Alright guys, time for a question for the hive:

I know it's probably been asked a million times, but I'm working on my 2nd SBR build. I recently built a 10.5" .223 upper that runs like a champ and now want to build a 7.5" upper. I know what a bear these shorties can be to get running right so here's my question to members who actually HAVE a 7.5" and can answer with ACTUAL KNOWLEDGE BASED ON PERSONAL EXPERIENCE and not some theory they heard from their brother's neighbor's cousin's friend. Please don't take me as coming off as a jerk, I just want to get it right the first time.

Please school me on what type of gas tube length/type (i'm going to have to go gas operated and not piston due to my budget) I'm going to have to run. Also do I need to open up my gas port and if so to what diameter? Also, what type of buffer do I have to go with, H, H2, etc? If there is anybody out there that has a 7.5" that runs reliably please post your specs. I'm not trying to steal anybody's flavor but I don't want to end up like so many posts I've seen where poor guys are 6 months into a build and still can't get it running right. I took people's advice on my first SBR and that baby runs without a hiccup, so I'm hoping to do that on this build as well. Also, if you guys got any pics, please feel free to post them, i'd love to see some of your guys' rigs.

Thanks,

Bravo

Buy a Noveske, either from Noveske or Wes Grant at MSTN.

The one I have experience with was actually an Olympic 6.5, and the fucker ran! We were surprised. Using a car buffer even.

I was nervous about building my 7.5" upper because of all the horror stories I had heard. I'm very happy that after about 1000 rounds, its been 100% reliable. It has a H buffer, the gas port has not been opened up, and for the first couple months it had a standard A2 flash hider. I guess I just got lucky.



Pics of my gun, and a few others, can be found here http://www.ar15.com/forums/topic.html?b=6&f=22&t=282762
 

Right on man, I love that setup Kyle. That's exactly what I'm "shooting" for. Lol. Hey man I was wanting to build my upper from scratch. I have everything but the barrel, gas tube and low pro gas block. Did you build yours from scratch or buy a complete upper? What is the gas tube length? Do  I just buy a pistol length gas tube? Does the gas port need to be opened up at all, if so to what diameter? Oh and what kind of buffer are you running, H, H2, etc? Sorry for all the stupid questions man.

Bravo

If you are building a 7.5" then yes you need a pistol gas tube. I run a 9mm buffer, BCM extractor up grade and M16 carrier. Gas port size can vary. Usually about .078 on a 7.5". Some guys get by with smaller and some have to go larger. Imine was .064 from the factory and wouldn't cycle.

Sweet 7.5" AR you got there Kyle!!! Real Sweet!!!

I think a 7.5" AR will be my next SBR build, after my 10" Benelli SBS project.


teamroper

I run a 7.5 at first I had a spikes sst buffer but it would not feed at all
went back to a standard buffer and now its fine runs like a champ
I would say buy the best barrel that you can once you shoot this thing
you will not want to run anything else

If you're on a budget, get a DPMS Kitty Kat. Put an O-ring around the extractor, use at least an H-buffer and you should be good to go.

Right on guys, thanks for the posts. And badass pics so far on these builds, keepum coming!!!!!.

Ok, new question;
I have a guy here locally that makes barrels and is probably going to be making me this 7.5" after all. He's actually the one that made my 10.5" barrel, but he doesn't know much (anything) about SBR's. That was fine on my first build because I just used a standard carbine length gas tube and so he didn't have to move the gasport from where it normally sat on all the 16" barrels he was turning. But this 7.5" is a bit trickier because he does not know where the gas port needs to be exactly. I tried explaining to him that 7.5" pistol uppers exist and he was a bit lost, so it looks like i'm going to have to do the research on where the heck the gas port is located exactly along the barrel. The gasport on my 10.5 is .067" in diameter and runs like a champ so I might start there, if it needs to go bigger he can do that, but can anybody tell me how far from the tip of the threaded end of the barrel the gasport needs to be. I was just going to buy a pistol length gas tube and he was going to just "eyeball it" so to speak but I would rather have an actual exact measurement to give hime as to where it needs be rather than eyeball that sucker. So if any of you 7.5 owners can make this measurement for me that was be fucken awesome. Sorry for the trouble guys, i just want this sucker to run as good as yer alls'.

