GGG Match Ammunition

[Invicta]

I am looking for ballistics charts for over 500m for GGG .308 Win Match Ammunition. Can I simply plug in the bullet characteristics into a 4DOF calculator with the known initial velocity of the ammo and use that prediction for over 500m shooting?

 

[daniel.chisholm]

Hopefully someone else will reply with more up to date information, but when I fired GGG .308Win in 2015 at Bisley it was a Sierra #2155 loaded to 2900-ish fps (from memory; actual measurements from the batches being fired were posted at the time on notice boards).

So, unless they are using a different bullet, why not just use the predicted ballistics info from a #2155 Sierra at 2900fps m.v. (or actual measured m.v. from your rifle)?

 

[Ned Ludd]

As long as the velocity you use is an actual velocity measurement from your specific setup, and you know with certainty the bullet is the #2155, all you have to do is plug those values and the appropriate atmospheric conditions into a ballistic calculator as @daniel.chisholm suggested. Using a generic "box" velocity value will only get you as close as the box velocity value is to your true velocity with that specific ammunition. It might be close, it might not.

Once you have reasonable predictions from a ballistic calculator, they should get you close enough at longer distances, although no ballistic calculator should be expected to be spot on to a single elevation turret click at every distance, on every different day. You can tweak the settings and record the values to improve your dope over time as you encounter various conditions, etc.

 

[Invicta]

As long as the velocity you use is an actual velocity measurement from your specific setup, and you know with certainty the bullet is the #2155, all you have to do is plug those values and the appropriate atmospheric conditions into a ballistic calculator as @daniel.chisholm suggested. Using a generic "box" velocity value will only get you as close as the box velocity value is to your true velocity with that specific ammunition. It might be close, it might not.

Once you have reasonable predictions from a ballistic calculator, they should get you close enough at longer distances, although no ballistic calculator should be expected to be spot on to a single elevation turret click at every distance, on every different day. You can tweak the settings and record the values to improve your dope over time as you encounter various conditions, etc.

Much appreciated - that sounds fine, so all I need to do now is measure my actual velocity out of the box and confirm my bullet values to use the ballistic calculator. Plainly there will still need to be some experience ploughed back in to my actual numbers, but hopefully it will get me close enough to the curve to hit the target at least! My GGG is the GPX15 .308 175gr Match Ammo. Any help on the actual bullet design would be great! The data sheet suggests a HPBT BC of 0.496 and an out of the box Velocity of 810 m/sec +/- 7 m/sec.

 

[Invicta]

Hopefully someone else will reply with more up to date information, but when I fired GGG .308Win in 2015 at Bisley it was a Sierra #2155 loaded to 2900-ish fps (from memory; actual measurements from the batches being fired were posted at the time on notice boards).

So, unless they are using a different bullet, why not just use the predicted ballistics info from a #2155 Sierra at 2900fps m.v. (or actual measured m.v. from your rifle)?

Maybe a 168 grain, as the 175 grain has 2657 fps. Would be nice to have 2900 fps! Although I do have a 26" barrel, so maybe I have a bit more than 2657 fps!

 

[Laurie]

The GGG 308 Match supplied under the GB NRA contract for use in UK 'Target Rifle' is loaded with off the shelf Sierra 155gn MKs p/n 2155 as Daniel Chisholm says in post 2, nominal MV 2,925 fps in a slightly 'tight' 30-inch barrel. Actual MVs will obviously depend on the barrel internal dimensions, length, chamber freebore and condition.

