You have a buffer length problem, with it being too long if bolt face on charging handle pull can not get begin the bolt catch.

But let me back up and the first AR-10's, where long stroke action, where the bolt would stop 1/4"~1/8" in front of the back edge of the ejection port window, and still make it behind the bolt catch.

The came the long stroke actions, but on a shorter receivers, when the bolt has to travel behind the back of ejection window, to make it past the bolt catch.  

The problem here, is during the dead blow effect stall of the B/C at back of stroke, not where  the spent case to be cleanly pivoted off the bolt face and clean out the ejection port window since it being blocked by the inside of the receiver, so case tags the inside of the receiver, and you end up with spent case still in the action to cause a jam with the live feed.  

To semi solve the problem of short action/long strokes for the 308, manufacturers went to double ejectors on the bolt face, so the spent case was retained longer that back of stroke sall, and  but retained by the extractor, and the double ejectors adding more force to the spent case to make sure it was pushed off the bolt face and out the ejection port, when the bolt is moving back forward.


So unless the bolt is double ejector'd, the  correct length buffer will get the bolt back behind the catch to solve that problem, but going to have jam problems when the spent case is defected back into the action and stays there isntead.

Simply, if the back of bolt catch in front of the back of ejection port, or is behind the back of ejection port.  This will tell you if you have a long stroke on a long stroke action where the bolt should stop before retracting behind the back of ejection  port, or if you have a long stroke on short action that the bolt face has to retract behind the ejector back edge in order for the bolt catch to work, and would needed  a double ejector bolt to prevent the spent case deflected back into the action to cause spent and live case jams.

Receiver extension depths the same, and if not using a A2 receiver extension end piece for something to bolt on to the end of the receiver extension, is A1 bolt in play?

Hence butt stock end bolts come in two different lengths, one being the shorter A1 bolt, and the other being the longer A 2 bolt, since spacer will take up some on the length.


A-1 butt stock bolt.


So A2 bolt, used without spacer, will end up with end of bolt protruding into back of receiver extension void, blocking the amount that the buffer can come back.

Also, shotgun the upper open enough, and a good angle, to take a photo to  show me the location of the back of bolt catch, against the back of ejection port window.  Hence want to see if the action is a short action, where the bolt does have to retract past the back of ejection port window in order for the bolt to catch the bolt face for last round hold open.

I'd make sure the Gen 1 Lower isn't being "hit" by the BCG at the lowers buffer tube threads.

Your photos appear to show about 3/4" difference between the 2.

PSA Gen 1 lowers used both the DPMS pattern buffer tube ( typical AR15 Carbine tube ) and the Armalite / Vltor length carbine buffer tubes ( 3/4" longer then the DPMS pattern )

I realize you said they are the same buffer setup parts.... but...

Unfortunately , by using the 2 different ( non-interchangable ) patterns,  buffers would get mixed up frequently.  

The end result was short stroking when the wrong 3.25" buffer was used in a DPMS pattern / AR15 carbine tube.  And looking like your 1st photo.

And when the Armalite / Vltor length buffer tube was used... with the shorter wrong 2.5" buffer.. it would bang into the Gen 1 lowers buffer tube threads and damage them, while making for sporadic function.

Can you measure the interior depth of the 2 buffer tubes... and post pics of your recoil parts.. buffers, recoil springs ( and count the coils )  ?