Intrigued by Ackley improved cartridges

[JimT]

Not much chatter about the 260 AI, I was under the impression that was one of the main cartridges to Ackley ize
What’s up with that?
J

I would encourage you to read Ackley’s write ups on the .263 Express and .260 A.A.R. in his reloading handbook. Appears he never even opined on a 260 AI type cartridge. He called the later cartridge “a very fine 6.5mm cartridge.”

On a separate note, he was not a fan of improving either the 25-06 or the 6.5-06.

 

[JFrank]

I just made a mental note to google it up.
I’ve always felt the 260 to be an outstanding cartridge capable of excellent accuracy, now fix up the brass thing with a 40 degree shoulder and tighten up the twist rate a smidge .....shooter!

 

[Twicepop]

What would the 7.62x39 AI be considered? I figure with it's extreme taper it would improve a whole bunch!

Performance wise that should put it somewhere above the 30-30, and close to the 300 Savage.

 

[TAJ45]

I've read that an AI of the 260 is one of the least productive. As stated, the taper is minimal. The shoulder is the only area helping the final tally of pluses.
Another point is Bryan Litz has published extremely detailed info re velocity and twist rates. A difference iirc of well less than 10 fps.
This gives me pause for thought as "James Calhoun" stayed w 13tw for his 19-223, even when a savvy customer urged him toward faster. I have yet to see how his 44s print compared to the 32, 33 etc. Another project .

 

[centershot]

I have always wondered why cartridge manufacturers did not just make their examples like Ackley from the start?

 

[TAJ45]

I have always wondered why cartridge manufacturers did not just make their examples like Ackley from the start?

For some flavors, the 40° shldr does not feed as well. Think why "all the military cartridges" are sloped. 1000% reliability prevents those "Oh Shugar" moments.

 

[Brians356]

I have been told that for every 4% volume increase a 1% velocity increase may be realized.

The 4:1 ratio is what John Barsness steadfastly preaches, but it's both too general to apply across the wide spectrum of cartridges, and obviously too conservative considering certain examples such as 250 AI. Many popular cartridges are already "overbore" and cannot benefit much from improving. But cartridges well under bore capacity, and which improve into an efficient shape, can obviously gain much more velocity than the 4:1 formula predicts.

Consider Sierra's data for 250 Savage and 250 AI, with 100 gr bullet. (Accounting for the 2 inch longer barrel used in their AI data, I will subtract 50 fps from the AI's max velocity.) The 250 Savage tops out at 3000, the 250 AI at 3150 (adjusted). That's conservatively a 5% increase. The 250 AI gains about 11% - 12% case capacity. Let's again conservatively take the higher number 12%. What's the resulting ratio? 2.4 : 1. That nearly twice the velocity gain the 4:1 rule predicts.

Note: When I consider Sierra's data for 250 AI conservative (in the above exercise), consider that the 250 AI case is virtually identical to the Creedmoor in capacity, and body dimensions and shape. In Hodgdon's data the 6 Creedmoor from a 24-in barrel pushes 100-gr bullet to 3217 fps, and the 6.5 Creedmoor (less bore constriction) reaches 3297 fps. Nosler's data for 6.5 Creedmoor (also 24-in tube) reaches 3272 fps. So I'm confident that 3250 is reasonable for 250 AI, which would be an 8.3% increase over the parent 250 Savage.
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[Brians356]

For some flavors, the 40° shldr does not feed as well. Think why "all the military cartridges" are sloped. 1000% reliability prevents those "Oh Shugar" moments.

Yeah, but with an Ackley you only need the first shot, don't you see?
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[acloco]

My thinking is rounds like those based on the .308 W yield minimum gains when made into AI rounds as the body taper is only slightly modified leaving only the shoulder angle to be increased to 40*. The volume gain for the .308 W based rounds including the .243 W, .260 R would only be about 5%.>>>>.

In the PO Ackley book, 308 was

I have always wondered why cartridge manufacturers did not just make their examples like Ackley from the start?

Cost of SAAMI certification is the primary factor.

 

[fyrewall]

I guess the .250 AI is an example of magic ballistics. The Nosler manual has the .22-.250 case holding 40.9 grains of water and the .22-.250 AI case at 46.3 gr. H2O. This is a good approximation of what might occur with the .250 & .250 AI. It is a 13 % increase. Doing the 4 to 1 thing: gives a 3.25 % velocity increase over the tapered slopey shouldered .22-.250. Or, for the .250 AI, 1.0325 * 3000 = 3097.5 ~ 3100 fps. Yet everybody knows the .250 AI is a mini power house, the best of the AI family and must get 3200. My guess is if 3200 is achieved is at pressures greater than 60K psi and with slower burning powders like H4350. A fat charge of H414 with 87's would really drive a bullet out fast. Any published velocities & pressures? I could not find any published data on-line that gave more than 3100 or so for the .250 AI with 100's. If 3100 is the limit with 100's the 4 to 1 stuff is right on.


https://loaddata.com/Cartridge/250-Savage-250-3000-Ackley-Improved/3099

The Speer manual gives 3000 with 100's using CFE223 for the standard .250 .


