Been thinking about putting together a SBR AR for some time. I intend to shoot it in a couple local matches. AR only match to 300yds and a 2 gun match shooting a AR and a bolt rifle, AR max distance 400yds. Also just to have fun with it and work on my AR skills.
Looking at barrel lengths, seems like a 12.5 is a good spot. A good friend has a 12.5 he's zinging 73ELD's at 2500, respectful wind drift at 400yds. Drop down to 11.5, velocity drops quite a bit. I'll be shooting this suppressed only with a TBAC 6.5 Ultra 7. 11.5" is the shortest TBAC recommends. Having CompassLake cut/chamber the barrel(s).
Three of the smoothest cycling suppressed AR's I've shot are a 12.5 midlength, KAC 14.5 with their mystical top secret intermediate length and a 16" intermediate length. Going with a 12.5 midlength gas system. Myself and most everyone around me has had problems with adjustable gas blocks. These guys are putting thousands of rounds on their AR's yearly. Not guys shooting a few boxes a year... Going with a fixed gas block. Because of that will start out with a gas port hole I know is too small and drill them out in 1-2 thousands steps until the rifle functions with my handloads. Probably shoot a box or two a BlackHills MK262 to see.... I have a JP silent spring A5/H2 set. Will try that as well as a friends Vltor A5/H2/Tubbs spring on his SBR lower.
I planned on just having one barrel chambered. CompassLake cuts/contours/chambers from a blank. For a relatively small fee will chamber another barrel with the remainder of the blank. Max 2nd barrel length 14". Can't pass that up! Considering 14" midlength +1. WOA makes custom gas tubes.
The TBAC 6.5 Ultra 7 is direct thread 5/8-24. I was a little apprehensive about using a .750 gas block, muzzle .740 and threading 5/8-24. Not much meat/shoulder left. RainierArms offers a fixed .800 gas block. Went with those. Muzzle will be .795, feel better about that! Weight difference is nothing.
I've had this Noveske lower for about 10yrs. Time flies! Will E-file a form 1 in a couple weeks. Brought the Noveske with me to local shop to try on some stripped uppers. The Vltors fit nice and tight. While I was in the shop they swapped the trigger guard with a Magpul, looks much cooler! Also picked up a couple Lantac BCG's on a Black Friday sale. Snagged the used Noveske 11" NSR handgaurd from a friend. Need to pick up another handgaurd and a couple charging handles.
Even though these are short barrels I'm approaching this how I put together my precision 20" Bartlien upper. Will use oversized Bat Machine barrel extensions, thermally fit them on the upper. Simple to do, very little cost difference.
Not sure what I'll do for optics. A 1-6 or 1-8...? A few friends shoot these AR matches as well as 3 gun. I'll mess with their scopes before making a decision. They know what brands hold up.
Will be two months or so before I'm shooting these barrels, will post updates.
Offgrid and I have discussed the carbine-competition SBR concept for awhile now, especially since a mutual buddy used his 12.5" SBR so effectively in the past three 2-rifle matches. Offgrid is diving into the component issues more thoroughly than I -- nuances of the barrel extension to upper receiver fit, gas port sizing, cycling effects of suppressors. Such details can only help.
On the other hand, I have just hand off components to my trusty gunsmith, letting him fret over the details. Call me Mongo -- gunsmith is my pal. I do wish that my new barrel extension fit a little tighter to the upper receiver, however. When I think about it -- .998+ tube into a 1.000" hole -- there is some slop.
I expect to shoot the new 14.5" upper in January. Time will tell if I must rethink my strategy.
I have used only a NF F1 3.5-15x in the 2-rifle match we've discussed. Not the best option for the clays and reduced-size paper IPSC targets closer than 25 yards. But totally a kick-ass scope for steel 100-400 yards out.
The SBR guy used a 2-10x ffp Vortex for the last three matches. He was great from contact out to 250+ yards. Even 300-400 yards if dry dirt was behind the plates, so he could easily spot misses. But grass fields behind the targets made spotting misses a challenge.
The guys with 3-gun backgrounds tended to use 1-6x scopes, both ffp and sfp. They totally kicked it out to 200-ish yards. The 300-400 yard targets were a real challenge, however. I saw and heard my share of mag dumps to ring a piece of steel.
In late 2018, two Nightforce reps used the new 1-8x ATACR on their carbines with very good results. They didn't win, but they placed well. They also used reticle holdovers and wind holds for all longer targets -- no dialing.
I'm still debating. Maybe my 2-10x Vortex. Maybe the trusty 3.5-15x NF, and maybe with a red dot on a 45-degree offset.
Maybe I just need to get my head out of my backside on the couple of stages that I seem to choke on each match....
Looks like a lot of thought and planning has gone into these builds...so I plan on following and looking forward to the updates and the finished projects.
Well thought out plan, 12.5" seems to be the ideal balance between compactness and velocity.
I stepped up from 10.5" to 11.5" on my sbr due to a 200fps gain.
I am still pondering building a RECCE type upper with a 12.5" barrel as most of my shots are limited to 300m.
Can't waiting to see your results, chrono and accuracy
Good video on thermo-fitting barrel/barrel extension to a receiver. With Bat Machine offering oversized barrel extensions, makes this easy.
12.5 midlength is nothing new. Especially on dedicated suppressor set up. This guy has sold/installed hundreds of 12.5 mids for 10yrs+.
This guy along with Noveske has been doing longer then "standard" gas systems for a long time.
Knights Armament uses a intermediate gas length on their 14.5/15. No doubt a large part of why their rifles cycle so smooth.
