Sighting in with 165 gr bullets

F

Fish_Scientist

New member
I'm not certain if this is a question best suited for the Reloading or Rifle forums, but:

For the sake of argument, let's say my Remington 700 .30-06 is sighted in with 165 gr Remington CoreLokt rounds hitting 100 yards at 2.6" above zero. Let's also say that I've just started reloading .30-06 cases with 165 gr Speer HCSP bullets over 45, 45.5, 46, and 46.5 gr of IMR-4895. How can I tell which load my rifle likes best? If velocity affects bullet trajectory and my reloads are not identical to the Remington round, would I need to re-zero with each different load to determine which produces the tightest groups?

Thanks for your help -

Fish
 
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First off, forget where the bullets hit at 100 yards, assuming their on paper of course.

Now load of 10 rounds each of your powder load, shoot 10 round groups and see which charge works best in your gun.

Now sight in your rifle to hit 2.6 inches high @ 100 to match your Remington factory bullets.

You'll find the Remington will shoot a bit faster then the re-loads with the power charges you listed, but not enough to make a whole lot of difference at normal hunting ranges.
 
Absolutely. Let me give you a case in point. A few years ago, I picked up a .270 to play with. I bought 4 flavors of ammo from Wallyworld. I had 1 each of Win, Rem, and Fed 130 grn PSPs and 1 box of Rem 150 grn SPs.

Without adjusting the scope, the Rem and Fed 130's grouped to the same location (just low and left of the target). The Winchesters (same exact bullet weight mind you) grouped high and right. The difference between the two groups was over 4 inches.

The 150's looked like a shotgun pattern.

Bottom line, anytime you change flavors of ammo you have to recheck your zero until you have confirmed how those flavors behave in your particular rifle.
 
Doyle said:
Bottom line, anytime you change flavors of ammo you have to recheck your zero until you have confirmed how those flavors behave in your particular rifle.
Click to expand...

So flavor also includes variability in powder charge, huh? Same bullet, same powder, but different charge means different flavor. Gotcha. I had always thought that identical bullet with identical powder would have meant same flavor and any changes in velocity would have only affected energy levels.

Does this mean that changing anything--within a given bullet weight--(i.e., bullet manufacturer, case manufacturer, powder, powder charge) means that you've created a new load? Primer included? On one hand, I can see how it could get very frustrating trying to determine the best load for a given rifle. On the other hand, it's fascinating to think how much interaction there is between cartridge components.

Always learning -

Fish
 
For some rifles, it seems like any little change affects group size and point of impact. I was lucky with my pet '06; it seems to digest anything with little variation of point of impact beyond some relatively minor horizontal displacement of the group center.

I've always sighted in for a center-of-group impact point that's two inches high at 100 yards. If I change bullets, I figure on some sort of testing for group size and some new sight-in point.

Whether 150, 165 or 180, the difference in trajectories to 300 yards is not enough to notice for a deer rifle. They're all going to be around six inches low, give or take an inch. Bambi never has noticed...
 
I wouldn't go rechecking zero after a primer change (but that's just me). I would, however, recheck zero after pretty much any other change. One of the things that affects POI is barrel harmonics. If you change the speed of the bullet (by changing powder load for example) you have the potential for changing the harmonics enough to cause a shift in POI.

Now, if you are talking about a 100yd deer rifle then the POI shift may be negligent enought not to worry about. However, a 1" change in POI at 100 yds becomes 3" (or more) at 300 yds. That is enough to make me want to rezero every time I change ammo.
 
Elementary

The load your rifle likes best is the one that produces the tightest groups . Then rezero if POI has shifted from POA !
 
I see some confusion being created and will attempt to not confuse further. Yes any change including primer will potentially change the poi on the target. Different primers burn at different rates with more or less flame than others causing changes in velocity that will change poi. Sometimes not enough to notice, but sometimes quit a bit.


No you do not have to change your scope setting for each "test firing" of new loads. simply aim at the same spot on the target for each round fired. After you have determined the most accurate, safe, load for your rifle then zero your scope for that ammo. Changing your scope for a few grains of powder change will aggrivate you for no reason.
 
Changing anything, can change POI and groupings.
Just because bullets may be the same weight, their shapes and BC's can vary dramatically, affecting bullet flight.

As everyone has said, forget about scope adjustments. As long as you keep the same point of aim, it's all about the tightness and consistency of the groups.
It's advantageous to have more power rather than less in a scope for this, and you always want to have it at max magnification if conditions permit. This makes your point of aim more precise on each shot.
 
One-load rifle

If you only hunt one type of game with the rifle in question, once you arrive at an optimum load, there's little need to change it. Game won't know the difference.

My Remington Model 7, 7mm-08 puts bullets from 130-145 grains close enough to each other that re-sighting isn't necessary. Wish I could say the same thing for all my rifles.
 
All of the posters are correct but are commenting on the observations not on the cause.

The reason there is variation in point of impact with different bullets of the same weight is the reaction of the barrel stock combination to the detonation of a catridge.

Manufacturers don't use all the same powders and loads, even if the stated muzzle velocity and bullet weight is the same.
Bullet shape also has an effect based upon how much of the bullet is in contact with the bore.

The reason is that the round detonates and compresses backwards against the bolt as the powder burns and creates a shock to the barrel that makes it move vertically. As the bullet moves down the barrel, the contact with the rifling makes the barrel oscillate.

So the barrel is moving up and down at the same time it is moving in a circle.
The speed of the bullet and the length of the barrel determing if the bullet exits the barrel when it is moving up or at what part of the circle that it is oscillating in.

