BigUglyMan
CGN Ultra frequent flyer
- Location
- New Scotland
Why not just buy a 30-06 if you want to drive a 150 at 2900?
Horizontal difference between bullets
- Thread starter ckc123
- Start date
Why not just buy a 30-06 if you want to drive a 150 at 2900?
Because I have a 30-06.. I use the 300 rum as a "backup" in case the 30-06 has problems in the field.. just like I use hot loads on the 30-06 as a backup for the 300 in the field..
barrel time and recoil are responsible for the change in POI. the lighter bullet, being higher velocity, leaves the barrel quicker than the heavier bullet, and also doesn't have the recoil force of the heavier bullet. the muzzle of the rifle is starting to recoil as each bullet starts to move down the barrel and recoil forces are higher for the heavy bullet, which also leaves the barrel later, hence the difference in POI.
BigUglyMan
CGN Ultra frequent flyer
- Location
- New Scotland
Wow...just, wow.
From an earlier post:
"But the main reason the heavier slower bullet hits high is the "in barrel time" of the bullet. With the heavier bullet the recoil of the rifle is also greater and the barrel time is longer, so the rifle barrel is higher in recoil when the bullet leaves, causing the heavier bullet to hit higher on the target."
I don't know how to put this other than plain and simple: there is no recoil until after the bullet has left the barrel, when the barrel can no longer influence the direction of the bullet.
If you think about what happens when the primer goes off: powder starts to burn; pressure builds; bullet starts to move; powder continues burning; pressure continues to climb; bullet moves down the barrel, eventually leaving the muzzle. Up until this point in time, the gun/bullet have been one unit. At this point the gun is exerting an unbalanced force pushing the bullet forward and the rifle backwards into your shoulder.
As much as I hate to refer to a couple of Hollyweird special effects guys, one of the Mythbusters episodes showed a 44 Mag revolver caught on high speed video, shot from a rest (probably a Ransom rest). On the high speed video, you can clearly see the flame from the cylinder gap, the bullet leaving the muzzle, the fireball and then the recoil/muzzle jump, in that order. I believe it was the episode where they were trying to ignite a natural gas/air mixture in a room , to check out the scene from a movie where shooting through a carton of milk prevented a natural gas fireball.
I do also recall reading one guys theory that the building pressure in the barrel sets up shock waves within the barrel (not the bore), changing its dimensions very slightly, and causing the barrel to vibrate. According to his calculations, the barrel shock waves were faster than the speed of the bullet down the bore. He was comparing the speed of sound in steel to the speed of the bullet in the bore.
The bottom line: I am not convinced that recoil will affect the point of impact. Barrel harmonics, yes.
Stan
"But the main reason the heavier slower bullet hits high is the "in barrel time" of the bullet. With the heavier bullet the recoil of the rifle is also greater and the barrel time is longer, so the rifle barrel is higher in recoil when the bullet leaves, causing the heavier bullet to hit higher on the target."
I don't know how to put this other than plain and simple: there is no recoil until after the bullet has left the barrel, when the barrel can no longer influence the direction of the bullet.
If you think about what happens when the primer goes off: powder starts to burn; pressure builds; bullet starts to move; powder continues burning; pressure continues to climb; bullet moves down the barrel, eventually leaving the muzzle. Up until this point in time, the gun/bullet have been one unit. At this point the gun is exerting an unbalanced force pushing the bullet forward and the rifle backwards into your shoulder.
As much as I hate to refer to a couple of Hollyweird special effects guys, one of the Mythbusters episodes showed a 44 Mag revolver caught on high speed video, shot from a rest (probably a Ransom rest). On the high speed video, you can clearly see the flame from the cylinder gap, the bullet leaving the muzzle, the fireball and then the recoil/muzzle jump, in that order. I believe it was the episode where they were trying to ignite a natural gas/air mixture in a room , to check out the scene from a movie where shooting through a carton of milk prevented a natural gas fireball.
I do also recall reading one guys theory that the building pressure in the barrel sets up shock waves within the barrel (not the bore), changing its dimensions very slightly, and causing the barrel to vibrate. According to his calculations, the barrel shock waves were faster than the speed of the bullet down the bore. He was comparing the speed of sound in steel to the speed of the bullet in the bore.
The bottom line: I am not convinced that recoil will affect the point of impact. Barrel harmonics, yes.
Stan
a ransom rest holds the firearm very securely, so the effect is not noticeable. if you wish to test this out for yourself take your firearm,whether it is a rifle or a handgun, shoot a group off a rest with a loose hold and fire a group with a very tight hold. it is much more apparent with magnum handguns loaded with heavy bullets, and the effect is magnified by the centerline of the bore being very high above the grip. recoil starts when the bullet begins to move,it's physics.
