7mm STW Throat Erosion Measured

General RE LEE

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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.
 

MagnumManiac

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I haven’t checked my throat erosion as yet, we’re in another lockdown so no shooting yet again, but if you’re using a single base powder of real slow burn, it will be quite progressive on throat erosion.
I tested 2 barrels in 300WM some time back, 1 really liked RE25 and the other really liked H1000, the latter had 1/3 more elongation in the throat while the RE25 barrel had a lot more haze cracking with the same round count.
The H1000 barrel was setback and re-chambered at 1132 rounds, the RE25 barrel was at 1648 rounds when it was setback and re-chambered.
Have seen this a few times now.
My old 22-250 ran 760 only, the newer ran Varget, the older barrel (CM) lasted longer than the new barrel (SS).
It really is how hot the powder runs in YOUR application that determines how much throat erosion you get.
My custom 25-06 erodes by .020” every 100 or so rounds with RE25.
Double base powders are reported to burn hotter, but they also yield more energy per specific gravity than single base and therefore often use less powder for the same output. Then you have ball powder that behaves totally differently in a cartridge than stick powder and even though double base, it burns the coolest of the lot.
Hope this makes sense.

Cheers.
 

Lenwood901

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has anybody ever tested neck tension and if more tension helps the throat or just doesnt matter its alot of powder
 

highdrum

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Man that sounds like an extremely high rate of erosion. My best friends 28 nosler went at a rate of about 0.008" per 100 rounds. This was using 86gr Retumbo pushing 195s @ 3090fps.
The best way to check lands is to pull your barrel and seat a bullet long. Then drop the round into and upside down chamber pushing it into the shoulder of the case. The cartridge will likely not lift freely, use a pocket knife to pry the case up. Seat the bullet a little or a lot deeper depending on the resistance to remove the case. Once you get to a point of very little to no resistance, you should be able to pry it up with your pinky fingernail.

Another method involves stripping the bolt of the firing pin assembly, and ejector. You essentially do the same as previous method, but instead of using your finger force to remove the round from chamber, you let the weight of your bolt do the talking. Once your right at touch or a thou or two off, the bolt handle should fall **** on its own weight with zero resistance.

Always do this after you clean your barrel, as carbon build-up in the throat/freebore area will give false measurements. Horandy oal tools get you close but more than likely what a person calls lands with Horandy tools is probably jammed anywhere from 5 to 10 thou.
 

highdrum

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If anyone has a new barrel recommend I appreciate it.
I'd suggest a bartlein mod400 alloy. I recently had a 6gt prs barrel spun in mod400. Granted I'm only burning 36gr H4350. But after 450 rounds my throat hasn't moved. This barrel gets hot a d stays hot shooting matches with 9-12 round strings in 2 mins all day in 90° weather. I'm a believer in it.
 

Bghunter338

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I'd suggest a bartlein mod400 alloy. I recently had a 6gt prs barrel spun in mod400. Granted I'm only burning 36gr H4350. But after 450 rounds my throat hasn't moved. This barrel gets hot a d stays hot shooting matches with 9-12 round strings in 2 mins all day in 90° weather. I'm a believer in it.
I was just going to say he should probably look at that one😉
 

Muddyboots

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One potential solution is to try shooting Hammers since it has been my experience jump is irrelevant to them. If it still shoots well with them, you might get few more rounds down barrel before having major barrel work done.
 
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