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What 7mm bullet do you recommend for 1 mile?

How do you determine BC at a mile. I would not know where to begin.

As Skwerlz pointed out, it starts with whatif games with your ballistic solver and what you're after is the shot to shot differences in BC, not the average BC you set the turret with, because the difference is the larger contributor to vertical. By 2 miles, with pretty much anything, it dominates the problem.

If you're looking for something to do out in the middle of nowhere while you wait for your barrel to cool down, play games with your solver to develop a sense of how large something needs to get before it's a problem. I've done it the most at ~2K. More or less, kinda sorta, at 2K 1 moa, 10 fps, and 1% BC variation all contribute about the same amount to the vertical spread. There is no point in working on reducing the group size from 1 moa to 0.5 moa if the next 10 shot string is going to have a 30 fps spread and 3% range in BC. It's more productive to work on the largest problem first.

If you're trying to "true" a solution, air temperature also needs to be considered. 10 F is about the same as a 1% change in BC at 2K. Shooters recognize pretty quickly that the wind at the firing position isn't the same as the wind down range. It's pretty easy to have a 10 degree difference between ground level and it can go either way. Fortunately, the air temperature doesn't change much during a string, so it's not a factor when you're evaluating BC spread.

If you can't find a vertical rock wall, there is another effect that tends to reduce the apparent vertical spread. I call it the danger space effect because I haven't seen a popular colloquial for it yet. I've seen the term "danger space" used in 2 contexts. The first is how much can your range estimate be off and still achieve a hit on a given size target. The second is the distance you need behind a berm to keep people and things safe from shots over the berm. What I'm referring to here is at long distances, there is a large difference in the firing solution between a half mil low hitting just below the target and what appears to be half mil low but is also 20 yards in front. If you've ever heard an account of "I hit a mil low, came up a mil, and still hit a mil low", what really happened was they hit a mil low and 50 yards ahead of the target, then a mil low just ahead of the target. An even more frustrating version is 1 mil, 3:00, no call on the next shot. The first bullet went over the target and hit 25 yards back with enough drop to look like 3:00, the second went over the top and landed in the blind spot behind the target. If you're not setting your own targets, when they ask for volunteers to paint targets, it's in your best interest to go out there and figure out distances to different landmarks at the target.

Tracking BC spread starts with brute force correcting the vertical on each shot for the actual velocity. I use plus or minus 1/2 moa for the error bars. Balancing resolution with potential errors, 2K seems to provide a good balance. It's still just a course estimate though. I'm guessing the BC spread estimate disappears into the fog of the other variables somewhere between 2 and 3%. What you're looking for though is when it pops out above 3%. After a couple barrels, it'll just be that looked like too much vertical for that velocity spread, that range, and these conditions. I'll factor in the round count and changes in velocity since break in.

Where does BC spread come from? Differences in bullet shape or weight are where shooters usually start. The largest bullet to bullet shape difference comes from the difference in meplat size on HP bullets. This is what length sorting is about. In one of the Litz books, AB came up with 1% per 0.010" difference in length for a 200 grain 30 caliber hybrid. That'd need to be scaled for difference calibers, weights, and bullet shapes, but it gives a sense of the size and a starting point for sort criteria. That isn't the end of it or may not even be largest part of it though. All bullets fly with varying amounts of yaw. Some bullets damp it out better than others, reducing the differences as they fly down range. Some bullets don't show as much difference in BC for a given range of yaws. I'm guessing this is what the 15-20% of caliber flat, hard edged, meplats are about with the bullets that are known for low BC spreads. That yaw can also come from the bullet engraving unevenly or being bent as it enters the throat. This only gets worse with wear. Too much pressure can do it as well.

Welcome to the looking glass!
 
AB Millenium is my current favorite. I have AB Analytics for my desktop.

The Hornady 4Dof works really well for the Hornady bullets. When it's working.

I have an Apple and Android tablet. Years ago, the Android version of the AB app was a lot better. These days, one or the other of the Hornady will usually be working. Having options can also come in handy when trying to interface with things like spotting cameras.
 
