Rifle Scopes Scope box test expectations?

[jlow]

I am ready to do a box test on my NF scope, my question to the hide is since nothing is absolutely perfect, how accurate should I expect the results to be?

I plan to have a box that is 19 MOA on each side shooting three rounds of sub-MOA handloads at the middle and after each adjustment for the corner shots. Specifically my question is how far from the theoretical target in the corners would one consider the scope to be doing well or fail?

 

[Topstrap]

Re: Scope box test expectations?

I'd guess depending on the distance, you'd expect group size and it to be right on the money after each adjustment. If it isn't spot on at 100 yards or whatever distance you pick to do the test at then making an adjustment at 1000 yards based on a miss call you'd expect it to be right. You should probably do that test multiple times so you can have a wider test base to compare.

Assuming you already did a verticle tracking test thru a few revolutions the box should be perfectly square and return exactly to where you started taking into account your normal group size.

Topstrap

 

[doc76251]

Re: Scope box test expectations?

Doing the box test A$$uME's 2 very certain things.

1. You have a rifle and a load that can consistently shoot sub 1/4 MOA.

2. You are capable of the same standard as the rifle.

I don't know too many folks that can do that time after time shot after shot, myself included.

Soooooooo, what do you do?

Understand the limitations of the shooter and platform.

Inject enough movement in the dials to establish whether it is the shooter/rifle/ammo or the scope.

To minimize errors and maximize travel, shoot the box at 50 yards and dial at least 20 MOA in any and all directions.

Enjoy!

Cheers,

Doc

 

[jlow]

Re: Scope box test expectations?

Thanks guys, all good questions.

First, I will be doing the test at 100 yards to minimize environmental conditions on the ballistics. The rifle is based on a LaRue Stealth 20” upper and is with my handloads sub-MOA capable, not ¼ MOA. Here is a 7 round group I did yesterday off the bench using a Lead Sled again at 100 yards – group size is 0.614 MOA.

I don’t think I will be ¼ MOA capable anytime soon, but am not convinced that this is absolutely necessary for this assessment. The reason being that I will be shooting three round groups and so will be using their average value to assess where the true POI will be.

I also think that it would be almost impossible to judge a difference between ½ vs ¼ MOA off in terms of the’s capability scope since there is just too much human/mechanical/environmental conditions which could affect that outside of the scope itself. However, having said so, I would still like to know what is reasonable in terms of errors for the scope.

I don’t shoot 1K but do shoot at 600 yards and so that would be my practical benchmark. I plan on shooting the center again after initial center shot and going around the box to confirm the ability of the scope to return to zero.

 

[jlow]

Re: Scope box test expectations?

Surprised no one on the hide that has done this would share their experience with us?

 

[Lowlight]

Re: Scope box test expectations?

I dial from top to bottom of 4ft ruler and use FFS to calculate the exact amount of travel. Gives me the exact error to the 100ths.

On video I have shot box tests similar to your description mostly I travel about 10 mils as opposed to 20 MOA which is the bare minimum to test. You have to figure how much error you might see. For an example there was a .5MOA scope that actually only adjust .43MOA so at .07 x 20 you need to be close enough to not mistake this for group size and shooter error.

Generally speaking you want the reference point to have a horizontal line and the group should touch it. In the age of ballistic computers calibrating the scope so you know the actual adjustment range is vital.

 

[dcjs]

Re: Scope box test expectations?

Shooting a scoped rifle in order to do a "box test" is a very poor way of testing a scope for proper tracking. You will only gain very little insight into potential problems, and to get even that little, you need to do a lot of shooting with a very accurate rifle/shooter/conditions setup.

The proper way to check the tracking is bolting the scope to a solid table with some kind of fixture and turning the knobs while watching the reticle move on a test target.

 

[jlow]

Re: Scope box test expectations?

