Before I go through the hassle of putting reduced power JP3.5 springs in my DPMS Sportacle, is it even OK to do?  I have no idea if 308 AR's require full power hammer springs for ignition or not.

As a general rule of thumb, if you are shooting hard military primers or CCI 34's / 41's (Military primer commercial replacements) you may have some issues.
If you are shooting commercial primers you generally won't have problems. If problems do pop up, switch to Federal primers (one of the softest but also one of the highest quality) and your problems will likely go away.

If you have problems with Federal primers, pull the springs out and see how far you can throw them :-)

Good Luck,
JW

In the larger guns, reduced power JP hammer springs are common with failure to activate.

JP makes a brown hammer spring for the AR10 that is heavier.

If you go this route, you really need to have a lightweight hammer.

I had problems but this is shooting surplus 7.62.  Went back to mil spec springs.

Nough said above.

I replaced one of my G2S hammer springs with a JP on an AR15 and it works awesome.

I'm replacing mil spec single stage with a Geiselle G2S on a DPMS LAR-308, but i'll just use a mil spec spring or keep the Geissele spring.  Thanks guys.

G2S not for AR10

Change in plans.  Apparently G2S is not for LR308

Not sure why the G2S is not suitable but I am running an SSA /SSA-E in a DPMS G2 and ran an SSA in an older DPMS LR .

EDIT: I remember now that there can be issues with the hammer binding against the carrier and the hammer may also drag on the radiused corners inside the trigger compartment once the hammer pin is installed.

G2S has issues in some 308s...like the old RRA triggers. don't remember the exact issue but I'm pretty sure it's fixable by removing a little material off the hammer. No personal experience but I've seen write ups about it. Also seen 308s running fine with a G2S. As far as light springs, I've run into issues with light strikes on surplus ammo, steel,  and aguila brass using a 4# timney AR15 trigger as well as a 3# velocity. Finally went to a hiperfire.