You know I can't really fix rifles over the Internet just by willing it to happen...right?
JK
Sorry, no...I haven't used that part.
The positioning of the catch (most important, the height of it relative to the bolt) is a key factor. How far the bolt travels on a shot is critical as well.
Wear/tear, the position of the trigger unit in the lower, the fit of the upper to the lower, the position of the bolt in the upper, the recoil spring...can all affect the two parts working correctly together. It's one of those simple-complicated things. Tracking down what's off where isn't easy though.
If it'll lock back every time on an empty mag when you are manually racking it but not otherwise, then the bolt isn't traveling rearward enough on a shot. It can obviously absolutely travel enough (or else it wouldn't lock back when you manually rack it). That's also a good sign that the positioning of the trigger group and upper/lower receivers are ok.
The things that affect how much the bolt travels rearward are:
- oring seal on the nozzle to the inside of the cylinder (needs a drop or two of oil)...good seal = more pressure build up = faster rearward speed/more force
- compression length and strength of the recoil spring...if it won't compress enough with a normal shot then the bolt stop won't engage. If it's binding alot (lube it) then it'll slow down the bolt and might stop it from travelling far enough back
- "timing" of when the knocker retracts and stops feeding gas (that's really not adjustable...they're fixed parts)
How fast the bolt travels back...and how fast it travels forward...is affected by:
- the strength of the recoil spring...strong = slow back, fast forward...weaker = faster/further back, slower forward.
- the weight of the bolt + guide...heavy = slow to start recoil cycle and more gas use and more impact to rear hinge plate...light = more rearward speed and less impact force
- resistance from the guide's wheels...drag = slow bolt both ways
* bomber's super lightweight bolt is very light
First, try lubing all the bearing/contact surfaces...o-rings, etc... These guns like lube.
After that there's not much to do without modding/fitting parts, and that'd be hard to communicate in writting.
Best of luck.
***EDIT***
Brian M has a very good point about the mags. If the main knocker valve is stiff then it might not be dumping enough gas.
Lt is right too....I gotta do some work now
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