Any Ideas or explaination for......

[WDSWIFT]

Not long ago I had loaded up 2 different 150gr loads for my '06. All componets were the same except one was "brand A" bullet and the other was "brand B" bullet. brand B had to be seated slightly deeper to stay off the lands. Both were pointed and boattailed.
To my satisfaction both shot in the same group at 100 yds. No clear winner, and no need to adjust the scope. Approximately .6-.7" groups. Both bullets are approx. 3100fps at 15' from the muzzle.

Here is the problem, when I went to check them for groups at 200 yds, brand A shot about a 5-6"(five to 6 inch) group and brand B shot a cute little group of under 2 inches. No wind, same rifle, same target,same ruler, and the same nut on the trigger (me). Any Ideas? WD

 

[Nodak Hunter]

How many groups have you shot? I don't put much faith in one three or five shot group. I prefer to shoot either four three shot groups, and average them to get an idea of a load's accuracy, or I'll shoot one ten shot group, allowing proper barrel cooling between shots.

I have found that a 10 shot group is about 40% larger, on average, than the average of four three shot groups. The largest three shot group is usually pretty close to the size of the ten shot group.

That's how I do it anyway. I don't think you have a large enough data base with one small group to learn about the load's real accuracy. Oftentimes, I'll shoot a 1.5" three shot group on one morning, and the same load an hour later may net 1", and an that afternoon I may get a 5/8" group with it. The next morning, I get a 3/4" group. That averages .97". If I had happened to go off of the first group, I'd have a different view of the load than a four group average.

It's almost a guarantee that if I do my 10 shot method with this load, the group size will be about 1.4" or so.

So, if I say I have a rifle/load combo that shots 1.2 moa, that's for ten shots, not three or five. I think guys oftentimes start talking about how accurate their loads are from the BEST group it's fired. We tend to remember our best groups, or make excuses for the not so good (well, four out of five shots were 1/2", and the fifth made it 1.2", must've been my fault). Raw data can't lie, but we emotional humans tend to twist it a bit for our own purposes.

So, to finally answer your question, shoot three more groups with each load to see what's REALLY going on.

 

[WDSWIFT]

Ndak, Good to hear from ya first of all, and thanks for the response.
I have shot three 4 shot groups with these two afore mentioned loads and got about the same results out of them.
I put a lot of emphasis on the placement of the 1st shot from a cold barrel. And although the 3 after it are very important to me, I feel if the first one goes where I want it, then I may not need the other 3.
With brand A at 200 yds first shot accuracy was not consistant either. Brand B on the other hand had acceptable first shot placement accuracy. What I'm wondering is why such good accuracy at 100yds and yet marginal at 200yds out of brand A. WD

 

[Nodak Hunter]

Bullet stabilization has many different factors affecting it. Obviously length of the bullet vs. twist rate, but others are also involved, such as concentricty of form, fore and aft point center of mass, bearing surface length of bullet, etc.

When a bullet is spinning in it's flight, the point isn't pointing directly at the target, spinning perfectly on a non changing axis. Rather, the point of the bullet is slightly wobbling (yawing). As the distance increases, the effect of yaw on the bullets path becomes more pronounced.

I would suspect that brand B has less yaw to it's rotation than brand A. It's not enough to be noticed at 100 yards, but will be at two hundred. I would suspect that you would notice it even more at three hundred.

Of course, were these same bullets to be fired out of a different barrel, or at different velocities, the results might be reversed.

 

[danr55]

Wayne, I think you answered your own question in the first post. You said that brand B was set deeper to stay off the lands. That would indicate that B was slightly longer therefore, has a higher BC and is a more stable projectile. I would be willing to bet that the farther you get out, the worse A will do.

You might try pumping up your load for A a little bit. If you can get a little more velocity, you may be able to get more stability. Often shorter bullets shoot better with higher velocities and longer bullets will stablize at a lower velocity. That's not a rule, just something I've picked up from doing it.

 

[WDSWIFT]

Danr According to my Point blank software; Brand A has a b/c of .435 and brand B has a b/c of .449 and a slightly fatter olgive than brand a, thus when I chambered a "dead round" to set up my bullet seating die off of this is the way they came out.

Brand A bullet IS longer than brand B.

This will make Shakey happy to read, if I take these bullets any faster I'll have to go to a 300 Win mag with the bullets as my load in the '06 is just about as far as I want to safely take it.

WD

 

[Nodak Hunter]

One last truly technical thing to consider -

Maybe your rifle just doesn't like to shoot Brand A.

 

[danr55]

Wayne, Something doesn't compute. If brand A is longer, has a larger ogive radius, it should have a higher BC. Measure the two with calipers. The bullet that is longer from front to back will have a longer axis of rotation. That should be the more difficult bullet to stabilize.

The longer bullet will be more stabile over extended ranges, but will be more difficult to stabilze initially. Once it is stabile, it should resist deviation better than the shorter bullet.

 

[WDSWIFT]

One important piece of information that I should have put on this in the first place is that the barrel is a 1-10" twist, and is floated, with the action bedded in a wood stock, and I've duplicated the phenomena with 2 different scopes. Sorry about forgetting that. WD

 

[WDSWIFT]

Well, now my Ole Buddy MLM has duplicated this phenomena out of 2 of HIS '06's. Same brands of bullets, very similar results. We're going to check some of the SST's against Brand B later this week.
I'm going to do another type of check and if I get the same or similar results, I'll just send the data to the Mfg. of Bullet A and see what they gotta say. WD

 

[danr55]

It's possible that you have a defective lot of bullets. Highly unlikely, but possible. I would tend to believe that you just haven't found the sweet spot for the longer bullet to stablize. Vary the load a couple of tenths of a grain and see if that changes the results any.

 

[MLM]

First of all , thanks WD and DanR and Nodak. I have been shooting from a differeent batch and using different powders than WD. I shoot 5 shot groups and let them cool between shots! I even have been using two different 06's. I have been getting the same results as WD. I personal belive the problem is the brand of bullet in the 150 grain weight. I had the same problem with a 300 WM I was setting up for a hunt. As all good reloaders I tried the 150 , 160 and 180 in the 300. I had the same thing happen with the 150 grain bullets WD is talking about. I finally went to the 165 for Mule Deer and 180 for Elk. I was looking for the 150 to work for the long range Muley that bed in the middle of the day. But is was not to be! I had tried different powder load and every thing I can think of. I am now having a lucid moment, I think I will give up on the 150 grain bullets in this brand for shooting in the .308 cal, rifles. The only one I did have luck with was a Bolt action 308 that did well with this bullet. Oh well, time goes on and we try to learn why certain things happen and Dad did not have that much moeny to keep sending me to school for all I need to know!