155 grain "Palma" Match .308

Bead,

Jeff is on the right track. I ran some of the numbers on Sierra's ballistics software. Even though I'm not a real competition shooter, I couldn't pass it up when I saw it in action at the '04 SHOT show. I set the velocities equal so you could see the entire picture.

Sierra 155 gr. HPBT Palma Match
Velocity: 2500 Ft./sec. (very low for this weight)
Drop @ 1000 yds. (inches): -512"
Energy (ft/lbs.): 433 ft./lbs.

Sierra 175 gr. HPBT
Velocity: 2500 Ft./sec. (very good for this weight)
Drop @ 1000 yds. (inches): -471"
Energy (ft./lbs.): 577 ft./lbs.

All it takes is another 100 ft./sec. on the 155 gr. Palma Match to get the drop even with the 175 gr. (-471"), but the energy remains lower. When the drop is equal, the 175 gr. still hits with 110 ft./lbs. more energy. Using the numbers as a guide, my opinion is the heavier bullet is used in a sniping role because it hits harder and resists wind drift better. I'm not a sniper, but hopefully that's more than an educated guess.

I'm glad someone brought this up, because it brings up some interesting points.

Lets look at the raw data for the three (3) federal .308 match loadings. And then I'll try to explain why the palma is not used

Here are the three loads
168gr at 2600fps
175gr at 2600fps
155gr at 2950fps

At 1000 yards the total drop and energy for the three loads are:
168gr 456" 537 ft-lbs
175gr 437" 609 ft-lbs
155gr 356" 604 ft-lbs

Um, I would have to say that for 1000 yard .308 shooting, the 155 palma load is clearly superior. Its drops 100 full inches less then the 168gr, and 81 inches less then the 175gr and the energy is nearly identical. Well, 350fps is a whole bunch faster at the get go, and is why it does so much better. The 155 gives up some in BC, but the extra velocity more then makes up for it. These numbers were computed using a copy of the free "Point Blank" ballistics/reloading software. Its not as good as sierra or others, but the numbers are close enough. (you'll see very similar results from other software, numbers maybe slightly different).

So, why is the 168 and 175 used? The sectional density is a little better on the heavier bullets (allows better penetration), but thats not something that clearly dictates bullet selection. The big reason is because humans are creatures of habit. The 168 was the first real match loaded cartridge to hit the market, and is now ingrained as the de-facto. The 175 has gained inroads because it is better then the 168, but mainly because the military adopted the m118LR with the 175 gr. This, coupled with most all BDC (bullet drop compensators) being set to the ballistics of the 168 make it very difficult for the 155 to make any progress.

I do plan to start doing some evaluations with the 155 and see just what its sniping potential may be. Stay tuned on the site.

MEL

I will not disagree with mel, but have one piece of information to add that changes the picture substantially. I was asking this same question not too long ago, when I was testing the 155 Lapua Scenar (BC of .508), which is considerably lighter than the 175 SMK, but has a higher BC than that bullet. (when you hold one in your hand you know it flies like crazy sharp sleek nose, very little curve to the ogive.)

What the box of 155 SMK Federal Gold Medal ammo does not tell you is that the 2950 fps muzzle velocity is based upon use in a 30 inch barrel. The 2,600 fps for the 175 and 168 is based upon a 24 inch barel. If you want an accurate comparrison between the two you need to compare the 155 at approximately 2,825 fps (at least according to my QuickLoad software). At 2,825 fps, the 155 and the 175 are traveling at virtually the identical speed at 1,000 yards, but the 175 holds much tighter (nearly 20% less drift over 600 yards) into the same amount of wind.

Don't get me wrong, my 155 Lapuas eat the 175SMKs for lunch when I shoot the Lapus at any velocity above 2,800 fps and nearly any range up to and potentially beyond 1,000 yards. But then again my Lapua 155 Lapuas also kick butt on the 155 SMK at every yard line that I've ever shot them (the Lapua BC is nearly 20% higher).

It is worth noting, that in the Gun Buyer's annual #30 (the latest one) the Federal Palma load is run out of a 24 inch barreled Howa custom, and measured 2903 f.p.s. over a PACT Chronograph.

Upping the barrel length to 26 inches, as on the Remington 700P, should improve velocity a little bit, bringing the speed of the round very close to Federal's published figures out of a 30 inch barrel.

Palma shooters routinely use barrels even longer than 30 inches, and it is doubtful they are gaining much extra speed for the extra few inches, as the .308 loaded in any configuration is done burning powder long before the 26 inch mark.

At the risk of offending someone, which I apologize if I do, I submit that a 26 inch barreled rifle will produce speeds very close to Federal's figures, close enough to ignore the importance of the 30 inch barrel, thus giving plenty of reason to compare the 175 and 155 grain rounds.

I would very much like to see such a comparison done, if only to satisfy curiosity.