Where Does the Barrel Point On Firing Pin Impact?

[Bart B.]

Where does the rifle barrel point when the firing pin slams into the primer before it burns the powder and bullet starts to move out of the case mouth?

A. Above the aiming point equal to bullet drop at target range.

B. Above the aiming point equal to bullet drop at target range plus sight height above bore axis.

C. Above the aiming point equal to sight height above bore axis.

D. None of the above. (If D is selected, please mention where you think the barrel points when the firing pin strikes the primer.)

 

[FL-NC]

Hopefully down-range!

 

[REB]

Well I voted A but only because my mouse pad accidently clicked when scrolling over it. My answer is none of the above.

Without outing a lot of thought into the process my answer would be the barrel is pointing above the target at an angle that matches the trajectory path of the particular round being fired. That is assuming the sites are adjusted for point of impact at the distance you are shooting. That is going to be different for each load even in the same rifle. Take a look at any ballistic trajectory graph and you see that the bullet travels on an arc. This arc is different for each loading and distance the rifle is zeroed at.

 

[murf]

d - bullet drop minus muzzle rise is the answer.

murf

 

[BCRider]

In this case it'll be "D".

There's no way to know exactly how the rifle will react to the recoil forces. Rifle weight, power of the round (recoil impulse) and even how the rifle is supported is all going to seriously stir the pot on this one.

 

[Llama Bob]

d - bullet drop minus muzzle rise is the answer.

murf

This is the correct answer, assuming a horizontal rifle. For non-horizontal shots, things are a little different.

Muzzle rise depends on the recoil of the round, the geometry of the rifle, and how it's held in place.

 

[Sam1911]

It will have to point in alignment with the base of the initial leg of the nearly parabolic curve the bullet will describe in flying to the target, considering that such curve is modified to reflect the losses in speed due to air resistance. That could be described as "above the target equal to bullet drop" if you want to look at it that way.

There is a very, very slight recoil effect moving the gun before the bullet leaves the barrel, but it is a minuscule fraction of the total recoil motion of the gun -- almost immeasurably little muzzle rise before the bullet is gone and no longer affected by the gun itself. So the angle of the barrel is, in practical terms, entirely controlled by the asymmetric pseudo-parabolic arc of the bullet's flight.

 

[taliv]

it could be pointing anywhere. doesn't really matter as long as it's close enough and moving in the right direction so that the barrel is pointing in the right spot when the bullet exits

 

[ontarget]

With my flinch, probably about a foot low and to the right.

 

[mavracer]

It would be B: less the amount the barrel rises due to recoil.
After a bit more thought A minus the barrel rise.

 

[murf]

the only difference between bart b.s first question and second question is muzzle rise from the bullet traveling down the barrel (and a bit more than a millisecond). am i missing something here?

murf

 

[taliv]

Imagine a high power shooter standing holding a figure 8 wobble and starting to pull the trigger as his front sight is coming into the black. Most of that is lock time. But some of the time is interior ballistics.

At the Prs match last weekend we shot a moving target at 500 yards. Most people held a mil in front of the target to hit it but times vary by shooters because of different equipment, ballistics and reaction times.

I'm just saying wind, position and moving targets are three very practical reasons the answer may not be just "above"

 

[Bart B.]

Stationary targets are implied in my questions. Sorry if that condition wasn't understood.

murf, you're right about the difference between the two questions/polls.

 

[MistWolf]

All y'all are making this question more complicated than it really is. The answer is D, None of the Above. The top part of the illustration explains why. Ignore the bottom part, it's there to quash a misconception that isn't part of today's program
View attachment 743312

 

[BCRider]

the only difference between bart b.s first question and second question is muzzle rise from the bullet traveling down the barrel (and a bit more than a millisecond). am i missing something here?

murf

Yep, that's what I got too. So the only difference is in what change in the direction of hold is forced by the recoil of the round.

And it doesn't matter if it is a millisecond or even less. Recoil might not move a rifle as much as a handgun but it WILL move the gun a little. So that's going to slightly or somewhat alter the direction of the bore before the bullet leaves the barrel.

 

[BSA1]

D - None of the Above.

Unless the gun is being fired from a machine rest the gun position depends on the shooter's ability to hold the rifle steady while pulling the trigger as smoothly as possible. That is a big reason target guns have very light trigger pulls and some target guns have electronic triggers

 

[J-Bar]

Sam 1911;

The big double rifles used for dangerous African game have to be "regulated" for a particular load to make sure the heavy recoil doesn't pull the point of impact off the intended target. Otherwise the hunter might be something's lunch. I don't think that would be a minuscule effect, do you?

 

[taliv]

Ok target is stationary but muzzle is still always moving.

 

[benEzra]

I can vouch for the fact that a 40gr .223 shoots significantly lower than 55gr does out of a Mini-14. Even though 40gr has less drop, the rifle rotates more during initial recoil shooting 55gr. Lightweight deer rifles often shoot high with heavier/hotter loads also.

 

[Sam1911]

I believe that double rifles need to be regulated. That term almost always has to do with making two barrels on the same gun shoot to the same point of impact at a certain distance. (Really, the paths of the two projectiles CROSS at the intended distance.)

And of course, sights always need to be adjusted to align point of impact with point of aim with the specific load.

I'd need to see something very persuasive to explain any large difference in sight adjustment strictly due to gun movement during recoil.

This video shows (rather poorly) the effect. Yes, the gun's going to recoil a lot. But the bullet is MUUUUCH easier to accelerate than the gun.

https://www.youtube.com/watch?v=qm_xuzHHuG0

Does it move? Of course. Acceleration starts in the gun and the bullet at the same time. But the actual distance of barrel travel is very small in the time before the bullet is out of the bore. Is it significant? Is it minuscule? I guess that's a matter of semantics.

 

[Bart B.]

Double rifles are "regulated" by toeing in the last several inches of the bore so their bore axes cross at 10 to 40 yards downrange; 60 and 70 caliber ones the closest; 35 and 40 caliber ones the furthest.

 

[barnbwt]

Is the subject of this thread/poll a;
1.) Joke?
2.) Riddle?
3.) Pointless nerdery?
4.) All of the above?

TCB

 

[macgrumpy]

Refer to Pejsa's drop formula for horizontally-fired projectiles.

http://mathscinotes.com/2015/05/pejsa-bullet-height-versus-distance-formula-for-a-zeroed-rifle/


The key here is that we were asked about the relationship between the bore line and the point of impact, not the line of sight and the point of impact.

The height of the sight has nothing to do with how far the bullet drops from the bore line, it's all just bullet trajectory - basically the amount of drop due to gravity for the time of flight over the range.

 

[Walkalong]

Where Does the Barrel Point Upon Firing Pin Impact on Primer?

A couple of quick thoughts.

D.

While the gun does move a little during firing, and that has to be taken into consideration (And kept consistent if we want to shoot accurately), it doesn't happen until after the firing pin hits the primer.

After the primer is hit and the powder is set off, the muzzle rises a little, and now "A" is correct for when the bullet leaves the barrel.

The scope height affects where our scope gets adjusted to for a certain yardage. It doesn't affect bullet drop.


But I am looking forward to the explanation when Bart is done teasing us and lets us in on the secret.

 

[lysanderxiii]

D - None of the Above.

Unless the gun is being fired from a machine rest the gun position depends on the shooter's ability to hold the rifle steady while pulling the trigger as smoothly as possible. That is a big reason target guns have very light trigger pulls and some target guns have electronic triggers

Even in a machine rest there is some movement.

Nothing is THAT rigid....