Shocked at how much throat erosion

[goodgrouper]

The Alliant powders are double based which means there is nitro-glycerin in them and that equates to slightly higher flame temperatures. But it is only a slight difference according to Alliant-often less than 100 degrees.

 

[Marine sniper]

I'm trying to imagine what your tool looks like and how it works. It sounds something like the Stoney point tool without the threaded brass on the end? I have never found that tool to work well enough. In my tool, there is an easy .010" worth of slop in the materials and fit which is enough to render it useless when dealing in thousandths.

The best method is still the low tech magic marker on the bullet method. Of course, you have to have an original bullet left to keep re-checking. Just my 2 cents.

I have issues with the Stoney point tool in a few of my rifles as well; it is due to how shallow the lead into the throat is cut. A very shallow lead, 1 degree or so, makes it more difficult to get a good "feel" on the bullet when it enters the throat. Shallow leads are common in target rifles and chambers.

 

[Rymart]

I use the same tool and method as Allan Griffin for measuring OAL. The tool works well for me and is pretty repeatable (within +/- 0.0015). I prefer it over the stoney Point. There is some 'feel' involved with the measurements, but otherwise they are easy. I usually take 3 measurements and average them, often they are all the same

 

[Alan Griffith]

Steve,

I guess I didn't make it clear enough in my post. I did use the "same" bullet from my original measurements in Nov 2006.

The reason I posted here was to find out if my .13" loss is normal or if I may have somehow messed up.

GG,

When I get a chance I'll try and post some pics.

 

[Steve Shelp]

Steve, just to clarify, after the initial firecracking and erosion, on several barrels in 7mm Mag, the barrels were toast. Once the barrels were replaced, and the powder was changed to H4831, we saw no more firecracking or excessive erosion. The barrels, that originally showed the erosion, would no longer perform to the standards, that were required of these rifles. Examination of previous take-off barrels, before we started using R22, showed no excessive erosion or fire cracking, even after 1500 rds. The barrels, same manufacturer, that were used with the R22 propellant, showed excessive erosion in as little as 450 rds.
The ammo, used by this agency, is loaded by an outside contractor, who must keep pressure, velocity and accuracy within very tight tolerences.

Eddie,
Not sure what to say. I don't doubt your data. The data I base my opinion on is several barrel makers over several years in keeping stats for 600 and 1000yd competition. If there was an issue with double base powders being harder on barrels it would show up real quick. But we haven't seen this. I'm talking about keeping track of match stats across many states, all barrel makers, over an 11 year time period and nobody can conclusively say that double base powders are harder on a barrel during this time. This is one big advantage of competition shooting. You get large amounts of data in a shorter period of time for things like this.
Please don't get me wrong. I'm not saying your data is false or incorrect. But it does contradict the results of a much larger sampling size over a much larger period of time. Obviosuly something doesn't add up here. What cleaning solvents were used, rate of fire, etc etc?? We don't know.
Excessive erosion in 450rds would have competition shooters in a hissy fit. And nobody is complaining that I know of.
Again, I didn't post this to be arguementative. Only that a much larger sample size hasn't supported this arguement over a long period of time.

The reason I posted here was to find out if my .13" loss is normal or if I may have somehow messed up.

No problem. Being you used the same bullet.... then .130" of erosion is very excessive. Why... would be hard to say at this point without returning the barrel to as-new conditions and starting over. Have you fire-lapped the bore by any chance?

Steve