Ackme’s Guide to the Mechanics of Airsoft – PART 1 – Hopup

PART 1 – Hopup

Hopup is your best friend and worst enemy. It gives a much greater range to your bb but it gives it very strange flight characteristics. It imparts a backspin to the bb allowing it to “float”. This gives the bb a much flatter trajectory and longer range (if adjusted right).

How Does it Work?

The barrel of an airsoft gun has a small hole in the top near the back [FIG 1]. When a BB is chambered it is pushed into the barrel and be held by a rubber bucking that goes around the barrel and has a nub that protrudes into the barrel through the hole [FIG 2]. A hopup chamber [FIG3] holds the bucking in place and has an adjustment mechanism to control how far the num protrudes into the barrel. When fired the nub on the rubber bucking catches the BB at the top and causes it to spin [FIG4].


FIG 1 – Airsoft Barrel


FIG 2 – Hopup Rubber Bucking


FIG 3 – Hopup Chamber


FIG 4 – Internal Workings of Hopup Chamber

There is a dial on the back of the hopup chamber that can be rotated to raise and lower the rubber nub in the barrel. The more the nub protrudes into the barrel the more backspin gets imparted to the BB and the farther it will rise when fired [FIG 5].


FIG 5 – Backspin Diagram

Adjusting your Hopup

There is no one right way to adjust your hopup, it’s a matter of personal preference and play style. Most players prefer to have their hopup set to a middle range where the trajectory is fairly flat with a slight rise near the end of flight [FIG6 A]. Adjusting your hopup lower gives you a shorter range but a more pradictable ballistics path, this can be useful when using optics during shorter range or CQB style games [FIG6 B]. Adjusting your hopup higher will make it harder to hit targets as the BB will "hump" very suddenly at medium range and go over your target and will have a just as sudden drop at the end of it’s flight path making it harder to hit your target, but will give you a slight range advantage [FIG6 C].

One problem with hopup is when you have to hit a target hiding behind an obsticle or at the top of a hill [FIG 7]. Having your hopop set too high will cause the BB to ‘float’ over the target or impact into the obsticle creating an area that you can’t engage [FIG 7 B & C]. In this case lowering or disabling your hopup in the field will be the only way to take out a target[ FIG 7 A].

The "Magic Bullet" Trick

In rare cases when a target is hiding behind a tree or over steep obstruction you may want to overadjust your hopup and angle your gun in such a way as the BB will ‘curve’ using the hopup. Using this trick you can curve your BB and hit targets around corners and behind obstructions that are otherwise impossible. While I’ve never heard of this techinique being called ‘cheating’ (and honsetly I’ve never seen anyone use it but me, and only in a few cases), it may be seen as bending the rules a bit, so use your best judgement.


FIG 6 – BB Trajectories when fired flat
A – Low Hopup: Flat but drops early
B – Medium Hopup: Slight rise but greater range
C – High Hopup: Rises at range and suddenly loses height


FIG 7 – BB trajectories when fired at an angle and over an obstacle
A – Low Hopup: Can hit targets low to the ground and obscured by a low rise
B – Medium Hopup: Can hit targets if they are above an obstruction but not behind it
C – High Hopup: Can hit targets at a greater distance but needs clearance at range to hit targets

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