This is why you need a muzzle erosion gage.

[Hummer70]

A good friend came by yesterday on the way back to Florida. He bought a new Savage tactical rifle and he had called me and said it wouldn't shoot and I thought that sounded kind of strange and was interested in determining what was wrong. He had already called Savage and they told him to send it in.

He brought me a target that showed groups with all the different ammo that did not look like anything I had ever seen from Savage rifles in new condition.

First I checked the headspace and it was nice and snug like I like it and everything mechanical checked out, scope was tight etc

He had four kinds of ammo with him all match stuff and I took some Fed Match I knew would shoot and some LC Match and we went out back and gave it a run. He had three variations of 168 Match and one 175 Fed Match and it all his groups were 2" plus.

In other words it shot like a light barrel hunting rifle with bullets walking around and only occasionally enlarging holes and while my groups were better than his something was not right and I initially figured bore not broke in. I ran my ammo through it and my groups did not print anywhere near what I knew it should do. The only thing I could figure was it was not broke in yet.

I had just never seen a Savage heavy barrel shoot anywhere near that big.

After shooting I ran the bore scope down and the bore was very impressive. The rifling looked very good and there was evidence of nice even contact of the bullet in the grooves all the way around.

We went back to loading room and cleaned it and I set him up with a rifle log and I took the headspace reading and we recorded that and told him when he came through again drop by and I would give him another reading for his log.

Then it struck me that I have a CMP Muzzle Erosion Gage and thought I would show it to him and I showed him how it worked and I could have dropped my teeth (if they were store bought) when I eased gage in muzzle. It went 2+ ! ! ! ! ! I couldn't believe it and I took it back to shop and fired up the bore scope again for a look at the crown.

Ran the bore scope in the muzzle and noticed there was nice uniform copper deposits up until the last 3/8" inch and there was no copper from there to the muzzle ! ! ! ! ! THERE WAS NO COPPER ON TOP OF THE LANDS OR IN THE GROOVES! ! ! ! !. The bullet was free flying before it left the muzzle! ! ! ! A "2" reading means the top of the lands are .302" and not .300"

I told him not to touch it, pack it up just like that and send it to them with a letter asking them to look at new perfect throat and then have a borescope looksee inside the muzzle.

I wanted to get a pic of both ends of the barrel but it was getting late and they had to hit the road to drive to south Florida. He thinks he has someone down there with a bore scope/camera set up to take the pics before he sends it back. If I get them I will post them as it will be very educational.

I called my friend Bruce Woodford who wrote Fulton Armory FAQ: The Infamous Throat Erosion Gauge He has never heard of a new barrel reading "2".

So now my friend has shot up about 140.00 worth of ammo only to find a bad barrel. If he had bought it used I would have simply chucked it up in lathe and put him a 11 deg crown on it at the last point it showed full bullet contact with the barrel and I am sure it would shoot like it was supposed to then.

Thusly if you are shooting 30 cal you need a muzzle erosion gage

 

[Jim243]

Interesting to know, I am surprised that the barrel got through Savage QC without being rejected, I was under the impression that each barrel goes through the air gauge test before being put on a rifle.

Strange indeed.
Jim

 

[Jerry45]

I wonder if that was the problem with my NEW Remington SPS Tactical. It was doing exactly the same thing. Smith used his bore scope and all looked good. Didn't use an erosion gauge. I had it re-barreled. Maybe someday I'll have someone else check out the original barrel. It's boxed up in the shop. I'll be seeing how the new barrel shoos tomorrow.

 

[Mobuck]

A ME of "2" is quite satisfactory for a military match rifle to still be in the upper end of it's performance. IIRC.
I've seen several Springfields and Mausers that had been freebored back 1/2" from the muzzle to clean up cleaning rod damage that still shot good groups.

 

[Bart B.]

All the 7.62 NATO Garand barrels I wore out had no copper wash for the last 2/3 to 3/4 inch of the bore at about 5000 rounds when accuracy got noticably reduced. They all shot under 1 MOA at 600 at the time but started out better. The solid steel cleaning rod used did its thing lapping away the bore and groove surfaces. But the "belled" muzzle was the same for every shot fired between cleanings. All those M1's used by fellow team members had no copper wash the last several fractions of an inch of the bore depending on the number of rounds fired.

At the USN Small Arms Match Conditioning shop in San Diego, they always used a throat erosion gauge on such barrels and they averaged a "5" reading when accuracy was no longer acceptable. I'm not aware of any 'smith checking barrels with a muzzle gauge, they all knew steel cleaning rods wore the metal away. There was no copper wash for the better part of the last inch of the bore on all the match barrels they replaced.

Most custom barrel makers gauge their work and put a mark on the muzzle end where the bore/groove diameters start to open up 1 or more inches back from the muzzle. That's where the 'smith installing them should cut them off. Gun drilling the blank then reaming and rifling it bells the muzzle end as well as the breech end. Chamber reamers take out the bell at the breech end.

 

[Orlando]

Brand new barrels will not always measure 0, I have seen them up to 1 1/2 and still be accurate