Throat erosion - what is regarded as "normal" ?

[ecomeat]

I am hoping some forum members might share their experience and views on what they regard as normal, or acceptable throat erosion, particularly in 284 Win barrels
I have used a Hornady OAL gauge with a Sinclair Nut for nearly three years and have been totally confident with my measurements. I have always used a cleaning rod in one hand, and the OAL unit in the other, carefully pushing Left/right/left/right hand etc, making sure that I was getting a true measurement of a gentle "touch", and using the same Sinclair Nut, along with a quality micrometer to set my seating depths.
I had fairly recently noted minimal erosion figures of just 0.001" (Bartlein with 300 shots fired), 0.002" (Bartlein with 620 shots fired) and 0.005" (Maddco with 660 shots fired.
Took extra care yesterday, and am totally confident that my measurements are accurate, but to my great surprise I found :
Maddco has 0.026" erosion of lands with just on 700 shots fired, compared to new.
First Bartlein has just 0.005" erosion with 670 shots fired
Second Bartlein has 0.010" erosion with 330 shots fired.

Are these figures in the realm of what experienced shooters would regard as normal erosion of the lands, for the number of shots fired ?

My first Krieger 6 x 47 Lapua barrel was absolutely toasted with 1150 hot loads using AR2209, but with almost 6" of the barrel absolutely firecrazed, the actual measurable erosion to the lands was only 0.001" according to my tools. I wasn't expecting much more than that with my 284 Win, so have been quite surprised by my results from yesterday.
Thanks for any input !
Tony

[DenisA]

G'day Tony,

FWIW. In my limited experience I believe that the rate of barrel demise (fire crazing) and the lands being burnt and moving forward are related but different and not proportional.

My first experience was with a factory 6BR Savage barrel. The lands burnt forward over .020" in 1500 rounds. .015" in the first 600. The rate was very aggressive at the start and then slowed heavily. The bore is heavily burnt now, I'd guess at least 3" at 2500 rounds and the land position hasn't moved for about 600 rounds.

Speaking with Stuart E in the past, I learnt that PhillJ uses a 1 degree lead on their lands. It serves 2 purposes. Firstly to make the barrel less sensitive to ogive shape and seating depth as it gives the bullet a more gradual introduction to the lands and it also gives the lands less edge to burn away quickly as the barrel begins and continues its life.

Point being, I suspect all barrels will be different based on the reamer and inturn, land angle. A square edged land would burn away much faster than a 1 degree land as the corner is quickly burnt off on an angle.

My .284 which is a custom barrel has only moved .002" from shot 380 through to 1500. Bearing in mind the slight dimensional difference between different batches of bullet.

I was caught out badly with the 6BR wondering why it stopped shooting well in the early days. Found that the lands were moving quickly and now recheck my land position and seat accordingly every firing.
As a side note, as I'm sure you and everyone else are fully aware, the land position should always be checked with a bullet from the same batch that your loading. I was caught out with that too in the early days of reloading. .015" difference from base to meplat datum line between batches of 105g VLD Target.

[ecomeat]

Thanks for the input, Denis.
Phil chambered all three, so they are all done at the 1 degree you mentioned and all done with the same reamer.
The Maddco lands are basically a 90 degree square shoulder, whereas the Bartleins are a canted lands, so are a much blunter shoulder.
I certainly make sure I am using a sample from the current "batch" for all measuring.
That 0.015" variation that you had was a bit wild ! I have to admit that Mr Berger has been very, very good with everything that I have measured .
My 6mm 105 gr VLDs are great, never more than 0.001" difference from base to Ogive, and the 180 gr VLDs and Hybrids that I have separated had well over 90% within 0.002". While my shoulder was mending, I measured and separated 500 pretending to be busy. The Hybrids are just as good, so far. I will get a little more serious in sorting them when my current batch runs out. There are three separate batches in my next 2000 Hybrids, unfortunately.
Tony

[Brad Y]

You also have to realise that some barrels are made from "harder" steel that others. I dont mean to say that the grades may be different, but most people around the scene would agree that maddco barrels tend to be softer and wear out a little quicker. At least they do in my area. But they shoot as good as anything else I have seen. Where as kriegers and bartleins (Im lead to believe with the latter) seem to take a bit longer to wear.

