Thanks for the additional info.
I think most stove pipes (meaning spent case is sticking out sideways) are caused by the brass slamming the deflector or back of ejection port before the extractor has let go.
Think about the process.
- The extractor serves it's purpose pulling the case from the chamber without slipping off the rim. You seem to be good here.
- As the case is pulled rearward the ejector forces the front of the case to the side which begins as soon as it clears the front of the ejection port.
- The bcg is still accelerating rearward and the extractor (now a pain in the ass) still has a grip on the rim. As a side note when the ejector pin is fully extended, the extractor still has a hold of the rim. So with the exception of the double ejector bolts like Toolcraft's the case doesn't release until the bolt carrier hits the bump stop at the back of the buffer tube. If the bump stop doesn't hit till the bolt face is 3/8" behind the deflector then the case hits the deflector first while its still angled forward & gets deflected back into the gun causing stove pipes.
Assuming BCG gauges correctly there are Three causes I'm aware of for this:
- Weak or hung up ejector. Fix = Check spring tension. Pin should have a slight chamfer, move freely in bore, and be lubed.
- extractor has very sharp corners requiring more brass angle out before letting go. Fix = break corners with a jewelers file & polish.
- To much over travel on bolt carrier & this seems to be a common on DPMS large platform AR's. A little more detail on this below.
Large frame AR's have a lot of quirks due to lack of mill spec such as 3 different specs for trigger pin locations on DPMS pattern lowers etc.
It's real easy to mismatch buffer tube, spring, & buffer combo on a large frame. For example I selected a Magpul UBR Gen 2 which has the A5 length buffer tube included. The A5 is a little longer then a carbine buffer, but allows a rifle buffer length spring to be used. I added a JP OD ground rifle length + pressure buffer spring and a XH 8.5 oz buffer from heavy buffers (XH requires the longer A5 tube). Seems a pretty well thought out combo & per the quote from heavy buffers below should be tits right?
Wrong.............well not entirely. The combo is good, but I had to add 3 quarters in the back of the buffer tube to correct over-travel. With 3 quarters it has about .070 beyond the bolt stop. Ever wonder why you here of DPMS breaking the bolt stops? It's probably due to excessive over-travel. The carrier gets a good running start at it & hits it like a hammer.
I think a lot of the DPMS pattern upper receivers have the ejection port in the wrong location (see pictures below). Hell I doubt they're even consistent in port location - barrel extension from one manufacturer to another since there is no real spec. Maybe this is why most top tear large frame AR manufacturers use Armalight pattern receivers. Edit: I compared pictures of JP, Wilson, Knights, LMT, & LWRC. All Armalight style & all appear to have the rear of the ejection port further back then my DPMS pictured below.
AR 15 with bolt resting on bolt stop. Notice position of bolt face as it relates to shell deflector.
Now look at My DPMS with bolt sitting on bolt stop. It's recessed about .125 & no wonder these are so prone to stove pipes. Since extraction ejection is the same, you'd think the relationship between bolt face and deflector would be an important spec just scaled appropriately. It does not appear to have been on on my DPMS billet upper. FYI - I'm running the double ejector Toolcraft.
