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Jamison 408 Chey Tac brass updates....

 
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  #1  
Old 12-05-2007, 12:18 AM
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Jamison 408 Chey Tac brass updates....

TO all,

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.

All bonuses.

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.

Kirby Allen(50)
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  #2  
Old 12-05-2007, 12:28 AM
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Keep us posted

Thanks Kirby it sounds like some companies actualy listen to the consumers and they dont just say if you want them you get them as they come.

Keep us posted if you have Allen Mag cases that will help with decisions on making an allen mag or a base Chey Tac case to some.

Cheers Bill
Australia
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  #3  
Old 12-05-2007, 07:44 PM
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Quote:
I also noticed that while the alloy in the new Jamison cases is lighter, it also seems to be harder.
Low lead content of the alloy to make the brass most likely.
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  #4  
Old 12-10-2007, 12:24 PM
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Kirby

Will the neck thickness make any difference in my camber compared to the two star brass Iím using now? Also the rim thickness is the problem I told you I was having ejecting some rounds.

I notice you are running 145gr of 50-BMG is that for a speed of 3345? Iím using 142gr for 3380 last time I checked after the barrel brake in before the barrel brake in that same load was 3325 does that make any since.

Anyway once they get it figured out Iíll be getting some brass from you

Larry
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  #5  
Old 12-11-2007, 01:10 PM
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The neck thickness will be a thou or thou and a half smaller in diameter then the brass you are using now. Will make no real difference, only talking about .5 to .75 thou clearance on both sides of the bullet.

In fact, your cases may be a bit to tight, if that is the case, you will probably see some pressure drops with the new brass which may allow you to load to where you are with less pressure.

That is very common to see the velocity shift like you have before and after break in. Before break in, the barrel is somewhat rough, if you want to call a finely polished Lilja barrel rough!!!

As it breaks in, the bore diameter will increase slightly and the rifling land edges will round slightly, all reducing friction and pressure will drop.

In a conventional chambering, this may not be as evident, when your putting 142 to 145 grains of powder under a 300 gr bullet, it shows up more obviously. That is sure why you are seeing it.

ALso, as the throat wears it gets larger in diameter. This allows a bit more blowby around the bullet so some of the powders energy is lost ahead of the bullet. This is why older barrels tend to loose velocity compared to when they were new.

Make any sense????

Kirby Allen(50)
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Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com
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  #6  
Old 12-18-2007, 10:05 AM
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408 Jamison new batch

I've got this guy Johnnysg@optonline.net telling me for 10 months now that he was shipping it to me. Last week he e-mailed saying he has new brass.Is the brass any good???? I'm a man of my word this guy is not.


Thanks Stephen
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  #7  
Old 12-18-2007, 11:16 AM
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I would like to try one of these rifles but not until the brass situation is completely solved with the users verifing that this has indeed happened.
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