Long range shooting the M1A/.308 - what matters


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Groovski
November 28, 2007, 12:04 AM
Most long range shooters already know this stuff, I suspect, but I've never seen a good explanation of what factors really matter when trying to hit a target with .308 at distances up to a 1000 yards, and why. So I decided to investigate for myself, since I'm still getting up to speed to understand why all the anecdotes I hear are true. I understand things better if the math (ballistics) matches what countless shooters have observed in the field that I've read about. That said, I'm sure I've got some things wrong and made some bad assumptions, but my math seems to jibe with what people have observed. Please feel free to rip it apart if you don't agree ;).

Most of this math is based on a Fulton Armory M1A NM Scout shooting Lithuanian surplus .308 at a torso-sized steel target about 16"Wx33"H

I am using the online ballistics calculator assuming typical conditions in my area:
http://www.eskimo.com/~jbm/calculations/traj/traj.html

Ideally, I'd do something like this:
http://mywebpages.comcast.net/jesse99/shooting600yards.html
but I am using some math shortcuts.

I also use the Root mean squared rule to combine MOAs from two different sources to estimate the combined MOA:
http://www.boomershoot.org/general/AccuracyWind.htm#General

I am assuming the following ammo/ballistics:
M80 Ball 150 gr, 0.195 G7 .308

The Lith surplus was chronographed at my last range trip at 2850fps with a standard deviation of 33fps, although this seems quite high for standard M80 ball ammo. Maybe it's my barrel.

Conclusions. So anyone interested doesn't have to read through the long math part, my conclusions are as follows:

- The math verifies the "rifleman" concept, which I understand as: take a 3-4 MOA rifle, put it in the hands of a marksman with a knowledge of wind and elevation ballistics for average conditions, give him basic (not match grade) ammo, and he'll be pretty accurate to 500 to 600 yards on a torso sized target. No fancy ballistics or laser rangefinders are needed (assuming he can range the target to 10% or so) and be moderately good at reading the wind. All he needs is his rifle, zeroed fairly close to his conditions. I'd even venture to say if he has more like a 2-3 MOA rifle (like a standard grade M1A), he can definately be one-shot/one hit to about six hundred yards.
- 800 yards is about the limit of basic ammo pecision for the M1A for a torso-sized target, and between 600-800 yards, you really need to be careful about ranging precision and probably start drawing sketches and ranging multiple objects unless you have a laser or other accurate rangefinder - unless of course you can dial in trial shots. You also need to be fairly good at reading wind. A skilled rifleman with an accurized M1A, match ammo, and some honed skills could probably still be accurate at this range, even on the first shot.
- For consistent hits at 800 to 1000 yards, you definately need a match grade/accurized M1A and match grade ammo. Also, a lot of little things start conspiring together to throw off your shot, like temperature. A one size fits all ballistics table isn't going to cut it if you can't take trial shots to dial your target in. Ranging the target is critical, and even if you get everything right, hitting a torso target at 1000 yards is very tough with a rifle like the M1A. One shot/one hit is even more difficult, because you need to range, read wind, know whether conditions (and the ballistics for those conditions) very accurately and adjust for things I haven't even thought of. This is where the difference between a .308 bolt gun with higher muzzle velocity and higher inherent accuracy really makes a difference in hitting the target or not, assuming you are up to the task of taking advantage of it. If you can make one shot/one hit shots at this range with an M1A or bolt gun under a variety of conditions, you are truly a very skilled marksman/sniper. At this range, it sure wouldn't hurt to have a rifle cant indicator, either.
- Assuming the shooter is much more accurate than the rifle, MOA at 100 yards is probably a pretty good indicator of rifle/ammo precision. Even out to 300 yards, assuming the wind is not a factor, the MOA is probably indicative of the rifle/ammo, unless the ammo is bad. Beyond that, all sorts of things like muzzle velocity variations, minor wind variations and things beyond the shooter's control start making MOA "grow." It would not be unusual to expect a 0.5 MOA shooter/rifle/ammo at 100 yards to have 1 MOA or less accuracy at 1000 yards - it's just the way the math works.

