GGG 308 Ammo

[Laurie]

Thanks for that correction Ian - I hadn't realised GGG also had a 175gn product. So, it might be fine Eddie, but you'd still be much better off begging, borrowing, stealing, or buying a chronograph as you're otherwise very much shooting in the dark.

Of course, much depends on what distance(s) you plan to shoot over. Short barrel 308 Win rifle owners frequently encounter serious problems at 800 yards and beyond, especially if they've not worked up to 500 and 600 yards beforehand. The usual problems are one of or, a combination of, three issues:

1) bullets that go transonic, then subsonic before reaching the target due to low MVs and relatively poor BCs (ie high drag). Nearly all bullets are adversely affected to some degree at least by these transitions (wind drift is exaggerated and group dispersion increases), but there are a number of older design 168gn bullets that become unstable in these conditions.

2) over-estimating MV and bullet BC sees the shooter woefully underestimate the elevation come-ups needed on the sights and hence bullets strike very low.

3) Linked to 2) the scope lacks adequate elevation adjustment range, especially if not mounted on a tapered rail / mounts. In this case, even when the shooter knows of his/her POIs, the sights or scope can't be raised enough to get onto the target.

To give an example, should the GGG ammunition use the 175gn Sierrra MK (which is a good stable design and copes as well as most and better than many with trans/subsonic speed transitions), its required 'come-up' for 1,000 yards from a 100 yard zero are:

2,350 fps MV .......... 51-MOA (subsonic after 800 yards)
2,400 fps MV .......... 48-MOA (subsonic after 800 yards)
2,450 fps MV .......... 46-MOA (subsonic after 900 yards)
2,500 fps MV .......... 44-MOA (subsonic after 900 yards)

(G7 BC of 0.243 as measured by Bryan Litz; 59-deg F air temperature; 1,000 ft altitude ASL assuming Orion is up in the Welsh hills).

That 7-MOA difference from the 150 fps MV between 2,350 and 2,500 represents around 75 inches in POIs in vertical terms, 1-MOA at this distance being 10.46 inches.

You are doing the right thing going to a professional training outfit with the experience to assess the issues and who've seen and know every ballistic pitfall known to man, sheep and shooter. They'll keep you on the straight and narrow and you'll learn a great deal. If you don't know the ammunition's MV, I'm sure that they will provide a chronograph alongside checking your short-distance zero before you get into the longer-range stuff. Have fun!

[edcm]

Laurie

Thanks again for the time and effort that you have put in.

Eddie