Rifle Scopes My SWFA 1x6 POI shift--what's acceptable?

[CallMeChaz]

After researching here and some other sites, I bought an SWFA 1x6. Never spent that much on an optic before, so I had my fingers crossed. Initial testing was good news-bad news (maybe)? Fired a small group at 6x, 50 yards. Used the mil system to adjust POI. One adjustment put me dead center at 50 yards Kewl--I like the matching mil reticle and turrets!

Fired another three shot group at 50 yards, all touching. So far, so good. Switched to 1x. Put three shots in the same hole and one just off. Sorta good, except POI shifted 1-1/4" to 8 o'clock. Even my much less expensive variables don't shift. I also read FFP optics don't shift POI due to the mechanics. Myth? (obviously LOL)

Anyone running SWFA low powers that can comment?
If not, in general, is that an acceptable shift in a scope of this caliber?

Your thoughts are appreciated, as I don't know if I need to contact SWFA.

BTW, I was please to find I can shoot comfortably with both eyes open at 1x, even though I'm left eye dominant. I'll post some more results as I get used to this unique optic.

 

[SomeOtherGuy]

Most likely explanation is that your shifted-POI group was shot with either ammo or technique that changed the POI, not the scope.

Second most likely explanation (really a variant of the first) is that your eye was not centered for your 50 yard first groups and you set the scope adjustments based on a parallax situation, which you apparently held consistently. When you switched to 1x the parallax disappeared and your new POI was off, not because something in the scope is off but because you went from groups based on parallax to groups not affected by parallax.

I would try your setup again, preferably at 100 yards since that's likely where your scope's parallax is set, therefore a group fired at 6x at a 100 yard target shouldn't shift when you switch to 1x even if your eye wasn't centered when shot at 6x. I would also try another shooter and be sure the ammo is identical from group to group.

 

[CallMeChaz]

Most likely explanation is that your shifted-POI group was shot with either ammo or technique that changed the POI, not the scope.

Second most likely explanation (really a variant of the first) is that your eye was not centered for your 50 yard first groups and you set the scope adjustments based on a parallax situation, which you apparently held consistently. When you switched to 1x the parallax disappeared and your new POI was off, not because something in the scope is off but because you went from groups based on parallax to groups not affected by parallax.

I would try your setup again, preferably at 100 yards since that's likely where your scope's parallax is set, therefore a group fired at 6x at a 100 yard target shouldn't shift when you switch to 1x even if your eye wasn't centered when shot at 6x. I would also try another shooter and be sure the ammo is identical from group to group.

First of all, thank you for the thoughtful explanation and not just an opinion. I agree that consistency in testing is key. The ammo was from the same case, and two shooters got the same result--8/9 o'clock shift at 1x.

Let me see if I'm following your logic. Assuming the scope is corrected at 100 yards for 6x, zeroing 6x at 50 may have introduced parallax. Backing off to 1x would have rectified that, producing a correct but potentially different POI? If so, it seems a plausible explanation except I did shoot a 10 shot group at 100 yards (6x) before I left that day.

That group exhibited no windage shift whatsoever--only the expected, 12 o'clock 1-1/2" high grouping. That would seem to indicate that parallax at 6x is well controlled from 50-100 yards. If parallax at 6x is controlled at 50 yards, my 1x POI should be the same, yes? At least that's my objective conclusion.

From a more subjective assessment, I just now rested my rifle and looked for visible parallax movement at both settings, at 50 and 100 yards. I have to say that (with the exception of my parallax adjustable scopes) this appears to be the best corrected scope I own. There is no discernible movement from either target at 1x, nor the 100 yard target at 6x. At 50 yards I wouldn't say I see movement at 6x, just reticle blurring as I move my eye out of the box. Certainly nothing resembling an 1-1/4" jump!

I'm assuming you would consider this amount of shift unacceptable. Considering the new information, do you feel I can assume this is not "operator error", but a problem with the scope?

 

[SomeOtherGuy]

First of all, thank you for the thoughtful explanation and not just an opinion. I agree that consistency in testing is key. The ammo was from the same case, and two shooters got the same result--8/9 o'clock shift at 1x.

