare against as the "root activities" of this site are those personal activities which involve the use of nature, preferably (but not necessarily) for the enjoyment of nature, such as
traveling in or through nature (hiking, kayaking, snow-shoeing, etc.),
staying in nature for a longer duration (camping, survival skills, etc.),
observing nature (bird watching, plant identification, etc.),
activities which naturally accompany the above, whether because they (4a) complement each other very well or because (4b) TGO depends on it (rock climbing [is sometimes necessary for traveling from A to B, often necessary for mountain traversal]), or (4c) it depends on TGO (hunting [requires all 3 of the previous points]).
Elaborating on point 4
Point 4 and its sub-points a, b, c are, I think, the real sticking points here where people disagree.
For the last bullet point above, activities which the previous points depend on are necessarily on topic, even if performed in a non-outdoors way. Example: while rock climbing as a sport, especially when done indoors, might technically be off topic, to close those questions as such would be both legalistic and hair-splitting.
Rock climbing is necessary for many activities which fall squarely into the previous points, and it has been done many times as a necessary means of travel through nature. Some indoor sport rock climbers very well might not care a lick about The Great Outdoors, but others might be doing it specifically as preparation for an upcoming The Great Outdoors activity, and advice will often transfer between the two. That is, even if an indoor rock climbing question is asked by someone who never plans to do it outdoors, the answer helps The Great Outdoors anyway, and those doing mountaineering will find it useful.
So the previous paragraph was about point 4b, sub-topics which the 3 main points above rely on (ie: to get around may require rock climbing), but I strongly suggest that the other way around, point 4c, is also on topic: sub-topics which rely on those 3 main points.
Whether you agree or disagree that the act of hunting in and of itself is a TGO type of activity (that is, whether you agree that killing an animal is part of TGO), nobody can deny that hunting is generally accompanied by, and often strictly requires the other TGO activities. Technically, somebody could put up a deer stand just off the side of the highway, drive to it and use it without ever going into the woods, and drive away when they are done; but that is not how it is generally done. Hunting often requires hiking, plant and animal identification, tracking, blending into nature, sometimes camping, etc..
If an activity which relies on all of these definitely TGO activities were considered off topic, then where would it be on topic? Does each and every such activity need to have its own Stack Exchange site?
A corner case
And then there are the corner cases: If hunting and trapping are off topic, what about the purely TGO survival question "I'm lost[/stuck/ran out of supplies/whatever] deep in the wilderness. How do I make a trap that can catch something to eat?" or the same thing but about a bow and arrows. That is strictly a survival question, and those are known on-topic here, but it's also about trapping. If I had not already read up on survival trapping and watched lots of videos about it, I would probably be asking exactly those questions here, and I wouldn't be surprised if someone else already has.
That then suggests that perhaps the 3 main points above actually do rely on hunting, just as they rely on rock climbing. So perhaps hunting/trapping are necessarily TGO.
Deeper dive: activities 1 level away - merely related to TGO activities
Now let's dive down to the next level. Shooting in general. Should shooting be on topic? This might be range shooting or sport shooting. Range shooting is to hunting what indoor rock climbing is to TGO rock climbing, so I insist that range shooting be viewed the same way as indoor rock climbing when making the on/off topic determination. Sport shooting though... I'm not sure, I suppose it depends.
Would a competition indoor rock climbing question "How do I calculate the score for this type of rock climbing competition?" be on topic? I don't know a lot about competitive rock climbing, so forgive if that previous example question sounds silly, but it makes the point. A question about sport shooting rules should be viewed the same as that. And we do have (a) question(s) about competitive shooting scoring. There was a question about the differences between different archery scoring methods between North America and Europe. I am not sure if that should be on topic or not, but a question about how to improve your aim to be able to hit the kill zone on the target would be on topic.
