How much throat erosion is “normal”

[VinceMule]

The learning curve can be somewhat disconcerting at times, for sure. An $89 Teslong bore scope is the best money a serious shooter can spend. Keeping the carbon from building up in your barrel is a huge factor in extending the barrel's life.

1 MOA accuracy requirement is a lot different from a 1/4"-3/8"-1/2" MOA accuracy requirement. 1 MOA is probably all a guy needs to shoot deer at 600 yards.

 

[VinceMule]

Frank, my 6 Dashers have around 1100 rounds of usable "best" barrel life and at 1400 rounds, the barrels are completely shot out. H4895 burns very, very hot.

 

[tomsd]

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

Beautiful answer. Wish I had read this before I let my gunsmith (who built Sniper rigs for Navy Seals here in SD) - rebarrel the custom barrel on the ole Springfield 06 (due to throat erosion he said). It was my dad's hunting rifle when I was growing up - I carried it a few times - and think he won it in a card game.

Usually for hunting big Mulies - I had the Winchester lever action Model 94/32 Winchester special - with a 4x fixed Weaver Scope - but the 30.06 also had a custom Timney trigger and a beautiful blond stock and 3x9 40 MM Simmons scope. The very last shot from that rig was DEAD CENTER - and I mean - DEAD CENTER - at 100 yards.

The new barell - never did really break it in - Aggggg - was snooting about 3 inches - and I sold it to my buddy - whose Uncle had originally built it He wanted it more for sentimental sake - and I bought am inexpensive Mossberg in 30.06 - which shoots just fine for hunting purposes - a little over an inch with factory ammo.

 

[Tiny Tim]

TinyTim, you have something special with such a small amount of leade growth. I would be very interested to know your load in a PM! Thank You!

I have shot the barrels out of a dozen 243 AI's at least, p. dogs, chucks, jack rabbits, 12T, zero freebore, 70g at 3850 on formed cases with Win 760. We converted over to AA2700, and cci 250 gets the SD down to 9 fps.

I urge you to get a bore scope, you would see any burr as the bore scope magnifies 25x. It would be crappy machine techniques or a dull reamer that left a burr in the throat, and I have looked at many. Anything is possible. HEAVY reamer chatter could cause an irregular reading as the chatter got smoothed by firing.

I measure the CBTO with a bullet when the barrel is brand new. I put that bullet in a tiny plastic bag in the die box, and use that bullet throughout the life of the barrel to measure leade growth.

Also, when the gunsmith is chambering your barrel, he has to cut 1" off the front, and some also cut 1" off the back. I have my gunsmith run the reamer in to the depth of the shoulder body junction. This is called a neck Checker. This simple barrel stub can now be used to insert a case into and measure the headspace length of fired and sized cases. Also, when the barrel is brand new, this Neck Checker can be used to establish the CBTO length because the barrel stubb has the leade angle cut into the lands, a duplicate of what is in the rifle chamber.

I am a firm believer in the interference point created by the AI 40* chamber.

Vince, I'll have to get load info to you tonight when I get home. As a side note, 80 grain Hammer Hunters and 105 Berger HVLD have basically same CBTO in my rifle. The AMAXs were 2.192 when gun was brand new. Only had a hundred so I never checked that length again after break in. I simply assumed the difference to be ogive profile.
As I said before, I was surprised at the level of fire cracking I saw when inspecting the chamber for a carbon ring and bronze brushed the neck and throat area prior to checking this dimension, so there should be no burrs. There is certainly some degradation of the throat area and a bullet could be forced a few thousandths further, but the basic dimension hasn't changed much.

This is primarily a hunting rifle and it's taken me about 4 years to put that many rounds down the pipe.

 

[2Old2Care]

I came very close to allotting some of my "gun stuff" budget to a borescope and a concentricity gauge. Reading things like this convinced me that sometimes ignorance is bliss and to leave well enough alone if what you're doing is working for you. Bought more brass and powder instead

I finally bought a bore scope so that I would know when a barrel was clean and not be wasting time and effort, or thinking it was clean when it really wasn't. Of course, I 'ruined' a couple of barrels on old family rifles when I saw just how pitted they were, but the targets said the bore was still 'good enough' so I've managed to not rebarrel them. I'm personally very happy that I have a bore scope and wish that I'd purchased it sooner, but learning that every little flaw is magnified and looks way worse than it really is was the first important lesson I had to learn. Now its practical and fun.

 

[VinceMule]

I measured the throat growth on my custom and Rem 700 varmints in 243 Win every 100 rounds, and I have always seen the throat grow....always, in My attempt to maintain 3/8" groups for varmint. The custom SS barrels I used were usually Hart or Shilen with powders used was IMR 4064 with Fed 210's.

Again, Winchester 760 and AA2700(burning rate of H and IMR 4350) slowed the rate of throat growth.

If the 243 Winchester had a .400 long neck, I think that we would see a radical decrease in the rate of throat growth. The 6 SLR addresses some of this issue with just pushing the shoulder back and creating a longer neck.

The 80g sierras at 3400 fps make chucks take off like they were shot out of a circus cannon when hit! 80g Bergers. are nowhere near as effective as the 80g Sierras on fur, coyotes included.

 

[mannup1515]

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

YouTube Eric Cortina about "stop chasing the lands" and many other subjects… He has his podcast also and interviews many top shooters.
I too have been afraid to get a borescope…
Reloading and shooting is like Alice in Wonderland… How far down the rabbit hole do you want to go…
My humble opinion is if the gun shoots to what you want and need, don't touch it…
But… if chasing the lands helps you mentally with confidence and it shoots good doing it, go for it…

 

[VTbluegrass]

Ignorance is indeed bliss. My model 700 in 270 that was made in the late 70's and rode in my good buddies Toyota before I was born, lived in a humid basement and I personally I have seen shot to blistering hot/can't shoot the mirage before I bought it has an unknowable round count. Shot just fine for deer hunting with 150gr corelokts. I decided to load for it and to get to the lands nothing less than a 150 will do and still have some bullet in the neck to hold.

