Thursday, March 26, 2015


We have all heard of the Nerf Mega Bigshock by now, and spring upgrades and .50 cal conversions have already been thrown around. I figured I would snag one to mess with.

[insert stock photo of a factory Bigshock here]

Out of the box, it was obviously underwhelming. I took 4 chrono shots which hovered around 58 fps.

This is the piston group disassembled:

The rod is some kind of soft plastic, probably PP, like a Triad rod also seems to be. The end plate has speed holes from the factory.

The piston head has a thick molded rubber pad from the factory (Please do not argue about whether to remove the AR!) and is attached with one of these press fit pins instead of a screw. Hasbro seems to skimp on this lately and I am not sure why, a hard enough yank and you will rip that fastener right out. With spring upgrades, getting rid of it is mandatory.

I ran an 8-32 tap into the rod and installed a screw with plenty of thread engagement.

It is interesting to note that the piston on these is not keyed to the rod. It can be rotated freely. This may be useful if the step on the piston where the sear engages gets worn, to extend the life of parts.

Watch out with the rubber bumper. It should stay on fairly well, but if you don't have a large washer or screw head, it could get dislodged. You may want to CA it to the piston.

The rear barrel plug is solvent welded to the frame and is designed as a cosmetic part with the stock shell. I, however, have discarded the shell, so this will not be retained, a simple plug will be fabricated. AR is a standard D'Andrade valve, just bigger, and has a rubber insert.

There is a step in the barrel, not just the peg supports, which prevents inserting dart foam past the end of the tight section of the bore. I ground this away carefully, since I want to load darts flush like I do with my .50 caliber Jolts.

Spring is nearly identical in dimensions to a Buzzbee Tek spring.

I tried out this Tek spring plus a stock Swarmfire spring and bagged 78 fps. I then settled on a shortened Everbilt which produced about 91 fps and is very nice and snappy. Proper data on the final build will follow when I have enough ammo to do a shoot.

This hole was found in the piston head. Be careful, it goes through to the backside and is how the usual AR vent port is implemented. Fill it with Devcon or the like.

Speaking of vents, this is a type of ported cylinder. The two bulges on the outside of the grip are where two slots, like transfer ports of a two-stroke engine, are, which prevent any compression until the last approx. 1.25" of stroke. Yes, some may complain about "those dreaded holes in the PT" and "nerfed performance potential", but for the stock barrel, there is probably nothing wrong with this and little to gain, in fact there may be something to lose by changing this feature.

However, if you will put a longer barrel on one of these, it can be trouble. Cartaya has already discussed de-porting the Bigshock the hard way.

The stock O-ring seals perfectly. If the barrel is plugged before firing, this one will hold pressure for well over 15 seconds without leaking at all, and has minimum friction. Don't tamper.

And here is the result. I cut off a bunch of webs, ribs, tabs and other now-unnecessary shell provisions on the outside of the frame and end plate and reshaped the front of the trigger guard, which do help quite a bit with comfort. The top tab on the muzzle was kept as a front sight post. The plug in the back of the frame is a piece of sheet bonded to 3/8" of 1/2" PVC which was filled with epoxy putty for dead volume removal.

Shoots real nice. It has some serious snap to it, feels exactly like a scaled-up version of my .50 cal Jolt should, and oddly enough these darts seem to get more accurate the faster I shoot them.

Obviously, with a .50 caliber insert you could get some serious velocity on a micro. I am not doing that, since a major part of the appeal of these things is the 20mm hand cannon factor and the utility of shooting darts often assigned anti-armor and enhanced damage effects. Also, about those rear frame plugs, there is no reason to make them fixed. I made mine fixed because again, I am just going to muzzleload a mega. I have seen concepts for RSCB feed tubes placed there. A convenient fitting for modularity is a 1/2x3/4 CPVC CTS bushing. Hint hint.


  1. How were you able to remove the permanent pin in the plunger assembly?

    1. By prying it out with any suitable tool, it is just a press fit with some serrations to grip a bit better. There isn't anything permanent or durable about it, and that's the main reason for replacing it with a screw.