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Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by trigger103, Apr 11, 2012.
What could I see or expect if I AI my 6.5x55. What would the benefits be,if any.
According to the P.O.Ackley load manual you can expect around 100fps muzzle velocity increase over the non-AI version.
little bit faster.
Don't forget though, some of the best benefits aren't on the performance side but have to do with increased barrel/throat life, longer case life, and more consistent burns. All very good things in addition to the potential velocity gains. And with the PO you can shoot the standard cartridge in the new chamber to fire form and usually still get fine accuracy. With Ackley improvements the datum line stays the same for head-spacing. This makes fire forming very easy and also allows the use of store bought ammo if needed.
In my HVA 1540 with a 26'' barrel 123 gr scenars loaded with 55.5 gr of Vithavuori 560 gives around 3250 Fps and 63500psi
Suberb precision is achived with55Gr of N15(Similar to RL22\MPR) and 3100Fps\61500Psi with same bullets
Where are you deriving the Pressures from?
Quickload or are you using some kind of test fixture or extrapolating from load manuals?
3250 is better than a lot of 6.5-06AI's....
EDIT: Actually I was thinking 140's. But the Velocity is still surprising close to 6.5-06AI
Making an A.I. out of the 6.5x55 is one of the best to do it with IMO. It has a lot of taper in the original form and other good reasons were already given.....Rich
An interesting but rather long read on Ackley cartridges and their performances. I copied this from another forum a long time ago. The gent writing it would agree with you elkaholic. He liked the 6.5x55 AI. The portion on the 6.5 is highlighted in red.
[FONT="]Good to hear from you and especially about those fine old-time Ackley Improved cartridges. As you know, Ackley was far ahead of his time…and far ahead of all the commercial cartridge companies in improved design. He was our last great cartridge experimenter who could and did write about his work. Today we seem to have arrived at a point where we have experimenters and we have writers, but the two almost never meet! The great Ackley handbooks, Volume I & II, Handbook For Shooters & Reloaders, is in need of updating, but it would be a major undertaking and would require the input of some top experimenter and/or writer. If you inspect the loading data in those two books you will immediately notice the outdated, discontinued powders and the fact that he almost never gave barrel lengths along with velocities. Also, a number of the cartridges in Ackley’s books listed data from other sources such as directly from the designer who estimated most velocities, optimistically. But in spite of these minor disparages, Ackley’s books are still the experimenters bible, just loaded with technical information not found elsewhere.
Before getting into your questions concerning the Ackley cartridges with the best percentage improvement, smallest improvement and the ones left in the middle, perhaps you would have an interest in Ackley’s background…just to pass on to your friends in the hot stove league involved in the Ackley arguments during cold winter days. Parker O. Ackley was born in Granville, New York, graduated from Syracuse University in 1927 and nine years later started his first gunsmithing business in Roseburg, Oregon, 1936. He was with the Ordnance Department during World War II and then moved on to Trinidad, Colorado to open what was to become one of the largest custom gun shops in the country. He also taught at Trinidad State Junior College where his gunsmithing school became world famous. He moved on to the Salt Lake City, Utah area where he continued his shop and did a great deal of experimental gun work. Along the way he became widely known as a gun writer where he passed on his knowledge of the trade. He left us all in 1989 at the ripe old age of 86.
The first cartridges designed by Ackley in the so-called Improved shape simply straightened out the tapered case body, giving the original factory designs a more straight walled dimension and leaving the shoulder angle the same. While this proved to reduce back thrust on the bolt, it still showed some case stretching in the neck and shoulder area that resulted in continued case trimming. When he changed the shoulder to something like 30 degrees the case lengthening slowed and by the time his designs reached 40 degree shoulders, all case lengthening stopped, within reason. It became common to reload those cases 15 – 20 times without having to trim them. Thus, the benefits of the famous Ackley Improved cases became reduced back thrust and elimination of case trimming. Case extraction became easier and more positive and loading pressures could be increased safely, resulting in higher velocities. Another interesting feature of these Improved chambers is the fact that standard factory cartridges can still safely be fired in the rifle. There are some die makers that still offer Ackley dies with the milder shoulders, so when ordering loading dies it is prudent to specifically request the 40 degree shoulder model.
Now to get on with your questions. There are more than 20 Ackley Improved cartridges, plus dozens of Ackley Wildcats, but some have about gone into obsolescence because the parent cartridge is no longer being loaded by the factories. Thus, brass is difficult to find. Of those that are alive and well today, the percentage of velocity gain over factory loadings ranges from about 3% up to 17%. A couple of others exceed this gain, but the parent cartridges are no longer being chambered for by the rifle companies. When we compare the Ackley Improved cartridges to handloaded standard factory rounds, the velocity gain ranges from zero up to a little over 12%. From this you can see there are a few Ackley Improved cartridges that may not be worth the trouble and expense to chamber for. But on the other hand, there are several that will simply blow you away with their new velocities, especially when compared to some of the much larger factory belted magnums, the big boomers.
