Please help educate the ignorant. When I was in the USMC I had a 20" M16 with open sights. 25 years later and the eyes not what they used to be I want/need optics. I ended up with a Leuplod MK4 MRT 2.5-8 scope so I have the optics covered. I want to build or purchase a precision AR with an 18" barrel. Is there anything to be gained by using a matched Megalithic rifle length upper and lower over a more traditional upper/lower. Barrel would most likely be a Rainier Arms ultra match. This rifle will only be used to poke holes in paper or ring steel plates out to around 600 yards. Other options would be to purchase a complete 18" precision upper and lower from the likes of BCM. If I go the traditional upper/lower route is there a 15" rail that would be the best for this application?
I have 2 DD CHF S2W 18" barrels and they’re both sub 3/4 MOA with mk262 clone loads. Neither are in a monolithic upper.
I bought a Rock River Arms upper in their R3… it’s a tack driver out of the box. I reloaded some 77 smk’s. yeah its a keeper. they guarantee you 3/4 MOA accuracy with a lot of their uppers. not many big name brands will do that.
5 shots at 100 yards. the squares are 1 inch. 
Thanks for the info gents, exactly what I am looking for. Any thoughts on which 15" rail would be optimal? I have also been looking at a Noveske Gen 2 lower with a Vltor upper. Thoughts, am I tracking right?
what’s your goal in your rail, functionality to hang all sorts of trinkets or light? I like the Lancer Carbon stuff and even AA’s carbon rail in 10 inch
I’m looking for rigidity. Probably just an Atlas bipod.
I have a few carbon ones with just a single rail attachment at the bottom for my Atlas and Harris bipods. nice and light, but some of the new key mods are cool and very light
Accuracy Evaluation of a Noveske 18” SPR Barrel
Noveske’s 18” SPR barrel is a stainless-steel barrel that has a medium contour and a 0.750” diameter gas block journal. The gas block journal for this barrel is designed for Noveske’s low profile gas block and the journal is only one inch in length; standard length gas blocks will not work with this barrel. Fortunately, Noveske’s pinned and set-screwed low profile gas block is included with the barrel (as well as an intermediate length gas tube.)
The Noveske SPR barrel employs an intermediate length gas system which eliminates the short-stroke issues that are sometimes encountered in cold weather with some 18” barrels that utilize a rifle length gas system. The barrel extension has “M4” feed-ramps. The barrel has a 1:7” twist rate and polygonal rifling (not a polygonal bore.)
The chamber found in this barrel is Noveske’s proprietary Noveske Match mod 0 chamber that “was developed to fire MK262 Mod 1 on AUTO in hot environments." I installed the SPR barrel in a Colt M4 upper receiver and free-floated the barrel with a LaRue Tactical 12” handguard.
I conducted an accuracy (technically, precision) evaluation of the Noveske 18” SPR barrel from my bench-rest set-up following my usual protocol. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group reduction techniques (e.g. fliers, target movement, Butterfly Shots).
The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Pictures of shot-groups are posted for documentation.
All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The free-float hand-guard of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.
For this evaluation, I used one of my standard match-grade hand-loads topped with Sierra 55 grain BlitzKings. When fired from my Krieger barreled AR-15s, this load has produced ½ MOA 10-shot groups at 100 yards.
Three, 10-shot groups were fired in a row from the Noveske SPR barrel from a distance of 100 yards with the resulting extreme spreads:
0.812”
0.732”
0.873”
for an average 10-shot group extreme spread of 0.81”. The three, 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius of the 30-shot composite group was 0.28”
The smallest 10-shot group . . .
The 30-shot composite group . . .
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nice reply, how much did it set you back? after all that, with the left over cash from the RRA I think in will buy another RRA and get the same results with a non Polygonal barrel [emoji12]
You didn’t get the same results with your RRA.
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LOL I will go and shoot a 30 shot string for you. but to be far how fast did you shoot? I will accept this challenge.
Molon. Thanks for taking the time to put this together. I already have a Noveske mid length carbine that is quite accurate for what it is. I never really considered a Noveke SPR until now. I will certainly put it on my list of rifles to consider if I decide not to go with a purpose built rifle.
Sorry Molon, how do you calculate the 0.28 number? I get the AVERAGE for the three ten shot groups. To me, composite means adding all the hits together (which seems what the picture shows) and running that as an actual group of 30 shots. The thirty shot group would then have a group size of the largest grouping. But that isn’t what you are calculating. 0.28 mean means what? 50% of the time you will be inside a circle 0.28? Is that like a cpk number like they use with nuclear weapons?
Out of curiosity, what kind of procedure did you use to mount the barrel? Anything special about the bolt?
Thanks
A PRIMER ON THE MEAN RADIUS
The Mean radius is a method of measurement of the dispersion of shot-groups that takes into account every shot in the group. It provides a more useful analysis of the consistency of ammunition and firearms (accuracy/precision) than the commonly used method of extreme spread.
The typical method used to measure a group consists of measuring the distance between the centers of the two most outlying shots of a group. This would be the “extreme spread” of the group. We are essentially measuring the distance between the two worst shots of a group. Take a look at the two targets below.
Most people would intuitively conclude that the second target shown is the “better” group. Measuring the two groups using the extreme spread method, we find that both groups measure 2.1”. Once again with the typical method of measuring groups we are measuring the distance between the two worst shots of the group. This method tells us nothing about the other eight shots in the group. So how can we quantitatively show that the second group is better than the first? (Yes, we could score the groups using “X-ring” count, but this does not give us any differential information about all those shots in the X-ring.) This is were the mean radius method comes in. It will give us that extra information we need to better analyze our groups, rifles and ammuntion. If I just reported the measurements of the two groups above using the extreme spread meathod, without a picture, you would assume that the two groups were very much the same. Using the mean radius method shows that the second group is much more consistent. It has a mean radius of 0.43” compared to 0.78” for the first group.
