Gas Gun Seating Depth

[TennJed]

Currently doing development for a 6MM Predator/Grendel. Looked in Hodgdon load data but nothing for the bullet I'm running. Loaded it to MAG length and went for it. I was already over max pressure when I found a fairly decent group but wanted it closer so started going away from the L/G and groups got better. There was a tradeoff where the further from L/G the.slower the round. Currently at a comfortable .369MOA in 2700'

As previously stated 6 arc is very particular depending on bullet selection. Long heavy will be seated mag length or close to it with some 58-95s will need to be seated much shorter. These weights may be heavily jammed at 2.60. I just finished load development for berger 95 classic hunters in my proof research 6 arc barrel 2.17 OAL was .020 off. I ran some 95 SMK blems to break the barrel in and loaded them @ 2.60 mag length with .030 jump. With my proof 6 arc barrel and the bergers I treated it much like a bolt gun.

Thanks, I may be using 90 gn Sierra TGK's. Right now I'm playing with 105 Barnes match burners, but they are very inconsistent in weight and length

 

[TennJed]

All, mechanical and combustion systems have harmonics. The gas gun also has sonic and pressure waves.

It all relates to bullet exit timing and where the tip of the barrel is pointing at bullet exit at the muzzle.

Bullet seating affects both the burn rate, pressure, and therefore bullet exit timing.

So yes, bullet seating can still be a thing on an AR regardless of whether it is gas or mechanically operated.

Thanks, I thought the same thing since all barrels have whip/harmonics.

 

[TennJed]

Nope. I seat at mag length and let it roll.

Thanks, what caliber and what is the MOA?

 

[RUFFIAN R - NY]

need to keep psi up to work the action !!!!!

 

[Eric H]

I'm running the 80ELD-VTs in an 8 twist

 

[TennJed]

I'm running the 80ELD-VTs in an 8 twist

Thank you

 

[Mike D Texas]

Thanks, what caliber and what is the MOA?

6.5 Grendel and 22ARC.

Less than MOA for 5 shots typically.

 

[Hudge76]

I've played around with seating depth mainly on my 6 ARC and 6.5 Grendel gas guns. Honestly, I did not get vastly different t results so I just started going COL listed in the manuals or within .005" of it for .223/5.56 and mag length for 6 ARC and 6.5 Grendel. I chose mag length for the ARC and Grendel, as I only have two brand of mags for them, but numerous different ones for the .223/5.56 ones.

 

[waspocrew]

Mag length is the restriction here. I still check to see how far off the lands I am. If I can start at .020" off and still fit in the mag, great. If not, I'll just load to mag length and call it good.

Haven't loaded a ton for my 6 ARC yet (AR) since it shoots the factory 108 ELDM ammo extremely well.

 

[TennJed]

6.5 Grendel and 22ARC.

Less than MOA for 5 shots typically.

That's great! What I'm looking for. Thank you

 

[TennJed]

Mag length is the restriction here. I still check to see how far off the lands I am. If I can start at .020" off and still fit in the mag, great. If not, I'll just load to mag length and call it good.

Haven't loaded a ton for my 6 ARC yet (AR) since it shoots the factory 108 ELDM ammo extremely well.

Thanks!