LOBO
Well-Known Member
Kirby, thanks for the reply. That 6.5 really has my attention! Looks great!!
Allen Mags?
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Fiftydriver
Official LRH Sponsor
Brian,
For the requirements you list for your upcoming project, the Dakota would be my very first choice as it will meet everyone of your requirements nearly perfectly. I am not sure if you will reach a full 3100 fps with the 156 in a 26" barrel but you may come very close. Will be interesting to see. I guess I need to build a 257 AX and find out!!!
My 257 Allen Mag with the 142 and 156 gr ULD RBBTs actually has about 10 grains more capacity then it really needs with the current powders available such as WC872. IT certainly works well but it would work even better with slower burn rate powders but that would equate to using coal for gunpowder I think /ubbthreads/images/graemlins/grin.gif!
That said, I would predict that the 257 AX would come withing 200 fps of matching the performance of the much larger Allen Magnum. Perhaps even a bit closer then that but we will have to see. With the 257 caliber, I will admit the AX will be a much more user friendly design as would your wildcat and very similiar in performance.
In the larger calibers though the Allen Magnums will offer a larger peformance advantage simply because the current powders are more appropriate for these bore volume to case volume ratios.
The reason I went with the 300 Dakota over the 7mm Dakota was that I wanted to drop case capacity roughly 10-12 grains off the 257 and 6.5 Allen Magnums. Playing with some sample brass of both the 7mm and 300 Dakot I found the 300 would give me exactly what I wanted.
TO be honest, the 7mm case would work just as well and if you like longer necks it would be the one to use for sure.
I did not move the shoulder forward on the 6.5 AX. When I neck down the brass, I simply maintain the original 32 degree shoulder and then use a 0.004" crush fit to headspace the chamber on a virgin case to control case stretching. This is the simplest way to do things, no shoulder position changes really, just the fact that decreasing the neck diamater will move the shoulder/neck junction farther forward.
I ordered in 200 pieces of 300 Dakota brass and instantly found some problems with consistancy. It appears they are in the process of switching over to a different alloy as I got two very different types of brass in this order. Three of the 20 round boxes had brass that was very bronze in color. Similiar to the Lapua cases. The other two boxes were bright yellow, like that of Winchester or Remington.
The interesting thing is that the bright yellow colored cases weighed on average 23 grains less then the bronze colored cases!!!!
Internal case capacity was within 3 grains on average with the lighter cases having more capacity. Obviously the heavy cases are using a denser alloy in the brass.
In load testing, the light cases would top out sooner in pressure then the heavy cases. This is the performance differences I have found so far.
Light cases:
120 gr Ballistic Tip...........3410 fps
140 gr Partition...............3200 fps
Heavy cases:
120 gr Ballistic Tip...........3525 fps
140 gr Partition...............3320 fps
With the light cases, it was at these velocities that the primer pockets were maintaining tightness. Anything over this would result in loosening primer pockets on the third firing or so.
Same with the heavier cases but I did not push the issue to the point of opening the primer pockets to find the limit. The 140 gr Part. level is pretty comfortable as I have 4 firings on these cases and they are still plenty snug.
I feel I got a mixed batch of brass as they are trying to switch over to the new brass. Lapua is supposed to be producing the Dakota brass starting this fall and winter so when that happens consistancy will be top notch.
Good Shooting!!
Kirby Allen(50)
For the requirements you list for your upcoming project, the Dakota would be my very first choice as it will meet everyone of your requirements nearly perfectly. I am not sure if you will reach a full 3100 fps with the 156 in a 26" barrel but you may come very close. Will be interesting to see. I guess I need to build a 257 AX and find out!!!
My 257 Allen Mag with the 142 and 156 gr ULD RBBTs actually has about 10 grains more capacity then it really needs with the current powders available such as WC872. IT certainly works well but it would work even better with slower burn rate powders but that would equate to using coal for gunpowder I think /ubbthreads/images/graemlins/grin.gif!
