To me, it looks like your ejector spring (s) are weak. ( maybe ? )

However, check the extractor.... It should have slightly rounded ends on the claw, if it doesn't, the claw might be holding on to well and not allowing the fired case to "roll" out and release readily.

And which double ejector BCG ? The one with the ejectors side by side ? .. or the spaced apart ejectors ?

Which 308 JP SCS weight are you running ?

And "maybe" a piece of the fuzzy side of adhesive backed Velcro on the case deflector would cause less case bounce.

Example...

Is this short action (upper window), with long stroke action that has the face of the bolt retracting back past the back of ejection port with full handle pull to get back past the bolt hold open,

Or,

Does face of bolt stop 1/8"~1/4" in front of back ejection port window with full charging handle pull to get behind the bolt catch instead?

If the later, then just need to make sure that the extractor has full control of the spent case rim on the pull.

If the former (dpms USGI II design), then will need the correct  B/C in play, as well as the correct tension on the ejector springs, since the spent case has to be held to the bolt face of back of stroke impact, and does not leave/pivot off the bolt face until the bolt does start to move forward once the rim of the case has cleared the back of ejection port.


Long stroke, short action upper receiver bolts on the right.



As for how to tell what action length (upper in play), just look at the location of the bolt hold open catch through the ejection window.
If face of bolt has to retract behind back of ejection window to get past the bolt hold open, then its a long stroke, short action upper receiver.

Designed to be long action,
https://photos.google.com/share/AF1QipMivUp-IOvnNTZKHA69mOUhyyt0cwtRTZ5SnjJXk350V0xgauDu6M2oVRpRspBCUA?key=ODEwa0xCYVNWVE1nQkoydlBVSFFhX2twUWZROVJn

So since the bolt face only needs to come back about 1/8" past the catch on rearward stroke (dead blow of the buffer will do the rest), pull the buffer and drop a quarter into the receiver extension behind the buffer.  This will have the bolt face stopping about 1/8" in front of the back edge of the ejection port window, and plenty of room for the spent case to be cleanly pivoted off the bolt face and out the ejection window at rear dead blow stall of the buffer.

Now on the extractor off the bolt face, use a small jewelers file to remove any burs found on the side of the extractor claw, as well as the sides of the rim relief channel on the extractor as well.


Hence burs on the side of the rim relief channel will prevent the extractor  center snapping all way down tight to the case rim itself.


Burs on the side of the extractor claw will prevent the center section of the extractor claw from being able to get a good bite on the rim during the pull.

Next, use a spent case to push the ejector into the bolt face off the extractor, and make sure that the ejector is not biding in the bolt face channel.  Hence if ejector side slot was not lined up correctly when roll pin was pressed in, could be causing the extractor to bind up.  If you do have binding, then pull the extractor, clean up the ejector channel and bolt face channel, and install new roll pin (while holding extractor in correct index so new roll pin and be punched in cleanly without bending it again.


If you still have problems, install a #60 O ring around the extractor spring, and put the extractor back in the bolt,  The O ring will add more tension to the spring, to make dam sure that the extractor is not dropping the case during the pull out of the chamber, to the all the way back position.

Note, chamber will self polish via live fire and cleaning in time, so when the O ring only last about 500 rounds and you need to remove it, should not be needed again.

So long as bolt will lock back on last round fired out of the mag (catch in front of the bolt, and not just catching the bottom of the carrier),  bolt unlock timing is fine.

As for chamber (Ogive leade space), free drop the round in question into the chamber with Bolt removed, use a wooden dowel to tap the back of the round in the chamber to make sure that case shoulder is tight to chamber shoulder, then tilt muzzle up, and live round should fall out of chamber.  If it sticks and you have to use a cleaning rod to knock the live round back out, take a good look at the round.  If marks on the case from say a the chamber not chamber brush cleaned with CLP from the start, or is the problem bullet embedding into rifling from the ogive of the bullet being too long for the ogive of the chamber.  Also to point out, if the later, then spent primer is going to tell the story with is flattened out to the sides of the case primer pocket, since the bullet embedding at loading is causing higher than normal working pressures of the round.

Middle primer border line, while one of the right is showing working pressures over the top.


Simply, with the 168gr ammo, it uses slower burning powder, and this increases the barrel gas pressure to unlock the bolt a little earlier.  With most rigs in 308 set up to run mil spec ammo, not a problem, but since it does mean that the bolt is going to unlock a littler earlier with the bore residual pressure a little higher, need to make dam sure that the extractor can pull the case out of the chamber, and not drop the case on the way back  as well.  

Yes, we can play the heaver buffer game to slow the unlock back down, but may cause problems with the rig not correctly stroking when feed lighter ammo instead.  So as long as the above tweaks solves the problem (clean ejection of the spent case) leave the buffer in play for now.  If still having problems like not enough dead blow stall for the spent case to pivoted off the bolt face with the above, then may have to go to heaver buffer to control the stroke/produce the correct rearward stall instead.