This is not really a reloading question, but….

I have two different loads for one rifle. One is slow with a heavy bullet. One is faster with a medium weight rifle. I sighted in with slow bullet. I then shot some of the faster bullets. I expected them to impact the target higher (which they did), but I didn’t expect them to impact to the left (which they did).

Why? Why did they impact to the left?

Barrel whip, and shooter whip. Both move differently and the bullet spends a lesser amount of time in the rifle with the faster loads. Usually I expect faster to shoot lower, right and left is always interesting...

Sounds like barrel whip too. Heavy, slow bullets always hit high and fast, lighter bullets hit low. Barrel time combined with barrel rise from more recoil with the heavy bullets should always be higher.

The rate of spin on different bullets can cause the right or left precession.

Bedding. If your forearm tip has a pressure point, it would be a place to start.

quote:

Originally posted by Winchester 69:
Bedding. If your forearm tip has a pressure point, it would be a place to start.

300-221 cartridge in an AR-15 with free float tube and sound suppressor

I think my best option is to get another scope with Larue QD mount. So that maybe in the future. But for now, I will document it and shoot with the mil. dots.

Sometimes bullets of the exact same wt. & brand can shift by changing powder. It's that entire barrel harmonics thing.

ddunn,

Not sure that any or all of the aforementioned causes for the bullet striking off center are correct.
I too shoot a 300 Whisper but it is a heavy barreled pillar bedded single action bolt on a Rem XR action that is as solid as the rock of Gibraltar. The trigger is a Jewell with an 8 oz let off so trigger jerk is unlikely and I can usually set 5 in a.25 " grouping at 100 meters.
When I change even so much as the type of primer, recently went to a Mag. small rifle from "regular" the grouping wnet 1/2 inch high and 1" left. Load was 7.5 gr. Accurate Arms #7 with 220 gr Sierra HPBT Match, using once fired 221 Fireball cases as the parent case.
Cases were trimmed to 1.335 and neck turned and run-out is less than 0.001"
This was done just last week and I shot the different loads side by side.
Each grouped perfectly but off by that amount previously noted.

My guess is that when I drag the Ohler chrono out there will be a subtle ,or not so , increase in velocity that causes an ever so slight variation in barrel harmonics and that "pushes" the grouping off .

Anyway, that is my observation of the phenomenon.

Gary

quote:

Originally posted by ddunn:
..Why? Why did they impact to the left?

Hey ddunn, I agree with the folks that suspect it is probably a simple change in the Barrel Harmonics.

quote:

Originally posted by ddunn:
..I think my best option is to get another scope with Larue QD mount. So that maybe in the future. But for now, I will document it and shoot with the mil. dots.

No need to do that unless you just want an additional scope. Are you aware that it is "easy" to Zero a single scope with as many different Loads as you want?

quote:

Originally posted by Hot Core:

quote:

Originally posted by ddunn:
..I think my best option is to get another scope with Larue QD mount. So that maybe in the future. But for now, I will document it and shoot with the mil. dots.

No need to do that unless you just want an additional scope. Are you aware that it is "easy" to Zero a single scope with as many different Loads as you want?

Tell me more

Don't take this as "Talking Down to you", cause there are many, MANY folks that just never thought about this. You do not have to do Step A or B, but that means you are starting with the Reticle not Centered.

A. First off, you "Center the Reticle" in the scope so the crosshairs are in the middle of their Adjustment Range. On some scopes you just turn the adjustment to the end, then reverse the process and count how many turns it takes to go to the other end. Finally reverse once more and go back half way. Do that for each Turret. DO NOT force the turns, because you can damage some scopes by trying to go beyond the end point.

B. Or..., Cut two "V"-shaped notches in the edge of a box and set the scope into the "Vs". Line it up so you can look at some small object way off in the distance. Rotate the scope in the "Vs" and you will notice the Center Point of the Crosshair creates a circle around that object if it is not in the middle of the Adjustments. Make adjustments to the scope until the center of the crosshair stays steady on the object and it is Centered.
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Mount the scope in the rings. I really like the Burris Signatures because they provide numerous benefits. One is that they allow using Eccentric Inserts to do some initial Coarse Scope Adjustments to correct for variances in the Action/Barrel alignment and variances in the Bases. Most rings will do, but you end up using some of the Adjustment Range when you don't need to.

Now the scope is mounted on the Rifle.

1. If possible, Bore Sight the rifle by removing the Bolt and looking through the Bore at an object off in the distance. Then without moving the Rifle, look through the scope and see where it is aligned. Let's say the Crosshair appears to be aimed-in 2" Right and 2" High at 25yds, and your Scope has 1/4" Adjustment Clicks at 100yds.

