Have a FA lower machined from an 80%. All pin hole locations are in spec.

Assembled with a burst kit and wouldn't run in burst. Checked timing and it appeared to be radically late.

Initially assuming I had an out of spec lower, I removed material from the sear catch on the hammer.  Had to take a pile off to even get to the late (.080) gage. Finally got some burst action (although not reliably) at around .094". Massaged a little bit more off and next thing I know, the autosear isn't catching the hammer at all. Went from almost correct time to nonfunctional with less than .005" material.

Is there a difference in the sear or safety selector or something in the burst setup that changes the action or angle of release of the sear?  It seems to be purely related to the relationship between the sear and hammer, everything else is OK.

Also, need an m4 burst hammer.

You have a full auto lower that was machined from an 80% lower?

INCOMING !!!!!

I'm guessing he has a Post-1986 Dealer Sample, also known simply as a "Post Sample".

He's probably a FFL/SOT dealer/manufacturer. At least I hope so.

I've never heard of having to file down a sear to make a burst kit work especially if a lower is in spec. Was the sear and the burst kit all new and name brand. like colt?

EDIT: Corrected spelling

I beg to differ, in that if all pin hole locations were actually in spec, it'd run properly.

Most of your timing differences come from use of a DIAS, with different (non-military) uppers, whose takedown pin post dimensions can vary a lot, since it's not a critical dimension for a registered full-auto receiver or a semi-auto receiver, but the DIAS dimensions index on the post dimensions. This leads to shimming or trimming to get the DIAS in time.

A properly-located RR full-auto sear, in a properly-dimensioned FCG well, with properly-located hammer and trigger pin holes won't have those timing problems.  If you've got a factory RR to compare to your 80%, you can try lining things up with transfer pin punches to see which holes are off, by how much, and in which direction(s).

Oh, I know what a Post Sample is, I have had a few in my hands. I am a FFL/SOT as well, I was just surprised he posted in the manner he did, normally If I am talking about regulated items on an open forum, I will state that I am a FFL/SOT.

That was the reason I asked.

I would hope so as well.

I also agree, it sounds like an out spec lower, time to get the mic our and looking at a lower blue print.

:| 07/02

I just presume that most people with multiple years and decent post counts aren't posting dumb shit.

Anyway, the relation of the hammer pin hole, trigger pin hole, sear hole and takedown pins (which situates the upper in relation to the lower) are all identical to our full auto that runs like a top and times out just fine.

To see what I'm seeing, the sear would have to be about .060" too far forward (it isn't), or the bcg would have to be way out of spec (proven uppers same behavior).

Good to hear, I gave up presuming or assuming anything these days when it comes to the BATF!

My IP is public record, they can come audit earlier than usual if they like.