Need help with what to do about a oversize and elongated slide stop pin hole

SO, after years of shooting my .45 I noticed the groups were no longer groups at 50 yards. I found the slide stop frame hole on the left side to be elongated and oversized. I ordered an EGW  oversized slide stop, .203" and had to ream the right side of the frame to fit. It still is just a bit freer on the left side. 

I shot many 50 yard targets with my go to load and bracketed that with more or less BE in hopes that the groups were now tight. But no joy: it holds 9 ring at best. 

Any insights or how to correct this would be helpful.

thanks Mark

I'm certainly no gunsmith, but wouldn't the barrel lugs need to be fit to the new diameter pin?
Phil

What model gun are you using?

Also, pics?

Curious about an elongated hole

EGW sells .206" diameter slide stop pins plus. You will need a .2065" reamer. Might help if you can get a #4 or #5 wire gauge end mill so as to locate the hole better. You will need a milling machine to do that.

Before you go changing pins and what not it may be wise to evaluate the other areas of barrel fit. If the slide pin is worn likely other areas have wear as well.

This is on a Caspian frame. The slide stop pin was .198-.199" measured in different locations along the pin and exhibited normal to little wear. The left barrel lug wear on the pin was less than the right. The barrel lugs do not show any wear that I could see and the oversized .203 pin fits snugly into the link and moves snugly on the lug ramps but does not bind. The barrel is a Kart Exact fit. 

It appears to me that the hole on the left side of the frame was elongated or oval towards the front and the hole accepted the .203 pin with just a very slight snugness but moved freely. The right side hole on the frame would not accept the .203" pin until I reamed the hole and then had to relieve the top side of the hole to allow the pin to move freely as it was binding. It was my thought that the holes were not drilled and reamed square on the frame from the factory or that the cast frame warped on heat treat.        

I hope this helps 
Mark

Slide stop pin should Not fit snug in link! There should be 4 to 5 thousandth clearance, that's quite a loose fit for .203" diameter especially in hole .136" wide.
 If hole was due to improper machining by Caspian you would not had good accuracy before. However pin hole on right and left sides especially hammer and sear pin hole are quite often not straight.
But the larger size in the slide stop pin usually helps in keeping the hole straight. I like using solid carbide cutting tools because they are quite rigid.

If the lug wear on the original pin was not even, the barrel was not fit correctly. As one side showed more wear than the other, that probably translated to the slide stop pin hole over use. What does the link look like?