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Converting the 300 Ultra Mag?

15516 Views 28 Replies 12 Participants Last post by  2Bits
I have been pondering this for sometime now and would like to hear from others if there are any negatives in doing this project other than spending money.

I am considering converting a 300 Ultra mag model 70 Winchester Classic Stainless into making a 338/300 Ultra mag out of my current rifle. Question is how much more percentage wise will it give in power (if any) over the already produced factory gun of Remington in a 338 Ultra mag?
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You will get roughly 5 to 6gr more powder capacity. Probably good for another 50 to 100fps with moderate bullet weights.

Quite a common wildcat now. For reg. hunting, probably not worth the hassle. For LR shooting of 300MK, bigger is better.

Mystickplayer thanks for the come back. I have decided to go ahead with this project and be the proud owner of a wildcat in a 338/300 Ultra Mag in spite of what some say about the recoil. It should make me a good long range elk buster in the near future. I maybe wrong but with a good stock, it shouldn't kick anymore than a friend of mine's 340 Weatherby. ;)
Should work

With a cannon like that, you should be able to get your elk even when it is hiding behind a few trees. That is a big stick.

The stock design is very important to recoil control, as is the recoil pad (try some of the new polymer pads). Getting something that fits will pay big time. Ensure that there is lots of pad contact with the shoulder. Some really straight stocks only leave the heel in the shoulder pocket. You may have to look at some drop depending on your shoulder/eye distance.

Monte Carlo stocks might be just the ticket dispite what the press says. The elevated comb does not cause the stock to roll anymore then a flat comb. All you need to do is extend the MC comb line to the butt and voila a straight stock with more drop.

The way to stop the cheek slap is the have the front of the comb LOWER then the rear so that as the rifle goes back and up, the comb does not hit you.

The Lazzeroni stocks have an exaggerated comb shape but work with his monsters. Shotgun stocks and lever gun stocks are the worse possible design for scope mounted heavy kickers.

I like my stocks to be shaped so that when I bring the rifle up, I do not need to hunker down or twist in order to look through my scope. My head is as upright as possible. For my build, this means a Monte Carlo stock or at least one with some heel drop, higher scope rings. This helps me shoot better in the standing and sitting positions where 90% of my shots are going to be.

Enjoy you cannon...

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I was shooting my .340 this weekend, I chronographed a load that I'm planning to use for hunting. The load uses a 210gr Barnes XLC X bullet and about as much RL-22 as will come out of a RCBS Uniflow measure with one pull of the handle. It was 95+ degrees yesterday, and I wanted to shoot this load to make sure it was REALLY safe. I noticed some minor pressure signs, so I know this load really is a max load, as was indicated in the Barnes #3 manual that I took it from. I've shot it before when it was in the 70's and experienced no pressure signs, but didn't take that opportunity to chronograph the load. The velocity was 3250 fps, how much faster do you think your new toy will be? I realize that some prefer heavier bullets in these rounds, but I've had problems making heavy X-bullets shoot in many guns.

P.S. I use a KDF muzzle brake on mine when target shooting.
Well guys I was almost talked into leaving this project by the way side, for fear of the recoil stopping my heart. Ya just can't believe all ya hear these days or read in the newspaper.:D

Mystickplayer............ I am researching those stocks myself at the present time and hope to come up with a solid solution that will help out with sighting through the scope without pains and recoil too......thanks!

Nap....I can't really say one way or another, but I do know that the Barnes XLC blue bullet in the 210 grain is all a hunter would need for elk. One of my hunting buddies uses that same bullet in his .340 Weatherby. He says its the only caliber for him, or bullet for that matter. He has shot 3 shot one hole groups with his gun at the rifle range. I witnessed the shooting myself. One gun hunts all, in his words.

I am debating on the barrel maker at the moment. I been thinking about one of those 26 inch stainless barrels that has been fluted. Others say they aren't worth the exspense and don't cool any better than a plane barrel, as far as hunting in the field.

Now getting back to that 210 grain Barnes XLC bullet, it does penetrate 25 % deeper than other brands of bullets. We did some testing ourselves a while back with my friends .340 Weatherby into 50lb clay (modeling crafts) blocks so the lighter weight 210 grain bullet should I figure, penetrate as deep as a 225 grain Nosler or 230 grain Bear Claw into a bull elks body. If I get close to 3200 fps with any kind of accuracy, I will be happy as a birthday boy sitting behind his cake LOL.:D
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If you are on a tight budget, consider the Adams and Benette barrels from Midway or those from ERShaw. Should give you MOA or better performance if properly installed.

For hunting, you don't need match grade accuracy. Elk are pretty big targets. You also don't need a lot of shots, hopefully, so the benefits of heavier contours or fluting are just for show. Get a contour that is as heavy as you want to carry in a length that makes sense in the terrain you hunt.

A big long barrel works great on the range but when up to your eyeballs in deadfalls or trees, I would rather have a lighter, shorter pipe. The lose of 100 to 200fps is not going to make the elk any less dead if I put the bullet in the boiler room.

For me, my hunting rifle has to perform in the field. I must be able to carry it for a long time and put it quickly into action (why I pay so much attention to stock shape and balance). The rest is just fluff that gets in the way...


