Sighting-In Handloads Question


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BBDartCA
September 17, 2011, 06:14 PM
If two bullets are of the same weight, and similar shape, and all of the other variables are the same, should the groupings be that different between the two? Here is what I have going on.

Have decided this year to hunt all big game with the same load. 180g Nosler Partition # 16331 with 56.2g IMR 4831 with WLRM primers.

Since Nosler bullets are anything but cheap, I've done most of my work up and practice with Hornady 180g #3070. Same powder load and primer type as above. I got a big box of these Honady's dirt cheap a while back. Both Nosler's and Hornadys loaded with mixed fired brass from my gun, all neck resized. When seating the bullets, I've done my best to have the same amount of bullet in the case to try to keep case pressures similar between the two. The resultant COLs between the two are very close.

So today I went to the range and shot about 50 rounds. Started with the Hornady's and after 35 rounds or so had things dialed in nicely. Got down to a 1.25" group at 100 yards which for me is good. Gun is a Remington 760 pump with Sightron 2-7x40 scope.

So I then loaded up the Noslers. Did not have the benefit of a spotting scope. Went and picked up my target and found the groups to be just as tight as with the Noslers, but they were grouping about 2" up and 2" over from where the Hornady's group.

So is this normal with bullets of the same wight to give such different performance? Bad part is I have no time left to go back to the range to reset my scope for the Noslers before my hunt next week. And I'm pretty much out of the Hornadys. Good news is on the way home I went to a gun show and found 2 unopened 50 count boxes of 180g Partitions for $10!


The Nosler, BC 0.474, SD 0.271
http://images.wholesalehunter.com/prodpics/noslpic16331.jpg

The Hornady, BC 0.425, SD 0.271
http://www.hermes.sk/sub/hermes.sk/components/com_virtuemart/shop_image/product/d3a14f7782b439a908fe2cb2caa24129.jpg

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Horsemany
September 17, 2011, 06:30 PM
Yes it's normal for them to shoot to a different point of impact. Just take a few Partitions to the range a week before season to fine tune your scope. A couple of inches should be pretty simple to adjust.

kingmt
September 18, 2011, 12:05 AM
just as tight as with the Noslers, but they were grouping about 2" up and 2" over from where the Hornady's group
Where did they group though? Is the group 2" high of POA left or right? Most scopes are 1/4" per click so 8 clicks on each nob gets you there.

snuffy
September 18, 2011, 12:10 AM
What caliber, I assume it's a 30-06 from the bullet weight, charge, and the rifle.

As for the difference in the two groups, That's entirely normal, in fact predictable.

The same thing applies to factory ammo. If you buy a box of, lets say, winchester 180 power points. You use all up, getting where you want to be for sight in on a target. You return to the store only to find they have sold out. So you buy a box of 180 Remington core-lockt thinking same bullet weight, same sight in. You miss the biggest buck you've ever seen opening day. It was a long shot, but your aim was sure. You check your sight in after that to find you were off by nearly a foot at that long range. The sight in was off by 3 inches at 100 yards.

2 things were the same with your 2 bullets. The weight, and the fact that they're both lead core bullets. The construction is very different. The Hornady is a simple cup & core bullet, with a so called interlock. The partition has 2 cores separated by a solid web of copper jacket, a much "harder" bullet. Enough difference to affect group placement on the target.

It WAS a good plan, BUT you didn't allow enough time to make the switch from one bullet type to another.

Tim the student
September 18, 2011, 01:21 AM
Yup, normal, IME.

gamestalker
September 18, 2011, 03:39 AM
First off, I"m surprised you aren't having any problems with necked brass for a pump. But if it works reliably for you, then don't fix what not broken.
But now to your question. I saw some strange results not long ago with two bullets of same weight with the only real diference being one was a BTSP, and the other a Hot Core SP not BT, Both are Speer. I loaded both to identical specification, 70.0 grains of RL22. seated to .010" off the lands, and necked mixed head stamp brass, and both were fired from the same action, a 700 SPS 700 RM 24" barrel.
Relative physics and 30 + years of reloading experience has taught me that a BT will out perform the square heel bullet. I test fired a box of each and recorded the velocities and other pertinent details and was surprised to find that the square heeled Hot Core had a consistent gain of 150 fps compared to the BT, someting I found to be odd. Even though 150 fps may not seem like much variance, but when considering how much thinner one jacket or how much softer a lead core may be in comparison, the reality of those elements effect on performance factors becomes seriously evident when printing them at 100, 200, and 300 yards and beyond. The BT which was the one that lacked performance in comparison had a thinner jacket and it's core was considerably softer.
I think what your experiencing is very simular in effect, in that, the two bullets your working with have very different construction properties, with one producing more efficient use of the gases. Elevation variances at relatively close range being 100 yds - 200 yds. can be fairly easily explained but the general size of the groups makes it far more interesting and involves a level of study that probably goes a bit deeper than most of us average reloader's can easily undertand. So the best thing to do and what I rely on is just a couple of straight forward look at the details, and then loading the bullet that is prodiucing our facorable or desired results.
Keeping a tracking sheet to record how each bullets performs is more important than many may think.

FROGO207
September 18, 2011, 06:07 AM
Well you know that the pattern is tight so when you arrive at the hunt there should be an opportunity to check the scope zero. Just dial it in there and you are good to go. You know where it is hitting so in the scope info it should tell you how many clicks to move the aim to get it close.10-15 shots at max and off to hunt.:D This is what I would do.
Call it a learning curve.:o

BBDartCA
September 18, 2011, 01:17 PM
Thanks guys. I'll either head out on the 1st hunt (wild boar) with the Hornady's if I can scrounge up some or call in sick to work to site-in with the Nosler.

Zero problems cycling ammo in my 760 with Lee collet neck sizing. The only time I have had feeding troubles in any of my 760's is when I shot a friend's reloads (full length sized), and when I full length sized some virgin Winchester brass.

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