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Author Topic: 338-378 Weatherby Questions  (Read 6905 times)

Offline bearpaw

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338-378 Weatherby Questions
« on: February 03, 2017, 05:59:36 PM »
Sportsman's Warehouse had some rifles marked down so I bought an Accumark 338-378. I also purchased two boxes of empty cases for handloading so I am wondering if anyone has developed a load for one of these rifles that they liked? I'm really curious what powder seems to work best for most people? THANKS for any info!
« Last Edit: March 10, 2017, 10:30:53 PM by bearpaw »
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Offline bearpaw

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Re: 338-378 Load Data
« Reply #1 on: February 03, 2017, 06:02:20 PM »
I've got a new VX-6, 3x18x50, that I could put on the rifle, but also thought about getting a Nightforce. The gun is still in the box, I don't know if it shoots well enough to justify a Nightforce?
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Offline JimmyHoffa

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Re: 338-378 Load Data
« Reply #2 on: February 03, 2017, 06:12:04 PM »
I find H-1000 to be best powder so far.  Retumbo has been fine too.

Offline bearpaw

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Re: 338-378 Load Data
« Reply #3 on: February 03, 2017, 06:14:06 PM »
I find H-1000 to be best powder so far.  Retumbo has been fine too.

Are you getting the kind of accuracy you wanted? I know it's not a custom rifle but I'm hoping for pretty fair accuracy.
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Offline kentrek

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Re: 338-378 Weatherby
« Reply #4 on: February 03, 2017, 06:24:46 PM »
We did some work on with 300 grain bergers, don't Remember exactly load details but it was 1/3 minute load

Next time I go make bullets il get you the details if you're interested in running the big bergers

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Re: 338-378 Load Data
« Reply #5 on: February 03, 2017, 06:29:13 PM »
I find H-1000 to be best powder so far.  Retumbo has been fine too.

Are you getting the kind of accuracy you wanted? I know it's not a custom rifle but I'm hoping for pretty fair accuracy.
It does alright.  For out of the box with load 1 just under an inch at 100 yds and load 2 right at an inch.  Even with the fluting, it heats up fast so at the 5th shot it begins to open.
load 1-200 gr Hornady Interlock, 9 1/2 M primer, 105.0 gr H-1000 , 3.71" avg of 3050 fps
load 2-250 gr Hornady Interlock, 215GM primers, 112.0 gr Retumbo, 3.73"  I get avg of 3070 fps

and like always with internet load data, bounce it off credible sites.

Offline bearpaw

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Re: 338-378 Weatherby
« Reply #6 on: February 03, 2017, 06:31:08 PM »
We did some work on with 300 grain bergers, don't Remember exactly load details but it was 1/3 minute load

Next time I go make bullets il get you the details if you're interested in running the big bergers

I know a guy using 300 bergers in a 338 Edge with excellent results. I had planned on getting some to try.
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Offline Come Get Some

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Re: 338-378 Weatherby
« Reply #7 on: February 03, 2017, 08:44:24 PM »
A buddy of mine has this gun, 300 Gr Berger ,I will check to see but I think he uses 50 BMG. Great groups . Shoots clays at 550 all day with no effort. I will get the load tomorrow. Lots of damage from the 300 Berger.. We were in New Mexico, he shot a mule deer at a little over 600 yds. I watched the round in the Leica's . Looked like a tracer. Smoked the deer. Wasnt even close to a game.

Offline elkinrutdrivemenuts

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Re: 338-378 Weatherby
« Reply #8 on: February 03, 2017, 09:10:40 PM »
Where? And how much for the rifle?

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Re: 338-378 Weatherby
« Reply #9 on: February 03, 2017, 09:19:35 PM »
110 gr RL 25 with 225gr tsx most accurate and can use the full case capacity.  Kicks less good to 1000 yards and works with short 26" barrel.  Like any big 338 - especially 300 gr - group sizes dont grow as much after 200 yards once bullet settles down.  i.e. 1" group at 100 might be 3" group at 500. 

The new accumarks may be different but the old ones usually needed a bedding job and timney trigger to get moa/sub moa groups.  I expect new accumarks triggers can be lightened enough to work ? 

I read that this stuff works great for 300gr pills:  http://gibrass.com/gunpowder.html  order: WC-872 and load to H-870 DATA - max 109 gr.
« Last Edit: February 03, 2017, 10:20:40 PM by Magnum_Willys »

Offline Taco280AI

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Re: 338-378 Weatherby
« Reply #10 on: February 03, 2017, 10:44:41 PM »
How much did the rifle go for?

Offline Dan-o

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Re: 338-378 Weatherby
« Reply #11 on: February 03, 2017, 10:56:21 PM »
How much did the rifle go for?

