Head space issue?

[F. Guffey]

Is a micrometer to measure round objects.

I can not find the question mark, if I take liberties I could add the word 'there' between 'is' and 'a' to make it "is there a micrometer to measure round objects"?

The answer is Yes, I have close to 20 bladed micrometers, the best tools for measuring something round , in my opinion' is home made.

F. Guffey

[Jwilson904]

Originally Posted by tobnpr

Missed something, somewhere...
You've owned the rifle for 20 something years...just getting around to shooting it? Or did this issue just suddenly manifest itself?

Did the smith check longitudinal clearance on the bolt nose recess?
I'm thinking that if this were cut too deeply (much more than fifteen thousandths clearance or so) you'd have too much unsupported casehead hanging out there resulting in separations despite correct headspace.

Only shot factory ammo in it for the first 17 years and never even looked at a spent case. Got into reloading for it and three cases have split on the 2nd firing. Then I bought new Norma cases and they show sighns of case failer after one firing.

[Unclenick]

Your measurements looked OK. The .307" reading on the bullet is probably actually 0.308, but your caliper jaws flexed. 4V50 Gary's suggestion to use a micrometer instead of a caliper for diameter measurements is sound. Even the cheapies are good enough for hand loading purposes. CDCO Tools has one for $17 with carbide faces, ratchet and tenths of a thousandth resolution. Just remember to wipe the anvils and close them to zero the thing to look for any offset you need to add or subtract from the final reading. Usually, due to temperature expansion, there are a couple of tenths or so.

Did you experience any resistance to chambering with the reloads?

Edit:

One more question: Are you applying any kind of crimp? If so, try some of your lower loads with no crimp. I'm trying to think of some way the cases could be distorted during reloading.

[Jwilson904]

No resistance chambering. I did put a good crimp on them with a lee factory crimp die.

[tobnpr]

Check bolt nose clearance.
Wire solder/Plastigage held on the bolt nose w/grease, cam the bolt over onto the barrel breech.
Pull/measure to determine clearance.
I still think you may be dealing with a case that's unsupported above the casehead causing the split case right at the location where the web thins.

This could have been a factory defect, with factory ammo stretching excessively at the casehead on the first firing but not enough to split. I do not agree with the smith attributing to overpressure when there are no other signs (flattened primers, hard extraction) that would manifest.

[Jwilson904]

Originally Posted by tobnpr

Check bolt nose clearance.
Wire solder/Plastigage held on the bolt nose w/grease, cam the bolt over onto the barrel breech.
Pull/measure to determine clearance.
I still think you may be dealing with a case that's unsupported above the casehead causing the split case right at the location where the web thins.

This could have been a factory defect, with factory ammo stretching excessively at the casehead on the first firing but not enough to split. I do not agree with the smith attributing to overpressure when there are no other signs (flattened primers, hard extraction) that would manifest.

I am lost here ?

[mehavey]

I'm begiiiiiiiiining to smell unsupported/overly-large case head/diameter clearance at the rear of the chamber.

What is the before/after diameter of the case just at the web start?

[Jwilson904]

.464 unfired
.469 fired

[mehavey]

Doing the math, the means the case has stretched 16 thousandths circumferencially right at the web inteface.

UncleNick: Your thoughts?

[4V50 Gary]

My bad. I meant to type, "Use a micrometer to measure round objects."

[Jwilson904]

Originally Posted by 4V50 Gary

My bad. I meant to type, "Use a micrometer to measure round objects."

I just ordered one.

[F. Guffey]

Doing the math, the means the case has stretched 16 thousandths circumferencially right at the web inteface.

UncleNick: Your thoughts?

If he did not measure before and again after, circumferentially? I would suggest we stick to diameters. Unless someone has reinvented the procedure the normal case head increase in diameter is .00025" for factory ammo.

.464 unfired- .469 fired

the difference in the two diameter measurements is .005". Before we move on to 'circumferentially' we need to understand case head expansion. If normal is .00025" .005" is 25 x normal, that is scary. If the measurements are accurate there is a 'big' chance the case head separation is expected.

In the sequence of events the case body locks onto the chamber walls. After that comes the argument about the firing pin and case getting into a race for the front of the chamber. If when the case locks onto the chamber wall and the clearance is between the bolt face and case head there is not much of a problem if the case head increases in diameter .00025" (however) if the case head increases in diameter .005" and the case body is locked onto the chamber the case head starts to separate from the case body.

And then there has to be an explanation: The case head is crushed, when the case head crushes it gets shorter from the cup above the web to the case head.

I have tested receivers that were sold to me as being suspect; I will tell you an increase of .005" in the diameter of the case head is an adequate test load.

After that? I measure case head protrusion from the chamber. I am not the one that suggest forum members purchases a bucket of bolts hoping one will off set the length of the chamber to reduce head space.

