Thread: Anyone played with 223AI?

Originally Posted by Jaco Goosen

Generally the improvement is 5 to 8% in my experience. The 223 will gain 100fps with the heavies and a bit more with the lighter projectiles.

The calibre with almost no gain when acklied is the 308Win. It gains less than 10fps, with 1 to 2fps gain to be the norm.
@zimmer I like your reading material mate. For me the big gain is in shooting the heavies at a little faster speed.

Agreed, My 6.5x55AI was chronoed the other day at 3015 fps shooting the 140 Amax, so about 8-10 % higher than the standard version.

Greetings All,
I did a bit of work a few years back developing a decent load for the 129 grain projectile in my standard 6.5x55 so repeated it for the 140 grain. The Hodgdon data includes pressure in CUP (Copper Units of Pressure). The pressure is kept down to around 46,000 CUP due to some of the weaker actions that the round is chambered in so what would the velocity be an a more normal maximum pressure of say 52,000 CUP? Using the increase in pressure form the start to the max load and extending that to the higher pressure produced a velocity of about 2,750 fps. No surprises here as this is what factory Norma 140 grain loads chronographed about 30 years ago. Next question was how much additional velocity should we expect from the AI case. A quick search on the internet produced a capacity of 57 grains of water for the standard case and 62 grains for the AI. I don't know if these are total case capacity to the mouth or capacity with projectile seated which is more accurate but it will do for our purposes. This amounts to an increase of about 9% but the increase in velocity is only proportional to 25% of the increase in case capacity or 2.25%. This was worked out a few years ago by John Barsness aka Mule Deer. This explains why we don't get 4,000 fps from the .300 Win Mag which has 50% more capacity than the .308. Actual velocity increase for the AI case, at the same pressure is only about 50 fps bringing us to 2,800 fps.
So how do handloaders get 3,000 fps form the 6.5 AI? The answer is more pressure and lots of it. Going back to our pressure calculations at the start pressure is now approaching 60,000 CUP using the soft Speer projectile from the Hodgdon data. Well above the hottest current cartridges. Some may choose to go there but not me. I often hear no pressure signs mentioned and wonder what is being talked about as to me there is a big fat pressure sign sitting on the screen of the chronograph.
Regards Grandpamac

Originally Posted by grandpamac

Greetings All,
I did a bit of work a few years back developing a decent load for the 129 grain projectile in my standard 6.5x55 so repeated it for the 140 grain. The Hodgdon data includes pressure in CUP (Copper Units of Pressure). The pressure is kept down to around 46,000 CUP due to some of the weaker actions that the round is chambered in so what would the velocity be an a more normal maximum pressure of say 52,000 CUP? Using the increase in pressure form the start to the max load and extending that to the higher pressure produced a velocity of about 2,750 fps. No surprises here as this is what factory Norma 140 grain loads chronographed about 30 years ago. Next question was how much additional velocity should we expect from the AI case. A quick search on the internet produced a capacity of 57 grains of water for the standard case and 62 grains for the AI. I don't know if these are total case capacity to the mouth or capacity with projectile seated which is more accurate but it will do for our purposes. This amounts to an increase of about 9% but the increase in velocity is only proportional to 25% of the increase in case capacity or 2.25%. This was worked out a few years ago by John Barsness aka Mule Deer. This explains why we don't get 4,000 fps from the .300 Win Mag which has 50% more capacity than the .308. Actual velocity increase for the AI case, at the same pressure is only about 50 fps bringing us to 2,800 fps.
So how do handloaders get 3,000 fps form the 6.5 AI? The answer is more pressure and lots of it. Going back to our pressure calculations at the start pressure is now approaching 60,000 CUP using the soft Speer projectile from the Hodgdon data. Well above the hottest current cartridges. Some may choose to go there but not me. I often hear no pressure signs mentioned and wonder what is being talked about as to me there is a big fat pressure sign sitting on the screen of the chronograph.
Regards Grandpamac

