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  1. #1
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    Default .338 Imperial Magnum Chassis fun project

    Good members, always great to be in a discussion with fellow members. I am doing the planning on a long distance fun shooting rifle for shooting days at our rifle club and for my own fun experiences. I did some extensive reading and looking at many, many chassis designs that I can incorporate in my own design when milling the chassis from a solid bar of high grade aircraft aluminum . This will all be done freehand milling work with a lot of marking blue spray/veneer measuring techniques and .0001 mm accuracy milling work.

    The project will consist of three parts..butt the stock , the action inletting and the front barrel part the butt stock will be attached to the action/barrel part by stainless steel bolt/nut system..

    Weight distribution steel weights adjustment felt recoil dissipation system/add/adjusting weights to chassis.

    The action inletting /barrel /front barrel chassis extension will be milled from a solid piece of high grade aluminum .
    Caliber : Donor barreled action- HOWA .338 Win Mag caliber
    Reamer : .338 Imperial Magnum (404 Jeffery neck down to .338 caliber
    Go/no-go gauges
    100x .338 Imperial head-stamped brass
    Re-loading dies
    Bi-pod
    Scope: 5-25 x 50 First focal plane Military spec

    Rationale :
    Fun shooting long distance rifle design /long range practice shooting rifle personal use .
    Duration build : 3 x years

    I would like and welcome all opinions/suggestions and remarks as well as hearing from members who has a similar project in mind or already did a similar project...Let us make this a fun discussion and feel free to upload as many photos as possible on this thread.

  2. #2
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    Default Re: .338 Imperial Magnum Chassis fun project

    I think the correct term is "similar to 404 Jeffery".

    I only mention this in case you think you might be able to fallback on 404 Jeffery brass for it one day. The case rim can be turned down, but Jeffery brass is only rated for 50,000 psi.

    If in fact the cartridge was based on actual 404 Jeffery brass, case life was very short.

    The situation for high pressure cartridges "based on" Jeffery or Gibbs is the same. Gibbs is also low pressure, anything modern "based on" Gibbs cannot use necked down Gibbs brass.

    For your intended purpose, you should verify the operating pressure of the cartridge. It claims to outperform Weatherby, which is a serious claim. The 378 case family has 140 grains capacity.

    It can only outperform in one of two ways - provide much more case capacity or run at higher pressure, and Weatherby can run at 65,000 psi. Verify the Howa action is rated for whatever the pressure is.

    Get the rifle weight close to 12kg, with a Beast brake from Gunwarrior, and you will be able to spot your own impacts.

    For 140+ grains of powder in a relatively small bore, you need a 30+ inch barrel to get full performance.

    338 Edge can equal that performance. Brass for the Edge is 7mm RUM necked up with no other changes.

  3. #3
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    Default Re: .338 Imperial Magnum Chassis fun project

    414 Gates, good to hear from you. The .338 Imperial Magnum is an original 404 Jeffery brass casing neck down to a .338 caliber without any blow out of the 404 Jeffery case.

    Length of barrel: Brux barrel 34" inch long

    This was the first ever design using a 404 Jeffery case as is. No changes made to the 404 Jeffery case at all.

    It is not a barrel burner and will have the same barrel life as a .30-06 hunting rifle.

    It has a low chamber pressure since this is a case designed by the Germans in the 10.75 x 73 caliber..the English thought it a good system to build their 404 Jeffery on the German principle.

    The reason why this Canadian designed caliber by Aubrey White did not get of the ground was due to Argentinian Military company was not able to manufactured good quality brass in a specific time frame .

    This brass did not make it in time and was a whole year behind the scheduled time frame. A few rifles were manufactured but due to the brass issue the Imperial Magnum range of calibers , 7mm Imperial Magnum, .300 Imperial Magnum, .331 Imperial Magnum, .338 Imperial Magnum and the .360 Imperial Magnum range calibers all based on the original 404 Jeffery/10.75 x 73 caliber did not manage to get into production.
    This is where the Remington and the Winchester as well as the Dakota concepts sprout from. Remminton used a blown out case of of the 404 Jeffery to build their .300 and .338 Remminton Ultra Magnum and Winchester their .300 Short magnums based calibers ....

    The .338 Edge was just changes made by Shaun Carlock to the angle of the neck of the Imperial Magnum case similar like the Ackley improved version.

    This .338 Imperial Magnum will be a lighter recoiled version of the .338 Lapua Magnum for sure. This is why I opted for the solid aluminum chassis that will enable me to add /remove weights incorporated into the chassis body.

    I already bought 140 Imperial Magnum head-stamped brass of excellent quality , go/no go gauges/reamers as well as re-loading dies for the .338 Imperial Magnum from Aubrey White , the originator of this range of magnums. This will be a fun shoot rifle the barrel will be " I will be profiling it to a taper but not too much going for a tapered Bull barrel..it will never be used to hunt ..only long range fun shooting
    Brux barrel 34" .338cal /8.5 rifling twist straight barrel blank

    Please find attached the technical specs of this caliber and if you wish to know more about this caliber/range I do have the real history available for you as being written by the Originator /designer of this magnum caliber.
    Attached Files Attached Files

  4. #4
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    Default Re: .338 Imperial Magnum Chassis fun project

    Maybe a correction is in order..take a look at this page ...this is in regards to the parent case of the Edge
    https://en.wikipedia.org/wiki/.338_Edge

    7MM Remminton Magnum.:

    Parent case:
    .300 Remington Ultra Magnum( 404 Jeffery parent case)

  5. #5
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    Default Re: .338 Imperial Magnum Chassis fun project

    Another interesting caliber that I will build is based on a 404 Jeffery /10.75x73 caliber case as well..it is the 9.3 x70DWM the only pre war rifle build by a German gunsmith by the name of Scheevy .

