1. How concerned are you about differences in trajectory data when zeroing your rifle at one elevation above sea level and then shooting at a significantly different elevation? For example, you zero at 8000 feet and then shoot a match at 5000 feet without the opportunity to check zero or to rezero. Are there methods you use to deal with the fact that the zero distance will change somewhat at the lower elevation?

I know that some ballistics calculators have the option of entering original zeroing environmental data and having them automatically calculate the changed zero distance using the new data, but not all. My Kestrel doesn’t have that feature, nor (as far as I can determine) does the online JBM. When I queried the company that makes the Kestrel, the suggestion was to zero at a closer distance (100 yards) to minimize the differential effects in changing elevation.

2. Based on discussions here (and my own experience) I know that if a soft rear bag-type support is allowed to sink when the gun recoils vertical stringing can result. I’m reading a military sniper training manual, and it almost seems to discourage any sort of rear bag rest—evidently for that reason—and therefore seems to say that we should use our hand only on a firm surface.

What do you think of that? I do what I can to ensure that the rear support doesn’t move or sink when the rifle is fired, but I have never thought of dispensing with it entirely (and don’t intend to without good reason). I believe it would be very hard to achieve the same level of stability without one. Thoughts?

1. I was first concerned with different 100-yard zeros at different altitudes when I attended my first precision rifle class at Rifles Only in Texas. My 308 bolt gun was zeroed for 7,000' DA summer conditions in northern Colorado, ASL of about 4,500'. The course in Texas in November had +1,000' DA to -2,000 DA, depending on the morning, with ASL of about 40'.

In the briefing prior to field work, Jacob Bynum (owner of Rifles Only) stated there would be no difference in 100-yard zero, to which many of us students didn't think was right. Jacob was right -- no change in zero for me, and I had the largest altitude swing of anyone there.

The same questions arose when Rifles Only held classes in eastern Colorado a few years later. ASL of about 4,000', with DAs of 6,000' to 7,000'. Jacob used me as an example, as he knew I experienced no zero changes on any of my rifles with DA swings of up to 10,000'.

Now with a subsonic chambering and a low-BC bullet, there must might be different 100-yard zeros. I haven't run the numbers. I bet it's not a huge difference though, even for chamberings like 22lr and 45ACP.



2. Poor rear bag technique is likely my biggest and most consistent technical issue. Offgrid, Alpine, a few other local PRS-shooters, and Frank Galli (ex-Rifles Only instructor and current owner of Snipers Hide website) have all said this to me in one way or another. It's taken me a few years to understand this, being all back of the short bus and stuff....

IMO, squishy rear bags are likely the easiest type of rear support in which this technique shortfall shows up. Look at F-class guys -- often a heavy bunny-ear bag, filled with heavy sand or shot, and virtually non-squishable. They have time to set up the shot, shooting their entire string at the same target.

Look at the PRS-type guys -- the potential need to adjust buttstock elevation dramatically from shot to shot, stage to stage. Squishy bags allow us to do this. But it also means if our technique isn't good, shots don't go where intended. This can come from relaxing the bag grip when breaking the shot. Putting downward pressure the stock with our heads. Not controlling recoil well -- bipod not loaded, buttstock not firmly against our shoulder, not lined up behind the rifle. I'm guilty of all of these technique problems, and they tend to push my POI up. In fact I just did these things for my first 6 shots with the 308 last weekend. I kept thinking my dope was off. Nada -- my technique was off. I corrected the technique and voila, shots are dead on for elevation at 100, 350, and 530 yards. Even in high winds.

I personally think a hard rifle support surface leads to a greater chance of bipod hop -- based on my own experience with Harris and Atlas bipods.

I learned from Alpine and offgrid to use a larger rear bag than I was originally using. I try to keep the rear bag as much under my shoulder as the rifle itself. I try to keep the rear bag fairly firm, using its compression cords. This helps to minimize the sinking of the bag in case I relax my squeeze grip. I try to only barely touch my cheek on the buttstock, instead of letting the weight of my head sink onto the buttstock. Then I weight the bipod at a reasonable level (but not super hard) and hold the buttstock firmly into my clavicle (but not super hard).

