POI shifts, cause?

F

fire4606

New member
I've got a Savage 10fcp-k topped with a Vortex Viper 6-24x50.

The gun always groups, but it get minor, or to me major POI shifts between sessions.

Go to the range and shoot 3-4 five shot groups and it will be right on.

Come back days later with similar weather conditions and it will be hitting a 1/2" higher that whole session.

Same session shoot a group 5 shots 1/2 moa hitting maybe 3/4" hi and the next group is similar and then the next group might hit right on a 3/4" shift.

I'm confused if I've got something loose in my mount, or if my view through the scope isn't consistent, I do pay attention to scope shadow but I don't know.

Warne 20 moa one piece base and vortex tactical rings, I've had the scope off once and it showed no wear around the ring locations.

I'm a new shooter to this kind of shooting so I'm stuck trying to decide if it's me or a loose mount.

Would something loose in the mounting setup be able to shoot decent groups?? Likely me??

Tks
 
How are you supporting the rifle?

difference in grips, bipods, sandbags and whatnot can affect.

I don't think you'd be able to shot nice grioups if there was something wrong with the mount
 
Loose mount would cause a wandering p.o.i., the really oddball thing about your "symptoms" is that they occur when you shift your p.o.a. a few inches to shoot another group- and then p.o.i. is consistent, but shifted for that entire group.

No way a bullet can know if it's part of the last grouping, or the start of a new one...

Some things (like a change in ammo, cold bore shots and shooting from a completely cleaned barrel, or adding a suppressor or brake to the barrel) will change the p.o.i...but this isn't your case. I have no idea how it can shoot tight groupings, but their locations relative to your point of aim change with no changes on your part.

My vote is that, somehow, it's you. Checking for a loose scope/mount is simple enough...
 
If your rifle is grouping pretty well during sessions but not grouping well relative to the last session, I would suspect your set up and not the rifle.

When you set up, do you always use the same bags? If you are using range bags, some might be full and some partially empty.

Do you always rest the stock at the same place fore and aft as before? Remember, partially filled or empty bags will allow the stock to rest deeper or not as deep in the Vee.

Are you shooting off the same type surface? The recoil can change from wood to concrete.

Do you sometimes, depending on the seating provided at the bench, use two bags? Three bags? Just one bag?

Are you absolutely sure you are gripping the stock and touching the trigger the same way each session?

All these little things can contribute variation to your grouping.

I have shot loads that group very well and some not so well and I am talking about the SAME loads.

I switch calibers a lot and find that when I move from a 22-250 to a .308, it takes some time for me to get "in the rhythm" and that after shooting a bit, my groups settle down. Maybe that is happening to you also.

HTH
 
Can be many things. I had fits with a rifle until yesterday I finally got it diagnosed. One of the premium lines of scopes premium scope was crapped out. When I adjust side focus the cross hairs moved over the paper. I put the rifle in tac bags and locked it down at 100. As I moved the side focus up in yardage, the cross hair moved up and left, then stright up, then started moving left again. Down in power, the exact opposite. It repeated the same path perfectly. I called customer service and they sent a new scope out next day air and told me put the old one in the box and send it back. I won't say whose scope did it because their customer service has always been very good to me and everybody screws up now and again. All I am saying is regardless of whose name is on the scope, it may be bad.
 
There are several factors that can affect POI from day to day. Sunlight, moisture in the ground causing water vapor, cloudiness, mirage, wind velocity and direction, your hold against the shoulder, rifle position on the bags, and scope parallax, if not adjusted for that distance. Air temperature/density, rifle temperature, and ammo temperature can also cause impact variations.

Rifles that have free-floating barrels are less subject to variations in rifle position on the bags and the amount of down-pressure on the forend.

Mirage is visible, but water vapor isn't, so it's effects can't be estimated accurately. On partly cloudy days, when the sun comes out, bullet impacts will rise, due to mirage and/or water vapor. For any change in conditions, it's wise to shoot sighter shots on another bull, to see what's happening out there.
 
Thanks for the info,

Real bench at the range, same bags used each time they're mine personally, used the same way each time bit I've never been super exact on the front bags placement, didn't think it would have to be as the rear bag always moves to adjust for elevation etc...

I pay attention to scope shadow and was of the impression if I had no shadow anywhere around the edges I should be lined up right...

Reynolds I will look at a target at range next time I'm out and adjust the parallax and see if it does what you describe..

Thanks for the info guys
 
Pitcher,

The last few sessions have been at 730 am when the range is open temp, humidity, and wind almost identical. Winds minimal or none, temp 63 to 66 degrees humidity low 90's.

Can't recall for sure from memory as I didn't record but I believe it was sunny out each time also with sun at my back
 
Ridge runner,

Thanks hearing action bedding screw torque from other sources also, just can't seem to find the specs on how much to torque them.
 
I have a 10 FCP in an HS-Precision stock. I pulled this info off of the Savage Shooters forum. It works for me.

1. Slip the action into the stock.
2. Stand the stock on the butt pad and push down on the barrel to ensure the barrel lug is tight against the bedding block.
3. Tighten the forward most screw (short screw) to 10 in pounds.
3. Tight the other action screw (long one just in front of the trigger guard) to 10 inch pounds.
4. Repeat step 3 & 4, increasing 5 inch pounds each time, until the screws have been tightened to 40 inch pounds.
5. According to HS precision, their stock can be tightened to 60~65 inch pounds, although Savage does not acknowledge that spec.
 
About 40 inch pounds, but each rifle is a bit different. Kind of have to tune them. I have heard the bolts will strip at around 15 ft. lbs. Never stripped any, but never put that much torque on them either. I would not go over 50 inch pounds. If you need more than 50, something else is out of whack.
 
