Is that with a 100yd zero?

quote:

Posted 12 September 2011 08:59 Hide Post
Is that with a 100yd zero?


Lar45

All were sighted 1" high at 50 yards except the .500 JRH that was center at 50 yards. It seems to have less drop. My boolit is 440 gr and a near WFN design.
The JRH is the only gun I have that when sighted center at 50 will still hit near center at 100.
Take all from the .44 up and as the caliber gets larger and boolits heavier, drop gets less no matter the meplat or ogive.
If I can keep this scope from coming loose I will shoot from 50 to 100, to 150 and 200 yards and post drops with a 50 yard zero.

I found this BC calculator at Handloads.com :
http://www.handloads.com/calc/
You can enter the bullet weight, caliber, and nose shape to get an estimated Ballistic Coefficient. It will also give you a trajectory table.

We'll also need the sight height(center of bore to center of scope) for your scope.

This will be great to see if the ballistic calculators come close to reality.

everybody keeps saying to actually shoot the guns. i have and have stated it several times, you will not vary much at all from the ballistics calculator. a couple inches in the most extreme case. i'm gonna say it again so i can say i did, but any idea the 500 heavy and slow is as flat as anything faster and lighter from a 475 or 454 has to do with the recoil and barrel transit than an actual trajectory being as flat.

quote:

Posted 13 September 2011 03:03 Hide Post
everybody keeps saying to actually shoot the guns. i have and have stated it several times, you will not vary much at all from the ballistics calculator. a couple inches in the most extreme case. i'm gonna say it again so i can say i did, but any idea the 500 heavy and slow is as flat as anything faster and lighter from a 475 or 454 has to do with the recoil and barrel transit than an actual trajectory being as flat.

This is not true because sight adjustments have removed barrel rise.
It is only true if you sight for a light fast boolit, then shoot a heavy one without changing the sights.
Every weight boolit and velocity will have a different POI but once sighted for the boolit, nothing will change at any range. You can read true drop with proper sight settings.
Sight in a.44 with 240 gr bullets at 50 yards, then shoot 200 yards with a 320 gr will give you nothing at all but sight in with the 320 at 50 and then your 200 yard drop has meaning.
Your barrel rise is exactly the same from 50 to 500, guns do not throw boolits UP.

Whatever the cause is it does not drop at distance when shot the way one would predict

Use Whitworth's 500L and the 525 grain load and verify

quote:

Your barrel rise is exactly the same from 50 to 500, guns do not throw boolits UP.

I have been pondering the difference between your data and the well proven math of ballistic calculation.

I agree with the first half of your statement, but could the gun be throwing the bullets up? Pretty well established that heavy and slow shoots to higher poi than light and fast with the same sight settings. Common reason given is the recoil begins before the bullet has left the barrel. If the barrel is rising with the bullet inside, and is still rising when the bullet leaves, wouldn't bullet have some vertical velocity?

Another thought: You are using a 4 moa dot, and use the bottom of the dot on the top of a target, correct?. Is "zero" where the middle of the dot is, or at the contact of the dot with the top of the target, or somewhere below?

How far above bore is your sight?

dvnv

quote:

Originally posted by dvnv:

I agree with the first half of your statement, but could the gun be throwing the bullets up? Pretty well established that heavy and slow shoots to higher poi than light and fast with the same sight settings. Common reason given is the recoil begins before the bullet has left the barrel. If the barrel is rising with the bullet inside, and is still rising when the bullet leaves, wouldn't bullet have some vertical velocity?

dvnv

Very good point. I was thinking the same thing.
I was watching some history channel show on guns and part of the program had shooting from a moving helicopter. The shooter had to give the targets a negative lead because the bullet already had some forward momentum.

A counter-point to this is if we have the barrel pointed up slightly then when the bullet leaves the barrel it will have some verticle velocity and will continue up until gravity takes over and pulls it down.

So either way the sight change should take the upward momentum out of the equation.

quote:

I have been pondering the difference between your data and the well proven math of ballistic calculation.

