Should always sight in when you switch cartridges. That just seems like common sense to me. The only thing those two cartridges have in common is that they have 150 grain bullets. You're going to have different brass, bullet design, powder, powder charge, bullet seating depth and probably primer.

 

I'm shooting a Savage model 11 and I experienced a similar difference between those two exact rounds. I went with core lokts since they grouped right around MOA (or as well as I can shoot) and they cost less than the Whitetails at my local bimart.

 

The hornady Whitetail rounds will outshoot core locks in every rifle I've seen.

 

Yeah, yeah...I know...Core Lokt's are horrible. Tell that to my rifle that prefers them over Hornady Whitetails, Federal blue and red box, Federal Fusion's, and several other much more expensive rounds that I didn't even bother to pay attention too well enough to have committed them to memory. I spent hundreds of dollars and far too much time trying all kinds of ammo in my rifle this year. Some of the expensive stuff shot just fine but since I don't take 600 yard shots at animals quartering away from me I don't need a bullet that explodes on impact or does the dishes for me.

150 grain Core Lokt's just love to make clover leafs out of my rifle and neither the deer I shot this year or the one my buddy put down using 180 grain Federal Blue box knew what kind of bullet killed them. There's absolutely nothing wrong with the old school soft nosed bullets...as long as you know and work within the limits they were designed around.

 

Yes you should sight in every time you change anything, brand, bullet weight, bullet construction, lot number. Slight variations can have huge impacts on your point of impact.
Both my dad and brother shoot 180gr hand loads out of their 30-06. Same bullet, same brass, same primers but different powders, therefore different velocity. My dad's rounds group 3" higher out of my brothers gun and have much larger groups, than his normal load.

Sent from my SCH-I535 using Tapatalk

 

Case in point...............

I went to the Canby Gun Club last Saturday to shoot on their 100 yd range (general site in days) as I do every year to check things out prior to hunting season. Last season I fell after I had harvested my deer and thought I'd hit my scope so I was particularly interested in where I was on paper. I also took two boxes of Remington 180 gr. Core-Lokt with me just in case I needed to get back on paper.

The first box was about half gone and when I shot it I was all over the place never really getting a good grouping. I'd adjust the scope a little one way then back the other but could not get the darn thing to group. I really was about to go have it all checked out by my gunsmith because I thought I had a bigger problem. So, after I had shot up the first box I thought I'd put a few from the second box down range to see. First set of three grouped nicely right where they should have. I adjusted the scope a little to the left and the second set of three grouped up at slightly (1/4") right of center at 1" high, right where I wanted it to be.

So, I couldn't believe the difference in the way the two boxes shot between each other. The first box wasn't consistent at all and the second was right on the money each set.

Just some food for thought when shooting factory ammo..............

 

I doubt bullet BC or velocity differances can account for a 2" POI shift, but barrel harmonic differances.... yep.
particularly with thin, full floated barrels.

Short of it is..... whenever you make ANY load changes, you need to recheck your zero.

 

I doubt bullet BC or velocity differances can account for a 2" POI shift, but barrel harmonic differances.... yep.
particularly with thin, full floated barrels.

Would this be the reason that my Savage .308 won't group 180 grain ammo hardly at all? I've read lots of guys having similar issues. I tried 4 different types and it was crazy how wild some of the shots were. I even had a friend fire a few of a couple different types because some of the flyers were off the paper and I figured it had to be me. Nope. He was all over the place too. Switched back to 150 grain and all was right with the world. I decided confidence in bullet placement was far more important than the extra 30 grains even for elk hunting.

 

Different point of impact with different loads is more common than finding two that group together.

 

I have shot core lokts before with decent success in this rifle, but was getting a tighter group with the hornady wt's. Then I switched to the rem cl and had to readjust. Now that I went through that box of rems I gotta get another box, but I think the hornady's were still working better and I'll have to adjust again if I go with those.

 

If you're going to try multiple types of ammo there's no need to constantly be cranking your scope around. Always put the crosshairs on the bullseye and don't worry about point of impact. Focus on group size. Once you figure out which ammo you're going to hunt with then you can dial it in to wherever you want POI to be.

Are you shooting from a bench to ensure it's the ammo/rifle and not you?

