Full Length or Neck Only; What's Best Resizing for Accuracy?

Bart B

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It's been mentioned that setting case shoulders back reduces case volume.

What about throat wear as bullets seated to the lands increases the case volume behind the bullet?

My 308 Winchester barrel throats advance about .001 inch every 30 rounds. 30 caliber magnums about every 13 rounds per thousandth.
 
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afp1

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I get nowhere near that much throat erosion. My current 300 WSM LR BR rifle's throat has moved .001" in 350 rounds. My 6 BRAs will go maybe .001" in 500 rounds. A factory 300 Win I had went .010" in 800 rounds. My larger bores don't move the throat too much. The 300 Win was babied, but I don't baby the BR guns.

That said, throat erosion will change a tune, especially if the best load is right at the lands. Ideally we find a load that can handle some increase in seating depth and still be in the accuracy node. Usually a .005" or more jam or a .015" or more jump tend to be tolerant.
 

Bart B

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I get nowhere near that much throat erosion.
Then we're using and doing different stuff.

US military method in 30 caliber rifles with their throat erosion gauge let it go in 1/10th inch further about every thousand rounds. .001 inch every 10 shots.
 

afp1

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Then we're using and doing different stuff.

US military method in 30 caliber rifles with their throat erosion gauge let it go in 1/10th inch further about every thousand rounds. .001 inch every 10 shots.
We are indeed talking about different stuff. It sounds to me like what you reference is expected erosion and likely applied to all 7.62s to include M-60 and M-240 machine guns. Once the barrel gets hot, sustained fire can cause a lot of erosion. I guess that could also happen in an M-14.

I measure my throats all the time with my modified Hornady tools, and also look with a borescope, so I know how much throat erosion happens with all the different cartridges I shoot.

The worst I ever had was a SS Sendero in 7mm Rem Mag I bought new in 1996. It's throat moved .040" in 400 rounds which matches the rate you are describing. The 7mm RM is known to be hard on throats, and some suspected Rem got a bad batch of stainless steel then (mid 90s). For that rifle I would shoot five in a row and then let it mostly cool.

I traded that 7 Mag in on a 300 Winny Sendero in 1997. I babied that barrel, shooting only three shot groups and keeping it cool, and that throat moved about .010" in 800 rounds.

After that I paid a lot of attention to throat erosion, moved to aftermarket barrels, and eventually upgraded to CRF M-70s from Remmys for hunting guns.

When I started competition 1000 yd BR shooting in 2005, my first rifle was a 6.5-284 with a Krieger barrel. It's throat went .038" in 830 rounds. LR BR is hard on barrels, especially the Heavy Gun class where we get the barrels warm to hot during the sighter period then fire 10 rounds in 30-60 sec for record. Also, the 6.5-284 is known to be hard on throats, and I was shooting in Tucson back then. The next year I build a 300 WSM and in 658 rounds it moved the throat .007".

In my return to LR BR a couple years ago almost everyone had just moved from the 6mm Dasher to the 6 BRA. The Dasher usually tuned at 2950-2980 fps even though it could shoot 100fps+ faster. The 6 BRA also usually tunes 2950-2980 and has a grain or two less capacity. The reason everyone went to the 6 BRA was because of the risk of the throat eroding over a multi day match and putting you out of tune.

Throat erosion doesn't happen evenly all the time. It usually moves slowly at first, stays, then jumps a little in the Dasher. We think the BRA is slightly less susceptible to all that.

That is my experience with throat erosion, and it is all anecdotal. I would not dispute what someone found under specific and controlled circumstances. My uncle was an FE and top turret gunner on a B-17 in WW-II. He was supposed to shoot in short bursts to preserve barrel life and accuracy. What he did was strat shooting as soon as an enemy fighter began the attack and held the trigger down until the fighter turned off. He said many a fighter would turn away when he saw he was being shot at. My uncle said he wore out a set of barrels on every mission. I am
sure the the allowable throat erosion was exceeds for the 50 BMG. The rifling might have been awfully worn too......
 

