I've been shooting in Run 'n Gun competitions here in TX, where the longest shots are about 500 yards on a target approximately 20" or so. We dont shoot for groups; you just have to make 2 hits and move to the next target. I've been using Wolf Gold 223 55 grain ammo and it's been working great overall. However, we had a pretty good crosswind at the last race and I was holding off about 6 to 8 MOA from the edge to get hits.  No big deal except that it felt strange having the vertical cross hair so far off the edge of the target.  Usually if I feel some wind, I just line up on the edge and that's good enough.

Other guys commented that they were able to aim for the edge or just off with 75 and 77 grain ammo. This prompted me to take a look at what I have on-hand and it turns out I have some Fiocchi exacta with 69 grain Sierra match kings. Haven't ever tried it, so I put the stats into the Strelok gizmo to see what my hold would have been for a 20mph full value wind.   Surprisingly, it said 14 MOA for the Fiocchi vs 12 MOA for the Wolf Gold. 12 MOA makes sense given where I was holding and my rough guess of 20mph wind. I figured the heavier 69 grain ammo would call for something like 8 MOA, so the result of 14 doesn't seem to add up. Hoping maybe one of you can clarify this for me.

For reference, I'm shooting a PWS mk114 with 1:8 twist and using Vortex Viper PST 1-4x (again going for speed over precision).  I don't have a chrono, but based on reviews, I'd guess the Wolf Gold is at about 3050 - 3150 fps. The BC seems a bit tough to track down. I assumed .269, which is what similar American Eagle xm193 claims.  I could be wrong though.  The Fiocchi claims a BC of .301 but runs a lot slower at 2735 stated and probably closer to 2600 in my 14.5" barrel.

Could the difference in velocity be causing the Fiocchi to drift more (according to Strelok anyway), despite the higher weight and BC?  Or is there something else I need to consider?  Thanks in advance.

Go a bit lighter with a 1:8. 69gr would probably be your best bet. Although the ammo cost will start eating you.

The 77gr SMK has a higher bc than the 69gr SMK.  It beats the wind better than the 69gr.  That said the 69gr shoots more accurately in a broader number of barrels IMO/IME.

Yeah, from what I've read, 69 grain should be great in this rifle. I'm still confused why Strelok would predict that the 69 would be blown horizontally nearly a foot more than the 55 grain. My only guess is that the 69s would be about 400 or 500 fps slower. Would speed have that much of an effect on drift?

I'll have to try some of these 75s.  Looks promising and price is not too bad.

With respect sir >>>  you guessed at every number (other than bullet weight and caliber) that you put into your calculator for several calculations.  I have little confidence in the accuracy of the results and I couldn't even begin to guess where the error might be.

The first step might be to take the 69s and the 55s to the range and test them side by side on a windy day to see if empirical observation agrees with the predicted outcome...

Yes, definitely some educated guesses in there, since Wolf Gold doesn't seem to publish their BC and I haven't chrono'd all these with my rifle. I definitely plan to get a variety of 69 and 75s to test side by side when possible, as you suggest.

I'm not sure I buy that data.  I just don't see it happening.  Unless you reload, the 77gr SMK (TMK especially) is about as good a BC as you're gonna get.  If you reload, the 80gr pills are available.

At 350yds, the 77gr SMK FGMM moves about 2 MOA less than the 69gr SMK FGMM.  That's in a gusting, 15mph or so wind in a very un-scientific setting (buddy's field).

I run a PWS as well!  Great rifle.  I have the mk116 and the mk111.  Both of the guns like 77gr bthp. Each gun is different but I've had great success with that.

I tried out a few different kinds of ammo from a bench at 200 yards on Friday.  Wind was breezy and variable, probably 5-7mph or so.  I held the center of the target on all shots. A few times I paused to let a stronger breeze quiet down, but mostly I just ignored the wind. Again , I was shooting my PWS mk114 with a 4x scope where the center dot is 1 MOA, so I wasn't expecting to stack bullets on top of one another. Also, I am not a bench shooter.  I'm sure that the gun and the ammo can do better in somebody else's hands, especially with a stronger scope.  

I also shot all ammo at 100 yards to see what the various drops were. I got 5 shot groups where the extreme spread was 1.5 inches from a few loads, including Wolf Gold and interestingly the federal fusion 62 grain soft points (which hit about 2 MOA higher than the wolf gold).  

At 200 yards, I found that the 69 grain IMI stayed pretty well centered on the target, with 4 out of 5 hits within 1.5 inches of center. Extreme spread between hits was 4" in a 5 shot group, which is fine for my purposes.

The 75 Grain Hornady Steel Match stuff did even better.  At 200 yards I dialed up 3 MOA from the zero I had for the wolf gold 55, just to make sure the heavier 75s stayed on the paper. Extreme spread was 3" in a 5 shot group. Obviously, hitting the dead center of the target was pure luck, but I'll take it!
http://Imgur.com/a/vxXWT

Today I took the Hornady 75s out to somewhere around 450 yards or so.  It was pretty windy, so I did have to hold the edge of the target to stay on paper.  I only shot 1 5 shot group, with an extreme spread of about 9 inches.  Not too bad for shooting off the hood of my car on a bag.  Was really just trying to confirm my holdover, which came to about 16 or 17 MOA.

1/8 will stabilize 80s just fine, especially in Texas.  

I'd go 77 or 75.