I agree with the first half of your statement, but could the gun be throwing the bullets up? Pretty well established that heavy and slow shoots to higher poi than light and fast with the same sight settings. Common reason given is the recoil begins before the bullet has left the barrel. If the barrel is rising with the bullet inside, and is still rising when the bullet leaves, wouldn't bullet have some vertical velocity?

Another thought: You are using a 4 moa dot, and use the bottom of the dot on the top of a target, correct?. Is "zero" where the middle of the dot is, or at the contact of the dot with the top of the target, or somewhere below?

How far above bore is your sight?

Once the boolit leaves the muzzle, it goes without a toss up. Nothing will change that, the boolit exits in line with the bore. You can not THROW the boolit anywhere else. Once the boolit leaves the muzzle in line with the bore I don't care if you waved the gun like a nut, the boolit goes where the bore was pointing at exit.

quote:

So either way the sight change should take the upward momentum out of the equation

That depends if you are catching it on the way up or on the way down. If on the way up it should appear flatter, if on the way down it should be steeper than predicted. Not sure the effect is enough to make much difference.

The 4 moa dot could though, depending on how it is being applied.

Gentlemen, think about it.

The sight adjustment ONLY removes the effect of barrel rise at the distance the gun is sighted in at.
If you have a 22lr sighted in at 50 yards, and shoot it at 200 yards the bullet will very closely follow its mathamaticly predicted trajectory.

However when you shoot a harder kicker like a 500, even though you have aimed properly, the barel has risen before the bullet has left the barrel, thus it is the same effect as aiming higher.

The harder recoil will adjust the actual "aim" of the gun before the bullet leaves the barrel.

Look again at my example of shooting the 308 rifle. At 500 meters, shooting at 500 meters, with a 500 meter zero, off a bench the gun is perfectly zeroed in.

Shooting off hand the rifle hits 2 moa higher, about 11 inches.

The only thing that has changed is the movement of the barrel, while the bullet is traveling down the barrel, due to the increased recoil movement while shooting off hand.

In a handgun if you combine higher recoil AND slower barrel time, you will signigicantly alter the sight alinment after the trigger is pulled, causing the handgun to be pointing higher, and thus causing the bullet to be released form the barrel with a higher point of aim.

You are NOT changing the mathamatical trajectory, the recoil is just causing you to be "aiming" higher, before the bullet leaves the barrel.

Yup, and let's just say that the barrel is pointing up at a 45-degree angle when the bullet exits. This has everything to do with the trajectory as it is starting out at a much greater arch.

N E 450 No2: No issues with your statement. My question was, using your example: If you have 2 identical rifles, one sighted in for 100 yds off-hand and the other for 100 yds from the bench, are the trajectories identical?

Or, in a more extreme example, if you had a 500L in a vise sighted for zero at 75, and one sighted zero at 75 off-hand, are the trajectories the same?

I am pretty sure if you rolled a ball (fast) down a horizontal board and measured the trajectory; and then did it again while raising the board (still keeping it horizontal) the trajectories would be different, assuming the both balls left the board at the same height. One had only horizontal motion, one had vertical and horizontal motion.

If you are talking about a handgun barrel that is rotating the barrel around some axis, and the bullet is leaving the same direction the barrel is pointed, perhaps the effect is non-existant or minimized. It seems like there could be a vertical component to its movement, more than just the angle of the barrel. I am not sure, ergo the question posed.

Whitworth: Not sure what you were pointing out...I am assuming all test guns and loads are sighted in for the same zero.

dvnv

dvnd, and others.

The trajectory for a given load in given athmospheric conditions does not change.

When you sighting a gun you adjust the trajectory to get the bullet impact you desire, by changing the angle of departure of the bullet. You are adjusting the trajectory/bullet drop, to suit your desires.

Bullet drop and trajectory are used by some people interchangeably, differently by others and that is where the cofusion lies.

Another example, I used a 308 rifle as a work gun for several years. PRECISE impact was very important, in its job function.

When fired prone off a Harris bipod, it had a perfect 100 yard zero.
When on the same day, same ammo I fired the rifle with a tight sling, prone, no bipod the group was always one MOA [equals one inch] lower, at one hundred yards.

