Range Report Danger Space Comparison 6mm vs 6.5mm

[RAWHDE]

I know most of the top guys in PRS/NRL are shooting 6mm so I was curious how it stacked up against the 6.5cm when it came to danger space (DS). I ran calculations for both rounds (Hornady 108gr ELDM & Hornady 140gr ELDM) on ballistics calculator and checked DS at various distances. If I did not completely screw it up, I found that the 6mm had a larger DS up to about 375yds, where the 6.5 then took over.
If this is in fact the case, I'm wondering why so many guys are running the 6mm, especially considering wind drift is greater with lighter round. Is less recoil and faster re-engagement of target what is driving it? Love to hear from anyone, especially guys actually shooting 6mm in matches.

If you run calcuations and came up with something different, please feel free to correct me. Thanks

Edit: **Please note that these calculations were run in two different apps (first in Ballistics AE and then JBM Solutions) and came up with different solutions. May have been user error on my part. Please see below thread. Apologies.

 

[morganlamprecht]

It’s recoil...easier to spot and see trace and thats what counts

the wind drift is basically a wash inside 800 where matches are won/lost

ranges are given and we have accurate range finders so up/down is rarely a problem among guys at the top

 

[RAWHDE]

Appreciate the response Morgan

 

[Steel head]

Yep, flat and fast with minimal recoil in a heavy rifle makes things a lot easier on a barricade or funky position.

 

[jbailey]

I ran JBM's "Danger Space" calculation for a 6mm 105gr Berger Hybrid at 3050fps vs a 6.5mm 140gr Berger Hybrid at 2900fps (both these are common loads), and the 105gr had a ~2yd wider "Danger Space" out to the 1000yds that the app solved for. So I'm not sure on your claim that a 6.5mm has a wider "Danger Space" than a 6mm.

I would recommend you find a 15+lb 6mm to shot from a non-prone position. You will immediately understand why guys love them. Feels like a BB gun.

 

[RAWHDE]

I ran JBM's "Danger Space" calculation for a 6mm 105gr Berger Hybrid at 3050fps vs a 6.5mm 140gr Berger Hybrid at 2900fps (both these are common loads), and the 105gr had a ~2yd wider "Danger Space" out to the 1000yds that the app solved for. So I'm not sure on your claim that a 6.5mm has a wider "Danger Space" than a 6mm.

I would recommend you find a 15+lb 6mm to shot from a non-prone position. You will immediately understand why guys love them. Feels like a BB gun.

Okay, thanks for double-checking my work. I certainly don’t want to mislead anyone. I used the formula that Litz gave in AB book (zeroed at each 100 yd mark, set max range for 100 yds past zero and calculated using 1yd increments). Based it on a 10” target and looked at 5” drop in front of and behind zero. Where did I mess up? This was my first time doing this.
Note: I used 2960 fps for 108gr and 2710 fps for 140gr - what I found on Hornady site. I think that was with a 24” barrel.

 

[jbailey]

I don't know where you messed up as that method sounds correct and is similar (the same?) as the JBM Ballistics app. If you want to try the JBM app, here it is:

JBM - Calculations - Trajectory

www.jbmballistics.com

Just make sure you check the box "Include Danger Space" on the bottom.

 

[1moaoff]

why does it matter for competition what the "DS" is? I'm asking in all honestly because I can't figure out a reason to really consider it as a comparison for caliber choice?

 

[RAWHDE]

I don't know where you messed up as that method sounds correct and is similar (the same?) as the JBM Ballistics app. If you want to try the JBM app, here it is:

JBM - Calculations - Trajectory

www.jbmballistics.com

Just make sure you check the box "Include Danger Space" on the bottom.

Okay, thx. I will check it out. I used the Ballistics AE App.

 

[RAWHDE]

Okay, thx. I will check it out. I used the Ballistics AE App.

So I just ran them in JBM using same as I did in Ballistics AE (Hornady 108gr vs 140gr ELDM) and you are correct, 6mm better out to 1000yds. Sorry for any confusion

 

[Romeo458]

Can someone explain this danger space for us less educated in terms.

 

[PAYDIRT]

Caffeine, hangover, wild night, lack of sleep, poor fundamentals, etc is the biggest "danger space" no cartridge will makeup for wobble during positional shooting. The meat and tatters are 400-700 and almost everything out there is fully capable at that distance.