We cannot simply continue ad-infinitum with "Well, could A depend on B? B depend on C? C on D?" or literally everything would be on topic. For example, "TGO survival requires hunting, hunting requires shooting, competitive shooting sport requires shooting so in on topic. Oh, and law-enforcement requires shooting. The legal system requires law enforcement, judges require the legal system..." that just snow-balled out of control. Granted, that logic used some "this sub-topic depends on TGO" (point 4c), but it could also happen with "TGO depends on this sub-topic" (point 4b): "Apocalypse survival may require that I make my own vehicle, which needs tires, which needs rubber and molds, ..., ..., so this chemistry question about the optimal way to make the material for tire treads is on topic."
When judging these you should ask yourself "Could this be useful to anyone specifically in a TGO setting?" Let's pick on guns again since that's what started this question: unjamming a gun would be useful for TGO activities, though cleaning guns is (arguably) not on topic since that is not directly useful in any conventional TGO settings, reloading your own ammo is (arguably) not on topic since that is not directly useful to TGO activities, making your own shell casings is definitely not on topic, and shooting competition rules or scoring mechanisms is (arguably) not useful in a TGO setting, though honing shooting skills (even if asker is doing competition shooting) is useful to TGO activities and would be on topic.
So we have finally gotten down to where we can see some possible dividing lines. But what are those lines? They are a bit grey, and as Liam pointed out different people will have different opinions about where they are at this level.
Some criteria to use in these grey areas
Some things to consider could be:
How many uses of connecting logic does it require? (ex: Apocalypse survival, transportation, vehicles, tires, rubber, descent rubber that actually holds up well to use, natural rubber might not work for that so how do I use chemistry to make a good tire? That is too many points removed.)
Does it have anything to do with TGO? That is, not only "can it be done outdoors," but rather, is it necessary to core TGO activities, or is it something that a lot of people do as part of their TGO activities? (tire manufacturing is not done as a TGO activity and TGO does not rely on it directly)
Rock climbing in and of itself is necessarily a "The Great Outdoors" sub-topic. Questions that have to do with that are on topic; I don't care where you actually do yours if the question pertains to rock climbing. A rock climbing competition scoring method is highly questionable, and my opinion is that it would not be on topic.
Hunting/trapping is an activity in the spirit of the core TGO activities, and as a bonus it is essential to TGO survival. Shooting in general is absolutely a core aspect of hunting and it is generally done outdoors as part of TGO activities; shooting in general is in my opinion very close to the core of TGO. Knowing the absolute basics about shooting is obviously necessary for shooting, and knowing fundamental information about shooting tools is part of the basics. The mentioned question about revolver actions would be a shooting fundamental basic.
Asking about the timing for the revolver speed shooting world record (ie: When exactly did the clock start? When his hand touched the gun, when the gun was fully un-holstered or fully drawn? When?) has nothing to do with TGO and does not help anyone that is doing any TGO activities.
Asking about shooting competition rules is a grey area, but I suggest it is not really related to TGO activities. However, some people probably feel strongly opposed to me on that, as is evidenced by the fact that there is a sport which combines skiing with shooting. Apparently there is a large group of people that consider competition target shooting to be so close to their outdoor nature-traversing activities that they combine it with skiing. I would call that off topic, and I think this is right on the bitter edge of what anyone can argue is TGO on topic - if anyone argued in its favor I would not vote to close that since on topic is not defined as "What Aaron's opinion decides is on topic," and as Liam suggested we need to honor others' opinions.
So there is a deep dive into comparing definitely on topic questions, definitely off topic questions, questions right on the edge, and cases near the edge on both sides of it.
Please note that the examples given above are not arguments for or against specific sub-topics being considered on or off topic; rather, they are case studies to help us examine the logic behind them and to probe the boundaries and find types of questions that should be on or off topic.
I don't care if it's about guns, rock climbing gear, or something else; that part is entirely irrelevant. What is relevant is how the question fits into the theme of TGO, such as by using the logic above. And when in doubt for a corner case or grey area, err on the side of honoring the opinions of others. It is not injurious to you to see a question answered that you disagreeably thought was off topic and to have somebody helped.