Ammo Comparison

[Art Eatman]

Somebody asked me about the comparative accuracy of a couple of loads I tried out at 500 yards. So, I figured I'd check out several. Trekking from the front door to the corner of the porch where the benchrest lives, I tried out "Ol' Pet" with five loads. All groups were three shots.

1970 Weatherby Mark V, 26" barrel, .30-'06, with Canjar 2# trigger. Simmons 44 Mag 3X10 on Weaver mounts.

Handload, 165 Sierra HPBT 9/16" group 4" Hi, 0 wind.
Handload, 180 Sierra SPBT 5/8" group 1/2" Hi, 1" Rt.
Handload, 150 Sierra SPBT 1-1/4" group 0 Hi, 1-1/2" Rt.
Federal, 150 SP 7/16" group 0 Hi, 2" Rt
Hansen, 150 GI 1-1/8" group 3/4" Lo, 1-1/4" Rt.

I've no idea why the 150-grain handloads did so poorly. The group was a horizontal dispersion, which usually means canting. I tried a fourth shot, out of curiosity, but it didn't prove anything. I have gotten 1/2" to 3/4" groups with this load. I have also gotten just under 1" with the Hansen, in the past.

The dispersions of the group-centers from the aiming point certainly shows why a change of ammo requires re-zeroing of a rifle.

FWIW, Art

 

[Schmit]

Art,

I agree that a change of ammo(maker, bullet wt, bullet configureation, velosity) requires a change of zero.

But are you talking change of ammo or different lot #s of the same ammo and combining two threads? If we really want to get tecnical one could say that any change (lot #, maker, bullet weight, bullet configuration, humidity, tempature, altitude, etc, etc, ad nausium) could required a change of zero could it not?

 

[Art Eatman]

I was just thinking about the wider variety of stuff I shot today--and primarily the difference between the 165-grain and 150/180-grain handloads. I've seen guys assume "ammo is ammo", and if it's sighted in for one, it will be okay to substitute some other ammo at hunt camp. A four-inch difference at 100 yards is a bunch.

This also shows why I had to readjust the scope at 500 yards, when I went from shooting the 165-grain loads to the 180-grain.

Digressing to the 500-yard shooting: I'm still intrigued by the relative damage to the 1" thick steel plate. A GI-type load from a 20" .308 merely left a splash of lead. My 150-grain handload made a slight dimple; the 165-grain, a bit deeper--maybe 1/8". However, the 180 made a small "moon crater", with splashback of metal. 3/16" or so deep, 1/2" diameter. Significantly more damage. I'm guessing the 180 would definitely be more effective as a hunting load.

FWIW, Art

 

[Schmit]

> I've seen guys assume "ammo is ammo", and if it's sighted in for one, it will be okay to substitute some other ammo at hunt camp.

Hehehe... I know the type. They are the ones that usually end up not getting any game... or worse... hitting it and losing it.

I know one guy that hunted with s S&S shotgun. Used what ever ammo was on sale and never patterned it. Lord knows how many deer he wounded and couldn't retreive.

Maybe it was just my Marine Corps up-bringing but I check zero whenever ammo is changed. Hey, it only takes a couple rounds and a moment or so just to be sure.

 

[Dave R]

I would've expected the 180gr to hit harder at 500yds, but the difference sounds like more than I would've expected for a 10% increase in weight. I wonder if the bullet construction of the 180 made a difference in how hard it hit?

As I said before, my Rem 700 in .308 shoots tighter groups with all 180gr loads I have tried than with all 150gr loads I have tried. I once got one group of 150s that was as tight as most of my groups of 180s. I guess its just my weird rifle.

 

[Art Eatman]

After due reflection, experience and reading various articles about bullets--and from posts here at TFL, I'm coming to the conclusion that the 150- and 165-grain Sierra boat-tails are a tad on the "fragile" side. Maybe the 180-grain, being longer, has a bit thicker jacket toward the rear and holds together better. Just a guess; I don't know. I imagine I could ask the Sierra folks...

If a longer bullet stabilizes better than a shorter bullet, it could be that the twist is on the fast side of "usual". You'd have to do the cleaning-rod test to find out. The other thing is barrel vibrations--and if the barrel is free-floated, the harmonics might favor one load over another, regardless of bullet weight. You might try a very thin shim (about a five-pound pull to make room to slide in a piece of non-hygroscopic material) and see what happens.

Quien sabe?

Art