Lost in numbers, please help

[uirapuru]

Hello everyone! I will try to describe problem as simple and short as possible:

Few months ago I've measured my ammo's muzzle velocity with labradar - 3 shots showed average of 820 meters per second, producent of the ammo tells that usually it should be around 810 m/s. Described ammo is caliber .308 GGG with Sierra HPBT 175gr bullet.

I filled up my both ballistic calculators (Kestrel 5700 and Strelok Pro) with same rifle data and went this morning to a shooting range at 655 meters distance. I've used elevation from both calculators (they were the same) - 19.8U moa and all the projectiles went 40 cm high. After some tweaking and calculating I've found that proper elevation should be 17.7U moa.

After validating that, I went to my Kestrel gun and entered "Calibrate MV" and I entered that Drop... (elevation) is actually 17.7U and this updated muzzle velocity to 860m/s. Strelok gave me similiar adjustment of bullet speed. Both environments for today and labradar measuring were similiar (now - 12 degrees of Celcius, then - 15C). Rifle was the same - Remington 700 with right barell twist 1:12

Is it even possible that bullet went 50m/s faster then told on ammo box info from the maker? Was labradar faulty or gave me erroneous result? I'm sure there's something in front of my eyes but I can't see it, please help

 

[Near miss]

If you chronoed even few rounds succesfully it is unlikely the values Labradar gave you are a fluke.

I would guess that you might have a problem with your scope. According to GGG, the 175SMK load will leave 24" at 810ms so I am guessing you have a 24" or 28" barrel. It is very unlikely it would have 860ms velocity at -10C or below. In my experience factory ammo has a terrible temp curve in cold so the 820ms out of 24" is a very nice number, odd even.

While it is good to calibrate MV I usually try to stick with the MV labradar gives me because it lets me set temp tables that really help me get 1st round impacts during all seasons.
If you now shoot at 300m with the calibrated MV, you will probably swing a little low. Which will prove that it is not the MV that caused the POI difference at 655 meters. Probably just a click or 2 at max though.

But I would really check:
-scope elevation works properly, 5% error is very likely.
-ballistic calculator rifle and bullet profiles just to be sure.
-did you have the ammo at the ambient temperature when shooting 655m? Warm ammo could do you tricks.

 

[uirapuru]

IIt is very unlikely it would have 860ms velocity at -10C or below.

Sorry for my notation - it's not MINUS 10 degrees, I used it as a dash in sentence, sorry. I meant 12, 15 degrees in plus. Poland is not always that cold even in winter Today was beatiful warm day with +12C

But I would really check:
-scope elevation works properly, 5% error is very likely.

Other thing I've done today was validating my click value, in windage and elevation so I think scope is ok. It works fine and it's pretty robust (NightForce NXS), probably will last longer than me

-ballistic calculator rifle and bullet profiles just to be sure.

I will check this again, I'm sure there's something wrong. Friend of mine will get his own labradar in few weeks, we'll probably check everything at the spot

-did you have the ammo at the ambient temperature when shooting 655m? Warm ammo could do you tricks.

I think that ammo stayed outside long enough to have the same temp as environment, I gave few minutes to the ammo and rifle to level it's temp to the air.

 

[Near miss]

How familiar are you with the rifle? Were the shooting conditions similar to zeroing conditions like visibility, ground / rifle support point toughness, rifle equipment, personal equipment? 2moa is quite big offset even for that though, but it could be few marginal errors created the whole 2moa error.

I like chrono data because as said, it helps build temp table but what is more important is legit dope.
Do you have any other distances shot with the same or other ammo?
Have you gotten any other ammo to give you sensible dope that your ballistic calc matches with?

I could have bet money it is the scope, so I still want to ask how did you check the elevation was good?

 

[DocRDS]

The MV on your Kestrel is "knob" you turn to get the correct results. It is not your actual bullet velcity--they will probably vary slightly

Think of your Kestrel as radio. To get to the correct station you have to turn the knob. If I know that I listen to 101.1 FM, my dial should be right at 101.3, but often times it isn't (especially on old dial/analog sets). So if you are tweaking the MV in the Kestrel and it doesn't match your "measured" MV that's ok. The key values to match up are your elevations and distance. Does the Kestrel predict the right elevation at a given distance. If it doesn't there are 2 "knobs" to play with: MV and BC.

There are various rules of thumb but generaly <800 m/yds you change the MV to make the elevations match and >800 Yards, adjust the BC you input.

