New rifle defies physics?

H

Harvie

Inactive
I just got a new rifle for target shooting. Wanting good accuracy and cheap ammo cost, and access to a 200 yd max range, I chose a Savage Arms M93 .17 HMR (bolt action). Came with scope mounts, and I had a Barska 6-24 x 50mm scope not doing anything. Figured I was safe with the scope choice, even with the Massive recoil of the .17 HMR. ;) I used Weaver quad lock rings, and a variety of ammo from Winchester, CCI, and Hornady.

So, the puzzling issue… This was all done after difficulty sighting the scope/rifle in on paper. I could not get consistent groups at 35 yards. Fired 50 rds or so. After this trouble I sighted a light pole through the bore by using a bipod to support the rifle at a little over 300 yards out. I then adjusted the scopes windage to line up with the pole. I checked and rechecked without touching the rifle, and nothing had moved. Then at 25 feet I tried to hit a 20oz drink bottle. Bullet struck an inch or 2 to the left of the bottle. So how is this possible? If I lined the scope up to match the bore, then how is it lobbing bullets so far off to the left. I can’t figure out if it is the rifle or the scope. I was thinking it was the scope until the bore sighting resulted in that far left shooting, which was about 3 inches to the left at 25-30 feet.

Is there something to this I am missing? I have a 4x Bushnell I am going to try, but I am not so sure that it’s the scope now. Any suggestions?
 
Maybe its not the rifle?

Maybe its the scope or the mounts?

If your scope isn't mounted tight it'll move and thus your POI can move.

It could also be the ammo...

Of course maybe its not the ammo, rifle, scope or mounts... In which case there's more work involved.
 
Sounds like you may have a canting issue. Make sure the scope itself is level before adjusting it, and make sure the pole (or whatever you use as a reference) is perfectly verticle. With a 50mm lens I assume you are using high rings. This just adds to the cant if there is any.
 
Lock the rifle in a vice, bore sight it to something at 25 yards and see how it groups. That would determine if it was the gun or not. If you determine it's not the gun, I would put the scope back on and have someone actually bore sight it with a laser. Then try to sight it in at 25yds and see what results you get.


canting issue
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^This
Make sure you mounted the scope nice and straight, and the reticle is oriented correctly.
 
I have a .22 Hornet rifle that if you bore sight it, the bullet will hit a few minutes of angle to the right, yet it groups well. Barrel hamonics, the end of a barrel can vibrate like the tines of a tuning fork from the forces of firing the bullet and the bullet does not necessarily go where the hole in the barrel points to. That's why bore sighting is only used to get the gun on the paper, you still need to actually shoot the gun to do the final zeroing.

Another trick, shoot a 3 shot group at the range you want to zero the rifle at while aiming at a bullseye. Draw a new bullseye around that 3 shot group with a felt tip marker and then put that gun into a gun vice and position the gun vice to put the crosshairs on the bulleye you were aiming at. Now adjust your windage and elevation to put the crosshairs on the bulleye you drew around the 3 shot group. Now your gun is sighted in.
 
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I could not get consistent groups at 35 yards. Fired 50 rds or so.
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I'm a bit confused.

You coudn't get the rifle to group (place shots on top of each other) at 35 yards,
or you couldn't get the rifle to hit point-of-aim at 35 yards?

Straighten me out on that and then we'll talk 300 yards.
 
At one point not too long ago the Savage rimfires had a problem with the factory Weaver style mounts being too narrow. The rings would not clamp down tight enough. I had read about this quite a bit on RF Central and sure enough, when I bougt my 93R17 the rings would not lock down. Bought a set of Weaver mounts and problem fixed. Check yours.

It's been right at a year since I bought that rifle and don't hear of the problem any more, but there may still be some holdovers out there.
 
No shoulder fired rifle has its bore axis pointed at a point straight above the aiming place equal to bullet drop and sight height above the bore when the primer's struck. They all move a bit while the bullet's going down the barrel. Depending on how the rifle's held, the bore axis is usually a bit to the left (for right handed shooters) and low when the round fires. Recoil during barrel time moves the bore axis up and to the side. Large caliber double rifles' bore axes cross at 15 to 30 yards for this reason. Even the front sight on handguns is higher than the rear sight for the same reasons.

This is the reason why the same rifle and ammo typically require different sight settings for different people shooting it. I didn't realize this until I was preparing for my first long range team match "hot gunning" the same rifle and ammo. There was over a 1 MOA change in sight settings for each of us to zero. We got our zeros before hand so time wouldn't be wasted during the match.

