I have been playing with a 338WM, working up loads for some heavier bullets. I have been getting some serious case expansion in the form of what a oversized chamber (perpindicular to the axis) would give.
I picked up a couple of the fire-formed cases and measured the case diameters ahead of the belt. Forget what the exact measurements were but when I went back to re-measure I noticed that the measurements were different from what I previously measured.
I rotated the cases in my dial caliper and noticed the bodies were out of round by .001" at 90 degrees.
What would have caused the chamber to have been cut "out-of-round"?
I suppose in-consistancies in the barrel steel or a dull reamer?
I started neck-sizing and so far haven't noticed any problems in chambering any of the cases.

Most of the time if the chamber is cut on the lathe, a dull reamer or inconsistency in the reamer will just make a chamber larger diameter, not out of round though. Out of round is usually caused by hand work. In this case it may have been polishing of the chamber to clean up corrosion or something like that. Any significant out of round usually does cause chambering problems.

I have done a little machine work over the last 45 years and a little gunsmithing. I have long wondered how it would be possible to cut an eggshaped chamber. I agree with guncurtis2.
Butch

If you put a lightly oiled fired case in the chamber, can you rotate it with your fingers? If this is a winmag case, there should be enough to grab on to.

Can't tell a whole lot measuring a brass case. Pour a chamber cast and measure that.

I've seen chambers that had ridges formed from what I would guess as a result of having a solid pilot bouncing off the lands, but nothing egg shaped.

If a person, for whatever reason, went in and modified an existing chamber and didn't get the bore exactly right to align with the original, then I could see a lop sided, out whack chamber.

.001" with dial calipers???

There is no way you can trust that measurement. Dial calipers are only good to say plus or minus .002" at best. They don't repeat that close either. And I don't care what brand, when they were calibrated, how they were calibrated what ever.

If you want to get an accurate measurement you need to use a micrometer or set up an indicator on a surface plate. or if you really were set up a Optical comparator. .001" is a lot to ask of a dial caliper and little to worry about on a piece of brass.

Cast the chamber as mentioned above and measure that as the brass may not have accurately reproduced the chamber. This can happen with brass that has hard and soft spots in it. Brass being what it is this is not to uncommon of a material trait.

Butch I mentioned on a forum on Benchrest Central once of how in the world do you get a out of round chamber in a lathe. Many argued that it is possible. I still dont see how! Now I just keep my opinions to myself.

I was originallyt taught to never trust calipers below .003, and for that be sure i used consistent proper technique. calipers are "springy" and can be made to red what the user wants if the user is after a measurement in their head and not the size of the object

i have heard that something was going on with M70's chambered for something like the ultramags created a condition where the chamber was "squashed" if you will when the barrel was screwed in the action. that is the only thing i can remember when chamber was truly out of round. i never saw any of this firsthand and am just repeating what i read several places. maybe it was right, maybe it wasn't

one time i thought i reamed an out of round hole. then i got to looking at my lathe, my reamer, and my reamer holder and thought about each step of the operation i just performed. the more i looked at it the less i could figure how it was possible to ream an oval or egg shaped hole. it was a headscratcher for me until i looked. double slap to the forehead and a very loud "DUH!!!" was my response. set it up in a lathe and look at it for yourself. think about what an oversize hole vs. a round hole would be possible with a set up in the lathe

just out of curiosity, does anyone have first hand experience with the M70 issues with front ring size or chamber wall size being too small and causing chamber dimension problems when the barrel was torqued into the action?

The majority of the guys on the gunsmithing forum on BR.Com are neither gunsmiths or machinest. You might see anything on there.
Marc, didn't the Mod 70s go to real fine threads on the Ultra mags and WSMs as the diameter of the cartridges were quite abit larger than before? Not much wall between the chamber and the OD of the threaded tenon.
Butch

I saw this happen on an H&H with too big a chamber and loose headspace. When fired, I believe the case moved forward, then recoiled unevenly (differing case wall grip?) and the result was a bulge to one side.

i agree with the round chamber comments. If the barrel is turning and the reamer is held, it may cut a big chamber, but not out of round, which is not the same as off center. To cut an oval chamber, the reamer would have to oscilate back and forth repetitively at the frequency of the lathe rotation.

