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About a month ago, I was shooting my high mileage early MK25 with a chrome lined barrel at a longer range - 25 yards - when I noticed a few hits keyholed. Concerned, I took it out to 50 yards with some plotter paper. About a third of the shots were clearly keyholed and spread towards the outside; it may be higher percent since not all the shot landed on paper. Does this mean the barrel is worn out?? Should it be retired from night stand duty?? I was shooting 147 gr American Eagle and 124 gr Winchester NATO.

Normally, I don't let the barrel get too hot to touch. I added up my internet purchases and have at least 14k rounds through it over the years but no Russian ammo. I did use an aggressive cleaner that got a fair amount of copper residue out - judging by the color of the patch. Other than that, I'm out of ideas. I'd like to keep it by the bed, but I'm not sure if a tumbling bullet is going to work out.
 

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IDK how many rounds you've put through it, but buy another barrel, dude. The gun is fine. You may want to invest in a new recoil spring and spring kit, or send it in to Sig for a full service package. Or, if you want, I'll take it from you.
 

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Gelatin tests are performed at a distance of 10 feet.
Ammunition performance is calibrated at this range.
Is a combat situation with a pistol, you won't be doing 50 yds.
If it really concerns you, invest in another barrel and spend the rounds to
Verify.
 

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No centerfire SIG pistol bore should reach end-of-life at a round count of 14K.

Check your crown for marring, and inspect your lands and grooves carefully. You may have additional lead or copper fouling in there.
 

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I'd probably look into buying another barrel as well.

In the meantime, if you are worried about nightstand duty, I'd look at comparable ranges. How many 25 and 50 yard rooms do you have in your house; and, will you adopt me (and my family) if the answer is one or more?

My trigger work isn't great (I've been working on it), and currently I find shooting at 25 yards or greater to be a little disheartening. However, if I shoot a set at 7 yards (or so) I generally feel a lot better about my ability to defend my family and myself in our home.
 

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Gabe, keyhole rounds are normally caused by unstabilized projectiles. Factory ammunition should have enough velocity, so it has to do with the spin that should be imparted by the rifling.
Can you provide a picture of your bore, backlit with a white background?
Even using an ammonia based cleaner, which could "lift" some of the plating could cause some velocity loss, but the lands and grooves would still be there to impose the spin.

Brownells markets J-B Bore cleaning paste which is great for cleaning up excessive jacket fouling. Normally a problem with higher velocity rifle barrels.
BROWNELLS J-B® NON-EMBEDDING BORE CLEANING COMPOUND | Brownells

A quick question... have you shot any quantities of cast lead ammunition?
 

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I have about that through my EDC Mk25 and have no issues(and I shoot Tula a lot..). Even with aggressive cleaning, you shouldn't have worn through the rifling unless you're using some electrically assisted cleaning wheel(I'm thinking of a brush attached to a power drill).

I'm not sure I'd be able to tell if 9mm FMJ was keyholing or if it was just beating up the paper. Have you tried any other loads besides the 2 you mentioned, specifically a JHP? Pics of your target or of the barrel?
 

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One other thing, that isn't match grade ammo so don't expect match accuracy.

50 yards is a long ways for a pistol shooting bargain ammo to expect a 2" group.

$.02
I didn't read anything in the OP about 2in groups. He's asking about keyholing and took out to 50 yards to confirm the keyholing.
 

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I didn't read anything in the OP about 2in groups. He's asking about keyholing and took out to 50 yards to confirm the keyholing.
Right, but I have often experienced cheap plated ammo that really "tears" the target and it's not key-holing, it's just the the paper tears as the bullet punches through.

I have experienced key-holing with cheap plated 200 grain bullets in my 10mm going a bit too fast and they literally leave rectangles in the paper.

It is also my experience that cheap practice ammo is not gonna give great accuracy at 50 yards from a short barrel semi auto pistol.

I could be totally wrong.....
 

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Right, but I have often experienced cheap plated ammo that really "tears" the target and it's not key-holing, it's just the the paper tears as the bullet punches through.

I have experienced key-holing with cheap plated 200 grain bullets in my 10mm going a bit too fast and they literally leave rectangles in the paper.

It is also my experience that cheap practice ammo is not gonna give great accuracy at 50 yards from a short barrel semi auto pistol.

I could be totally wrong.....
I understand what you're saying.
 
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