M118LR, M24, 1100 meters

[RoverG79]

Shooting the other day using a M24 using M118LR and shooting out to 1110 meters. The area was a ridge line into a canyon below. I was using Bullet Flight and Atrag for my corrections.

1100m
85.2 deg
27.68 InHG
Angle -10 deg
Wind 5-10 mph from 9 O'Clock

It worked out to be
48 MOA for elevation
.75 MIL Left for wind
Velocity of 1161 fps at the target
Energy of 524 fps at target

The problem is the elevation correction was about 4 MOA short. Made the adjustment to 54 and started making solid hits.

Similar story with the M110's. We started having to add extra elevation after about 900 meters. 2-3 MOA at 1100 MOA

I figured a down draft was pushing the bullet down in elevation. Popped some red smoke down range and it did looked like there was a bit of a down draft about 150ft above the canyon floor.

What are your thoughts. Is it something screwy with the PDA, or was the wind pushing the bullet down an additional 44 inches.

 

[ida83704]

Re: M118LR, M24, 1100 meters

how accurate is the distance to target?
you were shooting downhill? what was the angle down to the target?(this will cause a high miss, but just asking)

scope adjustments in true moa?

lots of possibilities

 

[RoverG79]

Re: M118LR, M24, 1100 meters

Thanks good input.

The distance was accurate, used vectors and MK12's.

The shot angle was a -10, but this was factored in.

The scope adjustments were M3 and M2 knobs.

 

[Jon Lester]

Re: M118LR, M24, 1100 meters

Was the horus program trued to account for the velocity loss (bc Change)at the extended distance? Are you sure scope adjustments are correct?

 

[RoverG79]

Re: M118LR, M24, 1100 meters

As for the tracking of the scope, all the scopes were tested using the box method but not all the way to 54 MOA.

If it was only one gun, I would have assumed the scope tracking was off (still a possibility), but we had similar stories with 4 M110's as well.

The velocity was calculated for all the individual guns and each gun has its own saved settings in the PDA's.

*As for the velocity loss, I know there is a BC change, but I thought ATRAG accounted for this. Is this something that is manually input?*

 

[ida83704]

Re: M118LR, M24, 1100 meters

How did you calc the down angle?
That might cause this issue, if the calc returned improper results.

If all the guns were off then it is probably not muzzle verlocity or scope adjustments not 'true'

to determine the down angle correction did you use:
Riflemans Method?
Improved Riflemans Method
Sierra Method?

link to Sierra with each explained
http://www.exteriorballistics.com/ebexplained/article1.html

 

[RoverG79]

Re: M118LR, M24, 1100 meters

I calculated the angle using Vector Laser Range Finders. It was -10.4 DEG.

Thanks for the link, good read. I did none of those. Shouldn't ATRAG and BulletFlight automatically compute this when the -10.4 DEG is input?

I played around with inputing different angles, and it does change the MOA elevation, but not much with 10 DEG. I really didn't expect 10 DEG to change it much.

 

[RoverG79]

Re: M118LR, M24, 1100 meters

any more input?

 

[ida83704]

Re: M118LR, M24, 1100 meters

There are not alot of varriables to cause this

the list:

muzzle velocity
BC
air temp
barometer
humidity(minor factor)
distance
slant angle
corealis at 1100meters is minimal
scope adjustments
paralax

several of the above have been shown as not the cause and eliminated from the list of possibles

10 degree down angle correction is .985

shoot again and see if the results are the same

 

[8up]

Re: M118LR, M24, 1100 meters

I had similar results shooting Mk11 Mod 0 at that distance recently. Ran out of elevation, and still hold over at 1280 yards. I think my additional hold was 3.5 mil, but have to check the data book for what it was. I was not using a ballistic program though, doing it the old fashion way, UKD.

Similar terran also.

 

[Apex Motorsports]

Re: M118LR, M24, 1100 meters

Sounds like you might have had the output of the range finder as corrected for the angle cosine rather than true range and you compensated for the angle cosine again without knowing.

That or your BC data is incorrect. Not to uncommon for SMK 175's since the meplat gets deformed on most of the bullets by the time they get made into a cartridge. What did you use for the BC in the computation? But given the 44 inch error I would say it was more likely the range finder angle cosine. Does your dope agree with your firing solution?

