Thoughts on using the Kobra.


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benEzra
June 11, 2008, 06:27 PM
I posted the following on an AK forum, but I know there are a lot of AK aficionados here as well, so...


I run a Kobra EKP-8-02 (slimline button-cell version of the Kobra) on my SAR-1.

https://lh4.googleusercontent.com/-qsXQ_43rIzU/TxgwY4fQpnI/AAAAAAAAABI/BhMKEZq6Z8U/s497/gallery_260_23_3070.jpg

After about a year and a half of messing with it, shooting it, and even a little USPSA carbine with it, here are some thoughts and observations:

One of the first things you notice about the Kobra is that it is a very tall sight (3.8" from the bore axis to the center of the lens for the EKP-8-02; I assume it is probably the same for the AA models, but have never measured one).

https://lh3.googleusercontent.com/-WTVLxwmfHng/Txgwf8tr05I/AAAAAAAAAEM/_7kq3IrOd6Q/s912/gallery_260_23_20379.jpg

While a tall optic is usually viewed as a disadvantage (and it it prevents you from being able to cowitness the irons), it actually does have some advantages with regard to shooting at moderate distances. According to my ballistics program, with your typical 122/123 grain FMJ and JHP, if you zero the dot at 50 yards, you are only 2" high at 100 yards, close to dead-on at 200 (0.6" high), and only 14.4" low at 300 yards, which is about my limit with an unmagnified optic and 7.62x39mm anyway. The tall sight height keeps the bullet closer to the line of sight between 20 and 200 yards.

The downside of a tall sight height, though, is that at close range, the bullet starts out LOW. At the muzzle, the bullet is 3.8" below the dot, and angles up until it crosses the dot at 50 yards (assuming a 50-yard zero). BUT, the Kobra's other reticles give you lower aiming points that allow you to compensate some. The top of the chevron is right on around 20-25 yards, IIRC, but my favorite reticle for close-range shooting (like typical USPSA stages) is the T-bar:

https://lh5.googleusercontent.com/-GMBhM9Agf6c/TxgwaynB7GI/AAAAAAAAACM/7jVCu_3bAX8/s168/gallery_260_23_7964.jpg

At around 7 yards or so, the bullet trajectory crosses the bottom of the central bar, so anywhere between about 7 and 50 yards, the bullet will hit between the bottom of the central bar and the top of the reticle (even with the top of the "T"). Between about 7 and ~20 yards, the bullet will land between the bottom and the top of the central bar. So at close range, if you place the central bar of the T-bar over the target, you WILL hit it; at such close range, it's a pretty precise aiming point.

You can experiment with the dot-chevron reticle in similar fashion:

https://lh6.googleusercontent.com/-pmT7Me0R9kk/TxgwaO4lDHI/AAAAAAAAABw/U0-BRvM1xXE/s384/gallery_260_23_6447.jpg

The bullet reaches the bottom of the chevron between 10 and 15 yards if the dot is zeroed at 50 yards, so for unknown-distance shooting that might involve some longer shots, I prefer the dot-chevron since the T-bar lacks a precise aiming point for longer shots.

Another thing, not all that practical but interesting nonetheless. If you need to shoot from very low prone, or beneath low cover such as a vehicle, Sonny Puzikas and others have suggested turning the rifle sideways with the ejection port up and using the charging handle as a crude sight, to get the gun closer to the ground than the magazine will allow. Well, with an optic, you can just use the optic, if you can get an eye low enough. Just on a whim, I ran the numbers for bullet drop for a rifle turned sideways (sight height zero, no correction for drop) using the optic, and the bullet doesn't even drop an inch until 40 yards, and is only ~3 inches low at 100 yards. Left/right error is more pronounced; with the rifle turned sideways, the bullet starts out 3.8 inches left of the dot and drifts to the right, until it crosses the line of sight at an unknown distance (probably around 25-30 yards, but you'd have to verify at the range) and keeps moving to the right with increasing distance. With the rifle flat, left-right error will throw you off before bullet drop will, but a back-of-the-envelope guesstimate says that you'll still hit within 50-100 yards. Not sure if there's much real-world application for most of us, but it's interesting anyway. And I'll bet that if you used the T-bar reticle, aiming with the bottom of the central bar would greatly reduce lateral error. I may try it next time I get to the range, just out of curiosity (assuming the range is deserted enough that I can do so without getting any "Why are you shooting your rifle sideways like a doofus?" comments).

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MythBuster
June 11, 2008, 07:01 PM
The Kobra does not sit exactly over the line of the bore. It sits off to the left slightly.

If you get your windage zero dead on at closer ranges say 50 to 75 yards or so it will be WAY off at much longer ranges.

Dead on at 75 yards can mean it will shoot as much as two foot to the left at 300 to 400 yards.

