7mm STW Throat Erosion Measured

Radman

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Joined
Nov 23, 2019
Messages
246
Location
TN
7mm STW and 180 gn Berger VLD measured 3.258 CBTO to the lands back in the spring.

After range time and load development I measured yesterday and same bullet CBTO is 3.327

Is this major throat erosion? Now at 3.327 CBTO the bullet is not even fully seated in the neck and I’ll have to increase jump.
Do you allow any cooling time between shots?
 

Marine sniper

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Joined
Sep 11, 2005
Messages
643
Location
Washington State.
I strongly suspect whatever method you used to measure your throat is the culprit. If you are using the Hornady tool- they are not terribly reliable.

The correct way to do it is to remove your firing pin and extractor- if you did not do that you are going to likely get inaccurate results.

Here is a short video on the correct way to measure what you are looking for:

Scroll down to "finding your lands"
 

Charlielee

Member
Joined
Nov 11, 2013
Messages
8
Berger addresses this exact problem in a separate report on their website: https://bergerbullets.com/vld-making-shoot/.
In fact, they admit that load development could very well wear out the barrel when trying to “touch the lands”. This article talks about the sweet spot that could be a jump of up to .150”. It recomends a procedure to develope this sweet spot.
If you can look in the barrel check for cracking from heat on the lands. Hopefully the barrel is not ruined.
 

Lefty7mmstw

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May 13, 2012
Messages
4,985
Location
Dakota del norte
Honestly, I've never worried about enough about erosion to measure it... I simply look down the barrel and if the first couple inches isn't burned flat (or frosty from fire-cracking) and she shoots I'm good. I've fried out a few pipes and none of them gave a hoot about the little measurements until the barrel was about fried out anyway.
You will see movement in the throat, but the wear is not only at the very origin of the rifling so measuring it is really a false comfort. You really need to be able to measure rifling depth for the first few inches to make an educated guess as to what you have left for bore life, so break out the cerrosafe or just eyeball it like I do and let the groups tell you what's up.
 

General RE LEE

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Joined
Aug 21, 2020
Messages
689
Location
Middle Tennessee
Honestly, I've never worried about enough about erosion to measure it... I simply look down the barrel and if the first couple inches isn't burned flat (or frosty from fire-cracking) and she shoots I'm good. I've fried out a few pipes and none of them gave a hoot about the little measurements until the barrel was about fried out anyway.
You will see movement in the throat, but the wear is not only at the very origin of the rifling so measuring it is really a false comfort. You really need to be able to measure rifling depth for the first few inches to make an educated guess as to what you have left for bore life, so break out the cerrosafe or just eyeball it like I do and let the groups tell you what's up.

I eye balled bore with a LED light and the rifling is clearly visible starting from the base of the throat.
 
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