Why Powders shoot Different

[Poconolg]

If you have the same case prep, the same primer, same bullet and tension and seating depth but different powder they shoot different size groups, using the same rifle. What makes the powder do this?

 

[drop_point]

You've asked a question with so many different variables. I'll try to answer a few....but entire books could be written on the topic.

The barrel is a big tuning fork. The powders have different burn rates and different pressures at different points in the process of burning. The bullet is propelled at different rates. Therefore, the muzzle is at different positions of the "whip" when the bullet exits. Turbulence is different as the bullet exits the muzzle. The powder reacts differently within the case based on the case fill, etc.

 

[sandwarrior]

You've asked a question with so many different variables. I'll try to answer a few....but entire books could be written on the topic.

The barrel is a big tuning fork. The powders have different burn rates and different pressures at different points in the process of burning. The bullet is propelled at different rates. Therefore, the muzzle is at different positions of the "whip" when the bullet exits. Turbulence is different as the bullet exits the muzzle. The powder reacts differently within the case based on the case fill, etc.

Totally agreed. In short, harmonics, with each variable (powder burn speed and pressure) making it's own changes

 

[K22]

Totally agree with tylerw02 also.

However, with powders that are compatible with a given caliber and bullet, I've experienced the most significant impact on precision by the bullet selected. For example, in my varmint grade 223 Rem rifles (12" twist), H4895, Varget, Benchmark, and H335 shoot fairly the same grouping with 50 grain Nosler BT's, powder charge of course adjusted for optimum results for the specific powder being used.

Whereas in most of varmint rifle the 50 Vmax just won't group as tight as the 50 grain Nosler BT. However, the 55 Vmax does quite well. In my 8" twist 223 Rem's, the 60 Vmax out shoots everything I've tried.

However, there is no doubt that some rifle / bullet combinations prefer one powder over another for the reasons tylerw02 stated. Hence the need for careful load development to optimize the precision capability of your rifle.

 

[CharlieNC]

Using Quick Load or Gordon's Reloading Tool you can easily compare powder burning rate, energy, etc and p!ots of the pressure curves as the bullet is moving through the barrel. In addition to achieving the optimal barrel time relative to harmonics, the progressive burning nature also presents important characteristics to consider which I don't fully understand. Useful tools.

 

[Straightshooter1]

If you have the same case prep, the same primer, same bullet and tension and seating depth but different powder they shoot different size groups, using the same rifle. What makes the powder do this?

In addition to the things mentioned, besides the issue of heat of the powder when firing the cartridge, there can be significant differences with just the one powder you have on your shelf due to how you handle the powder. I'm referring to the humidity in your environment and its effects on the powder when exposed. Gun powder can absorb or lose moisture content to the atmosphere, and that can occur rather quickly, particularly when there's a large difference. For example, I live where relative humidity is often below 20%. When it's low the atmosphere acts like sponge and sucks moisture right out of the powder rather fast. Powder that has it's moisture content reduced will result in a faster burn rate thereby increasing velocity and upsetting the expected group sizes. If RH is the opposite and way high (like 90%), the powder acts like a sponge and will absorb moisture resulting in slower burn rate with slower MV's.

So, you see . . . as mentioned, there many different variables to your question.

 

[Ned Ludd]

Powder burn rates vary, as do their gas expansion rates. As a consequence, bullet acceleration in the barrel and thus muzzle velocity, can vary widely between powders. These factors affect barrel harmonics, which in turn, affect POI.