I got 1000 rounds on my 260 improved first chamber, a bit of cracking though it had some harsh treatment from trying 2213sc, but since it was shooting so well I only had half an inch removed before a new chamber job. I think I will get 1500-2000 rounds out of it before it needs a really good trim back to around 26 inches and be relegated as club and fireforming duties only. The next one I expect will go much better- well over 3000 with what I know now... The krieger shehane barrel seems to have moved about 5 thou over the first 500 odd rounds I have put through it, most of that was with ADI powder, Im up to 700+ (and still trying to find a load) and wear is much the same after changing powders.

I reckon if you can get 1000-1500 competitive rounds from a chamber thats pretty good. Any more is a bonus, any less I would be a little dissapointed with. Run a SAUM, 7WSM, 6.5x284, 6x47L, or anything else fairly overbore and you have to be prepared to expect a little less in barrel life.

[DenisA]

Sorting Bergers from the same batch has always resulted <.003" base to ogive variation, only a few being at the extreme upper end, though my previous example was based on comparisons from different batch numbers. I still have a few left over from different batches that I'll use for breaking in barrels down the track. I just re-checked and they definately vary that much.

[DenisA]

Another thought I have is that I don't think that the way the lands burn would be uniform around the exact point that the bullet contacts.
As you've seen with the bore scope, burnt lands (like a fire crazed bore) are not 100% smooth. There could easily be high spots or chunks that stop the bullet when taking measurements. If it was a high chunk (for want of a better term) that blew off after a firing, the next land measurement taken could show a significant movement.

Food for thought at least.

[ecomeat]

I guess that is possible, Denis, although my leade up the start of the lands (if that's what you call the 1 degree ramp) seems pretty smooth at the 25x of a bores cope. I am using KG2 as the second part of my cleaning routine, and it is filthy dirty liquid grey to use, but is very effective. it must be a mild polish, something like the red paste Jb Bore Brite. It isn't aggressive like the darker JB bore cleaning paste but does seem to do a great job cleaning and polishing.
Using KG2 every cleaning, I don't think mine would have the type of bumps that you are talking about, but I accept what you are saying to be highly possible , in general terms.

[ecomeat]

.
I got 1000 rounds on my 260 improved first chamber, a bit of cracking though it had some harsh treatment from trying 2213sc, .

Brad,
I am using 2213sc in all of my 284 Win loads, but it's the one "that works" for me, so I haven't changed.
I certainly have become super vigilant re getting all of the carbon out promptly, as it is definitely an issue in all of my barrels with that powder. Three barrels all shoot waaaaay better than me using it, so I have opted to keep going with it.
Although if I didn't have about 18 tubs in the locked cupboard, I would be sorely tempted to try 2217 ! Norm Nelson has made some glowing comments about it
Tony

[DenisA]

Hey Tony,

I gave my .284 barrel (1511 rounds) a thorough clean on Saturday night. I hadn't brushed it for around 75 rounds. I borescoped it and found that I had all the copper streaking out though there were still specs of copper hiding amongst the first few inches of firecrazed bore. Also the burnt bore was black and I wanted to be sure that it wasn't hard ar2213sc carbon build up as previously discussed in another thread.

I patched the barrel with autosol, clean patched it and then wet patched it to get the polish out of the tiny cracks. Took quite a few clean patches in to see clean patches out, but the results are pretty schmicko. All the firecazing is shiney metal and no longer black, but crazed steel is still there none the less ............ Answers the carbon question.

The polish was far from severe and only pushing patches through in one direction from the action to the muzzle. No back and forth rubbing.

Anyway, I thought I'd re-check my land position after the polish which has been consistantly measuring at 2.3525" since shot 380.
It now repeatedly measures at 2.3555" using a bullet from the same batch that I've been running for a while.

I don't know whether the polish has removed burnt metal, fatigued metal, high spots or other, but the lands hadn't previously looked black so I don't think it was burnt powder. They were always shiney and clean steel after a brush and patch.

I don't believe that polish on patches could remove .003" of good SS.

