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Ackley Improved cartridges......are they worth doing???


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#1 GonHuntin

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Posted 23 December 2006 - 07:35 PM

The topic of Ackley Improved cartridges came up on another thread......thought I'd start a new thread instead of hijacking the other one.

Are ackley improved cartridges really worth the effort and expense??? Here are a few things to think about:

Most people that are claiming big velocity increases in AI cartridges are running WAY more pressure than the parent case was designed for! You can't overturn the laws of physics......the rule of thumb is:

At equal pressure, velocity will increase by 1/4 the percentage increase in case capacity.....in other words, you would have to increase case capacity by 40% to increase velocity by 10%!!

I know many will find that hard to believe....but it has been proven time and again...and I know many people claim huge velocity increases by going the Ackley Improved route......however, most of those people are greatly increasing pressure over what the parent case was designed for!! That doesn't necessarily mean it's dangerous......lets face it, many cartridges are loaded to lower pressure because of "weak" firearms......for instance, the 45-70.......factories generally load ammo that is safe in the weakest firearm that uses it......a Ruger #1 in 45-70 can certainly handle higher pressure than a trapdoor!!

The question is.......is it really worth it to ackley improve???? Think about this:

If your velocity increase is due to running higher pressure.......why not just run higher pressure in the parent case????

I am aware of the back thrust issue that is a consideration in certain firearm designs......but it is of little consequence in a modern bolt gun! If your Remington 700 can handle a belted short mag at 64,000 PSI, you can bet that action can handle a 250 savage loaded to the same pressure without ackley improving the case!!! HOWEVER, the weak link isn't the action, it's the brass cartridge case, and a 250 Savage loaded to 64,000 PSI is NOT safe!!!

Where am I going with this???? While the ackley improved case WILL stretch less.......and *MIGHT* help reduce backthrust (there are tests that seem to disprove this theory)......don't count on it giving you large increases in velocity without really cranking the pressures!!!

There is NO free lunch......ackley improving a cartridge does not repeal the laws of physics......Most of PO Ackley's load data was worked up without pressure equipment and probably without a chronograph.......in other words......he was guessing!!!

There is NO WAY to determine the actual pressure of your load without presure testing equipment...... flattened primers, stiff bolt lift, etc ARE NOT reliable indicators of safe pressure!!! I have seen reports from several pressure labs that show that some primers don't begin to show flattening until 70,000+ PSI!!!!

Yes, I have a few ackley improved chamberings........but they weren't done for the purpose of large increases in velocity.

Bottom line.......don't assume that an ackley improved chamber will give you significant velocity increases safely!!!

Cancer Sucks!!!


#2 purple220

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Posted 25 December 2006 - 09:23 AM

Good point GH. One has to look at the parent cartridge and see the overall increase in performance that they will gain,,,if any. There are many rounds out there that should not be Improved. A good gunsmith will or should, point out the possible gain and feasability. For some it is well worth the effort. They 250 Savage and 257 Roberts are two of the cases that are well suited for the AI treatment. I have yet to see how a 223AI is that much better than the 223. I personally have had two 257AI's and still have one built on a Rem. 700 action by Harold Broughton that I use regularly. Harold played extensively with the 30-30 round and had great success with AIing and developing other cartridges off of the case.

Long sloping case necks are most favored with Improving(22Hornet,250Sav.,257Robts, 7x57,30-06 based cases, 300H&H, etc.) . When the case is improved, generally it becomes more efficient in powder burning. Short, fat and Improved became the way of BR shooters and then cartridge manufacturing. Look at the WSM's, Ultra Mags and Weatherby Mags. They started out by Improving an established round.

I plan on in the future of having another AI gun built. Probably be a 280AI. It will do everything a 7mag will with less recoil, powder and muzzle blast. Plus I can use a standard Rem LA.
With proper reloading procedures, an AI case is as safe as any other factory round. For me it is well worth the effort.

