I've been struggling to get a load that my home build Mega AR10 likes.  It'll strangely shoot PRVI 165gr SP's into pretty small groups at 100 yards:



But it didn't seem to like my 168gr Speer OTM loads with H4895:



This same load shoots well in my AAC-SD Remington.  I managed to get a box of 500 Sierra 175gr SMK's before prices went up on them and I decided to see if the rifle would like a heavier bullet.  It's got a 1/10 twist Rainier Match 16" barrel so I figured with the faster twist it might like the 175's better.

I loaded up a ladder with IMR 4064 starting at 41.8gr going up to 42.4gr.  Five rounds of each and weighed every charge.  I use a Dillon 550 with Dillon dies.  PRVI brass (I've got a couple hundred empties and they seem pretty decent) and Remington magnum primers.  I loaded them to 2.80 COAL.

I fired my first five rounds using the previously discussed Speer load with the usual results then moved to the 175gr SMK's.  I'm pretty sure I hit an accuracy node at 42 grains as this is what four of the five shots did....



Underneath the calipers is the fifth shot.  I was exited enough making "one big hole" that I pulled my fifth shot......

I know that the chances of that being my consistent group size is about 0.0% but I am happy.  I just loaded another 20 rounds with the same exact specs and if the weather holds we'll see what she does this weekend.  Hopefully my Remington and my M14 like this load as well.  Seeing as it's pretty close to M118LR specs I'm assuming they will.

Here's the rifle from last fall:



Specs are:

Mega MATEN Monolithic upper and lower
Rainier 16" Match 1/10 twist barrel
Geissele SSA-E trigger
IOR 4-14x scope in an ADM mount
Surefire SOCOM-762 RC suppressor with 3 prong flash hider mount
Slash's XH Buffer with Springco 308 carbine spring

I don’t think Mega ever made an AR-10.

It's a Mega MATEN large frame AR chambered in 308.  I purchased a matched upper/lower/rail set from AIM several years ago before Mega got bought out.  It is not an original Armalite, but few are.

I've had great luck with 8208 and varget in my Maten. Could try that if you have any on hand

Unfortunately I have neither.  I’m well stocked in IMR4064 and H4895.  One of my co-workers likes Varget but in the current drought I’m working with what I have.

For me, I found 4064 was MUCH better than varget/xbr8208 in my 308.  Varget was a close 2nd, but 4064 was more consistent for me.