The B476s are supposed to deal with transonic flight well. When a bullet slows and drops to transonic (less the the speed of sound) levels it often becomes unstable. Some bullets due to shape/drag are more stable than others.
I plan to use the 170 LB for long range target shooting comps. I recently took second place among some very respectable shooters and rifles in exotic calibres using the Lapuas. This was a smallest group comp at 100, 200 and 300 yards. I need to see if they have the legs for 1000yds+. First stop is the range for some chronometer work and load testing.
The first thing to note from the above photo is the shadow cast by the roof. As the sun moved the shadow would cut across the sensors creating error readings. This was remedied by moving the whole Chrono further back into shadow completely.
Loads and Safety.
It must be noted that these loads are relevant to my rifle only. Everyone MUST work up their own loads. Not only will loads differ between rifles in accuracy terms but also in safety. You should work up loads in small increments taking particular care to inspect every fired case. Look for marks on the brass, bulging or cratered primers, anything unusual. Also it is important to feel the bolt lift. If it begins to stiffen then you know you have pressure issues. Never increase loads when pressure signs are noted. Any other rounds should be dismantled with a kinetic hammer and reused with a lower, accurate charge weight.
Load Testing 23/7/14 .308 Win
Rifle: Remington 700 SPS action and barrel, 26″ 1-12 twist, Manners T5 stock, Badger Ordanance pillar bedded mini chassis, Recrowned by SYSS.
Scope: Vortex Viper PST FFP 6-24.
Weather: 77F, 2.978Hg@115ft Sunny. Light 2-5mph wind from 4 ‘O clock.
Ammunition: Lapua .308 Brass, once fired and neck sized to Reddings 335 bushing. Deburred, chamfered, pockets cleaned. Lapua 170g LB B476 bullets seated at 2.833″ TR140 powder, CCI LR primers.
Crono set up 10ft from muzzle.
44.8g: 2604, 2583, 2576
44.9g: 2709, 2731, 2732
45g: 2783, error, error
45.2g: 2809, 2756, 2740
45.4g: error, error, 2624
Chrono repositioned as shadow cast by the roof began to cut across the sensors and cause errors.
Chrono set up 5ft from muzzle.
45.5g: 2688, 2704, 2699
45.6g: 2715, 2699, 2732
45.7g: 2724, 2787, 2745
45.8g: 2726, 2721, 2743
45.9g: 2766, 2760, 2726
46g: 2741, 2754, 2760
46.1g: 2777, 2731, 2751
46.2g: 2772, 2754, 2777
46.3g: 2754, 2755, 2754
46.4g: 2799, 2754, 2766
No pressure signs at all.
Based on the data I have decided to explore 46.3 grain loads. I will test some different bullet seating depths next time to see if accuracy can be improved. To be honest I’d be surprised if I could improve much upon accuracy. Some of these 3 shot groups were down to .347MOA which is phenomenal from a nearly standard Remington 700. 275xfps gives me around the same as the HPS sniper rounds. I know the military do a pretty thorough job of load testing and development so I decided to quit there before risking any over pressures. All together a very pleasing day of testing.