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Ok dunb question on 762x39

3.6K views 15 replies 3 participants last post by  Archangel301958  
#1 ·
Try to look over my stupidity for a bit while i play catch up on 7.62x39 ballistics. My rifle is the rifle also used by our church security team so anytime i change the optic i have to be able to tell the other guys where to hold. So kinda learning the trajectories on the run.
With a crosshair tactical scope on a waser , cutting one ragged hole at 25 yrds with 124 gr ammo will that bullet hold a paper plate size group at 100 yrds assuming the guy behind the rifle is doing his part?

I dont have ready access to 100 yrd range right now.
 
#3 ·
Thinking granddaughters will deer hunt with it also. Be easier if they can just aim for the kill zone that have to use ky windage.
My friend sent a message this eve to come on the 100 yrd range on his farm is now cow free. Lol. . Ill hit it after the weekend

Thanks for the replies.
 
#4 · (Edited)
First, your exact question (I think):

If the accuracy is good enough for one ragged hole at 25 yards, yes group size should be only about 4 times bigger at 100 yards as tumbling absolutely should not be an issue with 124 grain ammo. That would be well within a paper plate.

On what isn't your exact question:

If you are zeroed at 25 yards you will be a little high at 100 yards, maybe 5 inches. The exact figure will depend on how high your optic is. If not accounting for that rise then maybe some bullets will fly over the plate.

As to what's the "best" zero for your application, that is going to depend on the ranges it is needed for. There is no one answer. Anything reasonable (25 yard zero, 25 meter zero, 50 yard zero, 50 meter zero, 100 yard zero etc, etc, or "an inch low at 25 yards, "2 inches high at 100 yards," "6 inches high at 100 yards" etc) will work but not if it is surprising the guy using it, pretty much as you were saying. What's "best" will depend on what's needed. E.g., if you don't think there will ever be a need past 200 yards, you want guys to be able to do well on paper at 100 yards, and for church defense closer might be really important as well, 50 yards would not be a bad decision and would require less correction at 100 than 25 would. That's an example not a recommendation.

A 25 zero is very good if you need a range out to 300, as they are about the same. But if the rifle will never be shot to 300 then that aspect is irrelevant and you'd be "rainbowing" up more than you need at 100 and 200. So you might prefer some figure of your choice low at 25 yards.

If shooting distance will be limited to 200 yards or only a touch past, being between about 3/4" and 1" low at 25, giving about an inch to 1 1/2" high at 100, has a lot to be said for it with a 2 MOA red dot because the bullet will be within or barely skimming the red dot or be within an inch of point of aim everywhere from 25 yards to 200 yards. I mean on average not every particular bullet. Basically, shooter error and rifle inaccuracy will be more important than trajectory error over that entire distance. Again, not a recommendation as what's best for you, an illustration of picking something that can work for a person if the situation matches up.

If the priority is for the guys to get center hits at 100 yards when you have access to only 25 yards, try getting it to hit about an inch and a quarter low rather than dead zero at 25.
 
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#5 ·
Thanks for the reply.
I can get about 50 yrds to sight in. I seriously doubt my rifle will be fired at any living thing past 150 yrds.
The goal im trying for though the ammo supply changed since my first post to 154 gr sp tula, is as flat a trajectory as possible out to about 150 yrds . Hopefully flat enough to stay on paper plate using a red dot and no holdover or under.
I could keep up with the adjustments but if could not be me near the rifle if needed and i doubt the other team members would remembef them under stress.

From your reply im thinking a 35 or 50 yrd zero may be flatter to 150 yrds ?
 
#6 · (Edited)
Yes.

Mostly when not able to zero long I set for a particular amount low at 25 and can't say from memory on 35 and 50 zero for exact results but will run ballistics shortly for illustration on what they do.
 
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#7 · (Edited)
Approximate, given variations in optic height, velocity etc and not having a BC for the Tula I plugged in the same as for a 123 which over long distances would be a significant error, but for an idea. The first inches figures are 123 grain at 2400 fps, the second figures are 154 gr at 2100 fps

35 yard zero:
Yards inches
25 -0.6, -0.6
50 +0.8, +0.8
75 +1.8, +1.6
100 +2.4, +2
125 +2.5, +1.9
150 +2.1, +1.3
175 +1.1, 0.2
200 -0.4, -1.4
225 -2.6, -3.4

50 yard zero:
Yards inches
25 -1.0, -1.0
50 0, 0
75 +0.6, 0.4
100 +0.8, 0.2
125 +0.5, -0.6
150 -0.4, -2
175 -1.7, -4.3
200 -3.7, -7.2
225 -6.2, -11

The 50 yard zero is super flat and close to point of aim, far moreso than the shooter probably, from somewhere less than 50 yards all the way out to 125 and still is only a couple of inches low at 150. But past 175 it's falling below point of aim fast.

