i am trying to find out if any one knowes about a mount for a 12ga mossberg shotgun to the bottem of an ar type rifle ?

Quoted: Cant really do it easily. KAC makes one out of Rem 870s called the masterlock. But having one or making one usually requires a shorter than legal shotgun barrel. So all the propper licensing that entails is required.

I thought it was a Masterkey.  

The Mossberg is a tough one to mount in this manner because of the location of the safety.  The Mossberg safety doesn't allow the shotgun to be mounted as high as it needs to be. Pump shotguns that go under the AR need to be mounted as high as possible, right under the axis of the bore.  Because the AR is linear in that the barrel, action and stock are all in direct line, anything mounted and fired under that line needs to be either very low recoil or mounted as close to that axis as possible.  There have been a lot of shotgun mounts like this that have come and gone, most would break under repeated recoil torque.

The KAC unit works really well in this manner.  The mount is very low, but very long, along the entire length of the receiver, none of this barel clamp at the front/ Mounting stud at the rear stuff like so many others.

We really need to tack this question.
Seems like it gets brought up fairly often.
Makes sense though - would be a neat accsy to have.

ok found a thread from feb about the masterkey no mention of mossberg there . the safety is an issue thow . still is there a mount out there for sale?  the lenth is not a concern as a 18" shotgun with it mounted like a m203 is the same length as a bayonet mounted. however i have asked this question on gun broker if  an aow is mounted to a rifle is it an sbr now? the reason i ask is because a14" barrel that has a removable brake is not legal rifel barrel but weld it and now its legal. so if the shotgun is bolted on it isent  permanentaly atached  there for no sbr correct? like a 40mm atached to an ar its a dd the launcher can be a pistol rifle its the barrel thats the dd not the ar so does this make any sense?

Quoted: ok found a thread from feb about the masterkey no mention of mossberg there . the safety is an issue thow . still is there a mount out there for sale?  the lenth is not a concern as a 18" shotgun with it mounted like a m203 is the same length as a bayonet mounted. however i have asked this question on gun broker if  an aow is mounted to a rifle is it an sbr now? the reason i ask is because a14" barrel that has a removable brake is not legal rifel barrel but weld it and now its legal. so if the shotgun is bolted on it isent  permanentaly atached  there for no sbr correct? like a 40mm atached to an ar its a dd the launcher can be a pistol rifle its the barrel thats the dd not the ar so does this make any sense?

If I understand you correctly...

An AOW undermounted on an AR becomes a Short Barreled Shotgun or SBS.  The idea is that the stock for the AR becomes the stock for the shotgun too.  It becomes shoulder fired and is no longer an AOW. Whenever the shotgun is mounted underneath the AR, it has a stock (the AR stock), so whenever it is attached it is an SBS.  It does not matter if you permanently attach it or not, shoulder-fired is shoulder-fired. Technically speaking, if you set-up an AOW shotgun to be mounted underneath the AR, meaning holes were cdrilled, the mount mounted, etc, you already have an SBR even if you didn't actually mount the AOW at all.  The presence of the AOW shotgun, an AR and the mount/interface between the two weapons could constitute "Constructive Possession" of an unregistered SBS.

The AR that this is being mounted on is not legally effected in any way by the presence of the shotgun, but the rifle (by definition being shoulder-fired) effects the legality of the AOW shotgun in the manner described above.

This is a reason why KAC Masterkey units are registered as SBSs and not AOWs by the factory, eventhough they do not have a stock.  The presence of the undermount can legally imply use on a rifle and could get a purchaser in a legal bind the moment it was brought home from the dealer. The moment the owner or person in control of an AR rifle comes into the control of a Masterkey, there is an NFA violation, even if the two are not assembled.  Another reason is that Remington does not usually sell or make available stripped receivers or  stockless models that could be used for an AOW build.

Regarding M203s, it is not their presence on an AR that makes them DDs, it's the bore size and, incidentally, the ammunition it fires.  A 40mm bore is WAY beyond the .5" bore diameter allowed in Title I firearms law.  The 40mm bore is also recognized as firing and designed to fire explosive projectiles which is another qualifier as a DD.  It doesn't matter if the M203 is standalone or mounted underneath a rifle, it's a DD by virtue of the barrel. The 40mm bore is greater than .5" and that particular bore size fires explosive ammo. Same as an M-79.

The M203 stripped receiver however is NOT a DD because it does not have a barrel attached, so there is no bore size nor is there an ammunition reference to determine it as a DD.  It is a Title I firearm and can be purchased as a standard firearm receiver through any FFL.  Some people buy stripped M203 and add a 37mm smooth-bore barrel creating a "flare launcher" and avoiding the DD issue entirely.  Because 37mm smooth-bore is generally reserved for signalling devices (smoke or flares) and no one makes an explosive or anti-personnel round (buckshot or slug) for it, it is exempt from DD status eventhough it has a bore greater than .5".  37mm launchers are not even firearms when purchased as such, but using the M203 receiver method to create one, it is a Title I firearm.

