Buffer retaining pin too tall?

[davsel]

I'm building an AR using:

Wilson Combat lower
Hera billet upper
ACE SOCOM stock
Bushmaster LPK
Bushmaster semi-auto BCG
Rainier CH

After assembling the above parts, when pulling back the charging handel, the rear of the bolt is hitting the buffer retaining pin - dead center above the cut-out in the bottom of the carrier. If I pull the rear takedown pin and raise the upper a hair, the BCG will retract into the stock. I visually compared the length of the buffer retaining pin to that of another bushmaster rifle, and it appears a bit longer. The buffer tube is correctly installed over the retaining "cup."

My questions are:
Has anyone else had or heard of this problem?
Can I simply file down the length of the pin - ensuring it still retains the buffer?

[BPTactical]

While it is possible the pin portion is too long there are a couple of other things to look at. At first guess your buffer tube is very possibly 1 turn shy of optimum. While it may be keeping the retainer in place it is possible that one more turn of the buffer tube will hold it a bit lower do the bcg will clear.
Try that before you start whittling.
I can measure a buffer retainer later tonight so if you want to double check the length before you break out the sawzall give me a yell.

[davsel]

I will attempt to give it another rotation tonight. I'll also swap pins with another working rifle and see what effect it has on either one.
I was really just curious if this was a "common" problem. I did not think so - as I could not find info on the web regarding shortening buffer retaining pins.
My greatest fear is that the BCG is not lined up properly (hitting too low) with the buffer tube - bigger problems!
Hopefully I will swap in an old pin tonight and all will be well.

[BPTactical]

Pretty uncommon but given the way the manufacturers are cranking out parts I have seen more "anomalies" then I ever have before.

[davsel]

Figured it out. It was no the carrier hitting the buffer pin that was stopping the reward travel. It was the charging handle itself hitting the castle nut on the newly installed ACE SOCOM stock. How I missed this before, I will chalk up to a late night. I put the Hera upper on a Bushmaster lower with an older version of the ACE SOCOM stock and it works fine. The Bushmaster upper also works fine on the Wilson lower with the newer version of the ACE SOCOM. Aparently the Hera upper sits slightly lower than a forged upper. The difference in the stocks is that the older one uses an aluminum "pinch" ring/backing plate that pinches down on the buffer tube. The newer stock uses a castle nut and backing plate to lock the buffer in place. The castle nut is almost twice as thick as the "Pinch" ring. I then swapped stocks on the lowers, put everything back together, and all is well.

Messing with this billet upper reminds me of owning a custom motorcycle - off the shelf parts often do not work.
I believe I'll sell this build off and pick up some mil spec parts for a replacement.
Thanks for your help BPTS.