Rifle Precision. It's not an exaggeration to say many people are obsessed with how accurate a rifle is is in terms of MOA. I believe my rifle is currently shooting the Lithuanian surplus about 2 MOA in my hands and is probably capable of 1.5 MOA as-is, or if I'm lucky 1 MOA with match grade ammo. What does this mean for it's effective range? How much would I actually improve if I had a 0.5 or even a 0.25 MOA rifle? I've been under the misconception that a 2 MOA rifle is a 2 MOA rifle at any range, not just 100 yards. I've heard that MOA tends to grow with range, but just assumed it was due to varying winds, which have more impact at longer range. This is not the case.

What accounts for the growing MOA at distance is not only varying winds, but varying muzzle speeds, and probably other factors as well. Given the chronograph data on the Lithuanian surplus, I can tweak the ballistic calculator to account for varying muzzle velocities and see the effects. Assuming mean plus 1.5 standard deviations as a cutoff, about 1 out of 7 shots will be a "flier" due to the varying muzzle velocities alone. I'll assume this is a proxy for MOA precision. For the Lith surplus, this means about 1 in 7 shots will have a muzzle velocity that differs from 2850 fps by 50 fps or more. Running the ballistics calculator gives no detectable difference at ranges up to 300 yards, about 0.5 MOA at 600 yards and about 1.4 MOA at 1000 yards. I assumed a 15 mph wind, so for calm conditions, the numbers would be slightly less. It's clear to me a sub-MOA rifle doesn't do much good at long range if you aren't shooting consistent loads (match grade ammo).

It appears that handloads, or at least match grade ammo can achieve as low as 15 fps deviation based on looking around the web, so using the same method as above, match grade ammo (same bullet weight and mean velocity) would result in differences of: 0.2 MOA at 600 yards and 0.6 MOA at 1000 yards. This is no surprise - you need good, consistent ammo to take advantage of an accurate rifle at long range, especially beyond 600 yards.

The ballistic calculator confirms that an error in the shooter's hold, or the way the rifle barrel whips results in a constant MOA error at any range, so MOA does not "grow" with distance.

What is surprising to me is that the accuracy difference between regular surplus (at least Lithuanian surplus) and match grade ammo should be unmeasurable at ranges under 300 yards if the only difference is muzzle velocity. If it is detectable, then something else is going on, like the varying loads are causing the barrel to whip different directions or amounts or it is impacting the shooter or rifle in some way. Maybe this is one place where the difference between a bull barrel and a thinner barrel starts to matter. I'm assuming the difference between match grade ammo and regular ammo is simply the powder charge, but in reality, variations in bullet diameter and weight all would have an impact. Also, match ammo would almost certainly have a different loading/bullet weight/powder than the Lithuanian surplus, but sisnce I don't have any statistics for match grade ammo in my rifle, I'm assuming it's solely due to charge variation.

Given a 0.5 MOA rifle, shooting sub-MOA at 1000 yards means everything else (shooter + ammo) is probably about as good as it can possibly get. Again, no surprises.

What about a rifle like the M1A? If I am shooting the rifle at 2 MOA using Lith surplus, I figure I should be able to shoot about 2.1 MOA at 600 yards and 2.4 MOA at 1000 assuming I get everything else right. Assuming I can improve that to shooting 1.5 MOA at 100 yards, I should be able to shoot 1.6 MOA at 600 yards and 2.1 MOA at 1000. Given the 16"Wx33"H steel target, it's clear I should be able to hit it all day long at 600 yards, but will miss a quite a few at 1000 yards, assuming of course I get range and wind right and there are no problems with the "subsonic threshold:"

http://www.fulton-armory.com/M1A_long_range.htm
http://yarchive.net/gun/rifle/supersonic.html

Splitting the difference, 800 yards is probably the effective range of the rifle, which jibes with what the military tends to report for the M-14, which I believe is with M80 ammo, although using M118LR round would probably help between 600-800 yards. The math seems to work. Assuming 1.5 MOA rifle+shooter and match grade ammo, I should be able to shoot about 1.6 MOA at 1000, and assuming I get everything else right, hit the target consistently, with a miss here and there. That's a big "if" for me personally, especially with any wind, but it's not out of line with what I've heard M1A NM rifles are capable of at 1000 yards, so again, the math seems to work.