That said, I would predict that the 257 AX would come withing 200 fps of matching the performance of the much larger Allen Magnum. Perhaps even a bit closer then that but we will have to see. With the 257 caliber, I will admit the AX will be a much more user friendly design as would your wildcat and very similiar in performance.
In the larger calibers though the Allen Magnums will offer a larger peformance advantage simply because the current powders are more appropriate for these bore volume to case volume ratios.
The reason I went with the 300 Dakota over the 7mm Dakota was that I wanted to drop case capacity roughly 10-12 grains off the 257 and 6.5 Allen Magnums. Playing with some sample brass of both the 7mm and 300 Dakot I found the 300 would give me exactly what I wanted.
TO be honest, the 7mm case would work just as well and if you like longer necks it would be the one to use for sure.
I did not move the shoulder forward on the 6.5 AX. When I neck down the brass, I simply maintain the original 32 degree shoulder and then use a 0.004" crush fit to headspace the chamber on a virgin case to control case stretching. This is the simplest way to do things, no shoulder position changes really, just the fact that decreasing the neck diamater will move the shoulder/neck junction farther forward.
I ordered in 200 pieces of 300 Dakota brass and instantly found some problems with consistancy. It appears they are in the process of switching over to a different alloy as I got two very different types of brass in this order. Three of the 20 round boxes had brass that was very bronze in color. Similiar to the Lapua cases. The other two boxes were bright yellow, like that of Winchester or Remington.
The interesting thing is that the bright yellow colored cases weighed on average 23 grains less then the bronze colored cases!!!!
Internal case capacity was within 3 grains on average with the lighter cases having more capacity. Obviously the heavy cases are using a denser alloy in the brass.
In load testing, the light cases would top out sooner in pressure then the heavy cases. This is the performance differences I have found so far.
Light cases:
120 gr Ballistic Tip...........3410 fps
140 gr Partition...............3200 fps
Heavy cases:
120 gr Ballistic Tip...........3525 fps
140 gr Partition...............3320 fps
With the light cases, it was at these velocities that the primer pockets were maintaining tightness. Anything over this would result in loosening primer pockets on the third firing or so.
Same with the heavier cases but I did not push the issue to the point of opening the primer pockets to find the limit. The 140 gr Part. level is pretty comfortable as I have 4 firings on these cases and they are still plenty snug.
I feel I got a mixed batch of brass as they are trying to switch over to the new brass. Lapua is supposed to be producing the Dakota brass starting this fall and winter so when that happens consistancy will be top notch.
Good Shooting!!
Kirby Allen(50)
royinidaho
Well-Known Member
[ QUOTE ]
Internal case capacity was within 3 grains on average with the lighter cases having more capacity. Obviously the heavy cases are using a denser alloy in the brass.
In load testing, the light cases would top out sooner in pressure then the heavy cases.
[/ QUOTE ]
There is something that I don't understand /ubbthreads/images/graemlins/confused.gif This is the second post (sorry I couldn't find the other) where stated the above.
Here's where I am in my old knoggin.
Been using Win cases for any cartridge I load for versus Rem cases as the Win cases have greater volume. It has been my experience that Rem cases reach pressure and velocity limitations. This has been the case with 222, 270, 338 Win and 375 H&H.
I also think that for a given powder weight the longer the COL the less the velocity and pressure.
This is opposite to what you are saying, I think /ubbthreads/images/graemlins/frown.gif Thus I think I'm missing something. With your brass are the heavier cases stronger?
Just trying to learn something here. /ubbthreads/images/graemlins/crazy.gif
Internal case capacity was within 3 grains on average with the lighter cases having more capacity. Obviously the heavy cases are using a denser alloy in the brass.
In load testing, the light cases would top out sooner in pressure then the heavy cases.
[/ QUOTE ]
There is something that I don't understand /ubbthreads/images/graemlins/confused.gif This is the second post (sorry I couldn't find the other) where stated the above.
Here's where I am in my old knoggin.
Been using Win cases for any cartridge I load for versus Rem cases as the Win cases have greater volume. It has been my experience that Rem cases reach pressure and velocity limitations. This has been the case with 222, 270, 338 Win and 375 H&H.
