338-408 chey-tac powders
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NZ Longranger
Well-Known Member
Augustus,
There's a simple little barrel life calculator that I'll see if I can post up a link to. Can't remember where I got it from. Anyway, it takes bore size, powder weight, powder heat potential and chamber pressure into account. The powders with the highest heat potential are the worst barrel burners, all else being equal. Unfortunately I haven't been able to find the exact heat potential figure for 869, but presume it to be similar to H870 which was its forerunner. It produces the same velocity for the same pressure as H870 but doesn't have the extreme temperature variability and carbon fouling issues that H870 has.
Anyway, this calculator gives 869 a 30% barrel life increase over 50BMG, and this is backed up by what we see through the bore scope down our barrels. Its takes very little time before you see significant fire cracking with 50BMG, 50 rounds and its there. By 300 rounds they look shocking, and by 500 they're pretty much gone for all money. Depends on how you shoot them of course, so some will get more, some will get way less. We have only completely shot out one 338 barrel with 50BMG, but if you ask around amongst those who've shot the 338/408 a lot, I think you'll find its the consensus of about where it sits. Be interesting to hear some other comments on this?
We've shot out plenty of big 7mm barrels with 50BMG, and have seen the same thing verses 869. Comparing like with like, we don't see the same level of fire cracking with 869 until you've fired nearly twice as many rounds. So far we've only chambered Lunatics in button rifled barrels, like Liljas, Broughtons and Trueflites. I have some Bartlien cut barrels here to try, which going by our experience with cut Kreigers in 7mm could extend the life significantly.
And in the 338 Lunatic for the same 67,500psi pressure (measured with Oehler 43 Bal. Lab, not just a guess), we get about 100 fps more with 869 than 50BMG. Viht 20N29 produces getting on for the same velocity for pressure as 869, and should have even better barrel life in theory due to its lower heat potential, but we haven't shot it enough to say yet. 869 is just so easy to work with, so long as you aren't getting hangfires, which is why we shortened the case 75 thou.
Greg
There's a simple little barrel life calculator that I'll see if I can post up a link to. Can't remember where I got it from. Anyway, it takes bore size, powder weight, powder heat potential and chamber pressure into account. The powders with the highest heat potential are the worst barrel burners, all else being equal. Unfortunately I haven't been able to find the exact heat potential figure for 869, but presume it to be similar to H870 which was its forerunner. It produces the same velocity for the same pressure as H870 but doesn't have the extreme temperature variability and carbon fouling issues that H870 has.
Anyway, this calculator gives 869 a 30% barrel life increase over 50BMG, and this is backed up by what we see through the bore scope down our barrels. Its takes very little time before you see significant fire cracking with 50BMG, 50 rounds and its there. By 300 rounds they look shocking, and by 500 they're pretty much gone for all money. Depends on how you shoot them of course, so some will get more, some will get way less. We have only completely shot out one 338 barrel with 50BMG, but if you ask around amongst those who've shot the 338/408 a lot, I think you'll find its the consensus of about where it sits. Be interesting to hear some other comments on this?
We've shot out plenty of big 7mm barrels with 50BMG, and have seen the same thing verses 869. Comparing like with like, we don't see the same level of fire cracking with 869 until you've fired nearly twice as many rounds. So far we've only chambered Lunatics in button rifled barrels, like Liljas, Broughtons and Trueflites. I have some Bartlien cut barrels here to try, which going by our experience with cut Kreigers in 7mm could extend the life significantly.
And in the 338 Lunatic for the same 67,500psi pressure (measured with Oehler 43 Bal. Lab, not just a guess), we get about 100 fps more with 869 than 50BMG. Viht 20N29 produces getting on for the same velocity for pressure as 869, and should have even better barrel life in theory due to its lower heat potential, but we haven't shot it enough to say yet. 869 is just so easy to work with, so long as you aren't getting hangfires, which is why we shortened the case 75 thou.
Greg
NZ Longranger
Well-Known Member
Yep. Just heading out for a wander, will post up some pics of our versions tomorrow when we get back.
Greg
Greg
royinidaho
Well-Known Member
I'd go with Joel's and Kirby's recommendations regarding powder. But.........
I'm wondering why you'd want such a pecker wood caliber when you'll save some bucks by simply jumping to the 375.
jmason
Well-Known Member
I'm wondering why you'd want such a pecker wood caliber when you'll save some bucks by simply jumping to the 375.
You joker! You helped me decide! BTW I ordered the reamer, and Go gauge tonight.
JUDD
Well-Known Member
Are you doin straight cheytac?
jmason
Well-Known Member
OK, no "improvement". But did you find it worse in any way? Did you measure ES?
You say in your test that "As far as matching burn rate perfectly to the case capacity I would say H-50BMG, WC872 or US869 are a bit better choices for the 300 gr SMK, BUT for a much lower pressure load that still offers 3500 fps performance and fine accuracy, 20N29 seems to be as good as any in the 338 Allen Mag."
I live in Switzerland and have a 338/408 in the works. The availability of 50BMG powder is not so good here, but VV is easy to find and also cheaper. Additionally, the lower pressure you describe in your test should contribute to better case life.
NZ Longranger also indicate potentially better barrel life.
So even if VV 20N29 does not provide any improvement on the target, there seems to be advantages as far as pressure, case and barrel life are concerned.... Or am I missing something?
Link to Kirby's test:
http://www.longrangehunting.com/for...ita-vouri-20n29-velocity-accuracy-test-16943/
NZ Longranger
Well-Known Member
Sorry guys, been meaning to take a pic of our 338's and get it up here for a while. Too busy hunting!
