7.62x39 bullet drop & learning MOA

[Nathantc]

Ok so i built a savage axis with a match 7.62x39, 22" mcgowen barrel in the proper 310 bore. Shoots better than most here would ever take my word for.
That said im shooting 123g HP Barnaul (packaged as wolf). I zeroed at 100 yards. ammo on a cold barrel 3 shot group stays 1" or less. Now today i decided it was a good day to stop simply holding over and start learning MOA and scope dialing. At 200 yards i hit just under 4 3/4" low. Am i correct that comes to 2.25 MOA. I was busting normal sized water bottles repeatedly after dialing up 2.25 on my swfa 10x.
Probably boring to most here but i felt 7.62x39 would be an awesome practice rifle due to it having recoil (lighter rifle with no brake). TO ME the recoil feels very close to my heavy 300PRC with a brake. It's just a LOT cheaper to shoot than 300prc. When i have time i'll invest in some ar500 steel gongs instead of just buying bulk packs of water bottles at sam's lol.

All of this said, i need to invest in a ballistic chronograph. I know nothing about them so i figured the hide would be a good place to start asking. I know my custom 22" match barrel and tight headspace is producing faster speeds than the 16" test barrels used in all the data charts that could be found online. Everywhere i look says i should be 6-7" drop at 200 yet im less than 4.75". I'm still learning but that seems like a big difference to me. Anyway without a chronograph, any and all ballistic calculators are more of a guessing game. This is going to be the same for my 300PRC except would have cost me 200 times more today to figure that out lol.

Im shooting on my own private property, was a perfect day as there was absolutely no wind. Not even enough to disturb my brothers cigarette smoke.

Rifle im messing with in its current state

factory bull barrel stock with sporter profile barrel (boyds pro varmint on the way)
PTG bolt head with stock savage 223 parts
.310 mcgowen barrel 1-10 twist 7.62x39 MATCH
Headspaced to the ammo being used as it's pretty consistent and will be the only ammo used.
Vortex rings on egw 0 moa base
SWFA SS 10x42 MOA-Quad

​

 

[Nathantc]

By the way, owning property and a semi truck with step deck trailer makes for a very very nice way to shoot prone. I can open up to 480 yards out here. Gotta travel when i want to reach out farther. There is just under 8 miles of thick woods before the nearest anything past that tree line. Though hard to see in the photo im shooting down into a valley. So about 100 yards before that tree line is our creek, then its all uphill for about a mile from there. Was a beautiful day for shooting.

 

[6.5SH]

Barnaul lists 2536 fps for that round but doesn't say what barrel length.
Assuming your stated 16" is correct, the rule of thumb is a gain of 20-25 fps per inch.
If we go on the low side at 20 that gets you to 2656 fps which puts you at 5" of drop at 200 yards per JBM. So are in the ballpark there.

JBM - Calculations - Trajectory

www.jbmballistics.com

 

[Nathantc]

Barnaul lists 2536 fps for that round but doesn't say what barrel length.
Assuming your stated 16" is correct, the rule of thumb is a gain of 20-25 fps per inch.
If we go on the low side at 20 that gets you to 2656 fps which puts you at 5" of drop at 200 yards per JBM. So are in the ballpark there.

JBM - Calculations - Trajectory

www.jbmballistics.com

huh didn't know that. I did however study 7.62x39 and barrel length and found that at 24" it actually began to slow down. 23" being the fastest it would go, 22" offering the best standard deviation. Trouble is the article never mentioned what ammo was used, or what bore diameter barrel blank. So i gambled on 22". That said the 20-25 fps per inch is kinda cool to know. If accurate i must be a shade faster than 2656 being less than 5" drop. Range at 200 was tested with a rangefinder. My sight in zero was measured by tape measure at 100 yards from muzzle to target, then used the rangefinder to check and see how accurate the rangefinder itself is. Not exactly scientific but should be good enough.
2656 puts me close to .308 speed though doesn't it. I really need a chronograph.

 

[6.5SH]

There are more assumptions in that calculation; scope height and atmospheric info were at JBM's defaults.
If you enter your exact info it may change it some (maybe better, maybe worse). You can then alter the velocity to get it to match your drop and have a pretty good estimate.

 

[Nathantc]

There are more assumptions in that calculation; scope height and atmospheric info were at JBM's defaults.
If you enter your exact info it may change it some (maybe better, maybe worse). You can then alter the velocity to get it to match your drop and have a pretty good estimate.

awesome, bookmarking that link. How do i find the BC of a bullet when its not listed by the manufacturer. I'm sure that info is provided when selecting projectiles for reloading, but how does one figure this on ammo such as this?
I pretty new at a lot of this. I'm a hell of shot, just starting to learn in better detail other than learning holdovers in my scope.