I also think that for a given powder weight the longer the COL the less the velocity and pressure.
This is opposite to what you are saying, I think /ubbthreads/images/graemlins/frown.gif Thus I think I'm missing something. With your brass are the heavier cases stronger?
Just trying to learn something here. /ubbthreads/images/graemlins/crazy.gif
brianwinzor
Well-Known Member
Kirby, Thank you once again for lots of great information.
You mentioned that the capacity of the of the 257AX and 6.5AX would be about 10 - 12 grains less than the 257 AM (123 grains 8700), so I assume that the fireformed 6.5AX cases had a capacity of about 110 grains.
The 6.5 AX achieving 3500+ with the 120, and 3300+ with the 140 grain bullets is still impressive performance.
Regarding slower ball powders for the 257AM, have you investigated or tried to access NobelSport's Vectan SP13, which is a ball powder that is made for the 50BMG. I note that on several burning rate charts it is listed as the slowest burning powder available. A description of the powder is at this link: http://www.peterlawman.co.uk/vectan.php
On the basis of your data, I estimate that a 7mm Dakota necked down to .257 would probably have about 100 - 103 grains capacity, and if Lapua goes ahead with manufacturing the Dakota cases, it would be the clincher in my decision to use the 7mm Dakota case for my project.
I look forward to hearing more progress reports on the development of the 6.5 (and 257 AX). Brian.
You mentioned that the capacity of the of the 257AX and 6.5AX would be about 10 - 12 grains less than the 257 AM (123 grains 8700), so I assume that the fireformed 6.5AX cases had a capacity of about 110 grains.
The 6.5 AX achieving 3500+ with the 120, and 3300+ with the 140 grain bullets is still impressive performance.
Regarding slower ball powders for the 257AM, have you investigated or tried to access NobelSport's Vectan SP13, which is a ball powder that is made for the 50BMG. I note that on several burning rate charts it is listed as the slowest burning powder available. A description of the powder is at this link: http://www.peterlawman.co.uk/vectan.php
On the basis of your data, I estimate that a 7mm Dakota necked down to .257 would probably have about 100 - 103 grains capacity, and if Lapua goes ahead with manufacturing the Dakota cases, it would be the clincher in my decision to use the 7mm Dakota case for my project.
I look forward to hearing more progress reports on the development of the 6.5 (and 257 AX). Brian.
Fiftydriver
Official LRH Sponsor
Roy,
It has been my experience, if you take the same powder charge and load two different brand cases, the one with the smallest powder capacity will produce the higher velocity of the two with this same load.
That said, on average, you can load Win brass to higher pressures then Rem brass simply because the brass used in the Win cases is "harder" then the Rem brass and resists case head expansion and primer pocket loosening better then the softer Rem brass.
In my tests with the two different types of 300 Dakota brass used in my 6.5mm AX. The two cases have very similiar case capacities with the 23 grain lighter case having about a 3 grains larger powder capacity.
This tells me that dimensionally the two cases are very similiar as far as case head thickness, body wall thickness and such. The reason they are so different in weight is because the allow used in the heavier case is simply more dense then the brass alloy used in the lighter weight cases.
In the top velocity potential I listed, these are NOT for the same load in each brass. Instead it is the top level that I could reach that was 1 grain under the point where the primer pockets began to loosen after three firings.
In the heavier cases I was able to reach 90.0 gr of WC872 under the 140 gr Partition with 91.0 gr resulting in primer pockets beginning to loosed at what I feel is premature timing.
With the lighter weight cases, they reached the level of primer pocket loosening at roughly 86.0 gr of WC872 under the same bullet.
This tells me that the denser alloy handles the higher pressures better then the light cases. I am sure the chamber pressure with the heavy cases is significantly higher then the other loads. Thus the reason for the higher velocity potential.
What I am saying is that the heavier brass is able to handle this higher pressure level better then the light weight brass.
Does that make any sense /ubbthreads/images/graemlins/confused.gif?? Probably did not help any!!
Kirby Allen(50)
It has been my experience, if you take the same powder charge and load two different brand cases, the one with the smallest powder capacity will produce the higher velocity of the two with this same load.