I don't have a real point to this story other than the observation that the lands have moved .003" from a relatively mild polish procedure. Something has been removed from the lands very easily, though stayed put through firing over the last 1120 rounds.

In conclusion, borescopes just cause more confusion and create more questions ...................... pretty sure someone told me that before I bought it.

[Brad Y]

I have found it can carbon glaze a barrel if not kept clean. And chemicals just dont seem to do the job 100%- hence why people are using iosso, JB, KG2 etc. By the sounds of it Denis had what I would consider the start of bad fouling. That carbon crackling ends up hard and sharp and rips copper from bullet jackets. When you use abrasive cleaners occasionally it removes it and you think that 'firecracking' is no longer there.

2213sc obvioulsy works fine but your doing the right thing in keeping on top of carbon fouling mate, Ive fallen victim twice now of heavy carbon fouling and both times each barrel tends to be rougher and copper foul quicker.

I tend to favour faster powders now so they can burn at a high enough pressure to not foul as bad- 2206H in the dasher (you should see how clean it is- unreal!), 2209 in the 260, and the shehane... well god knows Im still figuring that sucker out. I now give my warm barrels a few patches of hoppes and leave in in there for a few hours to soften carbon before I clean it out with a proper clean.

[KHGS]

Hey Tony,

I gave my .284 barrel (1511 rounds) a thorough clean on Saturday night. I hadn't brushed it for around 75 rounds. I borescoped it and found that I had all the copper streaking out though there were still specs of copper hiding amongst the first few inches of firecrazed bore. Also the burnt bore was black and I wanted to be sure that it wasn't hard ar2213sc carbon build up as previously discussed in another thread.

I patched the barrel with autosol, clean patched it and then wet patched it to get the polish out of the tiny cracks. Took quite a few clean patches in to see clean patches out, but the results are pretty schmicko. All the firecazing is shiney metal and no longer black, but crazed steel is still there none the less ............ Answers the carbon question.

The polish was far from severe and only pushing patches through in one direction from the action to the muzzle. No back and forth rubbing.

Anyway, I thought I'd re-check my land position after the polish which has been consistantly measuring at 2.3525" since shot 380.
It now repeatedly measures at 2.3555" using a bullet from the same batch that I've been running for a while.

I don't know whether the polish has removed burnt metal, fatigued metal, high spots or other, but the lands hadn't previously looked black so I don't think it was burnt powder. They were always shiney and clean steel after a brush and patch.

I don't believe that polish on patches could remove .003" of good SS.

I don't have a real point to this story other than the observation that the lands have moved .003" from a relatively mild polish procedure. Something has been removed from the lands very easily, though stayed put through firing over the last 1120 rounds.

In conclusion, borescopes just cause more confusion and create more questions ...................... pretty sure someone told me that before I bought it.

Buying an endoscope does not make one a doctor, 5 years of university does that! Moral of this is that one needs experience to interpret what the borescope is telling you. Removal of carbon can change the throat wear measurements quite considerably. One light application of Autosol will not remove any measurable amount of metal. The metal that has been removed by normal use has been replaced by carbon. The normal average throat "wear" in a .308 is .010" to .015" per 1000 rounds, this average has been determined by measuring hundreds of .308 barrels over many years. .284 barrels will "wear" more than .308 barrels this is a fact of physics. This also brings up another point, measuring throat length is an in-precise activity & there are many reasons for this which would take too long for me to write here. Let me say that .003" is about the tolerance you can expect for these measurements depending on how the tools are used & how well the tools are used.
On precise leade angles, after a undetermined amount of rounds the leade will become something quite different to what was originally cut. Contrary to popular belief some of the most accurate barrels I have fitted have had leade angles of 2 degrees 30 minutes to 3 degrees 30 minutes so go figure, beats me, perhaps some popular theories are just that, theories.

Keith H.

[DenisA]

Always appreciate your experiences and input Keith. Cheers.

I suspect that the contact point of the bullet to the land changes as the lands erode because the lands are not the same shape as the ogive.
In the case of a fresh chamber, the upper edge of the land may be the contact point and that upper edge may be the first part to burn away. The new contact point could now possibly be 20% or more down the length of the lands leade due to the rounded ogive of the bullet.................. possibly the integrity of the contact point may increase as the contact point moves further away from the edge of the land and out of the concentrated flame.