Other people buy the stripped M203 receivers and build their own 40mm M203s on a Form 1 to save some money.

But if you intend to use your AOW as an undermount, you need to Form 1 it into an SBS to be in compliance.

All of this being said, AOW, SBS or 18" Title I shotgun, I would be very hesitant to use just any mount for the purposes of undermounting a shotgun.  The recoil of the shotgun will present problems for the rifle it is mounted under if the mount is not done correctly.  I wouldn't touch a mount that didn't attach using screws along the top length of the shotgun receiver.  Mounts that use a barrel clamp and the shoulder stock attachment point at the rear of the shotgun receiver, as most of the units I've seen use, can be unsafe, will not last and can damage the AR.

thank you for the info also the mounting is somthing ill have to look at if i  can figureout how to do it legally and not have a real long barrel. does anyone know the minum length for a shotgun? overall not barrel . here in al. we cant have sbr's but not sure about sbs's.

I always liked the M16/shotgun setup on Predator had that dont mess with me mojo  btw how was that mounted?

The M203 stripped receiver however is NOT a DD because it does not have a barrel attached, so there is no bore size nor is there an ammunition reference to determine it as a DD.  It is a Title I firearm and can be purchased as a standard firearm receiver through any FFL.  Some people buy stripped M203 and add a 37mm barrel creating a "flare launcher" and avoiding the DD issue entirely.  Because 37mm is generally reserved for signalling devices (smoke or flares) and no one makes an explosive projectile for it, it is exempt from DD status eventhough it has a bore greater than .5".  37mm launchers are not even firearms when purchased as such, but using the M203 receiver method to create one, it is a Title I firearm.

Other people buy the stripped M203 receivers and build their own 40mm M203s on a Form 1 to save some money.

So i could go to my local fun shop and have him order me a 203 reciever from LMT and than fill out all the proper paper work and than buy the rest of the parts?  I heard the barrel was controled and to purchase that I needed to have the proper paperwork?

Quoted: So i could go to my local fun shop and have him order me a 203 reciever from LMT and than fill out all the proper paper work and than buy the rest of the parts?  I heard the barrel was controled and to purchase that I needed to have the proper paperwork?

No, only the receiver is controlled.  Everything else is just parts.  Some dealers may want to see an approved Form 1 before they sell you a barrel, but that is not law, just them covering themselves.

You could contact LMT, but I don't think LMT will help you.  I don't think LMT sells stripped receivers, they register the receivers right away to build full DD M203s.  You could certainly contact them and ask, but don't expect much.  The trouble is that operations at this level have a somewhat automated "path".  It's highly likely that the registration paperwork was sent in and approved before the receiver is even manufactured, making it impossible for them to even have a stripped M203 receiver that is not already registered as a DD.  Make sense?

Try mr40mm.com or Kent Lomont.  Both these guys usually have stripped M203 receivers.  Be prepared though, Mr 40mm makes his own, though very high quality and they go for about $2200.  Kent Lomont, last time I checked, had only Colt stripped receivers, which means about $3000 or more.  This is not a cheap thing to do, obviously.

If you want a true 40mm M203, then yes, you need to buy the receiver, submit the Form 1 and $200 making tax, then buy the barrel AFTER it comes back approved.  Only the barrel makes it a DD, so any of the other parts are okay to buy without an approved Form 1.  This is also how to go about building your own M79.

If the M203 receiver is already a registered DD, then you could still do it, it would just take a few extra steps and a lot more time.  The owner of an existing M203 DD can separate the barrel from the receiver (and I mean like sell the barrel, get it far away from the receiver) and send a letter to ATF NFA Branch explaining that the DD has been disassembled to Title I status and request that it removed from the NFA Registry.  Once that confirmation letter arrives from NFA Branch, that stripped M203 receiver can then be sold to anyone just as any standard rifle, pistol or shotgun.  But be aware, this is federal law.  Your state law may define DDs differently than the feds, so check that out first.

This principle, by the way, is the same for an SBS/AOW.  A Short-Barrelled Shotgun, as the name clearly states, is a "shotgun" and by definition a shoulder-fired weapon. An AOW created from a shotgun receiver is not actually a shotgun at all, it's considered a "smooth-bore pistol."  A virgin, never-before-built shotgun receiver or a built shotgun receiver that has never had a buttstock attached has not yet been defined as a "shotgun" because the lack of a buttstock prevents it from meeting the definition of "shotgun."  Until a stock is attached, it's in a bit of legal limbo and that can be exploited in the form of an AOW.  An M203 receiver is exactly the same principle.  Without the defining characteristics of a 40mm barrel, the M203 receiver cannot yet meet the definition of a DD.  It still meets the definition of a "firearm", just nothing further.  The difference though is that once a receiver, any receiver, has a stock attached, it can no longer avoid being defined as "shoulder-fired" and this status is irrevocable.  An M203 receiver can become a DD with the addition of a barrel and it can revert back to Title I status by removing the barrel and removing the weapon from the NFA Registry.