This would also make the impact point three inches lower at 300 yards.

SO the IMPACT POINT has changed. The only reason it changed was because of the difference in ANGLE OF DEPARTURE.

SO again the "mathamatical" trajectory, and "mathamatical" bullet drop have remained, but some would say the trajectory and bullet drop has changed.

So we have a definition of words, in play here.
Which what may be confusing some.

However what can not be disputed, is that IMPACT POINT can be changed by the recoil of the gun, because it is in play before the bullet leaves the barrel which changes the ANGLE OF DEPARTURE.

In effect with the handguns you are AIMING HIGHER because of the recoil of the gun.

In the rifle example you when I went to the sling I was not aiming as high, because with the sling I had less muzzle rise.

So you can effect the ANGLE OF DEPARTURE up or down, depending on what you are doing different to the muzzle rise.

In my rifle examples the recoil of the same gun is different.

In the handguns we are talking about it is simply that if both a 475, and a harder kicking 500 [especially if the 500 has higher recoil and longer barrel time], the 500's ANGLE OF DEPARTURE [AOD] is more rthan the 475 and it causes the 500 to actuall be "aiming" higher than the 475.

This causes it to look like it has a flatter mathamatical trajectory, than the 475, but IT DOES NOT, it is its higher recoil/longer barrel time causing it to be "aimed higher".

well said, you did much better than i have over this topic. i've not put it into words that well.

despite your very very good explanation some will still imply that the science involved doesn't apply to pistols and less so to really big bore pistols.

i also have had the hardest time believing anyone can accurately gauge the aim point from an iron sighting handgan at 300 yards. i tried to do so on a coke can and could barely see the coke can at 300 yards as it wasn't contrasting well colorwise with the vegetation behind it but that's an object several inches tall and wide and i'm supposed to believe this aim point can be narrowed down to a 2 x 2" area to accurate gauge drop? not likely even with a red dot.
(my vision is 20/15 btw)

Here is another example.

Many 44 Magnum revolver shooters over the years have reported that when they zero their handgun for full power 44 Mag loads, with say a 240gr bullet, with 2400 powder, and then shoot that same bullet over a charge of Unique, with a lot less velocity, the have the same impact point as the faster full power load.

Now how can this be true, as the faster load has a flatter "mathamatical" trajectory.

The reason is that the slower load has a longer barrel time, it has lower recoil as well, but the KEY is it has longer barrel time.

So the barrel actuall rised more, while the bullet is in the barrel, causing it to have a higher angle of departure, and thus you are actually aiming higher, so it higher, that its mathamatical trajectory.

Now all 44 Mag shooters do not report this, because how they hold the gun effects how much muzzle rise thay have with the full power loads vs. how much they have with their light loads.

The mathametical trajectories of both loads remain the same but the two different shooters have different rates of muzzle rise, and thus their angles of departure between the two loads are different.

tradmark

Thanks. I agree with your "aiming a small target at distance" thoughts.

For example, I can shoot about as good, actually sometimes better, at 1000 [that is one thousand] yards, using the same rifle, same ammo, in a High Power rifle match.
That is because the black bulls eye is as big as the hood on a Cadillac.

So I have no problem getting a repeatable point of aim.

Put a coke can at 1000, heck I cannot even see it without a scope, and a good one at that.

For good testing with iron sights you need a bigger target ie aiming point, for consistant results.

Some of us would need a bigger aiming point than others.

N E 450 No2:

Thanks for your reply, not sure you understood what I was getting at (probably not well explained by me).

I understand the concepts you describe. I'll try a different way.

If you shoot at 1,000 yards with a stationary barrel, and shoot that same gun while it is moving 50 mph (lets say horizontally), the path of flight (I called it trajectory in my earlier post) would be different, correct? The rate of drop would be the same, but the moving barrel shot would continue to drift in the direction of movement all the way to the target, correct?