Or if you dialed for the elevation adjustment your scope may not be tracking properly.

 

[Ragnarok]

Re: M118LR, M24, 1100 meters

I can see in bullet fligt, you need to add sea level pressure, and then set the actual altitude. Or if you are using a castrel, you can use the actual pressure from the castrel unit, but then you need to set altitude to zero, to obtain correct data.

 

[99v6red]

Re: M118LR, M24, 1100 meters

Thats nuts I hope to shoot that far some day!

 

[Killswitch Engage]

Re: M118LR, M24, 1100 meters

might i ask was the mirage bad or significant? i have had the same experience with the same load out of my m40 at 1k. i have found it was a direct result of mirage forcing the target down or "changing" your perception of where it is. when the mirage is low or gone my dope was generally correct.

just a thought.

 

[RoverG79]

Re: M118LR, M24, 1100 meters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ragnarok</div><div class="ubbcode-body">I can see in bullet fligt, you need to add sea level pressure, and then set the actual altitude. Or if you are using a castrel, you can use the actual pressure from the castrel unit, but then you need to set altitude to zero, to obtain correct data. </div></div>

When setting it using pressure, altitude should be set to 0 as this is automatically calculated.

 

[RoverG79]

Re: M118LR, M24, 1100 meters

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMC_4_life</div><div class="ubbcode-body">Sounds like you might have had the output of the range finder as corrected for the angle cosine rather than true range and you compensated for the angle cosine again without knowing.

That or your BC data is incorrect. Not to uncommon for SMK 175's since the meplat gets deformed on most of the bullets by the time they get made into a cartridge. What did you use for the BC in the computation? But given the 44 inch error I would say it was more likely the range finder angle cosine. Does your dope agree with your firing solution?

Or if you dialed for the elevation adjustment your scope may not be tracking properly. </div></div>


It was several guns with the same issue. Can you explain the range finder angle cosine?

The dope was spot on at 900 and below, about 1 MOA low at 1000m and it came apart at 1100.

 

[VonReich]

Re: M118LR, M24, 1100 meters

Those M3A turrets make adjustments a pain in the A$$! I hate the increments on it

 

[im-ur-daisy]

RoverG79 M118LR is (varies weapon to weapon) is transonic or subsonic at 1100 meters. Your ballistic coefficient drops considerably so you're going to have errors of that magnitude. M118LR will shoot 1000 meters with about 38 MOA (varies weapon to weapon) of elevation but beyond that not very reliable.

 

[VKC]

Besides what was already mentioned. Remember that you BC will vary with velocity. At that distance your velocities are getting pretty low.

 

[one shot ST]

what was your muzzle velocity ?

 

[DAVETOOLEY]

With this statement you have ruled out all but one possible problem. This bullet is one that can have issues in the transonic region. The performance progressively got worse past 900. Now you know your limits.

 

[Emouse]

Dave,...this is an interesting thread given many of us shoot the M118LR load or something very very similar. You mentioned transitional instability at 900+. 900 to 1200+ is a long way still. Surely speed and the fact that at just 600fps residual, the BC over that final vector will be nothing like what it was at the muzzle???

 

[matt2143]

I saw similar issues with M118LR out of a 20" bolt gun beyond 900 yards. 1000 yard dope was 0.8 Mil off and 1250 was like 3+ mils off. I am figuring as the bullet enters mach 1.2 and continues to below mach 1 we are seeing stability go out the window.

 

[DAVETOOLEY]

Dave,...this is an interesting thread given many of us shoot the M118LR load or something very very similar. You mentioned transitional instability at 900+. 900 to 1200+ is a long way still. Surely speed and the fact that at just 600fps residual, the BC over that final vector will be nothing like what it was at the muzzle???

