Gunsmithing How much TE can I expect after 2600 rounds?

[ChrisGarrett]

Savage 308, 26" inch tube, about 2600-2700 rounds of moderately loaded ammo. 90-95% of them in 44grs range using Varget, IMR 4895 and RE-15.

I took some StoneyPoint/Hornady measurements maybe at 1200 rounds and got X, Y and Z numbers using the same brand, but not the exact same bullets that I used last week to remeasure and all were seating much longer.

From .020" to about .050" for a 178 AMAX. I measured 155 Palmas, 168/175 SMKs, 155/167 Scenars and the AMAX.

I have some dummy method measurements from the beginning, but I'm not considering them.

Is about .020"-050" of throat errosion from 1200-2700 rounds typical?

I figure the bullets are from different production lots, but they shouldn't be varying that much, so TE is the main issue.

It still shoots OK, so I'm not worried, but now I can load past mag length on some of them, for sure.

Thanks for the opinions.

Chris

 

[Victor N TN]

Re: How much TE can I expect after 2600 rounds?

Define "TE" as you use it.

 

[ChrisGarrett]

Re: How much TE can I expect after 2600 rounds?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Victor N TN</div><div class="ubbcode-body">Define "TE" as you use it. </div></div>

Hi Victor,

I guess my question was more for the gunsmiths out there, or barrel makers.

TE=Throat Errosion

Using the StoneyPoint/Hornady modified case and contacting the lands yields X, Y and Z COALs in a new gun with A, B and C bullets.

I got my gages at say 1200 rounds and measured A, B and C bullets and got X, Y and Z COALs. Now, after another 1500 rounds, I'm at X, Y and Z plus .020"-.050" and I was just wondering if this throat errosion is typical with a barrel that has said 1500 extra rounds down the tube?

Like I said, for me, it's shooting on par, but I'm definitely seeing a dramatic increase in COAL when reaching the lands.

Thanks, Chris

 

[Halfnutz]

Re: How much TE can I expect after 2600 rounds?

I was recently reading Glen Zedikers book "Handloading for Competition" He mentions velocity dropping off as the barrel start to erode. IF you have a "standard Load" have you checked the velocity or noticed a change in your come ups?

I don't know if it is a good way to tell or not, is the only reason I ask. IIRC he says when he has to add another .5 grain to get the velocity, he rebarrels irregardless of accuracy.

Also discusses himself or someone he knows that rebarrals once the throat erosion got to a certain point. I don't remember that number for sure but it seems like it was out there a relativly decent amount.

I'm going off of memory here as I don't have the book available at the moment. Just putting it out there as food for thought.

 

[nicholst55]

Re: How much TE can I expect after 2600 rounds?

Tagged. I have an opinion on the subject, but I'm interested to learn more.

When using a Throat Erosion gage the rule of thumb has always been that for every 1,000 rounds fired, the gage will insert one additional 'number,' or graduation mark, into the throat. A lot depends on how hot the barrel got (rapid fire or timed), and how hot the loads were.

So I would say that 2,500 rounds should show discernible wear, but nothing to warrant rebarreling - not with a .308. However, I'm not a gunsmith, nor do I play one on TV.

 

[sandwarrior]

Re: How much TE can I expect after 2600 rounds?

First, when you measure throat erosion, you have to use all the same components (even the same bullet), tools. Due to a small difference in ogives, and sometimes major over years, depending on manufacturer, you will get differences. The only way to eliminate differences is to use the same tool to measure with.

That said, so much depends, as mentioned above, on how hot the loads were and how fast they got shot. If you let the barrel cool substantially, between shots and loaded moderately, you wouldn't see much wear. I don't know about Varget but the IMR4895 and RE-15 are hot loads for that cartridge. At least for a standard throat. You may have a longer throat ans seat bullets out a ways. What are they chronoing? Typically with a 168 you should be between 2600-2630. You can get faster. But, that's hotter and causes more wear. 155's-2750, 175/178's-2550.

