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Posted: 7/13/2008 2:26:47 PM EDT
[Last Edit: 7/13/2008 2:27:26 PM EDT by Munition]
I'm going to build a 9mm AR. I see lots of different barrel lengths I have questions about. I don't own any 9mm weapon and have only shot pistols that belonged to buddies of mine. I have no idea what kind of performance and accuracy we are talking about here.

I'm split between two barrel lengths I cant quite choose from. the 7" barrels like here:



Or the smaller barrels that look somewhere in the 4" range like here:




basically I want to know the advantages and disadvantages of the two sizes.

I've heard that the really small barrels make the rounds come out sub-sonic. I do want a suppressor later on, but I also want something that will hit things at 100 yards or just over it.

So help me decide. Any input would be appreciated.
Link Posted: 7/13/2008 6:06:14 PM EDT
You need a short barrel if you will be shooting 147gr factory subsonics as they are loaded for pistol length barrels. If you load your own then you can make a 115gr round stay subsonic even in a 16" carbine and still cycle. The general test for a 9mm carbine is to maintain a 4" or better group at 100 yds but I have my doubts about the 4" long barrel doing that but who knows. One thing to make sure of is there are some 9mm 1:16 twist barrels out there and you definitely do not want one of those for your shorty as it will not stabilize the heavy bullets at subsonic velocities. Just my .02 worth.
Link Posted: 7/13/2008 6:13:46 PM EDT
Length of barrel doesn't affect barrel accuracy. How the barrel was made matters more. As to making rounds sub-sonic, it depends on your access to ammo. If you're a reloader, developing a sub-sonic 9mm load shouldn't be hard even in a 7".
Link Posted: 7/13/2008 6:26:08 PM EDT
I have a AR15/9 with a 5" Tros. I can easily hit clay's @ 100 yds.
Link Posted: 7/13/2008 6:45:55 PM EDT
I say it depends what you like, its like the difference between a Mp5 and the Mp5K. Not a big difference, but hey some prefer one over the other. I have both styles and i like them both. Also they both shoot the same, i think the 7.5" barrel i have probably has slightly higher velocities though over the 5" TROS barrel though. I like using a suppressor on the 5" barrel better because of this. If you want to add a flashlight and optics then i say get the larger 7" style. But if you want more a PDW style weapon then the 4" barrel is good.
Link Posted: 7/14/2008 3:24:31 PM EDT
Well I do reload my own rounds. I'm not really sure which mp5 I'd like. I've only shot a regular mp5 in Vegas at Osama Bin Ladin targets about 30ft away in a basement of this shooting place.

I have no idea what kind of accuacy we're talking about. From the replies I think I'm interested in the 5" barrels. Sounds like they are accurate enough at 100 yards. Hitting clays at that distance is exactly what I was looking for.

Whats the the twist rate of the 5" Tros? If I get a 9mm upper and chop the barrel to 5" what do I need to be aware of?
Link Posted: 7/15/2008 6:28:24 AM EDT
Whats the consensus on 10.5" barrels? That's the size I've got my eye on once my stamp comes back.

Kharn
Link Posted: 7/15/2008 7:19:18 AM EDT
It's all boiled down to personal preference. I love my 7.5" barrel, just short enough and long enough to help the bullet reach out a little.
Link Posted: 7/15/2008 4:07:31 PM EDT

Originally Posted By 5oulja:
It's all boiled down to personal preference. I love my 7.5" barrel, just short enough and long enough to help the bullet reach out a little.


What do you mean by, "enough to reach out a little"? I know its about personally preference. As of now I don't have any preference other than the look of the 5" barrels. I've never shot one so I have no idea.

Could anyone tell me what a 5" is capable of? what kind of things I need to watch for?
Link Posted: 7/15/2008 4:40:06 PM EDT
[Last Edit: 7/15/2008 4:42:14 PM EDT by MtDew69]

Originally Posted By rover15:
If you load your own then you can make a 115gr round stay subsonic even in a 16" carbine and still cycle.


No offense, but name the lexact oad or I'm calling BS.

