When it becomes harder to get a precise OAL measurement (by whatever your favorite method may be), is it a sign of throat erosion?

I use a Stoney Point tool and in most of my rifles, with a dead clean barrel, I've been able to measure to the lands with 3 bullets from the box; normally 2 of them will be the same, the third will be a thou or two off, and I will go with the ones that agree.

However, I have a .270 that's been giving me fits lately. Last night I tried to measure OAL and went through a dozen or more bullets, getting swings of .030" or more. The tool just didn't have the "crisp" feeling it usually does when the bullet touches the lands.

Anyone?

Maybe try a different brand of bullet with a different ogive. Sounds like the one you're using is hitting the lands right where they are washing out?

Something that you may already be doing but worth mentioning anyway is using a dowl in the barrel to move the bullet back and forth. This really helps me feel the lands better. Also when I use my Stoney Point guage I usually use the same bullet, although there is not going to be much differnce in differnt bullets there could be some.

Good luck

John,
Your problem sounds identical to mine with the Stoney Point OAL gauge. The problem was that the Rem modified case gauge had significant runout (using RCBS Case Master) and cocked the bullet to the side in the chamber during the test. Therefore, it would not give consistent readings depending on which way the case was oriented to the chamber runout. My solution was to full length size the Stoney Point case gauge and pushed a mandrel into the case neck to open it back up so the bullet would slide freely. The gauge would now give consistent readings within .002.

Discussed the problem with Stoney Point. They never did admit anything. I think they were afraid I was going to sue them because I condemned a barel due to perceived throat errosion using their gauge. Since I had altered my case, I had no evidence. They did nothing.

Suggest that you contact Stoney Point and they may do something about it. I tried to find the old emails but must have deleted them. Tell them that another customer compained to them in January/February 2003.
Ron

Throat erosion isn't always throat erosion. Sometimes it can be a buildup of copper fouling in the bore. In any event, in a clean barrel, you can see it. the lands will be worn and washed out looking.
I would recommend cleaning with a good copper remover, such as Wipeout, a couple times before you make any drastic modifications.

I have a retired gunsmith friend, age 81, that has a 308 Norma Mag barrel that he had on one of his rifles and he claims it had over 8,000 rounds (full power loads) through it before he deemed it unservicable and replaced it. When you look through it, you can easily see how washed out the throat is.

The rifle was clean down to barest metal before I started. I measured several bullets in the comparator and they came out exactly the same.

I checked neck runout of the modified case this morning and found it did have significant runout (about .005"). But since I had the case oriented the same way every time (just so it would be easy to reach the thumbscrew to lock the adjustment), I'm not sure how that would affect it.

It's strange because I've always found this device to give very consistent measurements before, with this and other rifles.

John,
When I had the problem with the Stoney Point case that I described above, I turned the case tool about 90 degrees and found that I received significantly different readings. The variation in readings was about from .050 to .070 until I modified the case (re-sized and expanded the neck).
Ron