That said, on average, you can load Win brass to higher pressures then Rem brass simply because the brass used in the Win cases is "harder" then the Rem brass and resists case head expansion and primer pocket loosening better then the softer Rem brass.
In my tests with the two different types of 300 Dakota brass used in my 6.5mm AX. The two cases have very similiar case capacities with the 23 grain lighter case having about a 3 grains larger powder capacity.
This tells me that dimensionally the two cases are very similiar as far as case head thickness, body wall thickness and such. The reason they are so different in weight is because the allow used in the heavier case is simply more dense then the brass alloy used in the lighter weight cases.
In the top velocity potential I listed, these are NOT for the same load in each brass. Instead it is the top level that I could reach that was 1 grain under the point where the primer pockets began to loosen after three firings.
In the heavier cases I was able to reach 90.0 gr of WC872 under the 140 gr Partition with 91.0 gr resulting in primer pockets beginning to loosed at what I feel is premature timing.
With the lighter weight cases, they reached the level of primer pocket loosening at roughly 86.0 gr of WC872 under the same bullet.
This tells me that the denser alloy handles the higher pressures better then the light cases. I am sure the chamber pressure with the heavy cases is significantly higher then the other loads. Thus the reason for the higher velocity potential.
What I am saying is that the heavier brass is able to handle this higher pressure level better then the light weight brass.
Does that make any sense /ubbthreads/images/graemlins/confused.gif?? Probably did not help any!!
Kirby Allen(50)
Fiftydriver
Official LRH Sponsor
Brian,
I must have reported the case capacities of the Allen Mags wrong as the 257 and 6.5mm Allen Magnums have basically the same case capacity of the standard 7mm RUM case which is around 116 vs. 116 gr of WC872.
The 270 Allen Mag DOES have a case capacity of 123 gr on average which is where I may have misprinted the capacity information.
This is how the case capacities come out for an average of five cases of each round, all filled to the mouth with 872:
6.5mm AX.........104 gr
257 AM...........116 gr
7mm RUM..........117 gr
270 AM...........123 gr
7mm AM...........127 gr
As far as the case capacity of the 7mm and 300 Dakota parent cases. The 7mm holds 93.0 gr filled to the mouth with WC872 and the 300 holds 99.0 gr filled to the mouth.
The 7mm has a longer neck but the 300 has a larger diameter neck so I sould predict the neck volume on each is very similiar. Basically they are within 6 grains capacity of each other. If you improved the 7mm Dakota case I would say you would be in the 98-100 gr range for total case capacity, basically what you predicted.
I will have to do some reseach into SP13. May be very usefull!! Thanks for the ling.
Kirby Allen(50)
I must have reported the case capacities of the Allen Mags wrong as the 257 and 6.5mm Allen Magnums have basically the same case capacity of the standard 7mm RUM case which is around 116 vs. 116 gr of WC872.
The 270 Allen Mag DOES have a case capacity of 123 gr on average which is where I may have misprinted the capacity information.
This is how the case capacities come out for an average of five cases of each round, all filled to the mouth with 872:
6.5mm AX.........104 gr
257 AM...........116 gr
7mm RUM..........117 gr
270 AM...........123 gr
7mm AM...........127 gr
As far as the case capacity of the 7mm and 300 Dakota parent cases. The 7mm holds 93.0 gr filled to the mouth with WC872 and the 300 holds 99.0 gr filled to the mouth.
The 7mm has a longer neck but the 300 has a larger diameter neck so I sould predict the neck volume on each is very similiar. Basically they are within 6 grains capacity of each other. If you improved the 7mm Dakota case I would say you would be in the 98-100 gr range for total case capacity, basically what you predicted.
I will have to do some reseach into SP13. May be very usefull!! Thanks for the ling.
Kirby Allen(50)
brianwinzor
Well-Known Member
Kirby, Thanks for measuring the 7mm Dakota case capacity, and I estimate that the 93 grain capacity would reduce to about 89 - 90 once necked down to .257.