Rifle Cant. A shooting buddy has told me that rifle cant matters. Assuming a 5-degree cant angle on my rifle, the ballistics calculator computes about a 0.8 MOA error at 1000 yards. In fact, this error is pretty consistently high starting at 0.6 MOA at 200 yards. At a 10 degree cant angle, it's about 1.1 MOA at 100 yards and 1.3 MOA at 1000 yards. It's safe to say if you zero your rifle while canted, you may have problems later, or if you shoot with an inconsistent cant angle, your MOA will suffer. I'd guess that if you aren't paying attention to cant at all, you may not even notice a 10 degree cant. I'd guess a 5-degree cant is relatively undetectable without aid if you are paying attention. In my case, it could make the difference in hitting the steel target or not, especially beyond 600 yards or so. If you are at least consistent in the way you hold the rifle when firing and zeroing, can't won't matter a whole lot.

Wind. Any long range shooter knows about wind, but I've never really seen anything on how accurately the wind needs to be estimated. I'm guessing that I can't personally read the wind any closer than 3 mph without aid such as a windmeter and range flags. How much diffrence would that make? That's 0.8 MOA at 600 yards, 1.5 MOA at 800 yards, and 2.3 MOA at 1000 yards for a crosswind. About 800 yards is where I'm really going to feel the ability to read wind more accurately make a difference, at least when trying to hit a steel target. I can of course correct for wind error by dialing in, but wind conditions around here can change fairly rapidly.

Ranging Error. Assuming I have an object of known size, I can use my scope to range it. How accurately can I do this? I'm guessing 10%, especially if I don't know the exact size of the object, and maybe 5% if I do. If I'm really paying attention, and have the time, I could probably do better by drawing a sketch and ranging multiple objects and splitting the difference. At 300 yards, 10% error is about 0.8 MOA. At 600 yards, it's about 1.5 MOA. At 800 yards it's about 3 MOA and at 1000 yards, it's 6 MOA. A 5% ranging error would be about half these values. If given the opportunity to dial in your range, none of this matters, but if I need to hit that steel target at unknown range on the first shot, a laser rangefinder is probably a must beyond 700-800 yards or so. If I want to bump up my first-shot accuracy fairly easily between 300-700 yards, it certainly wouldn't hurt to have one.

Weather/Altitude. It's a given that you should zero your rifle whenever given the opportunity for changing conditions, but I must admit, I rarely do. How badly does this affect accuracy? If you shoot in St. Paul Alaska (a place in the US where the barometric pressure changes the most), the calculator says you'll see about 1.0 MOA variation at most at 1000 yards, if you zero for the average pressure. If you are in San Diego, where pressure changes little, you'd see 0.3 MOA variation at 1000 yards. For my purposes, barometric pressure matters little, but if you're trying to shoot a 0.25 MOA rifle at 800 to 1000 yards without the benefit of dialing it in, you probably ought to take it into account. In my area (Colorado), altitude varies quite a bit. A 500 foot variation results in about 0.6 MOA at 1000 yards. If I were climbing several thousand feet after zeroing the rifle at the start, I'd probably want to adjust for altitude and pressure if taking a 1000 yard shot. Unfortunately, both of the above (altitude and pressure) tend to move together in terms of throwing your shot off. Fortunately, temperature tends to move the opposite way - temperatures usually drop with increasing altitude, which decreases muzzle velocity and somewhat counteracts the effects of increased altitude and decreased pressure.

In the case of temperature, the ballistic calculator adjusts air density to account for temperature, but the powder temperature in the cartridge also impacts muzzle velocity. You get higher muzzle velocities with temperature, and as far as I can tell, it's anywhere from 1 fps/degree F to 2 fps/deg F:

http://www.exteriorballistics.com/ebexplained/4th/56.cfm
http://www.riflebarrels.com/articles/bullets_ballastics/long_barrel_velocity.htm

Abnormal temperatures also can have an impact on bullet stability, but I'm ignoring that:
http://www.frfrogspad.com/miscellb.htm#stabilize

Thus, temperature conspires in two different ways to impact accuracy, both before the bullet leaves the muzzle and after. So, for the situation of the M1A, assuming 2 fps /degree F, a 20 degree change in temperature can have 0.1 MOA impact at 100 yards, 0.8 MOA impact at 600 yards and 2.4 MOA impact at 1000 yards. Here in Colorado, it's not unusual to fluctuate that much or more during the course of a shooting day. If you're wanting one shot - one hit accuracy at 1000 yards, I conclude temperature needs to be taken into account beyond 800 yards or so. If you wait long enough, it's possible you may not hit the same target you were hitting previously at 800 yards or beyond if you don't account for temperature.