Thanks a lot for helping guys! A few questions:

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">I dial from top to bottom of 4ft ruler and use FFS to calculate the exact amount of travel. Gives me the exact error to the 100ths.</div></div>
Sorry, a little confused here. I understand you are looking at a 4ft ruler, just not sure what FFS is? Also would this be a scope locked on to a bench and just looking at visual movements?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">On video I have shot box tests similar to your description mostly I travel about 10 mils as opposed to 20 MOA which is the bare minimum to test. You have to figure how much error you might see. For an example there was a .5MOA scope that actually only adjust .43MOA so at .07 x 20 you need to be close enough to not mistake this for group size and shooter error. </div></div>
Looks like I need to extend at least my vertical component of my box to at least 40 MOA – thanks.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: David S.</div><div class="ubbcode-body">The proper way to check the tracking is bolting the scope to a solid table with some kind of fixture and turning the knobs while watching the reticle move on a test target. </div></div>
I understand the concept and it is a good one. The biggest problem I have is finding a way to fix the scope solid enough so that one, I can still maneuver it to the gauge down range, and two, when I turn the knobs it does not move the whole scope. Any suggestions?

 

[LoneWolfUSMC]

Re: Scope box test expectations?

Harbor Freight bench vise and proper padding. Just don't twist the handle too much or you may hear a "crunch".

Honestly, I test mine on the rifle shooting it because I will use it on the rifle by shooting with it.

I run a vertical test out to 9-10 mils (depending on the size of my target backer). I also run a tracking test like Frank has shown on the videos by sticking dots on the backer and measuring then dialing corrections to engage them from a known starting point. This demonstrates to me that the reticle and the turrets are equal. The vertical test tells me if the reticle and turrets are correct.

 

[azimutha]

Re: Scope box test expectations?

I've taken an old wooden yardstick (verified with a measuring tape first) and stapled it to the backstop to make sure I was setting up at 100 yards (just centered the reticle with the middle of the yardstick @ 18" and back it up a little until the whole yardstick fit exactly inside 10 mils). But otherwise, I agree with LoneWolf's reasoning. I'd rather test by shooting, even if there is a degree of error caused by shooter ability or rifle/ammo capability. If you're a consistent .5 MOA shooter, you'll do fine.

If it works better for you, Doc's suggestion of going to 50 yards will still test the scope's ability to track. It's an angle thing. Just be sure that the target is incremented in the number of inches/CMs that would be subtended @ 50 yards, e.g. 1.8" per mil or 0.5235" per MOA.

I really like shooting a dot drill with a 3x5 grid of 1/2" diamonds spaced 1 mil apart. Every shot's POA is the center bottom diamond. Although it is not a full 10 mil target I feel it still is a good indication of the scope's accuracy, especially if you dial up 4 mils and 1 mil left (to hit a far corner) then dial down 4 and 2 right to hit the right lower corner, then do the other two corners.

 

[jlow]

Re: Scope box test expectations?

Thanks guys for more great input and ideas!

<span style="text-decoration: underline">LoneWolfUSMC</span>: I have bench vise but did not think of using it, but yes it would probably work if I end up using this method.

In general, I like the concept of bolting down the scope and looking through it to see where it goes when I dial, but I am still not totally convinced that I can hold the scope down firm enough so that there is no movement at all. The scope is a NSX 8-32x56 and so at full power, even a very slight slippage will make a huge difference.

The flip side is that I do buy into the idea that testing the scope using live rounds is the true test of a scope i.e. with recoil. As it is, I loaded some rounds for a test overnight before I got David S’s response and so since I have the rounds, it would not hurt to give it a go. Will be doing one where the elevation range will be around 40 MOA. I figure I can always come back and do the bench vise cold test. Regardless, it is good to have more than one method so that I have a backup plan.

<span style="text-decoration: underline">Azimutha</span>: I will probably do it at 100 yards since I am comfortable with my rifle/loads at that range.

 

[turbo54]

Re: Scope box test expectations?

Don't forget to use the test to ALSO ensure your scope is mounted level.

Use a level on your target and be sure the target is square. The vertical and horizontal spreads of your shots can be measured to check parallelism with the edges of your target. If they're not, your scope is askew, or your holding it askew.

 

[turbo54]

Re: Scope box test expectations?