    He build a double rifle in this caliber for the German Military hero Herman Goering , one of Hitler`s five top generals. This rifle is still in a museum in Germany.


    The second rifle I know about was build by a gunsmith in Belguim he is not finished with the build but had shot it..his comment was that the recoil is extensive..but it killed every game animal he shot in a devastating manner..

    The third rifle I know of in this caliber was build by an American rifle builder on one of the rifle forums I am a member of.

    I am not talking of Drilling rifles in Germany and Austria at all..the 9.3 c 70 DWM is part of a lot of Drilling rifles designed /build in Germany. I am talking about a dedicated hunting rifle , double or center fired hunting rifle.

    I have the blue print of this caliber, the re-loading dies and will get PGR company cut the reamer from the blue print for me .This caliber`s parent case is the 404 Jeffery/10.75 x 73 case.

  6. #6
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    Default Re: .338 Imperial Magnum Chassis fun project

    Quote Originally Posted by Gert Odendaal View Post
    It has a low chamber pressure since this is a case designed by the Germans in the 10.75 x 73 caliber..the English thought it a good system to build their 404 Jeffery on the German principle.
    The original Jeffery is low pressure, necking it down raises the pressure.

    Just consider that 250 grains at 2900+ fps is not low pressure from a .338.

    Is there any pressure data for the cartridge as originally produced, with this load data ?

    The output exceeds current manufacturers load data for 338 Lapua at 60,000 psi. Is the Howa action rated for 60,000 psi ?

    The Dakota, Edge and Lapua brass itself is rated for the cartridge pressure, it's not just a change in angle or length.

    Perhaps check with the supplier what pressure the brass is rated for. Same for the Howa action.

    You are aiming for a reduced recoil .338 and will limit yourself to 338 Win Mag performance. The next owner of the rifle is not going to know that, and will use the loads on that sheet.

    To illustrate the point of brass design - I have 404 Jeffery brass weighing 294 grains. My Norma 300 RUM brass weighs 284 grains. RUM case capacity is 1 grain higher than Jeffery. I would not load a 404 Jeffery to RUM pressure, even though by weight, the Jeffery brass is "beefier".

    Based on the outcome of the pressure information, you should consider stamping the max psi for that build on the receiver, for the safety of those who will come after.

    Addendum :

    The load data says "THIS LOADING DATA MUST ONLY BE USED IN RIFLES MANUFACTURED BY IMPERIAL MAGNUM CORPORATION (IMC)."

  7. #7
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    Default Re: .338 Imperial Magnum Chassis fun project

    Interesting chambering. Pity it never made it into SAAMI or CIP specs. The .311 looks quite handy.

  8. #8
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    Default Re: .338 Imperial Magnum Chassis fun project

    I don't like the cartridge look, meaning shape of the olden cartridges, even the Lapua have a fat ass.

    The ones I really like is the 338 RUM and the 33 Nosler, where the best design is probably the Nosler.

  9. #9
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    Default Re: .338 Imperial Magnum Chassis fun project

    Jan, I agree, it really was the first ultra magnum design without the belt like the .375 H&H Magnum and the belted range of magnums.
    The 91mm COL /over all cartridge length should work good enough..I have opend up a Mauser 98 Mod Obendorf action to re-load from the standard 87 mm to a 91mm 8x68 S loaded round ..I am sure if I can get the .338 Howa barreld action , replace the barrel with a Bartlein or Brux barrel 30" inch , 1;9.5 twist it will be a great rifle ...I noticed the Bartlein rifle company do the following type of barrels:

    We only do single point cut style rifling. No button rifling and no broach cutting

    We call it Transitional rifling. Some will call it gain twist, progressive twist or incremental twist. We cut rifle virtually any twist into a barrel (subject to tooling etc…). We can start the twist out at 1-14 and end up at 1-7 and have it uniformly increase from the breech to muzzle. Also we can increase it very slowly say from 1-7.5 at the breech to a 1-7 at the muzzle.

    Some say bullets with the driving bands benefit from it as it doesn’t damage the driving bands as much. Also some have proven with lead bullets that just increasing the twist by as little as a .5 of an inch increase uniformly thru out the length of the barrels will help accuracy. We have the capability to provide any twist per length of barrel for the customer. We have not tested every possible combination of calibers bullets etc…. we can give our recommendations on things we hear, and barrels we shoot etc…

    I am awaiting a quote from the Bartlein barrel ..want to compare it with the price of the Brux barrel. I can look at Shilen as well..PAC-NOR makes great barrels as well although I do not know if they are up and running after the manufacturing plant was devastated by a fire and it burned down to the ground. There are so much options in this regards..

  10. #10
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    Default Re: .338 Imperial Magnum Chassis fun project

    Quote Originally Posted by Messor View Post
    I don't like the cartridge look, meaning shape of the olden cartridges, even the Lapua have a fat ass.

    The ones I really like is the 338 RUM and the 33 Nosler, where the best design is probably the Nosler.
    Messor, then you will like the Imperial Magnum, it is the same case profile..404 Jeffery is the parent case or the .300 RUM...
    404 Jeffery case = Remminton Ultra Magnum caliber, the .338 RUM in turn is based on the .300 RUM ...so this case is the one you will really ike and enjoy working with it Messor

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