HELP Needed : Throat Erosion

[Blobby159]

On the two last occasions I joined in on a reasonably long distance Club Shoot at Bisley Ranges my rifle - a Tikka t3 in 6.5 heavy barrel 'Sporter' Swede - was giving me mediocre and unpredictable 'accuracy' which was far and away off what I have been used to from it once a month over the last couple of years. I thought it might have been due to some kind of 'brain fart' whilst I had been reloading my regular range ammunition for it. So I broke down almost 200 fastidiously built rounds made from quality products, and loaded them again following resizing the case necks.


Back at the range on my last visit prior to "Lockdown" and @ 600 yards my bullets were falling anywhere from V-Bulls on out to 2s, where on a good day a few months earleir in the year I had shot a session of 1 x Bull and 9 x V-Bulls with the same rifle/ammunition mix!?? I was crest fallen and dumbfounded both!.....

Then I watched something on YouTube about the effects on the throat of one's rifle barrel caused by successive firings, particularly when using 'hot' rounds... So I wondered if THIS might be part of my problem, and set about re-measuring the absolute length of a cartridge made up from the same components (case and projectile) as my regular range load.. .... ....

DID I GET A NASTY SURPRISE !!!!! I now think I know why my rounds are wandering all over even a relatively close 600 yard target.. The C.O.A.L. (Cartridge Over All Length) of my usual, best range load has grown by, as near as damn it, 100 thousandths (1/10th) of an inch (about 95 thou' to be more exact)!!! .... So the throat of my rifle has LOST this amount of rifling length down the bore and out, with the erosion caused by the hot gasses and burning kernels... DAMN!!...

I have just set about reloading some rounds, again with the same best components (Lapua cases and 139gr Lapua Scenar bullets over a stout measure of IMR7828 SSC reloading propellant) and find that, if I set the bullets up so that they are the regular 15->20 thou' off the jammed into the lands length, the projectiles have hardly ANY shank now down into the case neck, holding the projectile both in the case and in a concentric arrangement with the rifle bore... like just 50 thou' or so, not much more than that!!.... Not suitable for rangework or any other form of shooting really...

So, now down to my URGENT and important (to me) question wherein I seek the assistance of other, knowledgable S.C. Members:-...
Given that I am now technically unable to build rounds of sufficient OAL to suit the loooong free-bore now apparent in my heavy barrelled Tikka t3 rifle, how best to recoup the situation please friends?? I am thinking I could :-
1). get the rifle rebarreled - which is an expensive option in the order of £600 plus, depending on the barrel I choose and whom I ask to do the work? The problem is solved but I will be binning a possibly still perfectly useable barrel in the process...??
2). ask an experienced, skilled Rifle Smith to take the current barrel off and set it back say half and inch or so - taking length from the effected chamber end of the barrel - rechambering and then setting the altered barrel back into the receiver. With this option I am all at sea as to whom I could ask (and trust?) to do this, and if I do find someone whom is appropriately skilled, the cost to me and the impact it MIGHT have on my rifle's accuracy?

Any other ideas please peoples?.. And any suggestions as to whom I Might ask to do the work in my option 2). above if feasable, and costs too please??

So There it is... Your considered assistance would truly be and fully Appreciated...

Kind Regards,
Blobby159

 

[John Gryphon]

Linda had that problem too i believe blobby....ha ha.

 

[Muir]

So. How did you get your original posting, "Help Required: Excessive OAL", and all the responses given, removed and this exact post "Help Needed: Throat Erosion" put up? I'd like to be able to that....
Or have i been too long and had too little coffee?

My response it still the same. Seat the bullet deeper. It's a shame to spend all that money on reloading dies and then just use a bit of the neck to hold the bullet. ~Muir

 

[1894]

My M700 243 has the same problem only more so

1. Throat my be rough and copper foul more quickly. Even if you find an accurate load you will have to clean more often. Periodic use of JB bore paste helps as well as regular wipeout or similar. I now have to clean about every 20 rounds.