F. Guffey

[F. Guffey]

I know; Federal cases are soft, so I am told.

F. Guffey

[Unclenick]

According to SAAMI, the minimum chamber diameter 0.200" in front of the head is 0.4708". He is not wider than that, so we could expect it to be that wide over the pressure ring. The question is whether the head itself is actually that big, and I can't tell from the photos that include the caliper exactly where it is landing.

Let's get a difference.

Jwilson, can you use the thinner tips of your caliper jaws to pick up diameters at the two locations shown below? Use your thumb and index finger to close the jaws by pinching them closed. This is less prone to causing flexing of the jaw at its beam way, where the measurement is made. You want to wipe off the jaws and pinch them for setting zero first, to keep everything on the same basis.

The idea is to get the head just immediately in front of the extractor groove relief angle and just at or immediately above where the crack forms (find the widest diameter, wherever that is without including brass actually blown open into a crack).




What Tobnpr is suggesting is getting a plastic gauging material behind a case or, if you have one, a 30-06 GO gauge. When you close the bolt on it that will thin it to the thickness needed to push the shoulder of the gauge or case all the way against the shoulder of the chamber. When you remove it, then it will retain that thickness so you can measure it with your caliper or, better yet, your new micrometer. This thickness will be the extra headspace that exists beyond the length needed by the case. It should be within about a thousandth or two of the difference you get with the case comparator when you measure new brass before and after, but it doesn't spring back, as brass does, so it's a little more precise. The best way to get this is using a GO gauge, so you get an exact number. A GO gauge is also something you can zero your case comparator on to get absolute difference measurements.

One other thing it occurs to me to check is if your bolt lugs are making even contact with the receiver lugs. Color the rear surfaces of the bolt lugs with a Magic Marker and open and close the bolt a few times to see if that marks both of them equally. If it only marks on, then the gun will have a pressure threshold above which it pushes the metal back into contact on both sides. This has the same effect as growing the chamber a little. It's not very likely to be enough distance to cause the problem, but worth checking. Some commercial ammunition is not loaded to very high pressures, and the difference between your pressure and theirs could still have an effect.

Let us know if not-crimping seems to make any difference.

[tobnpr]

^^^
Bolt nose recess for the M700. One of the "three rings of steel" as they say...recessed boltface, barrel surrounds the bolt shroud. Take a look at your bolt...
Note that you can have correct headspace (clearance between case/boltface), but if the recess for the bolt nose that extends into the breech was cut too deeply, the thin case wall ahead of the thicker casehead area could be exposed...and that thin brass is incapable of containing the 60,000 psi.

Putting P!astigage or solder on the NOSE of the bolt- not the boltface- will gauge the clearance that exists.

[BumbleBug]

JWilsom904, please take this information for what it is worth. I had a similar problem some 40 years ago with a brand new Rem 700 ADL .270. It would create a weak yellow line right where your pictures show when firing factory ammo. Subsequent reloads would crack & leak on the 2nd or 3rd firing, even with light loads. I took it to the local gunsmith & he said he found nothing wrong but because of the scoring from the leaking cases he polished the chamber. Fixed! No more problems. Don't know why but it worked.

My theory is the rough chamber caused the case to expand unevenly causing the case to stretch just like if the headspace was off.

[Jwilson904]

Originally Posted by Unclenick

According to SAAMI, the minimum chamber diameter 0.200" in front of the head is 0.4708". He is not wider than that, so we could expect it to be that wide over the pressure ring. The question is whether the head itself is actually that big, and I can't tell from the photos that include the caliper exactly where it is landing.

Let's get a difference.

Jwilson, can you use the thinner tips of your caliper jaws to pick up diameters at the two locations shown below? Use your thumb and index finger to close the jaws by pinching them closed. This is less prone to causing flexing of the jaw at its beam way, where the measurement is made. You want to wipe off the jaws and pinch them for setting zero first, to keep everything on the same basis.

The idea is to get the head just immediately in front of the extractor groove relief angle and just at or immediately above where the crack forms (find the widest diameter, wherever that is without including brass actually blown open into a crack).




What Tobnpr is suggesting is getting a plastic gauging material behind a case or, if you have one, a 30-06 GO gauge. When you close the bolt on it that will thin it to the thickness needed to push the shoulder of the gauge or case all the way against the shoulder of the chamber. When you remove it, then it will retain that thickness so you can measure it with your caliper or, better yet, your new micrometer. This thickness will be the extra headspace that exists beyond the length needed by the case. It should be within about a thousandth or two of the difference you get with the case comparator when you measure new brass before and after, but it doesn't spring back, as brass does, so it's a little more precise. The best way to get this is using a GO gauge, so you get an exact number. A GO gauge is also something you can zero your case comparator on to get absolute difference measurements.

