Throat erosion - a word of warning

[ejg]

We Europeans seem try and solve every problem with technology whereas in the US it seems to me they try solve the problem via more practice, work on the technique, get a better shooting instructor etc. Both have their place. When we went over to the states with our rifles to shoot with some Navy Seal instructors they showed me a thing or two. Generally we seem to need ultra light triggers to shoot... they manage with a standard weight because they know how to use them. I was well impressed with 500yd off-hand or kneeling shots into a frying pan. I think we lack of practical rifle shooting with proper instructors, we would especially benefit from it for hunting. Saying that the average quality of shooting in the UK and Ireland is possibly higher than on the continent.
edi

 

[NigelM]

Thanks for all your help on this thread guys, and to those who have sent PM's.

There is definitely something in the steel quality and hardening process. Whilst we can see through the steel specs that LW steel is slightly harder we don't know how the differing hardening processes used by the 416R barrel makers affect the properties of their steel The hardening process for each seems to be a well kept secret, industrial IP, and as such there is little to no data to be able to compare them that I can find. As a result there is no way to compare them other than experience.

What has come out is that there are two members of SD shooting the same chambering as be with the same bullets and slightly higher velocity with double base powders. They are not experiencing the same erosion as I am and both are using LW barrels. With all other factors being so similar I have to reach the conclusion that PacNor barrels are much softer than LW.

I would like to use a LW barrel in the new build but unfortunately they don't offer 6.5mm 7T barrels. Their highest rate of twist is 8T and that's not enough. As a result I will be trying a Bartlein in 7T.

I will also be switching to a single base powder, probably RS62, and coming down a velocity node. Heat of Explosion comes down from 3990 Kj/Kg to 3722 Kj/Kg and pressure will come down from 62kpsi to 58kpsi. Those two changes alone should prove significant. Unfortunately the change in powders and pressure will not allow me to compare the PacNor to the Bartlein in terms of wear which would have been interesting.

The current, slightly worn, 6.5x47 barrel will be relegated to hunting only, the powder changed to single base and the pressure reduced. At the lower energy level it will be for Fallow and smaller. It will be interesting to see how many more years it lasts for at it's reduced work load. I suspect quite a few.

And yes Muir, I do enjoy "getting into the weeds". If I get this one right It will cut wind drift at 1000m by about 22" (10mph 90 deg) and hopefully more than double the barrel life I am seeing. You don't get that sort of benefit by pulling the trigger more often. There is time for both thinking and shooting.

 

[CarlW]

I learnt a lot from this thread. Thank you, Nigel.
Kind regards,
Carl

 

[Yorric]

Don't forget that how a barrel is rifled makes a huge difference to the surface hardening down the hole. It has been long known & many rifle smiths don't like hammer forged tubes for re-chambering for that reason. I've long thought that a hammer forged barrel is more likely to have a longer service life because the wear surface is hammer hardened. The compressive stresses imparted into the rifling by the hammering action must resist the stress cracking (like shot peening significantly improves fatigue life).
My theory is that a hammer forged barrel/rifling that is lapped as a final process has the potential for an optimum barrel (wear/accuracy potential)

Ian

 

[NigelM]

Don't forget that how a barrel is rifled makes a huge difference to the surface hardening down the hole. It has been long known & many rifle smiths don't like hammer forged tubes for re-chambering for that reason. I've long thought that a hammer forged barrel is more likely to have a longer service life because the wear surface is hammer hardened. The compressive stresses imparted into the rifling by the hammering action must resist the stress cracking (like shot peening significantly improves fatigue life).
My theory is that a hammer forged barrel/rifling that is lapped as a final process has the potential for an optimum barrel (wear/accuracy potential)

Ian

Which backs up what's being said about LW barrels lasting longer.

 

[Laurie]

Remember too that it is not just the pressure / heat peak level that kills throats. The 'high-energy' RS powders also have 'EI' burning deterrent technology that sees a degree of infusion into the kernels and which provides a longer-lasting effect on burn rate / initial pressures than the traditional plain surface coating method. This extends the time period / bullet travel / area of rifled barrel subject to the peak pressure-heat environment. It contributes as much to (probably more than) these powders' extraordinary performance increase as the nitroglycerin level. If loaded up to the now available maximum pressure / MV this WILL reduce barrel life very significantly. (Incidentally, Nitrochemie objects to the double-base term on the grounds that the base mix has to be two main ingredients to be double based as applies to ball type powders and compounds like the old British Cordite, Nobel Ballistite etc. Nitrochemie and Vihtavuori - which bought Nitrochemie's NG infusion technology to create its N500 grades - say their powders are single-based 'high-energy' types. Same difference some would argue!)