2. Not all rifles/bullets require being close to the lands. Read the berger bullets article on finding COL for Vlds. Basically you test at 30thou steps. My TMK loads are best 60 thou off the lands

3. If it absolutely has to be close to the lands use a blunter bullet or consider a less sensitive bullet such as a hybrid

 

[zambezi]

My 6.5x55mm SE is very accurate out to 300m with cartridges whose CBTO is 2.337". As measured, the lands are at 2.589". So, accurate despite a 250thou+ jump. The projectile I am using is a monometal Barnes ttsx 120gr whose length is 1.321". All three cannelures are swallowed by the neck of the case at that CBTO. If your primary desire is long range target, then the ttsx is probably not optimum for your application.

But what I am thinking is that a suitable monometal may be your solution because the lower metal density will always translate to a longer projectile . Plus, if my experience is typical, monometals are not critical of large jumps/throat erosion tolerant.

Of the monometal target bullets available, Hasler looks interesting but not cheap, and not 139gr so new load work up required.

 

[308tikka]

If it is for target accuracy at long range, and you are competitive within whatever distance (unlikely with a stalking setup) then you need to either rebarrel or push the bullets further to the lands with current projectiles. Its that simple.

Or use jump tolerant bullets. What is your barrel count? If it is above 3000 on a stainless barrel you may find supreme accuracy (at long range) is itretrievably lost. Will that matter for stalking distances? Nope. Ive a barrel that was exceptionally accurate and lasted 9000 rds but then embarrassingly gave up the ghost in the middle of something quite important.

Barrels are a consumable. They wear out. Can you group <4” at 200yds? Go stalking.

 

[Laurie]

Your barrel may or may not be shot out. IMR-7828 is a pretty 'hot' powder (despite being single-based) and assuming you're running something around 49gn and the modern rifle 55,000 psi peak pressure, computed 'accurate barrel' life is 1,741 rounds on a one shot per minute firing rate.

Since you're using a factory rifle with a very hard hammer forged chrome-moly barrel, it's going to be a lot better than that, but still probably still somewhere within the 2,000-2,500 rounds envelope. Range use is HARD on barrels if using full-pressure loads - round counts mount up surprisingly quickly in individual sessions and barrels become hotter than you want unless you're shooting in a formal match setting that has 20 score shots plus a couple of sighters and maybe a few 'blow-offs' allowed.

When you hit the 100 thou' erosion level, even if the barrel isn't completely shot out you're way past the point where best performance has gone. If the throat is rough as a result of the erosion, gilding metal stripped off bullets quickly builds up in the throat / early part of the barrel, elevation consistency on the target deteriorates and the incidence of way-out fliers increases dramatically. (Pressure often rises considerably too due to heavy metallic fouling building up where the bullet enters the lands.) Apart from signs in shooting sessions, you'll see more copper affected (blue colour) patches if you clean with a bore solvent that has any copper remover in it. So, if not already doing it, the first step is to use a good copper remover and do it thoroughly and multiple times. That may or may not provide some amelioration. Step 1A is that with copper fouling removed have a gunsmith or someone in your club who knows his onions on barrel wear have a look up there with a borescope and tell you how things are wear-wise. If as bad as I suspect with that amount of erosion, setting the barrel back and rechambering isn't an option, it's a replacement job.

The 6.5s are lovely cartridges, but with the sole exception of the little Grendel they are not great choices for the high-volume range shooter who doesn't want to rebarrel. The similar case capacity but larger bore 7mm-08 gives another 1,000 rounds life over the Creedmoor, 260 Rem and 6.5X55 all other things being equal and the 308 Win a great deal more. A simple reference is to ascertain a cartridge case's capacity (in grains water) and divide that by the area of the bore.

overbore « Search Results « Daily Bulletin

Many people will be surprised to discover that you do these calculations and what they might regard as common, nothing special designs produce much higher values than they'd expect. For instance, 6.5 Creedmoor's ratio is very close to that of the 300 Rem SAUM short magnum (955 v 949). The 6.5X55 is worse, but runs at lower pressures (usually but not always in handloaded form too!) which discounts some of simple bore-capacity ratio effects. 243 Winchester is a seriously over-bore capacity design.

