308 100m zero.

[Heym SR20]

I don’t like to be critical of what other’s write but we really have to be careful of our advice

Beginners turn to this sort of thread for guidance

Let us not over complicate it or pretend there is some sort of magic involved

If you want to zero at 50m and work from there

Or..

Zero at 100

Or 1” high at 100

Or 200m

Who cares?!?

Just know your rifle, your ammo, your drops and wind effects

It doesn’t matter what the starting point is

What matters is that you know your tools, your land and your quarry

Keep it simple

Know your limits

Practice

If centre fire is too expensive then practice with .22LR

If there are any newbies out there that need to zero their rifle, practice the DSC shooting test, Or learn something about shooting at varied distances

I’m happy to give you a day FOC if you can make it to Cornwall

PM me

J

PS

MPBR is an abbreviation for Max Point Blank Range

Imagine a pipe (let’s say a 5” drainage pipe) between you and your quarry

Your ‘ line of sight’ is down the middle

A MPBR is the max range that the bullet will not deviate from within that imaginary pipe

It is a distance where you don’t need to worry about the exact range to target as you will still hit the critical area

You could have an MPBR for 6” or 4” or 3”

It is an infantry thing, but useful for us hunters

The US forces call it “battle sight zero” I believe

A very good post and pipe analogy is excellent.

Following on the one big challenge with choosing a single point to zero at is that you don’t know where on the trajectory curve the line of sight intersects the trajectory curve.

Starting at first principles. If bore is absolutely Horizontal and the sight line is parallel to the bore at say 4cm above the bore line, the bullet will hit the paper exactly 4cm low at the muzzle. The bullet starts falling immediately it leaves the muzzle so at 100m it will hit at say 10cm low (I don’t know the exact amount.

By zeroing you tilting the bore upwards so the bullet is fired in an upwards direction. It will fly in a curve. The bullet can meet the trajectory curve in one of two ways.

1) the sight line is adjusted so that it just clips the top of the trajectory curve. If you zero at 100m this is probably what happens. Any where after 100m the bullet strikes low.

Or

2) the bullet crosses the line of sight twice - first on the way up, then it curves over and again on the way down. Typically you get a first zero at about 60 odd metres and a second at around 200 metre, with the bullet being about 4cm high at 100m

However in 1) above you may well have set the sights so the bullet is still climbing at 100m, rather than the line of sight intersecting the top of the arc.

Indeed with all the ballistic apps etc on which part of the curve do they assume that line of sight intersects. At first crossing, second crossing or at top of trajectory curve?

 

[jthyttin]

A MPBR is the max range that the bullet will not deviate from within that imaginary pipe

It is a distance where you don’t need to worry about the exact range to target as you will still hit the critical area

MPBR is flawed by design. At max range, you will miss just over 50% of your shots.

Better approach is to find out the range that you can keep your shots, in field conditions, within certain area that you're happy with. Let's say 4" circle, and let's say the range is 200m. Then use calculator to see, if 200m zero keeps the trajectory within acceptable limits. That could be the imaginary tube you mentioned, but you need to allow some for shot dispersion ("group").

If you're happy with the calculation, zero at 200m. If not, reduce the zero distance (in the calculator) until you're happy, and zero at that distance (e.g. 180m). Then verify different distances by actually shooting (and gaining an understanding, what kind of shot dispersion / POI you can achieve at different distances, in field conditions). And your zero distance will be your true "MPBR" distance.

 

[Heym SR20]

MPBR is flawed by design. At max range, you will miss just over 50% of your shots.

Better approach is to find out the range that you can keep your shots, in field conditions, within certain area that you're happy with. Let's say 4" circle, and let's say the range is 200m. Then use calculator to see, if 200m zero keeps the trajectory within acceptable limits. That could be the imaginary tube you mentioned, but you need to allow some for shot dispersion ("group").

If you're happy with the calculation, zero at 200m. If not, reduce the zero distance (in the calculator) until you're happy, and zero at that distance (e.g. 180m). Then verify different distances by actually shooting (and gaining an understanding, what kind of shot dispersion / POI you can achieve at different distances, in field conditions). And your zero distance will be your true "MPBR" distance.

You state its a flawed design, and then go onto exactly describe how it works. The whole point is that it ensures that your bullets remain in the kill zone of the quarry intend.

MPBR on a head shot squirrel will be very very different to MPBR on chest shot moose.

And of course the theoretical bench rest accuracy is completely different to what most can manage in the field. I know that I can shot MOA type groups off a very steady position in perfect still conditions.

Field positions- things are very different. And as ranges lengthen the **** potential goes up exponentially.

 

[jthyttin]

You state its a flawed design, and then go onto exactly describe how it works.

