Question: Changing Mossberg Shockwave To 18.5" Configuration

[Phydeaux642]

I have a Mossberg Shockwave with an SBA3 brace and am considering changing it to an 18.5" configuration with an adjustable stock instead. I have access to a 20" 590A1 barrel for $135, but don't know if I want the extra weight out front with the added capacity and thicker barrel. The trouble is, 18.5" 590 barrels are non-existent. So, not being a shotgun guy, I would like to know if I can put a 500 barrel on the 590 receiver if I get a 500 magazine tube, spring and cap? And can I use the same follower or do I have to get one specific to the 500. Thanks.

 

[WestKentucky]

There’s some legal concerns that are bigger than the question of if parts fit. I feel like you would be better off just buying a separate gun to have your adjustable stock and longer barrel. You currently have a “firearm” and you would be transitioning over to a legal shotgun status.

 

[L-2]

If legal in the OP's state of residence, I'd convert the subject Mossberg Shockwave to an SBS (short barreled shotgun) using the ATF Form 1 e-file process (cost ~$250 + cost of whatever stock is obtained).

Edited to add:
Otherwise, I can't think of a reason why a 500 mag tube (of appropriate length to match the barrel, wouldn't screw into a 590 Shockwave receiver. The 12 gauge follower is the same part number between 500 and 590 guns.

 

[Phydeaux642]

No legal concerns from what I have studied. No different than turning an AR pistol into a rifle.
I don't want to deal with a tax stamp and dealing with ATF if for some reason I would have it with me when I enter another state. Asking permission to do so just irritates me if I already went to the trouble of getting a stamp.
Really would just like to know about the parts in question. Thanks.

 

[12Bravo20]

Actually you will want to reread all of the pertinent NFA regulations when it comes to shotguns. The Shockwave and Rem Tac are classified as "firearms" since they have NEVER had a stock attached nor are they designed to be fired from the shoulder. You can put a pistol grip on a "shotgun" but the barrel needs to be long enough to keep the OAL over 26". That is why all the combo kits come with a 20" barrel.

And comparing taking a "firearm" and changing it to a "shotgun" and then back to a "firearm" is not the same as changing an AR pistol to a rifle then back to a Pistol. The main difference, that will get you into trouble, is the fact that a smooth bore "pistol" is illegal to own/posses unless it is registered as an AOW

Here are some good points on the Shockwave:

https://www.ammoland.com/2017/05/mossberg-590-shockwave-firearm/#axzz6bvYkeUYX

I personally do not want to be the test case by converting a smoothbore firearm to a shotgun and then back to a smoothbore firearm. If you want to add a 18" or longer barrel and a stock and leave it permanently in that configuration, go for it.

I'm not a lawyer and I highly suggest that you talk to a lawyer that specializes in both Federal and State firearm laws

 

[12Bravo20]

And I forgot to mention. On the 410 Shockwave at least, Mossberg made the magazine tube short enough that a standard 410 590 barrel will not attached. And of course a 500 barrel won't work on the Shockwave either. I don't know if the 12 and 20 Gauge versions are the same or not. For the 410 version, you would have to also change out the magazine tube to fit a 590 or 500 barrel to it. And good luck finding a 590 410 barrel since Mossberg just came out with that model this year. 500 410 barrels are hard enough to find. Another consideration is the cost of all the parts needed to convert a Shockwave to an actual shotgun will add up quickly.

 

[Phydeaux642]

I have a 590 barrel available for $135 used. Magazine tube and spring for $60. Adjustable stock and tube for $50. Sell the SBA3 to make up for some of that. Should be into it for around $150. A 590 on Gunbroker is going for big bucks and they're not available anywhere else, so, I figure this is the cheapest way to get there.

 

[12Bravo20]

I have a 590 barrel available for $135 used. Magazine tube and spring for $60. Adjustable stock and tube for $50. Sell the SBA3 to make up for some of that. Should be into it for around $150. A 590 on Gunbroker is going for big bucks and they're not available anywhere else, so, I figure this is the cheapest way to get there.

Just remember that you will most likely have to leave it as a stocked shotgun once you convert it. Double check actual ATF NFA regulations.

 

[Phydeaux642]

I thought the term "firearm" was the broadest definition that ATF uses which would give you more leeway with these things. It would just be easier to go back to 1934 anf do away with NFA restrictions altogether.

 

[12Bravo20]

Well shotguns are a special breed all on their own. The NFA and GCA of 34 states that nothing with a bore over 0.500" in diameter is legal. They made an exception with a sporting clause that applies to smoothbore shotguns only. No rifles or pistols are allowed to legally have a bore diameter greater than 0.500" while shotguns are okay since they fall within the "sporting use" clause. The street sweeper and similar shotguns were banned because they have a bore bigger than 0.500" and do NOT meet the standards under the sporting use clause.

The GCS and NFA regulations do not make a lot of sense but we still must abide by them or face fines and/or jail.

 

[Phydeaux642]

Well, if I do the conversion I don't have any intentions of going back. A stocked shotgun is way more viable for me as a defensive weapon. The Shockwave has a bit of a cool factor, but I think I'm done with it.

 

[12Bravo20]

Well, if I do the conversion I don't have any intentions of going back. A stocked shotgun is way more viable for me as a defensive weapon. The Shockwave has a bit of a cool factor, but I think I'm done with it.

If that is the case, then you are good to go. Just makes sure to put the 18" pr longer barrel on before doing anything else to it.

 

[Phydeaux642]

Yes. I'm trying to figure out what parts I'll need. I guess I'll get the 20" 590 barrel for $135 used. A magazine tube and spring. And a stock of some sort. The follower and magazine cap from the Shockwave should work on the other magazine tube. I think that is all I will need. I'll sell the 14" barrel and brace to recoup most of the cost.