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Build question

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Old 09-12-2010, 03:26 PM
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Join Date: Jun 2004
Location: Texas
Posts: 1,027
Re: Build question

Shortgrass, I had an older Barnes (#3) reloading manual in the house and looked at it last night to get the rim diameter of the .300 WSM. It shows .473". I thought that was strange, but didn't look any further. After catching up on the thread this morning, I went out to my garage and looked at my Nosler manual and sure enough it shows .535". The .338 Win Mag bolt face will work with the .300 WSM.

Winmag, It still looks like feeding out of the magazine will be the biggest issue on the .300 Wby to .338 RUM, but Winchester parts might be available to convert the .338 Win Mag to a .300 WSM. The factory WSM box is probably shorter than the .338 box, but should be able to be fitted and bedded into the longer well.

Chad asked 3 key questions.

#1. No alteration to the bolt face would be needed for the .338 Win Mag to .300 WSM, and if required at all, altering the .300 Wby bolt face for the .338 RUM would be the slight chamfer on the inside front of the bolt lip, (and maybe touch the corner angle on the face of the sliding extractor).

#2 is the biggie. I don't know the answer to that one unless you're willing to single load.

#3. The .300 Wby ejection port should easily clear a .338 RUM fired case. The .338 Win Mag ejection port might be long enough to clear an unfired .300 WSM, so a fired case would have all kinds of room.

Never having done these conversions limits me to just reasoning my way through the process (pretty scary since I often miss something important), but with the other replies, maybe we've given you enough to go on.

Let us know what you decide to do. Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member

A big fast bullet will beat a little fast bullet every time
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Old 09-12-2010, 05:36 PM
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Join Date: Dec 2009
Location: Redmond Or.
Posts: 2,527
Re: Build question

Sorry I shouldve clarified;
The 338 win mag is a Browning A-Bolt, so it will be sold. I have not hered hardly anything good about building a Browning, and I dont want to start a build by going backwards. So the 338 will be sold to fund the 300wsm purchase in Model-70 Win.

My current Model-70, 300wby is the only one I wanna convert.
I have alot of thinking to do. I dont want to single load. and I want a carry gun, so Im staying away from the big stuff. But I do want a 338 to launch 225-250gr bullets with some authority to 800ish yards.
I realise that I already have rifles capable of this, but I am a firm beliver in overkill, thus the RUM chambering.
I already own a 270wsm and LOVE it-as most of you know-
If I got the 300wsm, for an ''inbetweener'', and had the 338RUM for the realy big stuff at extended range I feel I would be well rounded in the range I am currently comfy shooting at, and have room to grow a bit along the way. I dont think that the gun is gonna give me the tallent that some folks have, nor do I think I can make up for marginal accuracy with ''horsepower'', but I do think its a step in the right direction for being able to extend my range as my ability grows. Plus, someday when I have alot more $$$$$ than I do now, I would like to own a full on custom, dedicated long range rig, so the Rum chambering seems like even more of a good stepping stone/Leartning tool, for longer range shooting, and builds.
I just figured before I go dropping tons of $ on my 300wby for a brake, extending the length of pull, and some other issues, Id see if I had the proper makin's for a RUM conversion, without alot of headache.
P.S. Bigngreen, its not the super expensive one, its only about an $800 rifle, by todays prices. But its a safe queen and looks too sexy to shoot, so I may as well make something usefull out of it. Ie; If I already have a 270wsm, and am going to get a 300wsm, why have a 300wby?........when I can have a 338 RUM.
As far as the stock goes.......I dont wanna offend anybody, but I cant stand composite stocks, so I would either alter the one I have, or have to order a custom wood one with an aluminum bedding block inlayed...... LOTS of $$ that Id rather not spend if I could use/modify what I already have for now.
Like I said I have alot of thinking to do before I start talking to a smith with cash in hand. I tend to be ''rash'' when I have a dollar burning a hole in my pocket.
Thank you to all who have replied. This helps alot in making a decision of exactly what it is I want to do. Your comments are very educational, and I appreciate them all.
"Its not Rocket Surgery.....'

"I have No idea why that cop made me ride in the back seat, when I Clearly called Shotgun!"
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Old 09-12-2010, 06:02 PM
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Join Date: Jan 2007
Location: South Dakota
Posts: 753
Re: Build question

Now to really screw you guys up.