I'm not saying you're wrong if you get more velocity, just if you do you are causing more wear. If you go by the .050" erosion over the 1500 rounds that comes out to .003" per 100 rounds. That is a bit excessive for that case. Even .0012" per 100 (.020") is a little excessive but not all that bad.

Also, after a certain number of rounds you may start to see erosion speed up. Time to set the barrel back.

Edit:

The reason you will see erosion speed up after a certain number of rounds is because of manufacture process. Savage button rifles their barrels. Which is a good way to do it. But, in button rifling the material starts a little softer and is work hardened as the button is pushed/pulled through the bore. When erosion gets to the level below the surface that has been work hardened the softer material wants to give way faster. Understand there isn't a huge difference but a difference. That may be why your barrel seems to have accelerated in erosion. But, not necessarily.

 

[Halfnutz]

Re: How much TE can I expect after 2600 rounds?

Checked Zedikers book, and I can only assume he uses this in the case of a Service Rifle or a Match Rifle.

He claims "Middleton Tompkins" steps up powder charges in .1 grain increments to maintain velocity. When he reaches .5 grain increase to maintain the same velocity he rebarrells.

Zediker bases his off of "Target Performence" first..."If it stops shooting." "Get a new one" Otherwise his measured limit is .150.

I thought it may help at least to see how someone else gages it for themselves.

 

[ChrisGarrett]

Re: How much TE can I expect after 2600 rounds?

Thanks Sandwarrior,

A few things, I've got a longer barrel, so my velocities with the 155s, 168s and 175 are closer to the 2800s and 2700s respectively, so maybe a bit warmer, but I don't cram every last bit of powder into my cases when reloading.

Still, over the years, I've let the barrel get hot, no doubt and they're by no means mild loads.

Secondly, I had figured that, by not retaining the exact bullets used in the initial measurements, I'd be off some when using different bullets in the latter measurements, so point taken there.

I don't generally jam the lands with the aforementioned bullets, but I now have to be cognizant of the fact that I can go longer and I'll fiddle with my exact mag length (2.855" I think it is) and seat accordingly.

I was just curious as to whether or not, I was in the norm. I own four bolt guns, but only within the the last 18 months, have I been fiddling with the ST/Hornady gages, so going forward, I'll retain the same bullets and use them to insure consistency.

Thanks again, Chris

 

[sandwarrior]

Re: How much TE can I expect after 2600 rounds?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Halfnutz</div><div class="ubbcode-body">Checked Zedikers book, and I can only assume he uses this in the case of a Service Rifle or a Match Rifle.

He claims "Middleton Tompkins" steps up powder charges in .1 grain increments to maintain velocity. When he reaches .5 grain increase to maintain the same velocity he rebarrells.

Zediker bases his off of "Target Performence" first..."If it stops shooting." "Get a new one" Otherwise his measured limit is .150.

I thought it may help at least to see how someone else gages it for themselves.</div></div>

Halfnutz,

I seem to have a barrel that defies that. I got my 30-06 as a heavy barrel set up for long range, open sights. when I looked at it I thought Oh damn! The barrel is shot out. You can see erosion clearly in the lands. But, I wanted a donor action for my 7mm-08 project. So, I bought it anyway.

While doing the financial recovery of buying a new gun (and not selling an old one) I though WTH, Ill load some up. I had a ton of 30-06 brass, 500 168 Nos. CC bullets (and some sierra's) and some 175 gr. and 118LR's. I just loaded some up to see what it would do. Lo and behold this barrel with over <span style="font-weight: bold">.250 erosion</span> shot .5 MOA @300! Now, I don't want to tear it apart to build the 7mm. I just want to set the barrel back when it quits shooting.

 

[NYresq]

Re: How much TE can I expect after 2600 rounds?

Setting the barrel back two or three threads and cutting a fresh chamber is much cheaper then a new barrel and install. If its still shooting decently with the TE and want to tighten it up a bit, try setting the barrel back.

 

[Halfnutz]

Re: How much TE can I expect after 2600 rounds?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sandwarrior</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Halfnutz</div><div class="ubbcode-body">Checked Zedikers book, and I can only assume he uses this in the case of a Service Rifle or a Match Rifle.

