Math and Recoil

[260 Rem]

I have often wondered how far a rifle actually moves in the bags by the time the bullet exits the muzzle. Any math types that can help with the calculation? Let's use the example of a 308 Win rifle weighing 8lbs. shooting a 180gr bullet leaving the muzzle of a 24" barrel at 2600fps. The recoil velocity of the rifle is known to be 12.5 fps. I have no idea of what the barrel time is?
I understand the calculation will assume Free Recoil with no friction.
OK math types, do your magic.

[BuckCuller]

By doing the math the bullet will be affected by .000769 seconds of recoil but that doesn't include ecceleration of the bullet until it reaches the end of the barrel. Assuming the ecceleration is about 1170351.1053316 M/s2.
Formula dV=d1-d0.
It would come out to being effected by .000899 seconds of recoil.
The recoil is not much of a factor.
The person anticipating the recoil is more of an effect.
The gun will recoil approximately.0112375 of an inch by the time the bullet leaves the barrel.

[BuckCuller]

If you are also looking at loss of velocity of the bullet from free recoil it would come out to a loss of .004870768 fps.

[Deer Hunter]

The lock time on a rem 700 is 2.5ms, a Mauser 5ms
The time it takes a bullet from ignition to exit the barrel is around 2ms.

http://www.accurateshooter.com/techn...t-barrel-life/
http://yarchive.net/gun/rifle/lock_time.html

[260 Rem]

Thanks Buck ... what I am trying to "get" is the approximate recoil distance...which you reckon is about 1/100th of an inch in about .0008 seconds? That being the case, logic follows that what happens with the rifle by the time it has moved back 2/100's of an inch will have no effect on bullet path because it is long gone?

[260 Rem]

The practical application of this information helps with how I set my rifle in the rear bag. My "habit" is to position the heel of the stock's handgrip about 1/2" forward of where it will contact the ears as it moves back under recoil. I started to question my understanding after reading a link in which it was suggested that space should be 2 - 3". Sounds to me like the latter recommendation is quite generous and probably not necessary.

[marxman]

Watching slow mo videos the bullet is gone before a handheld firearm moves perceptably although in theory it must begin to move as soon as the bullet does. For sure it wont move a half inch before the bullet exits.

[pikergolf]

I'd be curious as to how much a lightweight rifles muzzle moves, from the act of the trigger breaking and the firing pin striking. Am wondering if it would have more of an impact than recoil.

[densa44]

It has been many years since Physics at Queen's but Newton's second law is older.

Wouldn't the rifle, bullet and hot gas be one "object" until the bullet left the barrel (my Prof was a Cuban and used to say left the nozzle!) thus not causing recoil until the exit?

The effect of the gas produced by the primer and the powder would have a significant effect on recoil too. For example 100 grains of powder leaving the barrel at the stated MV.

The OP got his wish, in Physics is was never just that simple.

[Bushrat]

Originally Posted by pikergolf

I'd be curious as to how much a lightweight rifles muzzle moves, from the act of the trigger breaking and the firing pin striking. Am wondering if it would have more of an impact than recoil.

I think your on the right track and definitely can have more affect than recoil. There is a lot happening in the time between when the trigger breaks, the firing pin slams into the primer and the pin stop shoulders inside the bolt. Most of this movement is away from the point of aim and happens before the bullet leaves the case or any recoil even starts. If you set up on a bench and dry fire your gun and keep your eyes on the crosshairs and follow through you will normally see a jump of movement of your crosshairs as the pin slams to a stop. This shows the gun has already moved off the point of aim before the bullet would have even started down the barrel and before any effects of recoil.

[sns2]

Originally Posted by 260 Rem

The practical application of this information helps with how I set my rifle in the rear bag. My "habit" is to position the heel of the stock's handgrip about 1/2" forward of where it will contact the ears as it moves back under recoil. I started to question my understanding after reading a link in which it was suggested that space should be 2 - 3". Sounds to me like the latter recommendation is quite generous and probably not necessary.

You're the best shot on the forum from what I've seen. Stick with what you are doing.