The peak pressure time / bullet travel issue isn't new in that match shooters have known for a long time that a cartridge loaded to the same pressures but with different bullet weights (using appropriate burning rate powders to match the bullets) will see a significant barrel life difference between the heaviest and lightest models, heavier being faster wearing. This has become very marked now in match use of 308 Win with 'Target Rifle' / Palma limited to 155gn and F/TR having adopted 200gn bullets as the virtual norm now with some using 210/215s. Allied to stiff loads (but often of single-based propellants, Viht N150 very popular), 2,000 rounds barrel life is virtually the norm now in F/TR at top-level whilst TR with its 155s, a bit lower pressure loads, and larger target rings sees at least double that in the same makes / steel grades of barrels.

As ejg says it is usually firecracking that ruins stainless match quality barrels whose relatively soft stainless steel grades suffer badly from this condition. Often a badly firecracked barrel will continue to perform well despite looking terrible in the borescope, but equally often 'something' bad happens that spells disaster. A common one is the tendency to lift bullet jacket material causing severe barrel 'coppering'. Whenever you see an FR-Class or F/TR competitor getting down on his knees pumping bore and copper solvent patches through the barrel between match stages, you know the barrel is on its last legs. This not only ruins long-range accuracy, but is often severe enough to cause a significant pressure rise as it builds up during a match stage and it's not uncommon to see people who've pushed a barrel a match too far pack up mid-stage and withdraw after suffering blown primers. The sudden collapse syndrome appears too in such cases - the early part of the rifled barrel sees a weakened patch literally break down. I had one such barrel in 308 some years back that literally lost its precision between shots hardly able to stay on the frame let alone 'black' in a match. Borescoping it afterwards (after removing the chunks of barrel jacket material spread around the first inch or two of rifling) showed a section of badly firecracked land just ahead of the leade had lost a chunk leaving a 'pothole' which looked huge in the borescope but which would have been less than an eighth-inch I imagine.

Chrome-moly steel barrels whether factory or in older match types allied to reasonable, better still lowish, pressures do erode, not only more slowly but much more smoothly. They will often continue to shoot well with huge amounts of wear as Edinburgh Rifles says of the 222 Rem he once had. Anybody who started out in match shooting without the ability to finance a new rifle as I did in the 80s was accustomed to buying 'well used' 308 1st gen TR rifles like Schultz & Larsens where like Edinburgh Rifles' example, there was no way you could get the bullet near the start of the lands and remain in the case-neck. I have a copy of an 'American Rifleman' article of long ago written by a Finnish ordnance officer of a barrel use v grouping test carried out by the Finnish army on a 7.62X54R service rifle with a new 'match' (selected factory production) barrel. This was a very rigorously conducted trial and full use of statistical techniques employed to 'smooth' results and show long-term trends. The test was abandoned at a round count somewhere over 14,000 rounds and although MVs ES values and group sizes had deteriorated, they had so by surprisingly small amounts. In fact group sizes only grew at all somewhere around the 10-11,000 round point. That's what 45,000 psi peak pressure, chrome-moly steel and proper / regular barrel cleaning gets you!

Andy-RV makes a very pertinent point about 4,000 BAR peak pressure apparently marking a dividing line in throat wear. That's around 58,000 psi and it's no coincidence that is what the large number of cartridges with allowed SAAMI MAPs of 60-62,000 psi are usually actually loaded to by the factories. It seems that relatively small increments on that value start to produce much accelerated wear. As another practical example, US F-Class shooters haven't really every taken to the 7mmWSM most restricting themselves to the smaller capacity SAUM and many, many more to the 284 and its slightly 'improved' variants like the Shehane and KMR, whilst over here the 7WSM is almost the norm at national league level. US competitors cannot believe our barrel lives though in the cartridge - 900-1,100 and they expect not much above half that, 600 being 'good'. (A primary reason they won't use it!) This is because our guys and girls generally forgo the last available 100-150 fps performance, also we 'pair-shoot' and they 'string-shoot', the latter being a much faster method and seeing much higher barrel temperatures.