He claims "Middleton Tompkins" steps up powder charges in .1 grain increments to maintain velocity. When he reaches .5 grain increase to maintain the same velocity he rebarrells.

Zediker bases his off of "Target Performence" first..."If it stops shooting." "Get a new one" Otherwise his measured limit is .150.

I thought it may help at least to see how someone else gages it for themselves.</div></div>

Halfnutz,

I seem to have a barrel that defies that. I got my 30-06 as a heavy barrel set up for long range, open sights. when I looked at it I thought Oh damn! The barrel is shot out. You can see erosion clearly in the lands. But, I wanted a donor action for my 7mm-08 project. So, I bought it anyway.

While doing the financial recovery of buying a new gun (and not selling an old one) I though WTH, Ill load some up. I had a ton of 30-06 brass, 500 168 Nos. CC bullets (and some sierra's) and some 175 gr. and 118LR's. I just loaded some up to see what it would do. Lo and behold this barrel with over <span style="font-weight: bold">.250 erosion</span> shot .5 MOA @300! Now, I don't want to tear it apart to build the 7mm. I just want to set the barrel back when it quits shooting. </div></div>

That's great. I was only passing along information that recently read, in hopes it would be of "some" assistance. How do you know for sure that it is .250 if you didn't have a starting measurement.

 

[nashlaw]

Re: How much TE can I expect after 2600 rounds?

I am with Sandwarrior on this one.

Several years ago, I bought a Winchester 70 in 22-250. I looked down the bore while at the pawnshop and have never seen such a mess! It literally had spiderwebs in it, not to mention the dirt, rust, etc.

I was into playing with junkers at the time(still am) and had took the barrel off, lapped the lugs and set the headspace back a bit. After that, I firelapped it and lo and behold, it shot about .75 moa. I did not shoot it a lot to see how my novice gun plumbing would play out over the long run, but it was fun and paid out in that case.

I believe G. David Tubb runs some abrasive-coated bullets through his rifles when the throat gets rough.

 

[sandwarrior]

Re: How much TE can I expect after 2600 rounds?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Halfnutz</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sandwarrior</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Halfnutz</div><div class="ubbcode-body">Checked Zedikers book, and I can only assume he uses this in the case of a Service Rifle or a Match Rifle.

He claims "Middleton Tompkins" steps up powder charges in .1 grain increments to maintain velocity. When he reaches .5 grain increase to maintain the same velocity he rebarrells.

Zediker bases his off of "Target Performence" first..."If it stops shooting." "Get a new one" Otherwise his measured limit is .150.

I thought it may help at least to see how someone else gages it for themselves.</div></div>

Halfnutz,

I seem to have a barrel that defies that. I got my 30-06 as a heavy barrel set up for long range, open sights. when I looked at it I thought Oh damn! The barrel is shot out. You can see erosion clearly in the lands. But, I wanted a donor action for my 7mm-08 project. So, I bought it anyway.

While doing the financial recovery of buying a new gun (and not selling an old one) I though WTH, Ill load some up. I had a ton of 30-06 brass, 500 168 Nos. CC bullets (and some sierra's) and some 175 gr. and 118LR's. I just loaded some up to see what it would do. Lo and behold this barrel with over <span style="font-weight: bold">.250 erosion</span> shot .5 MOA @300! Now, I don't want to tear it apart to build the 7mm. I just want to set the barrel back when it quits shooting. </div></div>

That's great. I was only passing along information that recently read, in hopes it would be of "some" assistance. How do you know for sure that it is .250 if you didn't have a starting measurement. </div></div>

When there is barely enough lands left in the barrel that you almost can't get a 208 A-max stuffed in the case when touching them...there's more than .250" erosion.

When you look at the lands in my barrel, they just barely show the leading edge of them. From there back they are rounded down on the corners for a ways back. I can see that with the naked eye. Normal lands look pretty steep from front edge/base of the lands to full height of lands. On mine, it's way back. Now, I also know that my barrel with 1-12" twist wasn't cut that way to handle heavy bullets. It's a matter of luck that mine does.