Question that has me stumped....

The Oregonian

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Been reading here for about a year...very knowledgeable folks, and I have learned more that I can describe.

I thought I had a few concepts understood, but reading on the Nosler site has me a little confused. Any wisdom from the clan would be appreciated.

The ballistics data for the 270 and 280 (not the AI), both shooting a 140gr AB. It lists the MV for the 270 at 2900 and the 280 at 3000. Why would the 280 be a fair amount faster, given that I think the 270 has a higher max chamber pressure in the SAAMI spec. I guess I had been assuming that they wouldn't be loaded to a different percentage of spec. Where is my understanding off (I assume Nosler doesn't have an error on their site)?

Side note - my understanding is that the 280 spec pressure is lower due to being developed as a semi-auto and in bolt form the 280 should be able to handle pressures closer to the 270.
 
Been reading here for about a year...very knowledgeable folks, and I have learned more that I can describe.

I thought I had a few concepts understood, but reading on the Nosler site has me a little confused. Any wisdom from the clan would be appreciated.

The ballistics data for the 270 and 280 (not the AI), both shooting a 140gr AB. It lists the MV for the 270 at 2900 and the 280 at 3000. Why would the 280 be a fair amount faster, given that I think the 270 has a higher max chamber pressure in the SAAMI spec. I guess I had been assuming that they wouldn't be loaded to a different percentage of spec. Where is my understanding off (I assume Nosler doesn't have an error on their site)?

Side note - my understanding is that the 280 spec pressure is lower due to being developed as a semi-auto and in bolt form the 280 should be able to handle pressures closer to the 270.

Look at the barrel twist rates (and sometimes barrel length) on the test rifles; .270 Win is 1:10" and the .280 Rem is 1:9.5".
 
From another thread posted my Michael Eichele

Bigger bores generate less pressure at equal velocities with equal bullet weights with equal barrel lengths. A 300 win mag will deliver 180s faster than a 7mm-300 win mag with 180s. Obviously the 7mm has higher BC potential with the 180s. When you step up to the 30 cal. 200 hybrid, the playing field is a little more level. Similar velocities with similar BCs. Smaller bores concentrate pressures more with the constricted area.
 
I believe that part is due to bearing surface (more friction with the longer .277 bullet) and the other is simply because there is more surface area for the gas to push on.
so a .277 cal bullet has .0603" cubed and the .284 bullet has .0633" cubed to push against.
That's my understanding of it any way:).
 
Pressure is applied to the bullet in PSI (Pounds Per Square Inch) and with everything being equal
the larger bore will normally produce more velocity Because there is more surface area to push against. (More Square inches).

Bullet design (Bearing surface) and barrel rifling does have an effect on velocity. But again if everything is the same, the bigger bore will be faster.

J E CUSTOM
 
What Barnes quoted from Michael Eichele...... it has to do with bore diameter/ expansion ratio.
 
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