 

[6.5SH]

Barnaul actually listed the BC for that one. https://www.barnaulammo.com/rifle-ammo/barnaul-762x39.php

For odd surplus ammo sometimes a published BC can't be located. Specialized equipment such as higher end Oehler units, ShotMarker (at distance) can provide a measured BC. A LabRadar can also provide a starting number to work from (it will be too high for an average BC at distance).

A more recent way if you have access to further distances and can precisely measure POA/POI differences is the "Weaponized Math" method listed on the main page of this site as well as in multiple threads in the forum. If you have the rest of the numbers you can figure out your one missing number.

 

[Nathantc]

Barnaul actually listed the BC for that one. https://www.barnaulammo.com/rifle-ammo/barnaul-762x39.php

For odd surplus ammo sometimes a published BC can't be located. Specialized equipment such as higher end Oehler units, ShotMarker (at distance) can provide a measured BC. A LabRadar can also provide a starting number to work from (it will be too high for an average BC at distance).

A more recent way if you have access to further distances and can precisely measure POA/POI differences is the "Weaponized Math" method listed on the main page of this site as well as in multiple threads in the forum. If you have the rest of the numbers you can figure out your one missing number.

using the JBM link you sent
.294 BC
123g .310 projectile
2,543 Barnaul's website datta and adding 120 for add barrel length 2663 FPS
the calculations put me a 4.7" drop at 200 yards (2.3moa) my scope is 1/4 MOA per click so 2.25 is what i dialed and seen to be correct in real world shooting. Man that computer has it figured out. Thanks again. Tomorrow ill use that JBM and shoot different ranges to see how well it works out. Its a start. Thanks again.

 

[Nathantc]

going to set up again when time/weather allows and give these ranges a try. Should be fun making myself a 300 yard dope card for my lil x39 plinker/pig getter. I'm so used to sight in, and then being afraid to touch the scope after the fact it messes with my mind to keep turning the elevation lol. Lots of youtubers and myself have confirmed that the swfa ss will track. This is all to get me ready for when i finally get my MK5HD for the 300 prc. Ill post here how accurate my results are vs what is in the photo.

 

[308pirate]

using the JBM link you sent
.294 BC
123g .310 projectile
2,543 Barnaul's website datta and adding 120 for add barrel length 2663 FPS
the calculations put me a 4.7" drop at 200 yards (2.3moa) my scope is 1/4 MOA per click so 2.25 is what i dialed and seen to be correct in real world shooting. Man that computer has it figured out. Thanks again. Tomorrow ill use that JBM and shoot different ranges to see how well it works out. Its a start. Thanks again.

You're like the first noob I've seen in like forever that immediately grasps how angular corrections work. Take that as the compliment that it is.

From now on never think of or measure drop in inches. Think of it in minutes of arc, since you have a graduated scale right in front of your eyes, inside the scope.

And since you understand the concept, working with milliradians (another angular measure) is just as easy.

 

[Nathantc]

You're like the first noob I've seen in like forever that immediately grasps how angular corrections work. Take that as the compliment that it is.

From now on never think of or measure drop in inches. Think of it in minutes of arc, since you have a graduated scale right in front of your eyes, inside the scope.

And since you understand the concept, working with milliradians (another angular measure) is just as easy.

thank you. Just needed to learn the conversion at 100 yards from inches to moa and then compare at 200 yards. Real findings vs what i could learn on google. Got pretty close, then asked here, and bam. Got even closer. Still waiting to have the time to play with it some more. So far im very happy with my decision to build a 7.62x39 rifle to practice/learn MOA before burning up 300 PRC lol. I dont reload yet so it would sting.
Ive always been a gun guy, just used to learn what hash mark in my scope to hold at a given distance. Wanted to be like the cool guys and learn how to do it the correct way.
As for the MOA vs MIL, my SWFA 10x made the choice for me as i like the center dot reticle of the MOA version better than the MIL version.

 

[6.5SH]

Once you get further into it and figure out the "MPH gun" stuff for wind you'll be switching to MIL.

Use what you have and learn it, but don't be afraid to try a MIL based scope. If you've not bought Frank's book do it.

 

[Nathantc]

Once you get further into it and figure out the "MPH gun" stuff for wind you'll be switching to MIL.

Use what you have and learn it, but don't be afraid to try a MIL based scope. If you've not bought Frank's book do it.

got a link to the book? I'm not afraid of MIL, just knew for sure i wanted this optic on this rifle for the center dot. Noticed the MK5HD im saving for can be had in MIL or MOA with very similar reticles so i could go either way when i drop the $2k on that bad boy. Why would windage be easier to figure in MIL. Thought they were pretty much the same, just different units of the same measurement. like CM vs IN. Please correct me if i'm wrong.