This produces good results for me. When I'm doing it right, with bolt actions I can consistently get groups in the .3" to .5" ballpark at 100 yards, for the rare times I shoot for groups. Sometimes even in the .2s. With AR-15s and the right ammo, .4" to .7" is pretty doable. I don't get the .1s and .2s that offgrid and Alpine produce with their 6mm rifles, but they have an advantage over me in both technique and equipment standpoints.

For shooting at a square range, or with limited need to adjust elevation to engage targets, a firm rear support probably makes a lot of sense.

Not concerned. Doesn't matter, all within shooter error. To prove my point shoot a five shot dot drill at 100yds, get up and down with your rifle between each shot. Which shot is your zero? Go to a different elevation, repeat, which shot is your zero?

Strongly disagree being discourage not to use a rear bag. Everyone will shoot better with any style of rear bag.

I'm held hostage at gunpoint 300yds away, bad guys head is barely exposed behind my head. I'm going to insist you use a rear bag!

Consider these.

http://bulletin.accurateshoote...by-marcus-blanchard/

https://jc-steel-targets.think...-prs-nrl-competition

FYI. I've put rounds on paper at 1050yds, stiff/heavy rear bag vs the light weight bag I've been using for several years. Held better vertical, point of aim/point of impact with the lightweight bag. Impact was .1 mils or so high with the heavy bag. Hmmmmmm.

When I first saw the question, I thought to myself, "that's an easy one to answer." Then I saw fritz's answer and I got a little confused and now offgrid's answer makes me wonder about my experiences.

I'm only talking about the first question here, as the second question does not apply to me. As fritz says, we F-class guys use a solid rear rest, packed hard with heavy sand and I mash the rear of the rifle in between the bunny ears before taking the first shot. My rear rest weighs about 25 pounds, definitely not something to use outside the square range competition circles. On my AR-10, I have an Accu-shot or whatever that gizmo is called, but I don't shoot positions and have never had the delusion that I was, would ever be, or ever wanted to be a sniper. I'm just an F-class competitor.

So back to the first question.

The way I first read it, my answer was going to be, "Yes, I am very concerned and takes steps to account for that." Then I read fritz's answer about how he knows his 100 yard zero doesn't change, irrespective of where he is. That got me scratching my head; where did that come from? Then offgrid offers the same answer and now I'm confused. Maybe I misunderstood the question.

So I'll go ahead and provide my original answer and then offer a thought.

When I travel to a range other than my home range, I am very concerned about how my zero will shift due to the location or conditions being different. When I went to Connaught last summer, I was extremely concerned with that because in ICFRA competition, you only get two sighters and they are convertible. There would not be a chance for me to shoot at the range prior to the first day of competition; it was a 3 day ride and the range use is very different at Connaught compared to say Bayou Rifles. It was a definite possibility that if I didn't make allowances for the differences and faced a windy day, I could be off target from the start and lose points very quickly.

What I did was to get the elevation of the range at Connaught, the orientation of the range (it was south-north, just like at Bayou,) the expected temperature and humidity for those days and then I spent some time at JBM.

I recorded the conditions that prevailed at the last two matches at Bayou rifles and used them to plot a trajectory with 1000 yards being my 0. Then I ran the same trajectory, but this time using the conditions that I would encounter at Connaught, still using 1000 yards as my zero. I recorded the difference in come-ups from 100 yards between Bayou and Connaught. This difference would be due to the changes in conditions. I think I found that it was less than 1 MOA. Connaught has a higher elevation than Bayou, meaning the bullets would fly faster but the temps would be cooler and the humidity lower, which would slow down the bullets. It was close to a wash, with Connaught needing another MOA or so. Then I had to convert 1000 yards to 900 meters and that MOA shrank down to a half or so. I then calculated a trajectory sheet in meters and got come ups for 700 and 800 meters based on the calculated 900 meter zero and on that Monday morning, my first shot at 700 meters was smack in the black, I think it was a 3 or 4. I was vindicated, my preparations were adequate. Moving to 800 and then 900 did not present any trajectory problems, I had the thing nailed.

The value that was critical for me was the amount of come-up from 100 yards at the different venues. I did the same the year prior for Lodi, and before that for Phoenix and this summer, I will be doing the same for Raton. Knowing the required come-ups from 100 yards for the upcoming location and comparing that to the come-ups from the latest match at Bayou, I just adjust my 1000 yard "zero" by that difference.