There are many sources of cartridge velocities available today. These include factory listings as well as the dozen or so reloading manuals. This means there are many different barrels being used to arrive at those velocities. And that is why we, as handloaders and experimenters, must utilize several loading manuals in order to arrive at some norm that can be our starting point. When searching for the proper velocities to pass on to you to answer your questions, I first took the factory listed data from several cartridge companies and used their best figures. Then I utilized Ackley’s book figures, plus data from various other sources where barrel length and chronographed velocities were shown. This meant that some information differs from that found in Ackley’s books due to using new powders, stating the barrel lengths and chronographing over electric chronographs instead of the old pendulum style used so often by Ackley. In all cases pressures could only be observed by common shooter’s methods, that is, by checking primers, primer pockets, case heads, extraction, case life, etc. Generally, pressure guns using the crusher-gage method and resulting in copper units of pressure (c.u.p.) are not available outside the ballistics labs. This is also basically true of the more modern electronic-transducer gages that record in pounds per square inch (p.s.i.). These methods of discovering chamber pressures result in disabling the rifle by drilling into the chamber or at least attaching wires to it. It should be remembered that pressures given in c.u.p. are somewhere around 15% lower than those found in p.s.i. recordings, and when using various books giving pressures be sure to notice when two different methods are being used.
The best velocity gain of all the Ackley cartridges compared to the standard factory cartridge comes with the .25-35 WCF with a 117 gr. bullet and a gain of about 25.6%. The second best is the .30-40 Krag and the 180 gr. bullet showing a velocity gain of 19.3%. Both are rimmed cases and neither one is being chambered for today. Therefore, we will start with the third best velocity gain of 17% as found with the little .250 Savage when converted to the Ackley configuration and loaded with the 100 gr. bullet. Our rifle companies have chambered for the .250 Savage from time to time, but it is rapidly becoming obsolete in spite of the many knowledgeable shooters who use it regularly. The factory .250 Savage load is 2820 fps, while the .250 Ackley attains close to 3300 fps. This little speedster can equal or exceed the factory velocity of the much larger .25-06, listed at 3220 fps. And it is being done with 15 – 20 grs. less powder which means a great deal less recoil for the same velocity and trajectory. This is downright amazing…. And all this is being done in a short action. This .250 Ackley cartridge is not shown in any modern reloading book that I know of. Some books do show another .25 caliber, the .257 Ackley, that lands farther down the line in eighth place for best Ackley percentage gainers. I have used the .250 Ackley for both varminting and big game hunting with outstanding results. [/FONT]
[FONT="]For the next best gain, number four in the chart provided, I am taking my writer’s prerogative to show a standard cartridge that Ackley did not work on, but is now known as the 6.5x55 BJ Ackley Improved, the initials being my own. In the early 1990s I thought the standard 6.5x55 Swedish cartridge would show nice gains if it were improved as an Ackley. Little did I know that Ackley never did it. But to make a long story short, I got busy and copied the Ackley design into the 6.5x55, with a great deal of input from Dave Manson of Manson Reamers (PS advertiser). With the 140 gr. bullet the velocity gain is 13.7%. Standard factory velocity is 2550 fps, while the 6.5x55 BJ Ackley gets 2900 fps. This is another Ackley cartridge that I have used extensively for hunting, and I have heard from several readers who use it in long range competitive shooting.
Fifth in the chart is a surprise – the .30-30 Ackley. It shows a gain of 12.9% over the factory load with the 150 gr. bullet. The factory shows a velocity of 2390 fps, and the Ackley can skip along at 2700, even from common lever action rifles according to Mr. Ackley. That just happens to be faster than the factory .300 Savage, and yet it is the good old fashioned, century-old cartridge, improved.
Sixth best gain belongs to the 7x57mm Ackley. Since we have properly verified loading information in the Speer #2 Manual, those are the figures we used and thus the Ackley beats the factory 7x57mm Mauser by 12.8%. The 7x57mm Ackley equals the factory .270 Winchester and does so with 10 grs. less powder and less recoil. Ackley said this cartridge has the ideal capacity for a 7mm, and is powerful enough for all North American big game hunting. I have friends who use this one, and it is outstanding.
The seventh place round is another surprise to most shooters. It is the .300 H&H Ackley Improved, with an increase over the standard factory round of 11.1%. The factory loads the .300 H&H with the 180 gr. bullet to 2880 fps, while the Ackley gives 3200. There have been a number of improved .300 H&H cases, including the .300 Weatherby. They all headspace on the case belt, so the case body can be blown out to most any shape. Loads for the Ackley and the Weatherby are the same. Ackley always stated that these blown-out belted magnums are all badly over bore capacity and greatly inefficient compared to the standard H&H. Barrel life is short and faults far outweigh all good points, which seem to be limited to perhaps better case life when headspaced on the shoulder instead of the belt.
And now we arrive at number eight, the .257 Ackley with a gain of 9.4% over the standard .257 Roberts load of 2650 fps with the 117 gr. bullet. The Ackley gets 2900 fps with the same bullet. If we use the Winchester +P load of 2780 fps for the Roberts, the Ackley gain drops to 4.3% and the cartridge is not worth chambering for. This shows very plainly how poorly the factories have historically loaded the fine .257 Roberts.
This takes care of the best eight Ackleys, in order, compared only to standard factory loads and not with all bullet weights available. And we must remember that every barrel gives different velocities, so those listed here may vary from what other experimenters might achieve.
I use the good old Peak strain meter,strain gages glued on the barrel over the chamber.Very helpful tool especially with ''non standard'' cartridges and the kind of powder I'm using,N15(same as MRP,50% cheaper but not as uniform from lot to lot).I also have a 6,5 -06AI where I tested 139 gr scenars and 140gr Accubond,same charge,The difference in pressure was no less than 7000psi!