147 yes
124 if the planets align
115 no way

as to the OP's question

I have 5" & 16" guns. IMHO if you are not going to be running a suppressor the 9-10" length seems to me to be best.
Link Posted: 7/15/2008 6:51:29 PM EDT
I will be running a suppressor. I don't want this thing to hit things well at 200 yards. just past 100 at the max is all I want to be able to hit things. I have no idea what kind of drop we're talking about.

I've already decided that at most I want a 7" but what about the 5"?
Link Posted: 7/16/2008 3:05:53 AM EDT
[Last Edit: 7/16/2008 3:12:53 AM EDT by Bajorn5]
I have a 5" and a 9.25" they work well out to 100 yds easy with a 50 yard zero.

Drop from 0-50-100 yds will be -2.5" 0" -6" range depending on load and FPS
The 9.25" is long with a Trident9 on the end but I use it more.

9.25"

http://i3.photobucket.com/albums/y92/bajorn5/Image-2.jpg

5"

http://i3.photobucket.com/albums/y92/bajorn5/Image008.jpg
Link Posted: 7/17/2008 1:38:43 PM EDT

Originally Posted By Munition:
I will be running a suppressor.



go with the 5" then
Link Posted: 7/17/2008 5:09:10 PM EDT
No problem. Been shooting 9mm autos for long time and for subsonics VV N320 is my favorite. Sometimes have to bump up to N330 but sounds a little "louder" to me for some reason.

115gr Rainier CC RN
3.3gr N320
OAL 1.140"

147gr Rainier CC RNFP
3.7gr N320
OAL 1.142"

Standard A2 buffer and spring, 16" barrel nothing special about the rifle other than being Oly type system.
Link Posted: 7/20/2008 6:45:52 PM EDT
I am romantically attracted to <6" barrels
Link Posted: 7/20/2008 8:59:45 PM EDT
Sorry guys but a 115 grain 9mm round can really pick up velocity all of the way out of a 16" barrel with some NATO spec ammo.

Other than hi capacity mags, seems funny to have a 4"-7" barrel when pistols can compete wise with that. Maybe a slight edge with a fixed barrel.

Think a tad longer and you'll be able to have a great carbine that you can really work with - if you have to.

4" - lower velocity and you might not be able to get the round to stablize.

7" - higher velocity and will stablize most rounds

I'd go 10" as a compromise. But it's your ha.rd earned money
Link Posted: 7/20/2008 10:49:40 PM EDT
Link Posted: 7/21/2008 1:50:54 PM EDT
but its not that simple. I just want to be able to hit cans at 100 yards with ease. but I want to be able to screw a YHM suppressor on the end of it as well. I don't need it to fire subsonic rounds out the barrel.

I load my own ammo for a reason so making subsonic rounds isn't a big deal for me. I absolutely love the look of the 5" barrels though. I'm just skeptical about the effective range is all.
Link Posted: 7/21/2008 3:40:55 PM EDT
Link Posted: 7/21/2008 4:14:05 PM EDT
so basically your saying that its very hard to hit cans at a 100 yards with a 5" barrel??
Link Posted: 7/21/2008 4:17:01 PM EDT

Originally Posted By duncan:

4" - lower velocity and you might not be able to get the round to stablize.




Short in pistol caliber is fine, look at the barrel length on a subcompact pistol.
Link Posted: 7/21/2008 6:13:24 PM EDT
Link Posted: 7/22/2008 2:38:15 PM EDT

Originally Posted By badazzar15:

Originally Posted By Munition:
so basically your saying that its very hard to hit cans at a 100 yards with a 5" barrel??


Its not impossible with a good barrel, we use Jarvis barrels 5" and 6" and they are pretty damn accurate. Its just going to be alot easier with a good 10.5".


Well I didn't want to buy an after market 5" barrel to be more cost efficient. I don't have all the money in the world so I thought that would be cheaper. What I planned on was buying a RRA upper and chopping the barrel to my preferred length.

I am skeptical about the twist rate is on the 14.5" 9mm barrel though, and wonder if the quality is well enough for me to just chop it to a 5" and still maintain performance.

Link Posted: 7/22/2008 5:31:49 PM EDT
IM sent
Link Posted: 7/22/2008 5:57:41 PM EDT
my 10.5 is alot of fun , although the 5" are amazing little beasts as well. I shoot mostly indoors at 75'
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