On the ball v extruded single-based issue, the US Army decided on a policy of ball-only for all standard non-specialist loadings when it adopted the 7.62 in 1957 and this has continued until now with that cartridge and its 5.56mm successor. There was a lot of controversy over this in the 1960s/70s and claims that this type is 'dirty' (as it was back then, no longer the case today in advanced grades such as P B Clermont's 'Ramshot' grades and recent Hodgdon / St Marks powders) and hard on barrels. Several intensive US Army studies in that period showed that there was no measurable difference in barrel life between the now standard mandated ball types and equivalent IMR single-based extruded types at service rifle / cartridge pressures. ie back to Andy-RVs 4,000 bar / 58,000 psi levels. (That's not to say that a double-based grade loaded to a much higher pressure would or wouldn't produce more wear at higher pressures.)

......... and then I remind people of RS's unique 'EI' feature for some grades, a game-changer in potential performance, but also in its potential for producing rapid barrel wear in max or over-max loads. ('EI' / 'high-energy' grades are: RS24, 40, 52, 60, 70, 80. Plain-Jane single-based non-EI grades are RS30, 50 and 62. These cover the loss of key lost Reach non compliant powders bar the missing 'link', one that provides a non-EI alternative to the 4831s.)

 

[NigelM]

Thank you Laurie for a very comprehensive answer.

I have read it a couple of times now and think you are agreeing with the conclusion I have come to. Or have I missed something?

Would a change from RL15 @ 62k psi to RS62 @ 58k psi and moving from a PacNor to a Bartlein significantly increase my barrel life?

 

[Laurie]

Would a change from RL15 @ 62k psi to RS62 @ 58k psi and moving from a PacNor to a Bartlein significantly increase my barrel life?

The first part ... possibly. (Perhaps even probably some change, but I'd not expect any vast improvement.) The second part also maybe but I'd say unlikely as the US barrelmakers tend to use the same steel grade. L-W does have a reputation for giving longer life than other people's stainless tubes though, even if it is hearsay evidence.

 

[scooby doo]

been in the same boat what i was told was that Remington metal was soft don,t put a bore scope down your barrel you will not be happy

 

[NullMac]

Ok stupid question time .....[emoji3061]

Why are folk obsessed with velocity?
Some just seem to want more more more FPS ....

I don’t target shoot, I get the long range you need your speed for working out drop etc

If there’s a load that’s accurate bit it’s not near max load why do folk keep chasing speed instead of accuracy / groups ?


Paul

Because velocity increases "danger space" which has benefits to hit probability

and

terminal effects are primarily about expansion (after shot placement) which is a function of velocity.

Accuracy is a function of the shooter so I presume you mean precision. We are shooting at big targets at short ranges (<=350yard) so we don't need great precision (or even good precision in reality). Nothing was ever killed by a group.

 

[20-250]

Nothing was ever killed by a group.

Tell that to my Great Uncle Albert. He was killed by a group of Germans in 1916.

 

[CarlW]

Tell that to my Great Uncle Albert. He was killed by a group of Germans in 1916.

I initially reacted with a 'haha'...and then a 'like'...but both felt wrong...anyway, you have my sympathy...

 

[Sharpie]

Thank you Laurie for a very comprehensive answer.

I have read it a couple of times now and think you are agreeing with the conclusion I have come to. Or have I missed something?

Would a change from RL15 @ 62k psi to RS62 @ 58k psi and moving from a PacNor to a Bartlein significantly increase my barrel life?

It appears to me that Laurie is advising that some of the latest wonder powders are not particularly good for your barrel. Their manufacturers have gone all-out for performance, for which some do have a genuine use. He should know.

As for the durability of the barrels themselves, their steel, whether they are hammer-forged, buttoned, even cut-rifled, that's not something that most of us here are likely to have to worry about, in our lifetime.

Particularly those whose idea of maintenance is to maybe run a brush and a patch through once/year, whether they think it needs it or not, or just pull a boresnake through periodically.

BTW, 0.5MOA performance doesn't mean being just being able to shoot a 3-shot group into a cloverleaf at 100 yards, once, whilst ignoring the times that it doesn't work, and ignoring the fliers, and assuming that it is just a matter of later twiddling a hunting 'scope to actually align the point of impact with where you are aiming. And that that will apply over all ranges.

Long range shooting, several 100s of metres, trying to get close to the V-bull, and putting many many rounds through the barrel, is a quite different discipline. Which does develop some skills applicable to hunting, but not vice-versa.

