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 375 H&H Groups
#4565993
09/13/13 11:57 PM
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Joined: Nov 2005
Posts: 5,422
DLALLDER
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I loaded up 3 different groups of ammo today, with everything being the same other than the bullet. Two of the groups were within a 1/2 inch of each other but the 3rd was 4+ inches high. The bullets were Nosler Partition, Hornady RN, and Sierra spitzer/BT. All were 300 grain. Would someone venture a guess as to why one bullet shoot 4+ inches higher than the other 2 loads. The only thing I can think of would be MV and if that is the case, which of the 3 is the fastest? The 2 that shot to the same point or the one that shot 4+ inches high?
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Re: 375 H&H Groups
[Re: DLALLDER]
#4566328
09/14/13 02:33 AM
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Joined: Dec 2008
Posts: 4,639
syncerus
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The sound / vibration harmonics are different with each load combination. The interaction of those harmonics with your rifle barrel / stock combination ultimately determines your point of impact. In this case, the harmonics of the first two loads appear similar and the third appears to be radically different.
NRA Patriot Benefactor & DSC Lifer
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Re: 375 H&H Groups
[Re: syncerus]
#4566629
09/14/13 04:56 AM
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Joined: Sep 2006
Posts: 33,133
kmon11
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junior
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Also the bearing surface of the bullet even though of the same weight can be enough different to increase pressure and cause a different point of impact. Have seen it more than once where the slower load actually hits higher than the faster loads, more time in the barrel so recoil has more time to affect the rise of the barrel during recoil.
lf the saying "Liar, Liar your pants on fire" were true
Mainstream news might be fun to watch
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Re: 375 H&H Groups
[Re: kmon11]
#4566998
09/14/13 02:19 PM
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Joined: Nov 2005
Posts: 5,422
DLALLDER
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Guys, Thanks for the responses. Kmon, I am thinking that the difference is due to bearing surfaces also. The Sierra spitzer/bt has the least bearing surface of the 3 and I would guess that it is the slowest of the 3, wish I had a chrono. Syncerus,Is it possible for 2 totally different shaped bullets to have similiar harmonics? Not questioning just asking? The 2 groups that shot together were the Hornady RN & the Nosler Partition. The Sierra spitzer is the one that shoots 4" high plus the 2 that shot together have flat bases (no boat tale).
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Re: 375 H&H Groups
[Re: DLALLDER]
#4567098
09/14/13 02:56 PM
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Joined: Nov 2007
Posts: 10,072
RiverRider
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The Partition and the Hornady RN could produce similar resistance in the bore. The RN would have a lot more bearing surface than spitzer-shaped bullets, and that will raise pressure. The way the Partition is constructed can have the same effect because it resists conformation to the bore diameter kind of like a monolithic bullet.
It would be interesting to see these loads chronographed.
![[Linked Image]](https://i.imgur.com/T84Bps5.jpg) "Arguing with you always makes me thirsty." -Augustus McRae
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Re: 375 H&H Groups
[Re: DLALLDER]
#4567232
09/14/13 03:55 PM
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Joined: Dec 2008
Posts: 4,639
syncerus
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Syncerus,Is it possible for 2 totally different shaped bullets to have similiar harmonics? Well, that's one of the mysteries of shooting. I've simply changed powders and had radical changes in point of impact. To my mind that's a change that is reasonably explained by the harmonics theory. The problem is that there are so many variables involved and that your point of impact is the net sum of all those variables. At the end of the day, the only practical solution is to load a few rounds, go shooting, and see what happens.
NRA Patriot Benefactor & DSC Lifer
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Re: 375 H&H Groups
[Re: syncerus]
#4567805
09/14/13 08:25 PM
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Joined: Nov 2007
Posts: 10,072
RiverRider
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I haven't looked real closely at what QuickLOAD will reveal on this, but I am willing to bet that you could duplicate velocity with two different powders with the same bullet and yet see different barrel times. This would bring barrel harmonics into the picture in a big way and result in different points of impact and different accuracy results. Fascinating, isn't it!
"Arguing with you always makes me thirsty." -Augustus McRae
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Re: 375 H&H Groups
[Re: RiverRider]
#4567845
09/14/13 08:37 PM
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Joined: Jan 2009
Posts: 1,590
cory_cooper
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copper is lighter than lead, there is more copper in a Partition due to the partition being made of copper so the 300gr bullet still weighs 300 grs but is longer and has more bearing surface than a similarly shaped traditional cup and core bullet. As kmon said this will lead to a change in barrel harmonics thus the change in the poi. That would be my best guess anyway.