If that is true, then I was surmising that a rising barrel might have a similar effect in the trajectory of the drop. I am sure it would be true if the whole gun was being raised (or lowered, as in my ball rolling down the board example), not sure it is true if the gun is being rotated as with the recoil of a handgun.

dvnv

dvnv

Think of it this way, the gun is aimed, then fired, and then IF the barrel is moved, in any direction, by ANY means, BEFORE the bullet leaves the barrel, the point of impact will be changed.

If the change is up or down, then the elevation of the POI will be changed [relative to the mathamatic trajectory].
If the movement of the barrel is side to side, then the 'Windage" will be changed.

What has been experienced by the 500L shooters,[and by me in other guns] and what they are saying is that Recoil, does have an effect on "POINT OF IMPACT", DIFFERENT THAN WHAT THE ACTUAL MATHAMATICAL TRAJECTORY would indicate.

Remember you change the point of impact at 100 yards BY ANY MEANS, changes the point of impact at 1000 yards ten inches.

Ie., a one MOA change in point of impact, by ANY means, changes POI at every distance ONE MOA...

Since differences in recoil, DOES change the angle of departure, IT WILL change the point of impact.

This is a GIVEN, it is a FACT...

The REAL QUESTION here is "Does the difference in the difference of the difference in barrel rise, caused by the difference of the difference in recoil, and the difference in barrel time, that caused the difference in the difference of the actual angle of departure, is enough to over come the difference of the difference of the flatter mathamatical trajectory of the 475L to over come its flatter difference of mathamatical trajectory, over its difference to the Math Traj. of the 500L, to make the "actual firing" in the field to be not that much of a difference???


I have NOT fired a 475 and a 500 in the fieds at the same time, so I do not have a Dog in this "fight".

But I DO see HOW and most importantly, WHY what the guys that have shot BOTH claim.


Most simply stated, if you change the angle of departure by ANY reason, you change the point of impact DOWN RANGE.

Changes in muzzle rise, WILL change the angle of departure, which WILL change the Point of Impact.

and consequently, if you have two different trajectories that do impact down range at the same point, midrange POI will be drastically different at some point. so, for example, the two guns are sighted in at 50 yards, hit roughly the same point of impact at 300 as well, the one with the more "lob like" trajectory is prolly gonna be several inches higher than the flatter load in the middle ranges.

quote:

Originally posted by tradmark:
and consequently, if you have two different trajectories that do impact down range at the same point, midrange POI will be drastically different at some point. so, for example, the two guns are sighted in at 50 yards, hit roughly the same point of impact at 300 as well, the one with the more "lob like" trajectory is prolly gonna be several inches higher than the flatter load in the middle ranges.

EXACTLY.

OK, now that if we have got all this trajectory stuff figured out....

WHAT if it WAS one guy with six guns???

quote:

Since differences in recoil, DOES change the angle of departure, IT WILL change the point of impact.

This is a GIVEN, it is a FACT...

The REAL QUESTION here is "Does the difference in the difference of the difference in barrel rise, caused by the difference of the difference in recoil, and the difference in barrel time, that caused the difference in the difference of the actual angle of departure, is enough to over come the difference of the difference of the flatter mathamatical trajectory of the 475L to over come its flatter difference of mathamatical trajectory, over its difference to the Math Traj. of the 500L, to make the "actual firing" in the field to be not that much of a difference???

I was figuring that both guns in question were sighted in for the same zero, lets say 75 yards. Hasn't all the angle of departure differences been accounted for? Won't the bullet that has the steeper angle of departure that tops out at 75 yards drop faster than the bullet that had the shallower angle of departure that tops out at 75 yards?

I was getting at something different...I'll try one more time. If you hit zero at 100 yards with a stationary gun, it hits a certain spot at 1,000 yards. If you move the gun horizontally (lets say 50 mph) and timed the shot to hit the same zero at 100 yards, it won't hit the same spot at 1,000 yards. You have not changed the angle of departure, just put the gun in motion. If you observed from a stationary position on the ground, it would look like the bullet was curving in the direction the gun was moving.

I was thinking that if you did that in a vertical direction, it would appear that the trajectory was flatter than it should be. I suppose the 75 yard zero would compensate for the effect, if it existed at all.