Mean radius as defined in Hatcher’s Notebook “is the average distance of all the shots from the center of the group. It is usually about one third the group diameter (extreme spread)” for 10-shot groups.
To obtain the mean radius of a shot group, measure the heights of all shots above an arbitrarily chosen horizontal line. Average these measurements. The result is the height of the center of the group above the chosen line. Then in the same way get the horizontal distance of the center from some vertical line, such as for instance, the left edge of the target. These two measurements will locate the group center.
Now measure the distance of each shot from this center. The average of these measures is the mean radius.
Once you get the hang of measuring groups using the mean radius it becomes very simple to do. While being very simple to do, it is also very time consuming. Modern software programs such as RSI Shooting Lab make determining the mean radius a snap.
The picture below is a screen snapshot from RSI Shooting Lab. The red cross is the center of the group (a little high and right of the aiming point). The long red line shows the two shots forming the extreme spread or group size. The yellow line from the red cross to one of the shots is a radius. Measure all the radii and take the average to obtain the mean radius.
Mean Radius Demonstration
Let’s say you fired a 5-shot group from 100 yards and the resulting target looks like this. (The X-ring measures 1.5” and the 10-ring measures 3.5”.)
The extreme spread of the group measures 2.83”, but we want to find the mean radius (or average group radius.) In order to find the mean radius we must first find the center of the group. By “eye-balling” the target most people would see that the group is centered to the left of the “X-ring” and probably a little high, but we need to find the exact location of the center of the group.
Locating the Center of the Group
The first step in finding the center of the group is to find the lowest shot of the group and draw a horizontal line through the center of that shot.
Next, find the left-most shot of the group and draw a vertical line through the center of that shot.
Now measure the distance from the horizontal line to the other four shots of the group that are above that line. Add those numbers together and divide by the total number of shots in the group (5).
2.50” + 1.03” + 2.01” + 1.30” = 6.84”
Divide by 5 to get 1.37”. This number is the elevation component of the center of the group.
Next we need to find the windage component of the center of the group. From the vertical line, measure the distance to the other four shots of the group that are to the right of the line. Add those numbers together and again divide by the total number of shots in the group (5).
1.76” + 2.54” + 0.45” + 1.19” = 5.94”
Divide by 5 to get 1.19” This is the windage component of the center of the group.
Finding the windage and elevation components of the center of the group is the most difficult part of this process. Once that is done the rest of the process is a piece of cake.
Using the windage and elevation components, locate the position on the target that is 1.37” (elevation component) above the horizontal line and 1.19” (windage component) to the right of the vertical line. This location is the center of the group!
Determining the Mean Radius
Now that we have located the position of the center of the group, the first step in determining the mean radius is to measure the distance from the center of the group to the center of one of the shots. This line is a single “radius”.
Now measure the distance from the center of the group to the center of each of the rest of the shots in the group. Add the measurements of all the radii together and then divide by the total number of shots in the group (5).
0.85” + 1.35” + 1.38” + 0.84” + 1.61” = 6.03”
Divide by 5 to get 1.21”. This is the mean radius (or average group radius) of the group!
Using the mean radius measurement to scribe a circle around the center of the group gives you a graphic representation of the mean radius. This shows the average accuracy of all the shots in the group. This demonstrates why the mean radius is much more useful than the extreme spread in evaluating the accuracy of our rifles and ammunition.
The table below will give you an idea of the relationship between the mean radius and extreme spread for 10-shot groups.
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ummm someone must be bored. I still see a large group that is over the .25 " mark, or am I looking at the wrong pictures… I wonder my group would be then with the mean radius… .005555 or so since it was a below a .25" with a flier that I pulled.
just giving you a hard time Molon
Thanks again Molon. This obviously took some time to put together.
Excellent explanation from you as always Molon, thank you!
As the barrel gets hotter the groups usually get larger especially when the barrels are thin. DCM barrels that are used in High Power competition are usually at least 1" in diameter under the hand guard. This is done because 80 plus rounds are shot and the heat causes almost no enlargement in group size which helps the competitors compete. Back when I was competing my Bushmaster DCM would shoot 20 round groups at 100 yds that would stay inside 1/2" with my reloads using 69 gr. Match Kings. Now I have a Colt LE 6920 M4 lower with a Geissele SSA-E trigger with a WOA 18" Varmint upper which I had WOA flute for me. ( under hand guard is 1" in diameter ) I have not shot more than one 10 shot group with 65gr. Game Kings that shot less than 1/2" 100 yd. groups. The 69gr. Match Kings measure 3/8" most of the time. It also weighs 10 lbs. with the scope and a full 20 round magazine.
Scroll down to post # 19.
Alg defense makes a great rail with a very sturdy barrel nut. Everything you need to install the rail is included and no torque wrench is required to get the barrel nut correctly installed. http://algdefense.com/rails.html
The alg rails are much better priced than any other rail of the same quality that I have seen.
I did a quick search for a bipod mount that will fit the mlok rail and found the following. It is made by magpul so it should be good. There might be something better though. http://www.midwayusa.com/product/317940/magpul-m-lok-bipod-mount-aluminum-black
very tight grouping, nice