This gets into the "over bore" cartridges. My guess is with newer powder formulations the pressure peak might be flattened allowing greater velocities for giant capacity rounds. In this case the 4 to 1 rule might have more of an application. The new Re 26 might be an example of getting max velocities with allowable pressures.

I would like to know how accurately Ackley measured his velocities and pressures.

 

[hunter67]

Performance Gain over Factory Ackley Comment 222 Rem. Mag. Ack. Imp. About 5% more powder capacity More useful if necked up to 6mm 219 Ack. Imp. Zipper 350fps above top 45-gr. factory Zipper load Recommended, but use 30-30 brass post-WWII 22 Swift Imp. Better extraction, case life Mechanical advantage with velocity equal to Swift 22-250 Ack. Imp. 50 to 100 fps, case life Use Swift data and buy RCBS dies with 40" shoulder 22 Sav. H.P. Imp. 300-400 fps with 70-gr. 228-cal. bullets One of best 22s with heavy bullets 243 Ack. Imp. Extraction, case life Mechanical advarltage; originally a customer request 244 Rern. Ack. Imp. Very little gain in any bullet weight Auth. note: use RCBS 6mm Ack. Imp. 40 in 6mm rifles 25-35 Ack. Imp. 500-600 fps with 100-gr. bullets Recommended, use 30-30 brass post-WWII 250 Sav. Ack. Imp. 300-400 fps with 100-gr. bullets Recommended, Ackley's all-time favorite 257 Robts. Ack. Imp. 300 fps with 100- or 120-gr. bullets Recommended. Ackley's "all-around" cartridge 25-06 Rem. Ack. Imp. About 200 fps with 100-gr. bullets Not recommended, despite customer success. "Overbore" 270 Win. Ack. Imp. Little or none with more powder Not recommended, factory 270 is better 7x57mm Ack. Imp. 300-350 fps with 140-gr. and 200-250 fps with 175 Recommended, more useful to avg. shooter than 7 mags 280 Rem. Ack. Imp. 250 fps with 140-gr. bullets Recommended, 7 mag veloc. in '06 case 30-30 Win. Ack. Imp. 250-300 fps with 150-gr. bullets Recommended, excellent for lever guns 30-06 Spfld. Ack. Imp. 100-150 fps in any bullet weight Recommended, equal to 300 H&H 30-40 Krag Ack. Imp. 500 fps with both 150s and 180s Good, but not many rifles can use. Hot 348 Win. Ack. Imp. 200-250 fps above 348 factory load Recommended, better case life, less thrust 35 Whelen Ack. Imp. 5% powder capacity, 100-150 fps in 200s, 225s. 250s Recommended, flexible big game cartridge

Out of Ackleys book

 

[L.Sherm]

Not true. 280 AI only gains 3.5% velocity. But it is probably neck and neck with 257 AI for popularity.
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Every 280AI that I have loaded for has been 200FPS faster than then 280 Rem everything being equall. Just as accurate.

 

[B23]

Cases with less taper that have been "improved" generally hide pressure signs much better than their parent case which causes most to run them harder and at much higher pressures than they do with their parent case loads which is why you often see these claims of big velocity increases.

Some of my favorites to read are when someone goes to an improved cartridge with very little gain in capacity over the parent case and they claim these big velocity increases and then say "and that's with no pressure" or "it's just a really efficient cartridge". If anyone thinks they're gaining 200fps over the parent case with only a few grains more powder and they're doing so without considerably higher pressures, they're delusional.

 

[Shinbone]

"hide pressure signs," or, they have less bolt thrust and thus can be safely run at slightly higher pressure?

 

[Brians356]

I guess the .250 AI is an example of magic ballistics. The Nosler manual has the .22-.250 case holding 40.9 grains of water and the .22-.250 AI case at 46.3 gr. H2O. This is a good approximation of what might occur with the .250 & .250 AI. It is a 13 % increase. Doing the 4 to 1 thing: gives a 3.25 % velocity increase over the tapered slopey shouldered .22-.250. Or, for the .250 AI, 1.0325 * 3000 = 3097.5 ~ 3100 fps. Yet everybody knows the .250 AI is a mini power house, the best of the AI family and must get 3200. My guess is if 3200 is achieved is at pressures greater than 60K psi and with slower burning powders like H4350. A fat charge of H414 with 87's would really drive a bullet out fast. Any published velocities & pressures? I could not find any published data on-line that gave more than 3100 or so for the .250 AI with 100's. If 3100 is the limit with 100's the 4 to 1 stuff is right on.


https://loaddata.com/Cartridge/250-Savage-250-3000-Ackley-Improved/3099

The Speer manual gives 3000 with 100's using CFE223 for the standard .250 .