 

Although barrels can respond positively, or negatively, to changes in bullet weight, unless the change is great, or twist rate marginal to stabilize the change, generally bullet weight has little to do with group size if velocity is adjusted to optimize barrel harmonics.
the problem with factory loads is..... you can't tweak velocity to optimize barrel harmonics.

All that you can do to optimize barrel harmonics is change the way the barrel vibrates. To do that, you make changes to the mass of the barrel, or how that mass vibrates. There are many ways to do that; sliding rubber donut weight (Limbsaver), adjustable recoil comps (Browning BOSS), and even an adj pressure pad mounted in the forestock (although I'm not a fan of this approach).

Regardless, a POI shift should be expected, and re-zeroing necessary.
Hunt'nFish

 

ALL different types of ammo will generate a different point of impact and the impact isn't just vertical. It can be horizontal as well. Your 1:10" twist barrel will handle 180 grain bullets just fine, but there may be a mental aspect to shooting this as well. If you anticipate greater recoil, you'll treat the trigger different. Unless you pull the trigger a lot, the shooter is usually the limiting factor. I also shoot the gun with about 5 to 10 warm-up shots and let the barrel cool down for about 5 minutes before running accuracy tests with a load. Once I settle on a load, then I zero my sights/scope for that load First shot will usually be higher with thinner barrels, cold-bore shot and freshly cleaned.

I shoot a lot of 308 (1,000+ rounds a year) and there is a huge POI difference between a 150 grain bullet cooking along at 2850FPS and a 168 grain bullet traveling at 2600FPS.

Also, when working up a load, in my guns, I found that the faster the bullet, the lower the impact. Take this example of a 178 grain load I worked up earlier this year. Notice on the top row of groups, the POI changed as velocity changed.


There are also high velocity and low velocity accuracy nodes that barrels like to shoot in when working up a load using the same bullet. I found that I had two really accurate loads with 125gr TNT's. One used 42.0 grains of IMR-4895 and then the groups opened up as I increased in .5 grain increments until I hit 45.0 grains of IMR-4895 where I found the second accuracy node.

Low node...


High node...


Minuscule difference in group size but huge difference in velocity. Unless you hand load, you just have to settle with what you get with off the shelf ammo. I also test groups in 10-shot groups, not 3. 5-shot groups are okay, but 10-shot groups will better represent where your POI will be with a given load. The adjust your scope for the center of that 10-shot group.

Tony.

 

Tony,

Thanks for that informative response. I don't think the variations in grouping I experienced were based entirely on shooter error though that may have played a bigger role than I've been accounting for. Other shooters on my gun experienced similar groups. Also, I did do a bit of bench rest shooting to remove that variable and still experienced some pretty wild groups with 180 grain ammo. It sounds like maybe I shouldn't give up on looking for a 180 grain round that shoots well out of my gun though. Maybe by next season I'll be set up for reloading and can start playing with different load configurations myself.

Thanks again for the advice!

 

Tony,

Thanks for that informative response.

Split the difference, try some 165's. My '06 shoots 180's ok, but loves 165's. Couldn't tell you about factory rounds, last one's I shot were about 15 years ago, and that was just to do basic barrel break in on my 35 Whelen. Once I had empties, to the loading bench I went.

 

Before you shoot the 180's, check the twist rate of your barrel. I have no idea the different rates the major manufacturers have produced over the years but it may be worth checking your individual rifle. There's a chance that model of rifle was never intended to shoot 180's and possibly the twist is slower than the 1 in 10 it should have.

Anyone who experiences poor accuracy with the heavy for cartridge bullets, should take the time to do this.

 

Interesting & informative direction this thread has gone. I ended up picking up another box of hornady whitetails (they were out of blacktails) and am headed to the range. Also wondering if anyone has had noticeable differences between the whitetail interlocks and superformance sst. I'm not sure I need the extra fps (+$10) in the sst's for brushy cascade blacktail hunting...

 

my experience last night with these two exact rounds chambered in 25-06 resulted in just under an inch difference in elevation at 100 yards. the SST were shooting half inch groups .5 inches over center, the AW were hitting 1.5 over center, even though hornady's ballistics chart shows their trajectory's to be nearly identical out to 500 yards.

rifle was a savage TH II with a free floating barrel. not sure how much that has to do with it but the difference in groups was very noticeable and the SST's were certainly tighter.