.30cal to AR silencer adaptor. Bore?

[Pond, James Pond]

A while ago, I was thinking about how best to get both guns suppressed (my .308 and my AR). Two cans was going to be expensive and no one seems to sell AR threaded cans.

Anyway, I had started a thread that broached this subject and one proposal had been to get a .308 can and fashion an adaptor that would allow its 1x18 thread to be threaded on to a standard AR.

This is something I have been investigating despite originally thinking it too expensive to consider.

I've found a place that might help but need some input. I do want the sound suppression but don't want to loose accuracy as my AR is not a match gun to begin with. Whatever I do, I want to maintain its existing accuracy as much as possible.

So, what diameter should the bore of the adaptor be?
.308"?
.224"?
Or something in between?

Furthermore, would the adaptor need any sort of crown cut to manage gases as the bullet passes from the barrel to the adaptor and then the can?

[Gunplummer]

Who knows what is inside your "can"? On the suppressors I have dealt with, the main tube is fairly close to the bullet diameter. It does not seem possible to most people, but if that bullet clips something internally, it will come out the side. This is going back 40+ years. I have no idea what the internals look like now, but I would guess alignment is still very important. That may be the deciding factor on a "Quick change" setup.

[skizzums]

it shouldn't as tight as .225. but any size over that should be fine. I don't see why it would make a difference since the inside of the can is obviously larger than .308

[Pond, James Pond]

I don't see why it would make a difference since the inside of the can is obviously larger than .308

My concern is that in the bore the gases are behind the bullet. When the bullet is in the suppressor there are all the baffles designed to slow the gases, but not the bullet.

However, once the bullet leaves the bore and traverses the adaptor bore space, there is no gas seal and there is little space for the gas to occupy.

I simply don't know if that bottle neck will have any affect on bullet trajectory.

One thing I did not mention in the OP and should have is that, because of the whole hassle of using crush washers each time an item is removed, this adapter will stay in situ whether the can is on it or not.

This means the adaptor should not affect accuracy with the can fitted and asa stand-alone barrel endpiece.

I will therefore lose my A2 flash suppression too.
I am thinking of perhaps mimicking the expanding cone profile of the A2.

Bottomline is that this adapter will become a permanent attachment regardless which rifle carries the suppression.

[Unclenick]

The reason the center holes through the baffles are close to bullet diameter is so the gas is forced to turn an enter the baffles rather than going around the bullet. Sending a .224 bullet through .308" holes won't do that nearly as well, so the suppression will be less effective. Additionally, if the adapter is over bullet diameter by much, gas will bypass the bullet there as well, increasing the total amount of bypass gas expelled at the muzzle, and making noise.

So, bottom line, you'll get some degree of suppression, but I don't know how much. If you have the thread adapter made, by itself it should not have any more effect on accuracy than counterboring a worn crown does (an operation done to improve accuracy without changing exterior profile).

To prevent destruction of the suppressor, you want to have the machine shop take the upper and check the adapter's runout and the suppressor's runout in situ. If the threads and crown were intended for a flash hider instead of a suppressor, you have to be careful they don't introduce runout. If so, the shop may have to square at least the edge of the crown to give the adapter a more perfectly square seat. But they should measure first to determine if it's actually necessary.

BTW, if accuracy of the AR isn't great to start with, recrowning may improve on it. A lot of production crowns are not quite perfect. A 90° crown cut on a lathe is an easy fix and if there is always either a flash hider or your adapter on the muzzle, you won't see it anyway.

[Sharkbite]

OP, I run the same can on my AR's and my 308 boltguns. That can is an AAC 762 SDN-6.

It uses a qd muzzle break type attachment system. Simply install the correct muzzle device on each of the guns you want to use the suppressor on and go have fun.

As to effectiveness of the 30cal can on a smaller bore gun, it works fine. A dedicated 556 can is smaller and lighter then its 30cal brother, but the added volume of the 30cal can makes it sound very close to the 556 can.

So, the downside of the 30cal can is a bigger then needed can on a 556gun. The added versatility makes it a winner in my book

[Pond, James Pond]

Thanks for the thorough insight, Unclenick.

I had also thought about simply cutting down my A2 flash hider and threading its shortened exterior. There is enough metal there to carry the thread and still be pretty thick.

I had not thought of the runout issue I'll have to ask how they hope to address that.

Suppression-wise however, I am less concerned. It will not quieten the shot the way a .22 cal silencer might, but I've read that the difference between a .223 correctly suppressed and ".30cal suppressed" is not that great so I think it will be OK.

The good news is that being a .30cal, it gives me about 2mm of total extra clearance around the bullet as it travels down the suppressor bore, so unless runout is severe (> 1mm over the 8" length of the suppressor) it should probably prevent contact.

[Unclenick]

Sharkbite says the larger volume of the .30 caliber suppressor will make up for the gas leakage, and I hadn't thought that through. So all may be well on that score. You are correct that the extra clearance is good insurance.

[Pond, James Pond]

Well, the more i think about it, the more I want the machinist to thread the metal of my flash-hider.

As I explained earlier, this is not a piece I ever really want to remove once it is made up. It will sit on the AR whether I'm shooting suppressed or not.

So the less deviation from my rifle's current specs the better and it should hopefully retain some flash hiding qualities too, so my carbine length gun will not blind me with every shot as it might if I ditched the hider and went for just a solid adaptor.

[Mobuck]

You know they make adapters for nearly any thread combination imaginable?

[Pond, James Pond]

You know they make adapters for nearly any thread combination imaginable?

Regrettably, "they" don't do it in Estonia! In fact, I'd be surprised to find one easily in Europe!!

I wouldn't know where to start.

[Mobuck]

AFAIK adapters are an unrestricted part.
SilencerCo (Silencer Shop) is a good start.
The Silencer Store.
eBay.
google muzzle thread adapters.

[Pond, James Pond]

Had a look. There are plenty of adaptors but none match my .308's thread: it is metric M18x1. Quite rare outside Sako rifles, I think.

So no joy yet.

Also I'd not be surprised if such items came under the ITAR (Sp?) list of restrictions on exports, but I don't know for sure.

[Mobuck]

If you have a SilencerCo Harvester, you just get a new $80 end cap. Otherwise, you should be looking for a VERY good machinist who can make up something. It will need to be nearly perfect or you'll encounter problems with mis-alignment.

[Pond, James Pond]

I've found a precision engineer (who also shoots) here who has a contact he feels would be up to it, so I hope they will be competent.