The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > The Smithy

Reply
 
Thread Tools
Old February 14, 2009, 12:20 PM   #1
Quadra
Junior Member
 
Join Date: December 28, 2008
Posts: 7
go no-go gauges in 6.5x55

I've been having trouble chambering once fired Lapua brass that have been both neck sized and fl resized in a new to me Krico 600 match rifle. I thought that it might be a tight chamber so I purchased clymer gauges for this caliber. The go gauge passed as did the no-go gauge. The no-go gauge is .004" bigger than SAAMI minimum chamber dimension for this caliber. The SAAMI website acknowledges that there is a difference between their min/max chamber dimensions and those of the European standard as dictated by CIP. From what I understand about the manufacturing process armsmakers must chamber their products to fall somewhere in between the mandated dimension to conform, not to a specified exact dimension. If my rifle as delivered from the factory had a chamber dimension that was not of minimum length and yet still conformed to the tolerance specification set out by CIP the only thing that the no-go gauge is telling me is that the bolt is closing on a gauge of that particular dimension. If it were a field gauge (I'm purchasing one)then obviously I know what I would need to do. The 6.5x55 cartidge case is manufactured by Lapua and Norma to the correct maximum dimension of .480 while North American brass is held to a maximum dimension of a nominal .473. The dimension of the gauge at the base is approx .473 and yields a sloppy fit in the bolt face as compared to the fit of my lapua brass measuring .478. I realize that these gauges are not measuring that dimension but shouldn't they more closely resemble all of the chambers profile and not just the point from the face of a closed bolt to the datum line on the chambers shoulder? When I close the bolt on a fl resized case it sometimes but not always refuses to go. I repeatedly cycled the action on a snug fitting case and saw a circular pattern lightly inscribed and there a small traces of brass shavings sitting in front of the breechface where the lugs engage. My dies are set a quarter of a turn beyond touching the shellholder and these cases fit two other rifles that I own with no problems. Does anyone familiar with this problem or caliber have any sage advice?
Quadra is offline  
Old February 14, 2009, 10:16 PM   #2
James K
Staff
 
Join Date: March 17, 1999
Posts: 19,979
It sounds like you really have a tight ("target") chamber but if factory rounds fit OK, and it passes the GO gauge, I don't think the rifle is at fault.

I think you have a resizing die that is not resizing quite enough. (Remember, loading dies have their own tolerances, and sometimes the tolerances "stack.")

Try calling the die manufacturer and asking about a tight die or an auto rifle die; the latter are generally smaller because auto rifles often have little seating power.

Jim
__________________
Jim K
James K is offline  
Old February 15, 2009, 12:38 PM   #3
Quadra
Junior Member
 
Join Date: December 28, 2008
Posts: 7
Small base dies

Thanks for the reply on that Jim. I'm going to run some North American factory ammo through it and see the result and then purchase some x-dies to see the end result of their use.
Quadra is offline  
Old February 16, 2009, 05:25 AM   #4
longrifles, Inc
Senior Member
 
Join Date: February 16, 2009
Location: Sturgis, South Dakota
Posts: 152
Lapua brass

First, regarding head space gauges and not fitting as tight at you'd like.

There's a reason for this. No single tool maker who caters to the gun industry has control over what other tool makers do or the tolerances they run.

To better put this in perspective, there's at least a dozen different 308 Winchester variants that all headspace off the same gauge, yet all have different dimensions.

Say your Clymer gauge was a 308 built for a SAAMI plain jane chamber and i built to a more resemble a piece of brass. Your attempting to check a minimum SAAMI chamber 308 variant and when you attempt to close the bolt the gauge seizes in the chamber ruining the gauge and requiring you to get out the cleaning rod to pound it back out. Once you remove it you see a nice ring/gall mark in your chamber.

Not cool.

This is why the gauge is purposely made undersize from the nominal chamber diameters. Otherwise you'd need a gauge specific to every reamer out there. That's not realistic and it'll lead to gunsmiths head spacing chambers with the wrong gauge. It's awfully easy to screw up now as it is and requires a guy to be very diligent and careful when setting up a chamber.


Now, for your problem.

Lapua brass, awesome stuff. I use it exclusively in my rifles. A while back I started noticing little shiny rings on my bolts and stuff. When I made the switch from Norma to Lapua brass on my 338LM I had to modify the bolt and extractor some to get it to work right. (Nesika action)

So what gives I wondered. I learned that Lapua brass runs toward the big end of the tolerance spectrum in a lot of their cartridges. If you have a chamber or a bolt face that is on the conservative side of the tolerance limit then its very possible to have issues.

I had to open my bolt face an additional .010" and whittle on the extractor in order to get mine to work right. I never had to do with with Norma brass.

My 6mmBR 300 meter free rifle also uses Lapua brass and every once in awhile I get a case that is a little fussy. It's not often but it does happen.
As with anything else, when you get to one extreme or another, the whole package has to be taken to the next level if you expect everything to work right.

Good luck

Chad
longrifles, Inc is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 12:26 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.06938 seconds with 9 queries