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I've been given the opportunity to assist with an SP89 upgrade. This will cover barrel removal, paddle mag install, clip/pin trigger frame, 3 lug barrel re-install, and refinishing. Here's a few pics of the project. I'll update/add more pics/text as time allows.
I forgot to take pics of the barrel removal even though it was straight forward. I cheat when removing the barrel pin. Instead of trying to clamp the receiver into a vise/jig and pounding the heck out of the barrel pin, I use an undersized end mill to drill out the barrel pin. The remainder of the barrel pin pops out easily. I use only carbide end mills (1/8" or 3/32" work well) since the barrel pin is incredibly hard. HSS and Colbalt end mills will not work and the bits will dull easily.

By dirtyeight
I placed the receiver (upside down) into the vise and milled out the lower paddle pocket area and took out the rectangular metal piece.

By dirtyeight

By dirtyeight
After cleaning out the magazine release area of burrs/machine marks, I used a clipped/pinned lower to determine where the dowel pin hole needs to be drilled. I used an automatic center punch to mark where the hole needs to be drilled.

By dirtyeight
The receiver is drilled with an undersized colbalt drill bit. The drill bit goes about half way through the other side of the ledge. DO NOT drill the hole all the way through!!! The hole is then reamed out with an 1/8" reamer.

By dirtyeight

By dirtyeight
The dowel pin is cut/trimmed to the point where it sticks out about the width of a dime shaved in half (very little material sticking out). Here's a few pics of the paddle release before welding. Notice the wide pocket area where the paddle will flop back and forth. This are will be cleaned up.

By dirtyeight

By dirtyeight

By dirtyeight
The paddle bushing is made out of steel round stock. The diameter is turned down a few thousandths smaller than the inner diameter of the paddle. The hole in the busing is also drilled slightly oversized.
WHY would the holes be drilled oversized? The oversized holes will compensate for any wandering of the drill bits or a miscalculated pilot hole. I've read several posts where a paddle magazine release binds or needs to be broken in.
The dowel pin hole is precisely 1/8". This hole is not oversized. The bushing is the key to a smooth install. TIME FOR BED, good night.
I forgot to take pics of the barrel removal even though it was straight forward. I cheat when removing the barrel pin. Instead of trying to clamp the receiver into a vise/jig and pounding the heck out of the barrel pin, I use an undersized end mill to drill out the barrel pin. The remainder of the barrel pin pops out easily. I use only carbide end mills (1/8" or 3/32" work well) since the barrel pin is incredibly hard. HSS and Colbalt end mills will not work and the bits will dull easily.

By dirtyeight
I placed the receiver (upside down) into the vise and milled out the lower paddle pocket area and took out the rectangular metal piece.

By dirtyeight

By dirtyeight
After cleaning out the magazine release area of burrs/machine marks, I used a clipped/pinned lower to determine where the dowel pin hole needs to be drilled. I used an automatic center punch to mark where the hole needs to be drilled.

By dirtyeight
The receiver is drilled with an undersized colbalt drill bit. The drill bit goes about half way through the other side of the ledge. DO NOT drill the hole all the way through!!! The hole is then reamed out with an 1/8" reamer.

By dirtyeight

By dirtyeight
The dowel pin is cut/trimmed to the point where it sticks out about the width of a dime shaved in half (very little material sticking out). Here's a few pics of the paddle release before welding. Notice the wide pocket area where the paddle will flop back and forth. This are will be cleaned up.

By dirtyeight

By dirtyeight

By dirtyeight
The paddle bushing is made out of steel round stock. The diameter is turned down a few thousandths smaller than the inner diameter of the paddle. The hole in the busing is also drilled slightly oversized.
WHY would the holes be drilled oversized? The oversized holes will compensate for any wandering of the drill bits or a miscalculated pilot hole. I've read several posts where a paddle magazine release binds or needs to be broken in.
The dowel pin hole is precisely 1/8". This hole is not oversized. The bushing is the key to a smooth install. TIME FOR BED, good night.