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Re: copper fouling

26 Dec 2011
@ 07:53 am (GMT)

Nathan Foster

Hi Tim, the front king screw should definitely not be bottoming out. This may well be the cause of your wide fliers.

You have two choices, either grind 40 thou / 1mm of the king screw and re-chamfer it, or if you want to re-bed the rifle, you can use the fresh bedding to lift the action up a tad and create the clearance needed. To determine whether this may be beneficial, check the current bedding to see how well it is adhering to the stock. Typically, the Browning and Winchester bolt action rifles have been given a squirt/blob from a hot glue gun in the area of the recoil lug. The stock is not keyed into or prepared in any way. Over time, cleaning solvents and oils attack this weak layer and accuracy is lost, usually at the most inconvenient of times. So check the bedding carefully with each dis-assembly / reassembly.

The bore may well be slightly oversize or, a more common occurrence of late is button chatter marks within the bore, resembling what looks like the threads of a bolt. This is caused by vibrations during the buttoning process and can be as a result of the use of inferior lubricants along with a host of possibles. The peaks of the chatter marks will be within tolerence, the troughs being over size. The projectile then rides on the peaks, obtaining very good accuracy without fouling while pressures remain very low. However; after a period of time and wear, as the peaks of the chatter marks are worn down, groups open right up. This is very common on Savage rifles and is, as of 2011, something I am seeing within Japanese bores.

On the other hand, the over all tolerneces may well be loose, it is hard for me to determine without having the rifle here.

The 44.5gr charge is usually fine in U.S made .308 rifles but not so for the Brownings as these are usually machined to tighter specs, the sweet spot being around 43 grains for 2670-2700fps (22" barrel). So there is definitely an element of lower than normal pressures there somewhere.

For now, I think we need a step by step plan of attack. What I would like you to do, is grind the king screw back a touch, just enough to relieve it. Try it at the range and see how it goes. The rifle may well settle right down. Better to do it this way than to go through the hassle of a proper bedding job, then find the bore has a problem.

When cleaning the rifle, I want you to listen for a whistling sound when using either a ram rod or pull though. If you hear this sound (also sounds like running your fingers across a pitched tent), the bore has chatter marks and the bullet will indeed be riding on peaks.

Merry Christmas, Nathan.


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