Quote:
Originally Posted by marlin1
with the 26" barrell compared to my old parker 270 with the shorter barrell , I noticed quite a difference but mostly in noise and barrell lift. what would the difference in fps be between 270 150 grain rounds and 7mm rem mag 140 grain . approx.
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Well your using two varing bullets in your analogy the Sectional Density of a 277" 150 gr. is 0.279 while the 140gr. 0.284" bullet is 0.248
The on game performance of the two will be totally different.(given similar constructed bullets)
Try comparing a 130gr. 0.277" (SD 0.242) and the 140gr. .284". Likewise the 150gr. 0.277" SD roughly equals that of a 160gr. 0.284"bullet.
7MM RM 140's in factory and a 24" bbl. I'd suspect real world velocities of about 3000fps.(never chronied 140's, but I have on 150's and 160, and 175's)
270Win velocities out of a 24" bbl, with 130's expect a real world velocity of about 2950fps.
Hmm lets see what that gets us for trajectories.
130gr. .277" Nosler BT @ 2950fps and a 200yd. zero.
300yds -7"(1565ftlbs) 0.343sec TOF
400yds -20.5"(1322ftlbs) 0.477sec. TOF
500yds -41.5"(1110ftlbs) 0.624sec TOF
140gr. .284" Nosler BT @ 3000fps same 200yd zero.
300yds -6.5"(1843ftlbs) 0.33sec TOF
400yds -19" (1590ftlbs) 0.460sec TOF
500yds -38" (1366ftlbs) 0.598sec. TOF
I guess if you feel a couple inches less drop and a couple hundred ftlbs constitutes a big enough difference to you then the 7mm RM is a big jump past the 270Win.
IMO it aint a big enough gap to haggle over, moving to a 30 cal mag from the 270Win is a bigger and more noticable difference, but alas that is not without it's own shortcomings.