How much throat erosion is “normal”

[gregw83]

Hey all, haven't been on the forum in a while, so I thought of a good question to get feedback on. I have a Savage M12 LRP in 243 win. It has about 270 rounds through the barrel, so I decided to get the oal gauge out and remeasure to see where it was at. Of those 270 rounds, 200 were 70gr blitz kings over 41 gr of 4064, and a box of factory ammo for barrel break in when it was new, and a few test loads. I found that I'd now have to seat them out about .015 further to reach the lands now. I know the 243 is well known for being rough on barrels, but is this within "normal" wear, or is that excessive for 270 rounds? It's not a real concern, it's a savage, so I can rebarrel it on the living room floor when I shoot it out, but I'm just curious

 

[std7mag]

Excessive or not for a 243 Win, alas is something i can't tell you.
I shot enough through my 7mm-08AI that i couldn't get it to hold a 140gr Berger VLD in the neck anymore and still reach the lands. 6,000 plus rounds.
But it was still hunting rifle accurate. 5 rounds in 0.78" at 100 yards.

I'd keep shooting it.

 

[FEENIX]

Hey all, haven't been on the forum in a while, so I thought of a good question to get feedback on. I have a Savage M12 LRP in 243 win. It has about 270 rounds through the barrel, so I decided to get the oal gauge out and remeasure to see where it was at. Of those 270 rounds, 200 were 70gr blitz kings over 41 gr of 4064, and a box of factory ammo for barrel break in when it was new, and a few test loads. I found that I'd now have to seat them out about .015 further to reach the lands now. I know the 243 is well known for being rough on barrels, but is this within "normal" wear, or is that excessive for 270 rounds? It's not a real concern, it's a savage, so I can rebarrel it on the living room floor when I shoot it out, but I'm just curious

Is there a change in your group that prompted you to measure the throat?

 

[can1010]

check for bullet touch at the beginning of load development and then put your tool it in the cabinet and forget about it. don't adjust anything until accuracy goes away and then there is only one way to go longer.
if accuracy suffers add .003 and test and continue adding and testing until it returns.
what you're seeing with measuring at 270 rounds is the slight change in throat angle and not throat erosion.
just like bore scopes, measuring all the time and having too much info is more of a problem than anything else. accuracy will let you know when to make changes

 

[Coyote Shadow Tracker]

^^^^^^^^^^
Don't do anything until accuracy changes. Then seating depth out a few thousands and see if accuracy come back.

 

[del2les]

Given my experience with numerous standard 243Wins, .015" after 270 rounds is in the ballpark for erosion. No big deal.

 

[Rflshootr]

A number of things contribute to the amount of throat wear. Bullet type, throat angle and powder. Powder is the probably the most influential. Or more specifically, the amount of powder burned. Any given barrel will only burn a given amount of powder before the throat has eroded to an unusable length. Whether you burn it in small amounts at a time or in large amounts, pretty much determines throat life. So, shooting light bullets with more powder as compared to heavy bullets with less powder, will burn the throat faster. As an example, a 6mm BR shooting the same bullet as a 243 Win, will have longer throat life simply because less powder is used. The change of the angle as was mentioned previously, is in fact throat wear. Any time rounds are fired, there is some amount of erosion, regardless of where metal is worn/burned away from the throat/bore. The amount you are seeing is pretty much in the normal range of what I have experienced with a 243 Win.

 

[VinceMule]

I shot out a lot of 243 barrels on Chucks, p. dogs, jack rabbits, and Coyotes. My primary load in custom and Rem 700 barrels was 39g+of IMR 4064 with an 80g Sierra single shot pistol bullet(no longer made). Just at the point where you see the very mildest pressure with this load, is where the best accuracy is. The velocity ran 3400 fps on custom 12t, zero freebore, 26" barrels. This

IMR 4064 and Varget are rough on barrels, and so is R#15, 4895s, and 8208. I measured the OAL to the lands every 100 rounds. When loading up several hundred, I would always seat the bullets .100 long, then adjust the seating depth to what the barrel liked.

