Hello and welcome back to another edition of The Rimfire Report! This ongoing series covers various firearms, practices, ammunition, and trends surrounding the wonderful and interesting world of rimfire firearms. This week we are taking a bit of a departure from traditional firearms and venturing into the world of NFA items. Normally you’ll be hard-pressed to find many uses for .22 LR in the NFA world outside of suppressing the humblest of rounds but this week we’re going to talk about 40mm grenade launcher sub-cal adapters otherwise known popularly as the “Hornet’s Nest” or “Beehive.”

The Rimfire Report: 40mm to 22 LR Sub-Cal Adapters – A Wall of Angry Bees

Photo: FullMag

Yes, You’ll need to Own a Destructive Device to do this

Let’s get the hard part out of the way – owning a 40mm grenade launcher. 40mm grenade launchers are completely legal to own and are actually quite easy to find online from reputable manufacturers and private sellers alike. The main hindrance to owning an M203 launcher is going to be first the price, and then secondly getting the paperwork filled out for a destructive device on an ATF Form 4. Normally getting something registered through the ATF on Form 4 isn’t that much of a problem and the M203 really only falls into the category because of the size of the tube (anything over .50 BMG that doesn’t have a “sporting” use is generally considered a Destructive Device).

Photo: FullMag

On average you can expect to spend anywhere from $1,200 to $2,500 on an M203 launcher depending on the configuration and type. Lewis Machine Tool sells them in various configurations from standalone launchers to underslung rail-mounted launchers. In addition, various other online retailers will have them for sale in a number of common configurations.

Photo: FullMag

What keeps many from owning one of these launchers is the exorbitant cost of getting any sort of useful ammunition for the launcher that won’t break the bank. Generally, anti-personnel ammunition is highly regulated and each individual projectile will carry with it the need for another $200 tax stamp. Chalk rounds used to be pretty popular but due to recent ATF regulations, they were deemed as explosive (specifically the complete M781 chalk round). While there is currently a workaround being made to allow for the use of these rounds without a tax stamp, for now, you’ll be hard-pressed to get anything “fun” for your 40mm grenade launcher with probably one exception – the Hornet’s Nest.

Photo: Ordinance Lab

What is A 40mm Sub-CAl Adapter?

Sub-caliber adapters do one simple thing: they make it possible for you to use smaller than normal ammunition in an otherwise larger bore firearm. Most of these Hornets Nest or Beehive 40mm to .22 LR sub-cal adapters generally feature 9 to 18 steel barrels that are all fired simultaneously. Most of them accomplish this by either using a large rifle primer or even a smaller caliber centerfire cartridge that has been cut and pressed into the back of the adapter. Both versions do this in order to push a piston forward that will hit all of the rims of the 22LR rounds simultaneously sending a swarm of .22 LR downrange in an instant.

Photo: OTB Firearms

These sub-caliber adapters occupy a unique position in that they are not regulated by the ATF when chambered in 40mm. One would assume these would exist for 37mm launchers but the main benefit of the 37mm launcher is that it is a smoothbore “signaling device” and therefore not classified as an NFA item unless lethal ammunition is used with it – so the second someone makes a Hornet’s Nest for a 37mm launcher, it turns your otherwise benign 37mm launcher into what the 40mm is already.

Photo: OTB Firearms

Generally, a Hornet’s nest launcher will set you back about $600 or so and that doesn’t include the cost of the ammo or primers you’ll use to shoot it – thankfully, .22 LR is still on the cheap side of things when considering what you’re getting into with at 40mm launcher. Other manufacturers have started making less expensive versions that cost around $400 but mileage and quality may vary depending on the manufacturer.

Photo: Small Arms Review

Are Sub-Cal Adapters Useful?

Depending on the manufacturer, some of these sub-cal adapters will either have rifled or smoothbore barrels. From what I have seen online, both types of barrels tend to have significantly degraded accuracy and a much looser grouping when compared to regular shotguns. My research revealed that even the rifled barrel versions didn’t quite stay on track and tended to drift about 1″ in group size for every additional 5 yards of distance. On the other hand, the smoothbore barrels tended not to stabilize the projectiles at all and they tumbled around and I’m sure at any significant distance you’d be faced with extremely large group size.

Photo: Small Arms Review – Groups Sizes at 10, 15, and 20 yards – Rifled Barrels

So while these fun pieces of gun accessory don’t quite have any practical or tactical usefulness behind them, I still don’t think that they should be discounted altogether. After all, what good are guns if you can’t have a little fun with them from time to time? I could see the 40mm sub-cal adapter being a great crowd pleaser at night when combined with some cheap .22 LR tracer rounds or perhaps it might be fun to just blow up some watermelons in the summer months. In any case, that is all I have for you today on The Rimfire Report and as always, thanks for stopping by to read and I look forward to your thoughts and comments down below!