Anyway, here are from left - 338 Thor (338/416 imp) x 300gn SMK, 338 Lunatic short x 300gn SMK, 338 Lunatic short x 252gn Cutting Edge, 338 Lunatic full length x 300gn SMK.
The 338 Lunatic came about totally from discussions with Kirby, is inspired by his 338AM, and all credit for the chambering goes to him! Its just we run tight necks on all our serious long range rifles, and Kirby wasn't keen on a tight neck reamer himself as he's prefers not to turn necks. Originally it was going to be called the 338AM tight neck, but then Kirby said we'd better change the name as well to avoid confusion, so we changed the shoulder angle and neck length as well. My son Jamie who designed the first rifle we built in it - a 32" barreled bullpup - named it "The Lunatic".
The short version allows us to use 869 with the 300 grainers without hangfires as I said previously. In the full length version you can't with the 300's, but can with 250's. VV 20N29 gave the most velocity for pressure with the 300gn in the full length version - and we are measuring our pressure via strain gauge and Oehler 43. We run the Lunatics to 67,500psi in strong custom actions with the Jameson brass. You can run it up to 75,000psi or higher without seeing pressure signs, so you have to be very careful loading this chambering. H50BMG gives very good accuracy, ES's, and is not affected by temperature, but is 75 to 100 fps off the pace in our rifles. 869 gives extremely good accuracy, 100 fps more velocity, better barrel life, great ES's, and is temperature predictable - that is we know how much our muzzle velocity is going to vary with ammo temperature, and use "Shooter" on an Android phone to allow for it.
Certainly Kirby and Joel are the experts with this chambering, but these are our experiences with it. We have used these cartridges extensively on the range and long range hunting for the last 4 years, and have killed lots of animals with them. They truly are unbelievable long range hunting cartridges!
Greg
Anyway, here are from left - 338 Thor (338/416 imp) x 300gn SMK, 338 Lunatic short x 300gn SMK, 338 Lunatic short x 252gn Cutting Edge, 338 Lunatic full length x 300gn SMK.
The 338 Lunatic came about totally from discussions with Kirby, is inspired by his 338AM, and all credit for the chambering goes to him! Its just we run tight necks on all our serious long range rifles, and Kirby wasn't keen on a tight neck reamer himself as he's prefers not to turn necks. Originally it was going to be called the 338AM tight neck, but then Kirby said we'd better change the name as well to avoid confusion, so we changed the shoulder angle and neck length as well. My son Jamie who designed the first rifle we built in it - a 32" barreled bullpup - named it "The Lunatic".
The short version allows us to use 869 with the 300 grainers without hangfires as I said previously. In the full length version you can't with the 300's, but can with 250's. VV 20N29 gave the most velocity for pressure with the 300gn in the full length version - and we are measuring our pressure via strain gauge and Oehler 43. We run the Lunatics to 67,500psi in strong custom actions with the Jameson brass. You can run it up to 75,000psi or higher without seeing pressure signs, so you have to be very careful loading this chambering. H50BMG gives very good accuracy, ES's, and is not affected by temperature, but is 75 to 100 fps off the pace in our rifles. 869 gives extremely good accuracy, 100 fps more velocity, better barrel life, great ES's, and is temperature predictable - that is we know how much our muzzle velocity is going to vary with ammo temperature, and use "Shooter" on an Android phone to allow for it.
Certainly Kirby and Joel are the experts with this chambering, but these are our experiences with it. We have used these cartridges extensively on the range and long range hunting for the last 4 years, and have killed lots of animals with them. They truly are unbelievable long range hunting cartridges!
Greg
NZ Longranger
Well-Known Member
We haven't shot 20N29 enough to be categorical about barrel life yet, but the calculator says its significantly better than H50BMG. It certainly had good ES's, but isn't as temperature unaffected as H50BMG, but nothing is! That's H50BMG's strong point for sure!
I intend to do more work with 20N29 in the full length version, but as we mainly shoot the short version now due to its performance with 869 being better than anything in the long version, its hard to make myself get around to it!
Greg
I intend to do more work with 20N29 in the full length version, but as we mainly shoot the short version now due to its performance with 869 being better than anything in the long version, its hard to make myself get around to it!
Greg
Thank you for input NZ Longranger.
I have no personal experience yet, but from what I have read on the LRH pages, it is clear to me that BMG50 is an excellent powder for the 338/408 family. I am, certainly, not trying to argue against that.
My point is simply, that even if VV 20N29 does not provide any direct improvement compared to 50BMG, it may be a good option for shooters (like me) who do not compete and who appreciate lower pressure and better barrel/brass life.
(There seems to be problems with hangfires. Maybe you tried different primers already, but I had frequent hangfire problems with my 338 LM when using CCI 250 primers. I changed to Federal GM215M and the hangfires disappeared completely.)
I have no personal experience yet, but from what I have read on the LRH pages, it is clear to me that BMG50 is an excellent powder for the 338/408 family. I am, certainly, not trying to argue against that.
My point is simply, that even if VV 20N29 does not provide any direct improvement compared to 50BMG, it may be a good option for shooters (like me) who do not compete and who appreciate lower pressure and better barrel/brass life.
(There seems to be problems with hangfires. Maybe you tried different primers already, but I had frequent hangfire problems with my 338 LM when using CCI 250 primers. I changed to Federal GM215M and the hangfires disappeared completely.)
