a friend of mine just bought a DPMS .308 Ar and wants to lighten the trigger pull up a bit. On his ar15 he replaced the hammer spring with a reduced power one and was wondering if there is one made for the .308 versions or are the lower parts interchangeable between the two versions. He asked me, but I have zero knowledge about the larger framed ar's.

LR308 and AR15 triggers can be interchanged but I don't think you want to put a lighter hammer spring on a 308. You can get better a better FCG that still uses a full power hammer spring.

what about the chip mccormick drop in?

http://www.nelsontactical.com/products/dpms-308-light-hunter-series-wchip-mccormick-trigger-lr308l-p-995.html

You can try Triggerwork.net... although, last time I talked to Bill it was $125 for lr-308 trigger. Personally, I think the Timney drop in is well worth the price and takes about 10 minutes to install.

IMO the Wilson TTU is way better than Timney AR10 trigger. I just put mine in my ma/ten tonite and my buddy has the same ma/ten build as I do except for the Timney trigger. He brought his ma/ten over tonight and Timney has  creep and the Wilson TTU is REAL crisp no creep at all. I have not live fired my wilson ttu  out of my rifle yet but I will this weekend.

ETA I do like how the wilson is held in place like a stock FCG. The Timney has 2 set screws with another 2 set to screws to make sure the others don't back out if that makes sense.

you can put in the yellow JP hammer spring and it will lighten the trigger pull a bit and still be reliable. but if you realy want to improve the trigger you need to replace the stock single stage mill spec FCG.
DPMS actualy has a very nice rock solid 2 stage. other wise if you want a single stage, the best i have used is the Chip mccormick drop in. smooth as butter.
if you will be useing the rifle for anything besides punching paper from a bench, i would stay away from any of the adjustable FCG's. even with locktitie they tend to come out of adjustment more often then they should, and it would REALY suck if that happened with the buck of a lifetime in the cross hairs(or worse)

thanks for the info guys, I'll pass this along to my buddy. He's a major cheapskate and has already said aftermarket triggers are too expensive, so he'll probaly try to get buy with the jp spring. The gun is just going to be used for hunting, so I'll warn him about the possibilty of light strikes and if he still chooses to go the cheap route, then at least he'll know ahead of time what could happen.

He probably won't be happy with a JP reduced power spring after he experiences no fires because the hammer doesn't hit the firing pin hard enough to ignite the primer.

If he has access to several standard AR-15 hammers and triggers, he can swap them around until he find a combination that gives an acceptable trigger pull using the standard hammer spring.

Bill Springfield charges about $50 for a trigger job on your trigger.  I installed the yellow spring mentioned above and polished the sear/mating surfaces on a set of Arkansas stones.  Moving slowly and using lots of oil I brought the surfaces to a mirror shine without removing any significant amount of material.  There is still a little creep, but the trigger is smooth and breaks clean and crisp.

Bill Springfield

I was getting light strikes on DAG surplus 7.62 with the timney AR10 hammer. Timney offers a stronger spring.