Question-6.5X55AI

[butchlambert]

A friend is considering a 6.5X55AI over the standard 6.5X55. He is thinking of doing this because he was told the shoulder angle would give him more throat life in his barrel. He doesn't care about extra velocity.
What are your thoughts?

 

[Rdlningcltchdmpr]

Who on earth came up with that hypothesis ?

 

[Rdlningcltchdmpr]

Red Apple's are better than green or yellow.

 

[Hopkins]

I suppose that it’s possible if you insist on trying to get 6.5x284 velocities out of 6.5x55 versus 6.5 x55 AI.

 

[butchlambert]

Red Apple's are better than green or yellow.

So is that an informed opinion or out of somebody's #@$? Red apples are better that yeller ones. Just tell me how you know and where can I read facts to back up your?

 

[butchlambert]

I suppose that it’s possible if you insist on trying to get 6.5x284 velocities out of 6.5x55 versus 6.5 x55 AI.

Velocity is not what he is looking for, just more barrel life

 

[wwbrown]

I do not have any definitive comparison between accuracy decline comparison between a 6x55 and a 6.5x55 AI but I can say my 6.5x55 AI gave me 6.5 x 284 velocities and an accurate barrel life less than 900 rounds. Prior to 800 rounds the cartridge was great, the nodes were wide and very easy to find temp stable accurate rounds.

Not directly answering your question, but may be an example of there is no free lunch. Some conventional wisdom thought that the case geometry of 6.5 x 55 AI would provide 6.5x284 performance with a longer barrel life than the 6.5 x 284 but I did not find that the case.

Your mileage may vary,
wade

 

[butchlambert]

Thanks for your help. Let me restate his question. Will the AI shoulder angle improve throat-barrel life? He's not looking for more velocity. He just wants to know if the shoulder angle will have less throat erosion with the AI.

 

[Hopkins]

I opted for the vanilla 6.5x55 over the AI because I stay in the low 2800’s with the 140-142’s and expect to get barrel life similar to a .308.
That is based on some advice I got from some Aussies and kiwis that were campaigning them 5-6 years ago.
So far so good but I’m still under 700 rounds.

 

[butchlambert]

The fellow lives in a country that barrels and all shooting items are very expensive and hard to get. If he were in the USA, another barrel every 1000 rounds would not be an issue.

 

[acloco]

I have not shot enough AI rounds thru two different options available to me, to say barrel life is extended.

My equipment may not tell the truth, as I use WS2 coated bullets.

One item that IS a nice benefit of AI, trimming brass is a thing of the past. After initial fireform, load again (after checking length), shoot again, THEN trim to length. Will not need to trim for at least 3 or 4 more firings.

Another SUPER side benefit of the x55 cartridge, x55 brass is usually tied with 223 as the LEAST EXPENSIVE Lapua brass. So, great brass on the cheap....who could complain?

 

[rardoin]

Butch, I have shot a 6.5 x55 Jourdan AI for the last 3 years in F-open. I run a 142gr at 2940 fps Vavg/ 30" barrel. Ny first barrel was pulled at 1800 rounds, throat a bit firecracked for 1.5"+ in but still holding the X-ring at 600yds and very competitive. However, I would say it is about done. I have several others barrels that have been in service and two over 1000rds and going strong. I use RL-23. I size back 0.0025" at the 0.400" datum and case growth has been minimal with 10+ firings on many cases (only lost one due to primer pocket expansion and one to partial neck separation due to a deep shoulder cut due to hamfisted neck turning). I am just starting to probe a slight depression on the inside of the case wall above the web at 10 cycles. I think the best advantage of the AI version is low case growth due to the reduced wall taper/steep shoulder angle and lower pressure to reach 2900fps+ with a 140gr class bullet. I don't have a competition plain vanilla swede so I can't say if the 40deg shoulder angle is kinder on the throat. The barrels do outlast a 6.5-.284 running the same velocities/bullet which is the premise upon which I chose that cartridge.

And, as mentioned, great brass is plentiful and cheap!

Robin

 

[Laurie]

Thanks for your help. Let me restate his question. Will the AI shoulder angle improve throat-barrel life? He's not looking for more velocity. He just wants to know if the shoulder angle will have less throat erosion with the AI.