This sounds wrong, but when correcting the "Bore Sighting", turn the Adjustments "opposite" what you normally would. In this situation, you would go 10-Clicks Right and backup 2-Clicks for a total of 8-Clicks Right. And 10-Clicks Up and 2-Clicks back for a total of 8-Clicks Up.

Going past where you actually want to be and backing up may not be needed in today’s scopes, but I still do it. (You used to have to do it to compensate for Gear-lash.) And now you are Bore Sighted.

Verify you are close with a shot at 25yds and make any Adjustment you believe is needed. Use the Normal Direction for your Adjustments now.

2. Sight in at whatever distance you desire and make Turret Adjustments to get the Point-of-Impact(POI) where you want it.

Now you have a couple of options. Fortunately, shifting between Loads only requires small Adjustments to the Turret Settings.

3. You can simply record the Turret Number Settings "on your Ammo box" for your Primary Hunting Load. Then if you want to Sight in another Load, simply make the Turret Adjustments and record "on the Secondary Load box" which direction you went and where you ended-up for that Load. Reversing the process returns you to Zero for your Primary Load.

4. But I prefer to Zero the Turret Setting for my Primary Hunting Load. Each scope is a bit different in how this is accomplished. Some have the Settings on a Friction Fit collar. You just hold the Turret in place and rotate the Numbers until “ 0 “ aligns with the Witness Mark. Or you may need to loosen 1 or 2 screws which hold it in place. If there is any question in your mind about how to do it properly, call the Customer Service Dept of your scope manufacturer and they can give you exact instructions for your Model.

Once I’m Zeroed (for my Primary Load), then if I want to get sighted in for a Second Load, I just turn the Turrets, record which way I went and what the Final Setting is for the Second Load. For example, the Second Load Notes might say: Right 4-clicks / Down 2-clicks. (R-4 D-2)

Then I can return to Zero for my Primary Load by reversing the process. But I ALWAYS go 2-clicks past where I want to be and then backup those same 2-clicks.

That allows you to Sight-In as many Loads as you want with the one Scope and still be able to return to other Load Settings. It is really not difficult or complicated. You simply use the Turret Adjustments to your benefit.

Best of luck to you.

Hot Core, That is a very good writeup.

Thank you for reminding me that I could set the zero colar on my scope.


My fear is/was that I will not adjust everything back properly and my first shot the next go around will be off significantly. We will see, a second scope may be in my future.

You are welcome. I believe a good many people would have multiple Loads for their rifles if they just thought about it.

Good Hunting and clean 1-shot Kills.

Yes, it seems obvious. (All with hindsight anyway.) I guess I got to doing it to some extent after using the peep sights on the range.

Always winding the damn things for wind and different ranges. So when I went to a target scope, much the same thing except it was much easier to aim off for a quick wind change if you wanted too.

So when I've checked my scopes, even the cheapest, with a bore sighter they all seem to track spot on. (Re. number of clicks to return, if not precise clicks to the inch.)

The power variation usually gives more POI change esp. cheap scopes.

Two loads shooting to a different point of impact in the same rifle? Unheard of. Get rid of the gun.

quote:

Originally posted by Stonecreek:
Two loads shooting to a different point of impact in the same rifle? Unheard of. Get rid of the gun.

Say what?

Hey cobrajet, I suspect he is trying to "buy" one of those rifles and is laying the preliminary "it's in pitiful shape" groundwork.

quote:

Originally posted by Hot Core:

A. First off, you "Center the Reticle" in the scope so the crosshairs are in the middle of their Adjustment Range. On some scopes you just turn the adjustment to the end, then reverse the process and count how many turns it takes to go to the other end. Finally reverse once more and go back half way. Do that for each Turret. DO NOT force the turns, because you can damage some scopes by trying to go beyond the end point.

B. Or..., Cut two "V"-shaped notches in the edge of a box and set the scope into the "Vs". Line it up so you can look at some small object way off in the distance. Rotate the scope in the "Vs" and you will notice the Center Point of the Crosshair creates a circle around that object if it is not in the middle of the Adjustments. Make adjustments to the scope until the center of the crosshair stays steady on the object and it is Centered.
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HC, as usual there is an easier way to do it than the way you do it!

Just press the objective against a mirror and you will see 2 sets of crosshairs, adjust windage and elevation until you only see one. I think Stoney Point sells a mirror if you need one!

quote:

Originally posted by woods:
...HC, as usual there is an easier way to do it than the way you do it!

Just press the objective against a mirror and you will see 2 sets of crosshairs, adjust windage and elevation until you only see one. I think Stoney Point sells a mirror if you need one!

Never heard of that Method. I'm going to stop right now and go try it.
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Well Duuuuhhh? Looked pretty DARK in the eyepiece. Do you reckon that's because NO LIGHT can get into the Objective???!!?!?!?!

So now we are even about the "Filing" on the Shell Holder.