Normal Throat Erosion

bolbmw

bolbmw

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Curious what people are seeing with throat erosion. I have a 24" McLennan stainless barrel in 308 that I shoot 155 scenars out of at about 2950fps. I've put about 500 of these down the tube and the throat has eroded about 0.004.

Typical? It's not what I would consider a hot load compared to what I've seen others doing with these bullets. I'm shooting with 46gr varget and I've seen recommended loads as hot as 47.8! I'm hitting near 3000fps with 46gr, and that's good enough for me!

Edit: I should mention that I am using the sinclair bullet seating depth tool for these measurements.
 
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Excellent question, I've allways wondered myself.
My .308 Savage factory barrel eroded so bad, I could not increase the COL anymore.
But, I did not measure it, wish I had now.
 
A bore scope is the best way to acess bore damage, but I have used the stoney point/hornady lock-n-load overall length guage to measure the throat erosion as well for years. If nothing else, it gives us a guide to measure change.

I measure the OAL of a given bullet when the barrel is brand new, and mark the OAL measurement on the bullet. Then store the bullet with the dies for that rifle. Periodically, I will check my OAL with this bullet to see how much change there is from the very first measurement. Its a guide only.

It has made me realise how much wear happens on calibers like 7mm Ultra, 244/6mm Ackley!
 
This of course assumes that my measurement technique is repeatable enough to accurately measure 0.04. I repeated many times to get down to a repeatable measurement that was +/- 0.01 while being very very careful in my technique, so I believe it is an accurate guide. It certainly wasn't easy and took more time than I would like to admit.
 
After getting to know one cal. very well, in my case 6.5x55, I add .001" to seating depth every 100 rounds.
This, with .015" jam ... which seems more critical to maintain for peak accuracy than a typical jump seating would be.
 
bolbmw said:
This of course assumes that my measurement technique is repeatable enough to accurately measure 0.04. I repeated many times to get down to a repeatable measurement that was +/- 0.01 while being very very careful in my technique, so I believe it is an accurate guide. It certainly wasn't easy and took more time than I would like to admit.
Click to expand...

Sounds doable, next barrel will get the OAL measurment filed away even before I fire it.
Thanks for the info folks.
 
bolbmw,

Is your decimal point at the right place, your showing 0.04 as in 40 thousandth which seems a lot for 500 rounds.
As dthunter mentioned if you did not measure with the exact same projectile the tolerance in the ogive could account for a portion of the difference, noted you shoot quality projectiles but mfg tolerances exist.
Just a thought.
 
RIFLEF said:
bolbmw,

Is your decimal point at the right place, your showing 0.04 as in 40 thousandth which seems a lot for 500 rounds.
Click to expand...

Yes, I've read on snipershide that this is not all that uncommon but it's difficult to get a consistent view on this sort of thing. I'll have to just keep track of it over the next few hundred rounds to see if it changes.
 
bolbmw said:
Yes, I've read on snipershide that this is not all that uncommon but it's difficult to get a consistent view on this sort of thing. I'll have to just keep track of it over the next few hundred rounds to see if it changes.
Click to expand...
Viking, says he adds .001 (thousandth) for every 100 rounds of 6.5x55 he shoots to stay at .015 jam, so 5x.001=.005 by your calculations 5x .04=.200 that is a mighty big difference.
On a .308 a compressed load starts at approx 47.0g because you start hearing the powder crunch when you seat your bullet. Your loads are not hot, but I am getting 2950 out of a 30" Kreiger with 45.5g
of Varget.
 
RIFLEF said:
Viking, says he adds .001 (thousandth) for every 100 rounds of 6.5x55 he shoots to stay at .015 jam, so 5x.001=.005 by your calculations 5x .04=.200 that is a mighty big difference.
On a .308 a compressed load starts at approx 47.0g because you start hearing the powder crunch when you seat your bullet. Your loads are not hot, but I am getting 2950 out of a 30" Kreiger with 45.5g
of Varget.
Click to expand...


Hah ####, you are right. I just double checked my numbers. It IS 0.004. D'oh. Will edit.
 
I am getting 2950 out of a 30 inch barrel with 155 Scenars using 46.0 gr of Varget. Lapua brass and Federal 210 Match primers. What brass are you using to get 2950 out of a 24 inch barrel?
 
maynard said:
I am getting 2950 out of a 30 inch barrel with 155 Scenars using 46.0 gr of Varget. Lapua brass and Federal 210 Match primers. What brass are you using to get 2950 out of a 24 inch barrel?
Click to expand...

