Dope cards and variables

[HoLeChit]

This is a great point, but how do manufacturers measure velocity for the box/specs? Does it really matter that much? With a 308 rifle it should lose an average of 25fps per inch of barrel lost from 26” to 16.5”. What barrel length do manufacturers calculate velocity for?

I just spoke with Federal (they emailed me back within 30 minutes, I am impressed). They stated that they use a 24" barrel for calculating velocity with 308win ammo.

 

[PBramble]

There is about 200 fps difference when shooting the same 308 ammo thru my 20" bolt action (2820 fps average) vs my 16" AR (2630 fps average).
So yes, it would make a difference.

Apples and oranges. You're including a gas system that bleeds it off too. Add a suppressor and pressures increase. The only way to accurately "guesstimate" the trajectory is to know your muzzle velocity. Even then, at longer ranges MV may have to be trued.

I don't think there is a standard length for test barrels. It can vary from manufacturer to manufacturer. But good on you for calling and verifying their info.

 

[magna19]

This is a great point, but how do manufacturers measure velocity for the box/specs? Does it really matter that much? With a 308 rifle it should lose an average of 25fps per inch of barrel lost from 26” to 16.5”. What barrel length do manufacturers calculate velocity for?

Unless it is stated you really dont know. Sometimes its a practical hunting rifle to a dedicated pressure test barrel. The muzzle velocity can be higher/ lower or the same velocity of your particular gun. You must check your own velocity to even begin using a calculator.

 

[magna19]

I just spoke with Federal (they emailed me back within 30 minutes, I am impressed). They stated that they use a 24" barrel for calculating velocity with 308win ammo.

Thats cool to know but what if your particular barrel is 22" and you get 35 fps more than their 24" barrel and didnt check your veloicty. You would have probaly deducted 50+ fps from your 22" barrel and got some bad dope.

 

[HiredHand]

My understanding is that bullet and ammunition companies can be creative with the ballistics information they provide. I’m sure it’s good enough to get you in the ball park, but you need to verify for yourself with your equipment.

 

[HoLeChit]

In the spirit of checking and verifying my velocities, does anyone know of a range or place that rents chronos?

 

[Trung Si Ma]

In the spirit of checking and verifying my velocities, does anyone know of a range or place that rents chronos?

If you're near Lawton, I can loan you one of mine. I have both a Pact Mark IV Chrono/Timer and a Magnetospeed.