Rifle build for NRA AR Tactical class

[Nature Boy]

We used to shoot a lot of matches on a Marine Corps base alongside Service Rifle shooters running ARs, M1As, and Garrands but we shot at F-Class targets and had to follow their magazine change rules.

That sounds more like an Across the Course match

 

[Nature Boy]

I see that the Rise Armament trigger is single stage. Many double stage triggers can be/are set up to take up most of the weight in the first stage with a second stage on the order of 1 1/2 #. If you're used to ounces it might take some practice but it's better than 4 1/2 all at once. Geissele is probably the most popular now.

I should have gone with a 2 stage trigger

 

[Nature Boy]

Stopped at the range to get in a little practice with this rig. The only changes I’ve made so far was the addition of a Ergo grip and an old cheek pad I had laying around



I basically threw a dart at the Sierra reloading manual and picked 25.1g of VV N140 with the 69g SMKs

I settled in at 100 yards and after some foulers shot 10 rounds. During the string I was making adjustments to my interface with the rifle, noting what yielded the most consistent results.



I continued for the 2nd 10 rounds. Kept my position behind the rifle consistent and worked on cheek weld and trigger squeeze



By the 3rd string I felt like I had figured out a few things and focused on shot to shot repeatability



Bottom line: the rifle has the accuracy potential to do well at 600 yards if I can drive it. The 4 1/2lb trigger is the biggest impediment. I ordered this 2 stage trigger from LaRue, which I hope will fix the issue

https://www.larue.com/products/larue-tactical-mbt-2s-straight-bow-trigger/

 

[Bartojc]

You will like the Larue trigger.

-Jeff

 

[gyp_c2]

This is the most interesting thread I've found in a while.
Hang Tight!

 

[Nature Boy]

Getting a sub MOA 10 shot group with an undeveloped load and 4 1/2lb trigger has me excited to see how much more I can squeeze out of it.

 

[Boomholzer]

+1 on the LaRue MBT-2, 4.5lbs. Especially if your budget doesn't agree with a Geissele.
To the OP, I just got a box of those Berger 85 LRHTs to try out.

Great stock for prone. You need to use the included spacer for a carbine buffer with the Gen3 if its not obvious.
The older gen had a simple flat head retaining screw at the back of the buffer tube. It's now a spanner wrench type. I think the Gen3s are also lighter weight.

 

[sevt_chevelle]

I believe magpul is releasing a lite version of the PRS stock, lighter weight and cheaper.

 

[JFrank]

Nice rifle, good shootin , good thread . Makes me think about finishing the build in my cupboard.

Thx @Nature Boy

 

[Nature Boy]

I’ll have to put off the Magpul PRS stock for a bit. When I was at the LGS the other day this beauty caught my eye. Because I have no willpower, it came home with me.

 

[Boomholzer]

Can't argue with your priorities. Magpul wares will be there tomorrow... and the days after. Nice!
Or better yet; Woooo!

 

[JFrank]

I’ll have to put off the Magpul PRS stock for a bit. When I was at the LGS the other day this beauty caught my eye. Because I have no willpower, it came home with me.

View attachment 1006996

Oh heck yeah !

 

[Bartojc]

Getting a sub MOA 10 shot group with an undeveloped load and 4 1/2lb trigger has me excited to see how much more I can squeeze out of it.

Yes as the # shots go up the chances for error do to. When I saw that group I was impressed. I’ve not had many developed loads do any better. If that were me I’d probably call it good

Proof that a lot of rifles are capable if the shooter is.

Nice shooting !

Jeff

 

[Nature Boy]

Trigger arrived today. UPS dude obviously knew what LaRue meant and stuck it behind the flower pot so it couldn’t be seen by anyone but us.

 

[Nature Boy]

I went to the range today hoping to finish my load test for the 85.5 Berger’s and encountered another problem.

Either my scope isn’t holding zero or these bullets aren’t stable in this barrel.

POA was the dot on the right. First shot hit at 10 o’clock, next 2 impacted on the next dot over.



Next group, POA was right dot, all 3 shots impacted on the left dot.