Let me see if I'm following your logic. Assuming the scope is corrected at 100 yards for 6x, zeroing 6x at 50 may have introduced parallax. Backing off to 1x would have rectified that, producing a correct but potentially different POI? If so, it seems a plausible explanation except I did shoot a 10 shot group at 100 yards (6x) before I left that day.

That group exhibited no windage shift whatsoever--only the expected, 12 o'clock 1-1/2" high grouping. That would seem to indicate that parallax at 6x is well controlled from 50-100 yards.

You are correctly reading my guess as to what might have happened.

If parallax at 6x is controlled at 50 yards, my 1x POI should be the same, yes? At least that's my objective conclusion.

If you have no parallax issues at 6x, then your groups at that distance should be the same regardless of magnification.

From a more subjective assessment, I just now rested my rifle and looked for visible parallax movement at both settings, at 50 and 100 yards. I have to say that (with the exception of my parallax adjustable scopes) this appears to be the best corrected scope I own. There is no discernible movement from either target at 1x, nor the 100 yard target at 6x. At 50 yards I wouldn't say I see movement at 6x, just reticle blurring as I move my eye out of the box. Certainly nothing resembling an 1-1/4" jump!

I'm assuming you would consider this amount of shift unacceptable. Considering the new information, do you feel I can assume this is not "operator error", but a problem with the scope?

I simply don't know enough to say whether or not this is operator error. Personally, the one time I was certain I had a weird scope issue, I later determined that I had most likely been shooting at one target while adjusting the scope based on impacts on an identical target below it, not realizing the difference. I'm not saying that THAT is what is happening here, but that I can't rule out your error.

Have you done additional group testing? I would try zeroing at 100 yards at 6x, then shoot a group at 100 yards at 1x and see if there is again POI shift, or not. It could be something funny happened the first time which was a one time issue and neither a scope problem nor your regular technique. It could be that there is some minor parallax that you don't see in testing but is enough to cause a 1" shift at 50 yards.

If you rule everything else out then of course I would contact SWFA about the scope. However, my understanding of the FFP design is that POI should not shift with a given POA regardless of magnification, because the reticle is magnified with the target image and therefore even if your aiming point is off center, it should be off-center by the same angular amount at all magnifications.

 

[SomeOtherGuy]

More thoughts:

1) What is the rifle? AR15? Barrel profile and is it free floated? Many AR15 rifles only shoot 2-3 MOA anyway, and any pressure on the forend of a non-floated gun will affect that too.

2) Likewise, what's the ammo? Match grade with known group sizes, or anything else?

3) It sounds like you are shooting 3-shot groups. A 1.25" difference in center of 3-shot groups doesn't mean a whole lot. I would be interested in what happens if you shoot 10-shot groups on different targets (or parts of one target), allowing the barrel to cool between shots and completely cool between starting each group. This would give a statistically more valid indication of any actual change in POI.

4) Another option to consider - clamp the rifle in a shooting vise, adjust it so it's perfectly centered at 1x, then zoom to 6x and see if the crosshair is still centered in the same place. Repeat from 6x to 1x. I would actually do this first if you have access to a shooting vise or can improvise one.

 

[Clusterfrack]

SOG's advice is good. You need more data. I'm betting on operator error, but I've seen enough bizarre problems with optics, including an SWFA scope, that I would not rule that out either.

If you have access to a laser boresight you could get this figured out without using any ammo.

Parallax can cause POI shifts, but 2.5moa? That seems like a big parallax error to me.

 

[CallMeChaz]

I simply don't know enough to say whether or not this is operator error. ...Have you done additional group testing? I would try zeroing at 100 yards at 6x, then shoot a group at 100 yards at 1x and see if there is again POI shift, or not.

...my understanding of the FFP design is that POI should not shift with a given POA

I haven't shot 1x at 100 yards yet. First order of business will be clamping it down and zooming the scope. With the amount of error I got, if it's the scope it should be obvious. If it's inconclusive, I'll reshoot the whole scenario. I've never had a scope issue before, at least nothing that wasn't obvious. I want to be sure b4 I call SWAF. Eliminate the obvious, and whatever remains, no matter how improbable, is the solution.

