300 WSM 152/137/124 Load development

[bjornf16]

From December 2021:

Staycation time, so plenty of trips to my local range.

Sako 85 300 WSM 11" twist
IMR 4166
Norma 300 WSM brass
CCI 250 LRM primers

Captured velocity with both LabRadar and Magnetospeed. They were within 1% up to 3300 FPS, then the Magnetospeed was registering significantly less velocity than the LabRadar. Not sure what is causing the anomaly. External battery pack on the LabRadar. Muzzle brake in middle of Magnetospeed "blast area". LabRadar was registering what I would consider "normal" increase with the powder increment; the MagnetoSpeed seemed to stumble after 3300 FPS.

Anyone else run across this issue with MagnetoSpeed?

Had rain early in the morning, so humidity was high. Temps in mid 40's.

152 HH was up first:
COAL 2.855"

H4166	Velocity	Comment
57	3000
57	3008
58	3034
59	3119
60	3170
61	3238
61.5	3264
62	3271	No pressure signs

Without any pressure signs, looks like I have room to go.

 

[bjornf16]

137 Hammer Hunters up next. (This is where I start seeing discrepancies between LabRadar and MagnetoSpeed)

COAL: 2.850"

IMR 4166	Velocity (LabRadar)	Comment
59	3138
60	3206
61	3242
62	3320
63	3325
64	3400
65	3461	3398 MagnetoSpeed (M/S)
65.5	3478	3414 M/S
66	3501	3500 M/S
66.5	3550	3517 M/S; No pressure signs

No pressure signs above. Room for more powder...

 

[bjornf16]

124 Hammer Hunters.

COAL: 2.796"

IMR 4166	Velocity (LabRadar)	Comment
62	3383
63	3401
64	3447
65	3511
66	3594	3542 M/S
67	3678	3606 M/S
68	3722	3650 M/S; Hot barrel, sticky bolt, light ejector smear
68.5	3726	3663 M/S; Cold barrel, no pressure signs
69	3755 (estimated)	3692 M/S; no pressure signs

Looks like there is still more room for this combo.

I underestimated pressure points for each of these bullets.

Sending off the rifle for a new MPI Custom carbon fiber stock (this OEM plastic stock is sticky all over). Once the rifle returns, I'm sending it out to cut the 24.4" barrel down to 22.4" (yes, the advertised length was incorrect). Then out for cerakote. So may be a while before I pick this up again...

 

[bjornf16]

From February 2023:

Looks like an improved 137 HH has been released since my initial testing.

For African plains critters, is there a consensus on which bullet performs the best?

 

[bjornf16]

joe16 said:
The new one. The old one killed fine, the new one kills a tad bit more efficiently.

 

[bjornf16]

ButterBean said:
bjornf16 said:
Ok...between the 137 and 124, which bullet?

For what you are wanting to do the 137

 

[littlebighorn]

Please report your settled upon load, bjornf16! I'm still playing with my own 300WSM.
Thanks

 

[bjornf16]

Range update today with the new 137 HH:

Loaded 66.2 grains of IMR 4166, 1/4 turn crimp with Lee FCD

6 shots; only 2 registered on Labradar: 3567, 3620 fps. All had stick bolt lift.

Think I'll back down to 65.5 grains and try again.

Edit: Temp 70° F today, compared to 40° F original test.