Yeah, inquiring minds want to know!
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Offline b23

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Re: 338-378 Weatherby
« Reply #12 on: February 03, 2017, 11:47:58 PM »
If you're interested I still have two brand new boxes of Nosler Custom 338-378 ammo loaded with 225gr Accubonds.

Offline bearpaw

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Re: 338-378 Weatherby
« Reply #13 on: February 04, 2017, 03:39:07 AM »
Thanks for all the info everyone!

110 gr RL 25 with 225gr tsx most accurate and can use the full case capacity.  Kicks less good to 1000 yards and works with short 26" barrel.  Like any big 338 - especially 300 gr - group sizes dont grow as much after 200 yards once bullet settles down.  i.e. 1" group at 100 might be 3" group at 500. 

The new accumarks may be different but the old ones usually needed a bedding job and timney trigger to get moa/sub moa groups.  I expect new accumarks triggers can be lightened enough to work ? 

I read that this stuff works great for 300gr pills:  http://gibrass.com/gunpowder.html  order: WC-872 and load to H-870 DATA - max 109 gr.

I've got some 225's and also some 160's and 185's I was going to test. The 160's were right at 3450 fps out of my 340, they should come out of the 338-378 like a varmint round. We've shot two bear and an elk with the 160's out of the 340, dropped them all, the elk was a little over 500 yds, bullet passed through all 3 animals. I'm not sure if the 338-378 will stabilize the 160's but plan to find out. There was very little recoil shooting them out of the 340, I would expect the same out of the 338-378 with such light bullets. I understand that if I'm shooting much farther than 500 I'll probably need to use heavier bullets. I'm hoping to shoot without the muzzle break but will probably have to use it for the heavier bullets. I'm really curious to see how much different these bullets shoot with and without the MB.

How much did the rifle go for?

Yeah, inquiring minds want to know!
Sportsmans Warehouse had Accumarks for $1695, I found this one in a Utah store when I was there hunting. That's the lowest price I've seen anywhere for a new 338-378 Accumark. I would imagine some of their other stores have the same deals.

If you're interested I still have two brand new boxes of Nosler Custom 338-378 ammo loaded with 225gr Accubonds.

Thanks for offering but I already have some weatherby brass and I want to use all the same brand of brass. Advertise it on here, I would think someone will want it.
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Offline yorketransport

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Re: 338-378 Weatherby
« Reply #14 on: February 04, 2017, 10:20:56 AM »
I worked with one for a little while for a guy and had good luck with H1000 and Retumbo for pretty much every bullet weight. They're a little too slow for the super light Barnes bullets, but still work pretty well. I was never really happy with how that particular gun shot with bullets under 225gr. The big cases get a little finicky with light bullets and I had more consistent loads with heavy weights. I've never played with Reloader 33 but it my be worth checking out as well. The best advice though is to only use the Federal 215 primers if possible. Regular large rifle magnum primers seem to struggle when you try to ignite over 100 grains of powder and you end up with random velocity swings or odd pressure signs.

I've got a new VX-6, 3x18x50, that I could put on the rifle, but also thought about getting a Nightforce. The gun is still in the box, I don't know if it shoots well enough to justify a Nightforce?

I think the VX-6 is perfect for a hunting gun. Other than the Nightforce SHV, their scopes are all huge and make a mid weight rifle too top heavy for my liking. Plus I still think the NXS is over rated. I've had a few and none of them really impressed me. The ATACR is a different story though!

Offline b23

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Re: 338-378 Weatherby
« Reply #15 on: February 04, 2017, 05:11:27 PM »
I suggest getting a very good rings and mount setup for your 338-378.  I had a NF NXS on my 338-378 Accumark and had a heii of a time keeping the scope from moving around.  After using two different sets of rings ended up putting a Near Mfg. 3 ring Alphamount on it and that did the trick because it never moved again.

Never messed with any bullets lighter than the 225's.  In my opinion the factory barrel is the weak link and is much to small of a profile for that big Weatherby 378 case.  Whenever I started to push the throttle down the groups would open up into the inches but if I kept all my loads very moderate it was about a 3/4-ish MOA gun.  The powders I used were H1000, Retumbo, and 7828ssc.  For the most part they all shot about the same size groups and accuracy loads were usually within 50 fps of each other.

If you're looking to do precision work, you could be a little disappointed but if minute of elk is good enough, you'll likely get along just fine with it.

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Re: 338-378 Weatherby
« Reply #16 on: February 04, 2017, 06:29:34 PM »
Good hunting round👍
Can be a little disappointing as a "long range" prospect.
Mine loved 300 mk's and lighter accubonds, but suprisingly, nothing in between..
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Offline yorketransport

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Re: 338-378 Weatherby
« Reply #17 on: February 04, 2017, 07:00:54 PM »
I suggest getting a very good rings and mount setup for your 338-378.  I had a NF NXS on my 338-378 Accumark and had a heii of a time keeping the scope from moving around.  After using two different sets of rings ended up putting a Near Mfg. 3 ring Alphamount on it and that did the trick because it never moved again.