Get your windage zero as far away as you can. Then it will only be just slighly off at coser ranges. Not enough to make any real difference.

benEzra
June 11, 2008, 10:52 PM
I think you may be thinking of the PK-AS, which is offset to the left? The Kobra, at least the EKP-8-02 on mine, puts the center of the lens directly over the bore. Mine is zeroed at 50 and is still centered left/right at 200.

http://tantal.kalashnikov.guns.ru/media2/pkasadjustmontage02.jpg
PK-AS (left offset)


http://tantal.kalashnikov.guns.ru/media2/kobra10501.jpg
Kobra (centered over bore)

According to Tantal,

http://tantal.kalashnikov.guns.ru/kobra1.html

The filtered lens allows crystal clear viewing and the mounting bracket (which is an integral part of the sight) is centered over the bore for comfortable shooting by both right or left handed end users.

chris in va
June 11, 2008, 11:26 PM
My friend has that PK-AS on his Arsenal. What a PITA that thing is to adjust. Too high, off to the side also.

I'd like to get something that sits right on the centerline, has a Weaver rail and doesn't cost over $50. Most I've seen are too high off the cover.

Coronach
June 11, 2008, 11:29 PM
Ditto. I have yet to see a combloc sidemount rail that doesn't offset the optic way left or sit it up unacceptably high.

Mike

rocinante
June 12, 2008, 07:50 AM
I have a kobra on my saiga. Great write up I will keep and absorb.

stubbicatt
June 12, 2008, 07:55 AM
I like the Kobra for fair weather shooting, but it is useless when it is snowing. Ugh.

benEzra
June 12, 2008, 10:12 AM
I'd like to get something that sits right on the centerline, has a Weaver rail and doesn't cost over $50. Most I've seen are too high off the cover.
You can get something like this:

http://www.sportsmansguide.com/net/cb/cb.aspx?a=359268

but then you have to get something to mount to it, and the Picatinny rail and the necessary mount under the optic raise the optic higher.

Ditto. I have yet to see a combloc sidemount rail that doesn't offset the optic way left or sit it up unacceptably high.
Given the 7.62x39mm's rainbow-like trajectory, a tall sight height has advantages in terms of keeping the trajectory close to the line of sight. The downside is that you're low at close range, but an optic (Kobra or not) with multiple aiming points can help mitigate that.

It's a tradeoff, but I'd rather have the Kobra's sight height compared to something right over the bore. Also, the Kobra lets me shoot from a heads-up position instead of having to scrunch my head down like you have to do with an AK using irons or a cowitnessed red dot. Shooting head-down with glasses doesn't work out so well for me due to edge distortion.

I like the Kobra for fair weather shooting, but it is useless when it is snowing. Ugh.
Doesn't snow around here. I've shot the Kobra in light rain (it's waterproof), but I imagine a hard rain could also obscure the reticle if you let water build up in front of the projection lens.

MTMilitiaman
June 12, 2008, 03:28 PM
I run a Kobra EKP-1S-03M on my Romanian AK. I have never noticed it being to the left of centerline, and seriously doubt if it is. I shoot left handed, and having the optic even a tiny bit off the centerline would be noticeably more awkward. Mine isn't, and while it is a little high, it is low enough to allow a much better cheek weld than the PK-AS-V red dot I had on it before.

Here is another pic through the Kobra, at a 16 inch wide torso target at 50 yards:
http://i99.photobucket.com/albums/l308/MTMilitiaman/Guns/Kobraviewchevronwithdot.jpg

And the optic on my rifle:

http://i99.photobucket.com/albums/l308/MTMilitiaman/Guns/AKKobraleftside.jpg

http://i99.photobucket.com/albums/l308/MTMilitiaman/Guns/AKswithoptics.jpg

Coronach
June 12, 2008, 04:27 PM
Given the 7.62x39mm's rainbow-like trajectory, a tall sight height has advantages in terms of keeping the trajectory close to the line of sight. The downside is that you're low at close range, but an optic (Kobra or not) with multiple aiming points can help mitigate that.

It's a tradeoff, but I'd rather have the Kobra's sight height compared to something right over the bore. Also, the Kobra lets me shoot from a heads-up position instead of having to scrunch my head down like you have to do with an AK using irons or a cowitnessed red dot. Shooting head-down with glasses doesn't work out so well for me due to edge distortion.It's the lack of cheekweld that annoys me. A cheek piece will solve it, but it gets slower when you want to switch to irons.

Mike

benEzra
June 12, 2008, 07:58 PM
The Kobra sits too low for you to use the irons without whipping the optic off the rail. You can see under some other eastern-bloc sights (the POSP comes to mind), but your field of view is too obstructed to be practical; looking through the little space under a POSP is like trying to see the world through a 2-foot-long paper towel tube.

You can still use the front sight post and the bottom of the Kobra aperture as a rough aiming system if the sight goes down in a pinch, but it will shoot a bit high that way; if you need to hit something 100 yards out, you'll do better to just yank the optic off.

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