Shooting off-hand, from field positions, is one thing. Improvised rest, fencepost, tree, rucksack etc. better. Use a pair of sticks, better. Quad sticks, possibly better still. Bipod also good, if it it is actually practical to use one in the field.

Good luck to those who claim that they can do that, every time, sub-MOA.

 

[NigelM]

It appears to me that Laurie is advising that some of the latest wonder powders are not particularly good for your barrel. Their manufacturers have gone all-out for performance, for which some do have a genuine use. He should know.

As for the durability of the barrels themselves, their steel, whether they are hammer-forged, buttoned, even cut-rifled, that's not something that most of us here are likely to have to worry about, in our lifetime.

BTW, 0.5MOA performance doesn't mean being just being able to shoot a 3-shot group into a cloverleaf at 100 yards, once, whilst ignoring the times that it doesn't work, and ignoring the fliers, and assuming that it is just a matter of later twiddling a hunting 'scope to actually align the point of impact with where you are aiming. And that that will apply over all ranges.

Long range shooting, several 100s of metres, trying to get close to the V-bull, and putting many many rounds through the barrel, is a quite different discipline. Which does develop some skills applicable to hunting, but not vice-versa.

Shooting off-hand, from field positions, is one thing. Improvised rest, fencepost, tree, rucksack etc. better. Use a pair of sticks, better. Quad sticks, possibly better still. Bipod also good, if it it is actually practical to use one in the field.

Sharpie,

Laurie and I have had a good chat offline and I fully understand what he's saying. It's not black and white, as usual it's various shades of grey.

In terms of barrel life, I do have cause to worry about it in my lifetime and I'm interested in learning more about what's better than that I'm currently using. It's never too late to learn.

I am very aware of what 1/2 MOA means. I'm not a keyboard warrior and I'm not talking with any lack of experience.

Long rage shooting isn't over several hundreds of meters, it's 1000 meters plus. It is a very different discipline to hunting but I have no doubt at all that it makes me a far better shot as a result of the understanding I have about ballistics. That doesn't mean I shoot deer at LR, the 30 odd I have shot so far this year have averaged about 75 meters in woodland and 190 meters on the hill. About 1/3 have been shot off sticks, most of the rest have been prone from pack or bipod and one has been off a stone wall, so plenty of different positions.

If you don't have anything relevant to add to the original post and the very good discussion that has followed then it's probably best not to post at all.

 

[VSS]

I learnt a lot from this thread. Thank you, Nigel.
Kind regards,
Carl

I learnt something too. A new expression: "Getting into the weeds...".
Thank you Muir.

 

[Woodsmoke]

I initially reacted with a 'haha'...and then a 'like'...but both felt wrong...anyway, you have my sympathy...

I have no such scruples. I p*ssed myself laughing

 

[Muir]

Nope, we are not. ISTM that this is a discussion about long range target shooting, which is quite different from shooting deer and other species. And a popular sport here. Where a 0.5 MOA 5 shot group on a perfect target (not showing the other less-so-perfect ones) at as little as 100 m (with declared flyers) doesn't even begin. I'd dare to surmise that target shooters, in our clubs,far outweigh those who actually use a sporting rifle to cull deer.

It's different here. Those who are fortunate to have the opportunities can cull as many deer in a year as you have maybe shot in a lifetime.

Others who don't have such opportunities pay for them, perhaps only being able to afford a few outings/year. Nevertheless, despite being a small country we have an abundance of deer. Find a good operator and the chances are high. From my records I have averaged over 1 per outing. Maybe that is why it is a popular destination for hunters from other countries who appreciate the opportunities, and the quality.

We can't just buy whatever rifle we take a fancy too, and as many as we want (each one has to be justified with "good reason"), then amuse ourselves. Every one has to be justified, and it is quite reasonable to try to get the best out of what we have, even if that doesn't align with your perhaps more relaxed ideas.

Well Hell. I guess I've told. We don't know anything much about long range shooting and quality hunting opportunities. That's why few people ever to come to the US to hunt. ~Muir

 

[User00033]

Farkinell. @Sharpie, wind yer neck in.

Here in the land of the long white cloud, it is broadly accepted that to have a cat in hells chance of reliably shooting 1000m+ gongs, paper or animals, the shooter must be able to reliably shoot one hole groups, without exception, at 100m, with their rifle and load of choice. With a 7mm or .30 cal magnum that's ~0.3 MOA. One hole. Then, the shooter must step out and maintain the accuracy at a rate of roughly 1.1x or 110% per 100m, with all the vagaries the wind brings with it. So 300m is ~0.36 MOA, 600m is ~0.5 MOA and 1000m is ~0.7 MOA, or 20cm at 1000m. That's some shooting.

