Not sure this is the right forum, but the experience of the good people here leads me to talk about it. Bottom line - can a piece of the cartridge case head be shaved off and lodge in the bolt face in a way that affects accuracy?

Just back from an African hunt, and in sighting in the well-taste Sako 338 Win Mag I experienced very poor grouping at 100 yards. First shot was in the orange 1" dot at about 12:30. Next one was 3" out at 5 o'clock. Next was 2" out at 3. Tightened the bedding screws and scope rings/mounts, just in case. A few more shots confirmed the lack of grouping. Since I was on a leopard hunt, EVERYONE was raising eyebrows by now!

So I changed from the good Leica scope to a really good Leupold scope. Still problem. Gave it to my professional hunter to confirm and he did a funny thing. Noticed a tiny sliver of brass lodged in the groove of the bolt face. Removed it with a pocket knife, and now the rifle shot well. Used 15 shots, by the way, just to sight in. Quite a record....

Figuring the cause might have been that the alignment of the cartridge in the chamber was just slightly off.

Thoughts?

FYI - Lilja barrel, Barnes 225 TSX bullets, and a long ago developed load that has consistently produced 3 shot groups 3/4 - 1" at 200 yards.

(Got the leopard)

My thoughts are that small changes don't make for big accuracy problems. I think instead, there was something else that somehow got changed when he had the bolt out messing with it such as something shifted in the bedding and alignment while you were messing with it.

Tiny misalignment because of how the case fits in the chamber aren't going to move the point of impact randomly 5 inches overall. Similarly, binding of the cartridge because of brass pushing it forward in the chamber aren't going to cause random accuracy problems.

My experience with the 338 mag is that it isn't a fussy cartridge. Different brass, variance in loading, even mixing different bullet weights/designs won't make it into a 5 moa gun at 100 yards.

Seeing as you tightened bedding screws and changed scope and it still did not group, I can't imagine that something changed or shifted while the PH had the bolt out as ssdave is proposing.

If the outer rim of the cartridge was sitting on the sliver of brass lodged in the groove of the bolt face then the amount of misalignment of the case neck and bullet would be magnified up. The brass sliver wouldn't compress so something has to give at the front end of the cartridge which would be more than a minor amount.
I would expect if the chamber was minimum spec you would feel resistance on closing the bolt as the shoulder deformed slightly to allow the bolt to close into battery however if the chamber was on the generous side then the bolt could close without undue resistance as the cartridge could tilt misaligning the bullet with the bore.

Barring anything else that was changed while the bolt issue was being sorted I guess the cause of the sudden lack of grouping has to be the before and after effect of the sliver of brass.

This is a new one.

I haven’t the faintest idea.

My thought is if the sliver of brass was large enough to have any effect, you might not have been unable to close the bolt??

You solved the accuracy problem, but I cannot see what had caused it.

Someone might enlighten us.

No. That wasn't it.

I have solved somewhere between 50 and 100 rifles for Barnes bullets. Based on that work, a small sliver of brass lodged in the bolt face could very easily be enough to account for the inaccuracy. I have seen as little as .005 difference in seating depth make as much as 8 inches of group size. Likely the sliver was in a position which had the capability to force the cartridge base a little off center. Maybe also it sometimes lifted the cartridge base slightly off the bolt face tilting it somewhat and changing the seating depth a little.

Barnes bullets can be very sensitive to things like this in my experience. While almost any bullet could react to this problem with increased group sizes, copper monos tend to be worse.

quote:

Originally posted by miles58:
I have solved somewhere between 50 and 100 rifles for Barnes bullets. Based on that work, a small sliver of brass lodged in the bolt face could very easily be enough to account for the inaccuracy. I have seen as little as .005 difference in seating depth make as much as 8 inches of group size. Likely the sliver was in a position which had the capability to force the cartridge base a little off center. Maybe also it sometimes lifted the cartridge base slightly off the bolt face tilting it somewhat and changing the seating depth a little.

Barnes bullets can be very sensitive to things like this in my experience. While almost any bullet could react to this problem with increased group sizes, copper monos tend to be worse.

Sounds like a good reason to use other bullets than Barnes, unless you live where they're more or less required.

A minor and random problem causing an 8 MOA change in a rifle isn't acceptable performance. What if you got a grain of sand, which is typically .008 to .020 in size in the action? Even if closing the bolt crushed it down to smaller dia, it could easily cause the same problem as a sliver of brass.

That said, I've never had small foreign particles in the action cause noticable changes; but then again I use Speer, Hornady, Nosler, Sierra bullets, not Barnes.

If five thousandths makes that much of a difference then someone needs to call SAAMI and every brass, rifle, and ammo maker and tell them they are all wrong. Tolerances and all.

Wasn't the Leica scope and wasn't the rifle barrel, action, etc. Went shooting today to figure out something. Fired 1 fouling shot - same as in Namibia. Then grouped 3 into 0.7" at 100 meters. Group center was 2 1/2 inches from the fouling shot.

Same scope, same ammo, pleasing result. It had to be the sliver of brass stuck in the bolt face. That's the only conclusion I can come up with.

HT
Of course it was the sliver that caused the harmonic distortion. It went back to normal after it was removed.
A picture of the sliver on here would be nice not only out of curiosity. But, for identification of where it may have come from.

Do a controlled test using scientific protocol. Otherwise it is just a guess.

Be my guest.

As far as I can tell, the only variable between grouping badly three weeks ago in Africa and shooting acceptably today is the removal by the professional hunter of a piece of brass lodged in the bolt face ring.

I’m satisfied as of today that the scope and rifle are functioning correctly.

quote:

Originally posted by H T:
Be my guest.

As far as I can tell, the only variable between grouping badly three weeks ago in Africa and shooting acceptably today is the removal by the professional hunter of a piece of brass lodged in the bolt face ring.

I’m satisfied as of today that the scope and rifle are functioning correctly.

I think you're right, as of today it is function correctly. However, I'd be shooting it, and watching for the same thing happening again, to figure it out and fix it. Or, put a sliver of brass back in the same place, and see if it replicates.

Things that are fixed by magically doing a minor thing that shouldn't cause the problem are almost always something else intermittent, that we just satisfy ourselves were caused by the minor, easily fixed thing when they intermittently stop happening. I'd guess the problem will exhibit again someday; unless it can be repeated by putting a sliver of brass in the same spot. In the case of a sliver repeatably ruining the accuracy, I'd be measuring my chamber and try to identify why a minor misalignment can make a 5 moa difference, and fixing that. I'd not want an accidental minor misalignment caused by a spec of something to cause a problem at a critical time.

Send me the exact dimensions of the piece of brass in the bolt so I can duplicate the problem under test conditions. Otherwise, it is invalid.
I guess I cut chambers so that if you had a piece of brass in the bolt face, you would immediately know it because the bolt wouldn't close. Perhaps in a sloppy chamber to cartridge interface, it might move the ammo to one side, but the real question is, why is it that way in the first place?

The piece of brass that was in the bolt is somewhere in the dirt by the shooting range in a farm in Namibia. So, can't help you there.

Just a guess - the load is fairly hot and the brass had been fired (by me) a few times. I did notice that the bolt was a little bit stiff to open. So perhaps the camming action of the bolt on a cartridge shaved off a small piece of the rim. Fired or unfired cartridge, I don't know.

Like I said, just a guess as to how it got there. Backing off on the load a bit, by the way.