Question about using different grain of bullet to tune gas block

[Bringtherain]

In a couple weeks i get to go shoot my .308 build. I have been putting it off till I can go home and shoot it with my father. He helped me put it together and it makes for good father son bonding time.

My question is about using different bullet weights. I have some cheap 155 grain. And the some more expensive 168 grain. Will it matter which I use to tune the gas block? if I use the lighter bullet to get the gas flow right. Will it be over gassed with the heavier bullet? Or undergassed for the lighter bullet if I tune it using the heavier ones?

Sorry if it is a stupid question but I'm new to the AR platform.

 

[RTH1800]

For initial tuning anything will be fine. Optimally you will final tune with the load to be shot.

 

[lash]

 

[Bringtherain]

Thank you. Stupid question but I just wanted to know.

 

[RTH1800]

Not stupid at all. Good plan to utilize lesser ammo. More so in today’s environment.

 

[Yondering]

Thank you. Stupid question but I just wanted to know.

It may help to point out that there's a significant difference in power levels between commercial 308 specs and military 7.62, especially the common M80 ball rounds and similar which are weaker than most commercial ammo. There's a good argument to tune the rifle so it works with everything, but if you want it really tuned right for your 168gr commercial ammo, tune it for that. It's not about bullet weight so much as power of the charge inside.

But yeah, +1 to what the others said above.

 

[lash]

It may help to point out that there's a significant difference in power levels between commercial 308 specs and military 7.62, especially the common M80 ball rounds and similar which are weaker than most commercial ammo. There's a good argument to tune the rifle so it works with everything, but if you want it really tuned right for your 168gr commercial ammo, tune it for that. It's not about bullet weight so much as power of the charge inside.

But yeah, +1 to what the others said above.

This is a valid point. As an example, though not related to .308, I tuned my .224 Valkyrie to the Federal Superformance 90g to break it in with what I had. Then, when the hornady 88g ELDM match showed up, it wouldn’t even cycle the action. Essentially a single shot until I started over and re-tuned it for the 88s. That much of a difference in powder burn!

 

[RTH1800]

For absolute reliability I tune my AGB’s with a 24 hour cold soak of rifle and ammo in the coldest temps I will shoot in. It makes a difference. You will be slightly over gassed in warm temps but better reliability