My choice for a 7 twist was driven by the curiousity to shoot 90gr Bergers NOT to overstabilize the 80gr bullets.
This spring I started shooting at ranges from 1000yds to 1200yds. To my pleasure, both the 80gr Amax and Berger were superbly accurate hitting inside my 'moa' boulders. I would have no hesitation to recommend these bullets to F(TR) shooters wanting to campaign a .223.
Wind drift was also quite similar to my regular 308's (some are shooting super sized 308 loads so your mileage and safety may vary).
At these distances, ballistic data generated by JBM showed these bullets are indeed going transonic. To confirm that the bullets were well and truly subsonic, I dialed up the scope and launched them to 1400yds. Again, absolutely no issue in driving them onto my targets. The best part was I was holding MOA or better at this distance. Much better accuracy then I ever imagined.
One thing that was very noticeable though was the increased wind drift when the bullets went subsonic. If the winds were consistent, you could adjust but gusty conditions would push you some very humourous amounts.
So the first part of my quest had been reached. I had put together an inexpensive test bed that would shoot accurately. The bullets desired would go subsonic no problem, at least out to 1400yds. Wind drift/doping conditions would become super critical if I had any chance of hitting my accuracy goal at a mile.
Wind pushes the 80gr Amax/Berger about 1 min for every mph at a mile. Miss a wind call of 2mph and be off your target almost 3ft!
Reviewing the ballistics chart, I noticed that the drop from 1400yds to a mile IS ENORMOUS. The only way to make the journey was to have a super high 100yd zero/or be zeroed for 1450yds then dial up/use my mildots to get the rest of the way.
I was using an Elite 4200 tactical with 45mins of up. Rings were Burris Sig w/inserts. A scope with much more elevation would need less shimming of course.
The next task was shimming my EGW MOA base and rings to get a ridiculously high 100yds zero. I would need to be at least 36" high to have a chance at dialing in. I ended up shimming to 46" at 100yds which equates to approx 1450yds zero.
Yep, aim at the bottom of a piece of sideways plywood to hit at the top. With that task out of the way, I was off to see about making it that last 360yds.
Hard to see in the pic but there is quite a stack of shims under the scope base and the scope is angled with the front very low.
Well, weather and winds kept me pulling my hair out for a number of weeks. Strong gusty conditions, rain and even snow made things pretty miserable for about a month.
I finally got some clear but gusty winds and sent some out to a mile. My range is actually shooting into a top of a hillside clearing and ranges, using my Swarovski, at 1730/1745yds (close enough for me). The drop I am experiencing is less then a prairie mile but the flight time and distance are correct.
Initially, couldn't make out any bullet impacts due to the soft, wet ground. Going back to 1400 and 1500yds which were drier/dustier showed everything was working well but heading up the hill was like shooting into a black hole.
Frustrated, I made the hike in and flagged several distances. Lo and behold, I could see why bullets were not arriving where they were expected. That hilltop had some severe wind shifts and gusts rolling over the top which were much different from lower down the hill.
The 1400/1500yd targets were outside this whirlwind so hitting there was quite straightforward. Going to the mile would need calmer weather.
That weather finally came and bullets arrived on target as expected. The 80gr AMax flew superbly and was much more accurate at these distances then the Berger. In fact, the Berger did start to show some occasional HUGE vertical flyers.
Every now and then, a Berger would land as much as 30yds short. Given the lack of availability in my area and costs vs the Amax, I decided to stop shooting the Bergers and focus on the Amax which were working without any issue. Now the Bergers do shoot A LOT better at close distances so would be worth testing in any rifle.
I also tested some 75gr Amax which made the trip no problem as well. However, it was pretty obvious that these were being bounced around more then the 80gr Amax despite the higher muzzle velocity.
There is no escaping a higher BC for extreme range shooting. It does make a difference.
So I had proven to myself and my shooting partner that reaching out to a mile with a fast twist 223 is not only possible, it is quite straightforward to do.
Over the next weeks, I kept shooting and learning how to read the wind ribbons. I was starting to see that MOA, even sub MOA accuracy was indeed possible IF you could dope the conditions.