Regarding the comment:
With a 50mm lens I assume you are using high rings. This just adds to the cant if there is any.
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Not quite so. It doesn't add to the cant angle, if that's what's referred to. With the scope twisted out of plumb a given amount to the bore axis, it doesn't matter how high above bore axis it is; the angle's still the same.
 
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I tried to put a Barska scope on my 10/22 and ended up throwing it away. Nobody could sight that scope in because every shot you took kept shifting the reticle in some way making your next shot wildly off target. I replaced it with a cheap Simmons 22 fixed power scope and it worked beautifully.
 
Simple enough to try the Bushy since you have it...

Chase down other scenarios after you rule out the most likely and easiest to try.

Also- keep in mind that if the mounts are "off"- not parallel to the bore- you'll get exactly what you're seeing.

Your windage "zero" becomes good at only the range you sighted. Any closer, or further away, you're gonna be way off because the scope's line of sight and the bore's line of trajectory are NOT going to be parallel.

However, the rifle would still "group" at any given distance if this were the case.
 
"Good-eyeing" through the bore is not at all "sighting in". It merely allows you to be on the paper at close range. I commonly try to get dead center at 25 yards with a scoped rifle, which for centerfires usually means "fairly close" at 100 yards. Probably, the .17 HMR would be fairly close to this at 100, although maybe a bit low. I don't know...

Anyhow, group size and sighting in are two different things. The first is merely an indicator as to how the mechanical system is functioning. Tight groups = proper function. The latter has to do with the proper adjustment of the scope for the desired zero point.
 
mehavey, I had issues getting it to group at 35 yards. Out of the 50 or so rounds I fired, I got a single (consecutive) 3 shot groups that was good. the rest of the the time it was inconsistent.

Bore sighting at 300 yards looked good, but point of impact at 30 feet was 3 inches left of POA. I cant fire at what I bore sighted... so I will repeat this with my target at about 160yds as soon as I get the chance, and use the bushnell.

I will also check the mounts to be sure the rings are clamping on them tight.
It concerns me that the bore sighting is so far off of point of impact. I have never run into this before to this degree. Usually its such a small amount its not possible to tell if its the rifle, or the lack of accuracy of the bore sighting.

As for the barrel harmonics, can it really make a 6 or 8 foot variance at 300 yards?

Might be a week before I can get out to shoot, but I will post an update. Thank you all for the tips, I shall look into each point brought up.
 
One question answered, another raised...

I made it back out to the range today. I had the Bushnell 4x scope on the rifle. Bore sighting was off the point of impact by 7-8 inches to the right, and about the same down. At first I was getting groups of about 2.5 to 3 inches at 100 yards. Not really what I am used to shooting at that distance from a benchrest position. As I shot groups of 3 and adjusted the scope accordingly, I noticed 2 things. 1. That it felt as though I was reaching the limit of the scopes adjustment on windage, as it was starting to tighten up a bit. And 2, the 1/4 inch at 100 yards adjustments, are not, at least with this bottom rung scope. Once I had my groups fairly cented around the bullseye I hung a fresh target. 6 shots total. 4 of them I can cover with a quarter. The other two taking the group out to 1.25 inches. Not bad for a little old 4 power scope.

So the lack of grouping was the Barska scope. I was getting 2 inch and over groups at 30 - 35 yards with it. The puzzle remains however, why the huge difference between the bore sighting, and POI? After the range today I sighted down the bore again. Lined up on an object perfectly, and the crosshairs were 6-8 inches to the right. About the same as the Barska. The question is why? Is this normal, or do I have a rifle that's out of spec?

It seems to be grouping good, so I cant complain but so much...
 
The easiest way to fix the problem is to get some of the Burris Signature rings with the inserts. You can use the different inserts to move the scope back to optical center, so you can have enough windage adjustment.
 
if the scope is not lined up with the bore horizontally then your windage will be different for different distances, as to how much it would be off, I don't know.

It would have to be off about two inches to shoot two inches off if you are centering it on something that far away... could be a combination of that and a canted reticle.. if you're turning the rifle until the reticle is level, you could be offsetting this horizontal alignment even more... just a guess.
 
I'm sure it is not the gun my Savage Arms .17 HMR will hit 5 rounds in a circle the size of a quarter with out really trying. I used a laser pointer in the chamber to bore sight the scope on it.
 
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