One other thing it occurs to me to check is if your bolt lugs are making even contact with the receiver lugs. Color the rear surfaces of the bolt lugs with a Magic Marker and open and close the bolt a few times to see if that marks both of them equally. If it only marks on, then the gun will have a pressure threshold above which it pushes the metal back into contact on both sides. This has the same effect as growing the chamber a little. It's not very likely to be enough distance to cause the problem, but worth checking. Some commercial ammunition is not loaded to very high pressures, and the difference between your pressure and theirs could still have an effect.

Let us know if not-crimping seems to make any difference.

Fired case close to the extractor groove.467
Just past the web .468 little5

Unfired case .466 close to thr exractor groove
.465 just past the web


Only one lug rubs the marker off and the other does not.

[F. Guffey]

Note that you can have correct headspace (clearance between case/boltface), but if the recess for the bolt nose that extends into the breech was cut too deeply, the thin case wall ahead of the thicker casehead area could be exposed...and that thin brass is incapable of containing the 60,000 psi.

There is no part of the case that is exposed by the recess or bolt nose. The only part of the case that is exposed is the case head protrusion or unsupported case head.

F. Guffey

[F. Guffey]

The question is whether the head itself is actually that big, and I can't tell from the photos that include the caliper exactly where it is landing.

There was a time I though reloaders could invert the case and then stick the case head into the die backwards; and now? Not so much.

I have never thought a small base die had a small base because of the shell holder. Shell holder deck height is .125" meaning nothing above the case from the case head up to .125" from the case head gets sized and then there is the radius. Back to the increase in diameter of the case head, If the case head expands it did not stretch is has been crushed.

F. Guffey

[tobnpr]

There is no part of the case that is exposed by the recess or bolt nose. The only part of the case that is exposed is the case head protrusion or unsupported case head.

There absolutely would be, IF the bolt nose recess were counterbored too deeply- which is what I said....

[Unclenick]

Jwilson904,

Since you have just one lug making contact, you will want to consider having the lugs lapped to get uniform contact. It improves accuracy and prevents the stretching effect I described. Headspace would have to be reassessed afterward. It does not explain why commercial ammo fires OK unless it is just extra low-pressure loads. Commercial ammunition makers typically have a target velocity they want to reach without exceeded SAAMI pressure limits, and some modern slow powders can get them there with very modest peak pressure. You might also want to look at polishing as BumbleBug reported.


BumbleBug,

When you polish the chamber, and the last half to one inch, in particular, the brass slips against it more easily. This allows the area that stretches (the pressure ring) when pressure forces the case head back against the bolt face to be spread out over a greater length of the brass, resulting in it being less thin. Varmint Al has some good animations of this as analyzed by finite element modeling.

[F. Guffey]

There absolutely would be, IF the bolt nose recess were counterbored too deeply- which is what I said....

I understand what you said, I do not believe you do. The protruding case can prevent the bolt from closing if the case length of the case from the datum/ shoulder to the case head the case head is greater in length than the length of the chamber from the shoulder/datum to the bolt face.

The chamber supports the case, and the only part of the case that is exposed is the case head. The bolt nose is not part of the chamber; the counter sink is not part of the chamber.

F. Guffey

[F. Guffey]

When you polish the chamber, and the last half to one inch, in particular, the brass slips against it more easily.

I am not the fan of the cross hatch; when I look through the bore I want to see definition as a perfect reflection of the rifling on the chamber walls. There is something that makes sense about 100% contact. I want 100% contact between the chamber and the case.

100% hold is all I can get.

F. Guffey

[F. Guffey]

Note that you can have correct headspace (clearance between case/boltface), but if the recess for the bolt nose that extends into the breech was cut too deeply, the thin case wall ahead of the thicker casehead area could be exposed...and that thin brass is incapable of containing the 60,000 psi.

Where is the thin case wall exposed? The case is supported by the chamber and again; the only part of the case that is exposed is the case head.

F. Guffey

[F. Guffey]

But I do, Guffey.
You don't have a damn clue, you just like to argue.

How many M700's have you chambered? Any?

I do not understand where the anger comes from, you seam to be having trouble answering the question and you fail to understand the bolt nose is not part of the chamber. I would find no advantage to a deep counter sink for the bolt nose, I would find a disadvantage to one that had little to no clearance in front of the nose because of dirt, grit and grime buildup.

The one thing I would not want is a bolt nose with zero clearance, that would create a conflict between the closing the bolt and the bolt nose holding the bolt off the lugs.

I do believe someone should say something about the gas handling characteristics of the Remington. For many years reloaders were singing the praise of the strongest rifle in the world. And then it got better; an article was written about a smith? that chambered the 6.5MM50 to 30/06 and that was it; he stuck a 30/06 reamer into the chamber and started reaming. He chambered 30/06 ammo into the 6.5 barrel and puled the trigger. I said forget the rifle, give me those cases.

F. Guffey