Home Forums Hunting & Shooting Ask The Gunwriters Jamison calibers.

Been thinking of a build, and was thinking of a .284 jamison, or a .257 jamison. Anyone ever had any experience with them? The 7mm, seems to be about like the stw without the belt? I can't find any loading, or much about these cartridges. A place to reference these would also be appreciated. Don

Go with a 7mm WSM............Brass and data is readily available.

Isn't that what the WSMs are anyway???

Glad you mentioned those calibers. I remember the articles in Shooting Times, back when that was a good mag. Jamison is a good writer and gun experimenter. I think they did churn up about what the WSMs do, in similar case capacity.

I do agree that it would probably make more sense to go the WSM or SAUM route, especially if money is an option. On the other hand, why would a rifle looney care?

I don't think the WSM's have the same case capicity. I would venture to guess, that the Jamison versions, are Pre Ultra Mag. I'm not sure what the parent case is for the WSM's, but they have a .453 case head. The Jamison cartridges appear to be using the .404 size cartridge, as they have the .534 case head. I'd guess velocity would be arount the stw range. These are my thoughts, and not fact that is known, but looking at the case drawings, I think performance would be as stated in the stw range. Just looking to confirm this. Don

Didn't Jamison have a suit against Winchester for the WSM design?
Seem's he claimed the original design was his.
Didn't that have someyhing to do with his leaving Shooting mag?
Could be mistaken--

I've built several and still have one in 338 Jamison.

The cartridges are based on the 404 Jeffery, more or less the same as the RUM cartridges. When I built most of mine about the only brass available which you could use WAS the 404 Jeffery and RWS, Bell and Bertram were the only ones making it. Bell and Bertram were junk and RWS was/is great but very expensive at about $2 per case 12 years ago. It's no longer produced but Norma now makes it. The RWS brass was thicker in the web and once sized to Jamison, had a water capacity of about 60g of water. The Norma brass ends up with a bit more capacity than the RWS.

The dimensions of the cartridge are slightly different than the WSM's which mostly have a water capacity slightly higher than possible with the old RWS brass. With the introduction of the various RUM cartridges, that brass is usable for Jamison, the major difference being the diameter of the head, the RUM brass being about .010" smaller so that a slight alteration of extractors in controlled feed actions might be necessary. However, the positive is that you end up with about 3g MORE of water capacity which in the case of the 338, puts it within a couple of grains of capacity for the 338 Win Mag.

I also built several (4 I think,) 338 WSM's and the Jamison with the RUM cases WILL outperform the WSM very slightly and approach Win Mag velocity.

I've recently built a 300WSM and didn't even contemplate the Jamison simply because of the difference in desirability of the two rounds upon resale or trade. Another 25-50fps out of the Jamisons isn't going to make that much difference on game and "manufacturing" the cases isn't that much fun when you can buy the WSM's over the counter. Still, if you want something a bit different, it's a good cartridge in a short action.

Oh! And load data for any of the WSM's is virtually the same, maybe �g to 1g more of any of the propellants listed in load data for WSM when you use RUM brass.

bobski,
Thank you for some very good information. I currently have a 7mm RUM, and have been pleased with it. Was thinking of an odd ball build, but after reading your post, I don't think it's worth it. Thanks again for some great info. Don

Nilwood,

While you are correct about the diameter of the case head on the WSM cartridge line. You must remember that this is a rebated head design. The actual diameter of the cartridge is .556. It is virtually identical to the Jamison lineup except for the rebated rim.

My version of RCBS load predates the introduction of the RSUM and WSM lineups. But it does include capacity data for the Jamison. For comparison, I have included some of the capacity data from the program. This is cartridge capacity in gr/water to the base of the neck.
257 jamison..76.7
284 jamison..76.4
280 Rem......59.9
280 AI.......60.6
284 Win..... 58.3
7mm Rem mag..74.6
7mm STW......86.4
6.5 Rem mag..60.9
300 H&H......74.3
300 Win mag..79.2
300 RUM.....101.6

I don't believe you're correct about the dimensions or the parent cases.

The Jamison series is in fact on 2" 404 Jeffery cases. The WSM are essentially the same thing with only minor differences. The Jamisons are NOT anywhere near the capacity of the Ultra Mags as the RUM's are full length 404 based cases. The bolt head of the 404 is .545" the RUM's and WSM's are rebated to .532" to allow same bolt head fit as the belted mags. Body diameters are about .550" for all. Some of the Jamison calibers have been around for twenty years.

