284 versus 6SLR (243AI) comparative ballistics F-class options

[Trevor60]

to me F open is race gun class. you are able to run what ever you want with what ever bullet you want in order to better the next guy. a 284 is nice at 2950. seen guys get these numbers but why limit yourself to a 284 case when you can run a 7 wsm at 3050 or 3150.

.284 at 2950 is 5.3 min in a 10 mph wind.
7wsm at 3050 is 5.0 min
7wsm at 3150 is 4.7

if we take the high load for the 284 against a moderate load in the 7wsm the 284 is still behind by .3moa. you don't think it is much until you look at the width of the scoring ring that separates the 4 from the 5 and more importantly the 5 from the V ring. in open you are much more likely to have the V count determine where you finish overall.

As for the .30 cal no one is shooting the 210 in f open they are moving to the 215 and 230's if your going to select any bullet other then the 7mm then you need to pick one that is better then the 7mm BC and that leaves you with only the 215's or 230's unless Marshall has a 210 hidden that he isn't telling anyone one about.

the best part about competing is getting out to compete. It doesn't matter what you shoot or how you do. as long as you have fun doing it...we know people that shoot some type of loudandboomer and do they win sometimes and sometimes it is the other guy. If you work at it anyone can have their day no matter which cartridge they use.

However after a season or two you will start to see there are technical advantages of running larger cases with higher speeds.

All the best and hope to see you on the range.
Trevor

P.S.

If you really want to shoot the 6mm look at the 6CM (6mm Competition Match) it seems to be proving itself over the other 6's

 

[LaurieH]

Spent 2.5yrs working with the 223/90 in hopes of using this "physics" to let me shoot without recoil pain vs the 308/heavies. At Raton and every other range I have shot out to 1000yds, the smaller bullet was simply punished more for small wind reading mistakes or in bumpy air.

I am not saying the 308 shooters beside me didn't get moved around but when they got bumped into a high 10, mine was a higher 9. Same direction.

That and your views on larger calibre / heavier bullet are interesting Jerry. I agree that we take FAR too much note of pure wind drift figures in ballistics programs when comparing bullets, and especially in comparing cartridges and calibres. There are definitely other factors 'out there' that can and will affect long term consistency and performance over a season of shooting on various different ranges and in all weather conditions.

There are other factors I keep finding myself having to remind people of. If you shoot short to medium range, 'precision' (group size and consistency) often outweighs a perceived external ballistics advantage; that 10 mph 90-deg wind comparisons can be very misleading through exaggerating likely changes; the issue of a bullet's transonic / sound barrier performance can be important for many who want to try short to mid range kit at long ranges and don't really have the required velocities.

FWIW, I've done more than a few 'reverse calculations' on shot to shot wind changes from my match plots comparing corrected wind value changes after converting them back to what the ballistics program says they represent in terms of 90-deg wind speed changes. Perhaps I'm fortunate in the ranges I shoot over, but I find that even 'difficult days' usually see much smaller wind speed changes (on a 90-deg angle basis) than I had imagined would be the case, and I suspect most people imagine are happening. Take a match I shot in yesterday at 600 yards. Conditions were very difficult with 15-25 mph winds that were mostly headwind with an angle from around 11 o'clock, but with continuous speed changes and some noticeable angle switches too. The total range of corrected wind values on my plot for individual shots was 2.5 to 5-MOA, but the biggest single variation between consecutive shots was around the 1.75-MOA range, and half to one-MOA changes were much more common.

The cartridge was .260 Rem, the bullet the 123gn Lapua Scenar at 2,985 fps MV, its average G7 BC 0.265, a relatively light bullet, but one well suited to the 260 and similar smaller 6.5mm cartridges IMO. Very nice to shoot in an 18lb rifle off a front-rest with no recoil to notice. With an I7 'form factor' of c. 0.95, it's an efficient little bullet that is in line with that of most 140gn designs in the calibre, but not as good as the very best which get down to 0.9 or below.

Run the wind changes through Brian litz's PM ballistic Solver V2 with as close a simulation as I can get to the conditions on the day, and the overall wind speed range comes out at a 90-deg 7 mph wind change, but that was over the match as a whole where three of us shared a target and took maybe 45 minutes to an hour of shooting alternately. The biggest single shot to shot change I experienced equated to a 4.75 mph wind change at 90-deg, and the more common half, three-quarters MOA wind switches seen equate to 1.5-2mph wind speed changes at 90-degrees angle. All this on what we'd regard as an exceptionally rough day.

Now, what I'd like to have been shooting was .284 Win with a 180 VLD at ~2,800 fps. Run the same calculated winds through the program with a 7mm Berger 180 VLD and we get the following changes

2 mph 90-deg equivalent at 0.75-MOA becomes 0.61, a 0.14-MOA or 19% improvement (typical shot to shot change)
4.75 mph becomes 1.44-MOA, a 0.31-MOA or 18% reduction (largest shot to shot change)
7 mph becomes 2.13-MOA, a 0.37 or ~15% reduction (overall corrected wind variation over the match)

These figures assume no shooter input of course - the equivalent of choosing an average wind then shooting the whole match aiming at the centre and ignoring the flags. As the use of the 284 would have the same effect as reducing wind input (and need for accurate estimation of changes) by ~15-20% would I have got a better score? Yes, three shots that were marginally on the wrong side of the line would likely have moved inside the higher score ring.

Perhaps though of more interest, and greater effect would be the use of the 7mm cartridge on elevations. The 260 with 123gn Scenar is very good for a light bullet in this respect in my experience, but Diggle in the North of England is one of these ranges where a wind change often produces and elevation shift too. There was a lot of this yesterday, and while the wind usually pushes bullets down as it strengthens, something strange was happening as people, myself included were getting high shots. Overall, I dropped six on elevations including a really suprising 'three' at 11 o'clock, 11 of the 20 shots doing the 260's usual trick of creating a straight horizontal line.

I suspect as a general subsrciber to Jerry's argument, but cannot prove, that I would have recovered some of these lost points with the 284 and a heavier bullet, possibly four or even five out of the six with that number of shots only just above a higher score ring.

This sort of improvement obviously depends on the weather conditions and range features - I won't say my experiences yesterday were 'normal' - but shows the risks in using a smaller calibre, lighter bullet. But ................. only if you subscribe to the view that such combinations are more affected by 'lumpy' air.

 

[swissinn]

Can't wait to try my 300 lapua Magnum in F-open next summer. 225gr hornadys at 3050 fps have been extremely accurate at 1000m