How fast is fast?

[North Star]

I started loading 155 grain Scenars for target rifle shooting about 2 years ago and the results were decent. I bought 1000 Lapua .308 Palma cases to work with, so I am currently working with these unfired, but full length resized cases. My current muzzle velocity is around 2950 fps using a 30" Shilen target barrel, but is this fast enough? Are people finding better accuracy by driving these bullets a lot harder? By the way, I am using N140 powder.

[RobB]

For comparison (and every rifle is different and can handle different pressures etc.), I push 155.5 Bergers out my 31" barrel at 3100fps. Same cases as yours with small primers.
However, I found the best accuracy at 300yrds (using the Bisley electronic targets for load development) when I dropped 2.7 grains of RS52 (sorry, didn't have chrono on with reduced powder). Probably more to do with the harmonics of the barrel rather than speed.


Sent from my boing using "An application"

[WelshShooter]

3000fps with 155gr and a 30" barrel sounds in the right ballpark. Let's see what Laurie says on the matter as he is well experienced in this area.

[Laurie]

The ballistic norm for formal L-R prone shooting with the 308 for a generation has been a 'reasonable BC' bullet (ie the Radway Green 155gn FMJBT or original 155gn Sierra MK #2155) at around 2,950 fps MV. That just stays supersonic at 1,000 yards in most conditions. That's still what today's NRA procured ammunition is geared to offering from a 30-inch 'tight' barrel in good condition.

Since the Imperial, some other major national, and all major international prone 'sling' competitions see organiser issued ammunition to this standard, or a bit (50-75 fps) faster in some cases such as when the 4-yearly Palma matches are hosted by the USA, everybody competes on a level playing field.

Where handloaded / any bullet weight ammo is allowed as in most countries' FTR and 'US Rules' TR / Palma / Fullbore, this ballistics combination isn't competitive and somewhat hotter and/or heavier bullet combinations are the norm. Top US FTR shooters have moved to the 200 and 215gn Berger Hybrids virtually across the board, and the 185gn Berger LRBT Juggernaut is probably the most used bullet at club level for mid and long-range matches these days in that nation. Most sling shooters find the heavier bullets' recoil and torque outweighs the ballistic benefits although a few use the Juggernaut. 175gn is normally the upper limit here.

155s are being pushed out these days at 3,150 fps plus! (Lapua Palma small primer brass plus Reload Swiss 'high-energy' / 'EI' infused deterrents technology propellants.) The Palma case seems nearly indestructible, and now that home annealing has become commonplace allowing neck / shoulder metallurgy to be managed, 20 plus loadings aren't unthinkable any more. (At the OP's loadings, 200 Palma cases and an annealer would likely see the barrel's life out! I'd suggest selling 600 or 700 of them off unless you're planning on 50 years of shooting.)

What a 'competitive' or 'suitable' loading is depends as always on the discipline, the distances being shot over, and the level of competition / aspirations to win silverware. Learning to read the wind well for TR and FTR gains more points than an extra 200 fps MV once the ballistic basics have been achieved. What level is that at? Traditionally, people were well satisfied if bullets stayed supersonic at the 1,000 yard target if that was their maximum distance. Today, the aim is to stay at least 100 fps above that and better still to stay out of the transonic zone, these three metrics being ~1,125 fps; 1,225 fps; and 1,350 fps. To get the 155gn Scenar in out of the box form (ie no pointing done to the tip) to achieve that, the requisite MVs are 2,750 fps, 2,900 fps, and 3,075 fps. It's no coincidence that the highest of these MVs is widely used in national level FTR with the 155.5gn Berger BT Fullbore.

These are theoretical terminal MVs based on average BCs (albeit the reasonably accurate G7 variety). There is some empirical evidence that long-nose tangent ogive or Hybrid types cope much better with transonic speeds than the sharper nose to body junction VLD form (which includes the Scenar) and 308 155gn VLDs at 2,900-3,000 fps MVs therefore lose more speed between 850 and 1,000 yards than say the Sierra MKs or 155.5gn Berger / 155gn Hybrid.

All this is academic if the OP only shoots out to 600 or even 800 yards, although reducing wind drift is another big ticket item on the ballistic wish list even to these distances, its importance again affected by discipline / levels of competition / ambition.

Finally, there is the little (??!!) matter of precision. I'd take a loading that shoots into 0.25-MOA at 2,950 fps MV over one that struggles to get below half-MOA while doing 3,100 fps. How well the bullet holds elevation at the longest distance competed over is crucial too. especially in FTR with its half-MOA dia. 'V' and 1-MOA 5-ring. If you look at the top FTR shooters' match plots for Bisley or Altcar where wind usually doesn't have any vertical components (unlike Diggle and even more so Blair Atholl), they're almost horizontal lines often in a quarter-MOA band. That's what I'd be looking for from any 155gn bullet combination - getting there might (stress on might) be helped by going faster if it's not good enough now. If it is good enough now, stay where you are, learn to read the wind, get lots of trigger time in, and be thankful that your barrel life will be excellent.

My own FTR loads see the 155.5gn Berger at 3,050 fps or 168gn Berger Hybrid at 2,990 fps MVs from a 32-inch barrel. (Or they did - MVs have dropped by ~25-30 fps after 3,000 rounds down it.) Both shoot under a third-MOA at 100 yards, remain above transonic speeds at 1,000, and hold tight verticals.

[North Star]

Thanks for that Laurie. I did forget to mention that I'm primarily interested in accuracy at 1000 yards! I do only shoot traditional target rifle (not too many of us left in Canada!), hence I'm restricted to 156 grain bullets.

[Pete]

47 grains of RS52 in a Palma case behind a 155 Scenar does it for me. Around 3050fps from a 30" 1:11 Bartlein.

Pete