Almost without exception, the best accuracy is where the bullet was just .003 or so off the lands, and I am talking about 3/8" accuracy and MUCH less.

If your climate permits, AA2700 is the coolest burning powder to use, it is accurate and fast, with Win 760 being a great second choice with cci 250s taking the SD down below 10 fps.

In my custom 243's, the 60g Sierra HP, 70g Ballistic tip, and the 80g Sierra are instant Killers with amazing accuracy. We also had fantastic accuracy with the 65-75g Benchest bullets I made off of J4 jackets working excellent on p. dogs, chucks, and coyotes.

As your throat keeps getting longer, you keep seating your bullets out, then go to a bullet with more bearing surface to maintain accuracy, and look no further than a 100g Hornady btsp, 100g Speer btsp, 90g Speer, 95g SST, and Hornady 87g V max. Sierra .243 bullets are rare and since they are not available, I did not mention any of them. Nosler bullets are also not available.

R#26 with cci 250 primer will push the 100's at 3200 fps in the 243 unless you are running a short barrel.

ON all my custom barrels, I start off with zero freebore for varmint rifles, and this has worked fabulously on all bullets 80g and less.

AA2700 and Win 760 are fantastic powders for the 243 unless you are hunting in super cold weather.

On our p. dog hunts, I carried a 5-gallon bucket full of neck-turned 243 and 243 AI. I saw .070-.110 leade growth per bucket fired, depending on how hot and heavy the shooting was. We shot Max Heavy Varmint contour barrels that started off with 5" of straight on 12 twist barrels. The AA2700 and 760 was gentle enough on the barrels to where we could set the barrel back twice as 243 or AI, then the third chamber became a 6 BR at around 24". We did not let the leade get completely shot out before we set the barrel back, and by doing this, we got 10,000 rounds on Hart SS barrels. Kriegers may last longer, don't know. My hunting partner and I ordered Hart barrels ten at a time, as we were shooting 20,000 rounds a year and some years more.

 

[Rflshootr]

I shot out a lot of 243 barrels on Chucks, p. dogs, jack rabbits, and Coyotes. My primary load in custom and Rem 700 barrels was 39g+of IMR 4064 with an 80g Sierra single shot pistol bullet(no longer made). Just at the point where you see the very mildest pressure with this load, is where the best accuracy is. The velocity ran 3400 fps on custom 12t, zero freebore, 26" barrels. This

IMR 4064 and Varget are rough on barrels, and so is R#15, 4895s, and 8208. I measured the OAL to the lands every 100 rounds. When loading up several hundred, I would always seat the bullets .100 long, then adjust the seating depth to what the barrel liked.

Almost without exception, the best accuracy is where the bullet was just .003 or so off the lands, and I am talking about 3/8" accuracy and less.

If your climate permits, AA2700 is the coolest burning powder to use, it is accurate and fast, with Win 760 being a great second choice.

In my custom 243's, the 60g Sierra HP, 70g Ballistic tip, and the 80g Sierra are instant Killers with amazing accuracy.

As your throat keeps getting longer, you keep seating your bullets out, then go to a bullet with more bearing surface to maintain accuracy, and look no further than a 100g Hornady btsp, 100g Speer btsp, 90g Speer, 95g SST, and Hornady 87g V max. Sierra .243 bullets are rare and since they are not available, I did not mention any of them. Nosler bullets are also not available.

R#26 with cci 250 primer will push the 100's at 3200 fps in the 243 unless you are running a short barrel.

ON all my custom barrels, I start off with zero freebore for varmint rifles, and this has worked fabulously on all bullets 80g and less.

AA2700 and Win 760 are fantastic powders for the 243 unless you are hunting in super cold weather.

Just out of curiosity, how much did your seating depth change, let's say for about 200 rounds?

 

[can1010]

i can just about guarantee that the .015 he is seeing is nothing more than a slight polish of the angle and the removal of any burrs from chambering and not throat erosion, more than likely happened in the first 50 rounds or less and he never knew it.
throat erosion is when you start removing rifling from free bore dia. forward and total change of the angle. basically barrel break in and not erosion

 

[Tiny Tim]

How fast do you fire rounds? If it still shoots well, I wouldn't worry about it.

