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ghostsniper1
Posts: 2,645 Senior Member
My take on Ackley Improved.
ghostsniper1
Posts: 2,645 Senior Member
Well I am not a gunsmith by any means. But I do like to read and do research along with a pretty good understanding of physics and explosives (which black and smokeless powder qualify.) In reading on the idea of an Ackley Improved cartridge, I can easily see that less case taper and steeper shoulder angles will increase case capacity while also causing higher chamber pressures and a temporary (for a very brief, but important,) period of time. This brief period of time seems that it will actually be a slight restriction, therefore causing higher chamber pressures and a waste of powder capacity which will not benefit velocity much, if any. The gain seems negligable. The slight (original,) case tapers, will allow a more even flow of pressure to pass through the case as the gasses push the bullet through the barrel.
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I personally would rather not stock a wildcat, because I am not in a situation yet where I can reload on a large scale.
"Slow is smooth, smooth is fast, and speed is the economy of motion" - Scott Jedlinski
Smokeless powder burns.
From what I've read and have experienced so far, you are pretty well on Dan and Paul. But what I have found is that two in particular AI cartridges seem to pay off. One of these is the .280 AI and the other is the .257 AI. The 257 will put the .257 Roberts case in a class with the 25-06. It won't exceed it, but it will come close to it, close enough that the differences can be ignored. And as Jerm said, more capacity will let you take advantage of slower powders. I have had a .257 AI built now and shot it through the Chrony and it is very impressive so far. However I have not progressed enough in my loading to see the big differences because I still have about 2 grains of powder left to add.
Only one fly in the soup is that the one military surplus powder that is always talked about is still a great performer today, that being H4831. That and IMR 4831 have both been around a long long time. I don't think anything made now days really outshines both of them by much. Some of the hottest loads on this planet are still made with both these powders and that includes some big case magnums too. H 4831 is very slow. IMR is almost as slow. There isn't much slower out there. So while overall powders have improved, two of the slowest came from the 40s and 50s. That's when Ackley was doing all this.
Son that's somebody with nothing to do with his time but keep me in trouble with mom.
A deflagration has a subsonic flame front while a detonation is supersonic or fast approaching it. A deflagration can turn corners while a detonation won't. That's why a detonation will destroy equipment. It is a super fast high pressure flame front that is faster than the speed of sound That's why it is so distructive because that flame front doesn't turn corners well. It takes out piping and equipment in its way. It also produces such pressures that the equipment in the immediate vicinity won't stand the pressure. In our first incident a deflagerating flame front was produced. They said it was below the speed of sound, but fast approaching the definition of a detonation. In the second incident a flame front traveling at approx. 1200 FPS traveled up through a column tearing it to pieces and sending pieces of half inch plate as big as automobiles a quarter of a mile or more around the plant. I realize this is a bit off subject but it can help explain the difference in these two flame fronts.
Son that's somebody with nothing to do with his time but keep me in trouble with mom.
As someone else said, the larger capacity case will reduce chamber pressure everything else being equal.
With regard to these improved cases there is a little known fact other than just increasing the case capacity. It is that these cases minimize the body taper. This results in a much more efficient combustion chamber. Also, and more importantly is that this lack of taper decreases the thrust of the case head against the bolt. Ackley calls it bolt-thrust.
Additionally, a case with minimum taper decreases the need for trimming which, in turn, increases case life.
I know it's nit-picking, but accuracy of terminology is what separates us from the editorial press.
Regards
Dan
Then perhaps you should look at the 257 AI more closely
insert foot now
The difference is BIG now and HUGE back then
Another benefit is bettr headspace control on cartridges like the 35, 375 and 40 Whelen. These rounds all benefit from the sharper shoulder. Note also the JDJ cartridges based on the 30-06 case. Jones has blown the case out to the ma with the shortest neck possible. He basically improved the AI!!
Case stretching is also reduced. Cases like the 22-250, and even the 25-06, 270, etc benefit from the sharper shoulder in that they do not stretch as much per firing. This saves time trimming the cases and the case will last longer, all else being equal.
"The Un-Tactical"
Tell me about it. That's what I'm dealing with right now. But I feel my smith and I will figure it out. There's too many Mausers out there that have been AId. And it's very close to being right. Some of my problem is the cartridge head trying to slip under the extractor. I polished the bolt head and the inside of the extractor. It helped a little but needs more work. I don't think it's the feed rails but i'm going to take it back to my smith and let himd see for himself. I borrowed a reem from someone here and I chamfered the chamber mouth but I'll have to take it to the range and check it out and see if it helped. But I can truthfully say I have gained at least 200 FPS and that's just with 100 grain bullets. I want to see what it has done for 115 Grain Bergers now.
Son that's somebody with nothing to do with his time but keep me in trouble with mom.
What?
Clear your PM's-I cannot respond to you.
"The Un-Tactical"
Another good one to AI is the 250 Savage.
Since I shoot Single-Shot actions I don't have the feed issues that some (not all) have.
Plus, you can Improve (not a true "AI") the case by raising the shoulder and even get more capacity yet, if you so desire.
This is what my 338AX and 375 Snipe-Tac does.
By improving the 338 Lapua Magnum cartridge in my 18" single-shot specialty pistol (Rem. XP-100) I get what a factory Remmy 700 338 LM does in a rifle velocity wise-Actually a tad more:cool2:
"The Un-Tactical"
One of the supposed benefits - put forth by Ackley himself - is that there is less stress on the action due to what he calls bolt thrust. A tapered cartridge, such as the .30-30 will want to wedge itself backwards out of the chamber against the bolt when pressurize. A less tapered round will direct chamber pressure perpendicular to the bore and won't slam as hard on the bolt face. Ackley validated this concept by improving a 94 Winchester and bench testing it with the gun's locking block totally removed. The bolt stayed closed.
Another benefit of a less tapered case with a sharp shoulder that the P.S. Magazine Benchrest eggheads theorized about is longer throat life for any given pressure level due to how the cartridges burn powder. A shallow shoulder angle acts a funnel that allows the front of the powder charge to "sandblast" its way down the throat before it has a chance to ignite. Sharper shoulders create more of a log-jam effect that keeps more of the powder in the case until it has a chance to convert to gas. Obviously, running any cartridge as hot as possible will reduce barrel life, but this theory indicates that before conversion, there was a lot of hot gas AND abrasion, but after conversion, the main wear factor is just the hot gas.
"Nothing is safe from stupid." - Zee
Is that based on any research?
Did you read the link on the 257AI I provided that you asked for?
Do you think there is much difference between a 257 Roberts and a 25-06 ?
As quite a few members have stated some of the cartridges had minimal gain while a few in particular had quite an impressive gain
If you are shooting the same weight bullet at the same muzzle velocity using the same amount of powder, which law of physics are you violating when you get less recoil in one rifle versus the other?
The implication, if I understood it correctly, he is getting close to the same MV's as his RM with less recoil since he is using less powder than he does in his 7RM.
"The Un-Tactical"
I think he's referring to perceived recoil and not mechanical recoil.
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain