How to calculate recoil/ eye relief needed?

[SD198]

Hi all - possibly a stupid question, but is there any way to calculate the amount of eye relief required to safely use a scope on a specific rifle? I have just ordered a scope with 45mm eye relief that I am concerned might not be enough for my .308 (which has a heavy varmint barrel and with this scope and my mod will weigh 5.5kg - shooting Federal Powershok 150gr, muzzle energy 2650ft/lb, muzzle velocity 2820fps).

Cheers

 

[potshotpat]

I remember reading a few years ago a similar question. The response that I remember that made sense to me was, using a garden bench the scope fixed to the bench. Chin on bench for eye relief and a straight edge upright for measuring distance from eye to scope. Then back to rifle. PS there's no such thing as a stupid question. I hope mines not a stupid answer

 

[Kalahari]

In my rather worthless and free opinion, I would reckon 4" (100mm) on a 308.

David.

 

[Tim.243]

Hi all - possibly a stupid question, but is there any way to calculate the amount of eye relief required to safely use a scope on a specific rifle? I have just ordered a scope with 45mm eye relief that I am concerned might not be enough for my .308 (which has a heavy varmint barrel and with this scope and my mod will weigh 5.5kg - shooting Federal Powershok 150gr, muzzle energy 2650ft/lb, muzzle velocity 2820fps).

Cheers

The eye relief will come from your shoulder and cheek weld on the stock in a repeatable position. Same as gun mount on a shot gun. mine is the same for a .22lr as a .270. bullet weights fps makes no difference.

 

[SD198]

I definitely don't need 100mm as my eye relief with my current scope is only 60mm (and never been "scoped"). My new scope is also a digital scope, which I have read some people say you can shoot with any eye relief without affecting accuracy (although I presume you might not get a full picture through the scope if your head was too far back)

 

[McKenzie]

I need a really long stock (lop of 16 1/4”) which was absolutely perfect with a S&B 6x42. I then fitted a Swarovski variable for a while & I just couldn’t get it to work as the eye box was too long. I’d have had to add yet another inch to the stock which seemed ridiculous so sold the scope & went back to the 6x42 which did everything I needed anyway & was one less thing to worry about.

 

[Selous]

I generally look for 90mm for most deer to large game calibres, especially in light rifles that some people love. My son had a 8x56 scope on his lightweight 308 with 80mm eye relief and a few times I felt the scope touch me, fortunately not hard. 90mm seems fine for most rifles but for calibres over .375 I like more than 90mm or use a red dot.

 

[Mungo]

Hi all - possibly a stupid question, but is there any way to calculate the amount of eye relief required to safely use a scope on a specific rifle? I have just ordered a scope with 45mm eye relief that I am concerned might not be enough for my .308 (which has a heavy varmint barrel and with this scope and my mod will weigh 5.5kg - shooting Federal Powershok 150gr, muzzle energy 2650ft/lb, muzzle velocity 2820fps).

Cheers

I think 45mm might be too close, though I don’t think there’s any standard way to estimate the right distance. It will depend on things like your hold, the stock fit and whether you’re shooting prone or standing.

I did try to work out what I needed once with an unmoderated .270. I got hold of a bunch of empty toilet roll tubes, and cut them into 0.5 increments, starting at 3cm. Blu tacked them against the objective lens of the existing scope. Settled into a shooting position, got a friend to measure the eye relief, and proceeded to shoot one shot. Kept increasing the length of the tube until it hit me.

It sort of worked, bar the fact that it was very hard to resist the urge to flinch. If memory serves, I needed about 7.5cm clearance with that gun when shooting from a bipod.

 

[SD198]

Thanks Mungo- I am thinking that as I know 60mm is ok for me with my rifle, I will see how am eye relief of 60mm looks through the new scope first. If I need to get closer to the new scope I will probably try your method. The manufacturer of my new scope has indicated that as it is digital "any eye relief will work to a degree" (by which I presume they mean it will not affect accuracy/ parallax, but would presumably reduce the picture size through the scope), it has been tested with .308 (Which might simply mean it can withstand use on a.308) and that it should be fine on a .308 " if you are careful" (Which does not fill me with huge degrees of confidence!).

 

[Mungo]

Thanks Mungo- I am thinking that as I know 60mm is ok for me with my rifle, I will see how am eye relief of 60mm looks through the new scope first. If I need to get closer to the new scope I will probably try your method. The manufacturer of my new scope has indicated that as it is digital "any eye relief will work to a degree" (by which I presume they mean it will not affect accuracy/ parallax, but would presumably reduce the picture size through the scope), it has been tested with .308 (Which might simply mean it can withstand use on a.308) and that it should be fine on a .308 " if you are careful" (Which does not fill me with huge degrees of confidence!).

Digital?

Which scope?

I was helping a friend zero a new digital scope at the weekend. He collected an absolute beauty of a cut on his eyebrow. Blood all over the place.

Though that was with a 7mmRM

 

[SD198]

Arken Zulus

 

[gixer1]

1) Get a small mirror….

2) Take the rifle out to a target or a soft bank or other suitable back stop.

3) Chamber a round and fire into the target/bank/backstop…

4) Lay rifle down.

5) Check mirror, if any bleeding, bruising or blindness is viewed, increase eye relief by 1/4” towards the barrel.

The above should be video’d and posted after test is complete.

Similar video for reference below.

 

[SD198]

Ha ha! I remember that scene from The Last Frontier v well - hence my concern!

 

[Heym SR20]

A lot depends on

1) how good are you at controlling recoil

2) shape of stock, angle of butt pad and the rifle recoils.

3) your shooting style and in particular position of your head

4) do you shoot mostly prone or from a sitting or standing position. Prone tends to angle your forehead and top of eye socket towards the scope.


Worst scoping I have had was my combination gun. It had a steeply buttpad, and a lot of drop on the stock. Probably for somebody very round in shape. It kicked upwards and stock would slide down my shoulder. It had a wooden end to the stock which didn’t help either.

Squaring the end of the stock and adding a recoil pad helped a lot. But adding a leather cheek piece helped much more as it stopped the rifle kicking up. I would have liked to move scope forward, but claw mounts prevented doing so.

Never had an issue since.

I always like to mount a scope so its good for prone shooting. But this can mean you need to push your head a little forward for a seated or standing shot. With a prone shot there is nowhere for your body to go with recoil. With a standing shot your whole body can move with the recoil.

 

[SD198]

Thanks! I almost always shoot standing off sticks, occasionally kneeling off sticks but never yet prone. The stock is per the pic below- you can't see it, but the buttpad is a pretty soft thick rubber at pretty much 90 degrees. The recoil has certainly reduced since I changed to this heavier stock- and the butt certainly stays in my shoulder. I always thought the best way to control recoil when standing was to lean forwards into the rifle- although I think you are suggesting it might be better to try to move backwards with the recoil?

 

[Hook'N'Bullet]

Hi all - possibly a stupid question, but is there any way to calculate the amount of eye relief required to safely use a scope on a specific rifle? I have just ordered a scope with 45mm eye relief that I am concerned might not be enough for my .308 (which has a heavy varmint barrel and with this scope and my mod will weigh 5.5kg - shooting Federal Powershok 150gr, muzzle energy 2650ft/lb, muzzle velocity 2820fps).

Cheers

I shoot .308 and once you get behind the gun with proper alignment and cheek weld it shouldn't be an issue.

 

[Klenchblaize]

A lot depends on

1) how good are you at controlling recoil

2) shape of stock, angle of butt pad and the rifle recoils.

3) your shooting style and in particular position of your head

4) do you shoot mostly prone or from a sitting or standing position. Prone tends to angle your forehead and top of eye socket towards the scope.


Worst scoping I have had was my combination gun. It had a steeply buttpad, and a lot of drop on the stock. Probably for somebody very round in shape. It kicked upwards and stock would slide down my shoulder. It had a wooden end to the stock which didn’t help either.

Squaring the end of the stock and adding a recoil pad helped a lot. But adding a leather cheek piece helped much more as it stopped the rifle kicking up. I would have liked to move scope forward, but claw mounts prevented doing so.

Never had an issue since.

I always like to mount a scope so its good for prone shooting. But this can mean you need to push your head a little forward for a seated or standing shot. With a prone shot there is nowhere for your body to go with recoil. With a standing shot your whole body can move with the recoil.

Item 3^

Some will no doubt argue that if you are supporting a rifle as you should according to the book all will be fine. You can however spend a lifetime shooting in a style other than Best Practice with no negatives. That is until you encounter a rifle with unfamiliar recoil!

K

 

[nun_hunter]

How you hold the rifle will affect the required eye relief to prevent you getting "scoped".

I fitted a rear add on to my Creedmoor rifle and shooting prone and seated with a decent hold of the rifle there is no issue and I think the eye relief is supposed to be a similar 45mm.

Laying prone but having to be bent almost 90⁰ shooting sideways to get a shot, I did catch a bit of the scope hitting me as I only had the lightest hold on the rifle and the butt wasn't firmly in my shoulder.

 

[Heym SR20]

I think the biggest challenge is lack of understanding these days on how to control recoil, and it seems that novice shooters are growing up with a view that a very light hold, and a rested position is the only way to shoot. This stems, I think from benchrest and heavy long range sniper style shooting with bags, bipods and non trigger hand controlling the butt, with shooters initially starting on PCP type air rifles.

If there is enough weight, and / or minimal recoil because of cartridge, muzzle break or moderator, this probably works. But with lightweight rifles and reasonably stout cartridges then this is a challenge. And 308 definitely has enough recoil that in a light rifle that doesn’t fit it can be troublesome. For that a 243 can also be irritating to shoot.

I am just old enough and started shooting long enough ago that learning to handle recoil was a prerequisite to accurate shooting. First centrefire rifle I really shot was as 14 year old cadet was .303 No4, and that certainly kicked if you didn’t hold it tight. And we all grew shooting spring powered air rifles, and they certainly jumped about. Bipods etc were unheard off. If you wanted support you used a sling or a bag.

And as for shotguns, in the 1980’s straight gripped side by sides still were the norm. And again you soon learned a firm grip on the barrels dramatically tamed a 12 bore.

I don’t have a lot of experience on image intensifing type optics, but they do seem to have a smaller eyebox with eye closer. And often they seem to need quite an unergonomic hold. Probably fine to shoot with minimal recoil. But I wouldn’t want to shoot one on a kicky rifle.

 

[Greener Jim]

....non trigger hand controlling the butt...

If there is enough weight, and / or minimal recoil because of cartridge, muzzle break or moderator, this probably works.

And if you have been away a while from large rifles and you ignore this, plus don't have a brake or mod, and it is a normal weight setup you get what is pictured

Eye relief is 90-100mm. Will hold forend next time, just like I did before I was spoiled by 22 and 357!