What to do about a dangerous QB-57

[Black Mamba]

My beloved little QB-57 has developed a nasty problem.

It isn't staying cocked all the time and it feels like the sear is unable to hold the piston back. Twice the gun has fired while I was locking the cocking arm back in place.

Now, as you all know, I did a tune on this thing awhile back but I'm unable to figure out what is wrong since I didn't mess with the sear OR the connection point for it on the piston. I DID replace the original spring ( it was seriously bent ) with a B3 spring. It was probably 4 coils longer than the original BUT I also replaced the spring guide with a delrin custom that had less preload on it than the original.

Can someone give me some ideas as to what I can do to fix this? I'm a little fearful of messing with the sear/piston connection and I don't have another, smaller spring on hand but can buy one if suggested.

I dunno, I love this little shooter and want it right again.....help!

[shadow]

I wonder if the B spring might be creating alittle extra stress on the sear engagement area even with less preload and not letting it get seated in and holding. I wouldn't think so since one is being installed into mine. Did you do any polishing  on the trigger and sear and I've noticed on one of my piston's that the ingagement area on the piston was very shallow and didn't allow the sear to catch, tossed it. I did a tune on one of my B's and it was doing the same thing so I broke it down doublechecked everything and all looked good. I put it back together and began cocking it and cocking it when atlast it started to seat itself in and since then she's been cocking and locking up just fine but only after I made sure with bump test that she wouldn't go off on me. Ed

[Black Mamba]

I didn't polish the trigger or sear on this one Ed.  I actually thought the trigger was fine right outta the case.  I left it alone.

I'm beginning to feel like that spring might have too much load to it.....

[shadow]

Kinda sound's that way, just alittle to much to hold the sear in place. :0 What's your next move cause I know you don't want to stick the tweaked spring back in. Ed

Greg, one thing to check is that the transfer rod from the trigger to the sear box isn't rubbing ANYWHERE on the stock, especially at the bottom right behind the opening for the trigger. It may be limiting your trigger's returning to full forward position. My stock had a short, shiny spot right at that point where the rod had rubbed, and that was causing the trigger to hang a little bit. I just took a small carving gouge (a trained mouse with sharp teeth would do as well ;~), and deepened the area till there was plenty of clearance under the rod at that point.

Hope that helps.

Bryan

[Black Mamba]

I'll check that out Bryan.  Thanks.

[mikeiniowa]

Check your sear engagement, it maybe to small, adjust it to full, makes for a long pull but you can then adjust it out until you have the problem again.

Had the same problem recently with one of my B2's. Finally reached the conclusion that the spring on trigger, which incidentally holds the trigger sear in place, had weakened. I had a job locating a replacement spring for this so found a 'near enough' in my local ironmongers, rolled the two together and cut a piece of heat shrink tubing to go over and hold them together. I didn't shrink the tubing, just slipped it over as a nice reasonably tight fit. The added tension on that spring now holds the trigger sear down nice and tight. Result? No more slipping sear and a lot safer rifle. I personally never mess with the actual sears unless they are really bad. It is so easy to rub off the thin layer of case hardening, in which case the whole shebang will need re-hardening. No actual extra heaviness on the B2's trigger pull, which was always atrocious anyway. But it might help you. I hope so. Regards Walt.

[MatchAG]

Hi, I just received a QB57 myself and was very intrigued by the lower power, small and unique design. I really like the idea of this gun and it seemed fairly accurate although more hold sensitive than I would have liked. After around 100 pellets though, the sear would not always engage while cocking and then about the third time this happened the gun went off while I was closing the cocking lever. It definitely scared me and since I shoot indoors I'm extremely glad I just shot a hole in the ceiling rather than shooting something more expensive. I'm not sure if this is a problem with the design, so I am on the fence whether to exchange it or get credit toward a different airgun. Again, I really want to like this gun. It even has a place in the pistol grip to store pellets! I also bought a b3-3 which has no trigger safety or receiver block mechanism but the B3 hasn't had any problems yet other than coming with a bent barrel. Is this a design problem with these or did I get a lemon?

Thanks,
Mark

[70GTvert]

On a B3 that had that problem, it was the piston. Poor metal allowed it to wear more than one would think. My fix on the B3 was to grind the portion the sear engages on the piston with a slightly straighter angle. That took care of it there. Another thing that caused poor engagement was that trigger spring, does the QB 57 trigger setup look/act similar?

[Black Mamba]

Well, way back then I fixed my QB-57 by taking Mike's suggestion.

I took the sear out and make a more pronounced catching point for the matching part.  Worked like a charm and works good to this day.

[MatchAG]

Well, they are willing to exchange it for the price of return shipping. Would you recommend exchanging or repairing this one? Thanks