Howdy.

Been under the weather a bunch recently.  Decided to muster up some energy and I built a new host for my RDIAS.  Previously, I have ran over 1700 rounds through my 9MM AR platform with the same FCG and RDIAS without issue.  Drop in and runs perfectly.  With this new host, I am experiencing a few different issues depending on how I try to correct the RDIAS placement.

Host Information:
- LWRC M6A2 @ 10.5" upper | H2 Buffer | POF Anti-Tilt tube
- Seekins SP223 lower.  
- Geissele SSF FCG.
- RDIAS

Observations:
- No shimming: while shooting full auto, it will burst two rounds and then stop.  It will leave the hammer forward (uncocked) and no round in the chamber.
- Shimming rearward (moving the RDIAS towards the butt stop) : while shooting full auto, it will shoot 1 round.  It will leave the hammer forward (uncocked) and 1 round in the chamber.  The round has a primer strike which wasn't enough to fire the round
- Shimming forward (moving the RDIAS towards the barrel) : while shooting full auto, it will burst two rounds and then stop.  It will leave the hammer forward (uncocked) and no round in the chamber.

The shimming method was using little cut pieces of gorilla tape, one layer at a time.

- I have shimmed it as far rearward as it could possibly go, getting to the one round fired and light primer strike (4 pieces of tape to get it to that rearward position)
- I have removed one layer of tape each time until it begins to Burst (3 layers removed, 1 layer on).  It will ALWAYS burst two rounds and ONLY two rounds.  It will always leave the hammer forward and nothing in the chamber.
- I have shimmed it forward to the maximum frontward position using tape (3 layers of tape).  Each layer forward, it will ALWAYS burst two rounds and ONLY two rounds.  It will leave the hammer forward and nothing in the chamber.

I have put the Upper on an RR lower and it dumps mags all day long.

Reading the RDIAS timing website, the light primer strike issue is indicative of the Early timing when I shim it back (which makes sense).

I have tried to follow the Quaterbore timing guide, although it leaves a little to be desired for me.  What I did was put the AR15 upside down.  After shimming the RDIAS forward, I would look through the Mag well at the bolt carrier and watch it close in on the outer ring of the barrel feed ramps.  I picked a 5/64" (.078) drill bit, used the back end (shank part) and put it between the carrier and the outer metal part of the bold carrier (not the bolt).  I found that it would drop the hammer right before contact between the carrier and face of the feed ramps.

So... help?  I cannot move the RDIAS any further forward (retard the timing).  I have gone from end to end (late to early) with slivers of tape one at a time.  It is pretty black and white; it will either fire 1 round and leave a light primer strike or it will fire two rounds and leave the hammer forward with no round in the chamber.  Nothing in-between.

Thanks,
Mike

I'm assuming it fires fine in semi? How does the function check feel? Does the hammer fall early if you ease the bolt via the charging handle into battery with the trigger pressed and the selector on auto?

When you shake your H2 buffer is their weights that slide back and for inside it or is one of the solid ones? The solid ones will not work well in a close timed full auto since it is not doing the job the buffer is designed for. The buffer's moving weights actually hammer the bolt carrier back closed when it tries to rebound from hitting the barrel extension. A solid buffer will not do this since the is no secondary hit on the carrier to counteract the rebound.



Ok, assuming you have a buffer with moving weights inside, then your upper rear lug maybe a bit longer than normal tolerance for the design of the auto sear. You can further shift the RDIAS body forward by removing some material on the rear of the lug. This will make the timing later. This assumes that your hammer is in spec as well as the lower receiver. You can try other hammers and hope that you find one where the auto sear surface is a little larger and therefore will time later. Failing that, if you have a high quality file and are good at file work then you can remove some material from the rear of the lug but never from the RDIAS.