 

[Ned Ludd]

According to their website, the GGG GPX15 .308 175gr Match ammunition has a 175 HPBT bullet loaded over double-base powder. A picture of the box also has the Sierra logo on it, which would suggest they are using the 175 SMK. The box velocity value of 810 m/s translates to ~2658 fps, which is closely in line with other commercial 175 SMK loads.

http://www.ggg-ammo.lt/en/ggg-308-win-design-gpx15

Invicta - the average G7 BC for the 175 SMK is listed at 0.243, the average G1 BC is listed at 0.473 (Litz, Ballistic Performance of Rifle Bullets, 2nd Ed., 2015). You can use either of those values as inputs in a ballistic calculator with your actual muzzle velocity, together with the appropriate atmospheric conditions and elevation, and the output should get you pretty close at longer ranges from your 100 yd (or m) zero. I typically use the JBM Ballistics Simplified online calculator (http://www.jbmballistics.com/cgi-bin/jbmtraj_simp-5.1.cgi) and it routinely gets me within a few clicks at distances out to 1000 yd if my input values are solid.

 

[Laurie]

My GGG is the GPX15 .308 175gr Match Ammo. Any help on the actual bullet design would be great! The data sheet suggests a HPBT BC of 0.496 and an out of the box Velocity of 810 m/sec +/- 7 m/sec.

Hearsay has it that this round also uses an off the shelf 175gn MatchKing. Litz's average G1 BC of 0.475 through his testing appears to confirm that being reasonably close to the claimed value. For ballistics programs Litz's measured average G7 BC of 0.243 provides a more accurate metric for 500m and longer distances.

Most factory 308 Win nominal MVs are measured in an industry 'standard' (internal) dimensions and chambered (the European CIP in GGG's case, this being a Lithuanian make) 24-inch barrel. Depending on your rifle's spec and condition, the quoted 810 m/s MV may be well out, and you really need the actual MV in your own case. However in the absence of a chronograph and the relatively short range of 500 metres, it'll be close enough to get you going, unless you intend to shoot in something that doesn't allow sighters.

 

[David101]

wrong thread sorry

 

[eric32]

Use a 300 yard drop

Measure drop from 100 yard zero in inches on a target

do not adjust sights or scope for a 300 yard

Measure offset in inches

then mess with the velocity numbers to line up the drop in inches

That will get you a good idea of a trued velocity

 

[Invicta]

The GGG 308 Match supplied under the GB NRA contract for use in UK 'Target Rifle' is loaded with off the shelf Sierra 155gn MKs p/n 2155 as Daniel Chisholm says in post 2, nominal MV 2,925 fps in a slightly 'tight' 30-inch barrel. Actual MVs will obviously depend on the barrel internal dimensions, length, chamber freebore and condition.

Thanks, so not the same round then.

 

[Invicta]

Use a 300 yard drop

Measure drop from 100 yard zero in inches on a target

do not adjust sights or scope for a 300 yard

Measure offset in inches

then mess with the velocity numbers to line up the drop in inches

That will get you a good idea of a trued velocity

Many thanks - that was going to be my calibration method!

 

[Invicta]

Hearsay has it that this round also uses an off the shelf 175gn MatchKing. Litz's average G1 BC of 0.475 through his testing appears to confirm that being reasonably close to the claimed value. For ballistics programs Litz's measured average G7 BC of 0.243 provides a more accurate metric for 500m and longer distances.

Most factory 308 Win nominal MVs are measured in an industry 'standard' (internal) dimensions and chambered (the European CIP in GGG's case, this being a Lithuanian make) 24-inch barrel. Depending on your rifle's spec and condition, the quoted 810 m/s MV may be well out, and you really need the actual MV in your own case. However in the absence of a chronograph and the relatively short range of 500 metres, it'll be close enough to get you going, unless you intend to shoot in something that doesn't allow sighters.

Many thanks. Will investigate further!

 

[jim1903a1]

There is a sight in range at Bisley if you want to try that. The range distance is something like 72.5 feet and you shoot at a target calculated to simulate 300, 500 ,600, 900, and 1000 yard distances. The target looks like a ladder test with the different yardages and is designed for the Sierra 2155. I dont't remember any targets for the 175gr bullet but you might ask. The sight dope I got wasn't perfect but it definitely got me on paper. Last year, the seat of my pants told me the MV was around 2900fps. It would be neat if someone would find room in their luggage for a MagnetoSpeed, just for curiosity.