 

[6.5SH]

Available at Amazon and from GunDigest:

Precision Rifle Marksmanship: The Fundamentals - A Marine Sniper's Guide to Long Range Shooting: A Marine Sniper's Guide to Long Range Shooting: Galli, Frank: 9781951115104: Amazon.com: Books

Precision Rifle Marksmanship: The Fundamentals - A Marine Sniper's Guide to Long Range Shooting: A Marine Sniper's Guide to Long Range Shooting [Galli, Frank] on Amazon.com. *FREE* shipping on qualifying offers. Precision Rifle Marksmanship: The Fundamentals - A Marine Sniper's Guide to Long...

www.amazon.com

Precision Rifle Marksmanship: The Fundamentals – A Marine Sniper’s Guide to Long Range Shooting – GunDigest Store

www.gundigeststore.com

 

[Nathantc]

Available at Amazon and from GunDigest:

Precision Rifle Marksmanship: The Fundamentals - A Marine Sniper's Guide to Long Range Shooting: A Marine Sniper's Guide to Long Range Shooting: Galli, Frank: 9781951115104: Amazon.com: Books

Precision Rifle Marksmanship: The Fundamentals - A Marine Sniper's Guide to Long Range Shooting: A Marine Sniper's Guide to Long Range Shooting [Galli, Frank] on Amazon.com. *FREE* shipping on qualifying offers. Precision Rifle Marksmanship: The Fundamentals - A Marine Sniper's Guide to Long...

www.amazon.com

Precision Rifle Marksmanship: The Fundamentals – A Marine Sniper’s Guide to Long Range Shooting – GunDigest Store

www.gundigeststore.com

thanks, just ordered it on amazon. Been a long time since i read a book. Internet kinda took over. Thanks again though. This is pretty fun so far. Exciting to punch in the numbers, dial the scope, and hit at a new distance on the first try. Its like being a kid at christmas lol.

 

[6.5SH]

Read this thread a few times along with the videos:

Calculating mph rifle

At a recent match, many on my squad were describing their wind calls in terms of mph, by saying eg: I used a 5mph wind( rather than describing it in terms of mils). These were good shooters doing this. (I just got on their squad by accident). Where can I learn about this technique, and...

www.snipershide.com

 

[308pirate]

thank you. Just needed to learn the conversion at 100 yards from inches to moa and then compare at 200 yards. Real findings vs what i could learn on google. Got pretty close, then asked here, and bam. Got even closer. Still waiting to have the time to play with it some more. So far im very happy with my decision to build a 7.62x39 rifle to practice/learn MOA before burning up 300 PRC lol. I dont reload yet so it would sting.
Ive always been a gun guy, just used to learn what hash mark in my scope to hold at a given distance. Wanted to be like the cool guys and learn how to do it the correct way.
As for the MOA vs MIL, my SWFA 10x made the choice for me as i like the center dot reticle of the MOA version better than the MIL version.

Use a free online ballistic calculator and get your answers in your angular units of choice. And if you must know 1MOA=1.047 inches per hundred yards.

The issue with MOA scopes is that unless you do a precise tracking test it's difficult to know if the reticle and adjustments are really MOA (1.047"/100 y) or exactly 1 inch per hundred yards (si called IPHY adjustment.

Food for thought

With milliradian scopes you know that every .1 mil click will always yield .36 in per hundred yards.

In any case, all of the above is academic. What really matters is that your reticle scaling and turret adjustment increments match (MOA/MOA, IPHY/IPHY, MIL/MIL) and you never think in linear units.

 

[Hetzer]

I didn't know Frank had a book. I ordered it also. Thanks for that bit of info!

I started reading this thread because I have a somewhat similar rifle. I bought a Howa barreled action on sale from Brownells and put it in a Boyds Varminter (I think) stock. I've shot a few rounds through it to build up some brass stock and break it in but nothing all that serious. I bought some Geco ammo from AIM to use as the brass source, then some Lapua 123gr bullets while they were on clearance at Midsouth. Maybe Lapua has discontinued that bullet, I'm not sure.

I had read an article about how they make a good training round due to the basically lazy down range performance. In essence a good training round for learning to deal with the wind. I thought it worth giving a try. I'm lagging on getting back to it however.

OP looks to have a nice place to shoot. That's pretty awesome.

 

[Nathantc]

well thanks to the commander and CHEAT, i'll be scrapping this rifle. Cheap ammo is 100% the only thing that makes a 7.62x39 rifle worth owning. I will not buy x39 at .308 prices. So possibly soon the barrel, bolt head, and magazine may be up for sale. This is postponed until something comes up. Damn sure not buying 7.62x39 at all for more than .40 a round.