Norma now has the 338 Norma magnum. I have the reamer on the shelf and just finished a "lab rat" rifle for an ammunition manufacturer that's filling big big orders for the LE/Military crowd.

Looks like a winner so far!

Have a great weekend.

Chad Dixon
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Old 09-12-2010, 07:38 PM
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Join Date: Jan 2005
Location: OK
Posts: 2,145
Re: Build question

I finished a win 70 long action in 338 edge a couple months ago and it was pretty straigt forward. I added a wyatts box in the CRF action. That takes a little bit more work then in a 700 but is very doable. Think it was a 4 fluted packing gun.
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Old 09-12-2010, 09:14 PM
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Join Date: Jun 2004
Location: Texas
Posts: 1,027
Re: Build question

Yeah, from what I've read, I have the same impression of the A-bolt as a candidate for customizing.

I have no problem confusing the issue either. Have you thought about the .340 Wby on your .300 Wby donor? It's about 200 fps faster than the .338 Win Mag, and the ones I've had loved the 250gr Nosler Partition factory load. That combination is poison in a carry weight rifle. A muzzle brake is not necessary, but felt recoil is high in a light rifle. It won't hang with the RUM, but can get within 150 fps with the 250gr Nosler, and the aforementioned Barnes book shows the 2 cartridges in a dead heat with 200gr and 250gr Barnes bullets. Both the Nosler and Barnes books used 26" barrels for both cartridges. As barrel length increases, the RUM will pull away from the Wby with all bullet weights because of the greater powder capacity, but in a carry weight rifle, they are closer together. At 2800 fps muzzle velocity, the .340 (250gr Nosler) drops to 2000 ft/lbs at 510 yds, with 1900 fps retained velocity. At 800 yds it's down to 1300 ft/lbs and 1500 fps. Still supersonic, and accurate, but below the 2000 ft/lbs that has been recommended for Elk. Been wanting to do it because my home built .340 likes that bullet too.

I ran the .338 RUM at 2990 fps muzzle velocity and came up with 1477 ft/lbs at 800 yds with 1627 fps retained velocity. It drops to the 2000 ft/lb threshold at 600 yds, with 1930 fps retained velocity. Not nearly as much difference from the .340 as I expected. I got these numbers off my Oehler Ballistic Explorer. I ran them at 25' above sea level with 90% relative humidity and 70 deg F. The G1 ballistic coefficient of the 250gr Partition is .473.

How's that for muddying the water? Tom
Texas State Rifle Association Life Member
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A big fast bullet will beat a little fast bullet every time
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Old 09-13-2010, 09:22 AM
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Join Date: Dec 2007
Location: NW PA
Posts: 94
Re: Build question

The 338 RUM will move a 210TTSX at nearly 3350 and in mine at 9.3# and a Vais brake it is a pussycat. The 338 Norma w/300gr MK at 2720 in the same wt..gun will get your attention. Both the Norma and Edge will eaqsily do 2750 with the Berger VLD-with a 250yd zero that is -220 @1000yd and 2400 ft lb. Shawn sure got the Edge right, what say Spectom?
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Old 09-13-2010, 09:37 PM
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Join Date: Jun 2004
Location: Texas
Posts: 1,027
Re: Build question

RJ, I didn't compare the Edge because Winmag said he preferred not to fireform, buy custom dies, etc so I just made the comparison with the factory RUM cartridge. The velocities your RUM is getting are great, especially out of a 26" (or shorter?) barrel.

The .340 is a good balance of performance, weight, and moderate barrel length for a carry rifle. Mine has a Lawton sporter weight barrel with a composite stock and 4 x 12 x 40 Leupold scope. Everything except the MK V action is very light, but the rifle still weighs 9 1/2 lbs, and the 26" tube plus the Holland brake makes it a little longer than ideal for a quick handling carry rifle. Obviously the 250gr Partition isn't intended for long range work, but is a very fine stopper on game. I don't load 300gr Bergers or Sierras in the .340. My opinion is that they are too heavy for it. Conversely, my .338 x .378 shoots lightly loaded 300gr Sierra Mkhp's at 2780 fps, and 200gr Ballistic tips (not lightly loaded) at 3500 fps. It is a fine long range gun, still supersonic at 1700 yds with the 300gr Sierras, but it is too long and heavy to qualify as a carry rifle.

That's about all I have to say.

Good hunting, Tom
Texas State Rifle Association Life Member
NRA Endowment Life Member

A big fast bullet will beat a little fast bullet every time
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