Proper way tp measure

What is the right way to meassure a chamber's demensions? Should I remove the barrel and take it to a GS or do it myself?
As some of you know I am having problems with a 308win. and have had many recomendations on what to do,and most were/have been done, from stock changes(3) to different powders,different bullets,I even tried a different front rest and a different shooter,4 different scopes to no avail.
Now it is time to change directions and see if maybe the chamber was cut out of specs.I know that seating a 155 grn. bullet into the rifling gives me a coal meassurment of 3.133.,is this too long.I know the book calls for a COAL of 2.770-2.080 thats a 0.360 difference. I usually back off .020-.025 off the rifling so backing off over 0.300 seems a little extreme.
Anyone else think the chamber may be the problem with this gun? Or am I going in the wrong direction?

If you want to do this,then get yourself some creosafe(spelling)
And make a chamber cast to see what you have...Maybe it's not
even a 308....good luck...this stuff works great....John

It's called "Cerrosafe."

Read post #4 in this thread (http://www.saubier.com/forum/showthread.php?t=8358) for some tips.
The process does not look too difficult and it may allow you to resolve this.
Disclaimer: I've never used Cerrosafe, so my opinion is not based on experience.

The total COAL from shell base to bullet tip is 2.810" in Lee's 2nd ed.
3.133" seems like an extremely long way. 3.133-2.810=.323", that's more than 5/16 of an inch longer than SAAMI?

rjtfroggy, I agree with skypilot.

I would recommend you load some rounds so the COAL (Cartridge Overall Length from base of brass to tip of bullet) meets SAAMI specifications. So what if the "jump" is .035 or .040? Most factory rounds are assembled to this length and those rounds shoot pretty well in most rifles. If your rifle shoots well with this much "jump" do some fine tuning to seating depth before you start switching barrels or measuring chambers. The fix you are seeking might be simpler than you imagine.

Good luck.

John I believe you are reading the figures incorrectly. I could live with a 0.040 jump, but the jump in mine will be closer to 0.360 not 0.035 big difference.

Quote:

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Originally Posted by rjtfroggy

What is the right way to meassure a chamber's demensions? Should I remove the barrel and take it to a GS or do it myself?
As some of you know I am having problems with a 308win. and have had many recomendations on what to do,and most were/have been done, from stock changes(3) to different powders,different bullets,I even tried a different front rest and a different shooter,4 different scopes to no avail.
Now it is time to change directions and see if maybe the chamber was cut out of specs.I know that seating a 155 grn. bullet into the rifling gives me a coal meassurment of 3.133.,is this too long.I know the book calls for a COAL of 2.770-2.080 thats a 0.360 difference. I usually back off .020-.025 off the rifling so backing off over 0.300 seems a little extreme.
Anyone else think the chamber may be the problem with this gun? Or am I going in the wrong direction?

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I think you have some incorrect numbers on that length. If you are measuring it with a Hornady or Stoney point tool, there is a very good chance that the modified case has a larger neck than is in the chamber,not letting it chamber all the way, giving you a false reading. That extra .360" is approx the length of the neck.
I just cut a barrel stub with my reamer and seated a 155 Sierra to touch the lands and the overall length is 2.795".
I find that most barrels with this chamber shoot the best with .040" jump.

I still say MAKE a chamber cast to see for sure...It is fairly easy to do or have someone help you with.

Like I said it is the only way your gonna know for sure what you have there....Why waste more time on it until you
know FOR SURE...

Quote:

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Originally Posted by acemisser

I still say MAKE a chamber cast to see for sure...It is fairly easy to do or have someone help you with.

Like I said it is the only way your gonna know for sure what you have there....Why waste more time on it until you
know FOR SURE...

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I do know for SURE...I chambered it.

Thank you Fred. I am going to order a Sinclair tool later this morning, I didn't like the Hornady(borrowed it).
I've been loading to these dimensions and I am thinking this is the problem.I will check in the mean time the old fashion way by inserting bullet in case then chambering and gently remove and meassure.

whatever you say...lol have a good one

RJ, I didn't like the Hornady set up either and now use the Sinclair and also their comparator. Let us know what you find.

Ordered the Sinclair tool and it has already shipped so maybe by the end of the week I will have at least one answer.
I'll post up the results.

After many many meassurement with the Sinclair tool and by the old fashion way I have found so many different lengths that I think I am either doing something wrong or the chamber isn't right. The closest I can come to Fred's 2.795 is 3.088 with a fl sized case for a 0.293 difference.
So no more playing with this barrel I will contact NSS once things settle down after my mother in laws funeral tomorrow.
Might just scrap the 308 target gun all together and go with the 243 or save some $$$ and start using my 260.

Back to top for an update.

RJ are you confusing a chamber dimension measurement with a SAAMI standard cartridge measurement? For example you measure 3.088 total overall cartridge length base to tip using the Sinclair tool. This was to find the total length of an assembled cartridge/bullet combo that would touch the lands in your chamber. The reload manual, Lee 2nd edition list SAAMI length @2.810. That 2.810 is so any and all .308 factory ammo @ 2.810" will fit in any .308 auto, lever or bolt gun.


You however are looking to load a cartridge to the length that custom fits your chamber as far as length. So think about this. Any factory .308 cartridge you can buy will not exceed the SAAMI length of 2.810" and will physically fit in your chamber. However you wish to custom assemble a cartridge that will be a custom length based on your chamber and your freebore and the lands as a reference.


I would think about loading to your chamber dimensions and at the jam or jump you wanted, with the obvious thought of possible pressure issues(being near the lands) and magazine interference length.
Hope this helps.

I will inject my 2 cents. If you are getting different measurements then something is wrong with what you are doing or your tools. I mean a .002 or .003 difference is fine, but if your difference is in the .1 or close there is something wrong. Take it to a local smith and let him measure it. Im sure you have spent more money by now than what a professional smith would have charged you (good thing is now you have those tools for future ref). They do this very often and are familiar with the process. Good piece of mind...