Savage recommends 30-35 inch-pounds for action screws:

https://savagearms.zendesk.com/entries/23573437-What-is-the-torque-spec-for-my-action-screws-

But, I don't think that's your issue. Action screw torque changes would tend to open/shrink group sizes (accuracy)- not point of impact without a change in accuracy.

It's important to realize the distinction in point of impact as relates to point of aim. Point of impact can change based on certain variables, without a change in accuracy.

While a defective scope, or loose mount, can cause shifts in p.o.i. and even hold them for a number of shots, for them to change at exactly the same shot you move to change (new) grouping- doesn't sound logical from a hardware perspective. Since you acknowledge you're a new shooter, suggest you let an experienced shooter drive the rifle to see if the results differ.

Anyone can have an "off" day. I've gotten somewhat used to my teenage son's griping about it being the rifle when he's having one. After listening to it last weekend while we were working up loads for his AR-10, he asked me if I could do better....got behind the rifle, put five shots into 3/4"...and walked away grinning. It's nice to still be able to shoot better than my sons, LOL...
 
Tob, AZ, Reynolds,

Thanks for the info, they are torqued to 30 in lbs now.

Initially kind of felt it was me though I've never had this kind of issue in the past with 6 or 7 hunting rifles, but still feel it could be me.

I've reworked my cheek piece to try to make it easier to obtain a more consistent cheek weld, torqued the action screws and am going to try one others suggestion of reading glasses since my near vision does get out of whack some now at 45 yrs old...

I will also look into someone else shooting it though I would need to be able to hook up with them on multiple back to back sessions to try to duplicate the issue...

And yeh I understand bad days, couldn't shoot rifle worth a damn today, but on the flip side couldn't miss with pistols....I hear ya

Side note, I did have the action out of the stock a while back to adjust the trigger and followed the directions in the owners manual which were very generic, in reference to the action screws it was "tighten back down starting with the top one first" .... Nothing else so that's all I did, no idea how tight they were other than I know I tightened them gingerly knowing I was screwing into aluminum...
 
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First, I am assuming that you are using the same loads or factory ammo for each session and finding that the POI changes when everything is being kept constant.

I find that when testing different loads, the POI will change with velocity and seating depth changes even when using the same bullets and powder.
If I change powder and bullets, I see even more changes in POI with every load change even in the same session.

I you keep the conditions constant with respect to ammo - brass, bullet weight, powder charge, seating depth, and primers - then try these experiments and see if they cause changes in your POI.

Test 1 - Go through your regular drill to set up on your bags and set up on your point of aim.
Do whatever breathing and set up approach that you always do.

Then, with your cross-hairs on your POA, close your eyes for 10 seconds.
Open them and see if you are still on your POA.

If the new POA is to the right, shift your body slightly to the left and you'll see the POA move. Shifting your body in the opposite direction will move the POA the other way. Setting up for each session or ever for each group can cause you to aim by using your muscles instead of your set up. That will yield different POIs even though your POA appears to be on target.

If the POA has moved after you relaxed, your POA changed because you had adjusted your POA using your muscles. When your muscles relax, your POA finds your resting position - that is called your natural point of aim and that is where your bullet will impact even if your POA set up controlled by your muscles is slightly different. If your POA didn't move, you were at your natural point of am and muscling isn't the problem.

Test 2 - go through your normal set up.
Just get the shadow in the scope to go away and take your shot. See if the POI is at your POA.
Then move your head slightly closer to the scope and take the second shot and see what happens to the POI compared to the first.
It should be off the initial shot. If you always are exactly in the same position behind the scope - right on the center line, then scope positioning isn't your problem

Third test - press the stock tighter into your shoulder and see where the next shot goes. The POI should change again.
If you always can manage to keep the stock pressure on your shoulder identical from shot to shot and session to session, then this isn't your problem.

What could be happening is that your set up for each session is slightly different - closer to the scope, a bit more muscling of the rifle, or having the stock tighter into your shoulder. Your body position and what you 'feel' is right might be slightly different during successive sessions and it will cause your POA/POI to be different, even for the same ammo.

If you clamped the rifle in a test stand, you probably wouldn't see as much effect caused by positioning, muscle, and set up varitions, but the shooter is included in the rifle set up and unless the shooter can be sure that the set up is identical for every session, variations might be creating the conditions the would move the POI compared to your POA. Yes, the variations can also include temperature, humidity and other external conditions. I have long since given up expecting my set up to be identical for each session. For that matter, I find that when I start at the range I will set up slightly differently than when I am tired toward the end of a long range session.

The changes aren't on the order of inches in POI but they can cause variations of an inch in cases where multiple effects combine. I do not have the body control that really great shooters have but I don't do all that badly even though I know my own limitations.

I find the I have to regularly 'go back to basics' in my set up to get the best results even during a session.

I find that from session to session I have to find what eliminates most of the muscling that might be occurring, reestablish the right position behind the scope and get into my natural point of aim position if I expect to minimize variations in my POI for a given POA. Once I find the 'zero' for that given day or portion of a session, I get into the zone and, if I pay attention to the details, concentrate on my breath control and stay in the same position behind the scope, I get really tight groups and they hit where I was aiming.

If I get distracted, get lazy, or even start varying how tightly I press the rifle into my shoulder, I can get groups or even individual shots vary POI from my POA.
 
Another variable to check: Did you change the scope magnification between groups? The mechanics of the variable power scope can create a change in poi as you adjust magnification. Even the most expensive, well built scopes can show this condition. It is not a flaw in the scope manufacturing unless it is excessive. It should be repeatable and consistent. When you put it on each power setting it should hit the same poi it did last time it was set there. Shoot a few groups at different settings and see what happens.
 
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