I was at a local gun shop over the weekend and discovered they were having a customer appreciation sale. Lot's of discounts and specials. I wasn't really shopping for a gun. Went there for ammo. While I can always use another gun (who can't?) I really have my needs pretty well covered. But one gun I have been kinda wanting is a little .22 auto. Just for plinking
tin cans and such. So when I spotted this Sig Mosquito at a really good price (under $300), I decided I needed to take it home.
Now, I've read some really mixed reviews on this gun. Lots of complaints about feed problems, ejection problems, etc. But I just liked the gun. First .22 auto I've seen that looks, feels and operates like a full size auto. The controls are identical to other Sig pistols. It even has a decocking level. When was the last time you saw that on a .22. And hey, I'm a gunsmith right? Yeah, I know. Sort of. In any case, I felt confident that I could correct whatever problems the gun had. If not, hey. It was a cheapy.
I took it to the range that same day and tried it right out of the box. Name a problem that an automatic can have, and this gun had it. Failure to feed, failure to extract, failure to eject, stove pipe, misfires. This gun did it all. Now I know that this gun is notorious for liking only certain types of ammo, especially
CCI mini-mags. And it did indeed shoot better with them then with other ammo. But it should do better than it does. A lot better. Especially coming from a company with Sig's reputation. So I went home and dismantled it.
First thing I looked at was the firing pin, since that seemed to be its biggest single issue. I'd say 50% of the time I had to double tap to get the round to fire. In my gunsmith classes, Bob Dunlap says many guns today are assembled by "blind high school dropouts on drugs". Well one of them made the firing pin on this gun. First of all, it was too short. With the maximum possible extension, the firing pin barely protruded from the bolt face. Which explains why looking at spent cases showed only a slight dent in them. It's a wonder that double tapping even fired them. The firing pin was also too sharp, almost knife edged. .22 firing pins should be blunt. And finally, it wasn't true. The tip was crooked. So I took the firing pin out. Completely reground the tip, giving it the correct size and shape. Then I relieved metal on the firing pin stop and on the back of the bolt face, allowing for proper protrusion. Tests with spent cases showed it was making solid, uniform indentations in the case rim.
Next I went after the extractor. All extractors should have positive engagement. This one had negative engagement. Or at least it would, if it had any engagement at all. In firing position the extractor made no contact with the shell casing at all. Big no-no. One extractor test for any gun, any caliber, is that if you place an empty shell casing against the bolt head, under the extractor, the extractor should hold the casing in place. It should not fall out. This one wasn't even close. So I took the extractor out. Reshaped the hook and cut down the stop, allowing it to cam in further and engage the case as it should. A quick test showed that it held a spent case firmly in place. I could then put a spent case in the chamber, close the slide on it, and manually cycle the slide. The spent case ejected every time. Something it would not do before.
And finally I worked on the breach. When fired, cartridges were either stubbing on the breech face, or doing a three point bind, with the nose just sticking into the chamber. It had a nicely formed feed ramp, which I gave a mirror polish. Then I looked at the chamber. The edges of the bore were sharp all the way around. Not quite knife edge, but almost. I applied the universal fix for .22 feed problems and slightly chamfered the top and bottom edge of the bore. Only a bit. A common mistake is to chamfer it all the way around. This induces head space problems. You still want the cartridge rim to seat firmly against the breach face. But a smooth chamfer on the top and bottom can help the cartridge get into the chamber and stop stubs and binds.
And finally, I cleaned and oiled it thoroughly, and reassembled it. I'm happy to say, that with about an hour's work, this little gun was transformed from a nightmare into a plinking machine. I call it the "Ammo Monster" now, cause it eats anything that gets near it. It is one fun little gun to shoot. And .22 ammo is
SO cheap. You can ventilate
tin cans all afternoon on a $20 bill. And do it well. At 7 yards, shooting offhand, it'll make 1 inch groups all day long.
Frankly, I'm shocked at Sig. They have some serious quality issues with this gun. But with a little work in the right places, it turns into a gun that is hard to put down.
By the way, this is the "Sporter" model with the barrel extension.
