This is a followup with pics for the Grendel build I was having sever vertical stringing problems with.  This is after some re-work by the builder.

Here's the rifle:



Here's the target results.  Last group lower right is best 5 shot group I've ever shot with anything.

What did they say was the issue?

Said he found evidence of gas leak around the gas block, so he replaced it, polished off the cerakote under the block (seems to me cerakote under the block is probably a bad idea anyway), and re-fitted the barrel & extension to the upper.

It was really bad, 6-8 moa of random vertical stringing.  First build he's ever had a problem with, guess I'm special.....

I love happy endings.

Specs of the build?  Looks like a great rifle.  Do you have any places to get it out on steel?

Build Summary:  
New Frontier Billet side charging upper (non-reciprocating),
NiB bolt carrier
Billet lower (builder puts his logo on it, don't know his source),
3lb Dark Sky SS trigger,
Satern 20" Liberty barrel w/matching bolt.  Threaded with thread protector for now.
AP Custom Ultra-light carbon fiber FF handguard.
Magpul ACL stock.
Harris Bipod.
PA 4-14 FF Mil/Mil Mildot scope on PA mount.

Yes, we have platforms out to 300yds with 3", 6" and 8" round AR500 gongs.  I've hit all 3 out to 300 with varying degrees of consistency and success depending on the rifle and my personal sukage level at the time,heh...  We need to mount the 6" with longer chains or wider mount points, it swings over the mounting bar when anything hits it harder than .223.  Can still shoot it after that, but it doesn't give as much which supposedly is harder on the steel, and the chance of hitting the mounting bar is higher.  The 3" doesn't have that problem likely due to longer and wider chains.  It is also a very fun setup for plinking with .22 lr at 100 yds.

This time it was the end of my range session by the time I got out to 300, hit the 6 a few times, then wind and mirage came up a bit, I was fatigued and dehydrated, and started missing, switched to the 8" and started missing 1/2 the time, decided it was time to go home, drink something cold and relax.

There is a local public range that has steel at 250, 500, 750, and 1000, but I haven't been out there with this rig since I got it back.

Nice rifle, congrats on getting everything straightened out.