There are a few things that are critical to use this successfully. You must know the trajectory of our load. This means the BC, the MV and all the conditions at your range. Then you must provide reasonable conditions for the range to which you are going and don't forget the orientation of the range. The difference in come-ups from 100 yards is the number I needed to work out. Once I had that, I was good to go and simply adjusted my scope's elevation accordingly. With the trajectory sheet for the range's conditions and my 1000 yard zero, I was all set for the other distances.

My thought:

In your case, I doubt very much your zero is set at 1000 yards, so things are much simpler. Your zero is probably 100 yards, which will be the same wherever you go. I would just create a sheet for the conditions as they should be at the range to which you are going. Make sure you have elevation, humidity and temperature and for long distances, you need to know the orientation of your shots compared to what you are used to lest shots leak out the right or left.

I live pretty much at sea level and have zeroed at a DA of near zero. I’ve then gone to Colorado and shot at a physical elevation of 5,800 ft on a hot day where the Density Altitude was around 9,200’. My zero did not change at 100 yards. Dialed elevations at 1000 yards were very different, as mentioned by previous posters, as atmospherics at longer distances in the higher DA had less drag. Same goes for muzzle velocity. I use a MagnetoSpeed and my MV In Colorado on that day was exactly the same as it was at sea level.

I should add that while the ambient temperature in Colorado was a little higher than my zeroing temperature, the powder I use is very stable, H4350, and on this particular occasion, my average MV was not affected.

This message has been edited. Last edited by: Sig Marine,

I trust JBM's ballistics calculations and I use the results for all my rifles. So I ran the numbers for my bullets & muzzle velocities, changed the scope-over-bore offset to zero inches, and input the POI zero at 1 yard. This is likely the best method to determine bullet drop over distance. I plugged Density Altitude at both 0' and 10,000'. Drops are rounded to the nearest .1".

6.5 Creedmoor 140 ELD-M @ 2,820 fps
2.3" drop for 0 DA
2.2" drop for 10,000 DA

308 Win 175 SMK @ 2,670 fps
2.3" drop for 0 DA
2.3" drop for 10,000 DA

223 Remy 69 SMK @ 2,805 fps
2.3" drop for 0 DA
2.3" drop for 10,000 DA

22lr RWS 40 LR match @ 1,000 fps
19.7" drop for 0 DA
18.9" drop for 10,000 DA

45 ACP Sierra 230 FMJ @ 1,000 fps
18.4" drop for 0 DA
18.0" drop for 10,000 DA

So....JBM states no discernible difference in POI at 100 yards for common centerfire ammo for DAs from 0' to 10,000'.

Subsonic 22lr match ammo shows an .8" difference at 100 yards. For a good shooter with match ammo in a quality rifle, this difference would be noticeable, but not huge. For 45 ACP handgun the difference is less than 1/2 inch. The best of the Bianchi Cup competitors probably couldn't see this difference.

As usual, some excellent discussion. Thanks to all.

Indeed, good info as always. My long range shooting is pretty casual, just a few of us with just enough coin to impress ourselves but not near enough to get the serious mojo. Working on a build component gathering quest now, chambering is leaning toward a 6 BR. Open to any views on that, barrel order is on hold until I make up my mind and refresh the purse.

quote:

Originally posted by TRshootem:

Working on a build component gathering quest now, chambering is leaning toward a 6 BR. Open to any views on that, barrel order is on hold until I make up my mind and refresh the purse.

6BR is great caliber. Very easy to tune, silly accurate, holds vertical exceptionally well, lots of fun to shoot.

I chambered a 6BR about four years ago, opened my eyes to what inherent accuracy is all about. Clearly see why the 6BR holds so many records.

Several friends have 6BR's. Most with 28" 8 twist barrels. Common load 29.5-29.8 H4895/105 Hybrids/2860-2900. 4000rds of barrel life is realistic. How consistent it is over that life...... A good friend pulled his barrel at 4300rds, shot the same load for the life of the barrel, 29.8/4895/105 Hybrids.

This got my attention! Fresh barrel, brass out the box no prep, zero'd my scope with a few rounds, then shot these 5 at 100yds. Still makes me smile So easy!!

https://s31.postimg.org/j416hy2e3/photo_7.jpg

The 6BR led me to the Dasher, 100-150fps increase in velocity.

What action are you going to use? Single shot or repeater? If repeater, AICS or AW cut? Max distance you'll commonly be shooting?

Sorry for the drift sigfreund.