The variations aren't large but it doesn't take much variation to cause a bullet to hit high or low or appear to be right or left.

In a perfect world you might even be able to predict where the bullet will hit, but there is another big variable, the barrel interacts with the stock and, even if bedded or free floated, the stock impacts the action of the barrel.

Confusing? It sure is.

You probably have all seen a higher velocity round with a lighter bullet weight have a point of impact below the impact point of a lower velocity round with a heavier bullet weight when you are testing loads.
It shouldn't happen based upon gravity - the slower bullet should always hit lower because time to reach the target, not weight, detrimines the amount of drop.

Explanation: if the barrel is on the up rise when the heavier bullet leaves the barrel and on the down swing when the lighter bullet leaves the barrel, the heavy bullet just may hit higher than the lighter bullet. In fact, it just proves that your barrel really isn't always pointed where you are aiming with your scope simply because of the dynamics of the barrel / stock reaction to the detonation of that particular round.
 
For a given sight-in POI with one weight of bullet, a heavier bullet can hit a bit higher due to the greater recoil causing a bit more muzzle jump. This is most noticeable with handguns, particularly the .44 Maggie when comparing 180-grain with 240-grain. If sighted in with the 180s, the 240s hit higher.

One reason for free-floating the forearm is to reduce or eliminate the effect of differential pressure between steel and wood as the barrel expands slightly with heating during a string of shots. The changing of the upward force of the wood against the steel (or the downward force of the steel against the wood, take your pick) commonly results in vertical stringing. Amazing what a change of only a few thousandths of an inch can do...
 
I don't want to hijack Fish_Scientist's thread, but it's beginning to veer off into territory that I'm curious about, so I have a question.

Rimfire5 said:
. . . .The reason there is variation in point of impact with different bullets of the same weight is the reaction of the barrel stock combination to the detonation of a catridge. . . .

The reason is that the round detonates and compresses backwards against the bolt as the powder burns and creates a shock to the barrel that makes it move vertically. As the bullet moves down the barrel, the contact with the rifling makes the barrel oscillate.

So the barrel is moving up and down at the same time it is moving in a circle.
The speed of the bullet and the length of the barrel determing if the bullet exits the barrel when it is moving up or at what part of the circle that it is oscillating in.
Click to expand...

I've read lots of posts that indicate that a free-floated barrel is more accurate than one that's not. If there's all this interaction between barrel, stock, action, cartridge detonation, etc., (& it stands to reason that there is) why are free-floated barrels better? It would seem to my (perhaps flawed) logic that a bull barrel, clamped down tight to a heavy stock, perhaps even a Mannlicher-style stock (is that the name?), would have less play to it than a free floater. Accordingly, shouldn't that be more accurate? What am I missing?
 
why are free-floated barrels better?
Click to expand...

They aren't "always" better. Here is the simple version. As the bullet travels down the barrel, it (the barrel) actually vibrates. It's called barrel harmonics. Any change in those harmonics could cause the bullet to exit the muzzle at a slightly different vibration than it did on the previous round. That difference is one of the causes of inaccuracy (i.e. poor grouping).

When a stock (particularly a wood stock) changes temperature or encounters changes in relative humidity, it changes shape (on a microscopic level). If that stock is touching the barrel then it has the potential of changing how that barrel vibrates as the bullet travels down. Hence, it could vibrate one way on one shot, then a different way on the next shot. By floating the barrel, it doesn't touch the stock so it increases the chance that all vibrations are the same.
 
Spats McGee said:
I don't want to hijack Fish_Scientist's thread, but it's beginning to veer off into territory that I'm curious about, so I have a question.
Click to expand...

No worries. Much of this thread has spawned some fascinating reading, touching on aspects of ballistics that I wouldn't have even considered. My question had been answered a while ago (i.e., if I'm already zeroed, that load which produces the tightest groups are those that my rifle likes best, so once determined, rezero with those loads) so relative hijacks or moderately off-topic ideas are certainly welcome.

Having just started reading the chapter on ballistics in my Speer manual, I'm beginning to realize why reloading for the perfect round could be so addicting. I like math, I like data collection, and I like data analysis. This should be fun.

Fish
 
Thank you, Fish, for allowing me to use your thread to ask, and than you, Doyle, for the information. That tells me what I was missing.
 
It would seem to my (perhaps flawed) logic that a bull barrel, clamped down tight to a heavy stock, perhaps even a Mannlicher-style stock (is that the name?), would have less play to it than a free floater. Accordingly, shouldn't that be more accurate? What am I missing?
Click to expand...

You're not missing anything... very observant post.
There is a school of thought that adheres to that reasoning. I can't think of the name of the company- but they sleeve rifle barrels into a stiff oversize "tube" (for lack of a better term coming to mind) using a high-tech epoxy, to create an incredibly stiff barrel. Wish I could find the link...pricey, too.

The whole concept behind rifle accuracy is consistency. We bed the action and install pillars to prevent movement, because if the action moves- and ends up in a different location after a shot- the next shot will have a different POI. Notwithstanding the "rigid" barrel concept- we know the barrel is going to move- as Rimfire 5 so eloquently explained- so the idea is to allow it to move freely. By so doing, whatever gyrations that barrel goes through, it will do it the same way, every time (with identical ammo)- consistency.

This is why it's particularly important to bed wood stocks. Wood changes dimensionally-big time- with changes in temperature and humidity. This causes changes in the amount, and locations, of pressure points on the action and/or barrel (if not free-floated)....inconsistency...
 
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