This gets into the "over bore" cartridges. My guess is with newer powder formulations the pressure peak might be flattened allowing greater velocities for giant capacity rounds. In this case the 4 to 1 rule might have more of an application. The new Re 26 might be an example of getting max velocities with allowable pressures.

I would like to know how accurately Ackley measured his velocities and pressures.

A lot to digest there, for now a few quick comments.

Be careful how you interpret Nosler's case capacity figures, they are not to the case mouth! They are net, to the base of the bullet seated to the stated COAL. So to compare the parent-to-AI capacity change, you must have a common bullet seated to identical COALs. Update: Look at Nosler's data for 55-gr bullet, seated to COAL 2.350" for both 22-250 and 22-250 AI. The net case capacities are 42.4 and 47.0, respectively. That's a 10.8% increase. (In my analysis above I used 11% for 250 AI). So your 13% is likely too high.

The most complete AI data offering (most cartridges) is from Sierra, but no pressures are published. So it's difficult to analyze velocity increase. I did talk to Paul Box there, who related to me the test pressures for both 250 Savage and 250 AI, both over 60,000, and within 500 of each other. That explains the 3000 fps from 100-gr bullet in 250 Savage (SAAMI max 45,000).

Sierra posts 3200 fps for 100-gr in 250 AI, and we know they round down to the nearest 100 fps. So Paul Box saw at least 3200.

I have all of Bob Jourdan's 250 AI data, I'll come back with his data later today.

(See below.)
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[AckleymanII]

AI's do hide pressure signs/bolt thrust, help this by not having a super slick chamber so the case can grip the chamber wall. Scotch brite the chamber walls or 320 grit the smallest, done at chambering time.

Makes me giggle when I read of guys wanting to run the same pressures in AI as the parent case.

There are many really great Ackley cases out there for Varmint hunters that I have played with.

I have never trimmed an Ackley case, and the 40* shoulders retard brass flow, unlike a 30* shoulder.

 

[L.Sherm]

So I guess were suppose to run a 280AI at 3100 because it's " over pressure" instead of 3200+ were it shoots the best with a 140 no sticky bolt, no ejector swipes, no flattened primers, no web expansion just like 99.9% of use look for because we have no other way of testing whether its "over pressure" or not.
I shoot my rifles were they shoot the best without any signs of what's stated.
I dont think after 3-280AI with the 140 at 3200-3220 in a 24" it was a fluke.

 

[L.Sherm]

This is Noslers data with a 26" barrel.
The load for my brothers 280A it's a factory Browning A-bolt with a 24" barrel that was AI ed it's 3220fps 2 gr under max listed for RL22, as soon as it's gone I'm switching his over to RL23

 

[L.Sherm]

I've never been able to get a 280 Rem over 3000fps with 140's out of a 24" barrel without some kind of signs of pressure.

 

[Brians356]

Here's Bob Jourdan's 250 AI data from 1997, 100-gr bullet, max velocities only shown, charge weights redacted. (He sent me his actual notebook page, not a copy. I've posted a photo of the page before.)

100-gr bullet, Rem. 700, 26" barrel

AA2520 ___ 3408 _ Ejector marks
H4895 ____ 3357 _ Overload
H414 _____ 3382 _ Maximum
H380 _____ 3337 _ Accurate
IMR 4895__ 3255 _ Accurate
IMR 4350__ 3183
H4831 ____ 2910 _ Compressed
RL-19 _____3051 _ Compressed
V160 _____ 3194 _ Compressed

Subtracting 50 fps to normalize to 24" barrel, and tossing the "overload" and "ejector marks" entries, we're left with 3 reasonable max velocities (adjusted) over 3200: 3205, 3287, and 3332.

Jourdan did not have several appropriate powders, such as CFE 223, RL17, RL15, or Varget. The latter two powders produced the fastest loads in Sierra's data, and CFE 223 often produces top velocity across the board in Hodgdon's data (next to Superformance.)

PS Steve Timm in Varmint Hunter magazine (April 1996) reported (from a 22-in barrel): H414 3186 fps (normalize to 3236 for a 24-in barrel.) "Best accuracy of any powder tested."
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