408 Chey Tac or 416 Barrett would be ideal for this stuff.
I've shot a 416 and loved it, could not believe the muzzle brake was so effective I could shoot and shoot and not flinch or worry about shoulder fatigue.
(Tip - don't shoot your AR 500 Plates at 600 with one lol)
------------
But more wondering visibility of bullet splash with 7mm
180 gr and above
If you want a 416, buy the 416 because nothing else is going to scratch that itch. I've shot with them and think in general the whole splash thing is overblown. There are days where the 416 splash also disappears and they're playing battleship with $10 shots instead of $1.50 shots. I get a little pale and shaky at the thought of joining the scrum for the premium 416 components.

The 408CT doesn't offer any more raw ballistic performance than the 300PRC or 338Lapua. On this one, if there's an itch that needs to be scratched, I suggest the 375 version. It's much easier to keep a fresh edge on the 300PRC or a 7. My whole ELR gear strategy has pretty much devolved into 1.25" blanks that I can easily source from a barrel broker. I chamber my own barrels, so it could also just be a case of everything looks like a worn out barrel.

It's counter intuitive initially that ballistic uniformity is the key to distance, but after you've watched it play out through the scope enough times it's internalized.

On scopes, I shot 5-20 Gen 1 Razors for years because I could find them for $1300. My current favorites are the 7-36 Gen 3s. I also have the 7-35 ATACR and a March. The Gen 3s have the best clarity at 100 yards of anything I own when they're zeroed and compared on top of 50 moa of rail. I'm assuming that clarity is also better at the top of the travel. I've bought them new for under $2500. I try for 30 mils in the scope and then 30 mils in a NF Wedge. I also have the Charlie Tarac. I prefer the Wedge because the mass is so much lower. Muzzle brakes reduce shooter perceived recoil, but the back and forth pulses they produce are hell on optics and their mounts. I can usually use the top magnification because I'm a fall/winter ELR shooter and the mirage issue is nonexistent below 50 F. I favor chassis with a full barrel shroud because it also helps with mirage. Mirage bands are not really an option with ELR muzzle brakes. I put a lot of effort into setting the gun up to track so the target stays in the field of view. Finding a low contrast target 1.5 miles away on natural terrain with a 35X scope is a non trivial set of fine motor skills that takes a while to develop.
 
Thanks so much for your time and response here Frank
Good to know 5R is beneficial for the BC
If I may ask, is it worth it to go with a Gain Twist for such a caliber
and what would you suggest to arrive at an 8 twist
For instance an 8.3 to 8.0???
If your going to run a gain twist… a .25 to .75 and no more needed in my opinion. I run a .25 on my RF barrels. Just give it something.

Or I’d just run a straight 8 twist.
 
162 or 180 ELDMs and 175 ELDXs transitions with no issues in an 8 or 9 twist.
Berger 168 hunting or target vlds, 180 vlds, 180 hybrids, 184 f open hybrids, 175 elite hunters, 190 lrhts, 195 eols, will all transition in a 8 or 9 twist.
190 Atips will transition in a 8.5 twist.
183 and 197 Sierras will transition in an 8 twist, but the 197s will need a 7.75 twist, or risk them coming unglued around 2200yrds. This is data from 980ft asl and at least 2900fps for the heavier ones, and as high as 3260fps for 162s, although I don't recommend cranking 162s or 168 Bergers over 3200, in a 8 twist.
The ability for a bullet to remain stable through the transonic zone is what you need, and all of these will do that. The mile is a cake walk, I first done it with a 168 Berger hunting vld from a 308, but the extra step to 2400, changes the game a fair amount. 180 hybrids and 190 lrhts are my go to for consistency. The others are plenty capable, but consistency is somewhat questionable at times.
 
If your going to run a gain twist… a .25 to .75 and no more needed in my opinion. I run a .25 on my RF barrels. Just give it something.

Or I’d just run a straight 8 twist.
I have had good luck with straight 8's
Have not tried a gain twist yet.
So of course I like others to be the test mule then gain from their experience.
I still don't know how much benefit a gain twist is unless a guy is maybe pushing the envelope of speed?
Supposedly it's only benefit is ensuring a tight seal the whole way down the bore.
Don't know if I've had a bad seal before but?
Sounds like good insurance anyways.
 

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