I came across another thread on the m70 375's wherein the owner stated that his rifle would not easily chamber once-fired brass. I have seen this with many rifles, including my 375. some, not all, of the brass will get tight with about 1/4 inch of bolt to go. After marking the case with sharpie, I do see some drag marks. I do remember firing these particular rounds and I experienced no problems with extraction. The chamber looks good, unlike some other M70's I have seen (frosted looking) so.. am at a loss. Can anyone help a moron like me to fully understand how this is happening? Must be a relatively simple answer, but the old noggin isn't coming up with the answer.

Thanks,
BAxter

Your chamber might be out of round or possibly have a headspace problem [for lack of a better term] where maybe one of the bolt lugs is not in full contact and upon firing the back of the case flexes, ie stretches in that direction.

Try this. Next time you go to the range mark your cases with a Sharpie. Chamber the rounds with this mark at 12 o'clock, and fire them.

Shoot several rounds in this manner.

Then see if the once fired cases go back into the chamber with this mark at 12 o,clock.
Then rotate the mark around as you try to rechamber the once fired cases.

Let us know what happens.

I don't know except that I find that normal for my (slight) over max hand loads. IE where I back off.

I guess what happens is the cam action on unlocking the bolt helps the case back out, but on rechambering it's all push and not so easily done.

search this forum using the terms "resizing 375"

I am not saying this is your particular problem, but a known issue with belted rounds is they have a problem getting resized next to the belt. Checking resized brass with a micrometer will help confirm this.

NE 450, you may be on to the issue... I put spome poor man's lamp black on the back of the lugs and cycles it to see what the contact area looked like. Not good...



On this pic, you can see that just the corner is rubbed off. Don;t be misled by the shiney arc across the full length of it, that's just the chamfer.



On this one, you can see a short of hockey stick shaped shiney part, right next to the barrel of the bolt and then right at the corner of the lug.

Looks like I need to get me to a smithy...

Whaddya think?

How is this resolved as it would seem to polish the lugs would make them even further away from the mating surface?

_Baxter

I have tried several times to cut an egged shape chamber and just can't do it. Pray tell how this can be done.
Butch

Butch
To cut an egg shaped chamber one must have a elliptical chamber reamer. These are rare and special reamers rumored to be possessed only by one named "Bubba" They can only used on special lathes that have "semi-conical" bearings. We mere lowly gunsmiths will never be privy to the exclusive knowledge required to produce these chambers.

quote:

Originally posted by butchlambert:
I have tried several times to cut an egged shape chamber and just can't do it. Pray tell how this can be done.
Butch

I think you can do it in two sloppy setups or by hand. Otherwise all misalignment gets you is an oversize chamber.
I have a 45-70 that has about 16 sides probably due to cutting too fast with an 8 flute reamer in an 8 flute barrel.

quote:

How is this resolved as it would seem to polish the lugs would make them even further away from the mating surface?

Its resolved, if necessary, by turning in the barrel a few thousanths.

I wouldn't rely on so called "poor man's lamp black" though. The smiths I have seen do this work mostly use a product called Dykem blue or Dykem Red.

quote:

Originally posted by butchlambert:
I have tried several times to cut an egged shape chamber and just can't do it. Pray tell how this can be done.
Butch

This will explain it, Butch. If it is not enough to satisfy your curiosity, I can provide additional links...

http://www.mmsonline.com/articles/060101.html

Best wishes,

AC

quote:

Originally posted by butchlambert:
I have tried several times to cut an egged shape chamber and just can't do it. Pray tell how this can be done.
Butch

Butch
You need more practice with your cordless B&D reamer driver . I can also see it happening quite easily when using a "pull through" type reamer.
IOW with the barrel fixed and the reamer spinning but able to "wander" in it's rear support.

quote:

Originally posted by butchlambert:
I have tried several times to cut an egged shape chamber and just can't do it. Pray tell how this can be done.
Butch

Too many RPMs and not enough pressure will cause all kinds of chatter and often a multi-sided "hole".
I always run reamers slow-even carbide, use lots of oil, steady pressure, and disengage the chuck towards the end and almost come to stop but not quite.
Proper use of an indicator helps too.
Andy

quote:

Originally posted by butchlambert:
I have tried several times to cut an egged shape chamber and just can't do it. Pray tell how this can be done.

Actually, it can be as simple as screwing a fine Concentric Chambered barrel into a receiver that is not "Round".

Look at the end of a M700 action and at the end of any other action that is not Round, like Baxter's M70. As the barrel is screwed in, the Stress is not Concentric on the barrel and causes it to deform a minute amount.

Out of round or non-concentric only takes a few tenthousandths(0.0002 - 0.0003) to create what Baxter or anyone else finds.

Getting a Concentric Chamber "illusion" can also be created by the specific Lot of Cases being Thinner along one side. That will cause uneven Stretching and Contraction as the Case is fired. This is as common as finding a democrat who thinks raising TAXES is a great idea.
-----

I've only had a very few Rifle/Case combinations over the years where the Case comes out perfectly Concentric to 0.0001". I have one right now and it is indeed a fine shooter. But that is also true for others that are not perfectly concentric.