Have a 243 AI. Just hit 700 rounds. Never checked CBTO since break in. Equal amounts of H4350, Staball 6.5, and H4831. Was looking at the chamber for carbon ring when cleaning. Yikes, alot of fire cracking in the throat are. Still shoots the same .5 MOA consistently.

All this is to say, don't worry about these things unless they affect performance. It's good to know and build a baseline of knowledge for the future. Perhaps better knowledge of this progression would come from monitoring every 100 rounds.

 

[VinceMule]

I will tell you one thing, IMR 4064 and Varget eat 243 barrels. I have seen .030+ in 200 rounds, shooting 80g at the accuracy node which is around 3400 fps in a 12 Twist, 26" barrel. On chucks, I went to Win 760, then AA2700 to keep the throat erosion and fire cracking down.

I have never had a 243 Win, either factory or custom that had its best accuracy with the bullet seated very far off the lands until I started shooting 100g bullets.
The exception to this rule was with 75g Sierra hp and 85g Sierra btsp, neither of which are available at this time, and not sure when they will make another run of them. I shot the leade way out of one barrel on a p. dog town in two days of red hot shooting, then went to shooting the 90g Speer(more bearing surface and flat base) which was very, very accurate in this Rem 700 Varmint.

Accuracy means different things to different people, and as a varmint rifle, I was looking for sub 1/2", close-range deer rifle-1.5" groups, and long-range (300 yards) 1/2" groups. 100g Hornady BTSP is fantastic deer and hog bullets, and the nice thing is you can get them now!

I believe that the shoulder angle and the short neck contribute to the lead growth, and I arrived at this conclusion by shooting a 6 Rem and 243 side by side on p. dog towns with same bullets and approx velocities.

On our varmint rifles, we liked minute of p. dog head at 300 yards, easily attained with load tuning.

 

[Rflshootr]

i can just about guarantee that the .015 he is seeing is nothing more than a slight polish of the angle and the removal of any burrs from chambering and not throat erosion, more than likely happened in the first 50 rounds or less and he never knew it.
throat erosion is when you start removing rifling from free bore dia. forward and total change of the angle. basically barrel break in and not erosion

I don't want to start an argument, but are you saying there was no change in the throat after the first 50 or less rounds of break in for the additional 220 plus or minus rounds that he has fired?

 

[M1A1ABRAMS]

I will tell you one thing, IMR 4064 and Varget eat 243 barrels. I have seen .030+ in 200 rounds, shooting 80g at the accuracy node which is around 3400 fps in a 12 Twist, 26" barrel. On chucks, I went to Win 760, then AA2700 to keep the throat erosion and fire cracking down.

I have never had a 243 Win, either factory or custom that had its best accuracy with the bullet seated very far off the lands until I started shooting 100g bullets.
The exception to this rule was with 75g Sierra hp and 85g Sierra btsp, neither of which are available at this time, and not sure when they will make another run of them. I shot the leade way out of one barrel on a p. dog town in two days of red hot shooting, then went to shooting the 90g Speer(more bearing surface and flat base) which was very, very accurate in this Rem 700 Varmint.

Accuracy means different things to different people, and as a varmint rifle, I was looking for sub 1/2", close-range deer rifle-1.5" groups, and long-range (300 yards) 1/2" groups. 100g Hornady BTSP is fantastic deer and hog bullets, and the nice thing is you can get them now!

I believe that the shoulder angle and the short neck contribute to the lead growth, and I arrived at this conclusion by shooting a 6 Rem and 243 side by side on p. dog towns with same bullets and approx velocities.

On our varmint rifles, we liked minute of p. dog head at 300 yards, easily attained with load tuning.

I picked up a nice lot of bullets with Hornady, Sierra, Nosler at a estate auction. Almost full boxes of 100. Many of which you suggested. And got the lot for I believe $36.00. Almost 1,000 different bullets. So I find you load data for the 243 Win very helpful. Thanks for the insight on what worked best for you. I may try a few of those after confirming in my older load manuals. And get a little more confident in what I am doing when reloading.