For humidity, a change from 0% to 50% has barely 0.1 MOA impact at 1000 yards, so it can be neglected.

Other Factors. I'm ignoring all the other factors such as scope accuracy:
http://www.precisionworkbench.com/3.htm

Coriolis force:
http://www.frfrogspad.com/miscellj.htm#Coriolis

or any other factors people have discovered that turn shots into misses.:rolleyes:

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Zak Smith
November 28, 2007, 12:21 AM
For atmospheric density effects on downrange trajectory, I found it helpful to index data off Density Altitude. (see explanation here http://demigodllc.com/datacards.php )

Run a 100-yard primary zero. This minimizes the effects of atmo density on your zero. Also does the same for wind drift during sight-in.

For temperature effects on ammo and muzzle velocity, try to find a load which is thermally stable. I have found Varget and H4350 to be exceptionally good in this regard (my .260 load changes less than 10fps from 5F to 95F).

You can do better than 15 fps S.D. with reloads.

For long-range hits, you really want a load which retains enough velocity at long range. Certainly solidly supersonic, but a load which is on its last legs at 900 yards will be a lot harder to make hits with than one which is still clipping along.

Provided the scope is relatively "square" on the rifle, and the reticle is relatively square to the scope body (ie, the erector tracks in-line, not at an angle to what you "see" as the scope's level), the eye is pretty good at levelling things.

To 1000 you can ignore Coriolis and Magnus.

Ranging is key. If you don't range the target to a certain accuracy, you have basically no chance of hitting it. (Alternatively, knowing your trajectory will let you know how much you can "estimate" or "fudge" this.)

Wind is wind. You learn how to make a decent first guess, but with most 308 loads having 70-100 inches of drift for a 10 mph cross, even a few mph error can cause a miss. You also learn how to track conditions over time, throughout the day, etc.

At most of the field-type matches, where we get one shot per steel target and no sighters, the vast majority of misses are due to mis-judging the wind, and the majority of the rest are due to bad position / bad trigger presses due to poor improvised shooting positions.

As for actual accuracy.. one the two ends-- A rifle that shot 1.5 - 2 MOA at 100 yards had a hard time keeping 50% of rounds on an IPSC target at 1000 yards. On the other hand, our rifles that shoot in the 0.2's and 0.3's at 100 seem to be able to shoot into 6-8" at 1000 yards pretty easily, provided the shooter is correctly tracking wind changes.



http://demigod.org/~zak/DigiCam/PRTC-2006/icon/B100_2011_img.jpg
article | Practical Long-Range Rifle Shooting, Part I - Rifle & Equipment http://demigodllc.com/icon/extwh3.png (http://demigodllc.com/articles/practical-long-range-rifle-shooting-equipment/)

http://demigod.org/~zak/DigiCam/AI-AWSM/icon/A100_1910_img.jpg
article | Practical Long-Range Rifle Shooting, Part II - Optics http://demigodllc.com/icon/extwh3.png (http://demigodllc.com/articles/practical-long-range-rifle-shooting-optics/)

http://demigod.org/~zak/DigiCam/TRG42AWSM/icon/D100_4594_img.jpg
article | Practical Long-Range Rifle Shooting, Part III - Shooting http://demigodllc.com/icon/extwh3.png (http://demigodllc.com/articles/practical-long-range-rifle-shooting-shooting/)

If you're in Colorado, come out and shoot with us!

ETA- also, it's critical to box test your scope before trying to apply your data to hit long-range targets. If the scope isn't tracking as advertised, it'll be an exercise in futility. BTDT...

TimboKhan
November 28, 2007, 12:26 AM
I've literally never felt stupider than I do right now, and whats worse, Groovski is a shooting buddy of mine! I am going to have to start studying so that I can talk on an equal level as you next time I go out....

Groovski
November 28, 2007, 02:33 AM
I've literally never felt stupider than I do right now, and whats worse, Groovski is a shooting buddy of mine! I am going to have to start studying so that I can talk on an equal level as you next time I go out....

That gave me a laugh - there's no need for that. I learn more from shooting with you than any book, my friend. Between you and Rockstar.esq, you're the whole reason I'm inspired to learn to be a better shooter! It's just I feel compelled to know the why as well as how.

Groovski
November 28, 2007, 03:27 AM
Thanks for the reply Zak.