PS want more penetration on game? Slow your impact vels down. If impact vel with those Barnes X are 2500 to 2800fps, it is highly unlikely you will find too many bullets in your game.
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Two of my hunting rifles have fluted barrels - one a regular chromemoly and one a stainless. When benchrest shooting here the ambient temps are already fairly high, so it doesn't take long to heat a barrel up. I can notice a distinct difference in barrel temps when firing equal numbers of rounds through them and placing my tender hand on them to check. Fluting does help in heat dissipation.

Wanting as long of barrels as possible and with heavy sporter contours, the flutes were basically desired to reduce some of the weight and for balance. Each tube is 26" in length for max velocity gain - one chambered in 6.5x.257 Ack Imp, and the other in 6.5-06. The fluting has accomplished what it is for and I'm very happy with the results.

BTW, the chromemoly is a David Van Horn barrel and the stainless is a Shilen.
I understand what you say about convenience and portability in the shorter barrels, but shooting a huge case like the UltraMags or Wthbys with a 20" tube would be a waste. I also understand that I don't really "need" a .340, it won't likely do anything in the field that my .35 Whelen AI won't. If I'm in the brush, I usually take a handgun with me anyway. I like flat shooting rifles, although I take more game with the more standard cartridges.

I don't know how the weather is where you live, but if you like to do bench testing without waiting a half hour between three shot groups, I'd reccomend a fluted barrel on the monster magnum if you're going to get the barrel in any sort of lighter contour. The barrel on my Mk V is pretty thin, when it's hot out, like it is now, you'll burn your hand on the barrel after 3 close shots. I do let it cool, but I know the throat on this thing isn't going to last forever, and that will be all the justification I need to get a new thin fluted barrel put on it.
As far as penetration with the 210gr bullet at 3200+ fps, I don't think there's an animal on this continent that it couldn't penetrate stem to stern within 100yds.
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You know my view kcih,

Why convert? Get a .338/.378 Weatherby and have the real thing!:D
I've looking at some of the HUGE rounds like you speak of. I'm pretty happy just shooting the REALLY BIG cases. I've got an order in a for a .416 Rigby, so maybe I'm not sane after all. From what I can tell from different data that I've seen, there is virtually no gain attained from going to .338-.378 unless you are using a rifle that has a 28+ plus barrel and are using the heaviest bullets available with a maximum charge of the slowest burning powder. This would be a setup that a long range target shooter would use and would be impracticle in a field situation, as the normal Weatherbys are somewhat of load to carry around unless you're in wide open territory. If you want one just to have the "biggest" that's OK by me, but I don't see it having any practicle advantage over the .340 in a field situation. The .300-.378 does do some things that are rather impressive, but I don't see having to put a new barrel on a rifle as soon as you've developed loads for the first barrel. That's based on what I've been told, not from experience.
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Well fella's I appreciate your come back on this project of mine. I shall secure a 26 inch stainless fluted barrel and see how things go down the road in a month or so. The stock will be a fiberglass or kevlar composite type. The scope will be a Leupold 4 x 12 for long range shooting well beyond that 350 yard marker.

Zeppelin......I already have the 300 Ultra mag and besides I don't care much for those muzzle breaks Weatherby installs or their cannons. This rifle is for long range elk hunting, I have a short barrel 338's to lug around in the dark timber, one with a short 23 inch barrel. It shoots a 250 grain Swift A Frame at 2650fps.

This 338/300Ultra mag will be doing some where around 3250fps I figure, give or take a foot or two, using the 210 grain Barnes XLC bullet or maybe the 225 grainer ( At 3140fps) if it produces a better group from the bench. Time will only tell! In any event it should prove to be a real thumper on those big bull elk in the future.
Why go to a wildcat round when the 338 ultra mag will give you all you need.

What is the case capacity of the 338/300 vs 300ultra mag???
I find it hard to believe that you will get 3250fps from that case. Its smaller the the .378 case is it not?

Now why stop at the .416 , jump up to the .450!
The .416 takes my front foot off the gound when I shoot it, man's gotta know his limitations.
:D :D Zeppy.......I already have a 416 Rem mag and the .458 LOTT, not to mention the 470 Capstick. There are a little short on yardage however. This project I have been working on for sometime, is one that gives ample bullet weight, along with plenty of velocity and not to mention down range kenetic energy to the target at 600 yards. I also like being the only one in camp with such a distinct caliber rifle. The barrel is stainless and fluted too, thanks for the advice guys. Oh, by the way it is on a model 70 pre-64 action, just like all my other big game rifles.......Cheers 2Bits! :D :D :D
check out 338 edge you should get a 30 " hart heavy barrel
Video: 338 X300RUM (338 Edge)

Go for it! I could not be more happy with mine.
I have a 338 X378 in a 14 pound Bench Pistol as well. The one pictured in the Video is an 8 pound center grip STriker. It carry's a 19" Benchmark 3 groove barrel. Regardless of what one might think on two different chronigraphs I am averaging above 2950fps with a 225 grain Accubond with the Edge! 2200FPE+ at 500 yards sure does it for me!

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Hammertyme.......Now that is one heck of a hunting pistol, jumpin horny toads!:eek: :D

I hate to ask you what your CCW weapon is these days!!!;) :D :D
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