25WSM

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At Williamsport we shoot 10 rounds for light gun also. A few of us can do 10 rounds in 20 seconds. Pretty hard on barrels for sure. The last 13 rounds I shoot are in one minute. My 6.5 Creed doing 2850fps gets 800 rounds before any firecracking starts. I then set it back to clean rifling again. My friend who I do barrels for ran his to 1400 rounds and I had to cut an inch out to clean it up. Throat erosion definitely is on a curve as I have very little to about 700 and then it starts to move much quicker. The 300wsm is very easy on barrels. I know guys getting 3000 rounds on them. I doubt I find out out for myself because my 300wsm is going to be a 7saum real soon. It's too hard to overlook the bc advantage of the 7mms compared to the 30s. And we usually have lots of wind to contend with.
Shep
 

afp1

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At Williamsport we shoot 10 rounds for light gun also. A few of us can do 10 rounds in 20 seconds. Pretty hard on barrels for sure. The last 13 rounds I shoot are in one minute. My 6.5 Creed doing 2850fps gets 800 rounds before any firecracking starts. I then set it back to clean rifling again. My friend who I do barrels for ran his to 1400 rounds and I had to cut an inch out to clean it up. Throat erosion definitely is on a curve as I have very little to about 700 and then it starts to move much quicker. The 300wsm is very easy on barrels. I know guys getting 3000 rounds on them. I doubt I find out out for myself because my 300wsm is going to be a 7saum real soon. It's too hard to overlook the bc advantage of the 7mms compared to the 30s. And we usually have lots of wind to contend with.
Shep
For as long as I have been involved with LR BR, though they have a lot of promise, the 7s never really seem to run as well as the 30s. That said, the 7 SAUM is the one to try.
 

Bart B

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For as long as I have been involved with LR BR, though they have a lot of promise, the 7s never really seem to run as well as the 30s. That said, the 7 SAUM is the one to try.
One thing in favor of 30 caliber bullets is their long, heavy ones are easier to make well balanced. They have higher BC for their weight and and least amount of jump off the bore axis as they clear the muzzle.

Some of us remember the problem Sierra had with their first heavy 7mm match bullets in the 1970. It repeated a few years afterwards with 6.5mm ones.
 

25WSM

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With the 7saum I'm using a smaller case to drive a much higher bc bullet faster than the 300wsm. Win win win. Less powder. Higher bc. Faster. Lower recoil. Win. Heck my 6.5 Creed out runs the wsm too. Way less powder. More bc. Same speed. Way less recoil. If my heavy gun had a standard bolt face it would be a 6.5creed.
Shep
 

afp1

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With the 7saum I'm using a smaller case to drive a much higher bc bullet faster than the 300wsm. Win win win. Less powder. Higher bc. Faster. Lower recoil. Win. Heck my 6.5 Creed out runs the wsm too. Way less powder. More bc. Same speed. Way less recoil. If my heavy gun had a standard bolt face it would be a 6.5creed.
Shep
Yeah I get all that, but on the whole, the 300 WSM seems to win more vs the 7mms and 6.5s in LR BR. The little 6mms are first, the 300 WSM next, then all the others. I run a 6BRA and just this year built a 300 WSM again for when conditions aren't as good.

Guys have been trying to make a 7 work for a long time. When I shot in the mid 2000s in windy Tucson, no one seemed to have a 7 that would keep up with my 300 WSM or my friend's Patriot. When I came back three seasons ago here in the PNW it was 90% 6mm BR and its variants.

I don't know why the 7s aren't dominant in LR BR. The 7 SAUM seems about perfect. Maybe like Bart said the 30 Cal bullets are more easy to make balanced. It's hard to run a 300 WSM light gun as fast as the 6s because it recoils back a lot farther in the bags, which makes it slower. So a 7 SAUM that was as accurate would be a definite sweet spot.

Out here it's almost all 6s except for a few of us knuckleheads have an occasional 300 or a 6.5 when we get lesser conditions. One guy does well with a 6.5x47 as his only gun but he only shoots 600 yds.

We'd have to revoke your BR credentials if you brought Creed to the line..... ;)

A guy here worked very hard to make a 7mm-08 IMP with small primer pocket. It looked great on paper but couldn't shoot the heavier bullets.

Maybe your 7 SAUM will be the one to beat start a resurgence of 7mms.
 

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