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Weatherby 338-378 grouping issues

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Unread 09-22-2010, 08:51 PM
Junior Member
Join Date: Mar 2010
Location: Sudbury, Ontario
Posts: 15
Weatherby 338-378 grouping issues

Hey guys. I've been having a difficult time trying to figure out why I am getting such terrible grouping with my Weatherby Accumark 338-378. At 100 yards, the accuracy is all over the place, and i'm talking 8" at times. The scope I am running is a Leupold VX-3L 4.5-14x50. I am shooting from a solid table, with the gun in a fairly heavily weighted down rest. I was grouping very well with my old Weatherby 300 mag in the same rest. Do you guys have any ideas for me? Whitetail season is fast approaching, and I'm running out of ideas.

Here is the load specs:

20 brand new brass, and 20 once fired brass
180 grain Nosler Accubond Spitzers
110.0 grains of IMR-7828
Federal matched 215 primers
3.763" total length

I wanted to eliminate as much as I could, so I picked up a new box of 180gr bullets, a new tin of 7828, and a new box of matched primers. I yanked the stock off the rifle to ensure there was no barrel floating issues, and everything is perfect, as I expected it to be.
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Unread 09-22-2010, 09:37 PM
Posts: n/a
Re: Weatherby 338-378 grouping issues

I had problems with the 250 gr. Noslers in my 338 Ultra mag, then I tried the Barnes 225 TTSX and put 3 shots at 300yds into 5/8ths of an inch. I did get the 180's to shoot OK.
Load the Barnes .050 off the lands and do your testing at distances of 200 to 300 yds.
Good Luck
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Unread 09-22-2010, 09:38 PM
Platinum Member
Join Date: Dec 2009
Location: Big Horn Basin, Wyoming
Posts: 4,330
Re: Weatherby 338-378 grouping issues

I have a couple ideas. for 1 an 8 inch group at 100 is unacceptable. that is a direct indication to me that something is loose. take the scope off and the rings `make sure the bases are tight. Also make sure none of the screws for your bases are not too long and bottomed out. once everything is tight lap the rings set your scope in there and shoot it again. if that doesnt fix it I would swap the scope with another to see if you get the same group if not you probably have a broken scope. Lastly my dad had accuracy issues with his accumark 338-378 (1.25-1.5" groups) he switched to Barnes Tripple shocks which are a good match to a freebore rifle like yours because they are not meant to be seated close to the lands.
Can I ask why you are shooting 180's out of a 338-378? that is way too light for that gun. Take advantage of that big powder can and shoot a minumum of a 225. 180 is suited for something like a 30-06.

" Real elk guns start with the number 3 or bigger and blow two holes, one in and one out." - My Dad
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Unread 09-22-2010, 09:52 PM
Gold Member
Join Date: Apr 2007
Location: ALASKA
Posts: 504
Re: Weatherby 338-378 grouping issues

Originally Posted by valin View Post
At 100 yards, the accuracy is all over the place, and i'm talking 8" at times.
If I saw this type of target, I'd look really hard (Dr. Rifle slow and thorough like) at the following-

Optic-Do you have another rifle you can put the optic on, and just shoot a group with to make sure you didn't shake a the guts loose on the VX3.

Optic mounting-Obvious visual inspection, then remove optic, remove rings, remove bases. Reassemble using a product like the Kokopelli alignment bars to ensure a stress free mount for your optic. If you don't have alignment bars, attempt to slowly and gently rotate your scope in the rings with the ring caps removed, exercising care not to mar your tube. If your scope acts bound up, that should serve as an indication that your optic mounting is putting stress in your optic. Reassemble and torque to mfg specs.

Action screws-check to ensure you have those torqued to 55-65 in lbs. Most smiths will suggest the front screw needs to be torqued to final torque first, then the rear action screw.

Barrel free float-you stated it is free floated, but most Wbys will have pressure point near the forend, used to establish a poor mans barrel tuner if you will. Either this pressure needs to be consistent from shot to shot, or free floated altogether.

Bullet weights-Try a three shot group with starting loads at 180, 210, 225, and 250 grain weights (or those you are interested in). Your barrel may like a certain bullet weight/velocity range vs. others....no need beating your head/wallet against the wall, let the rifle tell you what it wants to shoot first, then fine tune.

Use a vice/brace/led sled type dvice to get the big precision/accuracy issues sorted out. That's a boomer, and it won't be fun while you sort this out. Rule yourself out as a variable until you get it calmed down, then go back to your proven shooting methods for fine tuning.
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Unread 09-26-2010, 05:15 PM
Junior Member
Join Date: Mar 2010
Location: Sudbury, Ontario
Posts: 15
Re: Weatherby 338-378 grouping issues

I really do appreciate the input guys. I went back out shooting today, with a buddy of mine who runs the same rifle. I swapped out scopes, and ended up with the same result......still all over the place. We then fired my loads in his 338-378 and ended up with the same results, so therefore, the issue is in the loads. We also fired some 200gr. nosler accubonds on 104 gr. of IMR 7828, and the results were substantially better, but still not great by any means.

I have been doing some more research on this site on load data for my rifle, and am going to take all of your advice, and step up into a heavier bullet. I am going to order some Barnes Tipped TSX 225's. I would really appreciate it if you could recommend me some loads for these bullets. Is the IMR 7828 a good powder for this, or should I be switching?

I will be using Federal 215 matched primers.
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Unread 09-26-2010, 07:19 PM
Bronze Member
Join Date: May 2010
Location: Australia.. The worlds largest Island
Posts: 46
Re: Weatherby 338-378 grouping issues

Don't know if this will be of much help
.338-378 @ www.reloadersnest.com

338-378 Wby Load Data - Handloads.Com

LoadData - .338-378 Weatherby Magnum (Barnes Reloading Manual #3)
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Unread 09-27-2010, 12:40 PM
Silver Member
Join Date: Feb 2008
Location: north Alabama
Posts: 352
Re: Weatherby 338-378 grouping issues

Is this the first load that you have tried ? How did you come up with this load ?
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