Are the receivers on the 37 and 40 mm launchers actually different? Could it be viewed similar to our restricted vs non depending on barrel length?
The Colt 37mm and LMT 37mm M203's that I have seen and handled in the past (stateside) were identical to the 40mm M203's, I think most or all are marked 40mm as well. The only difference is the barrel. Im not talking about the fake cheap knock off 37mm smooth bore m203(ish) copies you see all over the place (spikes etc). Those are completely different.
This is an example of a real colt M203 40mm (even marked 40mm receiver) with a smoothbore 37mm barrel make it a non NFA item in the US. The receiver IS a real Colt M203 40mm receiver.
h ttps://www.armsunlimited.com/Colt-M203-37mm-Grenade-Launcher-for-M16-M4-AR15-p/r0811.htm
In the USA it didn't matter (and perhaps the ATF has changed its stance on that, im not 100% on the up on this) if it was a 40mm marked or capable M203 receiver as long as the barrel was a 37mm smooth bore and you DID not possess or fire anti personal rounds (its supposed to be a flare gun not a shotgun or grenade launcher) and did not possess or (obviously) install a 40mm rifled barrel on it (unsure about smoothbore but if its 40mm and accepts a 40mm GL round I think you're out of luck). If it met these criteria it was exempt from class 3 DD status as the ATF considers it to be a flare launcher and no longer a GL.
Here is an example of a US company selling non NFA non Class 3 real m203 receivers with no barrels:
h ttps://clydearmory.com/lmt-m203-40mm-3234.html
From the website:
Title 1 (non-NFA) receiver does not require a destructive device dealer to transfer. Barrel not included. Barrel-mounted receiver.
Please note- We can only sell a 40mm barrel after seeing an ATF-approved Form 1 for the receiver purchased. The buyer understands that the installation of a 40mm barrel without an ATF-approved Form 1 registering it as a destructive device is illegal, and assumes all liability for his actions.
That is for the US domestic law, nothing to do with rules in ITAR or the US state departments stance regarding the export of 40mm M203 receivers (with 40mm or 37mm barrels) and 40mm GL parts including exporting separate barrels from receivers. This also has nothing to do with controlled goods Canada's stance on these things. Canadian Businesses are supposed to be registered with Controlled goods to import and possess these types of GL's and the controlled items must be registered with controlled goods and stored according to the rules of the Controlled goods act. There are strict rules on who can have access to the controlled items and you are subject to periodic inspection. Only then can they be transferred to other businesses or individuals with a controlled goods licence. The US state department AFAIK only issues export licences for GL's for MIL/LE/Theatrical end users not for civilian end users but hey Ill admit I dont know for sure for all circumstances.
Controlled Goods Canada also seems to take an interest in the importation of any kind of deactivated GL, rocket launcher, AT weapon, etc that is under their jurisdiction. I believe they have taken the same stance as the RCMP when it comes to deactivated guns. They consider them to be live during import and must be imported the same as a live weapon of whatever class it was in before deactivation. Business's would have a hard time coming up with a legitimate reason for importing a "live" RPG-7 for example, and saying you are importing it to deactivate to for retail apparently isn't a legitimate reason to them. This is why the cheap deactivated RPG's, Super Bazooka's, Carl G's etc in the USA don't make it up here, and if you do see them here they arent cheap... somebody snuck something in if its recent, or it could have legitimately came in before ITAR, from another country, or before controlled goods cared about this kind of old junk.
EDIT: I was talking about the last gen of LMT/COLT M203's... I found this newer one at brownells for example that is marked 37mm, and then I found this info:
"LMT just confirmed again that the brownells M203's are not interchangeable with 40mm barrels and the brownells 37mm barrels are not interchangeable with Mil spec M203's."
Looks like this one is made very similar to a legit LMT M203 but is marked 37mm with a 37mm smooth bore barrel and cant accept a 40mm barrel so in theory it MAY be ok for export/import..... it should not fall under the controlled goods act in Canada, not sure what the US side would say for export but im guessing no
h. ttps://www.brownells.com/shooting-accessories/duty-gear/safety-amp-warning-equipment/m203-37mm-launcher-prod118458.aspx