Chamber Dimensions

[Edd]

Bottom line - I'm going back to my smith and ask him to push the reamer in another 0.030" or so. Whatever SAAMI says or doesn't, that should fix the issue.

Unless you move the barrel back, that won't fix it. That will create another issue in addition to the one you already have.

How did you find a Gunsmith that doesn't know how to chamber a barrel? Seems like there is still more to the story.

 

[Engineering101]

bigngreen

I don't get what you are saying at all. Seems to me if I push the reamer in another 0.030" the case will be further into the barrel over all (giving it more support). This will require threading the shank so it can be screwed into the action 0.030" further to reset the headspace. This should achieve what I'm after.

 

[Engineering101]

bigngreen

Here is a pic of the 26 Nosler case that was subjected to extreme pressure.

 

[IdahoCTD]

How far is it from the "belted" portion to the case head? In most rifles I've dealt with the measurement would be .175" or less. What your concerned with is the gap between the back of the chamber and the front edge of the bolt. If that distance isn't excessive, like over .020", then running the reamer in further won't do a thing except create excessive headspace. Your case looks like it's longer than .175" but that is just a guess. In reality, if you expanded a case that much you could have permanently deformed the barrel provided the barrel tenon is correct.

 

[Edd]

I have a new barreled action that isn't screwed together. It is chambered for that same size case. All bolts won't be the same but mine is for a BAT HR action. I just measured it. There is .145" of the case sticking out of the barrel.

 

[Engineering101]

Edd

Thanks for the info. As I mentioned mine is 0.273" which compared to yours is a bit too much.

 

[LONGSHOOTER]

You mentioned that head space is correct. How did you determine this?

 

[Engineering101]

Pacific Tool and Gage go and no-go gages were used to verify headspace.

 

[Edd]

You have a picture of the front of your bolt?

 

[Engineering101]

Edd

I don't have a picture of the bolt but it is just a standard Sako magnum bolt face with Sako extractor and an ejector cuts. The recess is 0.094" deep so the case has to stick out at least that far from the chamber or the bolt would hit the barrel.

If you look at the back of the barrel as it fits in the action, you can see there is about 0.2" of unused treads. On my other Sakos those threads are used and the cases fit much further into the chamber. My smith just screwed this up. Now that I recall he lost the piece of brass I gave him to use for setup.

 

[IdahoCTD]

It wouldn't have anything to do with using a piece of brass for set up. When you set up to cut the tenon you have to take measurements from the front of the action to the bolt nose and/or lugs to determine the length the tenon needs to be. In your case the gunsmith should have measured to the front of the lugs, used the shorter of the 2 measurements, and then subtracted his clearance. For me that would be .010" to .020" depending on what the rifle was used for. If the bolt face recess is only .094" deep and you add a max of .020" the cases should stick out of the barrel less than .114" (a full sized case would be a few thousandths less). The barrel needs to be set back about .160", if your .270+" protrusion measurement is correct, and the reamer run in to the proper headspace again. If those measurements are correct it's pretty amazing you haven't ruptured a case. I guess the Nosler cases are made pretty tough.

Here is a link to a picture of a Sako L61R bolt.

http://www.google.com/url?sa=i&rct=...yEXMYfSdRzhT3tDEv_bt2IQQ&ust=1423261831160719

 

[Engineering101]

IdahoCTD

Good info. Thank you.

 

[bigngreen]

The case "belt" from stretching occurs 0.273" from the bolt face which, just eyeballing the case, seems like a bit too much to leave unsupported. (Those of you who have a 26 Nosler - how far from the bolt face does your chamber end?)

At this point I should probably fess up that I have been "stretching" the truth a little (pun intended). The case that has the "belt" was one where the load detonated on me (due to little IMR7828SSC used) and I had to pound the bolt open with a hammer.

To say it was proof tested might be an understatement. Nevertheless it did bring this issue to light. This stretching also occurs but to a much lesser extent with "hot" loads as well. If I used my normal hunting load (140 grain Accubond at 3,300 fsp) I can't see stretching with the naked eye though you can see where the chamber ends as the case is still squished against the chamber walls and that leaves a "finish" on the case.

If you take all this and the picture to me your just running way hot and almost had a case head separation on a 80,000 psi load. Your case web is roughly .287 from the base of the case where your belt or separation starts, I suspect your case head looks like a belt because the body of the case has spring back, your case head does not and it's now been blow out to chamber diameter.

I measured a correctly headspaced and chambered RUM, I can see and measure the case web .287 from the base at .550, the case head behind this measures .547, it is not supported by the chamber nor should it be or it'll cause issues with chambering the round and extraction. Cases are not supposed to be supported by the chamber from the case web back so you end up with, in my RUM case with .287 unsupported case which better than .100 is inside the chamber.

You still maybe right and it's screwed but technically a normal RUM case head will be unsupported for about .287 even in a normal chamber.

 

[LONGSHOOTER]

B & G might be right. The web is in that location. The detonation might give you results that make you think head space is incorrect.

If it were my gun, I would pull the barrel, check case fit in barrel, barrel distance to breach, check lugs and abutments and barrel while I am at it, because it's open.