Estimating velocity for ballistic calculator? .308 GGG

[pnuk]

Hi all
Bit of advice needed.
I usually shoot at 100yds but have a chance to shoot at multiple distances up to 1100 soon.
I've shot out to 1000 in the past but not with this rifle.

I have a couple of ballistic calculators on my phone but no access to a chronograph before the shoot.

Are there estimates for velocity I can make to roughly work drop calculations?

I'm shooting a .308 with 20inch barrel with 1:10 twist.
Ammo is factory GGG using 175gn Sierra Matchkings.
(Sierras website gives a BC of .505 @ 2800fps and above / .496 @ 1800-2800fps / .485 @ 1800fps and below.)

Thanks for any advice.

[Mezzer]

Hi all
Bit of advice needed.
I usually shoot at 100yds but have a chance to shoot at multiple distances up to 1100 soon.
I've shot out to 1000 in the past but not with this rifle.

I have a couple of ballistic calculators on my phone but no access to a chronograph before the shoot.

Are there estimates for velocity I can make to roughly work drop calculations?

I'm shooting a .308 with 20inch barrel with 1:10 twist.
Ammo is factory GGG using 175gn Sierra Matchkings.
(Sierras website gives a BC of .505 @ 2800fps and above / .496 @ 1800-2800fps / .485 @ 1800fps and below.)

Thanks for any advice.

Pnuk;

Without a chrono you are quite literally, shooting in the dark. Save your pennies and purchase a chrono or find a friend who has one. I held off buying one for long enough but now that I have one I realise just how much time (and bullet expense) I've wasted. Even the best ballistic calculaters are worthless unless you can feed in an accurate velocity at which point they come into their own.
Go on, buy a chrono (and make a few friends). You know it makes sense

Mezzer

[pnuk]

Thanks Mezzer. I may well do that but the last chance I have to shoot before I go is tomorrow at Bisley so even if I get one I can't get one soon enough.

Shame the NRA don't have them to hire really

[ovenpaa]

You are missing too many variables to make an accurate estimate of drops as it stands. I have used QuickLoad to estimate MV's in the past with a known load however you are missing powder type and weight. Closest approximation I can think of is the M118 Ball which is around 2600 fps so I would have thought 40-41 minutes to get to 1000 yards with a 100 zero.

A far from ideal way of doing things and I do agree a Chrono is the way forward or shoot at a safe known shorter distance, note your drop and calculate the theoretical drops for longer distances.

[pnuk]

You are missing too many variables to make an accurate estimate of drops as it stands. I have used QuickLoad to estimate MV's in the past with a known load however you are missing powder type and weight. Closest approximation I can think of is the M118 Ball which is around 2600 fps so I would have thought 40-41 minutes to get to 1000 yards with a 100 zero.

A far from ideal way of doing things and I do agree a Chrono is the way forward or shoot at a safe known shorter distance, note your drop and calculate the theoretical drops for longer distances.

Thanks Ovenpaa

I think the GGG is meant to be very similar to the M118 so I had tried that formula myself. I think I'll get an hour on a longer range if I can and work out real world drop then extrapolate.

[JSC]

Not sure how much this is going to help, but I recently chrono'd the GGG 175gn ammo using an 18.5" 1:8 barrel and it averaged 2541fps.

With a 20" barrel, I reckon you'll be around 2580-2590fps.

[pnuk]

Really helpful thanks. I've currently been working with 2580 so glad to see that my estimate was in the right ball park.

[JSC]

You should be close with that. This may also help. These are the actual elevations I used with a 175gn load going at 2650fps out of a 26" barrel.
Yds. Mins Elevation
200 0.00
300 2.75
400 6.00
500 9.50
600 13.75
700 ?
800 ?
900 28.00
1000 34.00
1100 41.50
1200 48.50

[pnuk]

Just a quick update to say thanks to all who contributed, particularly Ovenpaa and JSC.
After eventually tweaking the estimated velocity to 2579fps, took it out to 500yds.
Dialled in STRELOK calculated 11.7MOA which put the POI an average 2.1inches below POA. Quite amazed to be honest that it was that close at that range. From this I can estimate more closely what the actual velocity is to get a closer calculation for the next time.

[pnuk]

And just for the record. By my reckoning that should make the velocity 2542fp/s to make the calc match the real world group.

Be interesting to see how close this is to reality when I chrono it.