Some things to think about here, firstly stating velocity/pressure without referencing barrel length and powder burn rate is not particularly useful. Pressure in internal ballistics is not linear, you can reach higher velocities with lower peak pressure by flattening the pressure curve or "increasing area under curve", usually by using a slower powder or/and reducing start pressure. Some of the new double based powders give benefits here. Or by simply using a longer barrel.
Looking at your conclusion of 60,000 CUP to gain 3000fps in a 6.5x55ai equates to around 73000psi. I would expect to see substantial case head expansion at those levels making the case unusable in a couple of cycles. If the users running their 6.5s at 3000 are getting good case life then I would suspect the pressure would be considerably lower than 60000 cup.

Originally Posted by sneeze

Some things to think about here, firstly stating velocity/pressure without referencing barrel length and powder burn rate is not particularly useful. Pressure in internal ballistics is not linear, you can reach higher velocities with lower peak pressure by flattening the pressure curve or "increasing area under curve", usually by using a slower powder or/and reducing start pressure. Some of the new double based powders give benefits here. Or by simply using a longer barrel.
Looking at your conclusion of 60,000 CUP to gain 3000fps in a 6.5x55ai equates to around 73000psi. I would expect to see substantial case head expansion at those levels making the case unusable in a couple of cycles. If the users running their 6.5s at 3000 are getting good case life then I would suspect the pressure would be considerably lower than 60000 cup.

Greetings @sneeze,
Thanks for your reply. I don't dispute any of the points you make on the newer powders, barrel length etc. My point was that most of the gains in velocity could be made with the parent case. I also said approaching 60,000 CUP so likely closer to 70,000 PSI. John Barsness also suggested in his articles that 70,000 PSI was around the level of pressure that hot shot handloaders worked up to by looking for pressure signs. I have loaded some pretty hot loads in the 6.5x55 over the years, initially through ignorance and recently almost caught out by the significant increase in speed of AR2209 about 20 years ago. There have also been some learnings about significant changes in velocity and likely pressure between different projectile of the same weight including projectiles of the same manufacture and cat no. Now I prefer to keep a decent safety margin rather than trying for that last erosive foot per second.
Regards Grandpamac.

Its an interesting topic. The calculation to convert cup to psi I was using is (cup x 1.516)-17902 which for 60000 cup gives 73000psi. Is there more accurate equation?
I have no idea what method Mr Barsness used to get to the 70000 psi for some handloaders but I have seen many discussions regarding the measurement of chamber pressures and many disagreements, even with modern pressure trace equipment. Greg Duely had an article on this some time ago and if I remember correctly he came up with a max of 65000 psi before case head expansion and function became a problem . Some one may have that article and could chime in? That would suggest even at 70000 psi you would be seeing issues. With some exceptions I will disagree with your claim that most gains could be made with the parent case , I think @zimmer has already pointed this out
The safety margin is another subjective topic and yes we will find our own comfort zone. From my perspective we know the weak link in the process is the brass case. If the case is getting over stressed then we will see case head expansion, loose primer pockets, extraction can become sticky. If none of these symptoms are present over time then I will be happy. Keeping in mind the safety margin for modern actions is substantial. I have a broacher here for the BSA majestic from the early 60s were they are testing the bolt lugs to 11 imp ton with out fail.
I also dont chase the last possible fps but I do like to realize most of the potential of a cartridge.