MPBR doesn't allow for shot dispersion. If you use circular kill zone, at max range "ideal shot" lands perfectly on the lower border of kill zone. So about half of the real world shots miss the kill zone.

The method I described allows for shot dispersion, and will result in shorter max range than MPBR. And more realistic understanding of shooter/rifle/ammo capabilities.

 

[tackb]

for nearly all centrefire deer calibres you can use the 2-0-9 system ,

zero at 200m and then it's 2" high at 100 and 9" low at 300

run any 'normal' deer round through your ballistic app and your bullet won't be far enough from that to matter

most people can remember 2-0-9 and it will get deer on the floor at most normal stalking distances

but the very best way is to shoot your kit a lot and become familiar with it!

 

[Foxyboy43]

Enuf of the alphabet soup already !
Zero your rifle at X yards or metres, spot your beast then stalk in to that distance - clue in the title….

 

[CBH Australia]

It’s common to have your .308 hitting 1.5-2” higher at 100.

The range might be measured in metres or yards and 100yards is 91m .

Without further confusion having it hit high at 100 will take a Fallow Deer or a Boar every time if you do your part. It needs to happen instinctively if you just shoot between 50-200

I recently found this site called

ShootersCalculator.com | Ballistic Trajectory Calculator

Calculates the ballistic trajectory of a bullet fired from a rifle, handgun or other firearm. Produces a ballistic trajectory chart and table that shows the drop, velocity, kinetic energy, windage, and trajectory of a bullet.

shooterscalculator.com

You can put in the data to make a chart to suit your rifle and ammo.

The 20” barrel should show a lower velocity than most longer barrels so it’s good to get good data. Can you verify the velocity with a chronograph to validate data? Can someone help?

Even if you use a velocity 100fps lower than the box value it’s a start.

You don’t need to complicate it until you start your own research and get accurate data.

I access a 200m range with increments at 25,50,75,100,150 & 200m

200 is a long way in the bush and I have shot a lot of pests in the past. I used a 20” 7mm-08 and own .308 and others.

Hitting an inch or inch and a half high at 100 I have been able to accomplish a lot of one shot kills on pigs, fallow and foxes.

Using a .223 hitting 1” high at 100m is commonly used in Australia and kangaroos are harvested commercially (headshots) from a vehicle rest with shooters instinctively holding on for most shots and not overthinking the shot unless there is wind or distance to consider.

A large roo head is smaller than a Roebuck head,

 

[CBH Australia]

Enuf of the alphabet soup already !
Zero your rifle at X yards or metres, spot your beast then stalk in to that distance - clue in the title….

Not so easy to always stalk to the set distance and not required.

The question is in the first post.

At 100 I suggest 40-50mm high at 100. 1-1/2” to 2” high.

I see a lot of “ Stalkers” in the UK using sticks on You Tube and some on open fields. 2” high at 100 will get him there. Groups over stick will open up more than a good group over the bench with a small definitive aiming mark or an inch or less.

 

[JTO]

I think I'll go with bowji john! "You could have an MPBR for 6” or 4” or 3” "

 

[billy_boyle_2010]

@

MPBR doesn't allow for shot dispersion. If you use circular kill zone, at max range "ideal shot" lands perfectly on the lower border of kill zone. So about half of the real world shots miss the kill zone.

The method I described allows for shot dispersion, and will result in shorter max range than MPBR. And more realistic understanding of shooter/rifle/ammo capabilities.

Totally agree. This is the exact point I'm making on another thread. MPBR is theoretical. When you factor in human error and group size at the extremes of the bullets path across its MPBR- it looks a lot less favourable.

 

[Foxyboy43]

Not so easy to always stalk to the set distance and not required.

The question is in the first post.

At 100 I suggest 40-50mm high at 100. 1-1/2” to 2” high.

I see a lot of “ Stalkers” in the UK using sticks on You Tube and some on open fields. 2” high at 100 will get him there. Groups over stick will open up more than a good group over the bench with a small definitive aiming mark or an inch or less.

Yeah I know - I was being mildly provocative….
Moi?

 

[jcampbellsmith]

...At 100 I suggest 40-50mm high at 100. 1-1/2” to 2” high...

Not much use for a 5kg or 6kg roe deer.
Regards
JCS

 

[CBH Australia]

Not much use for a 5kg or 6kg roe deer.
Regards
JCS

Then what point of impact would you sight a .308 at if the OP wants to hunt out to 200?

When we are shooting pigs it’s generally with a view to shoot every pig in the mob if possible so you might take a boat, the sow and follow up shooting the small ones too and any others running in the mob.

The target species size doesn’t change the rifle trajectory or point of impact