I could see one not being coaxial to the bore.
Butch

quote:

Originally posted by Art S.:
I saw this happen on an H&H with too big a chamber and loose headspace. When fired, I believe the case moved forward, then recoiled unevenly (differing case wall grip?) and the result was a bulge to one side.

i agree with the round chamber comments. If the barrel is turning and the reamer is held, it may cut a big chamber, but not out of round, which is not the same as off center. To cut an oval chamber, the reamer would have to oscilate back and forth repetitively at the frequency of the lathe rotation.

i have seen out of round chambers in barrels. I am not certain how they got that way, but I suspect that rythmic oscillation in the lathe set-up occurs more often than folks realize.

quote:

Originally posted by Alberta Canuck:

quote:

Originally posted by Art S.:
I saw this happen on an H&H with too big a chamber and loose headspace. When fired, I believe the case moved forward, then recoiled unevenly (differing case wall grip?) and the result was a bulge to one side.

i agree with the round chamber comments. If the barrel is turning and the reamer is held, it may cut a big chamber, but not out of round, which is not the same as off center. To cut an oval chamber, the reamer would have to oscilate back and forth repetitively at the frequency of the lathe rotation.

i have seen out of round chambers in barrels. I am not certain how they got that way, but I suspect that rythmic oscillation in the lathe set-up occurs more often than folks realize.

I think A.C. is correct but I am not sure of anything at this point. (could be similiar to a gravel road washboarding after it has been bladed - maybe??? once it starts it don't stop)
All I know is more than one case is oval.

KCSTOTT,
I don't need to precisely measure the amount of irregularity at the bottom of the case. I simply used the calipers as a dial indicator and it is more than adequate to show eccentric movement. The dial moves up and down roughly a .001". Haven't "micro'ed" it though.

I will be happy to measure with micro.. this weekend for you.

Butchlambert,
So far there is no noticable eccentricities to the bore axis. In laymen's terms it's head is still in the middle of it's shoulders, just the body is pooching out front and back.
Know what I am talking about?

quote:

Originally posted by Rae59:

quote:

Originally posted by Alberta Canuck:

quote:

Originally posted by Art S.:
I saw this happen on an H&H with too big a chamber and loose headspace. When fired, I believe the case moved forward, then recoiled unevenly (differing case wall grip?) and the result was a bulge to one side.

i agree with the round chamber comments. If the barrel is turning and the reamer is held, it may cut a big chamber, but not out of round, which is not the same as off center. To cut an oval chamber, the reamer would have to oscilate back and forth repetitively at the frequency of the lathe rotation.

i have seen out of round chambers in barrels. I am not certain how they got that way, but I suspect that rythmic oscillation in the lathe set-up occurs more often than folks realize.

I think A.C. is correct but I am not sure of anything at this point. (could be similiar to a gravel road washboarding after it has been bladed - maybe???)
All I know is more than one case is oval.

KCSTOTT,
I don't need to precisely measure the amount of irregularity at the bottom of the case. I simply used the calipers as a dial indicator and it is more than adequate to show eccentric movement. The dial moves up and down roughly a .001". Haven't "micro'ed" it though.

I will be happy to measure with micro.. this weekend for you.

Butchlambert,
So far there is no noticable eccentricities to the bore axis. In laymen's terms it's head is still in the middle of it's shoulders, just the body is pooching out front and back.
Know what I am talking about?

The thing is Dial calipers are not that accurate. and you did not say if you measured the case before you fired it. .001" TIR is fine for brass. What I'm getting at is you may be measuring a problem with the brass and not the rifle.

I''ll give the brass another looksy this weekend, but I did check several pieces of new brass and did not see anything wrong. Didn't really feel like opening all of the bags to find out.

It could be that your chamber is a tad loose.
Ifa case is lying against the chamber wall it
can only expand in the oposite direction.
This will result in a "bump". I would neck
size and fire again.

quote:

Originally posted by hawkins:
It could be that your chamber is a tad loose.
Ifa case is lying against the chamber wall it
can only expand in the oposite direction.
This will result in a "bump". I would neck
size and fire again.

Yep. That is normal for oversized chambers. One side of the case is always weaker than another and it will blow out in that direction unless spaced off the chamber walls with a thin strip of tape at the base of the case. Then it will blow out equally.

quote:

Originally posted by Bobster:
Yep. That is normal for oversized chambers. One side of the case is always weaker than another and it will blow out in that direction unless spaced off the chamber walls with a thin strip of tape at the base of the case. Then it will blow out equally.

Say What???

this makes remember a couple of m1 carbines i bought from the dcm years back. one had such an egg shaped chamber that the middle of the case still measured about 1/8" bigger in the middle. had to pound it out with a steel rod. The other one when i let the bolt slam home the barrel popped out

Bobster,
You sure lost me.
Butch

quote:

Originally posted by Westpac:

quote:

Originally posted by Bobster:
Yep. That is normal for oversized chambers. One side of the case is always weaker than another and it will blow out in that direction unless spaced off the chamber walls with a thin strip of tape at the base of the case. Then it will blow out equally.

IWhat???

think what he may be saying is that if you have an oversized chamber and DON'T want a fired round to come out with one side more expanded than the other and the head apparently off-center, you can center the case head fairly solidly in the chamber by wrapping tape clear around it, maybe even several wraps depending on how oversized and how thick the tape.

