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 Best barrel length for 9mm ar-15 to suppress?
REF296  [Member]
11/12/2010 10:54:47 PM EST
I have decided to get a 9mm suppressor for a glock and would also like to get a sbr 9mm platform. I have seen barrel lengths ranging from 5", 7", and 10.5" and was wondering what the best lenght is. I feel that if I wanted a 5" barrel I would stay with a pistol for ease of movement but I also know that a longer barrel can make a subsonic bullet supersonic. Is the 10.5" too much or would the 7" simply be better for other reasons? I am clueless in this world and any opinions are appreciated.
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JohnStoner  [Team Member]
11/13/2010 2:37:30 AM EST
I did 10.5" so would have the option of using super sonic ammo (hunting rabbits etc) but also use 147 and 158 grain ammo for subsonic. If it's just for a range toy the 4.5-5" is the sweet spot, as it will keep supersonic ammo subsonic. At 7" depending on your humidity/temperature/elevation supersonic ammo may or may not stay subsonic. By the time you've added a suppressor your OAL is between 10.5-13" if you go with the short barrel depending on suppressor used.
Terrato  [Team Member]
11/13/2010 7:11:36 AM EST
I went with a 10.5" Rock River Arms barrel for my 9mm AR upper. I like having the full carbine-length sight radius, and enough room to keep my support hand behind the muzzle (a bit dubious about setups with a short barrel and long hand guard that put digits out in front of it).

So far I have only been running my own 147gr subsonic hand loads through the 10.5", and have not had a problem with any rounds going supersonic. I have noticed that the velocity for those loads in the 10.5" AR barrel is only averaging 20-30 f/s faster than out of a 5.3" Glock 34 barrel. I hypothesize that factory ammo would give similar results, so the chances of it going supersonic in the long barrel but not in the short one are low, unless they are loaded to velocities right at the edge of the subsonic range.
r-2-k-b-a  [Member]
11/14/2010 6:35:53 AM EST
Originally Posted By REF296:
I have decided to get a 9mm suppressor for a glock and would also like to get a sbr 9mm platform. I have seen barrel lengths ranging from 5", 7", and 10.5" and was wondering what the best lenght is. I feel that if I wanted a 5" barrel I would stay with a pistol for ease of movement but I also know that a longer barrel can make a subsonic bullet supersonic. Is the 10.5" too much or would the 7" simply be better for other reasons? I am clueless in this world and any opinions are appreciated.


Most people shoot subsonic anyways and even if the barrel is 2 inches long, it will likely be supersonic anyways. I've never seen a 9mm AR barrel this short. Most 9mm barrel systems are 5 inches or more which means you need subsonic ammo anyways.

I would look at the TALON and Multimount system since you are looking at a dual-purpose can. Thats why I did what I did and it works like a dream. Just beware that the 9mm AR15 bolt is pretty loud itself :)
crazyelece  [Member]
11/14/2010 7:30:15 AM EST
5" is still the best. Your glock doesn't have a stock or an optic likely. The ballistics don't really improve (especially subsonic) through all the lengths you listed so the only true advantage is a longer sight radius if you take advantage of it. There are much better advantages to the 5" IMO with the smaller smg style of the 5" vs the rifle/ carbine style of the longer barrels.
GunDisaster  [Member]
11/14/2010 7:47:49 PM EST
I like the 5" barrel a lot just because it is compact and also when you buy pistol ammo it will you tell the velocity and it is usually tested out of pistols with 4" or 5" barrels so you know the ammo will stay subsonic in the short barrel. The longer barrels are also nice if the ammo stays subsonic then it is usually a little quieter with a suppressor, of course some subsonic ammo can go supersonic with certain makes. I like the 158grn subsonic ammo which stays subsonic is my longer 9" barrel.
PhatForrest  [Member]
11/14/2010 8:06:41 PM EST
Check out the Liberty Mystic. 9mm suppression in a multimountable, takedown can.

http://www.libertycans.net/mystic.html
gaspipes  [Member]
11/15/2010 8:22:15 PM EST
5" TROS 3 lug from Henry at Title2.com. His page is gone, at least the bookmark I had. Out of business???

In any case you can get the barrel from TROS USA
buffetdestroyer  [Member]
12/2/2010 2:25:04 PM EST
The reason why you don't typically see them below 5" on AR's is the blowback design may not accumulate enough pressure to cycle a round, especially if unsuppressed.

If you SBR a receiver, you can get multiple barrel lengths and get a wrench and swap them yourself to see what one you like better for your particular application.

Shorter barrels may be slightly louder than longer barrels depending on how fast the powder burns before entering the suppressor. If the powder is still burning as it is entering the suppressor, then you will get more heat and typically a slightly louder signature out of the suppressor.

The other thing to keep in mind is that your overall length may exceed the typical 16" carbine length you are shortening when a suppressor is added to a 10.5" or 7.5" barrel. However your velocities are typically faster and with heavier bullets exclusively, this may be what you want it for.

The Liberty Mystic is a game changer in the 9mm suppressor world! I have one on the way! It also works as a full power suppressor for .223, .300 Whisper, 7.62x39 as well as rimfire due to the monocore that is a take apart design!
skeeters65  [Team Member]
12/2/2010 2:37:31 PM EST
5" is what I found to be the optimal length
SMOKINSTEEL  [Member]
12/2/2010 2:39:21 PM EST
Here is my 7" with a Vortex FH. Im getting ready to pull the trigger on a can for it. I love the size and how it handles. It's a great gun to shoot.

GarrettJ  [Team Member]
12/2/2010 4:00:01 PM EST
Originally Posted By buffetdestroyer:
Shorter barrels may be slightly louder than longer barrels depending on how fast the powder burns before entering the suppressor. If the powder is still burning as it is entering the suppressor, then you will get more heat and typically a slightly louder signature out of the suppressor.

That is true in general, but is not always the case. When I first got my Trident, it sounded better on a 5.5" AR15 than on a 10" M16, shooting the same ammo. SWR later redesigned the mount and the sound reduction improved on the longer barrels as well.
Originally Posted By buffetdestroyer:
The other thing to keep in mind is that your overall length may exceed the typical 16" carbine length you are shortening when a suppressor is added to a 10.5" or 7.5" barrel. However your velocities are typically faster and with heavier bullets exclusively, this may be what you want it for.

Good point. Here is an 11.5" gun with an 8" can. It's nearly as long as a 20" gun.


For a suppressed 9mm upper, I went with the 5.5" barrel.


I don't know that you'll have a problem at the barrel lengths you mention, but I ran into an issue when I went too long with the barrel. I was getting a lot of bolt-over malfunctions when shooting suppressed with a 16" 9mm barrel. The extra back pressure from the long barrel and the can was causing the bolt to move too fast and the magazine spring wasn't able to keep up. I had to switch to an AAC rate-reducing buffer to get the gun to function correctly with that barrel / silencer combo.
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