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 Daniel Defense Big Hole Upper - UPDATE - problem solved!
Clicker58  [Member]
2/12/2008 1:08:07 PM EST
Here's the set up - I have a RR SP1 converted lower which still uses the original large front pin. Less than 2 years ago I bought a DD Big Hole Upper to allow for easier upper swaps since I shoot 4 different calibers with this gun.
Last spring I installed an 11.5" barrel (5.56) in this upper and all was well until late in the year. I began to have feed issues where the bullet nose would jam into the upper just below the barrel extension. I found that by using Magpul PMAGS the gun would run but it would mis-feed with any other mag.
Time to check this thing out and solve the problem as there was alot of up & down play between the upper and lower receivers. So I get out some hole gages and a micrometer I find that the front hole measures .326" instead of .315". I'm thinking that's a little on the fat side. I pull out some other uppers and go to work checking the front hole dimensions for the sake of comparison. Here's what I found starting with the problem child.

DD Big Hole Upper = .326"
Colt AR15 A2 HBAR upper (like new) = .318"
Colt SP1 upper (old beater) = .318"

Next a check of standard uppers using mil spec pin.
Oly A1 = .252"
J&T Hi Rise flat top = .251"
Bushmaster A2 w/FK forge marks = .250"
Unknown A2 = .250"
Unknown flat top = .250"

After review of these measurements It looks as if the standard pin hole is .250" and the pin itself is around .246". While the Colt large pin is .314" to .315" (my like new Colt is .316") and the hole will be a few thousandths larger which is the opposite of the standard 1/4" pin units.

So I'm thinking I have a defective DD upper with an enlarged hole that need to go back to DD. What to you guys think? Can you give me some measurements of your large pin Colt uppers with both the pin size and hole size?
I'd love to know what a DD upper in new condition measures if anyone has one.
Has anybody seen anything like this before?

I sent Daniel Defense an email describing the problem and they responded very quickly. They will replace the upper at no cost upon its return. Thanks DD, customer service doesn't get any better than that!
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