That's part of the problem with the NXS, it's so heavy that it want's to stay put while the rifle slides out from under it; stupid laws of inertia! :chuckle: Burris Signature rings are some of the best for holding a big heavy scope in place.

Offline b23

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Re: 338-378 Weatherby
« Reply #18 on: February 05, 2017, 08:37:38 AM »

That's part of the problem with the NXS, it's so heavy that it want's to stay put while the rifle slides out from under it; stupid laws of inertia! :chuckle: Burris Signature rings are some of the best for holding a big heavy scope in place.

Very true, NF scopes are heavy but just about all the good scopes are on the heavy side.

Offline BULLBLASTER

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Re: 338-378 Weatherby
« Reply #19 on: February 05, 2017, 09:30:12 AM »
My cousin shoots a 338-378 with 300 grain Bergers. He isn't running them real fast at all at 2650 but they shoot very well there. They really have to be pushed into the case to fit in the mag. But even at that speed they are absolutely devastataing on game.

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Re: 338-378 Weatherby
« Reply #20 on: February 15, 2017, 09:35:38 PM »
One interweb guy swears he gets 2950 fps with 116.5 gr RL33 and 300 gr smk with good accuracy. 
I'm going to start at 108 and work my way up and see what happens. 

Just Bought a box of these HSM's from Sniper Central as a baseline.  Can't believe they are that fast but we will see.....

3100 fps @ Muzzle
300gr Sierra Match King
Ballistic Coefficients
.768 @ 2300 fps and above
.760 between 2300 and 1800 fps
.750 @ 1800 fps and below

Offline b23

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Re: 338-378 Weatherby
« Reply #21 on: February 16, 2017, 09:13:32 AM »
One interweb guy swears he gets 2950 fps with 116.5 gr RL33 and 300 gr smk with good accuracy. 
I'm going to start at 108 and work my way up and see what happens. 

Just Bought a box of these HSM's from Sniper Central as a baseline.  Can't believe they are that fast but we will see.....

3100 fps @ Muzzle
300gr Sierra Match King
Ballistic Coefficients
.768 @ 2300 fps and above
.760 between 2300 and 1800 fps
.750 @ 1800 fps and below

I'd say 2950 w/RL33 is definitely doable but I don't know that your buddy will get very many reloads from his brass before he starts stretching primer pockets because his 116.5 of RL33 is a pretty hot load and 3100 would be a crazy hot load.

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Re: 338-378 Weatherby
« Reply #22 on: February 21, 2017, 09:58:55 AM »
One interweb guy swears he gets 2950 fps with 116.5 gr RL33 and 300 gr smk with good accuracy. 
I'm going to start at 108 and work my way up and see what happens. 

Just Bought a box of these HSM's from Sniper Central as a baseline.  Can't believe they are that fast but we will see.....

3100 fps @ Muzzle
300gr Sierra Match King
Ballistic Coefficients
.768 @ 2300 fps and above
.760 between 2300 and 1800 fps
.750 @ 1800 fps and below

Update: Fired these HSM factory loads off and got 2900 fps on my magnetospeed.    Accumark 26" barrel.  I'm reading 100 fps lower than factory spec on weatherby ammo so these may be 3000 fps ammo .

Way faster than anything in the Nosler load table - I don't know why Nosler is so conservative - they show max load with RL33 of 108 grains at 2731 fps out of 26" barrel but show the Lapua at 2750 with 10 grains less powder and a 2" shorter barrel.  ????  Must be in case someone tries their loads with a gun without the weatherby headspace.
« Last Edit: February 21, 2017, 10:23:50 AM by Magnum_Willys »

Offline b23

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Re: 338-378 Weatherby
« Reply #23 on: February 21, 2017, 10:32:42 AM »
Update: Fired these HSM factory loads off and got 2900 fps on my magnetospeed.    Accumark 26" barrel.  I'm reading 100 fps lower than factory spec on weatherby ammo so these may be 3000 fps ammo .

I'd trust what your Magnetospeed said long before I'd believe the velocity they claimed on the box.

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Re: 338-378 Weatherby
« Reply #24 on: February 21, 2017, 11:25:47 AM »
Printed out a chart to show my son why he should switch from 225 gr to 300 grain for ELD hunting.  Out to 800 yards he could even use same turrets for both the drop is so close but the energy difference is huge.
300 gr SMK VS 225 Gr. Weatherby Tsx .  Actual tested velocities. 


 

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