Yes BC changes with velocity loss. Sierra says 5% and Litz say 7% below 1500 FPS. I'm not intimately familiar with his ballistic programs but in this day and age I would think all would automatically adjust the BC for velocity. There are variables in this particular case that we can't evaluate. Muzzle velocity being one, a slight increase or decrease could have a pretty drastic affect at that distance but things tracked to 900 meters. Another is bullet quality or more specific meplat condition. A non uniform meplat will affect air flow and the BC. I won't get into all my testing but lot to lot not all 175 SMK's are equal in that department as are all HPBT's. I would like to see bullet holes on paper at those distances. It still gets back to everything worked until they shot past 900 meters. The question is, as you say most of the known world is shooting this bullet/round using the same ballistic programs, why are they having issues? With this lot of ammo something is happening. After almost 20 years of shooting extreme distances there's one thing I know for sure. No matter what programs you have, no matter how many books you have, the only that is certain is what you see through your scope that day. Observe, adapt, adjust and shoot more.

Let me add that if I was going to shoot those distances with a 308 I would move up to the 185-190 gr class bullet.

 

[bohem]

I would take a look at 3 things, in this order:

Scope tracking at the extremes of the range. I have had a lot of top shelf optics that tracked perfectly until the last 6-8 MOA or 2mils in each direction. It's a fact of life, and the only time that it became an issue was when I was in the last bits of range on the turrets.

MV vs. Temp and the actual MV's for each rifle with that specific lot of ammo at the current round count. As barrels wear and wear out the tendency that I've seen is for the velocity to drop. There are several reasons for this and my current 6.5 tube is slowing down each time I take it out, the barrel is starting to throw fliers vertically now too, "it's time".

I'm not saying that your barrels involved are worn out, not that at all. The point is though that if you checked the ammo from the rifle 500 or 1000 rounds ago, then take a look at rechecking the speed.

After you've confirmed these things, then it is also a known from Frank's testing at Gunsite that as the TOF increases past a couple seconds most of the ballistic computers on the market have issues and tend to under-compensate the elevation correction.

I'm pretty sure, but I may be mistaken, that both of the computers you're talking about showed the issue with big calibers past 2000yd where the TOF's are similar to the 1200+ yards that you guys were shooting with the 308's.

The BC can be a very real issue, switching to a G7 on the 175 SMK would be the way to go, though it doesn't solve the issue. The G1 vs. G7 argument just gets you a better fit to the actual drag vs. velocity relationship. You can get "just as good" on a G1 by using several G1's as velocity changes. In fact, if you use enough G1's and not enough G7's you can get a BETTER fit, but putting 10 different points into a ballistic computer tends to be unreasonable for a couple of reasons, not the least of which is getting good data from the bullet makers or 3rd party publications that even HAVE that many data points.

Nice shooting, BTW. 1200+ with a 308 is no short order.

 

[Emouse]

Yes BC changes with velocity loss. Sierra says 5% and Litz say 7% below 1500 FPS. I'm not intimately familiar with his ballistic programs but in this day and age I would think all would automatically adjust the BC for velocity. There are variables in this particular case that we can't evaluate. Muzzle velocity being one, a slight increase or decrease could have a pretty drastic affect at that distance but things tracked to 900 meters. Another is bullet quality or more specific meplat condition. A non uniform meplat will affect air flow and the BC. I won't get into all my testing but lot to lot not all 175 SMK's are equal in that department as are all HPBT's. I would like to see bullet holes on paper at those distances. It still gets back to everything worked until they shot past 900 meters. The question is, as you say most of the known world is shooting this bullet/round using the same ballistic programs, why are they having issues? With this lot of ammo something is happening. After almost 20 years of shooting extreme distances there's one thing I know for sure. No matter what programs you have, no matter how many books you have, the only that is certain is what you see through your scope that day. Observe, adapt, adjust and shoot more.

Let me add that if I was going to shoot those distances with a 308 I would move up to the 185-190 gr class bullet.

Well put Dave! Some of the ballistic prongs do indeed allow you to enter more than one BC value but I don't think any do this as such on the fly, given only the initial BC and range? This in itself would unravel the shooters calculation beyond the 900 yard mark substantially.

 

[Sako man]

I would take a look at 3 things, in this order:

Scope tracking at the extremes of the range. I have had a lot of top shelf optics that tracked perfectly until the last 6-8 MOA or 2mils in each direction. It's a fact of life, and the only time that it became an issue was when I was in the last bits of range on the turrets.