 

[CallMeChaz]

More thoughts:

1) What is the rifle? AR15? Barrel profile and is it free floated? Many AR15 rifles only shoot 2-3 MOA anyway, and any pressure on the forend of a non-floated gun will affect that too.

2) Likewise, what's the ammo? Match grade with known group sizes, or anything else?

3) It sounds like you are shooting 3-shot groups. A 1.25" difference in center of 3-shot groups doesn't mean a whole lot. I would be interested in what happens if you shoot 10-shot groups on different targets (or parts of one target), allowing the barrel to cool between shots and completely cool between starting each group. This would give a statistically more valid indication of any actual change in POI.

4) Another option to consider - clamp the rifle in a shooting vise, adjust it so it's perfectly centered at 1x, then zoom to 6x and see if the crosshair is still centered in the same place. Repeat from 6x to 1x. I would actually do this first if you have access to a shooting vise or can improvise one.

1) Windham Weaponry AR-15 carbine, HBAR, military handguard. All groups were shot with the handguard resting the same way on a padded rest.

2) Ammo is std Am. Eagle 55 gr FMJBT. Nothin' special, but it look like my WW likes them.

3) There was no center to these groups. Both groups had all shots touching. 6x was 1/4" (3 shots); 1x had 3 rounds in the same hole, and a fourth flyer. The 1-1/4 shift was distinctly obvious. Other than that, I was...pleased...considering I'm still breaking in the rifle!

4) Ditto on the vise--that's my first move tomorrow b4 I shoot again.

 

[CallMeChaz]

SOG's advice is good. You need more data. I'm betting on operator error, but I've seen enough bizarre problems with optics, including an SWFA scope, that I would not rule that out either.

If you have access to a laser boresight you could get this figured out without using any ammo.

Parallax can cause POI shifts, but 2.5moa? That seems like a big parallax error to me.

I've experienced parallax problems with scopes before, and no way they would shoot groups in the same hole, especially not twice in a row! And I have to concur that a 2.5 MOA from parallax would be a bit extreme. We shall see. Hoped to hit the range today, but not in the stars--now I gotta wait until Thursday. Arrgh.

"without using any ammo"--perish the thought! Ammo = bang = fun! I'm gonna secure it in a vise and dial it--that should be revealing.

 

[smokebomb]

Two different shooters had the same result? The exact same result?

It is difficult to comprehend, aside from a loose reticle or sticking erector assembly (or loose picture reversal assembly?), how your results are possible. Very interesting case!

A FFP reticle is located in the objective end of the erector assembly, versus SFP reticle being located in the ocular (rear) of the erector assembly, typically in the eye piece. As such, FFP reticle is not close to the magnification control.

Please keep us posted on your findings.

 

[SomeOtherGuy]

1) Windham Weaponry AR-15 carbine, HBAR, military handguard. All groups were shot with the handguard resting the same way on a padded rest.

2) Ammo is std Am. Eagle 55 gr FMJBT. Nothin' special, but it look like my WW likes them.

3) There was no center to these groups. Both groups had all shots touching. 6x was 1/4" (3 shots); 1x had 3 rounds in the same hole, and a fourth flyer. The 1-1/4 shift was distinctly obvious. Other than that, I was...pleased...considering I'm still breaking in the rifle!

4) Ditto on the vise--that's my first move tomorrow b4 I shoot again.

Just FYI, all shots touching with "groups" of American Eagle 55gr FMJ at 50 yards from a WW AR carbine is, well, among the best groups ever shot with that combination of factors. If the problem isn't resolved by vise testing, I would do 10 shot groups fired at a leisurely pace. I'm wondering if your 3-shot groups just happened to be in different spots by statistical chance, and if a larger group would have put the groups closer than any meaningful shift in POI.

Let us know!

 

[jdgray]

Parallax is a non issue if the shooter is centered behind the scope. If multiple shooters are getting the same result, I'd be looking at the optic. Any way you can lock the rifle in a gun vise, and dial the scope through the power ranges while looking through it?