Now a 1 MOA, 1000m gong is 30cm diameter. We just had some made in BIS400. Looks awfully small.

To achieve that kind of accuracy reliably, one must spend a lot of time researching, and some dosh, and a lot more time practicing, perfecting the discipline. Underpinning the discipline is science. Understanding the science is mandatory. Otherwise you'll waste your time and dosh.

A few of the community on here have the curiosity and intellectual wherewithal to try and master this sport, proper long range shooting. And they share this understanding as it develops, with us, for the fun of it, and numpties like me learn something with every post. I appreciate that.

The cynical twerps who appear to be typing whilst looking down a very long nose can go jump in a muddy bog.

@NigelM, have you looked at True Flite? Very good reputation for accurate, long lasting match barrels, made to the most exacting of standards.

 

[Sharpie]

dodgyknees, If you read what I have been saying, coolly, I think that you will find we are in complete agreement.

Long range shooting at small targets, however you define it, requires precision, and accuracy. I admit to having been exasperated by some of the posts, especially the glib one-liners, putting down the original post, or giving irrelevant anecdotes about knackered hunting rifles that still seem to work adequately, for their purpose.

Hence my diatribe about supposed 0.5MOA groups, which, as I said, don't even begin to get you started for this sort of thing, which seems to have touched a nerve. I think you are in agreement with me about this.

This thread has attracted a lot of noise from people who don't appreciate these requirements.

I enjoy researching the theory, science and practice behind this, as a process of self-education, having a science and engineering background, albeit in a different area. And learning from the real-world experience of those actually do this, at a high level.

My experience is limited to shooting paper targets out to 900 m on military gallery ranges, with target marking, where I can see exactly where every shot lands, rather than just trying to bang steel gongs at 1000m, or use live animals as long-range dynamic targets, which IMO teaches rather less.

NigelM asked several pertinent questions in his original post, i.e.:

"
1. Are PacNor barrels especially soft?
2. Are double based powders really that evil?
3. Should I be well below max pressures if I want to maintain a reasonable barrel life even when they advertise high max pressures?
4. Is Bore Tech particularly abrasive or corrosive?
5. Is cleaning bad?
"

I think that two or three of these questions have now been discussed. Perhaps we might move on to the others.

Laurie has explained some of what is going on, here and privately with NigelM. I've also studied the Australian Government Dept. of Defense paper to which I referred earlier, and found it a fascinating read, that might give some insight into the various barrel wear mechanisms that are in play here.

Here's the link again, in case you missed it the first time:

http://2poqx8tjzgi65olp24je4x4n-wpe...tanding-and-predicting-gun-barrel-erosion.pdf

So please, can we have a polite discussion, without the personal attacks ? I returned here to learn and share knowledge.

 

[NigelM]

Sharpie,

This isn't a dig, it's more a way of helping you understand why 3 of us have had a little crack at you and a few others have agreed with our comments.

The OP was asking some pretty specific questions. I wanted to check my experience against the experience of others in order to learn something and avoid making more mistakes in the future which will cost me time and money.

@Guesty , @trucraft , @pierred , @ChesterP and @Yorric all came back with experiences of barrel and steel qualities. @Rider , @Andy RV , @dodgyknees , @20-250 , @1894 and @Malxwal came back with powder experiences. @jon2 corroborated my experience with PacNor with his own experience and @Ronin and @ejg gave me some valuable experience from a gun makers perspective. @Laurie came back with his usual highly valuable and knowledgable contribution.

You have made 3 posts. The first stated the obvious. You then went on to talk about various shooting positions and questioned whether we really understood what 0.5 MOA really meant. You didn't manage any valuable contribution to the discussion apart from an Aussie military paper which whilst an interesting read didn't talk in any detail about steel types, hardening processes or any specific powders. Nothing we could make decisions or take any action upon. You managed to get fairly sharp responses from myself, @dodgyknees and @Muir, posts which were liked/agreed with by several others.

Perhaps you should think about modifying your tone of voice. Consider not talking down to your fellow members and showing a bit more respect for what some others might understand.

It has been a very interesting thread which I have learnt from and it appears a few others have enjoyed as well. Let's not spoil it.