The two unknowns for me, rifle balance and the gas port size. I've shot a Noveske (their medium contour) 12.5 midlength with a older TBAC can. Thought the balance was a little butt heavy. Barrel contour will be a little heavier then the Noveske, will see how that works out. Gas port. Exchanged a couple messages with the owner of AR15Performance and talked to the owner of MSTN. MSTN brought up the fact that the TBAC suppressors have more back pressure then say a SOCOM..... fritz has both cans, he verified a fair amount more gas with the TBAC. Going to start with a .0630 gas port, should be way too small, which is what I want. Then drill it out..... I don't want to go to a light weight bolt/buffer to get it to run.
I certainly get why gas ports are oversized on most factory barrels. Guy wants to shoot low cost, low pressure stuff. Hey, my gun doesn't cycle...
Here's a little background on this match, and why an SBR is a reasonable option for the AR.
It's a 2-day match in northern New Mexico, at an altitude of about 6,600' ASL. We have maybe 2 miles of walking between stages per day, and we must carry all our gear. Gear means precision rifle, AR15, binoculars, ammo for both guns, shooting sticks or tripod, fluids/snacks, and whatever else one wants. This past April's match was held right as a snow storm was ending -- the whatever else included Goretex jacket & pants, plus fleece.
At least half of our stages generally start with AR15 targets. But the match director almost always requires starting with pack on and precision rifle slung. The first half of such stages have close AR15 targets, which will be shot from standing position, with movement required from one target to the next. Meaning that we can't drop our pack and precision rifle to shoot the AR15 targets. Or maybe we can, but time pressures on the stage make multiple dropping and reshouldering the pack/rifle impractical.
Thus, a shorter and lighter AR15 is a valid option. So far, I've only used my 18" barrel AR in this match. I'm strongly considering using one of my 16" ARs. Maybe the 14.5" upper that's in the works.
|Drill Here, Drill Now|
Just a thought. Since you're going to be tweaking your gas port size, you could get a head start on this by initially setting up as an AR pistol (e.g. SB Tactical SBA3 instead of rifle stock) until your SBR is approved.
Ego is the anesthesia that deadens the pain of stupidity
DISCLAIMER: These are the author's own personal views and do not represent the views of the author's employer.
Have the 12.5 barrel/midlength gas upper together. Barrel is a Bartlien 7 twist/CLE chamber. CLE chamber is basically a Wylde chamber with a shorter freebore.
Thermo fit of the barrel extension/receiver couldn't have gone any easier. Best I can measure had .0005-.001 interference between the two, no way it was going together w/o heat appllied to the receiver. 10 seconds or so with a plumbers torch on the receiver, barrel slid on effortlessly. A few seconds to cool, not coming off. Easy Peasy!!
Ran 85rds through it for function, pressure, velocity test. Did not have a scope on it, red dot mounted to see where I'm going. Ulta 7 6.5 suppressor. Load for my 20" barrel is 23.7/Varget/77SMK. Shot 25 of those first. Lock back on last round, very soft shooting, smidge sluggish. Cleaned the barrel. Loaded 8208/virgin LC brass/77SMK/CCI450. 15 each 23.2, 23.4, 23.6, 23.8. Zero pressure at 23.8 will load 24.0 next time out.
Chrono 5rds each
So far so good, cycles very smooth, gas port seems about right, happy with the velocities, no gas to the face. Have a JP's SCS H2 buffer on it will put the upper on a friends lower with a Viltor A5/Tubbs spring/H2/H3 buffer to compare. The JP system sure is quiet.
Not sure what scope I'm going to go with. Another friend is going to loan me his S&B 5-25 on a AR cantilever mount. Use that for accuracy testing and see what I can see at what magnification at 400-500yds. Fun stuff!
.0630 is tiny for that setup. Retail barrels in mid-length 12.5" are more in the 0.070-.080 range.
I'm a bit surprised you're getting reliability with a heavy buffer. Does it still function unsupressed, or is this being tuned as suppressed-only?
Tuned for suppressed only.
Gotcha, I think that's closer to what the Hodge barrels are setup for- carbine weight buffer, suppressed, and full power NATO loads. If I remember right it's an 0.0690" port, and some of the newer retail ones are more ammo and buffer friendly running something like 0.0720". I'd have to go looking up numbers but that sounds right in my brains.
What sort of problems are guys you know seeing with adjustable gas blocks?
I just ask because I have been running them hard on 3 gun rifles and suppressed 'just for fun' rifles for quite a few years now with no issues. All of mine have been JP melonited steel blocks. Would like to know anything to be on the lookout for.
I had problems with these on my rifle.
The itty bitty tit on the end of the set screw that blocked the gas port eroded away.
As far as other brands..... making a blanket statement after seeing others at matches jacking with their gas blocks. Sure maybe some of those are from running their gas system on the edge of working. Never seen a guy with fixed block messing with his!
The only adjustable gas block I would consider is this guys. https://www.blackrivertactical...493/category=6464009
I would like to see a gas block manufacturer come out with a drill to size block. Ship with a gas hole as small as .050, drill to size....
I’ve never had a problem with an adjustable gas block. I have a JP and one I made....once I get them set to run nato ammo with the suppressor and without, I lock it down and never fiddle with it again.
"Violence, naked force, has settled more issues in history than has any other factor.”
― Robert A. Heinlein, Starship Troopers
How many rounds?
I don't keep a log or anything like that but my current 3 gun rifle has between 8-12k through it.
There was a guy who had a captive detent sliding plate system that could be drilled with three different port sizes.
It was a smart design. Guy had a death in the family and other priorities took him away from it I think. Can't remember the name.
I am half tempted to pull my 3-gun rifle apart today just to inspect the adjustment screw in my most heavily used rifle that as an adj gas block.
Smart, simple design.
Found several of his post regarding gas port size. He still has a few videos on youtube. https://www.youtube.com/channe...RTBMGsZVXJBnPfk8VabA
|Powered by Social Strata||Page 1 2|