Strange scuffed bullets after chambering

Hoping someone can help diagnose a problem I'm having with a shilen barrel.

While my CBI 260rem barrel is at the gunsmith having some work done, I swapped my backup barrel on - a prefit Shilen 260rem bull barrel from NSS.

I started working on handloads, used the hornady tool to measure the lands for some hornady amax 140gr. And set my seater for .020 off.

All was well with the rounds until I tried chambering them. Bolt required a lot of force to close, and also a lot of force to extract the round. This was with the ejector pin removed from the bolt btw.

Upon inspection, the projectiles have a scuff mark on one side. Unchambered rounds off the reloading press are pristine.

Measured runout, under .001". Just to make sure, I used the hornady concentricity tool to get some rounds dead on 0.000". And tried chambering them. Same deal - scuff on one side.

So I tried chambering some ABM 260rem match ammo, it chambered perfectly, little force required on the bolt, and zero marks on the projectile. I measured the projectile diameter - 0.2635". Measured my amaxes and they were 0.264".

I took a bore brush and cleaned the ever living crap out of the chamber. Then tried chambering a round, same problem.

So I am pretty sure the problem is not:

* dies scuffing the projectile
* runout
* jamming into the rifling
* ejector forcing rounds to scrape the chamber
* dirty chamber

Anyone seen this problem before? What else could the problem be?

http://i.imgur.com/BfBcNHa.jpg

The freebore diameter on your Shllen barrel is very close to bullet diameter. If you were to look at the reamer print the freebore dimension would probably read something like .2643 to .2645. When you only have a few "tenths of space on each side of the bullet even a full 001" can be a big deal. The fact your .260 factory ammo with smaller bullet diameter isn't having the problem should be your indicator. Factory chambers can be one or two thousandths larger than the bullet but that doesn't do much for accuracy.

Your bullets are nice and snug in the freebore and should shoot just fine. In fact they might shoot better than the smaller diameter bullets.

FWIW, where are you measuring the runout when using the Hornady gauge? At the neck? Bullet bearing surface? Shoulder? I prefer to use a run out gauge that supports the case just above the head and again at the shoulder. This tells me how the bullet is meeting the freebore.

You have a bit of an odd one, but I will warn you, DO NOT FIRE those rounds if they are anywhere more than mid level and better yet not.

It almost smacks or is a case (pun) of the case being sized for the other barrel. If not.

The issue is a pressure spike with no free bore to let the bullet move before the pressure builds. High pressure spike, can go well above proof.

All the times I have done this (gently ) in order to get a bullet in the lands back out, I have to tap the bolt handle with a plastic handled something.

You clearly are getting into the lands, I would back off another .020 and see what happens.

It seems you are just barely there with the bolt closing.

COAL is best measure on the shoulder of the bullet not the tip.

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Originally Posted by RC20

You clearly are getting into the lands

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i am pretty certain this is not the case.

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Originally Posted by RC20

COAL is best measure on the shoulder of the bullet not the tip.

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i am not using COAL. i am using the hornady seating depth gauge and the hornady comparator which measures off the projectile shoulder.

to better illustrate the issue, i deliberately seated a bullet extremely long to force it well into the lands, and used a marker.

you can see the scuffs start well before any rifling, and are only on one side of the projectile.

http://i.imgur.com/TNHazfT.jpg

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Originally Posted by Deadshot2

The freebore diameter on your Shllen barrel is very close to bullet diameter. If you were to look at the reamer print the freebore dimension would probably read something like .2643 to .2645. When you only have a few "tenths of space on each side of the bullet even a full 001" can be a big deal. The fact your .260 factory ammo with smaller bullet diameter isn't having the problem should be your indicator. Factory chambers can be one or two thousandths larger than the bullet but that doesn't do much for accuracy.

Your bullets are nice and snug in the freebore and should shoot just fine. In fact they might shoot better than the smaller diameter bullets.

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i talked with a gunsmith at PTG and he suggested that the chamber was reamed canted, which is why it is gouging one side only. he said a worn or undersize/tight reamer wouldn't do that. of course, he also suggested that their uni-throater could fix it :rolleyes:

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Originally Posted by Deadshot2

FWIW, where are you measuring the runout when using the Hornady gauge? At the neck? Bullet bearing surface? Shoulder? I prefer to use a run out gauge that supports the case just above the head and again at the shoulder. This tells me how the bullet is meeting the freebore.

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at the shoulder, and then a bit further down toward the tip. i was pretty happy i was able to get 0.000" on the indicator.

Bani, I bought a 260 from NSS and I had the same problem. My 308 was OK but I had to have the 260 rechambered.

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Originally Posted by Robinhood

Bani, I bought a 260 from NSS and I had the same problem. My 308 was OK but I had to have the 260 rechambered.

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was it also a shilen?

Yes. It shoots lights out now. I got the same marks as you are getting. The only thing I can figure is that the pilot was not concentric to the reamer. Would not expect that but I guess it could have been dropped. I'll never know. This was about 5 years ago.

I would have it bore scoped before I did anything. There may have been a chip jammed in there from reaming. I was impatient.

It was reamed with a tight freebore and off center slightly, due to machine setup or bushing slop. If it had a .0002" larger freebore diameter you wouldn't even know as you can see from the two different bullet diameters.

Its a lot more difficult to ream a chamber straight than one might think, especially in a production environment.

Not a big deal really, probably straighter than a factory chamber.

And that bullet scuffing is NOT the cause of hard chambering. Look for case/chamber size differences.

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Scott Evans is right on the money.

It's not a bid deal. Freebore/leade diameter is very tight and a hair off center, but will not affect pressure.

Shoot the ammo.

I've had one or two Shilens that showed similar scratch, just not as big.

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Originally Posted by Scott Evans

Its a lot more difficult to ream a chamber straight than one might think, especially in a production environment.

Not a big deal really, probably straighter than a factory chamber.

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Considering that production chambering is more likely than not done by just chucking the contoured barrel in a collet and not dialed in.

The 'smith I have chamber my barrels uses a Tru-Align Chuck and dials in the bore/groove so it runs true on it's axis the full length of the barrel, not just the breech end.

FWIW, this is one advantage of hammer forged barrels. Since the chamber is also formed along with the rifling by the mandrel the likelihood of the chamber being true to the axis of the bore is greater.

Quote:

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Originally Posted by Scott Evans

It was reamed with a tight freebore and off center slightly, due to machine setup or bushing slop. If it had a .0002" larger freebore diameter you wouldn't even know as you can see from the two different bullet diameters.

Its a lot more difficult to ream a chamber straight than one might think, especially in a production environment.

Not a big deal really, probably straighter than a factory chamber.

And that bullet scuffing is NOT the cause of hard chambering. Look for case/chamber size differences.

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Have you checked your loaded round on a concentricity gauge. Could be the ammo and not the chamber.

Tight freebore is a good thing. Shooting it will soon smooth out any tool marks.

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Originally Posted by m12lrs

Have you checked your loaded round on a concentricity gauge. Could be the ammo and not the chamber.

Tight freebore is a good thing. Shooting it will soon smooth out any tool marks.

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from the original post:

"Measured runout, under .001". Just to make sure, I used the hornady concentricity tool to get some rounds dead on 0.000". And tried chambering them. Same deal - scuff on one side."

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Originally Posted by bani

from the original post:

"Measured runout, under .001". Just to make sure, I used the hornady concentricity tool to get some rounds dead on 0.000". And tried chambering them. Same deal - scuff on one side."

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I have used one of these to polish out a rough chamber sucessfully

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