Why does magnum movement matter for rifle accuracy?

[mt terry d]

1/2" MIL one shot groups cold bore first round pop? ALL of them!

Jay

50 caliber. By golly I didn’t think if that

Well, heck My 223 shoots half that!!

 

[Colorado Cowboy]

1/2" MIL one shot groups cold bore first round pop? ALL of them!

Jay

I don't remember when it has taken more than 1 shot to kill any of the antelope, deer or elk that I hunt, yep first pop. 1/2" MOA is my 3 shot groups all are within 1/2" of one another at 100 yards, 1" of each other at 200 yds and so on. My Dad taught me to shoot and not waste ammunition. Wait till you have your shot and take it.
I only shoot 2 rifles on big game.....a 25-06 and a .300 Wby.

 

[K9kodi]

I concur. As I visualize a chamber with a cartridge, I can see the primer going off and igniting powder. Once pressure builds to send the bullet from its seat it def starts the recoil cycle.
Once the bullet exits the barrel the only movement left is energy moving (rifle going back) bc objects in motion wish to stay in motion until acted upon by opposing force (you).

Now what I would find more interesting then this debate would be, accuracy or point of impact when rifle is mounted into a sled or fixture that does not allow for any rearward movement of rifle vs one in the shoulder. Not that one from the shoulder couldn’t repeat accuracy results, the question is would it be different

 

[RockAndSage]

Point to note: Recoil is still being applied after the bullet leaves the barrel.

The amount is related to the mass of the bullet, the base shape and surface area of the bullet's base, the volume and pressure of gas coming out of the muzzle, and the profile of the muzzle.

For a microsecond, even after the bullet has left the bore, it still acts as a plug - all those factors I listed above affect how long and where the forces of those gasses are being applied.

The heavier the bullet, the wider the base, the flatter and less tapered the base, the greater the volume and pressure of gas right as the bullet escapes the bore, and the larger and flatter or concave the surface area of the muzzle face and crown, the greater the recoil.

A heavier bullet means it's hanging in the air in front of the muzzle fractionally longer, allowing the gasses to press between it and the muzzle just a bit longer, applying force against the muzzle and into your shoulder.

A wider bullet base means more surface area for the gasses to press against, with the same effect of more force transferred against the muzzle.

Muzzle face/crown shape is an issue of aerodynamics or fluid dynamics. Old-school sporting barrels that have a rounded or half-donut shaped crown, with the least overall surface area, allow the gasses to slip around without applying as much force into the gun. Large flat-faced bull barrel muzzles have a lot of surface area for gasses to press against right as the bullet is exiting. Maximum recoil though comes from a concave crown, which literally acts as a rocket nozzle - directing as much force as possible back down the barrel's structure. In something like a semi-auto pistol, that concave crown can actually enhance reliability as it increases slide-velocity rearward. But in something like a big-bore handgun, it magnifies recoil with no benefit.

 

[Bluefish]

I am trying to figure out if this is true. I would think that recoil only begins to occur after the bullet has left the barrel. if the bullet has left the barrel, how can gun movement effect where the bullet will hit?

Movement starts slightly after the bullet starts moving. Before it leaves the barrel. We have the force acting on the bullet which can be calculated by the area of the bore x the pressure. The rifle experiences an equal force going the other way. The rifle weighs a lot more so the acceleration of the rifle is slow while the bullet is fast since it’s light. F=MA.

 

[mt terry d]

I don't remember when it has taken more than 1 shot to kill any of the antelope, deer or elk that I hunt, yep first pop. 1/2" MOA is my 3 shot groups all are within 1/2" of one another at 100 yards, 1" of each other at 200 yds and so on. My Dad taught me to shoot and not waste ammunition. Wait till you have your shot and take it.
I only shoot 2 rifles on big game.....a 25-06 and a .300 Wby.

What’s your rifle’s cone of fire?

 

[UncleNommies]

I would also consider torque as a factor of felt recoil. A bullet leaving the case, engraving into the rifling, and being spun to an immediate ~250,000 rpm, will definitely cause the rifle to react with rotational movement. I guess that's why there are gain twist barrels or the new Proof PXT barrels. The immediate torque is more gradual as the bullet "slowly" spins to a final twist rate and perceived as less torque.

 

[mustelid_master]

Every action has an equal and opposite reaction—the bullet has to push against something to begin moving—thats the gun. It starts pushing as it starts moving. It STOPS pushing +\- as it leaves the barrel.

Dont believe me, believe your own eyes. Here’s a fb link to applied ballistics high speed video showing a rifle barrel moving before bullet exits barrel.

https://www.facebook.com/video.php?v=886716482687341

Movement starts slightly after the bullet starts moving. Before it leaves the barrel. We have the force acting on the bullet which can be calculated by the area of the bore x the pressure. The rifle experiences an equal force going the other way. The rifle weighs a lot more so the acceleration of the rifle is slow while the bullet is fast since it’s light. F=MA.

That's the money right there. I am now starting to remember why i got a C in dynamics.