My plan is to swap scopes and see if that’s the issue. If the problem persists then maybe it’s the barrel. I would think a 1:7 20” barrel would stabilize these bullets. Maybe it’s not 1:7 as advertised? Won’t know until I start eliminating variables.

I am leaning toward the scope. It doesn’t seem to be answering the helm when I make adjustments. The reticle is moving but impacts don’t seem to be correlating as they should. The mount is solid, or seems to be.

Any other ideas?

 

[Nature Boy]

Got to thinking about this some more. I’m still going to swap scopes in order to rule out a scope malfunction but as I’m sitting at the reloading bench trying to decide what to load the question of bullet stability came back into my mind.

I verified that I do indeed have a 1:7 twist using a tight patch on a cleaning rod and counting the revolutions. 1 revolution over 7 inches traveled. All good there.

The barrel length should only matter relative to how much speed you can generate with it so I took the chrono data from my first load test:

VV N140

23.4g = 2,527fps, ES 14, SD 6
23.7g = 2,612fps, ES 25, SD 12
24.0g = 2,662fps, ES 22, SD 9
24.3g = 2,680fps, ES 16, SD 7
24.6g = 2,720fps, ES 16, SD 8
24.9g = 2,733fps, ES 22, SD 9 (pressure signs here, there’s my limit)

Using the middle of the range charge weight of 24.3g, 2,680fps, 80 deg F, I plugged the 85.5 bullet into the Berger calculator and got this result:



Stability shouldn’t be the problem, so I’m back to thinking either my Leupold Mk4 LTR has taken a dump or the rifle doesn’t like the 85.5 / N 140 combo or something is amiss with the rifle itself.

 

[Nature Boy]

N 140 should be a good powder for this bullet. From Vihtavuori’s website:



I also have N 150 but I don’t think I could get enough of it in the case to reach the velocity I need.

 

[mavracer]

I built one for that but ended up selling it when prices were nuts.
You'll love the Larue trigger.

 

[JFrank]

We know it will shoot...I would definitely back track and check the scope base to rail and rail to receiver, basically start over with the mounting process.
I would ensure the barrel is tight also.

 

[horsemen61]

I’m curious to see what you find out!

 

[Nature Boy]

Update:

Finally got to my first 600 yard AR tactical match today.



The load I settled on was 77 SMKs and 24.4gn of N140. It performed pretty well.

Since I haven’t had much time to practice I took my time on the first match getting settled and messing with my shooting position. My score reflected it. Time expired with 3 rounds left and I had to take zeros on those.

That sorting out helped my second match score, which was much better with a 198 and 9 X’s

Conditions got tricky by the third match and I missed a couple of wind calls. Still, I netted a 196 with 5 X’s

Bottom line: I think this could be a great entree for those that would like to try competitive shooting but might be a bit intimidated by the unknown.

 

[Wreck-n-Crew]

Looks like you did pretty well for the first match. Once you got the timing down. I bet its like a whole other thing than what your used to! Lol

 

[Nature Boy]

Looks like you did pretty well for the first match. Once you got the timing down. I bet its like a whole other thing than what your used to! Lol

It is different than F Class and gives you more appreciation for the Service Rifle shooters (minus snapping into a shooting coat and slinging up).

 

[Nature Boy]

Update:

I shot my second match a couple of weeks ago and noticed accuracy issues that I couldn’t attribute to missed wind calls.

Went to the range yesterday with the goal of ruling out loads and anything else obvious. Whatever was effecting accuracy at the match became abysmal at the range.

As it turns out the hand guard was installed incorrectly and was putting pressure on the gas tube. It was also slightly loose. After re-installing it the right way I ran into another problem where the gas key no longer aligned with the gas tube and the bolt wouldn’t go into battery.

After some more fiddling I finally got it in working order. Here’s the before (L) and after (R)



Hard to believe but the proof is on the paper.

I also took @MCMXI ’s advice and installed a Magpul PRS gen 3 stock. Big difference. This configuration is rock solid

 

[Walkalong]

Sweet! Glad you got it figured out.