Which calibers tend to suffer the most with factory ammo when it comes to measured chrono speed vs advertised speed on the ammo box?

[Leatherneck]

Saw someone posting that a 7mm was shooting significantly slower with a certain ammo than advertised speed. Do you find certain calibers are better or worse for this generally speaking?

 

[JGRaider]

It's more rifle specific, not cartridge/caliber.

 

[William Sublette]

That's like asking which cars go different speeds with 87 octane.

 

[EastHumboldt]

The 6.5 Crudmore is the worst. Sometimes velocity is advertised at 2800 fps and the bullets will literally fall out of the barrel and roll around on the ground. Other times like if the weather is cold or hot or there’s a full moon or its Tuesday, they’re so hot they will actually execute a reverse parabola at a velocity of mcsquared and leave the atmosphere.

I don’t own one but I read this over on 24 hour campfire so it must be true.

It’s actually not a dumb question. It’s probably just a question that nobody knows the answer to.

 

[JGRaider]

Except for the fact that it was already answered.

 

[redneckbmxer24]

This is barrel dependent, not cartridge. You could take the same lot of the same ammo and shoot it from two different barrels of the same length and see as much as a 150fps difference.

You also have to consider that most factory ammo is measured from a quality 24-26” barrel and at an ideal ambient temperature and most factory ammo uses powder that’s anything but temperature stable. So go shoot it in a shorter barrel at freezing and it’s going to be way slower too.

Then you have to consider that the ammo changes from lot to lot mostly having to do with the powder or charge weight and they don’t list velocity for each lot. I have 5 different lots of ELD-X 143gr 6.5 Creedmoor sitting here and my newer lot was 90fps slower than the older lots on the same gun on the same day.

Basically you can’t trust what the box says and you can’t expect to have the same results as someone else. If you’re shooting factory ammo buy lots in bulk, chrono it, shoot it and repeat.