Idaho_Shooter Thanks for the info. Murphy, as my post said, was just looking for info, I did not think the Jamison versions were close to the RUM line. But wondered if they were velocity wise, faster than the WSM's or the Rem short mags. Specifically, was looking for data and info on the 7mm Jamison version. If the 280 AI, is close to the 7mm Rem Mag, and the case capicity is much greater on the Jamison, where does it fall in place in velocity? Just looking for answers to knowledge I don't have, not looking to Knit pick. Was hoping the 284 Jamison was close to the STW. That's all. Don

No problem and didn't mean to sound like I was pickin'. The 284 is one of the two calibers of Rick's that I have, the other the 338. There is no distinquishable difference between the Jamison and WSM from a ballistic stand point. Samo-samo. Maybe one grain of powder depending on brand of brass. The 7mm WSM is however a bit bigger case than the 270 and the 300. The shoulder was moved forward to prevent it from inadvertantly being chambered in the 270 WSM. This makes it a bit more capacity. There was no 270 Jamison (to my knowledge) so all his are same dimension to shoulder. This is similar to the way the 280 Remington's shoulder was extended to prevent chambering in the 270 Win. About .050" or there abouts, I think.

From a practical stand point, since we have lots of good brass for all of the WSM's, there is no need to have the Jamison built, unless you just want one, always a good reason.

If you want STW ballistics you can have that without a belt in a standard length action. It is called the 7mm Dakota. It is on a 2.5" 404 Jeffery case. They use the standard 404 rim diameter at .545" and trim to about 2.570". The fit pre-64 actions and Sako actions very well and they equal the capacity of the 7STW, 8mm RM, 358 STA, 375 JRS and the 416 RM. I have a few of them including the 416 that never was.

The case capacity, and thus the velocity potential of the 284 Jamison is very close to that of the 7 WSM and also the 7mm Rem mag.

Take another look at the chart I posted previously. The Jameson holds 76.4 gr of water while the 7 Rem mag holds 74.6 gr. That is a pretty negligible difference when compared to the STW at 86.4 gr.

The ten gr capacity difference between the 7 Rem mag and the STW is realistically good for about 150 to 200 fps with most bullet weights. The two gr difference between the Jamison and the 7 Rem mag would be good for about 50 fps. The 284 Jamison will fall far short of the capabilities of the STW. The Jamison just does not have the CC's to produce that many ponies.

On the other hand, a 257 Jamison or a 257 WSM would pretty much be equal to a 257 Roy. And that is nothing to sneeze at. I personally would choose a 257 SAUM as a more balanced cartridge in 25 cal.

Thanks for all the great info. Your a gun freak for sure. Hats off to ya. Don

I am looking at the 7 rem mag the wsm and the 284 Jamison reamer prints now and the are in case capacity
7 rem mag =80.80
7 wsm =79.70
284 Jamison=81.01
7 stw=92.70

This was covered in numerous threads here several years ago (search). Jamison experimented with and patented a cartridge that (IIRC) exhibited a ratio of capacity, length and caliber. He tried to interest and license Winchester rights to this patent - they ignored him and introduced the WSM concept anyway. He sued; they lost and paid big bucks. He was run out of town on a rail by the industry and disappeared for several years, although he seems to be publishing again.

They settled out of court, not exactly a loss and sets no precident

Oh, you can believe it set a precedent in the firearms industry--next time somebody arrives at their door with a patented idea, they probably won't copy it as they have so often done with other folks ideas in the past..........



Casey

I think Winchester should have sued Jamison or Winchester should have patented their idea.



"1964 Gun Digest page 299.
American Bulleted Cartridges by Kenneth L. Waters

284 Winchester

"An entirely new short-cased cartridge designed to give short action rifles ballistics fully equal to the longer 270 Winchester and 280 Remington rounds.

Case Length of the new round is 1/2-inch less than a 270, but a larger body diameter with decreased taper and sharper shoulder provided the same powder capacity. (same concept for the wsm)

This increase in body diameter introduced somewhat of a problem; it was necessary to keep rim diameter the the "standard" size (common to such caliber as the 308, 270, and 30-06) in order to permit use of the 284 with the existing bolt-face dimensions.
This sub-diameter rim is founded on the 425 Westley Richards cartridge, and was also used in the past in various German calibers."


There is nothing original about Jamison's cartridges. He copied or used the same idea from Winchester who
borrowed it from Westley Richards.