MV vs. Temp and the actual MV's for each rifle with that specific lot of ammo at the current round count. As barrels wear and wear out the tendency that I've seen is for the velocity to drop. There are several reasons for this and my current 6.5 tube is slowing down each time I take it out, the barrel is starting to throw fliers vertically now too, "it's time".

The BC can be a very real issue, switching to a G7 on the 175 SMK would be the way to go, though it doesn't solve the issue. The G1 vs. G7 argument just gets you a better fit to the actual drag vs. velocity relationship. You can get "just as good" on a G1 by using several G1's as velocity changes. In fact, if you use enough G1's and not enough G7's you can get a BETTER fit, but putting 10 different points into a ballistic computer tends to be unreasonable for a couple of reasons, not the least of which is getting good data from the bullet makers or 3rd party publications that even HAVE that many data points.

Nice shooting, BTW. 1200+ with a 308 is no short order.

First off this is an old ass thread, well kinda. That said interesting problem.

Totally agree with this poster, this is why..

1. it's easy to assume the problem lies in ballistics, what could go wrong with a scope, simple knob turn right? Well, not really. People often assume it's the math/ballistics because it's complex therefor laden with possible inaccuracies. You look at many box tests even for optics that track well like the HDMR and things can get weird around the tertiary, mechanical extremes in the erectors arise.

2. possibly MV? I am agreeing on this just out of anecdotal observation. I have a specific LOT of ammo that I chrono and get a stable MV. I go out the next day, same gun and ammo, shit is all over the map. Chrono it again on the spot with a Magneto and MV is off by 15 or 20 FPS, thats enough to cause havoc at LD. Could have been moisture in powder, ghost in the machine, a million little things etc....

3. Don't know enough about BC to comment. But what do you tweak first in ATRAG? BC or MV.... MV or BC.... you know where the bullet is landing but what data is lying to you? Perplexing?

 

[DAVETOOLEY]

[QUOTE 3. Don't know enough about BC to comment. But what do you tweak first in ATRAG? BC or MV.... MV or BC.... you know where the bullet is landing but what data is lying to you? Perplexing?[/QUOTE]

Back in the dark ages we had one ballistics program, no laptops or PDA's. Only a desktop at home. We were at times shooting custom made 178 gr. 7MM's. No data at all for anything that heavy. We knew pretty close what the velocity was and most of the time we could get charts to work by changing the BC number. In this case if good data was recorded out to 900 then it would be easy to play with either BC or velocity and get things trued to real world conditions. Just as long as something funny wasn't going on with the bullet. I've seen 7" 1000 yd groups with every bullet going through the paper sideways.

Here's something to consider for ELR shooters. If you have a favorite place to shoot don't use a 100 yd. zero. I'll explain. At our favorite mountain top in VA we had a 1000 yd. rock. We checked our zero on that rock and our charts used a 1000 yd. zero. Any error in our charts would be divide essentially in half on either side of the 1000 yd. zero. Half isn't quite accurate. 1/3 inside of 1000 yds. and the other 2/3's from 1k to 2K. I would think that could apply to any long distance shooting. If possible zero at distance then plug in that zero range.

 

[john_1182]

The biggest thing i have found with my .308 and 1100>1250m ranges are

transonic/ subsonic BC
and
Ammo temp

i went and chroned my ammo at differnt temps and when useing the balistic software i save the ammo in as diferent MV and temps.

the best investment for those ranges with my .308 was a IR gun for ammo temp.

1200m .308 175 BC .243 G7 2650fps at 21c ammo/ air temp

with air temp at 21c
15c ammo temp 18.7 mil
21c ammo temp 18.4 mil
27c ammo temp 17.9 mil

 

[Sako man]

The biggest thing i have found with my .308 and 1100>1250m ranges are

transonic/ subsonic BC
and
Ammo temp

i went and chroned my ammo at differnt temps and when useing the balistic software i save the ammo in as diferent MV and temps.

the best investment for those ranges with my .308 was a IR gun for ammo temp.

1200m .308 175 BC .243 G7 2650fps at 21c ammo/ air temp

with air temp at 21c
15c ammo temp 18.7 mil
21c ammo temp 18.4 mil
27c ammo temp 17.9 mil

Yeah, those are popping up more at competitions.