So given that barrel time/recoil just changes the angle of departure and nothing else, I can't see how a slower moving bullet is going to seem to shoot flatter than it should...assuming a 75 yard zero. dvnv

I think what is in question here is that the barrel rise will somehow give the bullet a flatter trajectory.
When the bullet leaves the muzzle it will have a horizontal velocity and a verticle velocity.(physics)
The Horizontal velocity will only be effected by the bullet cutting through the wind and will be slowed down.
The Verticle velocity will be effected by gravity. From the moment it leaves the barrel, gravity will be pulling down on it.

Take a ball and throw it up into the air, it will go up and start slowing down until gravity brings it to a stop, then it will change directions and start heading towards the ground picking up speed until it hits something that will stop it.

Let's take two 500L pistols. Both identicle shooting the same load. A 525gn bullet(BC .288) loaded to 1150 fps, and a scope mounted 1.5" above center.


clamp one in a vise so it doesn't move and sight it in for zero at 100yds.
The other we will shoot from the bench and adjust the scope until it is zeroed at 100yds.
We know that the second one will recoil when shot, but we take that part out of the equation by adjusting the sights and the angle the gun is held before fireing.
Both guns should shoot to the same zero at 100yds and should both be about 2.9" high at 50yds and be about 30" low at 200yds.

I think that the bullet should have some verticle velocity given by the recoil of the gun while the bullet is still in the barrel, but we adjust the sights for that so that it will still hit our 100yd zero.

I hope this was clear enough.

Lar45: I agree...so I don't see where the perception of a slower/heavier bullet having a flatter trajectory because of barrel time/recoil comes from, assuming it is sighted in for the same zero as another gun shooting something faster. If one believes the math (I do) then the bc differences aren't remotely enough to overcome the velocity difference at 200 yards either.

I am back to thinking it is about the 4 moa dot and aiming point...or that the guns are not really zeroed at the same distance. dvnv

Ok let me try to explain it like this.

The 500L guys say that their guns shoot "flatter" over distance than the "book" trajectory would indicate.

They claim this is so because of the higher barrrel rise before the bullet exits the barrel.

So, for this demo lets take 2 identical revolvers. Both are mounted in a fixed device.
One has its barrel parallel to the ground.

The other has its barrel angled up, say 20 degrees.
So as you can see it has a higher angle of departure. This simulates that this revolver has more recoil/more barrel rise before the bullet leaves the barrel.

BOTH REVOLVERS are sighted in at 100 yards...

Yet gun No2 has a higher angle of departure.

Baised on "book" [that is shorter to type than mathametical, but it is the same thing] TRAJECTORY at 100 yards the bullet from revolver No1 will hit the target in the center, and then be on its way down...

However in gun No2 the bullit will also hit center of the target, but it will still be on its way UP.

They BOTH have the same BOOK trajectory...

BUT, gun No2 will have a flatter "field"
trajectory.

Both revolvers are actualy sighted in at two distances, the first time the bullet crosses the line of sight, on the way up, and the second time, on the way down.

The first revolver crosses the line of sight twice between the muzzle and 100 yards. These distances are determined by its Book trajectory.

The second revolver crosses the line of sight the FIRST time AT 100 yards, the second time at a FARTHER distance, again determined by its BOOK trajectory.

The difference in the "Field" trajectory between the two is the ANGLE OF DEPARTURE.

Gun No1 will have to raise its angle of departure to hit at distances past 100 yards.

Gun No2 would actually have to lower its angle of departure to hit targets beyond 100 yards...

How far beyond, well, that depends on its Book trajectory.

For that to work, Gun no.2 would have to be mounted lower than gun no.1

I think we need to assume that both guns are shot side by side, not haveing gun no 2 in a pit shooting up to hit the same target.