The measurement from your chrono is just to get you into a ballpark. (I know I should be around 101, but if it looks like 102, that's ok--the sound from the radio is what I care about).

 

[KnowNothing256]

How sure are you that it was 655 meters? Another user recently asked a very similar question and discovered that the range to the target was the most likely source of error, not MV or bullet BC.

 

[uirapuru]

I wanted to thank you all, I've started to think and I checked everything step by step. I phoned my friend who knows this range better than I do and it seems that my rangefinder is broken.

It told me that distance was 655 meters, but its 602 in fact. I have not checked this manually (at least estimating range using reticle), my fault. When I use 602m in Kestrel and Strelok with 17.3U moa elevation, it gives me 817m/s, which seemes to be correct.

Thanks for forcing me to dig deeper and think

 

[KnowNothing256]

I wanted to thank you all, I've started to think and I checked everything step by step. I phoned my friend who knows this range better than I do and it seems that my rangefinder is broken.

It told me that distance was 655 meters, but its 602 in fact. I have not checked this manually (at least estimating range using reticle), my fault. When I use 602m in Kestrel and Strelok with 17.3U moa elevation, it gives me 817m/s, which seemes to be correct.

Thanks for forcing me to dig deeper and think

Hah! Love getting it right

Your RF might not be broken, put a new battery in it before trying anything else. Low battery levels will often cause erratic reasons; this is usually evident by either obviously wrong numbers (requires rough knowledge of the true range), and sometimes also from varying results on the same target.

Batteries are cheaper than a new RF, so try that first

ETA: erratic readings, not reasons lol

 

[GrumpyOleFart]

Ranging with your scope reticle, then use the electrickery.
Like reading a map and using a compass, old school is the best school.

 

[uirapuru]

Ranging with your scope reticle, then use the electrickery.
Like reading a map and using a compass, old school is the best school.

actually that's exactly how I've been taught. But then one day, you pay shitloads of money for shooting range and you want to do everything quickly and there you have it... My fault, I confess

 

[KnowNothing256]

Ranging with your scope reticle, then use the electrickery.
Like reading a map and using a compass, old school is the best school.

Sorry, but no, no it's not. If your targets are large/close enough, then you can always get away with a lot of errors, including ranging. For small targets at long distance, it is far too easy to introduce a small error in reticle ranging that will take you all the way off the target.

Using the reticle is fine as a sanity check on your range, but it is not at all consistent enough for smaller targets (<0.5 mil or so) at longer ranges (800+ yards). Will you get impacts? Yes. Will you get as many as you would with a decent LRF? No you will not.

Do you want to hit every time? Or do you just want to just learn to watch splash and give away the first round on every long-range target? I think most of us would prefer first-round impacts, and reticle ranging can't hold up to a LRF when everything counts.

 

[theLBC]

just looking at a basic dope chart for 175gr SMK @2600 ft/sec in my log book gices me 16.3 elevation for 600 yards. bc=.496.

 

[Near miss]

Sorry, but no, no it's not. If your targets are large/close enough, then you can always get away with a lot of errors, including ranging. For small targets at long distance, it is far too easy to introduce a small error in reticle ranging that will take you all the way off the target.

Using the reticle is fine as a sanity check on your range, but it is not at all consistent enough for smaller targets (<0.5 mil or so) at longer ranges (800+ yards). Will you get impacts? Yes. Will you get as many as you would with a decent LRF? No you will not.

Do you want to hit every time? Or do you just want to just learn to watch splash and give away the first round on every long-range target? I think most of us would prefer first-round impacts, and reticle ranging can't hold up to a LRF when everything counts.

To be fair he did not advise to shoot in between the rangefinding. Just to do both ways and compare the results of your milling against the laser.

I thought of asking about the range distance but since it was very specific 655m, I thought it was solid, bad luck that the laser failed.

 

[GreenCanoe]

How sure are you that it was 655 meters? Another user recently asked a very similar question and discovered that the range to the target was the most likely source of error, not MV or bullet BC.

Hey, I've learned and moved on from that shit, ok?!? Lol. BTW, I did end up picking up that Sig. It's like I'm fucking cheating, now!

 

[Enough Said]

Mechanically and mathmatically, you guys have covered it all.
Now physically, if the rear support is not firm, the rifle butt stock will dive in the bag, producing consistent high impacts.
I see this every class, and we highly stress firm rear bags consistently.
May not be the entire problem, but a ton of data errors can be corrected with correct fundamentals.