For atmospheric density effects on downrange trajectory, I found it helpful to index data off Density Altitude. (see explanation here http://demigodllc.com/datacards.php )

That definately looks like a good idea.

Run a 100-yard primary zero. This minimizes the effects of atmo density on your zero. Also does the same for wind drift during sight-in.

Now that you mention it, that makes a lot of sense. I was close to adopting by the "rifleman" school of thought where you zero for the maximum range (about 250 yards) where you can still hit the vital zone at any range less than that. It does make sense to shoot your zero at 100 yards and remove most of the things that could corrupt your zero. I wonder if shooting the zero at 100 yards, then adjusting it manually to the "rifleman's zero" at 250 and modifying your ballistic tables to match would give the best of both worlds?

For temperature effects on ammo and muzzle velocity, try to find a load which is thermally stable. I have found Varget and H4350 to be exceptionally good in this regard (my .260 load changes less than 10fps from 5F to 95F).

I'll certainly do that when the reloading bug catches me. Until then, I'm stuck with what I can buy, but if anything, this has taught me I probably need to hand load if I want to extend my range - something I knew, but just confirmed.

You can do better than 15 fps S.D. with reloads.

That would make a diffrence. How low do you think you can achieve?

For long-range hits, you really want a load which retains enough velocity at long range. Certainly solidly supersonic, but a load which is on its last legs at 900 yards will be a lot harder to make hits with than one which is still clipping along.

Thanks for confirming that.

Provided the scope is relatively "square" on the rifle, and the reticle is relatively square to the scope body (ie, the erector tracks in-line, not at an angle to what you "see" as the scope's level), the eye is pretty good at levelling things.

I just guessed at what my error might be, and maybe I overestimated. If I have some free time, I may do an experiment and try to measure how accurately I can level my rifle.

To 1000 you can ignore Coriolis and Magnus.

Duly noted.

Ranging is key. If you don't range the target to a certain accuracy, you have basically no chance of hitting it. (Alternatively, knowing your trajectory will let you know how much you can "estimate" or "fudge" this.)

I am discovering this, as I try to extend past 600-700 yards. Depending on where your target is, it's not easy to just dial it in, even if you can have sighter shots. If the ground behind the target is flat, you can spend a lot of time trying to guess range by spotting your misses. An accurate range to start with would make it much easier.

Wind is wind. You learn how to make a decent first guess, but with most 308 loads having 70-100 inches of drift for a 10 mph cross, even a few mph error can cause a miss. You also learn how to track conditions over time, throughout the day, etc.

Definately. I'll have to get better to extend my range.

At most of the field-type matches, where we get one shot per steel target and no sighters, the vast majority of misses are due to mis-judging the wind, and the majority of the rest are due to bad position / bad trigger presses due to poor improvised shooting positions.

It must be a lot easier to correct things when you know why you are missing. ;) At this point, it still takes me awhile to figure out why sometimes.

As for actual accuracy.. one the two ends-- A rifle that shot 1.5 - 2 MOA at 100 yards had a hard time keeping 50% of rounds on an IPSC target at 1000 yards. On the other hand, our rifles that shoot in the 0.2's and 0.3's at 100 seem to be able to shoot into 6-8" at 1000 yards pretty easily, provided the shooter is correctly tracking wind changes.

Thanks for that confirmation....it seems to jibe roughly with what I would calculate/guess. I'm guessing that shooting 0.6 to 0.8 MOA at 1000 yards with a 0.2 to 0.3 rifle means you are shooting darn close to perfection, after accounting for the ammo variation. Was that with .308 rifles?

article | Practical Long-Range Rifle Shooting, Part I - Rifle & Equipment
article | Practical Long-Range Rifle Shooting, Part II - Optics
article | Practical Long-Range Rifle Shooting, Part III - Shooting

Great articles. I refer to them from time to time.

If you're in Colorado, come out and shoot with us!

Definately! I'm right there in Loveland.

ETA- also, it's critical to box test your scope before trying to apply your data to hit long-range targets. If the scope isn't tracking as advertised, it'll be an exercise in futility. BTDT

Thanks, I haven't done this, but will. Do you recommend doing that visually or with actual rounds, or does it matter?

Here it's done with rounds (near the end of the article):
http://www.6mmbr.com/SchmidtBenderPM2.html

Here it's visually:
http://www.precisionworkbench.com/3.htm

I assume you adjust your ballistics accordingly if it's consistently off?

skinewmexico
November 28, 2007, 10:05 AM
I assume you adjust your ballistics accordingly if it's consistently off?