The 139gn Lapua Scenar is an absolute sweety of a design from the point of position tolerance. With an Rt/R shank to ogive ratio of 0.95 (0.5 = true VLD; 1.0 = true tangent ogive design) there are few 0.264" bullets that will accept large jumps as well. This tolerance has most likely masked the effects of throat wear by continuing to perform well even as erosion took the lands back enough to have long killed off many bullets' precision. All that happens with such a design is that MV steadily reduces with wear ....... UNTIL a wear / roughness level is reached where nothing is going to shoot well.

 

[Blobby159]

My 6.5x55mm SE is very accurate out to 300m with cartridges whose CBTO is 2.337". As measured, the lands are at 2.589". So, accurate despite a 250thou+ jump. The projectile I am using is a monometal Barnes ttsx 120gr whose length is 1.321". All three cannelures are swallowed by the neck of the case at that CBTO. If your primary desire is long range target, then the ttsx is probably not optimum for your application.

But what I am thinking is that a suitable monometal may be your solution because the lower metal density will always translate to a longer projectile . Plus, if my experience is typical, monometals are not critical of large jumps/throat erosion tolerant.

Of the monometal target bullets available, Hasler looks interesting but not cheap, and not 139gr so new load work up required.

View attachment 169855

Hi 'zambezi', and thank you for your considered response to my personal problem here. It is NOT one I had expected nor even anticipated and in my mind it is a wee bit left field, but I like it a lot... I really do LIKE IT!!!! You are correct in that the bullets thenselves are not cheap or anywhere even in the same Continent as 'cheap', but then it might just be an answer to my problem and as such IS cheap, and beautifully eloquent in its simplicity. Now I will have to research and find out just what is available in MY Country to answer this quest, I live in the U.K. you see, and cos our market here is mighty small when put up against almost even any STATE in the U.S. the returns for amy importer and/or retailer here are small to not worth bothering with where unusual products are involved, ESPECIALLY Shooting Products cos my Contry's Laws regarding the shooting sports can be a tad prohibitive (to say the very least).
But it offers a possible direction for getting around these disappearing throat lands in my - primarily though NOT exclusively - target use rifle.... I do occasionally take an occasional deer for eats, and use Nosler Partitions for the projectiles which are flat based near as damn it and I can seat out to the near lands for my accuracy load and still have a reasonable bit of the projectile base into the case neck, whereas the Lapua Scenars and other target bullets I use almost ALL tend to have deep lengths of boat tail to their rears and loose that into the case necks BEFORE anything gets "grasped" and held firmly.
Again, thank you!

ATVB,
Blobbs....

 

[Blobby159]

Your barrel may or may not be shot out. IMR-7828 is a pretty 'hot' powder (despite being single-based) and assuming you're running something around 49gn and the modern rifle 55,000 psi peak pressure, computed 'accurate barrel' life is 1,741 rounds on a one shot per minute firing rate.

Since you're using a factory rifle with a very hard hammer forged chrome-moly barrel, it's going to be a lot better than that, but still probably still somewhere within the 2,000-2,500 rounds envelope. Range use is HARD on barrels if using full-pressure loads - round counts mount up surprisingly quickly in individual sessions and barrels become hotter than you want unless you're shooting in a formal match setting that has 20 score shots plus a couple of sighters and maybe a few 'blow-offs' allowed.

When you hit the 100 thou' erosion level, even if the barrel isn't completely shot out you're way past the point where best performance has gone. If the throat is rough as a result of the erosion, gilding metal stripped off bullets quickly builds up in the throat / early part of the barrel, elevation consistency on the target deteriorates and the incidence of way-out fliers increases dramatically. (Pressure often rises considerably too due to heavy metallic fouling building up where the bullet enters the lands.) Apart from signs in shooting sessions, you'll see more copper affected (blue colour) patches if you clean with a bore solvent that has any copper remover in it. So, if not already doing it, the first step is to use a good copper remover and do it thoroughly and multiple times. That may or may not provide some amelioration. Step 1A is that with copper fouling removed have a gunsmith or someone in your club who knows his onions on barrel wear have a look up there with a borescope and tell you how things are wear-wise. If as bad as I suspect with that amount of erosion, setting the barrel back and rechambering isn't an option, it's a replacement job.

