RRA LAR9 Set Screw Inside Barrel?

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SJK12

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Hello everyone,

I have a Rock River Arms LAR 9mm AR pistol that I acquired from a dealer a while ago. It was listed as ‘New Old Stock’ although it showed obvious signs of being fired. Either way, I didn’t care because it was still in great shape. I took the gun out of my safe with plans to clean and shoot it. I’m glad that I did because I noticed an obstruction in the barrel that I didn’t notice before.

The obstruction was a set screw that threaded directly inside the barrel. I’m thinking that the threads were factory made as the machining was perfect, the rifling goes through the threads, and it is chrome lined. The barrel is confirmed to be 9mm, but with the set screw in place there is no chance of a 9mm round passing through it without a catastrophic failure. With the set screw removed, the barrel seems fine. The threads inside of the barrel go in for about one inch from the muzzle.

I have contacted Rock River Arms and the dealer I bought it from about this but have still not heard back. A Gunnutz and Google search brought up nothing.

In the mean time, I was hoping that someone on the this forum would have some insight. I’m not new to the AR15 platform as I own a Colt AR15A4, LE6920, LE6991, DD MK18, and HK MR223A3, but this has me stumped. :confused:

The first photo is without the set screw. You can see the threads inside of the barrel. The second photo is with the set screw - the barrel is now obstructed. The set screw will go into the barrel another inch or so. The last photo is of the set screw itself with a standard size allen key.

What the heck do I have here?

Thanks!

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The set screw is right inside the barrel. The first 1” or so at the end of the muzzle. Just picture a screw coming out of the barrel as if it were a 9mm round. It’s odd.
 
Are you saying that the first inch or so of the barrel has been threaded?? As in the "set screw" is screwed in along the long axis of the bore?? I read on the internet that some have tried an internal thread at the muzzle for a silencer/suppressor, but that would require the threaded bore to be much larger than the rifled barrel bore.
 
tiriaq said:
A screw threaded right through into the bore? That doesn't belong. Someone screwed up.
Click to expand...

Agreed. The set screw was itself is only about a half inch in length but screws into the barrel perfectly. I had no issue removing it with a standard size Allen key. It was hidden by an A2 birdcage flash hider. I have no doubt that if I didn’t catch it I would have kaboomed my gun.
 
Just install a plug screw that does not go anywhere near the bore. A hole like that will do no more harm than a gas port.
Shouldn't be there, though.
 
After seeing your pictures now in Post #1, Believe it or not, there is a discussion on Milsurp site about this kind of thread in a rifle barrel's muzzle - no one certain, but consensus seemed to be that is how "rifle lamps" were once made - thread muzzle to accept 1/8" NPT or similar thread, screw in the threaded rod used on a lamp socket light holder, run the wire down the bore, install a shade and screw a base onto the rifle butt, and "Wala!" - a 1950's man-cave "must have"...
 
I think I’m going to breakdown this ‘lil AR, buy another 9mm barrel, and rebuild it to make sure I don’t have a grenade here.
 
Leg said:
Movie prop gun for blanks?
Click to expand...

Actually, one of the C8 armorers at work that I talked to thought it was either for blanks or firing off less lethal options like sandbags by using a canister style attachment. There’s a small hole in the set screw about the diameter of a 22.lr round that would allow gas to pass through it.
 
Glad to see the photos; I'd assumed you were referring to a hole at 90 degrees to the bore.

Threaded bore like that, probably for firing blanks. The screw would have a hole drilled through it, the size of the hole being chosen to make the blanks function properly.

The barrel could be salvaged by being bored out to get rid of the threads - which really mess up the rifling.
 
Leg said:
Movie prop gun for blanks?
Click to expand...

Hey everyone, mystery solved. It turns out this firearm was an old movie prop converted to shoot blanks. I received a quick response from the dealer. We’ll see how shooting this thing goes. Thanks for everyone’s help.
 
Looks like you can still see some rifling on the threads. I feel like you'll get some interesting groups.

Both you and the dealer are lucky you didn't blow yourself up trying to shoot it. If they knew it was a movie prop, they should have disclosed it to potential buyers at the very least.
 
hbean said:
Ouch, that could had been a very dangerous oversight not disclosing it was modified to fire blanks
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Agreed. I guess it’s a good lesson for anyone to be sure to check your used firearms over carefully before hitting the range. The dealer seems willing to work with me on this with excellent communication. Either way, thanks to everyone that helped with this matter.
 
They sold you a firearm, once used as a movie prop, with a literal plug/BFA hidden inside the barrel beyond the muzzle device and didn't even disclose it to you? It's a very good thing you checked the bore of your firearm... If you had not and had shot the BFA instead you would've had a nice kaput barrel and might've even injured yourself or other people. This is why I inspect literally everything I buy, this is extremely irresponsible and dangerous of whoever sold it this way.
 
email the dealer you bought it from, ask them their owner's cellphone number because your insurance broker needs to talk to them! because you shot the gun that way and it blew up and now you have 1 less finger or something.

It will be really funny to read the reply back from them i bet.
 
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