I know a lot of people who rave about the 6BR and the Dasher. They do really well at shorter ranges, but out past 3-400 yards, when the wind blows they have issues.

I know guys who come to an MR F-class match with a 6mm when it's calm, and something else when it's windy.

If I were to start from scratch in LR and I was not constrained by caliber rules, my first stop would be the 6.5 Creedmoor. I would got to a 7mm only because of high-level competition.

quote:

Originally posted by NikonUser:
I know a lot of people who rave about the 6BR and the Dasher. They do really well at shorter ranges, but out past 3-400 yards, when the wind blows they have issues.

I think it depends on the type of competition. My experience is with steel/tactical matches, and 6 Dashers do well there.

I first saw some local guys use Dashers at the T3 Matches in northeastern Colorado. One of our 10 stages there was the long ball -- 2 shots each on 5 IPSC-sized steel targets, I recall distances of 1000 to 1300 yards, ridge-to-ridge across a couple of valleys. The match directors initially poo-pooed the 6mm chamberings, until they began producing higher scores than 6.5 and 7mm chamberings.

I've shot side-by-side with offgrid at the Raton, NM Whittington Center's tactical practice range, where we confirmed relative POI and wind deflection on steel at 690 yards. I recall right-to-left winds of around 10 mph, we broke shots at the exact same time, he aimed at the high right edge of the target, I aimed at the low right edge of the target. Both of our impacts landed on the left edge of the target, his stacked right above mine. Thus, even though we used different ammo and scope systems (mil vs. MOA), we could meaningfully talk about wind effects. I shoot 6.5 Creedmoor 140 ELD-M, he shoots 6 Dasher with bullet (I think) in the 105 to 110 grain ballpark.

In the actual tactical match at Raton, we have 4 long targets at 700 to 875 yards. IMO the Dashers in and of themselves don't do any better or worse than the 6.5s on these targets. The results depend upon the shooter's wind reading skills.

Again, I'm just talking steel targets, not X-rings. But out to 1,000 yards and a bit beyond, I don't see that the 6mm guys have a wind disadvantage to those of us with non-magnum 6.5mm chambers.

Good stuff guys, I always learn so much from you all.

quote:

Originally posted by NikonUser:
I know a lot of people who rave about the 6BR and the Dasher. They do really well at shorter ranges, but out past 3-400 yards, when the wind blows they have issues.

I know guys who come to an MR F-class match with a 6mm when it's calm, and something else when it's windy.

If I were to start from scratch in LR and I was not constrained by caliber rules, my first stop would be the 6.5 Creedmoor. I would got to a 7mm only because of high-level competition.

Those lots of people you know who have issues out past 3-400yds with 6BR's/Dasher's when the wind blows, need to work on their wind reading skills.

quote:

Originally posted by fritz:

I first saw some local guys use Dashers at the T3 Matches in northeastern Colorado. One of our 10 stages there was the long ball -- 2 shots each on 5 IPSC-sized steel targets, I recall distances of 1000 to 1300 yards, ridge-to-ridge across a couple of valleys. The match directors initially poo-pooed the 6mm chamberings, until they began producing higher scores than 6.5 and 7mm chamberings.

I held the high score at the above match with a 6x47/105 Hybrids/3030fps Believe fritz was at the match I shot that score. Didn't mind so much out shooting the big guns! Miss that match, very challenging terrain/wind, bummer it ended. That was my last 6x47 barrel. Dasher shoots inside the 6x47.

quote:

Originally posted by offgrid:

quote:

Originally posted by NikonUser:
I know a lot of people who rave about the 6BR and the Dasher. They do really well at shorter ranges, but out past 3-400 yards, when the wind blows they have issues.

I know guys who come to an MR F-class match with a 6mm when it's calm, and something else when it's windy.

If I were to start from scratch in LR and I was not constrained by caliber rules, my first stop would be the 6.5 Creedmoor. I would got to a 7mm only because of high-level competition.

Those lots of people you know who have issues out past 3-400yds with 6BR's/Dasher's when the wind blows, need to work on their wind reading skills.

I'll be sure and mention that to them at the next Match.

I appreciate those insights gents. We have access to land that would allow for some very long shots on steel, wind reading is part skill and some voodoo. I find my skill in this area is best suited to mid ranges and light bullets from years of sage rat eradication. I have some days that I look like I might be catching on...