Heavy 300 winmag velocities

[TwoNiner]

I'm researching building a 300winmag custom rifle to shoot the heavier .308 rounds like the 215 bergers and 220gr SMKs. I like the idea of a 200gr+ bullet bucking the wind better than my current 120gr 6.5mm (creedmoor) bullets. I shoot out in the desert and the cross winds can get up there (15-25mph).

I'm curious what velocities I should expect for a moderately loaded hand load? I'm not looking for an extreme pressure barrel burner load...just an accurate load with a repeatable POI.

My hornady manual shows 208gr a-max will go 2800fps with a variety of powders at max load, 2500-2600 at moderate load, though the book doesn't say what length of barrel they were shooting the load out of. It also has 225gr bullets of unknown model going around 2750fps at max load, 2500fps at moderate loads...again no barrel length. This seems pretty slow as my 120gr 6.5mm is speeding along at 2900fps from the muzzle presently with factory ammo. Are the heavy .308 rounds more effective out of a more powerful, higher recoiling cartridge?

 

[CanPopper]

My accuracy long for the SMK 220gr uses 65.4 grains of RE22 powder. Compared to my accuracy load for the Hornady 180gr SST of 74.4 grain of RE22 powder, the 180 grain kicks harder due to the increased powder.

Velocity for the 220gr I Chronied at 2740 fps while the 180gr does 3080 fps. To look at wind bucking ability, you can punch in the BC for the 220 and corresponding velocity and compare to the BC for the 180 and corresponding velocity. In a program like Shooter, you can punch in the wind speed and angle and see the corresponding horizontal adjustments.

 

[TwoNiner]

CanPopper,

Thanks for the data. What length barrel are you shooting out of?

I'm using jbm's online calculator to build a spreadsheet of drop/10mph wind/energy for the 300winmag to compare with my 6.5 to see what benefits I'll be getting.

 

[TacticalMirage]

my savage with a 24" barrel, 208 a-maxes with 77.2 grains of h1000 is moving them 2764fps. That's with the chrono set at about 10 yards

 

[Pappasniper]

I run 208 AMAX load of 75 gr of H1000 in both RWS and Norma brass. Shooting out of a 26' Krieger. Running 2850fps 7 yards off chrono. Half inch load in that gun and a 5R.

 

[CanPopper]

I have a 26" Rock Creek M24 contour 5R barrel.

 

[TwoNiner]

Here's the spreadsheet I've been working up. I did 3 common 6.5mm loads and the 3 loads you guys posted:

It looks like I should be able to achieve about a 25% reduction in wind drift with the 208gr a-max load between 500 and 1000 yards, and extend the supersonic range from 1275 to 1475 yards.

I'm surprised to see the 220gr SMK @ 2725 fps has almost identical drift and drop as the 140gr a-max with 25gr less powder, and less recoil. I haven't shot a 300winmag before...how's the recoil with those big 26" barrels?

 

[mwroseberry]

Have you considered 7mm calibers? Higher BC for the grain weight over the 30s and you can push them much harder. 180 hybrid can easily be pushed to 3000fps out of a 7rem mag and has a .673bc with less recoil then a 300WM. Then you also have the calibers with more HP like the 7STW. I plan to run my 7rem mag until I start to erode the throat then punch it to 7STW so I get more rounds out of my barrel. JMO

Good luck,
Merritt

 

[TwoNiner]

Threw in a .338 lapua for fun!

 

[mwroseberry]

Here is the info on the 7mm

Trajectory
Input Data
Manufacturer: Berger Description: Target Hybrid
Caliber: 0.284 in Weight: 180.0 gr
Ballistic Coefficient: 0.345 G7 (ICAO)
Muzzle Velocity: 3000.0 ft/s Distance to Chronograph: 10.0 ft
Sight Height: 1.50 in Sight Offset: 0.00 in
Zero Height: 0.00 in Zero Offset: 0.00 in
Windage: 0.000 MOA Elevation: 0.000 MOA
Line Of Sight Angle: 0.0 deg Cant Angle: 0.0 deg
Wind Speed: 10.0 mph Wind Angle: 90.0 deg
Target Speed: 10.0 mph Target Angle: 90.0 deg
Target Height: 12.0 in
Temperature: 59.0 °F Pressure: 29.92 in Hg
Humidity: 0 % Altitude: 0.0 ft
Vital Zone Radius: 5.0 in
Std. Atmosphere at Altitude: No Pressure is Corrected: Yes
Zero at Max. Point Blank Range: No Target Relative Drops: Yes
Mark Sound Barrier Crossing: No Include Extra Rows: No
Column 1 Units: 1.00 in Column 2 Units: 1.00 in
Round Output to Whole Numbers: No
Output Data
Elevation: 3.329 MOA Windage: 0.000 MOA
Atmospheric Density: 0.07647 lb/ft³ Speed of Sound: 1116.4 ft/s
Maximum PBR: 376 yd Maximum PBR Zero: 318 yd
Range of Maximum Height: 174 yd Energy at Maximum PBR: 2490.0 ft•lbs
Sectional Density: 0.319 lb/in²
Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (in) (in) (in) (ft/s) (none) (ft•lbs) (s) (in) (in)

500 -41.0 -41.0 11.7 11.7 2339.5 2.095 2187.2 0.566 99.6 99.6

1000 -243.9 -243.9 53.8 53.8 1765.2 1.581 1245.2 1.304 229.5 229.5

1500 -736.9 -736.9 142.5 142.5 1267.7 1.135 642.2 2.307 406.0 406.0

1900 -1515.1 -1515.1 262.3 262.3 1019.8 0.913 415.6 3.388 596.2 596.2

Max of 1900 yards and it wins in every cat. over all the rounds you have in your table. Unless your stuck on the 30 I'd go 7 if I was you.

Good luck,
Merritt

 

[TwoNiner]

Merritt,

Not sure I understand what you're saying about the performance of your 7mm rem mag.

The speed of sound @ sea level is 1116ft/s but @ 1900 your 7mm 3000fps 180gr projectile is only going 1019 ft/s so its subsonic. JBM show the round goes subsonic at around 1650.

Interestingly that 7mm load of yours beats the wind deflection of the .338 load I show in the chart @ 1500y (163" of deflection with the 7mm and 182" with the .338). That's pretty impressive. How many rounds do you expect to get out of your barrel before it loses enough accuracy to warrant a replacement?