This question apparently relates to the 'turbulence point' (TP) hypothesis. This runs on the lines that a highly erosive ball of partially burned powder kernels and super-hot combustion gas forms ahead of the charge body and this can be located either within the case-neck or just outside of the case-mouth depending on case shape and neck length. If within the neck, the throat is given some protection and for any given powder burn temperature / max pressure combination sees less wear than if the TP forms ahead of the case-mouth.

To see whether a design is 'good' or 'bad' in TP-effect, one takes an accurately scaled case drawing and laying a ruler on each shoulder extends their lines upwards so they intersect. If that happens inside the neck, it's 'good' and if outside, 'bad'.

A good example of this is the 243 Winchester which has a shallow shoulder angle and short neck as well as being pretty seriously over-bore capacity. Hence a well known barrel burner! The 6mm Rem with a longer neck and 26-deg shoulders v the Win's 20-deg allegedly gives better barrel life if loaded to the same pressures with the same bullets and powders. There are also various 243 Win variants which involve a simple one-pass through a sizer die to reform the neck and shoulder - Robert Whitley's 6mmSLR, the 6mm Competition Match and others. The SLR reforms the 243 Win case to that of David Tubb's 6XC with 30-deg shoulders and a considerably longer neck. Robert and many of his cartridge's users claim better performance and a significant upgrade to barrel life over the parent design.

The standard 6.5X55 case is pretty good with a generous neck length and 25-deg shoulders. The shoulder lines intersect right on the case-mouth as in the right hand drawing - better than the 100 year younger 260 Rem on the left where the 'TP point' will be outside of the mouth.

http://bulletin.accurateshooter.com/tag/260-remington/

Moving to a 40-deg shoulder will push the 'TP point' further back to being well inside the case-neck, so IF you accept the TP hypothesis as being a significant factor in barrel life it might be worth doing to enhance barrel life. Against that is the 'improved' case increases overall capacity so slightly more powder is burned to obtain the same PMax and MVs as the parent 'straight' version. .......... and who knows what effect a 40-degree shoulder in itself has on the characteristics of a very flexible and well-mannered cartridge in its original form when loads / pressures are kept moderate as your friend intends?

If restricted to Swedish Mauser type pressures and loads, the 6.5X55 gives very good barrel life for a full-size 6.5mm cartridge and that seems a better course to me. Of course where out and out MV maximization isn't the objective ............ Dare I suggest this and cause outbreaks of plagues of frogs, other biblical terrors, or simply anger and derision? Oh, to hell with it ...... Your friend could dare I say this adopt 6.5mm Creedmoor, a modern 30-deg shoulder case design and load it light to 6.5X55 Swedish Mauser pressures to give still yet better barrel.

 

[ebb]

I have also heard much of what Laurie has said. I am not sure if it is theory or fact. I would very much like to know. Some long held truths and gun facts are only in place cause people want to believe these things. Where is Harold Vaughn when you need him.

 

[Laurie]

I am not sure if it is theory or fact.

Unfortunately, that's so! The hypothesis does make a sort of sense, BUT many things in rifle and cartridge performance end up proving counter-intuitive. Certainly, the modified 243 Win chamber adopters, 6mm SLR and suchlike believe it - if you hunt up threads on them in the forum, claims of great MVs with heavy bullets and 3,000 + barrel round life are made by some. (I had an SLR chambered barrel on one of my rifles and its life was pretty well what I'd expect from a run of the mill 243 Win with the same loads, certainly nothing special - but there are so many variables in play, in particular the individual make of barrel, its production lot of steel as supplied from the foundry and its resistance to erosion - that I wouldn't draw any conclusions from the experience. I like Mr Whitley's design a lot - a 'sensible wildcat' and what a modern 243 ought to look like - and intend to have another barrel so chambered in due course.)

What I suspect - and gut feelings like this are frankly worth nothing really - is that it ('good' TP) does change things for the better, but its effects are marginal compared to other factors - case capacity and charge size to bore ratio, bullet weight, powder type and flame temperature, loads and pressures generated, rate of fire and barrel / heat, type of barrel and steel employed.