The 35 yard zero isn't quite as close to point of aim, being an inch or two high from somewhere past 50 yards to 150, again not really to an important degree for most shooters, but does way better further, still nearly dead-on at 225. But it seems you don't need past 150 anyway.
 
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#9 ·
You're very welcome! Have a great time!
 
#10 ·
Well something about my set up diesnt match the chart numbers . Probably my sight above bore which is 3 1/4 inches.

I was sighted in at 35 yards when we started.
At 50 yards my poi was about 2 in low.
Sighted in at 50 shooting 1moa groups dead on poa poi.

Called it a day came home. Decided just 4 kicks to shoot the 35 yrd target our back. Poi was 8 inches high!!.
So resighted back to 35 yrd zero which should keep me in the kill zone of 8 in aiming dead on out to 100 yrds which is what i need for my grandaughter this weekend . Going by the results i got today.
Next yr if im still around will have a 1 to 6 power mil dot scope on it for deer season on a low mount . Use irons and the red dot for everything else during the year .

I do have to say the 154 gr tula sp are more consistently accurate with no fliers than any surplus ammo ive shot in the AK .
 
#11 · (Edited)
Height over bore does make a difference and more height gives more climb to the path between exiting the muzzle and reaching zero at downrange distances such as 35, 50, and 100 yards. The figures above were on 2.5" height over bore.

That said, with a 50 yard zero and 3 1/4" over bore, basically the trajectory is almost laser-straight slight incline out to 50 yards, climbing basically 3 1/4", so it can't be 8" high at 35 yards. Instead it would have climbed only partway (about 35/50ths) of that rise and have been a little low. I am of course not saying your experience didn't happen, but rather that there must be another cause. The round won't have rainbowed up 8" at 35 yards and then be back to zero at 50. Something else happened. It must have lost the 50 yard zero between the range and home for whatever reason.

Also when starting out and being zeroed at 35 yards and now trying 50, the bullet would have still been rising and would not have been low at 50 but rather a little high. Again not at all disagreeing with your observation of having gotten a confirmed zero at 35 and subsequently seeing this at 50, just that zero seems not to be holding. Which makes everything impossible of course, super frustrating when that happens.
 
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#12 ·
Height over bore does make a difference and more height gives more climb to the path between exiting the muzzle and reaching downrange distances such as 35, 50, and 100 yards. The figures above were on 2.5" height over bore.

That said, with a 50 yard zero and 3 1/4" over bore, basically the trajectory is almost laser-straight slight incline out to 50 yards, climbing basically 3 1/4", so it can't be 8" high at 35 yards. Instead it would have climbed only partway (about 35/50ths) of that rise and have been a little low. I am of course not saying your experience didn't happen, but rather that there must be another cause. The round won't have rainbowed up 8" at 35 yards and then be back to zero at 50. Something else happened. It must have lost the 50 yard zero between the range and home for whatever reason.

Also when starting out and being zeroed at 35 yards and now trying 50, the bullet would have still been rising and would not have been low at 50 but rather a little high. Again not at all disagreeing with your observation of having gotten a confirmed zero at 35 and subsequently seeing this at 50, just that zero seems not to be holding. Which makes everything impossible of course, super frustrating when that happens.
Im not sure what happened.
I checked all mounts and sight all is rock solid.
My first shots at 50 but still on 35 yard zero were within an 11/2 poa just a shade high.

I had a 50 yrd zero grouping 3 shots in 1 1/2 inch groups after resighting to 50 yrds

Back home shot at 35 yrds produced 3 shot groups bullet holes touching but 8 8nch high of poa.
Ive resighted at 35 removed the sight , banged it beat it put it back on and zero remained the same .
I guess ill take the grandaughter out on the 35 yrd zero for her deer hunt. She wont have a shot over 50 yards anyway .
When i have more time ill ill try the 50 yard again . And later on i think im going to put a 1 to 6 lpvs on it for hunting to help my eyes out , then just use irons or reflex sight the rest of the year.

Still i cant find any thing not tight or not returnjng to zero on the rifle so i dont know what occured.
 
#13 ·
A mystery for sure.

Well, on the day of your hunt with your granddaughter either one it's zeroed at will give you quite reasonable results anywhere in the distances you need, so if it holds that 35 yard zero and it sounds like it is you're good to go!! :) And that's what counts.
 
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#14 ·
Image


That is the 10 rd group it shot a couple hours ago.
Zeroed at 35 yrds and shot from varying distances to 50 yrds. Removing the optic banging it around every 2 shots then putting it back on to make sure it is holding and returning to zero.

All i can put yesterday eve down too now is its not a good time of year for me. Lot on my mind. I may have simply shot the wrong target dot during a brain fart.

Anyway i think we are good to go for her Sunday hunt. Cant go Sat. She has a football game. All 78 lbs of her . On the boys team lol.

Lord shes wicked for 9 yrs old lol