Oh, another point: Do your testing up close so you can twist the knobs more!

 

[dcjs]

Re: Scope box test expectations?

Of course doing a simple box test is far better than doing nothing, but the only thing you can really check this way with any level of confidence is verifying the correct click value, and even doing that doesn't require shooting a box.

I would certainly not put a scope into a vise, but rather mount a piece of picatinny rail to a steady table or whatever else that is solid enough and then put the scope on the rail. Make sure to level the scope by putting a spirit level onto the elevation turret (in order to check for reticle cant).

When looking through the scope while dialing, you can see the movement of the reticle continuously in real time, vs. collecting not very accurate single data points by dialing and shooting groups.

Sure you can test a scope by shooting it, but getting the same information with the same level of confidence you will get by spending 10 minutes turning knobs on a test target will cost you hundreds of rounds and hours of shooting. Those that believe that "you should test a scope by shooting because you will use it for shooting" should consider this: It is the first shot after twisting the knobs that counts, so adjusting the scope and then shooting a group may result in one "flyer" that was actually the first shot of the group after which the reticle has settled. So the first thing to do is firing only <span style="font-style: italic">one</span> shot after adjusting the reticle, then twist back and to the previous position again, so you are always firing the "first shot" after adjusting. Another thing to consider is that the reticle may reach a certain position without problems when approaching it form one end of the travel range vs. the other end of the travel range, because the erector spring is compressed vs. relieved depending on the direction of the movement. So you would have to approach every single position you want to check from every one of the four directions, every time before the shot.

Once you have seen <span style="font-style: italic">how</span> a scope can misbehave during tracking and learned <span style="font-style: italic">what</span> can cause this misbehavior, you will understand that adjusting and shooting groups is a very weak tool when it comes to checking correct tracking.

 

[Lowlight]

Re: Scope box test expectations?

David,

One issue you failed to mention is a scope that when shot goes to hell in short order, sometimes shooting it, is the best way to find out if it will continue to work.

A great example is the rash of the Gen (1) 3-18X IOR scopes a few years back most seemed to fail around the 200 round mark. Something there failed and turning the knobs didn't provoke it, shooting it did.

From your standpoint you're looking at it from a point of production and repair, you test it once at a bench call it good box it and go, or you test it at the bench to diagnose the problem in order to fix it. We are interested in shooting it and seeing how it holds up the recoil, and does the adjustment match the reticle exactly as LW explained. This level over confidence is better for most than seeing if it can follow a sigher chart off the rifle. All that tells a "shooter' is, the scope is not broken out of the box, not that it can handle recoil.

The points are definitely valid, and if you have a calibrated chart in your garage would be a good thing to test before mounting but I would still test it on the rifle under recoil. This way if things do go wrong with 500 rounds under it, you'll know.

 

[Supersubes]

Re: Scope box test expectations?

I don' think there is much value in stabilizing the scope and watching tracking. They did that at the factory with nicer instruements than you can come up with.


I agree completely with David S. about the first shot after the adjustment. Run your box test forward and backwards a few times using single shots,the groups will distribute themselves.

 

[jlow]

Re: Scope box test expectations?

Great feedback guys! It is really useful to hear a debate about the pros and cons of the various methods!

<span style="text-decoration: underline">Turbo54</span>: Good point about leveling in terms of mounting, I got to remember to make sure the gun is also level when mounted on the Lead Sled too…

<span style="text-decoration: underline">David S</span>.: Point taken about approaching it from different position, can’t cover all the possible basis (cost too much as you pointed out), but I will make sure that I don’t shoot the three rounds at each location as a group but as singles and then come back at it from the opposite direction i.e. clockwise, counterclockwise, and back to clockwise)

<span style="text-decoration: underline">Lowlight</span>: I agree, that potential recoil-induced problem is one I was looking for with the round-based test.

I guess my take home message from reading about the two methods is that there are pluses and minuses with both methods which is what one would expect.