I would assume you replace your scope.

Zak Smith
November 28, 2007, 11:48 AM
Now that you mention it, that makes a lot of sense. I was close to adopting by the "rifleman" school of thought where you zero for the maximum range (about 250 yards) where you can still hit the vital zone at any range less than that. It does make sense to shoot your zero at 100 yards and remove most of the things that could corrupt your zero. I wonder if shooting the zero at 100 yards, then adjusting it manually to the "rifleman's zero" at 250 and modifying your ballistic tables to match would give the best of both worlds?
The purpose of the "primary zero" is to index the distance vs. "drop in angular units" curve at a known point.
http://demigod.org/~zak/firearms/dial_moa.png
Conceptually, you are sliding the curve up and down and need to get it set at a known point. You can do this at any distance; however, 100 yards has some advantages:

* it's virtually impossible for atmo density to change this point of aim (your primary zero won't be off due to atmo changes)

* even a full value of wind won't screw up your zero "too" much. Yeah it'll be off, but less than 1 MOA if you're totally oblivious to a 10mph cross, vs. over 1 MOA at 200 yards.

* it's far enough that you can discern differences in POI vs POA

* 100 yard KD ranges are very common, more common than 200-yard (or whatever)

Whenever someone says they run a 200, 500, whatever, yard primary zero on their long-range rifle that has a big scope with big knobs on it, I point to the knob and say, "That's what the knob is for." You want a 200-yard zero? Just dial it up to 1.75 MOA or whatever (it's 0.4 mils for my rifles). You mention a good point about having a good general-purpose zero pre-set on the scope for immediate use within the cartridge's point-blank range. Just dial the scope to the 250-yard dope and you're good to go. If you see a target within say 275, just point and shoot. If it's further, dial it.

How low do you think you can achieve?
With good loads in a good barrel, you can get to single digits.

On ranging and target backdrop- For practice, I like to place targets in front of hills both to aid spotting. However, in matches, we often place targets where it is difficult to spot misses, for just the opposite reason. :evil:

Another note on ranging- Sometimes because of mirage, light, target area, etc, you just can't range the target exactly using a LRF. At this point, you can pick other objects in the vicinity to range, keeping in mind the relative position vs. the actual target.

It must be a lot easier to correct things when you know why you are missing.
A big part of LR shooting is the homework you do in the weeks and months prior to the shoot, or event, or whatever, and maintaining confidence in the things you know. If there is one thing to remember when you start missing, it's that: if your rifle has been solid in the past, and has double-checked dope values, then you should keep confidence in your drop data and look for the windage error. Many times left/right errors appear to untrained spotters as "high" misses because they kick up dirt that splashes upwards.

I'm guessing that shooting 0.6 to 0.8 MOA at 1000 yards with a 0.2 to 0.3 rifle means you are shooting darn close to perfection, after accounting for the ammo variation. Was that with .308 rifles?
A variety of 6.5mm, 308, and 338LM.

Yep, that's the box test. If you can get the rifle steady enough so it doesn't move when you look through the scope and adjust the knobs, you don't actually have to fire. With an accurate rifle, it's just as easy to shoot if you don't mind burning some powder. With a 1-2 MOA rifle, it's going to be hard to conclude anything about the scope while shooting th rifle-- just too much "random" noise in the results.

If the scope is off, I agree with skinewmexico-- send it back and demand that it be fixed. Technically, you can adjust your data values by scaling them appropriately to match any constant click error, but now you have to crunch the numbers on every new dope sheet you print. Just get it fixed.

I'll be going out for LR shooting a few times before Xmas-- email me and we can maybe hook up.

-z

Groovski
November 29, 2007, 11:24 PM
You mention a good point about having a good general-purpose zero pre-set on the scope for immediate use within the cartridge's point-blank range. Just dial the scope to the 250-yard dope and you're good to go. If you see a target within say 275, just point and shoot. If it's further, dial it.

Genius. I can see there's no advantage to a Point Blank type zero, even for riflemen, if you simply memorize your 250-yard (or whatever it is) dope (or inscribe it on your turret). I realize most of this stuff is on your Practical Long Range Shooting Guides, but it takes awhile to sink into some of our thick skulls ;). After rereading your guides, I have to ask how often do you zero? I'm guessing at least when you have reason to believe your scope is off or whenever you change loads. Your ballistic charts take care of the rest.