[260 Rem]

Some interesting observations regarding trigger/firing pin movement, but I keep gravitating back to the effect of recoil based on my following observation.
I use the same action / trigger / stock / barrel contour combination with barrels chambered to 6 Dasher / 30 BR / 30 Dasher / 6.5 X 47L / 260 Rem / and 308 Win. The weight differences due to the variation in bore diameter are mere ounces.
On average, the lighter recoiling calibers group best.

[BuckCuller]

Originally Posted by pikergolf

I'd be curious as to how much a lightweight rifles muzzle moves, from the act of the trigger breaking and the firing pin striking. Am wondering if it would have more of an impact than recoil.

I think you would get more movement from actuating the trigger. But I think he is wondering how much free recoil he needs when shooting long distance for the bullet to clear the barrel.

[BuckCuller]

Originally Posted by 260 Rem

Thanks Buck ... what I am trying to "get" is the approximate recoil distance...which you reckon is about 1/100th of an inch in about .0008 seconds? That being the case, logic follows that what happens with the rifle by the time it has moved back 2/100's of an inch will have no effect on bullet path because it is long gone?

If you really wanted to get supper accurate you would have to add in a lot more minuscule factors like air density but when your dealing in hundreds or thousands of an inch and ten thousands of a second I don't think it matters.
Half of an inch of free recoil will be lots.
Sounds like your a way better shot than most to me anyway.

[spoiledsaskhunter]

Originally Posted by BuckCuller

By doing the math the bullet will be affected by .000769 seconds of recoil but that doesn't include ecceleration of the bullet until it reaches the end of the barrel. Assuming the ecceleration is about 1170351.1053316 M/s2.
Formula dV=d1-d0.
It would come out to being effected by .000899 seconds of recoil.
The recoil is not much of a factor.
The person anticipating the recoil is more of an effect.
The gun will recoil approximately.0112375 of an inch by the time the bullet leaves the barrel.

good god!

[Bergerboy]

The original post indicated free recoil with no friction. The rifle would stop when it hit the shooters shoulder or the ground.

[BuckCuller]

Originally Posted by 260 Rem

Some interesting observations regarding trigger/firing pin movement, but I keep gravitating back to the effect of recoil based on my following observation.
I use the same action / trigger / stock / barrel contour combination with barrels chambered to 6 Dasher / 30 BR / 30 Dasher / 6.5 X 47L / 260 Rem / and 308 Win. The weight differences due to the variation in bore diameter are mere ounces.
On average, the lighter recoiling calibers group best.

Some barrels flex more under pressure than others could be a contributing factor. But it would be very slight. Barrel may be the same except the metallurgy.
Small difference just like the same type of powder from a different batch.

[260 Rem]

Thanks to all for contributing to this thread...some good stuff to ponder. My take-a-way is to get the best results, there is a very tiny window and whatever you do, it must be repeatable to the "n"th degree. A tiny bit of palm pressure, a smidgeon of side pressure on the trigger, a slight change in grip on the forestock (if you do that)....has potential to send things south in a hurry. Attention to rest/bag set up when bench shooting is pretty critical in that first .01" of recoil.
So, when I wonder why my heavy recoiler won't give me sub 1/2 MOA groups, I'll be blaming myself less and deferring to the fact there ain't much I can do to quell the beast during that very violent millisecond

[densa44]

Thanks for the post BTW.

We know it is the shooter, after that;
1. The ammunition
2. How well it is "sighted in" ie. are you on a node?
3. environment, wind and temp.

There are others for sure but those are as far as I've tried to correct for. I don't weigh bullets or measure volume of brass, but I know others do.

I know this is only of interest to the "one hole" club but it fascinates me.

Is Cat around, he and Dick know a lot about this sort of thing.

[elkhunter11]

In order to do the calculation, you would have to assume a linear acceleration, which quite likely is not realistic, as the bullet won't begin accelerating until the pressure reaches a certain point. I personally don't worry much about recoil effecting the shot, unless I am shooting a springer air rifle.