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+--- Thread: Matching ballistics between 6.5G and 308 Win (/showthread.php?tid=17518)
Matching ballistics between 6.5G and 308 Win - BKKJ - 11-20-2018
First Post!
Im concurrently building an AR10 in 308 and an AR15 in 6.5. Both for big game hunting. Most my hunting occurs between 700' and 1300' above sea level, and 0-50 degrees F.
I'm wondering what velocities (read barrel length) will make the 308 & 6.5G ballistic equivalents up to say 600 yds or so (Ill never take a shot that long at a deer, but I do like target shooting that range and longer from time to time). Im planning to use the same vortex 2-10 LH HD scope on each one and it would be nice if my holds were similar for simplicitys sake.
For example, if I put a 20 barrel on my 308, and an 18 barrel in the 6.5G, would the holds be similar? Or should I just go 20 on each. I kinda like 20 for more velocity and less blast. (in case I don't have my electronic muffs on)
Lets say Im using high BC hunting loads in each case.
I know there is a lot variability here, but Im not quite sure how to determine this and Im just looking for a guideline. I understand the 6.5G outpaces the 308 WAY out there, so Im looking give up the difference in velocity to gain a bit of handiness.
Thanks
Matching ballistics between 6.5G and 308 Win - depletedyourcranium - 11-20-2018
No way to say without knowing what loads you're planning to shoot.
Matching ballistics between 6.5G and 308 Win - Drillboss - 11-20-2018
Here's a calculator to estimate velocity from different barrel lengths: shootersnotes.com/calculator/velocity-estimator/
Then use a ballistic calculator: http://www.shooterscalculator.com/ballistic-trajectory-chart.php
Looks like the trajectories are pretty similar out to 600.
Matching ballistics between 6.5G and 308 Win - Kswhitetails - 11-20-2018
Welcome to the Horde! As stated above, trajectories are pretty similar, but there is a pretty severe delta between them in the energy and velocity numbers at the muzzle. Wait though, the G catches up and passes the heavier bullet soon, and with the lower recoil, puts an other round on target sooner too. If I remember right, if you compare them setting the Grendel zero to 200 yards, it's very similar. Except for wind, which the G wins by quite a bit.
Matching ballistics between 6.5G and 308 Win - Sticks - 11-21-2018
Kswhitetails Wrote:...Wait though, the G catches up and passes the heavier bullet soon, and with the lower recoil, puts an other round on target sooner too. ...Not to mention a lighter overall rifle.
Matching ballistics between 6.5G and 308 Win - Sputnik - 11-21-2018
I would also add to compare the 6.5 Creedmoor into your mix. I believe Creedmoor beats the 308 and the .30 cal/7.62. The box of Hornady's Precision Hunter says 2700 fps with a 143 gr pill. Then you can reload 6.5 pills for both G and Creed. I believe I got a Creedmoor Criterion barrel from Fulton Armory that is way more accurate than I am.
Matching ballistics between 6.5G and 308 Win - BKKJ - 11-21-2018
Thanks all for the replies, I'm going to mess around with ballistics calculators a bit. Going to pick up a group buy 18 and hoping it settles in around 2500fps for most loads. am still waffling 308 or 6.5 Creedmoor on the AR10 build. Mostly due to plinking ammo cost. Also (to tie back into the original post) because I'm not sure what barrel length I want yet. Was entertaining either an 18 or 20 in 308. Probably would just go 20 in Creedmoor. I'm sure I don't "NEED" better ballistics than the 308. I'm just trying to decide if it's better to keep ballistics similar while upping energy or pay a little more and improve ballistics (that are already likely good enough) as well.
Matching ballistics between 6.5G and 308 Win - ErikS - 11-21-2018
I found in real conditions my 16in Grendel shooting 123s did not match my 308 past 300yds. Check the ballistic calculators closely and use realistic numbers for your Grendel. If you don't have a chronograph you won't know for sure so it take trial and error at ranges beyond 250yds or so.
Matching ballistics between 6.5G and 308 Win - BluntForceTrauma - 11-21-2018
ES, what bbl length for your 308?
Matching ballistics between 6.5G and 308 Win - ErikS - 11-22-2018
20in 308 vs a 16in Grendel. I found they differed quite a bit when I shot during a recent shoot that reached out to 460yds. I used a turrent marked for 308 and it worked great until the long 460yd shots, I was low with my Grendel.
Grendel load, 123 ELD at 2350fps
308Win, 168 SST at around 2600. (not as sure about the speed of the 308 load)
I was shooting at steel IPSC targets so any differences at the 350 and in targets were still on steel.
Matching ballistics between 6.5G and 308 Win - LRRPF52 - 11-22-2018
24" vs 24"
123gr SMK vs 175gr SMK
They're within .2 mils of each other out to 700yds for trajectory and .1 mils wind, in the Grendel's favor.
What I've personally seen from behind the spotting scope and with actual drop data is that the Hornady 123gr bullets fly about the same flight path as a 175gr SMK.
The 6.5mm 123gr Scenar and 123gr SMK have an edge over the .308 175gr SMK.
Where the real advantage lies is that shooters behind a Grendel can see their own impacts easily because the rifle didn't come off target as much as the .308s do, so follow-ups are much faster, as is the learning curve since you can see as a shooter what is happening, versus needing a spotter.