Call 'M and Kill 'M


#3 GonHuntin

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Posted 25 December 2006 - 11:14 AM

I don't buy into the idea of case design having a large effect on "efficiency"......the short mags opperate at higher pressure than the standard mags......run them both at the same pressure with the same effective barrel length and bullet, and the cartridge with greater case capacity will win the race everytime......the laws of physics don't bend!

Back to the AI discussion.......look at the case capacity of the 250..(info I found was about 46 grains to base of neck)....compare it to the capacity of the 250 improved....(info I found was about 50 grains to base of neck)..about 8% increase.....if you are seeing an increase in velocity of more than about 1/4 the percent of capacity increase, then you can bet you are running higher pressure than the original cartridge. With an 8% capacity increase, you should see a 2% velocity increase if the same pressures are maintained in both.

If you had a pressure lab and could measure the pressure of your ackly loads........then run a straight 250 at the same pressure, there wouldn't be much difference. I don't own a 250 improved, but I have seen claims that it will push a 100 grain bullet to 3200 fps.......while the standard 250 does about 2900 with the same bullet......that's about 10% increase in velocity......which would require a 40% increase in case capacity if the same pressure is maintained in both cases! Don't get me wrong, I'm not saying a 250 ackley isn't safe pushing a 100 grain bullet to 3200......I'm saying it doesn't get there just because of the improved case!! It would be very interesting to measure the actual pressure of the 3200 fps load and then run a standard 250 to the same pressure and see what happens! If we use our formula again......and we assume that the ackley case pushes a 100 grain bullet to 3200 fps at X pressure.......and we calculate a 2% loss in velocity because the straight 250 case hase 8% less capacity.......theoretically, we could run the straight 250 case at the same X pressure and get 3136 fps! So, the question still remains.......if you can run the standard case at the higher pressure and get within 64 fps of the ackley case.......why go to the expense and hassle of the ackley??? Don't forget, PO Ackley himself said the 250 ackley improved showed the highest gain in velocity of any of his improved cartridges......according to him, this is as good as it gets for ackley improvements!!

Just some food for thought!

Cancer Sucks!!!


#4 Bennie

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Posted 25 December 2006 - 12:46 PM

I agree with Gon on this, I don't feel that AI gains much of anything over just increasing your load capacity, especially in some of the sharper shouldered cases. When you are doing the increase in load charges be sure to look for signs of pressure (or over loading), the biggest being cavitation of the primer (learned that from loading my 264 too hot). No load is worth damaging you weapon or yourself, just learn to shoot better. :-P
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#5 RidgeRunner

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Posted 26 December 2006 - 06:32 AM

Gone's right sorta, but without pressure testing, how do you know how much pressure your running at?
with the sharp shoulders and minimal body taper,allow you run to higher pressurre before you see any signs.
there's not as much tolerance in the AI'd chamber specs, so you get better case life.
1/2 less trimming makes an AI worth it to me, and you get less bolt thrust with the same pressures.
RR

#6 GonHuntin

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Posted 26 December 2006 - 08:01 AM

[quote name='RidgeRunner' post='69337' date='Dec 26 2006, 06:32 AM']
Gone's right sorta, [/quote]

Does that mean I'm "sorta" wrong?? I sure would appreciate it if you would show me where I messed up!! :D

[quote]but without pressure testing, how do you know how much pressure your running at?[/quote]

That is the point......unless you have pressure testing equipment, you can't know how much pressure you are running.....however, the laws of physics can be applied and will prove that increasing the case capacity a small amount, by "improving" it, will not increase velocity substantially......it takes additional pressure to raise the velocity to the levels people are seeing.


[quote]with the sharp shoulders and minimal body taper,allow you run to higher pressurre before you see any signs.[/quote]

What pressure "signs" are you referring to??? Flattened primers are NOT a good indication of pressure! I can easily make primers very flat with minimum loads by simply pushing the shoulder back so that there is a few thousandths excessive headspace! Cratered primers are more an indication of firing pin hole clearance than pressure. Stiff bolt lift is also not a good indicator of excessive pressure.


