When I first started getting into airguns a few years ago it started with a Cummins "B3", a cheap Chinese air rifle that actually shot rather well out-of-the-box. As I found out later I actually had a hybrid variant - it was actually a B4-2 with no safety and a different rear sight. Regardless, power and accuracy were quite acceptable for the $20 I spent on it.
At the time I had no idea how lucky I was.
Eventually I found out what everyone else seemed to know - the low-end (and sometimes high-end) Chinese guns often need their owners to make 'em right, to take care of all the things that the factory neglected to do. Very often the effort isn't striclty speaking worthwhile, that is if one attaches a reasonable price to the time spent tinkering it. However, getting there is half the fun... and very often a bit of a challenge as well.
The QB51 I recently acquired from Self Defense Supply (SDS) upheld this Chinese tradition admirably. To those unfamiliar with it, the Industry brand QB51 is a lower-powered breakbarrel with a pistol grip, a folding skeleton stock, and what looks to be a Gamo-style safety in the trigger guard area. Retail on this puppy tends around $40 at the moment, but SDS had them for $26 before shipping (minimum order of $100). Since the gun always piqued my curiosity, I figured this was a good time to try it.
The gun, as delivered, would function - but that's about all I could say about it. This thing had the WORST case of barrel droop I EVER saw, to the point where a scope would be an absolute impossibility... even with an adjustable mount. Reason being that the dovetails milled into the compression tube are extremely short... I don't think anything but a set of skinny, single-bolt rings set as close together as possible will work. I was able to get a Powerline 3-9x32 scope to fit on it, but just barely.
When I had seen the type of safety this gun had, I hoped to find that it was equiped with a Gamo knockoff trigger as are the QB88 and the QB57, but no luck. This thing has a 'remote' trigger that connects to a direct sear via an actuating arm. The safety lever isn't hinged, it slides - and it slid only with the most adamant persuasion. I could not just flick it off with my trigger finger before shooting it... I had to pull it forward with the thumb of my left hand after cocking and loading the gun.
The trigger itself wasn't much better, but at least I could move it with my trigger finger. Velocity seemed OK compared to the factory advertised figures - it handily exceeded its 500fps rating with Crosman Wadcutter pellets. But it did seem like it oughta do far better... after all, its 26 lbs of cocking effort is awful close to a number of more powerful guns. The barrel has a short cocking swing, indicating a lack of leverage.
Loading the gun was problematic the first time - the breach seal consisted of a wad of leather smashed over the breech end of the barrel. It partially blocked the opening for the pellet! The breech was loose, too - an additional half-turn on the locking pivot bolt took care of that. It certainly wasn't loose in the vertical direction, though - the chisel-detent was not fond of moving.
Initial groups (with the open sights) showed some promise, so I decided to try and make this gun a usable shooter.
First thing I did was pry out the breech seal (such as it was), and recheck the barrel droop. As I suspected it was now substantially reduced, although not entirely gone. I filed about .004" off the breech mating face, and that about did it. I installed a #109 O-ring (with a .030" spacer behind it) for the breach seal. Dressing the detent chisel and applying moly to both the chisel and the pivot smoothed out the breech mechanism to something reasonable.
Next, I turned my attention to the safety. The safety and trigger assembly follows the standard Shanghai practice of using free-floating pins (no peening or 'e' clips) and is therefore partially self-disassembling... any untensioned pins tend to fall right out, so if you ever do one keep this in mind. The sliding safety was rough and got a good smoothing over with a hand file and some abrasive paper. However, I had to de-tension the friction spring a fair bit before it got to where it should be.
The trigger sear itself will be familiar to anyone who has worked on the B1 or B2 series rifle, to which this gun is certainly related. I dressed the trigger sear surface with a moto-tool on low speed, taking extra care not to alter the sear face angle. I gooped up the spring and innards with moly mud (30wt chainsaw bar oil and moly powder) and popped it back together.
The trigger was initially a little better... but only initially. It quickly got a LOT better, to the point where it started scaring me. A very light trigger pull with a direct sear mechanism is generally not a good sign. I surmized that the moly goo had worked its way to the sear, which should not be a problem since geometry (and not friction) should be keeping the sear in place. Just to be safe, I tore it down again and found that the notch angle in the piston rod was all wrong - it would tend to push the sear away from itself. I regound the angle to something more reasonable and put it back together.
