Bolt Bounce and GBBRs

If you’ve spent any time working on GBB ARs or seen our reviews of the VFC or GHK systems, you’ve probably heard of ‘bolt bounce’ as a potential issue. Since we have an upcoming video on our LR-300 build- which demonstrates quite a bit of bolt bounce- it’s time we talk in a little more detail about what exactly bolt bounce is, what problems it can cause, and how to address it.

Real-Steel

For context, while this is an issue that is also present on real-steel rifles, the consequences are a little different from airsoft. With a real firearm, when the bolt carrier comes slamming forwards it will typically bounce back just a few millimeters, then settle forwards again under spring tension. The issue is that if the hammer falls and strikes the bolt carrier while it is slightly back, on any competently designed firearm the hammer will not contact the firing pin, and the result is the gun just goes ‘click’.

On semi-only rifles, this generally isn’t a problem. The carrier has plenty of time to settle before you pull the trigger, so the ‘click’ will only happen if there is so much friction (or so little spring tension) that the carrier can’t return forwards on its own and gets stuck in that ‘slightly back’ position. 

In full-auto, however, the risk is that the hammer will fall just as the carrier is bouncing back, before it has a chance to settle back forwards. For most rifles this isn't an issue, but on designs that do demonstrate concerning bolt bounce behavior, there are a few ways to fix it. The AK family addresses this via a rate reducer in the fire control group, which delays the hammer from falling until the bounce has had time to subside. The AR family, in contrast, solves it with shifting weights in the buffer, which provide a deadblow effect to eliminate bounce altogether. We’ll come back to this.

Airsoft

On an airsoft rifle, the same effect manifests: The bolt carrier slams forwards, it hits the chamber, and it will typically bounce back out a few millimeters before returning forwards. But the practical consequences are considerably different, and in semi-auto there are several possible outcomes depending upon the particulars of the individual rifle:

1. The nozzle stays stuck in the hop-up while the carrier bounces back, but the seal between the nozzle and carrier is good enough to induce suction. This pulls air into the space behind the nozzle as the carrier comes back, then as the carrier comes forwards again, pushes it out the front of the nozzle. The ejected air can push the chambered BB to a different position in the bucking (affecting how much hop it receives when fired), or even eject the BB out the barrel entirely.

2. The nozzle detaches from the hop-up and stays with the carrier as it bounces back. This can pull the chambered BB out of the hop-up and cause a jam, or if the carrier goes far enough, even pick up a second BB from the magazine. In either case, the practical result is that a BB ends up somewhere it shouldn’t be.

3. Nothing unusual happens. The nozzle stays locked in the hop-up, but doesn’t seal well enough with the carrier to create suction, so air moves but doesn’t cause any major problems.

In full auto, there’s an added wrinkle. If the hammer falls while the carrier is slightly back, the gun will still shoot, but the carrier may prevent the hammer from pushing the valve knocker fully forwards. When this occurs, it may result in a ‘light strike’ with noticeably weak recoil and a sluggish cycle, or just lower FPS, in addition to any of the effects described above.

What To Do About It

If you suspect you may be experiencing issues as a result of bolt bounce, the easy way to check is to just record the gun cycling in slow motion and see what the bolt carrier does. If it does bounce back a noticeable distance, then it’s worth looking into solutions. Airsoft ARs seem particularly susceptible to this, but the fix is the same as it is for real ARs: Use a proper buffer with shifting internal weights, which as mentioned before provides a deadblow effect to eliminate bounce. On VFC or GHK, real buffers are drop-in and will typically solve bolt bounce entirely. On other guns, this can be fixed with a stronger recoil spring, or reverting aftermarket parts (eg metal nozzles or metal chambers) that may have induced the problem to begin with.

One other potential solution, as odd as it sounds, is the hop-up. There are a few GBB buckings on the market with openings narrower than 6mm. This provides resistance to the BB getting pushed through, which helps to combat overchambering (the tendency for some guns with particularly violent actions to punt the BB to an inconsistent depth in the bucking), slows the carrier on the forward stroke so that it bounces less, and helps keep the nozzle sealed in the bucking if there is bounce. Buckings with this behavior include Guillotine Airsoft, Tagart, Waldo Dynamics, Modify X-Range, or Maple Leaf buckings (with a small o-ring used in lieu of the included stiffener clip).

However, we want to stress that just because bolt bounce is observable does not mean there is necessarily a problem. For instance, as we covered in our review of the VFC AK, the first batch of that gun had considerable bolt bounce, but there were other mitigating factors that made this not an issue. Most airsoft bolt carriers will bounce to some degree, and most won’t experience any issues.

The practical takeaway here is that if a gun is behaving in a manner that just seems weird, it’s worth checking whether bolt bounce is present, and if so then trying steps to mitigate it. If bolt bounce is present but no problems are observed, then it isn’t something to worry about. Just be aware that it’s a possibility.

We hope this helps with troubleshooting your GBBRs, and you can look forward to that LR-300 video this Friday.