[quote]there's not as much tolerance in the AI'd chamber specs, so you get better case life.[/quote]

Chamber tolerance is purely a function of the equipment used to cut the chamber......an oversize or out of square reamer cuts an oversize chamber......ackley or not........

[quote]1/2 less trimming makes an AI worth it to me, and you get less bolt thrust with the same pressures.
RR[/quote]

Less case stretching is certainly a plus for ackley improved cartridge design, however, less case thrust is not a proven fact......and, even if it was, it doesn't really matter in a strong bolt action rifle! An action that will handle a short mag at 64,000 psi with a case head of .534" (Rem, Win, Savage, Browning etc....).....will certainly have no problem handling a standard 250 savage at 64,000 if you could safely run it that hard........remember, the larger the case head, the higher the back thrust.......so, in a modern bolt gun, reduced back thrust (if it really is reduced?) is NOT a good reason to go with an ackley improved chamber!

Cancer Sucks!!!


#7 RidgeRunner

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Posted 26 December 2006 - 10:27 AM

Does that mean I'm "sorta" wrong?? I sure would appreciate it if you would show me where I messed up!! :D
That is the point......unless you have pressure testing equipment, you can't know how much pressure you are running.....however, the laws of physics can be applied and will prove that increasing the case capacity a small amount, by "improving" it, will not increase velocity substantially......it takes additional pressure to raise the velocity to the levels people are seeing.


How much more pressure can you safely obtain? look at the SAAMI specs for the 30/06 and 270, same basic case but the 270 is rated higher. if its safe in your rifle does it matter what pressure it is? most of my improved chambers are in custom rifles so why not run it at the level of good performance that gives good case life?


What pressure "signs" are you referring to??? Flattened primers are NOT a good indication of pressure! I can easily make primers very flat with minimum loads by simply pushing the shoulder back so that there is a few thousandths excessive headspace! Cratered primers are more an indication of firing pin hole clearance than pressure. Stiff bolt lift is also not a good indicator of excessive pressure.


What pressure signs do you go by? one of my improved chambers called a 7 Allen Mag, the only pressure sign you get, your one warnihg is heavy bolt lift, the next shot the bolt won't open, no casehead expansion, no ejector mark, nothing but a heavy bolt lift.


Chamber tolerance is purely a function of the equipment used to cut the chamber......an oversize or out of square reamer cuts an oversize chamber......ackley or not........

Yes, but aren't most AI'd or improved chambers cut by an experienced smith instead of on a production line.
I know my 6.5 Gibbs, and my 7mm AM (7mm/338 Lapua AI'd to the max) FL resize easier than a 223 rem. fired in a production rifle. I know reamers get smaller as they are sharpened does it not stand to reason that production plants order reamers at max SAAMI specs to get fullest use from them? do you know smiths that order them at max size? the smiths I deal with order theirs to chamber as tight as possible.



Less case stretching is certainly a plus for ackley improved cartridge design, however, less case thrust is not a proven fact......and, even if it was, it doesn't really matter in a strong bolt action rifle! An action that will handle a short mag at 64,000 psi with a case head of .534" (Rem, Win, Savage, Browning etc....).....will certainly have no problem handling a standard 250 savage at 64,000 if you could safely run it that hard........remember, the larger the case head, the higher the back thrust.......so, in a modern bolt gun, reduced back thrust (if it really is reduced?) is NOT a good reason to go with an ackley improved chamber!


Not saying AI's are for everyone but some shooters really like them and the performance enhancements that they achieve.
RR

#8 GonHuntin

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Posted 26 December 2006 - 01:02 PM

Like I said.....I own a few AI chambered firearms.......so I'm not against them......but it is kinda hard to see any significant "performance enhancements that they achieve" when the numbers prove you can achieve nearly the same velocity by running the parent case at the same pressure you are willing to run the ackley version??? Granted, they do generally show less case stretch than the parent cartridge......but that is the only advantage I can see in anything except a break open action....... that MIGHT benefit from less backthrust if the AI version really does produce less backthrust......