The 6.5s are lovely cartridges, but with the sole exception of the little Grendel they are not great choices for the high-volume range shooter who doesn't want to rebarrel. The similar case capacity but larger bore 7mm-08 gives another 1,000 rounds life over the Creedmoor, 260 Rem and 6.5X55 all other things being equal and the 308 Win a great deal more. A simple reference is to ascertain a cartridge case's capacity (in grains water) and divide that by the area of the bore.

overbore « Search Results « Daily Bulletin

Many people will be surprised to discover that you do these calculations and what they might regard as common, nothing special designs produce much higher values than they'd expect. For instance, 6.5 Creedmoor's ratio is very close to that of the 300 Rem SAUM short magnum (955 v 949). The 6.5X55 is worse, but runs at lower pressures (usually but not always in handloaded form too!) which discounts some of simple bore-capacity ratio effects. 243 Winchester is a seriously over-bore capacity design.

The 139gn Lapua Scenar is an absolute sweety of a design from the point of position tolerance. With an Rt/R shank to ogive ratio of 0.95 (0.5 = true VLD; 1.0 = true tangent ogive design) there are few 0.264" bullets that will accept large jumps as well. This tolerance has most likely masked the effects of throat wear by continuing to perform well even as erosion took the lands back enough to have long killed off many bullets' precision. All that happens with such a design is that MV steadily reduces with wear ....... UNTIL a wear / roughness level is reached where nothing is going to shoot well.

Thank you for your personal reply here Laurie, I honestly appreciate this very much indeed. So I think you are saying that cos the 139gr Lapua Scenar projectiles are such "sweeties" with their cartridge seating depth / throat lands distancing AND the hardness of the modern chrome/moly factory Tikka bores has disguised my problem, especially in the most recent shooting exercises, till it got way past where it would have been obvious had I made other choices in rifle and projectiles used. This makes sense to me now, especially as this has only recently turned out to be a problem I ACTUALLY have noticed - more by accident than by design as it happens - and I was left initially wondering what the blue blazes was happening. I could get a decent cluster with my Lapuas but having problems with some of my other (target AND hunting) loads...
You are a Brit aren't you?.. Could you suggest to me some trusted 'Smith or Company that you would trust whole-heartedly with changing the barrel over to something a bit more exotic for me? Also, if it doesn't countermand some agreement or other that you had to sign into to help out on this site, what barrel might YOU suggest I get whomsoever to replace for me? My ONLY hard requirements are that a new barrel would have to be 2"8->30" long, of heavy sporter to medium target/varmint weight of similar contour to that which my current Tikka Sporter rifle has given me, constructed of a material with a top level of longivity and, if possible and NOT contrary to these earlier "wants", hammer forged for the same reasoning you specified in your response above.
I realise this is a bit of a stretch where "helping another shooter" is concerned, but if my request options are all compatable with a barrel type AND are replaced by the 'Smith and/or Company of your suggestion, would you be able to provide me with a rough guide to my costs please Laurie.... new, quality barrel and installation ??
As a final thought, is there ANY good in me asking for a new barrel replacement to be chambered in 6.5x55 A.I. instead of the vanilla 6.5 Swede please Laurie? I realise I will have to use a larger powder load to even get replaceble velocities for my current rifle load with the (outlawed) IMR7828 propellant, but would my shooting/competing with similarly hi-pressured loads of faster MVs using larger charges be an anathema to barrel life again please my friend??

Again I do most appreciate your involvement and assisitance here Laurie, truly I do!

Kind Regards,
Blobbs....

 

[Blobby159]

B.T.W. "Laurie" / "308tikka"/ "1894"..., I really didn't start with a fired rounds count so have little actual idea just how many projectiles have made the short, sharp trip up my rifle barrel, but it is certainly something like1500-2000 rounds if I am making as accurate an estimate as possible...
Another thing that has surprised me somewhat is this:-
A day ago I went to one of the fields where I set up my rifles and fired 25 more rounds of my regular Lapua Brass/ 139gr Lapua Scenar / IMR7828 SSC target loading to give me a rezeroed unit following having changed out my steel 20 MOA Picatiny 'scope rail for a direct 30 MOA replacement. Previous to this and the day before, I spent an hour or so THOROUGHLY cleaning out my bore which finalised with a decent period of lapping out with a proprietary bore paste, paying special attention to the first 6" or so of bore.
My three shot, final zero checking rounds gave me a respectable 0.75" neat cloverleaf cluster at a measured 200yds (my preferred zero distance with the rounds explained above)!?... Given that I too was initially thinking that my bore had been "shot out" this surpised me quite a lot as you will surely also acknowledge..... I am at a loss to explain this but more than a little happy for this to continue for as long as possible!!

