# Explain this to me



## TBL (Mar 27, 2012)

I have only been reloading for about 8 years so I am still learning new things all the time. Let me explain the phenomena I have experienced and hopefully one of you more experienced guys can help me to understand what is happening.
I have a model 70 in 300 WSM that I worked up a load for with a 168 gr. Barnes TSX at about 2900 fps. After tweaking the seating depth I was able to get the rifle to shoot a little less than 1 MOA pretty consistently.
I decided to work up another load with the same bullet but in 150 gr. After it was all said and done this load clocked in at 3300 fps and holds 3/4 MOA.
Here's the rub. The scope was zeroed with the first load. When I started shooting the second load with lighter bullets I expected the point of impact to be different in the vertical plane due to the lighter projectile and the increased velocity. The groups tightened up a bit with the lighter load but point of impact moved 2.5" to the right of the original 168 gr. load.Wind drift was not a factor as I only shoot for load development when the wind is light. I don't think the scope is a factor as it is a Swarovski 18X and the groups are consistent. 
I have thought about it a lot and the only thing I can come up with is that the bullet may not be spinning only on its axis but may also be traveling downrange in a long helix.Does this make any sense? I'm not able to come up with anything else that would change the POI 2.5" horizontally. What am I missing?


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## BradV (Jun 27, 2012)

TBL said:


> I have only been reloading for about 8 years so I am still learning new things all the time. Let me explain the phenomena I have experienced and hopefully one of you more experienced guys can help me to understand what is happening.
> I have a model 70 in 300 WSM that I worked up a load for with a 168 gr. Barnes TSX at about 2900 fps. After tweaking the seating depth I was able to get the rifle to shoot a little less than 1 MOA pretty consistently.
> I decided to work up another load with the same bullet but in 150 gr. After it was all said and done this load clocked in at 3300 fps and holds 3/4 MOA.
> Here's the rub. The scope was zeroed with the first load. When I started shooting the second load with lighter bullets I expected the point of impact to be different in the vertical plane due to the lighter projectile and the increased velocity. The groups tightened up a bit with the lighter load but point of impact moved 2.5" to the right of the original 168 gr. load.Wind drift was not a factor as I only shoot for load development when the wind is light. I don't think the scope is a factor as it is a Swarovski 18X and the groups are consistent.
> I have thought about it a lot and the only thing I can come up with is that the bullet may not be spinning only on its axis but may also be traveling downrange in a long helix.Does this make any sense? I'm not able to come up with anything else that would change the POI 2.5" horizontally. What am I missing?


It is most likely related to the recoil of the rifle and the harmonics/whip of the barrel.


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## dwilliams35 (Oct 8, 2006)

BradV said:


> It is most likely related to the recoil of the rifle and the harmonics/whip of the barrel.


 I'll go with that theory: which direction the actual muzzle is pointing when the bullet leaves it.
I've always found this interesting:


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## DUTY FIRST (Jun 23, 2012)

dwilliams35 said:


> I'll go with that theory: which direction the actual muzzle is pointing when the bullet leaves it. QUOTE]
> 
> That's really the straight forward explanation of it.
> 
> ...


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## deckh (Jul 23, 2010)

Two different bullet weights will cause different barrel harmonics...........


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## THE JAMMER (Aug 1, 2005)

deckh said:


> Two different bullet weights will cause different barrel harmonics...........


This one is not that difficult. The answer is above.

As said farther above also, any change, including bullet weight type whatever, will change the bbl harmonics, which will change poi. I never cease to be amazed at this.

I have some guns that the poi's are all over the place for different bullets. My new 300 aac, however, seems to put almost everything I load into it within about .5-.75" of the same poi. That's a reloader's dream. when you get it, cherish it, because it doesn't happen very often.

I will say that the one bullet that seems to have larger poi differences from "base loads" are the barnes bullets. They seem to have a "mind of their own" sometimes.


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## Bottomsup (Jul 12, 2006)

Google slow motion rifle barrel whip. You will be shocked how much the barrel whips with each shot as well as the scope flex.


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## Bottomsup (Jul 12, 2006)




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## mrsh978 (Apr 24, 2006)

*300*

TBL- save yourself some agony-use 180 grain bullets vs. the lighter ones on a 300. they are more forgiving that the lighter ones... I used to load 165 for deer thinking they were "better/faster"- they 180s have outperformed since I switched. btw I load for 9 different 300s.


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## TBL (Mar 27, 2012)

*Thanks*

Lots of good information! I appreciate all the feedback gentlemen.


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## CHARLIE (Jun 2, 2004)

Have had it explained to me by folks who make it very clear. The barrel is like a water hose swings around like a snake. Just try to have it in the same place every time the bullet leaves the barrel. (which aint easy most of the time).


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## jamesvaughan (Apr 29, 2012)

*Horizontal walk*

Last year i was working up loads for a 300 Weatherby Mag. For each grain of powder I increased, the groups walked appox. 1/2 inch to the right. IMHO the rpms increase making the bullet grab more air kinda like a curve ball. Has anyone tried Cutting Edge Bullets they are turning them on a lathe out of solid brass or copper making them perfectly balanced. When I was in Idaho last i saw them recover two deer they killed. One at 875 yds the other at 1270 yds.I wouldn't believe it but I was there.


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## MrG (Apr 10, 2005)

You guys amaze me! Learn something every day.


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## Superman70 (Aug 13, 2014)

Guns are very strange animals. A couple of years ago I put put a TC encore together for a boy. I have several different loads for 243s. 85, 87, and 100 grains. That gun would shoot them all into the same group at 100 and we never had to make the first scope adjustment. That poor kid thinks that I know a lot more than I do.


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## DUTY FIRST (Jun 23, 2012)

The best way to make a rifle shoot with less change due to barrel vibration is to fully glass bed both the action and barrel. That greatly dampens vibration and also has the effect of maintaining zero even with major changes in humidity and temperature. It take a bit more effort than leaving the barrel free floating, but is worth it. 

Using Brownells Acraglas Gel you can do it yourself and have a good looking and good shooting rifle.


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## Superman70 (Aug 13, 2014)

Anyone ever use the acraglass steel bed.


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## DUTY FIRST (Jun 23, 2012)

Superman70 said:


> Anyone ever use the acraglass steel bed.


The steel bedding is fine for synthetic stocks as it can be painted to match the stock. It's not so good for wood stocks as it can't easily be dyed to match various wood colors like the epoxy type Acraglass compound can. It's also a bit more runny than the gel, making it harder to do a neat job.

I don't really see any advantage to the steel bedding. It is claimed to be stronger, but the epoxy type is already so strong that any stock will be damaged before the bedding compound is. Both are nearly indestructible.

Also, if you ever need to make any bedding alteration, like if installing an aftermarket trigger requiring a little trim work to the bedding, the epoxy type is easier to work with.


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## Superman70 (Aug 13, 2014)

I knew there was a reason that I never tried it.


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## CHARLIE (Jun 2, 2004)

Back years ago we full length bedded the barrels and even put a wedge between the barrel and stock at the end of the stock. Sometimes helped and sometime not. Ended up free floating all my barrels just to keep it simple. Always heard that the wooden stocks would warp and change pressure points so most went to free floating. My guns are glass bedded with acraglas in the synthetic stocks and seem to work OK. Roughed up the stock to make sure the glass adhered to the synthetic. so far so good.


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