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I have a Tikka 595 in .243 fitted with pes over barrel moderator. Sporter profile barrel. Not sure of twist rate or round count.

Today I tried zeroing it for the first time. Bore sighted but not getting on paper at 100 ( 3 foot square target )

Tried a 25 yard target and found it was low and right compared to where it should be in relation to bore sighting.

More worrying - the bullets were impacting not quite fully sideways but slightly sideways leaving oblong holes. Adjusted sights to correspond.

Took pes off and tried again at 100 yards. Now on target but only managing 4" group and still slightly oblong holes.

Ammo used was 75gr Hornady SST ballistic tip.

My eyes may be deceiving me but I thought the last 4 inches or so of barrel had very faint rifling compare to that at the chamber end which is crisp.

I was wondering - seeing as the part of the rifling that SEEMS worn is the bit where the moderaror covers the barrel. Is it possible for that to cause overheating compared to the uncovered part, leading to localised wearing of rifling ?

Or maybe the previous owner left mod on 24/7 and corrosion is the issue ?

I gave it another thorough clean and will try lighter and heavier than 75gr next to see if its a bullet weight problem.

Next would be cutting off the offending 4 inches but I I was just wondering if any of you had seen anything similar ?

Unusual for a .243 to be shot out for the last few inches of the barrel, I would expect it to be more along the lines of no throat and fire cracked for the first 4-5 inches with rifling. They seldom seem to get past 1000-1200 rounds regardless unless shot very carefully and even then...

If memory serves, it's not unusual for the last few inches to wear more, save for throat erosion. Something to do with high pressure, small caliber bullets reaching maximum velocity at this point, with more heat and friction, resulting in more wear relative to the remainder of the barrel...

But agree with David, they don't last long either way....

I have previously bought second hand .22-250s and .243s before. I won't again!

Seen 223's go through the target sideways at 25 yards, lighter bullets cured it.

I had a rifle key holing end of last week, rifling was shot the full length of the barrel and gauged approaching .0025" oversize! It might be the twist is too slow for the bullet...

Just gave it a VERY good clean.

I can see a HUGE difference between the rifling at the start of the barrel and the muzzle end. Fairly crisp at the start but fades to pretty much smooth for the last 3 inches or so.

My best guess ? One or both of the following - Overbarrel mod meant that last 3" was getting hotter than the rest AND if left on 24/7 would have speeded up corrosion at that end.

I also measured the twist and found it to be a 1:10

Thing is, it is a 20" barrel at the moment so chopping off the worn bit will leave it too short at 16" ( according to what I read online )

Might be as well to just rebarrel ! The Tikka action seems to be a nice action so probably worth it.

No point in counter boring it I suppose.

Only last week I put a 22 calibre bore scope down some of the barrels in the scrap bin and the bad ones are smooth at both ends. I only looked at some 223 and a 243 and both showed this but the chamber end was by far worse.

Mattnall wrote:Only last week I put a 22 calibre bore scope down some of the barrels in the scrap bin and the bad ones are smooth at both ends. I only looked at some 223 and a 243 and both showed this but the chamber end was by far worse.

I really think the mod caused it - increasing heat in that end of the barrel and probably left on 24/7 without cleaning by previous owner.