Best Regards,
Blobbs....

 

[Blobby159]

So. How did you get your original posting, "Help Required: Excessive OAL", and all the responses given, removed and this exact post "Help Needed: Throat Erosion" put up? I'd like to be able to that....
Or have i been too long and had too little coffee?

My response it still the same. Seat the bullet deeper. It's a shame to spend all that money on reloading dies and then just use a bit of the neck to hold the bullet. ~Muir

"Muir" my friend.... I was uncertain if I had posted to an area where the people hopefully responding would be interested in my problem and therefore bothered with helpin out, and as my first day or so gave me zero replies (sort confirming my thoughts there for a while) I copied the whole query to the other forum area too!
It isn't a problem brought about by your lack of morning Jo, believe me! ️️️

 

[1894]

B.T.W. "Laurie" / "308tikka"/ "1894"..., I really didn't start with a fired rounds count so have little actual idea just how many projectiles have made the short, sharp trip up my rifle barrel, but it is certainly something like1500-2000 rounds if I am making as accurate an estimate as possible...
Another thing that has surprised me somewhat is this:-
A day ago I went to one of the fields where I set up my rifles and fired 25 more rounds of my regular Lapua Brass/ 139gr Lapua Scenar / IMR7828 SSC target loading to give me a rezeroed unit following having changed out my steel 20 MOA Picatiny 'scope rail for a direct 30 MOA replacement. Previous to this and the day before, I spent an hour or so THOROUGHLY cleaning out my bore which finalised with a decent period of lapping out with a proprietary bore paste, paying special attention to the first 6" or so of bore.
My three shot, final zero checking rounds gave me a respectable 0.75" neat cloverleaf cluster at a measured 200yds (my preferred zero distance with the rounds explained above)!?... Given that I too was initially thinking that my bore had been "shot out" this surpised me quite a lot as you will surely also acknowledge..... I am at a loss to explain this but more than a little happy for this to continue for as long as possible!!

Best Regards,
Blobbs....

I am nowhere near as knowledgeable as Laurie but I am not surprised. Enjoy your second honeymoon, it might not last but its free accuracy so take it!

 

[Laurie]

A day ago I went to one of the fields where I set up my rifles and fired 25 more rounds of my regular Lapua Brass/ 139gr Lapua Scenar / IMR7828 SSC target loading to give me a rezeroed unit following having changed out my steel 20 MOA Picatiny 'scope rail for a direct 30 MOA replacement. Previous to this and the day before, I spent an hour or so THOROUGHLY cleaning out my bore which finalised with a decent period of lapping out with a proprietary bore paste, paying special attention to the first 6" or so of bore.
My three shot, final zero checking rounds gave me a respectable 0.75" neat cloverleaf cluster at a measured 200yds (my preferred zero distance with the rounds explained above)!?... Given that I too was initially thinking that my bore had been "shot out" this surpised me quite a lot as you will surely also acknowledge..... I am at a loss to explain this but more than a little happy for this to continue for as long as possible!!

Best Regards,
Blobbs....

I am not surprised. Enjoy your second honeymoon, it might not last but its free accuracy so take it!

Yup 1894 has most likely got it 100% right. With a heavily eroded throat, copper fouling rises dramatically which as I said earlier affects precision and consistency, often raises pressures too. If this is the case (as I expect), you can keep the barrel soldiering on for a while, although you'll likely find that to keep precision acceptable, you'll have to repeat the heavy cleaning routine at short intervals. (An infallible guide to who has got a barrel 'on its last legs' amongst competition shooters is to see who, in multi-stage comps, gets down on his knees and starts scrubbing the barrel after each stage to start 'afresh' before he reports to his next detail.) So, you put the evil day off for a while, maybe even quite a long while with the factory Tikka barrel. With much softer stainless steel match barrels, the stay of execution is nearly always short as (having a now uncompetitive rifle in most disciplines these cut-throat days aside) once it gets like this, bits of land surface start breaking up and disappearing out of the muzzle with the bullet.

