I wanted to post this for some readers to discuss tolerance stacking. I’ve got what I believe is a classic example with parts that all seem to be in spec.
I bought a complete DD carbine when they first came out. I wanted a LW middie for my wife so I sold the complete upper and bought a new bolt and carrier, 16" LW middie, and stripped upper from DD to keep the rifle all DD. This upper and lower are the most difficult I’ve encountered to either take apart or put together. I used a plastic punch and gunsmith hammer to accomplish both of these. I figured after a few hundred rounds it would loosen up, no go, after 2000 rounds no change so decided to look into it a bit more.
I can watch the insertion of the take down pin at a very slight angle, easy day. Since it never improved and I am reluctant to take a bit to the upper I started switching out uppers on various lowers. I’ve currently got 2 BCM, 2 Noveske, the DD, and a Territorial lower. All have the same manufacturers uppers with the exception on the Territorial, which has a BCM upper. All of these are my builds with no factory complete carbines. Every one of the lowers fit every one of the uppers with the DD/DD exception. I also replaced the take down pin in the DD lower with no positive results.
I’ve never contacted DD and don’t plan on it as that upper fits on every other lower I’ve got just fine. Not even difficult to assemble or remove. I think this is a classic example of tolerance stacking. I believe it’s actually the upper that is the issue and am planning on putting the barrel on a spare BCM stripped upper I have and trading the DD to a friend that has lowers that the upper fits on fine. I’ve considered taking a drill bit and opening it up a bit but am reluctant as it fits everything else.
I know they do and am not unhappy with the product. I see this as a simple case of tolerance stacking. I doubt anything is out of spec with all of the other components fitting each other.
If the rifle works 100%, I’d either say forget about adn drive or, or if you’re worried about not being able to open teh rifle/clear a severe jam in a hurry then use a rat tail and open the hole just slightly. Personally, I’d just drive on - any jam that bad is probably not going to get fixed in time anyway, but that’s just me.
The fact that you are able to get the upper and lower together and apart, albeit difficulty, tells me that the amount of material effecting it is very small. What I would do is get a piece of very fine emery cloth, put some oil on it and wrap it around a dowel or pin that is a bit smaller than the take down pin and run it thru the upper’s hole a few times, say 15 to 20 passes, clean it up, and check the fit, if still super snug, repeat as needed. All total, 20 minutes of work, tops.
I bought and built 2 Noveske lowers using Colt LPK’s. The BCM uppers I had on them fit perfect and ran like champs. Then I decided to splurge on two Noveske uppers. Fantastic quality all around but there is one Noveske lower/upper combination that is absolutely un-workable without a hammer and a punch. Switch them around and they are fine needing only firm push with a finger tip or rap with a nuckle to break down.
I love my Noveske weapons and they aren’t going anywhere…then I realized I had two orphan BCM uppers. Grant fixed that with two complete BCM lowers…all happy now but poor.