Failure of this comes from a gun not sighted. Once sighted, barrel rise has no affect at all. Recoil has no affect. You have removed barrel rise. It has nothing at all to do with trajectory or drop.
Every single drop figure for any gun is based on the sight in distance
If I told you something stupid like my .500 shoots flatter because it recoils more, you can come kick my stupid butt!

no, it would be the case bfr if it was the same load and zeroed to the same spot.

bullet drop is bullet drop and for two cartridges with vastly different ballistics to be zeroed at the same point one will be elevated more so than does the other.
i have no doubt that some of you have your guns sighted in to hit the same point at distance as a flatter shooting load, but it rises more in between and many times makes the cartridges unuseable in in between ranges.

i don't care if you can get a 500L to hit the same point of impact a 300 yards as i can with my 454 if it's 7" higher at 175 yards. that is unless we're gonna be shooting at 300 yards gongs all day. i use my pistols on different sized game at varied ranges all the time. what was acceptable rise at varied ranges on buffalo is not acceptable when shooting black buck does.

i have the cartridges i have for a reason, i hunt an area of the country most times that does require further shots than many of you. i also hunt many many varied game animals at the drop of a hat and need absolute versatility.

N E 459 No2: I agree that a bullet crosses "zero" twice. Seems like where it crosses zero the second time is where it is sighted in. Besides, at handgun velocities it is pretty hard to have the bullet still rising at 75 yards, and if it is, it won't be near zero at 75...at least according to the book.

bfrshooter: Its your test results that seem out of wack. Your 44 mag drop sounds about right, the 475 and 500 drop don't. I was looking for a reason, sounds like barrel rise isn't a factor. Did you test the 44 with a dot, scope or open sights?

quote:

bfrshooter: Its your test results that seem out of wack. Your 44 mag drop sounds about right, the 475 and 500 drop don't. I was looking for a reason, sounds like barrel rise isn't a factor. Did you test the 44 with a dot, scope or open sights?

Doesn't matter. What controls long range drop is boolit weight, SD and ability to maintain more velocity.
Did you watch Myth busters try to swing a bullet around a person by swinging the gun hard like in the stupid movie? Seems as if the bullet always hit exactly where the barrel was pointed at exit. The bullet could not be moved from the bore line no matter how hard the gun was swung.
No matter how high a barrel is pointed at bullet exit, actual trajectory does not change, the arch will but if you drop a bullet at the same time you fire one, both hit the ground at the same time.You can't defeat gravity. You can't throw a bullet up from the bore line or sideways from it.
You can change POI at range by holding the gun looser then you did at 50. That is YOU, not a change in bullet flight. When YOU change barrel rise, it has nothing to do with trajectory. You do nothing but defeat the sight in of the gun.

quote:

Doesn't matter. What controls long range drop is boolit weight, SD and ability to maintain more velocity.

I agree that barrel rise isn't a factor. Bullet weight and SD do contribute to a flatter trajectory, but not nearly enough at 200 yards to account for your results.

So, did you test your 44 with a dot, scope or open sights?

If you would look at it a different way, and assume your drop results aren't correct, I bet you would be able to figure out why pretty quickly. dvnv

What BFR was shooting isn't what is in question here. What's in question is if a gun held in the hand has a flatter trajectory than a gun held in a vise. I say no, they are both the same.
You take a gun, clamp it in a vise and sight in for zero at 100yds. Then shoot it at 200yds, still clamped in the vise, and lets say it drops 30".
Then take the gun out of the vise and shoot at the same 100yd target. It should hit higher because of recoil and barrel rise...
So if you want to have it zeroed at 100 yds, then you adjust the sights so that it brings it back down to ZERO at 100yds. After being re-zeroed at 100, shoot it at the 200yd target and the drop should be the same 30".

Lar45: I agree, not sure anyone disagreed. My issue is with bfrshooter's drop result, and jwp475's statement that heavy and slow shoot flatter than one would think because of barrel rise.

I was looking for a way to explain the observations being made. Put out an idea that barrel rise could be giving vertical momentum to the bullet, but can't see how that would change trajectory once compensated for by sight adjustment.

So I am back to the start, which for me was...Why does bfrshooter get such different drop numbers than a ballistic calculator predicts? Or, Why does jwp475 think the trajectory seems flatter than it really is because of barrel rise (I assumed he had the same zero)? dvnv

Ok Gentlemen, then explain why a 10lb 1oz, 308 rifle shoots 11 inches higher at 500 Meters off hand, that it does off the bench?