So, you need to have a gunsmith look at the barrel some time soon who'll tell you where you (or more accurately the inside of your barrel) actually are. Ask on SD for recommendations for gunsmiths in your region known to do good work. He'll tell you whether your barrel is a knackers yards job or otherwise, and if so recommend a replacement profile, make and all the rest after talking things through with you about your type of shooting. He'll be able to make much better recommendations than I can from a distance.

6.5X55AI? Hey, you're a real glutton for punishment aren't you? If you run this one at all 'hot', barrel life will be modest to poor. You're virtually at 6.5-284 barrel-life numbers with a hot 6.5X55AI loading. In the early days of GB F-Class, the 6.5X55AI was pretty popular before the 6.5-284 took off and eclipsed it (not to mention 7mm short magnums and now the .300WSM all in 10-15 years). One problem with this choice is nobody does off the shelf dies for it, so it's either a custom die job or re-cut the internal case-supporting sleeves of Redding 6.5X55 Competition dies. When the cartridge saw a bit of competition work Norman Clark the Rugby gunsmith chambered a lot of people's rifles and did the die mods too. Over in the USA, a slightly different variant called the 6.5X55BJI (or 6.5X55mm BJ Improved) is apparently now more popular than the old Ackley version and its adherents claim wonderful not so say bl**dy amazing things for it (as such enthusiasts always do! ).

 

[Blobby159]

6.5X55AI? Hey, you're a real glutton for punishment aren't you? If you run this one at all 'hot', barrel life will be modest to poor. You're virtually at 6.5-284 barrel-life numbers with a hot 6.5X55AI loading. In the early days of GB F-Class, the 6.5X55AI was pretty popular before the 6.5-284 took off and eclipsed it (not to mention 7mm short magnums and now the .300WSM all in 10-15 years). One problem with this choice is nobody does off the shelf dies for it, so it's either a custom die job or re-cut the internal case-supporting sleeves of Redding 6.5X55 Competition dies. When the cartridge saw a bit of competition work Norman Clark the Rugby gunsmith chambered a lot of people's rifles and did the die mods too. Over in the USA, a slightly different variant called the 6.5X55BJI (or 6.5X55mm BJ Improved) is apparently now more popular than the old Ackley version and its adherents claim wonderful not so say bl**dy amazing things for it (as such enthusiasts always do! ).

So Laurie, I take it that your advice would be to give the 6.5x55 AI or similar options a COMPLETE BODY SWERVE, Yes?... I need no further indicatin or advice in THAT area then. My love of spending a small fortune on rebarreling every 18 months to 2 years or so is really not that great... In fact, I am SERIOUSLY considering selling my current rifle to someone for a good starting point for a specialist build and simply buying a completely NEW rifle again. That one only(?) cost me £1,700 and I now have all the ancilliary equipment - like reasonable quality 'scope, 30 MOA rail, muzzle brake, and stainless moderator, and the reloading equipment etc. etc. are ALL dialed in to making up pretty decent 65x55 Swede "feed" so that might be my simplest route Laurie...

Are you able yet to give me even a ball-park figure of the total anticipated costs with a decent barrel replacement please? Nothing too ambitious as I am nothing like the shot, nor as competative as yourself my friend, but I yet do appreciate my bullets hitting EXACTLY where I loose then off towards so I will spend money..... but only if absolutely required! Ha!
Kindest Regards and Sincere Thanks,
Blobbs......

I am nowhere near as knowledgeable as Laurie but I am not surprised. Enjoy your second honeymoon, it might not last but its free accuracy so take it!

Don't denegrate yourself too much "1894", you are pretty GOOD in MY book believe me!! And thank you too, I will enjoy my erm.... "second honeymoon" with my rifle and hope that my thorough cleansings DON'T have to happen that often. If I can get a session at a time down at the range (a Club Day @ Bisley a,ounts to 60 rounds max.) once a month for a few more months I MAY get a decent Chrissy present group-wise from the Wifey and my two grown up kids..... Maybe?? I will be dropping hints that even YOU can hear... Hahahahahahahhaaaaa!!...
Kind Regards to you too,
Blobbs.....