You might enjoy reading this recent backthrust test......

backthrust experiment

Cancer Sucks!!!


#9 RidgeRunner

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Posted 26 December 2006 - 02:07 PM

Interesting GH, I read the first part awhile back but didn't greydog had finished the test, my thoughts are that if the action flexed that much under the pressure of chambering a tight fitting round, would anything keep the brass from stretching or keep it from slamming the bolt pretty hard.
I was always under the impression that if the proper powders were used at near max pressure, most of the bolt thrust occured before peak pressure was achieved due to pressure holding the case walls against the chamber sides. I don't know have no way of proving it, just seems to me that a tapered case under pressure would in fact thrust more against the bolt than a straighter one at the same pressure cause wouldn't the taper act as a backwards wedge, always pushing away from the pressure?
RR

#10 GonHuntin

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Posted 26 December 2006 - 02:55 PM

RR

I was always under the same impression that the tapered case would have more backthrust.......but some of the stuff I've read lately indicates that the surface of the chamber wall has a much greater effect than the shape of the case. I do know that SSK left a fairly rough finish on the chamber walls of my 309 JDJ Contender barrel! After having visited with JD Jones on a flight to Africa, I'm fairly certain that he KNOWS what he is doing and that the finish on my chamber walls was not an accident!!!

Anyway.....this discussion was intended to make people reconsider some things that they have always heard and believed......I won't be selling or giving away my AI chambered firearms anytime soon.....but I'll take any claims I hear with a large grain of salt!!!! :D

Cancer Sucks!!!


#11 RidgeRunner

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Posted 27 December 2006 - 11:44 AM

[I'll check my ssk barrels, I never really noticed if they were rough or not, and thats surprising cause I'm pretty anal about inspecting my firearms.
RR

#12 jnclement

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Posted 27 December 2006 - 09:35 PM

You know, your arguement kills the whole marketing campaign for the short mags. But let's keep that quiet, since so many people seem to believe it.

I have ackley's solely so I have to trim brass less. I could care less about the rest of it.

#13 Don Fischer

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Posted 27 December 2006 - 09:51 PM

I think that the question of wheather or not their worth doing could be applied to many cartridges other than Ackley's. Would it be worth the effort to bore out a 6.5x55 to a 6.5x06? I have both and I'd say no, unless you just want something not very many others have. How about a 7x57 to a 280 Rem or even a 7mm Rem Mag? Again I'd say no, what is the real world gain? The only one that will really know the difference is the cronoghaph!

I don't have an Ackley but if I did, I'd like the 250. Not many people running around with a standard 250 much less and Ackley and any animal I shoot with it won't be able to tell it from a 257 Weatherby! And maybe most important reason for Ackley's, makes for a good discussion doesn't it? We get to talk about pressure and bolt thrust we can't measure. Remember when we didn't have a cronograph? Our loads were as fast as we said and who could say different?

#14 BayouCityBoy

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Posted 27 December 2006 - 10:37 PM

I have a couple of AI chambered rifles and I'm glad we all don't have to shoot the same 30-06 cartridge because there are no other choices.

Any bullet that a deer or coyote can't outrun works for me. The rest is all just statistics and hype as to which individual cartridge or type of cartridge is better. Again, I'm just glad we all have choices we can individually make from all the hype.....

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#15 THE BBC

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Posted 03 January 2007 - 12:50 AM

laws of physics don't bend is correct. with that said if you push a 55 grain bullet from a gun with 60000 psi, it will travel the same speed no matter which cartridge the pressure is produced in. it all goes back to the question of which weighs more, a pound of rocks or a pound of feathers.




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