I have decided to leave the 7mm Dakota as is and not try and improve it. The case has .014 body taper and I am a little worried that if I bring that back to about .009 to slightly increase capacity I may cause extraction problems.
Recently I spoke to a guy who has a .257 Banshee, and he mentioned that he had extraction problems with his case which only had .009 body taper in a case length of 2.660. (shoulder angle 35) He was going to get his reamer reground before his next rechamber.
I don't have any extraction problems with my 25/06 AI (40) and that has .012 taper (4665 head & .4545 shoulder) in a case length of 2.494. (Dakota is 2.500)
You also mentioned to me in a recent post on the .224 Clark, that the 30 degree shoulder is less likely to cause powder bridging problems, so on that advice I will retain the existing 30 degree shoulder on the 7mm Dakota case.
As I only have enough H870 (15lbs) for the next .224 Clark, and no prospect of replenishment, then I probably will have to use AR 2218 (relabelled as H50BMG in US)in the 257 Dakota with the 142 and 156 grain bullets. I will try to see if Vectan SP13 can be imported to OZ, but at this stage I cannot rely on that happening.
I will now go and purchase a Rem 700 SPS in 300 RUM for my donor action for the .257 Dakota, and then "flog off" the barrel and stock.
Bill (my gunsmith) said that trying to convert my Sako AV long action (25/06 AI & worn barrel) to the .545 boltface for the Dakota was not a good idea, as apart from bolt modifications I would need a magnum magazine box due to the wider case. Do you agree?
Bill (my gunsmith) also has told me to get a Rem 700 long action for my .224 Clark, and not use that Sako AV for that project. He has stated numerous times that if I want an accurate rifle use a Rem 700,(or custom) as it is much easier to bed and square up a Rem 700 than a Sako. Yet he has made my Sako L61R action 25/06AI into a sub 0.5 moa rifle.
So it looks like I am going to have to get more guns. Pocket says OUCH, but suppose it can't be all bad. Also, will have to decide what to do with that Sako AV action, initial thoughts are for a 280 AI. Brian.
I have decided to leave the 7mm Dakota as is and not try and improve it. The case has .014 body taper and I am a little worried that if I bring that back to about .009 to slightly increase capacity I may cause extraction problems.
Recently I spoke to a guy who has a .257 Banshee, and he mentioned that he had extraction problems with his case which only had .009 body taper in a case length of 2.660. (shoulder angle 35) He was going to get his reamer reground before his next rechamber.
I don't have any extraction problems with my 25/06 AI (40) and that has .012 taper (4665 head & .4545 shoulder) in a case length of 2.494. (Dakota is 2.500)
You also mentioned to me in a recent post on the .224 Clark, that the 30 degree shoulder is less likely to cause powder bridging problems, so on that advice I will retain the existing 30 degree shoulder on the 7mm Dakota case.
As I only have enough H870 (15lbs) for the next .224 Clark, and no prospect of replenishment, then I probably will have to use AR 2218 (relabelled as H50BMG in US)in the 257 Dakota with the 142 and 156 grain bullets. I will try to see if Vectan SP13 can be imported to OZ, but at this stage I cannot rely on that happening.
I will now go and purchase a Rem 700 SPS in 300 RUM for my donor action for the .257 Dakota, and then "flog off" the barrel and stock.
Bill (my gunsmith) said that trying to convert my Sako AV long action (25/06 AI & worn barrel) to the .545 boltface for the Dakota was not a good idea, as apart from bolt modifications I would need a magnum magazine box due to the wider case. Do you agree?
Bill (my gunsmith) also has told me to get a Rem 700 long action for my .224 Clark, and not use that Sako AV for that project. He has stated numerous times that if I want an accurate rifle use a Rem 700,(or custom) as it is much easier to bed and square up a Rem 700 than a Sako. Yet he has made my Sako L61R action 25/06AI into a sub 0.5 moa rifle.
So it looks like I am going to have to get more guns. Pocket says OUCH, but suppose it can't be all bad. Also, will have to decide what to do with that Sako AV action, initial thoughts are for a 280 AI. Brian.