FGMM brass with CCI BR2 primers. I'm only able to get about 5-6 reloads before the primer pockets start getting pretty loose but I have hundreds of once fired FGMM to work my way thru. I get ejector swipes with this load and loads closer to 47 have heavy bolt lifts.
 
maynard.
Chronys never lie… as long as they are consistent in their reporting, as you know, they have to be checked with real world, hands on shooting and drop measurements, to confirm or adjust true speed.
bolbmw,
There is something not quite right with your last comments, with the load you use, there is no reason to get only 5-6 reloads before primer pockets open up. What were those brass shot in the first time?
Were they FL resized with a SB FL die and trimmed to spec length before firing in your McLENNAN barrel?
Not prying just trying to understand.
Regards
 
bolbmw said:
FGMM brass with CCI BR2 primers. I'm only able to get about 5-6 reloads before the primer pockets start getting pretty loose but I have hundreds of once fired FGMM to work my way thru. I get ejector swipes with this load and loads closer to 47 have heavy bolt lifts.
Click to expand...

If your brass is only lasting 5-6 reloads and you're getting ejector swipes, how have you come to the conclusion that your load isn't "hot"? All the obvious signs are there to the contrary. I know FGMM brass has a reputation as being softer compared to others but still.

Not to mention that you're getting velocity numbers that appear to be reasonably high for your barrel length compared to what others have reported. I know there are other variables involved - I'm just sayin'.
 
This is once fired brass (168gr FGMM) that was fired in a previous rifle (rem 700p).

My brass prep routine is:
full length resize with a redding type S die to bump shoulder back .002 (measured with a redding instant indicator, calibrated to brass that has been fired several times out of this rifle)
trim to min length (2.005)
uniform primer pockets, chamfer neck (outside and inside)
deburr flash hole

Subsequent reloads get full length resized every time and case length is checked. Charges are metered with a rcbs chargemaster combo and bullets are seated with a redding competition seater. Seated 008 off of the lands this produces a slightly compressed load. In working up the load I went up to 47gr where I definitely found the limit - heavy bolt lifts and very visible ejector swipes. The 46gr load only produces minor swipes and bolt lift is normal.

I came to the conclusion that the 46 gr load isn't hot based on it being under published maximums and a common load for this projectile. I attribute the ejector swipes to the federal brass being soft, I have tons of it so I have not bothered to buy any others. After 5-6 reloads there is very little resistance when seating a primer (using the rcbs hand tool.) From what I have read online this is not unusual for the federal brass. Most seem to shun it completely.

This produces a very consistent round for the rifle, shooting 0.3moa at 250 yards (~1.5" groups) - I have found the 155 scenars to be more accurate at distance than they are at 100 yards. This rifle has an 308 obermeyer chamber, could this be a factor? Am I missing something important?
 
bolbmw said:
This is once fired brass (168gr FGMM) that was fired in a previous rifle (rem 700p).

My brass prep routine is:
full length resize with a redding type S die to bump shoulder back .002 (measured with a redding instant indicator, calibrated to brass that has been fired several times out of this rifle)
trim to min length (2.005)
uniform primer pockets, chamfer neck (outside and inside)
deburr flash hole

Subsequent reloads get full length resized every time and case length is checked.
Click to expand...
Charges are metered with a rcbs chargemaster combo and bullets are seated with a redding competition seater. Seated 008 off of the lands this produces a slightly compressed load. In working up the load I went up to 47gr where I definitely found the limit - heavy bolt lifts and very visible ejector swipes. The 46gr load only produces minor swipes and bolt lift is normal.

I came to the conclusion that the 46 gr load isn't hot based on it being under published maximums and a common load for this projectile. I attribute the ejector swipes to the federal brass being soft, I have tons of it so I have not bothered to buy any others. After 5-6 reloads there is very little resistance when seating a primer (using the rcbs hand tool.) From what I have read online this is not unusual for the federal brass. Most seem to shun it completely.

This produces a very consistent round for the rifle, shooting 0.3moa at 250 yards (~1.5" groups) - I have found the 155 scenars to be more accurate at distance than they are at 100 yards. This rifle has an 308 obermeyer chamber, could this be a factor? Am I missing something important?
Click to expand...
bolbmw,
By FL resizing your brass each time you are overworking it, which by all accounts is already soft. If you have an expander ball type decaping pin which can't be removed you are lengthening your cases each time.
Once my brass has been shot in my chamber, I only neck size with a bushing die, and even often use a Lee Collet die with the decaying pin turned 0.001 smaller to control neck tension on projectile.
It minimizes trimming, inside and outside chamfering, and reduces time in prepping work.
vviking. probably has summarized perfectly
 
I have shot 46 gr of Varget as well as 3-4 of my shooting buddies. We all shoot 30 inch barrels with Obermyer chambers. Barrels differ from Krieger to Bartlein to McLennen to Tru-Flight. Brass differs from Lapua to match prepped Winchester to Norma to HPS. Several different Chronys all give the same results of velocities between 2930-2960 with 30 inch barrels with any 155 gr bullet on the market. (trust me I have shot them all) I just can't see how you can be getting 2950 out of a 24 inch barrel.
 
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