6.5 Grendel Velocity..What is realistic?

[LRRPF52]

Muzzle velocity doesn’t change with DA but the speed of sound (transonic zone) does! That’s why I asked!

Yup. Tracking all that from aerospace experience.

We always had to check DA when planning flights since AFFTC and some of the airfields we flew out of frequently were well above sea level and hot in the summer, pretty cold in the winter, and close to the CA coast to where weather changes from the Sierra Nevadas were frequent.

It’s also a huge factor in weapons test, namely missiles. DA is totally different up in the higher altitude bands, and if a target is in the lower bands, it affects performance (range and terminal envelope) tremendously.

Same in the Army with planning for rotary wing operations or Air Load Planning, though the Load Masters and pilots work that out for the heavies. I went to the school for it though where we had to do the manual work, even though the Loadmasters have a computer for it where they enter in all the load weights to provide total cargo to the pilots/co-pilots/flight engineers.

For rotary wing, it affects what birds can go where, especially in places with higher elevations and high temps. Chinook (CH-47 and MH-47) was king in that space due to how much power it has with dual turboshafts. MH-53J AFSOC birds had a lot of power too.
UH-60s and AH-64s are limited in what loads they can carry and where they can go relative to higher altitudes and temps.

Cold air is almost always better for flying though when looking at lift and power-to-weight, which is why US fighters set their time-to-climb records up in North Dakota. Russians needed to find “warmer" places since they’re at Hudson Bay latitude. Their warm is not fun for a lot of us. I frequently tell people who I see shivering here in Utah, “Hey, this is a beautiful spring day in Finland."

Hot air gets really tricky for flying, especially at higher elevations. A lot of your single engine general aviation mishaps occur due to overweight, underpowered, and thin hot air.

But it’s great for bullets and retaining energy downrange. Layman answer to all of this is use faster twist rate if you’re worried about transonic range. This map is great for basic reference for where the higher elevations are in the US: