Rifle Scopes Rimfire Optic

[BallisticPrimate]

Anyone running a Bushnell 3-12 or 4.5-18 LRHS or LRTS on a .22lr? I'm putting together a trainer and since I've got these scopes I could repurpose one of them onto the rimfire. Obviously they parallax to about 50y, so not ideal but since most of my .22 shooting will be 50m+ I'm thinking they will be okay.

 

[Dthomas3523]

If you’re going to primarily training at 50+, you’ll be fine.

If you’re going to want to seriously compete in matches, you’ll want 25m or so focus.

 

[BallisticPrimate]

If you’re going to primarily training at 50+, you’ll be fine.

If you’re going to want to seriously compete in matches, you’ll want 25m or so focus.

Roger that, where would you steer someone for a dedicated rimfire optic, 1.5K budget? My S&B 3-20 will focus at 20m, but I'd prefer not to pull it off my match rifle if I can help it

 

[Dthomas3523]

Roger that, where would you steer someone for a dedicated rimfire optic, 1.5K budget? My S&B 3-20 will focus at 20m, but I'd prefer not to pull it off my match rifle if I can help it

Probably and Athlon Cronus in that price ranfe.

Or a vortex amg if you get a deal on a used one.

Also, the soon to be released NF nx8’s shouldn’t be too much more.

 

[beetroot]

Having 25m/yard parallax is a must for a 22lr in my opinion.
I used to think 50yards would be fine and you can dial back the magnification, but with all the good options out there why compromise?

I've just put a Vortex PST 5-25x50 on my 22lr and think it's fantastic for the price.
The 25m parallax came in handy from the instant I installed it, vs the annoyance I've had from the scope it replaced.

 

[BallisticPrimate]

Having 25m/yard parallax is a must for a 22lr in my opinion.
I used to think 50yards would be fine and you can dial back the magnification, but with all the good options out there why compromise?

I've just put a Vortex PST 5-25x50 on my 22lr and think it's fantastic for the price.
The 25m parallax came in handy from the instant I installed it, vs the annoyance I've had from the scope it replaced.

Thanks for the input. Why is 25M parallax a "must", can someone quantify the degree of error that parallax can impart at close ranges - probably a job for our resident optics wizard, @koshkin?

 

[beetroot]

Thanks for the input. Why is 25M parallax a "must", can someone quantify the degree of error that parallax can impart at close ranges - probably a job for our resident optics wizard, @koshkin?

The parallax error up close far worse than what you experience at longer distances.
The scope I replaced had 50yard parallax, I could just get it to work on max magnification at 40 yards, but anything less required dialing back the magnification.
From memory I had to drop it to 7x (twas a 3-15) to get a reticle that was even remotely usable.

 

[Dev L]

From my understanding, parallax error is at maximum with your head fully to one side or the other or top or bottom of view... AKA maximally off center. At that level, just before losing your view, you will have the parallax error equal half your objective diameter at double your parallax distance or your entire objective diameter shooting from one extreme side of your scope view to the other. When you reverse that, and shoot at half the distance of parallax, you get the same thing, but half as much, when the target is at half the parallax distance. So for a 50 yard parallax shooting at 25 yards using a 50mm objective you could have reticle movement of 25mm maximum or 1" of total increase in group size if you shot from edge of view. If your head was never off center from your scope you would always have zero parallax shift. In reality, we try to center our heads behind a scope, not shoot from an extreme offset, nor do we always shoot perfectly centered, though we try. So if you are not shooting from a barrier and even try a little you will not be more than halfway to the edge, so perhaps a maximum of .25" increase in group size by having your head off center for a shot here or there.

That is more than the total group size of a high end .22lr and parallax alone could make you miss left then miss right a 1 MOA target at close range just from head position with crosshairs perfectly centered on target. That means 25yd vs 50yd parallax can be more important than a rifle shooting sub MOA group size.

Also, remember that more magnification reduces deoth of field and reducing magnification improves the depth of field, or the range of distances in focus from your parallax setting. So reducing magnification might make your target in focus, but the lower magnigication wont stop your parallax shift of the reticle based on head position.

Also, you get a spherical aberration at closer distances that can cause a tiny bit of additional distortion and shift, but that is much stronger the further you get off center and also less than parallax error.

A scope that does 35 yards minimum parallax and disciined head positioning might cut it, at 25 yards, but 50 yards minimum will not, unless you are a perfect shooter with perfection in ability to sit in your optical center.

 

[Rebels010]

I've always been a fan of the SWFA SS 3-15x42 for rimfire trainers assuming you are ok with the reticle. It focuses down to 6 meters.

That said, since you already have the scopes, just run it and let your results be your feedback. That's assuming you already have some data on your training rifle.

 

[One1Bravo]

I put an Athlon Ares ETR on my rimfire.

 

[BallisticPrimate]

It's not so much a matter of parallax error is the fact that your parallax knob does function as a side focus at those ranges. You can't resolve the image without zooming out. So you might find yourself working your scope like a sound board when indexing multiple targets at different ranges, eating up time and complicating the process.

Copy that, good info, thanks.

 

[koshkin]

Lots of good advice here already.

On depth of field: the higher the magnification and the closer the target distance, the shallower is the depth of field in absolute terms. If you want to use your top magnification at 25 yards, it is a good practice to get a scope that is designed to focus down to 20 yards. In other words, leave yourself some margin. There is sample to sample variation and also some variation due to individual eyes.

Years ago I made a somewhat crude parallax calculator. I dug it up and made this snapshot. This is for a 4.5-18x44 riflescope set up to be parallax free at 50 yards and assuming a 2mm eye pupil (broad daylight):

Keep in mind that I made this a long time ago, so I do not remember offhand all the assumptions I made. It should be fairly close, but do not take it as gospel.

ILya

 

[BallisticPrimate]

Lots of good advice here already.

On depth of field: the higher the magnification and the closer the target distance, the shallower is the depth of field in absolute terms. If you want to use your top magnification at 25 yards, it is a good practice to get a scope that is designed to focus down to 20 yards. In other words, leave yourself some margin. There is sample to sample variation and also some variation due to individual eyes.

Years ago I made a somewhat crude parallax calculator. I dug it up and made this snapshot. This is for a 4.5-18x44 riflescope set up to be parallax free at 50 yards and assuming a 2mm eye pupil (broad daylight):

View attachment 7059413

Keep in mind that I made this a long time ago, so I do not remember offhand all the assumptions I made. It should be fairly close, but do not take it as gospel.

ILya

Thank you ILya, the amount of genuinely useful information on tap here never ceases to amaze me.

Hat Tip GIF - The Big Lebowski The Stranger Sam Elliott - Discover & Share GIFs

Click to view the GIF

tenor.com

 

[Dev L]

Ah, I see how reducing magnification could reduce parallax error due to "effective" objective size, thanks!

Your exit pupil is just objective size/magnification. If you have a scope that does not have an exit pupil spec at low power that matches what is expected, it is because the scope is not making full use of your objective lens. Since parallax error is based off your objective lens size you could calculate the effective objective size at minimum magnification.

Lets say you have a 50mm objective on a 2-10× scope. Your exit pupil at max magnification is 5mm because objective/magnification=exit pupil. At 2× it would be 25mm if it used the whole objective. Instead the spec is only 12.5mm so your scope is only using 25mm of the objective lens. You just use exit pupil x magnification = objective size to get effective objective lens size at low power.

Also, as distance increases by a multiple of the parallax setting, the parallax error doubles goes up by the same amount.

So if you are set to 50y parallax on a 50mm objective, your error goes from 25mm per side or 50mm total at 100y, to 50mm per side/100mm total at 150y, 75mm per side/150mm total at 200y etc.

 

[flatland1]

It's not unusual for me to experience some level of disappointment when I move down a notch or two in scope price range from the Kahles K624i or Athlon Cronus scopes I have on several of my CF PRS & 22RF precision rifles. So after mounting an Athlon Midas TAC 6-24x50 on a lightweight V-22 carbine, I was a little surprised at how pleasant it is to shoot behind the TAC. That's not to say that I don't appreciate the optical quality of the Cronus, but the TAC is no slouch - and it does focus down to 10yds. So, if size & weight aren't an issue, and you want the best at the top of the price range you mentioned, go with a Cronus. If you want something smaller & lighter, and would just as soon spend the price difference on a case of good 22RF ammo, go with a TAC.

 

[koshkin]

Ah, I see how reducing magnification could reduce parallax error due to "effective" objective size, thanks!

Your exit pupil is just objective size/magnification. If you have a scope that does not have an exit pupil spec at low power that matches what is expected, it is because the scope is not making full use of your objective lens. Since parallax error is based off your objective lens size you could calculate the effective objective size at minimum magnification.

Lets say you have a 50mm objective on a 2-10× scope. Your exit pupil at max magnification is 5mm because objective/magnification=exit pupil. At 2× it would be 25mm if it used the whole objective. Instead the spec is only 12.5mm so your scope is only using 25mm of the objective lens. You just use exit pupil x magnification = objective size to get effective objective lens size at low power.

Also, as distance increases by a multiple of the parallax setting, the parallax error doubles goes up by the same amount.

So if you are set to 50y parallax on a 50mm objective, your error goes from 25mm per side or 50mm total at 100y, to 50mm per side/100mm total at 150y, 75mm per side/150mm total at 200y etc.

One of the problems with the way scopes are specified is that the effective objective diameter on low power is usually not listed. If the exit pupil is listed and magnification is accurate, you can calculate it.

Another factor not usually taken into account is the size of the eye pupil. There is a fudge factor there because edge of the eye pupil can overlap somewhat with the edge of exit pupil while still delivering a somewhat decent image, but by how much is not clear. That means that you will get different effective maximum parallax at different times of day.

ILya

 

[BallisticPrimate]

Thoughts on the Vortex PST Gen 2 3-15 as a rimfire optic?

If .22 matches can be shot as close as 20m why do so many guys use scopes with 6x or 5x low end minimum magnification?

 

[Dthomas3523]

Thoughts on the Vortex PST Gen 2 3-15 as a rimfire optic?

If .22 matches can be shot as close as 20m why do so many guys use scopes with 6x or 5x low end minimum magnification?

Small targets. The high magnification helps a lot.

When you have a 1/4” on kyl rack at 25 or 50yds, you won’t be at 6x.

 

[Dthomas3523]

Or a .035mil dot on paper at 30 yds. Or a playing card sideways and toothpicks at 30-50yds.

 

[Hondo64d]

Roger that, where would you steer someone for a dedicated rimfire optic, 1.5K budget? My S&B 3-20 will focus at 20m, but I'd prefer not to pull it off my match rifle if I can help it

Nightforce SHV F1.

John

 

[beetroot]

Thoughts on the Vortex PST Gen 2 3-15 as a rimfire optic?

If .22 matches can be shot as close as 20m why do so many guys use scopes with 6x or 5x low end minimum magnification?

I've just put a 5-25 PST on one of my 22s.
I'm extremely impressed with the glass quality for the price, far exceed my expectation.

If you don't intend to hunt with this rifle then I see little disadvantage going for the 5-25.
But realistically, the FOV is so good on the Gen 2 PSTs I don't foresee the 5x minimum being an issue.