A big part of LR shooting is the homework you do in the weeks and months prior to the shoot, or event, or whatever, and maintaining confidence in the things you know. If there is one thing to remember when you start missing, it's that: if your rifle has been solid in the past, and has double-checked dope values, then you should keep confidence in your drop data and look for the windage error. Many times left/right errors appear to untrained spotters as "high" misses because they kick up dirt that splashes upwards.

I can see this is true if you have an accurate range. Thus, I'm sold on having an accurate rangefinder if I want to improve my chances of hitting it the first time or even correcting my shot if I don't. I can definately attest that trying to correct a missed shot at long range with no hill behind the target and a little wind, using a reticle rangefinder is an exercise in humility for a beginner. :rolleyes:


Followup:

Cant. As a follow-up, I rigged up a Rifle-cant-o-meter (basically a fixed pendulum)to test my skill at achieving an upright hold from the prone position. I took aim at a target, did my best to level the scope, then read the rifle cant on the Cant-o-meter, then repeated many times with other targets, pretending I was setting up each time anew. I did two tests, one with a view that included upright "clues" such as telephone poles, and one test where no visual clues were included, and found the following:

With clues:
Standard deviation = 0.67 degrees

Without clues:
Standard deviation = 0.74 degrees

In both cases, my mean was within about 0.25 degrees of true upright. What this says is I can apparently reduce rifle cant to within a degree when I pay attention to it, which is much better than I thought I could. Zak was correct in his first reply.

Assuming 1.5 standard deviations is close to the effect on MOA my cant would have, then this gives about 0.1 MOA at 100 yards and 0.2 MOA at 1000 yards. This imprecision isn't going to make a difference in my M1A, but precision shooters may want to consider the effect of cant angle. You'd have to balance the time to make a bubble level level versus the MOA gain. For me, it's not worth it.

These guys have a different view on cant, though:
http://www.shootingsoftware.com/ftp/cantech.txt

Powder Temperature. These guys show how to do tests on powders to figure out how they vary with temperature, except they measure pressure. They found that both powder temperature and barrel temperature affect pressure, which affects muzzle velocity downrange. I never considered barrel temperature, but they conclude it has even more impact than powder temp:

http://www.shootingsoftware.com/ftp/Pressure%20Factors.pdf

Other: A caveat on using standard deviation numbers:
http://www.shootingsoftware.com/ftp/Perverse%20Nature%20of%20SD.pdf

One major thing I forgot to look at is shooting uphill/downhill:
http://www.longrangehunting.com/forums/f19/up-downhill-corrections-22768/

Finally, these are some sources of more info on this stuff:
http://www.longrangehunting.com/forums/f19/
http://www.shootingsoftware.com/tech.htm

Zak Smith
November 29, 2007, 11:49 PM
Going sort-of in reverse order:

Here is an excellent analysis of inclined fire http://www.exteriorballistics.com/ebexplained/article1.html

In practice, you need a LOT of vertical height between you and the target to produce both the distance and the angle required such that a correction is needed. For shot like this we haven't needed to correct, besides maybe just aiming a little low of center http://demigodllc.com/photo/BSR-2007.03/?small=D101_3129_img.jpg

On powder temp and barrel temp-- this is one of those things that changes load to load and gun to gun. The barrels on my LR rifles don't change POI when heated and the loads don't increase in velocity significantly even with barrels too hot to grab. However, it's not uncommon to see both those effects.

On the angle/cant-- I admit I cheated a little. I tried a "level grouse" for a while. I found that at approx 1* overall travel, I was on average more accurate than it was; and when it was made more sensitive, it was too sensitive to be useful.

On the zero. My strategy for load development is to find an accurate load with good LR ballistics, and then stick with that load pretty much forever. A common trap is to keep messing with loads to find some marginal improvement-- instead of LR shooting and gaining confidence in the system.

I load in big batches, and I only tweak the load when I get a new batch of powder and it needs a few tenths of a grain of adjustment to get back to the same velocity. I've gone up to a year without making a zero adjustment; however, it's a good idea to verify zero when you have a chance. If everything's solid (load/rifle/scope), you should be able to show up at a different locale, dial to the target distance, and make a hit.

-z

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