Somewhere or other I have copies of an old American Rifleman article that some brilliant and generous soul put up on this forum a few years ago written by a Finnish Army ordnance officer of a test of round count v group dispersion that the Finns carried out on a service 7.62X54R rifle with over 14,000 round fired down the one barrel! It still shot well at that point, although groups started to slowly get larger IIRC at around the 10 or 11,000 round mark. My conclusions from this were that the benefits of a reasonable bore capacity ratio, modest (sub 50,000 psi pressures), use of Vihtavuori single-based powders are much greater than finessing case shape. Passing it around friends including some fine British gunsmiths who know all about barrel life from how often they see regular F-Class and BR competitors elicited the response that the barrel steel may have contributed just as much as these factors, and maybe even more. The stainless steel grade used in custom match barrels makes for super quality products and is easy to machine, but is sadly very 'soft' when it comes up against 60,000 psi + pressures and very hot gas. (Users of European Lothar-Walther stainless barrels have shown considerably better life as they use a harder grade of stainless - many gunsmiths dislike these blanks though.)

 

[Laurie]

.......... there is one certain benefit of the AI form though, almost worth adopting the improved chamber just for it - the near end of any need to ever trim cases back again as AI improved brass doesn't 'grow' in use and through FL sizing.

 

[eww1350]

Have the barrel treated with the Melonite process and barrel life will be much better that going with the A.I. version.

 

[carlsbad]

The cartridge that this argument applies better to is the SLR family. The 6.5mm slr takes a 260 shell, squares off the shoulders by pushing them back and you lose a grain or 2 of powder while getting a square shoulder and longer neck. It has often been said that the longer neck keeps heat off the throat...it makes sense but I haven't seen any real data showing it is more than a theory.

The cost is that you need to turn the necks because you've converted thick shoulder to nick and it is uneven.

I haven't spent any time on the 6.5x55 but I guess I should, it's the trendy cartridge now.

--Jerry

 

[AckleymanII]

I am a firm believer in the 'turbulence point' (TP) hypothesis. I saw this TP change the throat growth in 6 XC with a .400 long neck, made from 308 palma brass with Paul Bike's form dies. I have mentioned this two or three times on this board, but the work involved generates no interest what so ever. I shot H4350 and R#17. The tiny minute fire cracking started within 400 rounds of shooting 41.5g of R#17 and the velocity of the 107 in the 31" barrel was 3250. Leade however did grow very, very little over 900 rounds. I throated the barrel .145, and extended the neck with a PTG piloted neck reamer.

Those of us that shot out multiple barrels of 6 Remington and 243 on p. dog towns saw how the 6 Rem was easier on throats. I do believe that a longer neck than .325 is needed to see HUGE advantages in the 'turbulence point' (TP) hypothesis. As stated by Laurie, there are many factors involved.

An easy way to test would be to make a case like a 22-243 AI, fast twist, with a .400 long neck, approximately which would be easy to do when forming down Palma brass. Same thing with a 22-6 Rem AI when made from Lapua 30/06 brass. These calibers get 800-1000 rounds per barrel. If you were able to get 1400 rounds from a long neck, then you are on to something.

Paul Bike form dies along with a neck reamer is all that would be needed, and makes for a great Winter project.

To me, common sense dictates that as you approach 50g of powder, fire cracking and leade growth will increase no matter what kind of whistles and bells you have on the case or Bones from a dead black cat you may have in your pocket. Perhaps cooler burning powders are your only salvation.

 

[Laurie]

I am a firm believer in the 'turbulence point' (TP) hypothesis. I saw this TP change the throat growth in 6 XC with a .400 long neck, made from 308 palma brass with Paul Bike's form dies. I have mentioned this two or three times on this board, but the work involved generates no interest what so ever. I shot H4350 and R#17. The tiny minute fire cracking started within 400 rounds of shooting 41.5g of R#17 and the velocity of the 107 in the 31" barrel was 3250. Leade however did grow very, very little over 900 rounds. I throated the barrel .145, and extended the neck with a PTG piloted neck reamer.

That's good to know. I must have missed your posts on the subject. (AS Forum has become so big now, it's hard to take everything on board these days.)

hose of us that shot out multiple barrels of 6 Remington and 243 on p. dog towns saw how the 6 Rem was easier on throats. I do believe that a longer neck than .325 is needed to see HUGE advantages in the 'turbulence point' (TP) hypothesis.

Ah, that's also very valuable. That (6mm Rem superiority over 243 in barrel life) was what I understood, but with the decline in use of the Remington cartridge in recent years, I'd wondered if it was one of these 'shooting myths' / 'long-held truths' handed down from olden times of maybe 20-50 years ago that as 'ebb' says in his post are now difficult to verify and when tested sometimes turn out to be simply wrong.