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A customer dropped off a gorgeous Ruger M77 chambered in .338 Win Mag and claimed it was having issues extracting. They suspected the extractor might need replacing, as it would not even extract an unfired case from the chamber. They also suspected there could be trouble with the chamber.

Bore scoping the chamber did reveal some rough areas around the throat, but nothing alarming. I decided to tackle the issue of unfired rounds not extracting first. The extractor looked like it had been polished at some point, but it was still grabbing cases with the bolt removed from the rifle. With the bolt installed, sure enough, a live round would not extract and would simply fall out under its own weight.

I marked up the rim of a case with some Sharpie and chambered it. After removal I checked where the Sharpie was rubbed off. It looked as if the extractor was not quite making it far enough to get over the rim of the case. I begun to suspect headspace.

The problem was, I did not have any gauges on hand for .338 Win Mag. I called PT&G and they did not have any on the shelf. In the interest of getting the customer a quick answer, I decided to make my own.

I looked up the SAAMI spec for the chamber dimensions. On these belted cartridges, the headspace is not contrlled by the shoulder. Rather, it is the dimension from the case head to the front of the belt. .338 Win Mag has a max headspace of .227". I drew up a quick sketch using dimensions from the chamber and the cartridge spec, and then fired up the lathe. Finished product measures .277" and change. What's a few tenths among friends?

Now was the moment of truth. And sure enough, the rifle swallows the gauge. Curious, I decided to make a slightly more field expedient gauge. I took an unfired cartridge and began building up layers of tape on the case head. I admittedly lost count after 5 layers. It was around 7 or 8 that the bolt finally had trouble closing. Each layer of tape is around .004" thick. The case I was using had a headspace measuring roughly .220. The math works out that the rifle has a headspace approximately .020" over spec.

I am still waiting on a response from the customer on where he'd like to go from here. My hope is that he approves turning the shoulder back on the original barrel and rechambering it. I would obviously order some "real" headspace gauges before doing so.

Standby.

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How does a hunting rifle gain that much headspace? I would expect the bore to be worn smooth first.

I wonder it that is the original barrel. Maybe someone decided they wanted a 338 instead of a smaller cartridge, then screwed on a takeoff barrel.

Instead of tape, an idea you might try when checking very excessive headspace like this is to drill a primer-sized hole through your homemade gauge, then partially seat a fired primer. Chamber and extract it, measure the primer protrusion, and add that to the headspace of the gauge.

Or you could thread the hole for a machine screw and have an adjustable no-go to +field+ gauge. :)

Bruce
 
Has the customer contacted Ruger? Who knows if they still service a vintage rifle? If it's not modded, I would think that Ruger might want to correct it.
I will make sure Ruger is contacted before doing any more work. I am not optimistic they will fix it, for a number of reasons.
 
Is the receiver or bolt messed up at the lugs and causing the excessive headspace? Maybe someone did some serious bolt lug lapping or have been running their super velocity buddies loads through it.
 
Conclusion:

Ruger would not cover a repair, so the customer opted to have the barrel reworked. Before work was started, headspace was verified to be long with a set of Clymer gages.

Removing the action from the stock revealed the first clue as to why the headspace went out: there was a crude witness mark at the 6 o'clock position on the barrel.

As the barrel was removed, the second clue was revealed. The barrel was barely past hand tight. Single digit ft/lbs. It would appear this rifle was rebarreled at some point, and some details were overlooked.

I dialed in the barrel on the lathe and took off 1/16 of an inch from the breech face and tbe shoulder (16 TPI threads). I then picked up the old threads with the single point tool and chased them up to the new shoulder.

The barrel was re-timed in the receiver, and then the chamber reamed by hand. The rifle now extracts with ease.

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My concern would be with that headspace issue is going to continue. Setting the barrel back is a temporary fix. It would be interesting to know why the headspace increased so much. Just a thought.
 

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