Originally Posted by sneeze

Its an interesting topic. The calculation to convert cup to psi I was using is (cup x 1.516)-17902 which for 60000 cup gives 73000psi. Is there more accurate equation?
I have no idea what method Mr Barsness used to get to the 70000 psi for some handloaders but I have seen many discussions regarding the measurement of chamber pressures and many disagreements, even with modern pressure trace equipment. Greg Duely had an article on this some time ago and if I remember correctly he came up with a max of 65000 psi before case head expansion and function became a problem . Some one may have that article and could chime in? That would suggest even at 70000 psi you would be seeing issues. With some exceptions I will disagree with your claim that most gains could be made with the parent case , I think @zimmer has already pointed this out
The safety margin is another subjective topic and yes we will find our own comfort zone. From my perspective we know the weak link in the process is the brass case. If the case is getting over stressed then we will see case head expansion, loose primer pockets, extraction can become sticky. If none of these symptoms are present over time then I will be happy. Keeping in mind the safety margin for modern actions is substantial. I have a broacher here for the BSA majestic from the early 60s were they are testing the bolt lugs to 11 imp ton with out fail.
I also dont chase the last possible fps but I do like to realize most of the potential of a cartridge.

Greetings again,
There is no accurate way of converting CUP to PSI. At higher pressures the PSI figure is higher. At lower pressures the two are about the same and at very low pressures CUP can be higher. Some cartridges like the 7mm SAUM have a max pressure of 65,000 PSI so Greg's figure of the same as a boundary for problems seems a bit low. CUP measures the area under the curve of pressure and not the maximum pressure developed where PSI measures the actual maximum pressure. John did have access to pressure testing equipment but I can't recall what sort.
Regards GPM.

Originally Posted by grandpamac

Greetings again,
There is no accurate way of converting CUP to PSI. At higher pressures the PSI figure is higher. At lower pressures the two are about the same and at very low pressures CUP can be higher. Some cartridges like the 7mm SAUM have a max pressure of 65,000 PSI so Greg's figure of the same as a boundary for problems seems a bit low. CUP measures the area under the curve of pressure and not the maximum pressure developed where PSI measures the actual maximum pressure. John did have access to pressure testing equipment but I can't recall what sort.
Regards GPM.

CUP was measuring the deformation on a calibrated copper disk or cylinder after firing, I havnt heard of it showing area under curve before, is there a time component applied to it somehow to get area under curve as they do now with transducers? that would be interesting.
How did you come to 70000 psi from 60000 CUP? the equation I used is supposedly for the higher pressure range and yes there is a margin of error there so its not exact. .
Im running on memory here so I could be wrong about G Duelys numbers but 65000 as a max working load seems about right? That extra 5000psi to get to the 70000psi Mr Barsness is saying hand loaders are running is a substantial increase, and i would be surprised if brass was holding up to that abuse, but again so many variables and so little definitive information. .

Greetings,
As the pressure rises beyond the yield point of the copper cylinder the cylinder starts to deform and continues to do so until the pressure drops so the cylinder is deformed by both the pressure and the duration of that pressure. The cylinder is measuring work or pressure over time rather than pressure. Hence my description of area under the pressure curve. There is not an exact relationship between the work done and the maximum pressure developed as was discovered. Once this was understood the pressure unit was changed from PSI to CUP. The modern system measures pressure directly and pressure is in PSI again but a different one. There are just to many variables to give an exact conversion, the speed of the powder used being just one. As far as the relationship between 60,000 CUP and 70,000 PSI this was general and should have used the word approximately in there somewhere.
Case head hardness varies from cartridge. At one time the hot rod handloaders of the .30-06 worked up their loads in Twin City (I think) brass until the heads expanded and then loaded the same load in Denver brass which was harder and lasted for a few loads more. I hate to think what the pressure was. In those days post WW2 there was little pressure tested data, truly the intrepid years.
Regards Grandpamac.

Yes I understand the work done principal, I just needed to adjust my thinking a little but yes I can see how it would fit in a pressure under curve definition be it a pretty basic one on todays standards. Assuming there is no way of mapping the curve as we can now and with as you say a less than exact relationship between work done and peak pressure it seems to muddy the water even more.
I think Duely did the same in that article with different brass manufacturers, some being obviously weaker, Old sako brass I think yielded the best results.
Interesting chat
Merry Christmas