.308 v. 7mm-08 Varget max load question

pharmseller · May 1, 2017

I need some help understanding the difference between max charges for these cartridges.

The max charge of Varget for the .308 using 150 AB or Partition loaded to 2.800" is 46.5 grains.

The max charge of Varget for the 7mm-08 using 150 AB or Partition loaded to 2.800" is 41 grains.

The 7mm-08 is based on the .308 case. The bullets weigh the same. The shape is different, sure, but how is 46.5 max for one and only 41 max for the other?

P

Wincheringen · May 1, 2017

My guess is that the 7mm 150 is longer than the 308 150 and reduces case capacity.

SJB358 · May 1, 2017

pharmseller":15ihwi8i said:
I need some help understanding the difference between max charges for these cartridges.

The max charge of Varget for the .308 using 150 AB or Partition loaded to 2.800" is 46.5 grains.

The max charge of Varget for the 7mm-08 using 150 AB or Partition loaded to 2.800" is 41 grains.

The 7mm-08 is based on the .308 case. The bullets weigh the same. The shape is different, sure, but how is 46.5 max for one and only 41 max for the other?

P

Less bearing surface and less bullet for pressure to push on.

Guy Miner · May 1, 2017

Similar to the difference between the .270 Win & .30-06 with 150 gr bullets.
.
Nosler lists two loads that break 3,000 fps for the .30-06, and NONE for the .270 Win... The smaller bore rifles are often handicapped a bit re velocity, but sometimes have higher BC bullets. Ballistics is interesting stuff for sure.

Guy

TackDriver284 · May 2, 2017

The smaller diameter on the case mouth will create more pressure than the larger diameter case mouth. Example, a smaller nozzle will have more thrust force than a nozzle with a larger diameter using the same propellant charge on a rocket. Just my opinion.

Gunner46 · May 2, 2017

Bearing surface of the bullet against the barrel (friction) vs the area of the base on the bullet that the gas has to push with.

kraky1 · May 2, 2017

I think it's more a function of how fast the gas and pressure can get out of a smaller hole. Look at the 243 vrs 308...or 2506 vrs 3006.... the smaller the hole the slower the powder needs to be.
Think of a small funnel emptying compared to a big funnel.
Think of little guy beer farts vrs big boy beer farts......okay time to stop thinking!

mjcmichigan · May 2, 2017

Great question.
I liked two points in particular,
1) bearing surface/friction
2) gas escaping out a little hole vs big hole.

Thanks to all for the insight. It's important to learn these little things to be a safe reloader!

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