Loaded out to the lands I brought it back under MOA consistently so that makes me happy on paper. But I still constantly consider rebarreling. Before I had the tools to measure and read information about throat erosion I was content and happy in the knowledge that all creatures that had crossed the muzzle were in great danger and that's all that really mattered.

 

[mannup1515]

Ignorance is indeed bliss. My model 700 in 270 that was made in the late 70's and rode in my good buddies Toyota before I was born, lived in a humid basement and I personally I have seen shot to blistering hot/can't shoot the mirage before I bought it has an unknowable round count. Shot just fine for deer hunting with 150gr corelokts. I decided to load for it and to get to the lands nothing less than a 150 will do and still have some bullet in the neck to hold.

Loaded out to the lands I brought it back under MOA consistently so that makes me happy on paper. But I still constantly consider rebarreling. Before I had the tools to measure and read information about throat erosion I was content and happy in the knowledge that all creatures that had crossed the muzzle were in great danger and that's all that really mattered.

I read an article 20+ years ago of a gentlemen with a 22-250 used for prairie dog shooting… He could not see the rifling halfway down the barrel… It was still minute of prairie dog so he kept shooting it…
I have a 6 creed with a pac-nor 7.5 twist barrel (stiller tac 30) that I had set back at 1 k rounds…( I could see the Erosion visually) I have some regrets doing that because I had to go through load development all over again…
Pre setback I was shooting 115 dtacs @ 3025 fps jumping them .120"
I have no idea why it liked them there but it wouldn't shoot them just off the lands…So I did the "Berger .040 , .80, .120 test…it set personal records for me out to 600 yards after that…
I have a course of fire using the 25 yard timed and rapid fire pistol target…
The black portion is 5.5"…
I would shoot 200m,300m,400m, 500 yards, 570 yards…
3 shots each distance… My goal to keep everything in the black…
I would shoot against buddies of mine for score… I added a "Benchrest " bonus of 1 point for best group each distance…
It was a fun and humbling experience…
This course would definitely expose a bad load…
What was also neat is sometimes you may have a bad day calling the wind to get in the black at distance but when you drive up to the target and see 1/2" groups @ 300 meters and sometimes 1" groups at 500 yards you get that warm fuzzy…
Anyway (I got carried away lol) that particular rifle is one of two that I have been able to clean the course with…
Enjoy shooting your rifle… It will tell you when you need to throw money at it lol… I should have listened to mine…

 

[Tiny Tim]

No experience on pd's, but 80 gr HH @3600 just puts the smackdown on deer and make a 3.5-4" hole in coyotes at close range. Never been a one hole rifle but has always shot .5 moa in my mediocre hands.

 

[mannup1515]

I read an article 20+ years ago of a gentlemen with a 22-250 used for prairie dog shooting… He could not see the rifling halfway down the barrel… It was still minute of prairie dog so he kept shooting it…
I have a 6 creed with a pac-nor 7.5 twist barrel (stiller tac 30) that I had set back at 1 k rounds…( I could see the Erosion visually) I have some regrets doing that because I had to go through load development all over again…
Pre setback I was shooting 115 dtacs @ 3025 fps jumping them .120"
I have no idea why it liked them there but it wouldn't shoot them just off the lands…So I did the "Berger .040 , .80, .120 test…it set personal records for me out to 600 yards after that…
I have a course of fire using the 25 yard timed and rapid fire pistol target…
The black portion is 5.5"…
I would shoot 200m,300m,400m, 500 yards, 570 yards…
3 shots each distance… My goal to keep everything in the black…
I would shoot against buddies of mine for score… I added a "Benchrest " bonus of 1 point for best group each distance…
It was a fun and humbling experience…
This course would definitely expose a bad load…
What was also neat is sometimes you may have a bad day calling the wind to get in the black at distance but when you drive up to the target and see 1/2" groups @ 300 meters and sometimes 1" groups at 500 yards you get that warm fuzzy…
Anyway (I got carried away lol) that particular rifle is one of two that I have been able to clean the course with…
Enjoy shooting your rifle… It will tell you when you need to throw money at it lol… I should have listened to mine…

The gun was still shooting top notch when I set it back

 

[Paulstarr]

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

The real answer is easy,When your gun looses it's accuracy,as for concentricty gauge,leave it in the box it came in because any excess run-out on the case your rifle put it there if the brass you bought was good quality.As for bore scopes you must remember that what you see through the scope is just a small part of the complete picture because you need to rotate the scope and unless you used to using one all you are going to do is keep yourself awake at night.Gunsmithes there the boy's for using borescopes and delivering the good or bad news.
Hope this helps

 

[gregw83]

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

I haven't really spent much time on paper, so not certain. After shooting 2 boxes of blitz kings that were all seated the same, u decided to measure it again for the next batch I made up. It was more out of curiosity as to what is considered "normal", based off the actual measurements, because all I usually see is a round count, and people debating back and forth about it, but never the actual distance the throat grew by.

 

[FEENIX]

I haven't really spent much time on paper, so not certain. After shooting 2 boxes of blitz kings that were all seated the same, u decided to measure it again for the next batch I made up. It was more out of curiosity as to what is considered "normal", based off the actual measurements, because all I usually see is a round count, and people debating back and forth about it, but never the actual distance the throat grew by.

I probably shoot 50-100 rounds through a new barrel before I finalize a load development. I understand your curiosity but I do not worry much about throat erosion unless I have a reason to. I would probably have at least 10 different loads the life of a barrel.