Good lord, ok so after that unneccessarily long explanation, can you guys chime in with you gas port location measurements and diameters.

Thanks brothers,

Bravo

I would just order a barrel from a company that either makes them or carries them. Be a lot easier than messing with getting the measurements right.

Bravo:  My 7.5" started life with a cheap, non-chrome lined barrel from Model1 Sales and ran 100% from the first day.  After about 15,000 rounds I changed out the barrel for a Noveske and couldn't be happier (better accuracy).  The gas tube length is definitely "pistol length" and the gas port comes sized just right from the factory.  I have always run an Enidine Hydraulic buffer in mine and find it has less perceived recoil than the H3 buffer I tried did.  It also started out with the Noveske "flaming pig" KX3 muzzle device and while it did direct all of the concussive blast forward the fireball was too large in dim light.  I now swear by the Smith Vortex as it eliminates 99.9% of the flash.  Reliability was the same with and without the KX3 for me.

MadDog

I run a 7.5" SBR for SWAT purposes.  The rifle has been 100% from the start for me.  The upper is a Vltor MUR-1 with a Rainier Arms 7.5" Ultra Match barrel and  Noveske KX3.  I'm not sure of what the gas port size is.  The Rainier barrel ships with its own gas tube, and I have it mated to a Daniel Defense clamp-on gas block.  I am running a Young M16 BCG with a BCM extractor spring upgrade as well as an RRA 9mm buffer.

And the obligatory pic:

Nice set up Joe.

You might call the guys @ CMMG, I bought this DPMS Kitty Kat upper over 5 years ago from them and it has runs like a raped ape on top of my Colt M16A1 lower.  I think they make their own now.

Thanks Shadowcop.  The only thing I've changed on it since that pic was taken is the addition of a riser for the Eotech.  I found that with my helmet and gas mask that it was nearly impossible to get down on the stock enough to get a good sight picture.  The little bit of extra elevation makes all the difference.

-Joe

I've got a Noveske MUR upper with their 7.5" SS barrel and KX3.  It runs perfect.  Noveske opens the gas port so it runs without a hitch.



I'm thinking about selling it to get something I can run a suppressor on though.

$$$$$$ price please

What do you use/going to use your 7'5"s for?  Plinking/SHTF/PDW?  Have any of you found a round with decent terminal ballistics?

My 7.5" is for SWAT entry purposes, and would not likely see use past 50 yards (with 0-25 most likely).  I have to carry the department issued Federal Gold Medal 69 gr. SMK's.  They seem to perform relatively well in the limited testing I have done with them.



I have about $2500 into this rifle, including the stamp.

I've never had a problem with 7.5" uppers.  My latest is a Noveske Diplomat barrel group on an LMT upper.  I use an "H" buffer.  The KX-3 is supposed to help as well.

Can someone explain to me the difference in buffers.

I have a CMMG lower and 11.5 upper that runs fine.  I have a 7.5 upper that my Dad gave me and it would not cycle properly.  The spent case was not ejecting while the bolt was attempting to feed another round.

What do I need to get to fix this?

I assume the buffer needs to be changed.  There are no markings on my buffer in the lower and I bought this rifle (the 11.5) complete from a local dealer.

Thanks.

What kind of accuracy are you seeing out of your rifles?  Can you hit targets at 100 and 200 yards?  And with what barrel/ammunition?

It's not a 7.5 but close..here's a special run of a Noveke 8.5 VIS upper. I have a replacement Noveske 7.5" barrel on standby if I ever get enough rounds down it to wear it out..
she runs like a champ..did a 120 round mag dump one session w/out a hiccup..Currently have a little over 1400 rounds through her..I'm running a Aimpoint Micro now, ACOG was a spare sitting around at the time..Im running a H2 buffer and a BCM extractor uograde kit..