Same deal. Except this time I kept shooting it... and after a couple of dozen shots the sear started failing. So apart it came, and this time I went the other way with the angles... to the point that I now have POSITIVE SEAR ENGAGEMENT, and it takes a yank of about 7 lbs on the trigger to get it to fire. No doubt I could play with it and get it a bit lighter, but franky I don't think I'm going to go there. At least the sear is safe... and after having it 'auto-fire' on me, that 7lbs feels pretty good.
So now I've got a reliable sear, a safety that doesn't need a crowbar to operate, a fairly smooth and snug breech mechanism, and a decent breech seal. In other words the gun is now what it's supposed to be... and NOW I can actually evaluate it.
At 35" overall, the gun is a short one - shorter than a Gamo Cadet Delta. It's a lot heavier - the proliferation of steel and wood brings the weight up to about 5lbs 12oz. The pull length is a very adult-like 14", but the center of gravity is very close to the trigger giving it a very balanced feel. The large blocks of metal used for the folding stock no doubt account for a lot of this. The buttplate is adjustable in the vertical direction, and if I set it to the lowest position it brings the sights to my eye level very nicely. Looks goofy, though.
As mentioned before velocity is better than the factory claims, with 10 Crosman Wadcutters averaging 568fps. There was a 15fps spread, which really isn't bad for a cheap leather-sealed rifle. This rifle does have a very stiff spring but I suspect the short stroke powerplant is hampering it - at a little under 6 ft-lbs it only comes out to about 22% efficient.
The rear sight on the rifle is positively wonderful. It is a knockoff of the older, non-fiberoptic version of the Gamo Shadow/220/Sporter rear sight - and while the plastic moulding isn't up to Gamo standards, it works very well. With NO sideplay, solid detents, and a healthy adjustment range it puts the rear sights on plenty of more expensive rifles to shame - especially Crosman. I'll even argue that it's better than the 'micro-metric' sight that comes on the Gamo CFX and Whisper. If I can get these rear sights as replacement parts for a reasonable price, I think I'll be fitting them to a few of my other rifles.
The firing cycle is surprisingly docile - it almost sounds like a cross between a springer and a pneumatic. Quiet - and while there is a slight buzz after firing, don't be surprised if it goes unnoticed. In any event it is a good gun to shoot in the basement if you don't wanna wake anyone upstairs.
I took it to my 10-yard indoor range, and found that the tough trigger did make it a little difficult to shoot. However, one should keep in mind that this is a novelty gun that belongs to the B1/B2 family, and therefore low expectations are in order! Fortunately, though, the gun did not live up to these expectations.
Using the aforementioned skinny rings I was able to mount a Powerline 3-9x32 scope on it, and despite a small amount of visible barrel droop I had no trouble getting the elevation dialed in. The gun seemed to prefer Crosman Wadcutter pellets all-round, but the best group (by a tiny bit) was achieved with a Chinese domed pellet (like those sold by Archer Airguns). It came out to 3/8", although the Crosman was more consistent from one group to the next. The best Crosman group was about .4", and I suspect that all groups would improve as the gun breaks in over time... and almost certainly would improve with a better trigger. I was gratified to see a lack of vertical stringing, which tells me that the barrel lockup is consistent.
In the final analysis, the QB51 can certainly be a fun little toy. It doesn't have enough oomph to be a practical hunter, but it certainly has enough accuracy to be a decent plinker. But only after you take the time to make it right. I guess it's possible that I got a poor one and that another example might be OK out-of-the-box, but I wouldn't bet on it! Is it worth the money? I paid $26, and for that I'm not complaining... especially since fixing it required time and not money. At the more common retail price of $40 - well, that seems a lot to pay for a gussied-up B1, folding stock or no. It's a matter of personal preference, I guess. If you expect to invest a little time and have realistic expectations of its performance, I don't think you'd be disappointed.
Pictures are as follows:
1) Original barrel droop
2) Original breech seal
3) Reduced barrel droop after removing breech seal
4) Final barrel alignment after filing breech
5) New breech seal
6) Short scope grooves and rings
7) Rear sight
8) Hinge for folding stock
9) Complete rifle
