Over simplification?

[Reload Newbie]

As my name reflects I am new at reloading. An endeavor that I started as a hobby and to make sure I have ammunition to shoot when I want. I have what might be an over simplistic question but here goes! If a particular bullet has a sweet spot velocity, should that be what we are aiming for(pun intended) regardless of the type of powder we use to get it there? It seems to me as long as the bullets leaves the end of the barrel traveling at that speed it should behave the same way each time.
Can you enlighten me?

 

[nwmnbowhunter]

Different powders produce different speed, harmonics, pressure.

Generally that speed is only good for that powder.

Each powder needs it's own load development.

 

[6ShotsOr5?]

The barrel vibrates in a complex way - something called barrel harmonics. The answer is that the muzzle velocity and the direction of the muzzle at the time the bullet exits combine to determine the flight path of the bullet. Using different components can change the harmonics because the pressure in the barrel will reach maximum faster or slower depending on the components used. So yes, you are oversimplifying it.

 

[David Christian]

It’s not just the bullet. Barrel length, powder, primer, charge weight, seating depth, neck tension, case fill %, all play a role.

 

[jepp2]

It seems to me as long as the bullets leaves the end of the barrel traveling at that speed it should behave the same way each time.

You can learn a lot by reading this.

http://www.the-long-family.com/OBT_paper.htm

If you do agree with OBT (optimum barrel time), it will be surprising with 2 different powders, how different the barrel time will be, even though the bullets can leave at the same velocity.

 

[INTJ]

If a particular bullet has a sweet spot velocity, should that be what we are aiming for(pun intended) regardless of the type of powder we use to get it there? It seems to me as long as the bullets leaves the end of the barrel traveling at that speed it should behave the same way each time.
Can you enlighten me?

I have sometimes found that a bullet that shoots well at a certain velocity will still shoot well with a step faster or slower powder when it gets to that same velocity.

This isn't a sure thing but it is a decent starting point. That concept can be complicated by things like double based powders vs single based.

So the best bet it to test and see. Given current powder availability we might have to do this more than we'd like.

 

[jelenko]

^^ I and several others have found the same. We are looking for 1/2 to 3/4 MOA accuracy for many/most of our groups [which implies we're ok with some groups being larger]. But, just as stated, it works some/much of the time, but not always.

 

[RegionRat]

It seems to me as long as the bullets leaves the end of the barrel traveling at that speed it should behave the same way each time.

That is a fair enough concept if the system that launched that bullet was infinitely rigid.
A clamped up shooting machine comes very close to this type of behavior.

The main problem has already been explained. No practical rifle that is carried around or manipulated by hands is that stiff or damped. As a result, the harmonics and dynamic response of the gun, as well as the reactions of the rests, determine what we call the tune of the recipe. So even getting an identical speed isn't enough unless the pressure pulse is also identical.

 

[NZ_Fclass]

Once the techniques of reloading are mastered, getting the workflow done in the right order and assembling good ammo, the rest has to be learned from experience. And shooting long ranges accurately is the way to get that experience. Whether a hunter, benchrester or F-class, it's whats on the target that matters. When you shoot your first ton, or a group in the ones, you will have made a start.

 

[jackieschmidt]

Well, I can give you some real world testing from last week end.

We we’re testing my 103 grn 6mm out of my 6BR. We found a good load with 30.6 grns of N150 at a flat 2900 FPS over my Ohlear 35P Chronograph. Groups were nice and round measuring around .400 at 200 yards.

Switching to Reloader 15, we duplicated the exact velocity with over an inch of vertical.

 

[NZ_Fclass]

Well, I can give you some real world testing from last week end.

We we’re testing my 103 grn 6mm out of my 6BR. We found a good load with 30.6 grns of N150 at a flat 2900 FPS over my Ohlear 35P Chronograph. Groups were nice and round measuring around .400 at 200 yards.

Switching to Reloader 15, we duplicated the exact velocity with over an inch of vertical.

mmm...I have some 150 in the shed.

 

[jelenko]

with over an inch of vertical

Just for comparison, for 'cross the course', 1/2" groups at 200yards would be great.