This is all great stuff, but one thing I was looking for in the OP I am still wondering about which is if I do the test and the scope is off, how much is too much. I imagine one can adjust for it once you know how much it is off, but when would one say this is too much and it goes back to the factory? Not that I think this is going to happen for any reason as the scope appears to work, but just wondering.

 

[Lowlight]

Re: Scope box test expectations?

I should note, that I use a 4ft Level and not a 4ft Ruler, it was basically a complicated typo.

But I use the Level, which I level on the target board with a set of clamps, and then run the scope top to bottom. <span style="font-style: italic">(placing the crosshairs at the top, dialing up moving it down)</span> Because it's bright yellow it is easy to see and move along. A good front rest with a couple of rear bags, sandbags on the back of the stock usually keeps it still enough.

I wouldn't want to work with a scope long term that off more than 2 clicks +/- . One click off I can deal with, 2 puts it out of spec to me.

 

[dcjs]

Re: Scope box test expectations?

Frank,

of course recoil may lead to (additional) problems, but I believe in test setups that isolate potential problems as far as possible. Having a "clean" result when visually checking tracking can exclude irregular tracking as a cause of erratic first-round hits, while erratic groups can not be attributed to one specific cause without further investigation. Checking for consistent POI under recoil can be done seperately from the whole box test issue a lot more easily.

 

[jlow]

Re: Scope box test expectations?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">I should note, that I use a 4ft Level and not a 4ft Ruler, it was basically a complicated typo.

But I use the Level, which I level on the target board with a set of clamps, and then run the scope top to bottom. <span style="font-style: italic">(placing the crosshairs at the top, dialing up moving it down)</span> Because it's bright yellow it is easy to see and move along. A good front rest with a couple of rear bags, sandbags on the back of the stock usually keeps it still enough.

I wouldn't want to work with a scope long term that off more than 2 clicks +/- . One click off I can deal with, 2 puts it out of spec to me. </div></div>
Thanks lowlight! Not a problem with the typo but good reminder for me to bring my level!

Thanks for all the tips and advice!

 

[EventHorizon]

Re: Scope box test expectations?

Great thread and tagging for future reference.

 

[shootist2004]

Re: Scope box test expectations?

http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/References/

 

[TxShooter63]

Re: Scope box test expectations?

The box test is very valuable in checking scope function. You have to allow for your inability to shoot perfectly but there are many scopes that completely fail a box test. My guess is your NF will be fine but it never hurts to check.

 

[jlow]

Re: Scope box test expectations?

<span style="text-decoration: underline">shootist2004 </span>- Thanks for the useful links.

<span style="text-decoration: underline">TxShooter63 </span>- Yes this are my thoughts exactly.

 

[Mall Ninja308556]

Re: Scope box test expectations?

Is the main reason for a box test to see if the scope "clickers" are accurate or is it more the scopes ability to return back to a proper zero afterwords?

I did a quick and dirty this last weekend. I went up 10 clicks (mil/mil) right 20, then down 10 then left 20. At the end the scope went back to shooting exactly at "zero".

I also at the same time drew 1" dots 3.6" apart and put the target at 100 yards and leveled it. My mil dots lined up perfectly with the dots on the target so I know my reticle is accurate dimensionally also. I shot 3 round groups 10 clicks in between up a total of 40 clicks. The 3 round groups all lined up perfectly vertical, so I know I leveled my cross hairs perfectly (thanks to you guys).

 

[Lowlight]

Re: Scope box test expectations?

A box untaken with any thing less than 20" is pretty much a waste of time and energy.

Errors compound, in order to see the errors you have to compound them enough to add up to something significant. So you should box test what would essentially be 100% of the rifles max effective range. For a 308 that would be between 10 and 12 mils or at least 36MOA in order to test the accuracy of the scope. Some have a small fall off, so what if your scope is 5% wrong you need to move it enough to see.

The return to zero is important also but again, you need to move it enough to find a potential problem.

 

[LoneWolfUSMC]

Re: Scope box test expectations?

Many cheap scopes will return to zero. The tests I run are to check the turrets track the appropriate distance. Return to zero is easy to check for when doing a tracking test.

 

[Infinity]

tag for later