Last edited by cory_cooper; 09/14/13 08:37 PM.
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Re: 375 H&H Groups
[Re: cory_cooper]
#4567853
09/14/13 08:40 PM
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Joined: Jan 2009
Posts: 1,590
cory_cooper
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another thing to consider would be the differences in jacket material, this could lead to some variation in the poi
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Re: 375 H&H Groups
[Re: cory_cooper]
#4569003
09/15/13 03:56 AM
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Joined: Dec 2009
Posts: 1,599
ckat
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...there is more copper in a Partition due to the partition being made of copper...  
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Re: 375 H&H Groups
[Re: ckat]
#4569066
09/15/13 04:37 AM
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Joined: Dec 2012
Posts: 2,271
LuckyHunter
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I'm amazed you're shooting groups within a 0.50 inch of each other with a .375
Last edited by SheepHunter; 09/15/13 04:39 AM.
Lucky 7 Exotic Ranch located in Eden, Tx. Well managed self sustaining herds roaming our 3,000 acre ranch. First Class Lodging, Ranch style meals and qualified guides. 30+ species.
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Re: 375 H&H Groups
[Re: ckat]
#4570867
09/16/13 12:38 AM
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Joined: Jan 2009
Posts: 1,590
cory_cooper
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...there is more copper in a Partition due to the partition being made of copper... you should look at the cross section of the bullet. It is called a partition because the two lead cores are "partitioned", this causes the bullet to have more copper in it than a cup and core bullet of the same weight. just for future reference the molecular weight of lead is 207.2 g/mol, while copper is 63.546 g/mol. Now that would lead me to believe that lead is nearly 4 times as dense as copper, so if two bullets have the same weight and diameter but have different overall densities which would you think would be longer, if you guessed the least dense you would be correct.
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Re: 375 H&H Groups
[Re: LuckyHunter]
#4572163
09/16/13 02:21 PM
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Joined: Dec 2008
Posts: 4,639
syncerus
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I'm amazed you're shooting groups within a 0.50 inch of each other with a .375 You'd be surprised how accurate the large bore rifles can be. The limiting factor is almost always the optics, as eye relief is king, for obvious reasons.
NRA Patriot Benefactor & DSC Lifer
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Re: 375 H&H Groups
[Re: syncerus]
#4572303
09/16/13 03:21 PM
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Joined: Sep 2009
Posts: 19,325
ChadTRG42
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It is due to the barrel harmonics between each bullet. This is why I recommend shooters confirm their zero again when they change up anything on their ammo, especially changing bullets.
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Re: 375 H&H Groups
[Re: ChadTRG42]
#4572372
09/16/13 03:47 PM
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Joined: Nov 2005
Posts: 5,422
DLALLDER
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Okay I did some East Texas research and came up with these numbers, just measured 1 bullet of each and used my eyeball & micrometer as a guess where rifling would engage bullet.
Sierra Spitzer---1.378 OAL
.605 Bearing surface
Nosler Partition--1.340 OAL
.875 Bearing surface
Hornady RN--------1.173 OAL
.710 Bearing surface
Partition & RN are flat base bullets---Sierra is a boat tail
I sure if someone wanted the exact measurments, a visit to the web sites would give a truer picture.
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Re: 375 H&H Groups
[Re: DLALLDER]
#4572415
09/16/13 04:03 PM
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Joined: Oct 2004
Posts: 40,619
redchevy
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All I know is some are different and some are the same.
I have 6 different loadings for my 270 win rem 700 sendero that will group into a raged hole about the size of a nickel or quarter that range from a 90 grain hollow point travelling around 3300 fps to a 150 grain nosler partitions around 2600 fps all with the same point of aim and impact at 100 yards.
Last edited by redchevy; 09/16/13 04:03 PM.
It's hell eatin em live
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Re: 375 H&H Groups
[Re: cory_cooper]
#4573313
09/16/13 08:55 PM
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Joined: Dec 2009
Posts: 1,599
ckat
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...there is more copper in a Partition due to the partition being made of copper... you should look at the cross section of the bullet. It is called a partition because the two lead cores are "partitioned", this causes the bullet to have more copper in it than a cup and core bullet of the same weight. just for future reference the molecular weight of lead is 207.2 g/mol, while copper is 63.546 g/mol. Now that would lead me to believe that lead is nearly 4 times as dense as copper, so if two bullets have the same weight and diameter but have different overall densities which would you think would be longer, if you guessed the least dense you would be correct. I know - I was just giving you a hard time... Reading the excerpt from your quote (liberal news media style - out of context) makes it sound funny. Just lightening the mood.  Your statistics and explanation are impressive, though... 
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