Why does a 308 rifle shoot one inch lower, when fired prone with a tight sling, vs off a Harris Bipod?

I think it is caused by the change in angle of departure due to the difference in the amount of muzzle rise while the bullet is in the barrel.

What else could it be?

quote:

Lar45: I agree, not sure anyone disagreed. My issue is with bfrshooter's drop result, and jwp475's statement that heavy and slow shoot flatter than one would think because of barrel rise.

I was looking for a way to explain the observations being made. Put out an idea that barrel rise could be giving vertical momentum to the bullet, but can't see how that would change trajectory once compensated for by sight adjustment.

So I am back to the start, which for me was...Why does bfrshooter get such different drop numbers than a ballistic calculator predicts? Or, Why does jwp475 think the trajectory seems flatter than it really is because of barrel rise (I assumed he had the same zero)? dvnv

Heavy and slow does not shoot flatter then heavy and fast. Velocity flattens it.
Slow can mean more barrel rise but still, if you sight to allow for it, all measurements will be accurate and you will find it drops MORE then a faster boolit.
It SEEMS to shoot flat if you ignore sighting in.
If the boolit retains more velocity, it will shoot flatter.
All of my drop figures are from boolits started at near the same velocity. so the heavy ones will retain more velocity at distance, not because the barrel went higher.

quote:

Originally posted by N E 450 No2:
Ok Gentlemen, then explain why a 10lb 1oz, 308 rifle shoots 11 inches higher at 500 Meters off hand, that it does off the bench?

Why does a 308 rifle shoot one inch lower, when fired prone with a tight sling, vs off a Harris Bipod?

I think it is caused by the change in angle of departure due to the difference in the amount of muzzle rise while the bullet is in the barrel.

What else could it be?

Angle of departure sounds exactly right to me.

quote:

Posted 15 September 2011 23:26 Hide Post

quote:
Originally posted by N E 450 No2:
Ok Gentlemen, then explain why a 10lb 1oz, 308 rifle shoots 11 inches higher at 500 Meters off hand, that it does off the bench?

Why does a 308 rifle shoot one inch lower, when fired prone with a tight sling, vs off a Harris Bipod?

I think it is caused by the change in angle of departure due to the difference in the amount of muzzle rise while the bullet is in the barrel.

What else could it be?



Angle of departure sounds exactly right to me.


Lar45

100% true but sight the gun from the bench and shoot, then sight the gun from sling and shoot, trajectory will be exactly the same but with different sight settings.

bfr

The Book trajectory does not change.

BUT the "field" trajectory, will change IF there is a difference, in the angle of departure, caused by a difference in muzzle rise, due to the difference in the "hold" as the gun is fired.

I can assure you, IF you sighted in a gun, locked in a fixed device at 100 yards, and then shot that same gun and load held by hands, the gun would hit higher...

ANY time you change the recoil momentium of a gun you will change the point of impact.

[Also, those that have worked a LOT with double rifles, have really experienced what changes in recoil momentium can do with point of impact...]

bfr
If you agree that...
IF you shoot the same gun, with the same load, at the same distance, with different "holds" had have different zeros...

Then you are saying the same thing I am.

Differences in recoil, that cause a difference in the "Angle of Departure", will cause a difference in the point of impact.

It does not matter WHAT caused a difference in the angle of Departure, the same gun and load held differently, or different guns with different amount of muzzle rise/barrel time.

BOOK TRAJECTORY is caculated without figuring in any recoil/barrel time...

Actual FIELD trajectory is baised on recoil/barrel time. And that varies between position and from shooter to shooter...

You can take several shooters, have them shoot the same 308 rifle at 300 yards, that has a base zero at 100 yards, prone from a bipod.

The different shooters shoot the same rifle and load at 300 yards.

The standard Book up value is +4.5 MOA.

Some shooters will be dead on at +4.25 MOA, some at +4.5 MOA, some at 4.75 MOA, some at 5 MOA.
This is with the same rifle, same ammo, same day. I have repeated this test several times over 20+ years...

Only difference, recoil momentium caused by the different holds, by the different shooters.