I posted this on another forum as well.

So I received a used sig sauer p220 long ago as a gift. I decided to "customize" just about everything you can with aftermarket parts.

Lighter trigger pull
Day/night sights
hogue grips
adjustable trigger - I had a neighbor with a machine shop (who was also a professional shooter) help me with this because I have the old frame that couldn't fit the wide adjustable trigger. We ended up widening the trigger hole in the frame.

I shot it at a gun range (after upgrades) at about 15 feet and it did fine (had to adjust the sight a little but nothing unexplainable). Probably shot 200 rounds.

That was about 2 years ago. Recently I shot (18 rounds) at 30 feet and all of them went very low. Talking in feet, most not hitting target. My dad did a little better but still not ideal. We did not practice any between (not even point and dry fire).

I know it could (*cough*) be me but while I was cleaning it I took a closer look at the inside of the barrel and it looks like a previous owner had something about an inch down the barrel, continuously. Maybe he/she stored it on a rod/peg or something. It left both a little rust and also marks/dents in the metal. All of the marks/rust is along a circle about an inch down the barrel.

I'm going to start shooting again but should I replace the barrel first?

I see some barrels on websites going for about $150 - $200. Do they just drop in or would I need a gunsmith to assure proper fit?

If you get a factory barrel, it will probably fit and function without gunsmith fitting. But that’s not guaranteed.

If you’re hitting “feet” low at 10 yards, it’s hard to imagine that minor damage to the barrel would cause that. During the upgrade, was anything changed that might have affected barrel fit? I.e., the barrel itself or the locking surfaces on the slide? Fifteen feet isn’t very far and a skilled shooter can produce a single ragged hole at that distance with a P220. If there was nothing obviously drastically wrong with the gun mechanically and you’re now having hits that are feet low at 30 feet, I must suspect shooter error or something strange with the sights. What type of sights did you change to?

I’m also curious about the rust you’re seeing in the barrel. If you fired the gun after acquiring it from the previous owner, then any rust would have accumulated after you last used it. Minor rust wouldn’t survive your firing 200 rounds. The “ring” thing is confusing as well. Did you inspect the barrel after the most recent time you fired the gun? Have you cleaned the bore since then? If so, what is your method?

I did not do anything with the barrel or slide, mod wise. I said rust and what I should have said was pitting leftover from rust. It is the pitting and marks that form the ring.



https://1drv.ms/u/s!An11ye2qfPpy2WH0kGvqgD4EThjS

The pic probably didn't turn out well. Most of the marks are under the twists, in groove. But there are a couple marks on the twists, contact with bullet.

The sight I have is TRUGLO TFO™ Tritium/Fiber-Optic Sights

Based on what you’ve reported thus far and even the photo of the barrel give me no reason to believe that anything other than shooter error is causing the point of impact to be low by “feet” at 10 yards. As a minimum that’s what I would suspect at first, and therefore I would recommend having (an)other skilled shooter(s) try the gun to confirm or refute the problem’s being with the pistol.

Your experience reminds me of being approached nearly 20 years ago by another P220 user who was having problems of a similar nature, i.e., he was hitting a foot and more low at close distances. We went to the range together and from a rest my first five shots were a 1-inch group directly at the point of aim at 15 yards. I was able to identify and help him correct his recoil anticipation and he never had any serious difficulty qualifying thereafter. Although that was the most extreme example of shooter error causing a large point of aim/point of impact discrepancy, it wasn’t the only one I’ve dealt with in my 18-year career as a professional firearms instructor. With the one exception of a precision rifle shooter whose scope rings were loose, none was due to a problem with the firearm. To reiterate, I could be wrong, but I doubt it and recommend having someone else check the gun.

First concern I would have, if you see some evidence of barrel damage, would be a prior squib load.

Is there any damage to the crown at the muzzle? Has any work been done there?

Back in the 90’s I picked up a series 70 1911 that had clearly been badly damaged from moisture. The barrel was pitted end to end and lands and grooves were indistinct. It still shot impressive groups at SD ranges, all things considered.

Get a micrometer caliper and mic the barrel down its length. If there was damage from a squib, you’ll have a change in barrel outside diameter, especially in the area of the “ring”.

Did you try bench resting as mentioned above? Not just slapping down on a flat surface but using bags or blocks to stabilize. If not, try that first.