6mm or 6.5mm

When we discuss practical precision shooting we often get down to 6mm or 6.5mm.  There are some folks shooting in different divisions or folks that just want to shoot 7mm, 30cal, or even some 223.  This is just meant to break down and show the differences in the two that are used the most by those top 100 competitors in the sport.  This doesn’t mean you have to choose what they do or choose for the same reasons they do.  It just means they are good at what they do and it might be worth looking into why they use what they do.
 

Velocity and Projectiles Used for Comparison

I broke these down by using a 6mm pushing a 105 Berger Hybrid and 3050 fps and a 6.5mm pushing a 140 Berger Hybrid at 2750 fps.  If you are safely able to and want to run a load that's faster in your rifle or if you want to check a different projectile, you can of course run different data for your own comparison purposes.

Basic Breakdown

Generally, we think of the 6mm as having a little less recoil and the 6.5mm as having a little better barrel life.  There is also the difference in energy on the longer shots.  So, the 6mm will be a little easier to use on barricades, but the 6.5mm will show impacts a little easier at those longer distances that we shoot.  Keep in mind that the majority of our shots are 800-900 yards and in and there aren’t as many of those longer shots out at 1200 yards or more.  Also, we are seeing more target flashers on those long distance targets and that will make it easier for ROs to spot impacts and that may push even more shooters to the 6mm side.  There are some cases that do a little better or worse for each caliber as far as velocity and barrel life.  The case and the pressure you load to will have something to do with how fast you shoot your barrel out; along with a few other things like how hard you push your rifle during a match or practice.  This is meant to be a generalized statement to explain why some folks choose 6mm and others want 6.5mm.  Also, keep in mind that when we discuss practical precision and recoil, we aren't referring to a recoil that hurts you or makes it unbearable to shoot.  Recoil, in this discussion, is meant as being easy to spot your own shots (or not), even when you are in a less than ideal shooting position.  Most shooters find it critical to be able to spot their own shots to make fast corrections.

Data Comparison

The data comparison was made using Applied Ballistics Analytics.  The custom curve was used for each of the projectiles.  The second page of data shows a hit percentage with variables introduced.  This is at 1000 yards (actually 999.563 yards).  The left hand side will show the variables that were used to get the data output.  

6mm Data

6.5mm Data

What does it mean?

First, you can look through the data for yourself and decide what it means to you.  Some of the things I notice are that the windage is very similar between the two.  Most of us consider the wind to be one of the harder factors to overcome.  Keep in mind the generalized differences that were listed above under 'Basic Breakdown'.  Often we say that the elevation isn't as important since we are able to so accurately predict that part of the equation.  There are times where the lesser drop of the 6mm is helpful.  Basically, it is more forgiving to any mistake we make or if any part of our data is off, such as distance to target.   

Another Comparison

For this blog entry I ran one more chart to compare.  Currently, I am shooting a 6.5mm that pushes a 140 Berger Hybrid at 2787 fps.  This barrel is at about 2200 rounds and hasn't shown any loss in velocity so far.  I have considered going to a 6.5 SAUM for my next barrel, but loading it 'slow' to attempt to get as good of barrel life as possible.  For this, I ran the 6.5 mm 140gr Berger Hybrid at 2950 fps.  There are folks running the 6.5 SAUM for practical precision, but I don't see it used nearly as often as the popular 6mm and 6.5mm cartridges.  I believe it would be a little more difficult to spot my own shots using this, as compared to my current choice.  

6.5mm 140gr Hybrid @ 2950 fps

When you compare the 6.5mm 140 Berger Hybrid at 2950 fps to the 6mm 105 Berger Hybrid at 3050 you see that they are very similar in both elevation and windage, with the 6.5mm carrying more energy.  This idea is appealing to me.  I'm not sure yet that I will give it a try, but the appeal is there especially if the barrel would have decent life.  

Conclusion

When you compare these things you can see why it's difficult for some folks to choose one over the other. Many shooters have a few match rifles. One person may set up a trainer in 223 that's set up similar to their match rifle. Another person may have a 6.5 SAUM for windy days or matches that concentrate more on the longer range side of things. Hopefully this data will help some folks that are looking for the basic differences between the 6mm and 6.5mm choice for practical precision.


There will be more blog entries in the future covering more long range topics. Thanks for reading and feel free to share this or my other blog entries if you think it will help someone.