These are all just fleeting thoughts that are waaaaaay beyond practical value to me and therefor I stand to be corrected on all of it.

I think there are too many variables and unknowns in this subject to have anything but a 'land erosion average' over the life of a barrel. And even then it would be pretty broad and is obviously affected by cleaning regimes.

A figure like .010"-.015" for every 1000 rounds in a .308 sounds very practical and honest.

I'd love to see what you've seen through a bore scope Keith and I'd love to be confident in analysing and understanding what I see through it.

Cheers.

[KHGS]

The important thing is to be aware that you do not FULLY understand what you are seeing thru the borescope! The layman should use the borescope to check fouling levels & be aware that BLACK fouling must never be tolerated, it is much more of a problem than copper fouling. Using the borescope for anything else will require years of experience & the inspection of MANY MANY barrels.
Keith H.

Always appreciate your experiences and input Keith. Cheers.

I suspect that the contact point of the bullet to the land changes as the lands erode because the lands are not the same shape as the ogive.
In the case of a fresh chamber, the upper edge of the land may be the contact point and that upper edge may be the first part to burn away. The new contact point could now possibly be 20% or more down the length of the lands leade due to the rounded ogive of the bullet.................. possibly the integrity of the contact point may increase as the contact point moves further away from the edge of the land and out of the concentrated flame.

These are all just fleeting thoughts that are waaaaaay beyond practical value to me and therefor I stand to be corrected on all of it.

I think there are too many variables and unknowns in this subject to have anything but a 'land erosion average' over the life of a barrel. And even then it would be pretty broad and is obviously affected by cleaning regimes.

A figure like .010"-.015" for every 1000 rounds in a .308 sounds very practical and honest.

I'd love to see what you've seen through a bore scope Keith and I'd love to be confident in analysing and understanding what I see through it.

Cheers.

[DenisA]

Agreed, however, in anything we do there's only one way to gain years of experience and it starts with a small unconfident step and zero understanding however fruitless it seems.

Not knowing the answer should never be a reason for not asking a question.

[Brad Y]

While I dont own one, I do have access to one and yes it gets used to check how good or bad a job my cleaning regime does, or if I have a problem with a barrel not working. Normally its carbon fouling in the throat. Any black in there is carbon and needs to be removed. I like having barrels back to steel after shooting, as anything you dont get out gets shot over next time and gets harder and harder to remove. But a borescope is also good for running in new barrels. I can see if there are cross land marks from the reamer and if there is I use autosol to polish them down before firing. It saves alot of copper removal I have found. During run in you can see if the barrel is coppering up- I dont trust solvents showing blue anymore. If there is no copper, I wont clean, just another lightly oiled patch and fire again.

The other things that borescopes are good for is checking crowns, sometimes they look good from the outside, but you can see marks just inside with a borescope. Ive also seen rifles where people havent used a bore guide and have worn a groove into the top of the chamber at the case mouth/leade area.

I think they are worthwhile tools to have if you can afford one, but Ive learnt that looking at a barrel and seeing cracking everywhere isnt automatically 'dead' quite often that is carbon crackling and the barrel is perfectly fine.

BrettB has a 260 over here that has grown around 10 thou from memory (give or take a little in measuring error) running 140's at 3000fps. Its done around 900 rounds which is exceptional. The key I feel is that he does regular and thorough cleaning and never lets carbon build up. Where mine (a slightly different version and a maddco barrel) only got about 300 rounds at 2800-2900 before 10 thou wear. I had let it carbon up and I think that caused my premature wear. By last years WA Queens I had only 80 thou of bullet left in the case which I was worried about yet it still shot well. After the event it got a rechamber. There was some firecracking but I felt not enough to warrant a huge rechamber, just took half the existing chamber out and went again. Its shooting brilliantly and should be good for the rest of the year before a new tube is needed. Brett was talking about getting his done as well last time I spoke to him too, its shooting good so he doesnt want to wear it too much more and risk it needing 3-5 inches being cut away.