Question on velocities

[kentuckyMarksman]

I shot my first F-Class match this past Saturday. There were electronic sensors set up on all the targets that showed the point of impact on the target and the FPS of the round as it hit the target at 500 yards.

I was shooting a 308 load, using FGMM brass, Winchester primers, 43.5 gr Varget, and 168gr Hornady A-Max bullets. At 500 yards, my rounds were averaging 1780 FPS.

A gentleman shooting the relay after me on the same target was also shooting a 308 load. His load was using 42.3 gr Varget and a 185 gr Berger bullet (not quite sure which one), and his rounds were going about 1850 FPS at 500 yards.

With him using less powder and a heavier bullet, why would his load be going 70 FPS faster than mine?

My rifle is a R700 with the stock 26" SPS barrel. 1/12 Twist. Roughly 2500 rounds down the tube.

His rifle is a trued R700 with a Brux barrel, 1/11 Twist, I didn't ask him his barrel length, but it looked to be about 24-26". I asked him why he thought his velocities were higher, he said he thought that his match chamber in his barrel may cause higher velocities. He also said his barrel had a ton of rounds through it and he thought that may have smoothed everything out leading to less resistance and thus higher velocities. He thought my barrel had a pretty low round count. I don't know if all that makes sense to me...

Does that make sense to you, or any idea why his rounds would be faster than mine?

 

[Steel head]

Heavier bullet with a higher BC slows down less than a lighter bullet with a lower BC.

Even though his starting velocity is probably less by 500 yards and certainly at 1000 yards it will be going faster.

 

[kentuckyMarksman]

Heavier bullet with a higher BC slows down less than a lighter bullet with a lower BC.

Even though his starting velocity is probably less by 500 yards and certainly at 1000 yards it will be going faster.

That makes sense. Thanks!

 

[FCS]

In addition to what Steel head mentioned above, custom barrels are usually a little tighter / smaller land & groove diameter vs a Rem barrel.
Freebore in the custom chambered barrel is shorter, most probably.

What brass was used with the 185 Juggernaut? High probability it was Lapua brass, which has roughly 0.5gr less capacity than FGMM version 308 brass. Even though he used less powder, he was probably running a higher pressure load than you were.
168 Amax with 43.5 of Varget in FGGM brass from a 26" factory Rem 700 is about 2700fps.
185 Juggernaut with 42.3 of Varget in Lapua brass from a 26" custom barrel is about 2625 fps, best guesstimate.

Higher round count has opposite effect as throat erodes and jump increases, velocity will decrease due to change in leading edge of pressure curve.

Whole lotta variables left undefined in the equation, makes it really hard to give you a solid answer.

 

[kentuckyMarksman]

In addition to what Steel head mentioned above, custom barrels are usually a little tighter / smaller land & groove diameter vs a Rem barrel.
Freebore in the custom chambered barrel is shorter, most probably.

What brass was used with the 185 Juggernaut? High probability it was Lapua brass, which has roughly 0.5gr less capacity than FGMM version 308 brass. Even though he used less powder, he was probably running a higher pressure load than you were.
168 Amax with 43.5 of Varget in FGGM brass from a 26" factory Rem 700 is about 2700fps.
185 Juggernaut with 42.3 of Varget in Lapua brass from a 26" custom barrel is about 2625 fps, best guesstimate.

Higher round count has opposite effect as throat erodes and jump increases, velocity will decrease due to change in leading edge of pressure curve.

Whole lotta variables left undefined in the equation, makes it really hard to give you a solid answer.

Yeah, I'm assuming it was Lapua brass, and he told me his barrel likely had a tighter chamber, so that makes sense.

Right, I thought that he was likely confused when he said that velocities increased with the more rounds you had in a barrel. Thanks for confirming my theory.