And to bring these two things together, looking at the definition of a DD and applying it to shotguns, ANY 12-gauge shotgun receiver (Title I or existing AOW or SBS) to which is added a RIFLED (slug) barrel less than 18" in length becomes a DD.  The presence of a rifled, NFA length barrel meets the definition of a DD because of the rifled bore greater than .5" in diameter.

Quoted: thank you for the info also the mounting is somthing ill have to look at if i  can figureout how to do it legally and not have a real long barrel. does anyone know the minum length for a shotgun? overall not barrel . here in al. we cant have sbr's but not sure about sbs's.

Minimum barrel length for a Title I shotgun is 18".  Minimum overall length for all Title I shoulder-fired firearms is 26".  If you have an 18" barrel, you're fine on OAL.  

ok thankyou on the 18" barrel but the 26 " over all is still cloudy to me i get that rifle minum length is 26" if i remove the pistolgrip from my persuader then it is 25"or alittle over thats with a custom 18" barrel so does it have to be 26" or have a minum length barrel of 18 or both? now on a side line how about a muzzel loader 12 ga sxs with locks no restrictions on that right  or am i wrong again ? that would look cool and it could be the right length to fit nicly and as its for breaching or limited shoting than 2 shots should be enough. maby custom drums with 209 nipples sure ignition. any restrictions on ml's that you are aware of? thanks just throwing the ml. thing in the mix. still want a pump under my 9mm ar oops just thought of somthing you said about the aow being a pistol then if the ar is a pistol than an aow under it would not make it a sbs as it is mounted to a pistol so maby that would work yes??? i want to build this for me and looks not for a swat teem as i am a mechanic and all my buddys are also. but i like building or buying weard guns. thank you for all of your help

Quoted: ok thankyou on the 18" barrel but the 26 " over all is still cloudy to me i get that rifle minum length is 26" if i remove the pistolgrip from my persuader then it is 25"or alittle over thats with a custom 18" barrel so does it have to be 26" or have a minum length barrel of 18 or both? now on a side line how about a muzzel loader 12 ga sxs with locks no restrictions on that right  or am i wrong again ? that would look cool and it could be the right length to fit nicly and as its for breaching or limited shoting than 2 shots should be enough. maby custom drums with 209 nipples sure ignition. any restrictions on ml's that you are aware of? thanks just throwing the ml. thing in the mix. still want a pump under my 9mm ar oops just thought of somthing you said about the aow being a pistol then if the ar is a pistol than an aow under it would not make it a sbs as it is mounted to a pistol so maby that would work yes??? i want to build this for me and looks not for a swat teem as i am a mechanic and all my buddys are also. but i like building or buying weard guns. thank you for all of your help

26" minimum OAL refers to the shoulder-fired firearm WITH THE STOCK ATTACHED.  The firearm cannot be less than 26" with the stock attached.  With no stock attached, it need only meet the minimum barrel length.  This issue is a bit diferent than what I said about AOW shotgun receivers.  The "shotgun" is by definition a shoulder-fired firearm, it was originally designed to be fired from the shoulder by virtue of having had at one point, or currently, a shoulder stock.  But this doesn't mean the stock has to stay on the gun.  It DOES mean it cannot be used in a pistol build.

A shoulder-fired firearm with a collapsible stock needs to be 26" OAL with the  stock extended or in the position designed /intended to be fired from the shoulder.  Your Persuader does not need to have a stock, but the OAL when there is a stock attached must be at least 26".  Make sense?

I really don't understand the point of having a shotgun mounted beneath the barrel of an AR.  I'm supposing that the purpose is for use only as a breaching tool.  Firing the damn thing would be far too awkward, it would appear from pictures, to actually use it as a fighting tool.  It also appears however that  simply having the shotgun mounted would make the AR quite awkward to fire.  Seems like less return for your investment than a 203 and the cumbersomness that leaves you.  

To me it just seems more practical to have a very small, pistol gripped shotgun slung, and ready for use.  I have seen pictures of this, but never pictures of real end users with Masterkeys (other than staged photos).  I have also spoken to plenty of people who prefer the method I described.


Not bashing you guys who want to do this, just asking about the motivation/desired results/practicality you invision.


I'm sure the overwhelming response will be: "because it's fucking badass dude."

thanks  for the over all length 26" and the aow pistol thing well as far as the build goes im in limbo right now. but do any of youguyes know if abarrel length could be messured from the reciver if the barel was welded to it? like in the case of an ar with a welded barrel nut it couldent be removed then would that count as barrel length? or a mossberg 500 steel reciver with the barrel welded to it?  and as far as why to build this because it looks cool.