Ar 15 barrel mounting Problems, grooves under barrel not aligned w/front sight tower
Hope you guys can help me with problem or send to right area.
Installing SP1 barrel on SP1 upper, putting back to original.
The barrel mounts fine to upper, but trying to install pins into front sight tower is issue.
As I try and hammer pins thru sight into under barrel cuts the tower shifts out of line.
I know they go from RT to Lt and the pins are tapered.
Try as I might they will not align.
Took to Gunsmith and we discovered the under barrel cuts are off a few degrees.
If we mount the sight tower the front sight is 10 degress to the right?
Any suggestions for correction besides get new barrel?
He suggested a gas block as he has no CNC machine?
E mail works best
Is the front sight base (tower) that you're trying to mount original to the barrel?
No not original to barrel.
Originally Posted By straight20:
No not original to barrel.
Buy a FSB undrilled, then have it drilled to fit the existing grooves in the barrel.
Originally Posted By straight20:
No not original to barrel.
That's your problem. It is a very rare for two front sight bases to have the taper pin holes drilled in the same place. Because the holes are not in the same location as the original front sight base, you won't be able to fit the new one to the barrel. If you want a pinned FSB, the only route (to my knowledge) that you can go is to by an undrilled FSB (one that has yet to be drilled for taper pins) and have it fitted to the barrel.
Apparently the front sight base is not the factory original to the barrel. As the other posters indicated, switching the bases often results in misalignment. I'd sell the current barrel and get another barrel for $200-$250. Adco charges $90 to properly pin your Front sight base.
You could also just tap the hole in the bottom of the FSB under where the sling swivel goes for an 8/32 socket head set screw and use a 3/16 x 8/32 socket head set screw to hold the FSB on. You could, in addittion, tap the holes for the tapered pins to the same 8/32 (or drill and tap for the same 3/16" x 8/32 socket head cap screws "IF" drilling is neccessary). It works very well....<><....:)
Originally Posted By MSPRet:
You could also just tap the hole in the bottom of the FSB under where the sling swivel goes for an 8/32 socket head set screw and use a 3/16 x 8/32 socket head set screw to hold the FSB on. You could, in addittion, tap the holes for the tapered pins to the same 8/32 (or drill and tap for the same 3/16" x 8/32 socket head cap screws "IF" drilling is neccessary). It works very well....<><....:)
Member crackedcornish has done this to good effect. I've had one of his setscrew front sight bases for awhile and run a couple of hundred rounds through it with no movement. If you're interested, you might contact him to see if he still does the conversion.
Do not want to get new barrel, must use this one.
The undrilled FSB sounds good as well as the set screw.
Meeting with cnc gunsmith and will suggest each option.
who sells the undrilled FSB?
thanks for all help
I saw an undrilled FSB in the EE yesterday for $19....<><....:)
Mount and align the FSB you have, then have it drilled and reamed for oversize pins.
Bravo Company sells .625 front sight bases. They are F-marked, but that shouldn't pose a problem to zeroing the rifle.
thanks for all the suggestions, I bought the FSB undrilled on the EE, thanks.
I am going to try that route first, contacting machinest first.
This my be my first and last upper build.
The reason I am trying to keep all this original is my Obsession.
I have a Colt Sp1 Lower in .222, and just found the .222 barrel, very rare as you know.
So would like to keep original.
thanks Gang
Originally Posted By straight20:
I have a Colt Sp1 Lower in .222, and just found the .222 barrel, very rare as you know.
I sure would like to see pictures when you're done!
Originally Posted By 44Echo10:
Mount and align the FSB you have, then have it drilled and reamed for oversize pins.
As I understand the OPs dilemma, this makes the most sense.
Question... how would one align an undrilled FSB to match the original barrel's grooves?
Mount and align the FSB you have, then have it drilled and reamed for oversize pins.
Sure seems like the easy way to do it. I could see me screwing it up now but I'd eventually get it right.