Then, the pressure from firing will expand all the walls of the case pretty evenly in front of the case head, giving you a rather normal looking case with the head still pretty much centered.

I don't know if that works, but I have seen it recommended in loading articles back in the day.

quote:

Originally posted by Alberta Canuck:

quote:

Originally posted by Westpac:

quote:

Originally posted by Bobster:
Yep. That is normal for oversized chambers. One side of the case is always weaker than another and it will blow out in that direction unless spaced off the chamber walls with a thin strip of tape at the base of the case. Then it will blow out equally.

IWhat???

think what he may be saying is that if you have an oversized chamber and DON'T want a fired round to come out with one side more expanded than the other and the head apparently off-center, you can center the case head fairly solidly in the chamber by wrapping tape clear around it, maybe even several wraps depending on how oversized and how thick the tape.

Then, the pressure from firing will expand all the walls of the case pretty evenly in front of the case head, giving you a rather normal looking case with the head still pretty much centered.

I don't know if that works, but I have seen it recommended in loading articles back in the day.

That is exactly what I am saying. I've done it many times with oversized military chambers. I cut a very narrow strip of tape (3-4 mm wide)and wrap it around the base of the cartridge, just above the extractor groove. Add enough layers until it is a snug fit. Fireform and remove the tape. You will have perfectly coeccentric expansion rings.

quote:

Originally posted by Bobster:

That is exactly what I am saying. I've done it many times with oversized military chambers. I cut a very narrow strip of tape (3-4 mm wide)and wrap it around the base of the cartridge, just above the extractor groove. Add enough layers until it is a snug fit. Fireform and remove the tape. You will have perfectly coeccentric expansion rings.

Not only that, but it will be nicely fireformed to fit the chamber. If a person does NOT full-length resize the case afterward (just necksizes it) the case will last for many reloadings. If the loads are mild, they'll likely never need full length sizing anyway.

Actually, I did some of that myself back in the early 1960s, but didn't want to get into a lot of blather with folks who decry anything not perfect. It does work rather well as a practical thing of very little cost.

Many of the early M70 WSM's had out of round chambers caused by over tightening the barrels into the receivers.

As I said I would do, here are some measurements (with a micrometer) on a few cases that were at a more upper end of powder charge measurements. Please remember I am in the process of working up some loads with 250 grain bullets and playing with different slower powders i.e. RL-22 & IMR 7828. I have not reached max. with either powder yet.

5 cases measured then rotated appox. 180 degrees. Measurements were taken appox. .055" ahead of the belt which was the widest point on the case excluding the belt/head:

#1:.5150" - .5145" = .0005" difference
#2:.5149" - .5143" = .0006" difference
#3:.5150" - .5143" = .0007" difference
#4:.5141" - .5138" = .0003" difference
#5:.5145" - .5140" = .0005" difference

I tried to mic the unfired brass but it was too difficult to hold the micro in the same location on the tapered bodies as I turned the thimble. But as nearly as I could tell, the Winchester cases measured somewhere around .507"-.508".

All cases were expanded past the original case body shape and NONE were expanded to "one" side only to simulate a case laying in the bottom of the chamber. (a very noticalbe condition as I have a M-700 and a M-70 that have this trait) This could possibly be due to the belt area of the chamber holding the case body somewhat in good alignment with the bore. Maybe the rifle maker's reamer or whatever is oversized in the body and neck area only and not the belt??

This would tend to keep the case "head" more in alignment with the bore and not allow the case to lay in the bottom of the chamber.

As Westpac stated, a chamber cast would be the tell-all for sure. But as of now I am not haveing any problem with chambering a neck sized case - yet. I was merely wondering what would be the main cause of such.

I accidentally found the presumed out-of-round chamber when I had problems partial-length re-sizing some cases with a F.L. die. The die was shaving off brass as it neared the belt area. I purchased a new F.L. die and still noticed that it took quite a bit of effort to partial-length resize, much less full-length
re-sizing. I sent the first die, along with some sample cases, back to the manufacturer and they apparently either re-cut or polished it internally as there are shiny jaw marks on the outside. So I know the first die was defective.

I personally don't see how a case that is fire-formed and neck-sized in a out-of-round chamber would be very noticable when closing a bolt action unless the case was exposed to extremely high chamber pressures or unless the the chamber in question is off the charts with regards to being egg-shaped. I say this because the neck-sized case should still be the same circumference at any same point as the chamber. A bolt action has alot of leverage to force the case to re-shape itself only slightly.

Extreme pressures would cause the case to expand to a diameter larger than what the chamber would be normally. This is what causes bolt lift to become hard and case extraction to be difficult as the brass starts to flow into places not intended.


All 50 fired cases showed some variation and none were exactly concentric.

Forgot to mention that I bought the rifle new.
Tikka T3
(action is the smoothest I have ever worked)