TargetTalk

Total newb here when it comes to aperture sights. I'm putting them on a new rifle I'm building up. It will be used for biathlon (50 meters). Rear sight is an AirForce Adaptive sight. Fore sight will be a 22mm globe sight the make of which I have not decided on. I've read different recommendations concerning where in it's range of elevation the rear aperture should be set to measure it's height. These include: 1) at the bottom of the range, 2) in the middle of the range, and 3) 1/3rd of the way up from the bottom of the range.

1) seems to be inappropriate as there would be no more travel to adjust the aperture down. If you have a strong wind from the right side of the range downward adjustment would conceivably be needed as the wind may cause the bullet to rise.

2) and 3) seem reasonable with 3) seeming to make the most sense to my uneducated brain as I'm guessing one would want to have a greater range of upward adjustment for the rear aperture than downwards?

My reading suggests that height of the fore sight should be such that it brings the centerline of the fore sight aperture to the same height as the rear aperture centerline. Is this the correct approach in initially setting up the front and rear sights?

I'd appreciate any insight/instruction you all may be able to provide. Thanks in advance.

CJ

I guess it will depend on if you are only going to shoot the rifle at 50m or if you are planning on using it at other distances too. Gun fit will also make a bigger difference to the optimum positioning of the sight line. Most shooters find that they need the sights at differeing heights in each position, although as I believe you cannot change the rifle configuration during a Biathlon event you will need to find the comprimise that will work best for you.

It would be useful to know what barrel/action combination that you are using to build this rifle. Most of the major target actions have the rails for both front and rear sight at about the same level when the rifle is held horizontally. Most of the front globes are also built to a standard, non adjustable height. Most of the different 22mm globes that I have seen, mainly Anschutz (14 to 18xx series mostly, the 19/20xx are a bit different) as well as Walther and Centra branded units (I think Centra make the sights for Walther) all seem to have the tube mounted around 5 mm above the base. This will push the center of the aperture to about 16mm above the base. Many shooters use sight raising blocks to move the sight line higher, to maintain the best possible head position. The adjustable ones allowing much finer control. This is really important in the standing position as if the head is not upright it will affect the balance and induce sway. Adjusting the height of the front globe is not something one would normally have to worry about with most factory built match rifles, as the sight systems are designed to be compatable with them.

That will mostly place the center of the rear aperture just a little higher than that for 50m. This would normally put the adjustments somewhere in the middle of the range. It should certainly give you enough elevation left to comfortably get to 100 yards which with most of the common match ammo running at around 1050 fps will need between 6 and 8 moa (it will vary depending on the exact sightbase used.

There are both stepped block, and camming turnover designes for front globes that are popular with Dewar match shooters, they basically allow you to sight at 100 yards and then raise the foresight to make most of the adjustment down to 50 m/yds. Only needing a slight fine tune on the rear sight for ammo/sightbase/cant variations. This allows the shooter to keep a relativly constant head position between distances. This is really the only variation of front sight height being adjusted for zeroing that I am aware of in smallbore shooting.

Alan

CJ,

I think the instructions you have read may have been intended for Long-Range fullbore/Palma rifles. Having the rearsight low, gives maximum elevation adjustment for shooting out to 1000 yards. Alternatively when using one of the popular adjustable height foresights, major elevation adjustments for distance are made by adjusting the foresight, not the rearsight. The rearsight can be kept low. Remember that raising the cheekpiece may obstruct the bolt during loading.

As you are only shooting at 50m, you will only need enough elevation clicks to zero, and for wind. Yes it's good if the eyepeice is in the centre of the adjustments range, but unless your chosen rearsight has a very restricted elevation range, you should have enough. Some years ago I fitted a Steyr rearsight to an Anschutz rifle, it lacked enough elevation for 100 yards, but was fine at 50m.

If the foresight is a little too tall, so you cannot comfortable adjust the rearsight up enough, you can fit a raiser block under the rearsight. 4mm should be enough. Alternatively switch to a lower 18mm foresight tunnel.

BigAl and Tim S,

Thanks very much for your well considered replies to my questions. Your input is greatly appreciated.

By way of explanation. I'm building up a rifle based on a Primary Weapons Systems T-3 Summit action which is loosely based on the Ruger 10/22 action. The T-3 is a repeater however, not semiauto. The action has a toggle style bolt cocking mechanism which superficially resembles an Izhmash 7-3, 7-4. Unlike an Anschutz 1827F or an Izhmash biathlon rifle I'm not dealing with parts that are designed to work with each other in a unifed/integrated manner when it comes to sights, barrels etc.

Thanks again for your input.

CJ

In that case you will need a 10mm rail fitted on the receiver that can take a rear sight and at the muzzle end you will want to have a dovetail block fitted that will be at pretty much the same height above the bore line as the rear 10mm rail. I would suggest getting one made up to match the specification of the older Anschutz 14/18 series block. I suggest this pattern as it is specifically designed to be made up s a separate block. The only thing to note is that it is of a slightly different form factor to the standard 10mm rail. Specifically the shoulder angle is different, at I believe 60 degrees. That is the main difference although there may be a few other minor differences in the spec. All of the other front globe rail specs are for an integral milled type rail on the front end of the barrel, which I guess would be much harder to do in this case. If I were to see a separate block like that on the front of the rifle my first instinct would be for an Anschutz 14/18 series pattern, and that's what you would have.

Alan