Help Me Develop a 308 AR-10 Load

[Just-some-guy]

Hey guys, I have a homebuilt AR-10 DPMS platform based rifle; Criterion 18" chrome lined 1x10 twist rifle gas barrel with LR118 chamber, Lantac BCG and bolt, rifle length recoil system, Timney 4 lb. trigger, SWFA SS 3-15 optic. Rifle shoots and cycles well, no issues.

I have been shooting a couple of different loads through it and have been getting an average of about 1.5 - 2.5" MOA results. Sometimes I can get a 5 shot group that is better, like 1.25" MOA, some ammunition shoots worse. My goal is a reliable 1 MOA battle rifle; I think the rifle is capable of this and currently I am the weak link, however, I feel that I may not be shooting optimal ammunition for this rifle. I don't want to try to source 10 different factory loads to find "which one my rifle likes", as I am going to create my own ammunition for this rifle for when I want it to be accurate and the rest of the time shoot NATO ball and not really care about the results.

My current loadings that I have tested:

1. SMK 175gr. with BLC-2 and CCI 200 primers, PMC brass; ~ 2625 fps., shoots the best, usually about 1.5 MOA.

2. Hornady 178gr. AMax with Varget and Win LR primers, Hornady brass; ~ 2600 fps, shoots decent at 1.5 - 2 MOA.

3 Factory PMC Bronze 147gr. .308 off the shelf ammunition; shoots reliably, but is usually ~ 3 MOA.

I currently have access to the following components:

BLC2 and Varget powders
CCI 200 and WLR primers
168 gr. Hornady Match bullets, 175 gr. SMK's, Barnes Match Burner 175 gr., and Hornady 178 gr. AMax.

My main question is with an 18" 1x10 twist barrel should I be focusing on heavier, or lighter bullets? I have been contemplating working up a 168 gr load in a quest for better accuracy but maybe that is a fools errand and I should instead keep my current 175gr. load and work on my fundamentals. Maybe I am already at the law of diminishing returns and should just shoot the #1 load and be happy? I do like the BC of the heavier bullets as I often shoot out to 800 - 1000 yards

What would you do? If you were developing a new load for this setup what would you recommend / what has worked the best for you? It is entirely possible that the rifle and ammunition is currently outperforming my current abilities already and this is an utter waste of time...

 

[jmw]

I use 43gr varget with 175smk

 

[Dogtown]

Your barrel should shoot the heavies just fine. 175SMK with Varget is a tried and true combination, with somewhere in the 43-45gr range being very popular. But barrels can be weird and sometimes they just don't like certain combos. Best to experiment.

 

[Cr1775]

I never had luck with the 175's and Varget only the 168's and Varget. Did have much better luck with the 175's and IMR 4064. But did run into Varget again and am gonna try it again with the 175's in a different rifle.

 

[Dogtown]

Oh man, that was a rollercoaster.

 

[bghartm]

168's and 44 gn of Varget shoots in just about every 308 I have shot.

 

[BigBlastin300win]

Should i switch to varget over 4064? Best group i got was 3/4" on a few sand bags to hold the rail. Want to try 178's pretty bad but don't want to mess around wasting a ton of components.

aero m5 308 20" tbac 7
starline lrp
imr 4064
168 eldm
fed210m

Out of the the 3 3 shot groups on the hot end had 2 bullets touching on each group i chalked it up to shooter error and a horrible rest. Usually i have a front rest and rest bag or rest for bolt guns. With the 20rd mag I had to use sand bags. Bought 4064 thinking since it is cheap and easy to find it would work. Just thinking varget might be the ticket for $20 more and a little less availability.....any thoughts?

 

[MK20]

Try a Sierra 175 or the Hornady 178 over 41.5 grains 4064 in a LC LR case. With the Sierra that is the new MK 316 Mod 0 long range load for sniping.

 

[ODA324]

Try a Sierra 168gr TMK. I'm hitting as 1200 yds with one. The windage is rough on it but the BC is high enough when you go to subsonic around 950 yds, with a normal matchking, the tmk / tipped matchking will give you about another 150 yds before transition the velocity to subsonic.
It is going to be hard to get a high enough velocity to even get to 800 yds with an 18"bbl.
Velocity comes to play with grouping because of the time thru the bbl, thus this changes the harmonics. When your bbl rings at its natural resonance is when you get the most variation in bullet placement group. You can tune a bbl with weights, but you wor't like the looks for an AR.
Try a faster burning recommended powder for the grain bullet and work on the group byincreaon sing the load from the low side. If you see group spread in a mid charge load then keep going up as long as all indicators show the pressure is still safe. This might let you get out of the harmonics but most of the time it means you will change the powder. Vihtavori N540 is one of the best powders I have used and is what I use in my 308. Every primer pocket has to be the same, same seating depth and the same crimp. I weigh each powder charge to 0.1 grains.
There are some factory Federal Gold Metal Match in 168 or 175 grain you could try first but that come with a $$$ price tag.

 

[AZgeek]

Based on my testing in an AR10 platform with a 1-10 twist 18" barrel, the 155 Amax or the basic 168 BTHP from Hornady seem to perform well and the price is right. Given the variability in the AR10, it a giant rabbit hole chasing supreme LR accuracy IMHO. My use case is 600 yards on in.

 

[Doom]

Try the 175 with around 42. gr of Varget. That should get you close to a known load. COAL of 2.800”. The 168 should be around 1 gr higher. Work up to these loads. These are Federal, LC, Lapua brass charges. This should give a little lower velocity than what you are currently, and hopefully sub MOA.