Over-gassing/Timing Issues

[StoneHendge]

I don't think your issue is timing., Especially with an 18er with RLGS+1.  There's no way the case is going to move when it's under pressure - it's gripping the chamber walls a lot harder than the bolt can pull it.

Timing is usually manifested with extractor marks on the case head - the bolt tries to rotate while the brass is still under pressure and the metal in the case head gives since the case under pressure won't budge. Back when I played around with 22 Nosler, timing was so bad the rims on the stupid rebated case heads would literally bend from getting yanked so hard.

Your likely near your limit. I use 26.8 grains of Varget in converted Starline 6.5G with GM205Ms with a 105 RDF at 2450 out of my 16" and I know I'm just shy of max. I have an MLGS and get an occasional case head smear, but timing issues are more manageable than I thought they'd be.

With a AGB, I would try and go as light as possible with the buffer - you can always dial the gas down to compensate. The result is slightly less pulse/felt recoil but the biggest benefit I find is the reduced slam on return to battery, which throws your sight picture off as much as recoil, if not more.

What's your first sign's of pressure? I'm getting more pressure signs on the primers, ejector marks and extractor marks using Hornady 108gr Match (these don't belt) than the belting handloads.

That's the hard part with calibers that can have timing issues - sometimes ejector/extractor marks are pressure and sometimes they are timing. When they are from pressure, they usually seem to show up before flattened primers. I shoot a lot of .223 and 6x45 which don't suffer from timing (other than my 16" 5.56 with a carbine gas system), and they always seem to get smears before primers flatten as I get around published maxes. It wouldn't surprise me if you get pressure signs from Hornady Match - it's loaded at max and if you have a tight chamber and/or it's a warm day, it might be too much. I've heard plenty of stories of guys here in Phoenix who pierce primers with 5.56 ball ammo in 100+ degree days.

The easiest way to check is to turn off the gas for a few rounds. That's how I always get somewhat comfortable with ejector marks. And I mean somewhat, because even if you can alleviate them, the timing issue is still there and the extractor is still getting somewhat abused.