 

[jbailey]

Can someone explain this danger space for us less educated in terms.

one way to think about it is how exact do you need to be with your range estimation. It basically says how much error you can have in the range and still hit a target of a certain size. Typically 10" is used as the target height. You want this range to be longer. For example, a target can be 400 to 425 yds away (25 yds of "danger space") and the bullet will still hit it with one ballistic combination. Another ballistic combination could have a 405 to 420 yds range (15 yds of "danger space") and still 'hit'. Obviously, the first combo is superior.

You can solve for this long-hand, or you can use a ballistic app (like JBM above) that includes the calculation. It really isn't used very much, so don't hurt your brain over it. Generally and broadly, you want the fastest bullet that retains the most velocity - that combo is nearly always superior, whether it is wind deflection or "danger space".

But don't forget recoil. A 120mm smoothbore generally and broadly outperforms a rifled 6mm or 6.5mm but the recoil is a tad different. And as stated above, the recoil on a 6mm is the real reason why many shooters love them.

 

[RAWHDE]

Can someone explain this danger space for us less educated in terms.

I’ve added a picture below from Applied Ballistics to hopefully give you a better understanding. For the particular bullet being profiled, the trajectory “occupies the height of the target from 579 yards to 620 yards. This means that the 10” target is in the danger space of the trajectory for 41 yards (from 579 to 620 yards). Naturally, longer danger spaces increase the likelihood of a hit on the target.”

Basically, flatter flying rounds (better BC) will have larger danger spaces. However, depending on how far you are shooting and the rounds you are comparing, there is a crossover point. If you are comparing a lighter and heavier round, the lighter round with greater muzzle velocity will have a larger danger space but only to a point. That point being where the heavier round maintains it’s velocity longer and becomes more likely to hit the target after a specific distance. What that distance is makes a big difference when you are weighing in other factors, as was mentioned, like recoil, tracking shots, quick target re-engagement and the distance(s) at which you are shooting your greatest percentage of shots. Barrel life may be another factor but I’m not sure how much it applies here as I am not as familiar with differences between 6mm and 6.5mm.

 

[RAWHDE]

It’s recoil...easier to spot and see trace and thats what counts

the wind drift is basically a wash inside 800 where matches are won/lost

ranges are given and we have accurate range finders so up/down is rarely a problem among guys at the top

Morgan, do you ever see matches/stages with unknown distances?

 

[morganlamprecht]

Morgan, do you ever see matches/stages with unknown distances?

for 2 day prs/nrl, rarely...shooting 4-5 matches a year since 2016, i can only think of 1 for sure, maybe 2...where rangefinders were not allowed...they gave you 1 distance marker, with multiple targets closer and further away

there are other types of matches that are all unknown distance "in the matchbook", but you can range them before the stage starts...and other matches where you have to locate, range, engage all on time, but doesnt happen often in NRL/PRS

at new ranges/matches ive never shot, i verify all the target ranges myself before the stage anyways cause ive seen plenty of errors/typos over the years

if there is a all unknown, no range finder allowed match out there, i havent heard of it...im sure there is a smaller one somewhere tho

 

[jbailey]

Allegheny Sniper Challenge in WV used to have lots of UKD stages, if not most, but that was many moons ago in the days when 308 was the most common cartridge and a 6.5 Rem was a "hot" item. It was very hard, especially with a 175gr SMK doing 2600fps at muzzle. Moreover, the reticles we used were simple mil-dots or TMR, not the fancy reticles today with 0.1 and 0.2 mil marks everywhere. Back then, we certainly thought a lot about "danger space" as our "error budget" in our milling work.

There was also a match up in Lewistown PA, run by a guy Freddie W., which was UKD, or mostly UKD. I remember Team Blaster doing well in those events. That event was not as hard to range because Lewistown is a "square range" with berms at the 100yd lines out to 1000yds (ish). And in those days, most guys didn't own LRFs.

Now with LRFs everywhere, much faster/higher BC bullets, milling targets for their ranges is a lost art, and with it, worries about "Danger Space."

 

[RAWHDE]

Now with LRFs everywhere, much faster/higher BC bullets, milling targets for their ranges is a lost art, and with it, worries about "Danger Space."

Seems like it. I think it would be a lot more fun, even if only a couple stages every match, to test those skills/knowledge. But I’m old so...

 

[ZY100]

NH PRS match last month had a 21 round stage, all UKD, from about 175 to maybe 550. Combination of target sizes (33 and 66 IPSC i think), two minutes, no pre ranging.

Bit of a barrel burner....WAG’d with 300 yard dope and favored high/low on aim-point based on range estimates. 15 of 18 rounds fired...couldn't find a few targets in time. One was the close one!

Fun stage but a lot of points for a single stage that could go very well or very bad based on visual range estimation. Certainly a rifleman's skill....but bold move for a match.

ZY