You can't tell from that picture - revolvers come in most calibres although .45ACP is unusual in modern guns as its generally used in semi automatics (its normally engraved on the gun somewhere, but for the purposes of a story pick whatever calibre you want )
You can go to the various gun manufacturer websites and locate pictures and specifications for various revolvers. If firearm usage is going to be prominent or important in the plot and an author is unfamiliar, a little research will behoove the author in creating a story that won't annoy readers who are familiar with firearms. The result will be some readers being quite vocal and harsh in reviews and commentary. While this might not apply directly to the OP, here's an article, with suggestions, I wrote on the topic a while back: Firearms in Fiction
Unless you are Steven King in which case you can write shite like " I swung the barrel out of the revolver and checked the clip" and " he had 8 in the clip and one in the magazine" with impunity. King says that he is antigun and therefore not interested in getting the details right - but I can't help feeling that if I were anti gun, not writing a story with guns in might be a better bet. Mind you I had an American beta reader get very upset that a Mossberg 500 in one of my books had a magazine capacity of three - he went out of his way to tell me that the 500 has a mag capacity of 6 or 8 and included links to gun dealers and all sorts. And he'd be right - except that in the UK, pump action and semi auto shotguns are limited to a capacity of 3 by law, and have a stud fitted to prevent more than that being loaded. He was so incensed by my 'lack of research' that he totally missed the bit on the very next page where that is explained as the MC disassembles the gun to remove the stud , and the bit later on where he fits a sidewinder venom kit to increase his capacity further and give him changeable magazines which is a long winded way of saying that some people are idiots and you'll never please them regardless of how much research you do or experience you have
As you can see the "Join or Die" avatar, I am a pro-2A supporter. I am a gun owner, trained on them as an infantrymen and still learning about firearms. That's why I won't bother reading King's books or purchasing them since he wants to become political and wanting to strip my right away. He may be anti-gun but at least give respect in regard to firearm terminology. The main reason the beta reader you had was upset because it's a grave insult to talk about guns and come out ignorant of them. Think of this way, as a writer or Agent they take grammar seriously. If we submit manuscript with poor grammar, not properly done. It's indirectly insulting the people in the writing community who takes writing; thus grammar seriously. I may not be the best at grammar but I am still learning and doing what I can to progress. Anyways, especially when there is a huge political turmoil in the U.S anti gun vs pro gun right now. A "clip" is the worst slang for a magazine. It just shows the ignorance of the writer on firearms. A clip is used for ammo to hold an unit to insert into the magazine. There is no such thing as "assault weapons", assault is a verb but I still use it in my book to convey easier way for the reader to understand. I may sound hypocritical but I'm writing a Sci-fi book, so having weapons far advanced than our era. An assault weapon by definition is a M4 not an Ar15. It shoots fully automatic which illegal for an normal civilian to own but can go through insane screening to obtain one. That is why I can't take anti-gun folks seriously majority of the time. I would like to hold a logical and respected civil argument. The thing is how can I take their PoV seriously when their ignorant on firearm safety, terminology or any regards on fire arms. It's like someone who loves to write, knows every grammar rule like 2nd nature. Then have a novice writer tell them this is how it's done. The limit in UK may be 3 but people do break the law or get around modifying firearms all the time. The American revolution war was sparked over a failed attempt by British trying confiscate colonist weapons. The best way to learn about firearms in general is actually go out and use them(shooting range of course). Learn the safety how to use them, basic mechanics how they work, how breathing techniques work to help you aim better. Even the recoil are different from type of weapons you use. Guns are like golf clubs, each gun has a different use for a certain situation. For example, CQB weapons P90(fully automatic) or PS90(semi auto,civilian use) are designed for houses or buildings, with hallways or corners. I can go on writing about firearms but you get the jist of it.
This is true - but my point was that I am not ignorant of them... ex forces, civilian holder of several. As I said I was in fact completely right that a Mossberg 500 in the uk (where the story is set) will have its magazine limited to three … as I then explained on the very next page this limiter can be easily removed. So in fact it is my oh so knowledgeable beta reader who didn't know what he was talking about. Also I'd differ that there is such thing as assault weapons … that term derived from military usage for fully automatic rifles suitable for a military assault (a noun) on an objective. I tend to prefer the more modern term battle rifle but its essentially the same thing
