Jamison 408 Chey Tac brass updates....
I have been working with Jamison International to make me brass for my 338 Allen Magnum. As you know this is based on the 408 Chey Tac case. I am investing in tooling to get preformed, correct headspaced brass for my 338 Allen Magnum and 375 Allen Magnum.
First however we had to figure out the problems that Jamison was having with their 408 CT cases.
The first lot of brass I tested nearly a year ago was their original design. it had many problems:
-Necks way to thick
-Solid case head to thin
-Rim thickness to large
-Primer pocket to large
-Necks and shoulders had poor annealing
These cases would loose the primer pockets on the first high pressure firing, literally loose the primer pockets.
Jamison then changed the alloy they used in their cases but that was about the only change they made as they figured the harder alloy would solve the blown primer situation. They marked these cases with a double star on the case head to tell them from the original lot.
Unfortuantely, this did little to help the problems that the original cases had and Jamison really took a hit on this poor quality brass.
As a result, everyone went with TTI cases and soon, the TTI supply ran dry and there is no sign of getting that brass back. To bad because it was great brass.
Back to Jamison. With all the bad press, Jamison decided they better get their game together so they colaberated with many top minds in the industry to get the cases up to a high standard to compete and offer what we demand in a quality case.
While I was working with them on testing some prototype solid 338 projectiles, they also asked me to test some of their new cases and offer any input I could to make their brass better.
My comments to them were:
-Thin the necks to no more then 13 thou in thickness
-Increase the thickness of the solid case head, even if case capacity was decreased.
-Thin the rim thickness to no more then 62 thou.
-Anneal the neck and shoulder softer.
-Tighten the primer pockets so they were no larger then 0.2070" in diameter.
Early this week I received a batch of new cases that they wanted me to test. There were some dramatic improvements but still a couple disappointments, still, they are getting much closer.
For comparision, the previous lot of 408 CT brass that they sent me for testing lost the primer pockets with a load of 145.0 gr H-50BMG under the 300 gr SMK. Primers literally fell out of the case when they were ejected.
This time was a bit different. On the first high pressure firing, the primers held. When seating a new primer, the pockets were noticably loosened but still held the primers. On the second and third firing, the primer pockets continued to loosen but still hold primers sufficently to prevent any gas leakage.
On the fouth firing, the primer fit was looser then I like but the 4th firing was still safe so we went from loosing a primer on the first firing to cases that while the primers loosened , they allowed at least 4 firings at top end pressures.
I then dropped the load to 142.0 gr H-50BMG, velocity dropped from 3345 fps to 3268 fps. Again, the primer pockets behaved nearly the same, only difference was that one more firing could be had before I felt primer fit was to loose to reuse. This is a bit redused load but still a solid 300 fps more velocity then the next largest 338 magnum in this length barrel(32").
After seeing this I wanted to compare the new jamison cases to my idea of the gold standard in 408 cases, the TTI hulls.
Interestingly enough, the Jamison cases and the TTI cases averaged with in 0.1 grain of each other in case capacity. The Jamison cases are nearly 15 grains lighter in weight which tells us the internal dimensions are the same as the TTI but the alloy used is much lighter then the TTI alloy.
I do not think this is the reason for the loosening primers however.
The neck thickness issues have been corrected as well with these test cases. All ran from 0.0131" to 0.0135". Compare that to around 0.016" for the old cases. This is still thicker then the TTI cases but only by around 1/2 to 3/4 thou.
The neck annealing is also much better. On the old Jamison cases, I had to anneal the cases after the second neck down step or I would get crushed necks. With the new cases, they sized down to 338 caliber easily with no annealing. They should be annealed after forming however.
The solid head thickness has also been increased dramatically. It is now nearly identical to the TTI cases or nearly 40 thou thicker then the old head was. The rim thickness are also right on as none were thicker then 0.060" which functioned perfectly through all my 408 class receivers. The old cases did not allow proper extractor function because of their thicknesses.
I also noticed that while the alloy in the new Jamison cases is lighter, it also seems to be harder. The reason I say this is because the 145.0 gr load in the TTI cases resulted in slight but noticable ejector marks on the case head.
The new Jamison cases showed no sign of an extractor mark in any way telling me the case head is hard enough to resist setting back into the ejector hole in the bolt face.
So why do the primer pockets loosen up??
Of all the things I recommended to Jamison, they did every one except one, tighten the primer pockets. They are still running between 0.2082" to 0.2085" in diameter. I fully believe if the primer pockets would be tightened up to 0.2070" which is slightly tighter then the TTI cases, there would be no problem at all with primer pockets opening.
The reason I believe this is because the primer pockets loosen up the most in the intital high pressure loading. Then the primers continue to loosen but only slightly.
In the TTI cases, with this same load, the primer pockets will gradually loosen as the case is fired more and more. Its much more noticable from firing to firing with the TTI cases. Not so with the new Jamison cases, they loosen dramatically on the first firing and then level out after that.
What this tells me is simply the oversize primer pocket expands a certain amount on the first firing, they stabilizes after that. If the pockets were 1 thou tighter, that intital expansion would be much more limited and case life would dramatically improve.
I have passed on my findings and opinions to Jamison so we will see if they continue to modify the cases. Until they get the cases where I want, I will be holding my 2000 case order from them but as soon as they get it right, I will place that order and then once those cases are proven up to the challange, I will instantly place another order for 2500 338 AM cases and 2500 375 AM cases.
I plan on keeping cases in stock at all a times for customers once they get the cases where they need to be as far as quality goes.
They are working very hard to do this, at least they are putting in great effort to correct the problems they have had with their original design. That tells me they want to send out a quality product. It has taken some time and may still take a bit more time but I fully understand that they want to get it right this time before sending cases out to customers.
Have to appreciate that.
More to come.
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