375 Weatherby

R. A. Berry

 

 

 

 

THE RIFLE

 

Winchester M-70 Classic Stainless .375 H&H rechambered to .375 Weatherby using a Dave Manson reamer with 0.375 freebore length. Barrel 24 inches. Magazine box is 3.625 in length. The scope and mounts:  a  Leupold Vari-X III 2.5x-8x with Leupold QRW rings and bases, with square recoil stop on bottom of each ring.

 

RELOADING COMPONENTS

 

Brass: 

Hornady basic sized to .375 Weatherby, trimmed to 2.850, and necks annealed.

 

Primer: 

Federal GM215M

 

Bullets: 

250 to 350 grains

 

Propellants: 

Reloder 15

IMR-4350

H4831SC

Norma MRP

 

Average Temperature:  50 degrees F.

 

Chronographed 15 feet from muzzle.

 

Groups for 3 shots at 100 yards, center-to-center,  rounded to nearest tenth of inch.

 

The Load Data

 

Powder

Velocity

Group

Bullet & C.O.A.L.

77.0 Reloader 15

2755

1.3

250 Barnes X FB 3.600

77.0

2762

0.9

260 Nosler Ballistic Tip 3.600

78.0

2818

0.8

 

79.0

2845

0.9

 

77.0

2763

0.5

265 Groove MI 3.600

78.0

2782

0.6

 

79.0

2805

1.5

Ejector marks Do not use

77.0

2748

0.6

270 Bridger Brass FN 3.600

78.0

2779

0.8

 

79.0

2826

0.9

 

77.0

2708

0.7

270 Hornady SP 3.600

76.0

2607

1.6

300 Hornady Steel jacket 3.585

76.0

2611

0.9

300 Bridger Brass FN 3.604

77.0

2627

0.8

300 Bridger Copper FN 3.606

77.0

2669

0.5

300 Bridger Walterhog 3.720

78.0

2717

0.138

Ejector marks Do not use

73.0

2417

1.0

350 Barnes original 3.610

89.0 IMR 4350

2836

0.8

260 Nosler Ballistic Tip 3.600

88.0

2704

0.9

300 Nosler Partition 3.565

88.0

2759

1.0

300 Sierra GameKing 3.600

88.0

2680

0.8

300 Bridger Brass FN 3.706

87.0

2634

0.5

300 Bridger Copper FN 3.610

88.0

2676

1.4

Ejector marks Do not use

89.0

2719

0.6

300 Bridger Walterhog 3.726

87.0

2629

1.0

300 Barnes XFB Can 3.593

87.0

2671

1.1

300 Hornady FMJ 3.598

84.0

2502

1.6

350 Barnes Original 3.610

90.0 H 4831SC

2580

0.9

300 Bridger Brass FN 3.710

90.0

2556

1.3

300 Bridger Copper FN 3.610

90.0

2508

0.7

300 Bridger Walterhog 3.730

90.0

2550

1.8

300 Barnes XFB Can 3.620

90.0

2578

1.6

300 Hornady FMJ 3.583

85.0

2380

1.5

350 Barnes Original

89.0

2454

1.0

 

92.0 Norma MRP

2742

1.0

300 Sierra GameKIng 3.600

93.0

2773

2.5

 

91.0

2667

2.5

300 Bridger Brass FN 3.600

91.0

2633

1.0

300 Bridger Copper FN 3.600

89.0

2595

0.6

300 Bridger Walterhog 3.720

90.0

2616

0.8

 

91.0

2641

0.4

 

88.0

2512

1.0

350 Barnes Original 3.600

89.0

2540

1.2

 

90.0

2563

1.5

 

 

 

 

 

 

(All loads were crimped when possible, on cannelure, groove, or between driving bands. The 350 grain Barnes was not crimped.)

 

 

Weatherby factory load, .375 Weatherby (Norma brass and primer):  Advertised velocity is 2800 fps in a 26 barrel, so the below 24 velocity supports the claim very well.

Unknown

Powder

(N-204?)      300 Nosler Partition       3.565        88.5                    2734             1.1

 

Factory .375 H&H ammo fired in this rifle before and after the conversion from .375 H&H to .375 Weatherby:

Remington (advertised 2530 fps):

Before:         300 Swift a-Frame         3.555       ????                   2473             1.0

After:                                                                                               2367             0.8

 

This is a practical trip saver ammunition interchangeability.

When the point of impact of the above .375 Weatherby  factory load is +3.0 at 100 yards, the POI of the above .375 H&H factory load is +1.3 at 100 yards, IN THIS RIFLE.

 

The  Leupold Scope and QRW mounts held up very well, with no loosening or change of POI throughout the testing. Again, these are the latest version, with the square recoil stop on the bottom of each ring. The 6x48 base screws were replaced with the stronger 8x40 screws and red Loctite applied when the rifle was converted to .375 Weatherby.

 

The above maximum useful loads are likely just below the SAAMI maximum average standard for the .375 Weatherby:   55,152 CUP or 63,861 PSI.

 

The loads shown with ejector marks may be over this pressure level. Beware of ambient temperature effects. Work up from 10% below the maximum trouble free loads shown. I suspect Norma 204 powder would also be excellent.

 

Handloaders have the choice of new Norma made Weatherby brass with proper headstamp readily available now. This brass is about 20 grains lighter, and has about 3 grains greater water capacity than my brass formed from Hornady basic. Using the Norma brass will lower pressures and velocities versus these loads in Hornady brass, so  0.5 to 1.0 grains more powder, depending on type powder, might be used in Norma brass. A comparison of brass is shown below, also including the Winchester WW-Super .375 H&H brass that has been fire formed to .375 Weatherby (beware the shorterWW brass):                

 

Norma              Hornady             WW-Super

2.860                2.850                  2.832          (case length in inches)

228.3                248.4                  248.7          (case weight in grains)

111.5                108.2                  108.4          (overflow water capacity)

 

Bullet length is a consideration with the monometals. Using a longer magazine of 3.750 would allow the long bullets to be seated out and still function through the magazine, rather than being only single loaded into the chamber. A .375 Weatherby with a longer box than the usual .375 H&H would be an advantage here.

 

Moly coating might also be considered for possible improvement of some loads.

 

Finally, here is a list of some bullet lengths measured from those I had on hand:

 

235 grain Speer SP:                                             1.043

235 grain Barnes X:                                             1.210

250 grain Swift A-Frame:                                    1.122

250 Barnes XFB:                                                  1.272

250 grain Sierra GameKing:                                 1.180

260 grain Nosler Ballistic Tip:                             1.384

260 grain Nosler Partition:                                   1.146

265 Groove MI, copper FN solid:                        1.345

270 grain Hornady SP:                                         1.274

270 grain Speer SPBT:                                        1.295

270 grain Barnes XFB Cannelured:                     1.345

270 grain Bridger brass FN solid:                        1.323

285 grain Speer Grand Slam:                               1.252

300 grain Hornady FMJ (steel jacket):                 1.247

300 grain Hornady RNSP:                                    1.174

300 grain Sierra GameKing:                                 1.387

300 grain Swift A-Frame:                                     1.297

300 grain Bridger brass FN solid:                         1.473

300 grain Bridger copper FN solid:                       1.386

300 grain Bridger Walterhog:                                1.520

300 grain Barnes XFB Cannelured:                       1.472

300 grain Nosler Partition:                                     1.337

300 grain Winchester FMJ (steel jacket):              1.335

300 grain Winchester Failsafe:                              1.455

300 grain Hornady BTSP:                                     1.418

350 grain Barnes Original RNSP, 0.049 jacket:  1.425