What.. your not going to travel 12+ hours to go hunting and not bring an extra gun in case you drop the rifle and the scope goes off?????
So, got it. Lighter bullet spends less time in barrel because driven faster than the heavier. So hits lower. Barrel harmonics.
But, the 150 is traveling slower, so it is spending more time in the barrel than the heavier one, yet still you guys are telling me that the heavier one is hitting higher because of barrel time being longer. Really?? Care to start over?
These statements are wrong. Recoil begins when the bullet/powdercharge gases begin moving. Recoil does not just begin at the muzzle. The bullet/gases are not part of a gun/bullet unit. Also reaction to the rifling twisting the bullet begins with first acceleration of the bullet producing reaction torque on the rifle contributing to the lateral displacement on the target of different weight bullets.
NormB
I have to say, that my experience in using different bullet weights is that the heavier bullet has always printed signifigantly lower than the lighter, faster bullet. This has been with a limited range of rifle calibres; 7x57, .308, .30-06, 9.3x62. I've also found that changing the bullet or powder, keeping everything else the same, can change p.o.i.
Recoil begins the instant the bullet starts to move. Equal and opposite reaction.
Harmonics almost certainly has an effect, which is why the poi changes when you change bullet/powder.
Recoil begins the instant the bullet starts to move. Equal and opposite reaction.
Harmonics almost certainly has an effect, which is why the poi changes when you change bullet/powder.
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
Agreed with both of the following posters. Recoil begins the moment that something inside the barrel (powder gas, bullet) begins to move).
As to "why different POI", there are several different possibilities for that.
As to "why different POI", there are several different possibilities for that.
BigUglyMan
CGN Ultra frequent flyer
- Location
- New Scotland
Of course. I also have two pickup trucks but I don't feel the need to downgrade the power of my 6.4l Ford F350 diesel to match my 4.8l Chev 1/2 ton.
If these statements are wrong, what happens, then?
Yes, there is a reaction to the bullet moving down the barrel, but that only puts an internal strain on the barrel (lengthwise and torque).
Yes, it is physics. Until the bullet leaves the barrel, it is part of a closed system; ie. a single unit. There is a force acting on the base of the bullet, as well as the chamber, but that is internal. Once the bullet leaves the muzzle, the bullet's forward momentum is balanced by the gun's rearward momentum.
BTW, the powder charge (and hence its resultant gases) contributes to the felt recoil. Check page 454, Appendix B in Lyman's 49th Edition Reloading manual..
As soon as the powder ignites, the expansion of the gases, pushes the bullet forward down the barrel, and it also pushes the firearm in the opposite direction. Recoil begins as soon as the bullet starts to accelerate in the barrel. The bullet and the firearm are not one piece, and in fact they act as two projectiles, as the gases expand, driving both in opposite directions.
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
A key insight point in understanding why the gun can move while the bullet is in the barrel, is that the bullet IS NOT RIGIDLY CONNECTED TO THE BARREL AND IS ABLE TO MOVE INDEPENDENTLY. Yes there is friction between the barrel and the bullet, but to the extent that the friction is not able to hold the bullet completely still, the amount of relative motion between the bullet and the barrel that actually happens, is precisely the amount that the bullet and barrel are moving independently.
So while it is certainly possible to consider the bullet+barrel as a closed system, it is not a single 1-piece unit. Inside the closed system there are fundamentally two pieces, the barrel, and the bullet - each of these has a centre of mass, and a position. The system as a whole also has a centre of mass, and the system's centre of mass has a position. As a closed system, its centre of mass will not move, unless an exterior force is applied to the system as a whole (firing a round inside the chamber is something happening internally, not externally - so when the gun is fired, the centre of mass of the bullet + barrel will not move). When the gun is fired and the bullet starts to move inside the barrel, the barrel must move in the other direction, so that the centre of mass of the whole system doesn't move.
Sorry.. your not even comparing the same things.. doesn't prove your point at all...
The fact is that I have 1 gun that can be used in 2 different situations.. and I choose to use it that way..
Well, I can see there's a lot of theory, and a fair bit of thinking behind the recoil effect....
I can think of a couple of ways to measure / test what happens.
One is similar, involving only a skateboard and a baseball. Throw a baseball while standing on a skateboard, and again making the motions of the throw, without actually releasing the ball.
The other involves a computer, strain gages, accelerometers, a switch to detect a bullet leaving the muzzle and some data acquisition software. I might have to try this after I retire....
Stan
I can think of a couple of ways to measure / test what happens.
One is similar, involving only a skateboard and a baseball. Throw a baseball while standing on a skateboard, and again making the motions of the throw, without actually releasing the ball.
The other involves a computer, strain gages, accelerometers, a switch to detect a bullet leaving the muzzle and some data acquisition software. I might have to try this after I retire....
Stan
