bullet caliber, weight and long range performance

[Hamo]

It seems that the general idea for long range performance is to get a heavy projectile in a small caliber, giving a really good ballistic coefficient. A lot of wildcats neck down cartridges for extra fps, or neck up for a heavier projectile for stability.

for example, the 6.5*47 lapua has a small caliber, but heavy projectile and gets great long range performance,

roedale precision neck up the .338 lapua to 9.3 mm and claim .408 cheytac ballistics, accuraccy at over 2000m !! an argument for larger caliber projectiles

Whats your opinion on the best long range combination. (just to clarify, by long range, i mean the longest each cartridge is capable of, eg. a .308 based cartridge for say 800 - 1000 m, 338 lapua for 1500 m etc.)

 

[Steve Blair]

Loaded to equal pressures, the highest BC, practical bullet will provide the best wind-resisting performance. Even a .30 BR can drive a Berger 210 over 2400 from a 30" barrel. That bullet will outperform any lower BC bullet loaded to equal pressure in that cartridge.

If tactical or hunting use is a consideration, lighter bullets with flatter trajectory within a specific range of interest may be a better choice, reducing range estimation error effects.

Like solving engineering problems, it depends upon the requirements. Different requirements produce different solutions.

 

[Terry]

If the 600 and 1000 yard Benchrest matches are any indication the answer includes 6 BR, 6 Dasher (BR Improved), 6.5 X 47 Lapua, 6.5 X 284.

Terry

 

[RonAKA]

It is kind of a complicated subject, but can be simplified somewhat for normal ceterfire rifles in civilian use. Pressure is limited to about 60,000, so that does not change from cartridge to cartridge. But as bore size goes up, you get more push for the same pressure. The amount of recoil a person holding a gun is willing to take (or not suffer accuracy loss from) is somewhat fixed. The wind drift and thus long range accuracy is highly dependent on the ballistic coefficient of the bullet. Within a bore size the longer and heavier/denser the bullet the higher the BC. But, the longer and heavier it gets the harder it is to keep the bullet stable, and requires more and more spin. At some point the bullet blows up from the spin.

With this in mind you will find that within a bore size BC is going to be optimized somewhere around 0.6-0.65, and still have a bullet that can be stabilized. As the bore size goes up with with fixed optimum BC, the bullet weight goes up, and the recoil goes up. The cartridge tends to become more efficient due to the increased push with the same pressure, but at some point the recoil is unacceptable.

So to make a long story short, the optimum will be a bullet with a BC of about 0.625, and a recoil that you can tolerate. My thoughts are that 140 grain 6.5mm and 168 grain 7mm bullets are close to optimum, but if you can take more recoil go bigger in the bore...

 

[Laurie]

I agree with RonAKA's conclusions. There is another factor to bear in mind too re recoil - whether the cartridge and its rifle will be used off the bench or prone, and if the latter whether in F-Class (and whether off a front-rest or bi-pod) or in 'sling-shooting'. The amount of felt recoil and its effects on results varies according to the form of shooting.

This is one reason why the sixes and six-fives still do very well in benchrest at 600 and 1,000yd while the sevens have made major inroads in F-Class, and you still find a few .30 magnums in F. You feel the recoil a lot less and control the rifle better in prone shooting off a rest than off the bench, particularly if you're looking to get benched shots off fast, while the prone shot is marked before you shoot again. Testing .308W loads in a Barnard / Eliseo tubegun off the bench starts to become unpleasant with heavy loads behind 185s, and worse as bullet weight goes up, despite a 18-19lb all-up rifle weight.

I find it easier to get small groups with 155s than 200s. However, shooting the same rifle prone off a rest in F-Class is a real pleasure with heavy bullets. I simply don't notice the recoil and the rifle stays pretty well on target. Move to F/TR shooting off a bi-pod, and the recoil (and torque too) factors start to become a problem again at around 185gn. I don't shoot off the elbows with a sling anymore, but I note that many American Fullbore-Rifle shooters limit bullet weight to 175gn, especially the more senior guys, for this reason.

So, it's not just about internal and external ballistics - other factors come into play too. (It's one reason why we had a few .338 Lapua Mag F-Classers over here in the early days of the discipline, some of whom also tried their hand at 1,000yd BR. A couple of seasons and the rifles had all been sold on despite their being able to 'shoot through' significant wind changes at long-ranges.)

Laurie,
York, England

 

[Steve Blair]

Quite right, but it is worth noting that recoil is not absolute and tolerance varies considerably with shooters. I shoot Berger 210s in F-TR @ 2620 fps and have no recoil problems, either bench or prone. There is a benefit I have noticed other than the great BC of the BT-LR. If my shooting position is not correct, I will get lateral displacement. This has helped me identify my "natural" position and shoot more consistently. When my position is correct, I can see the hits at 300 yards or more.

 

[whiskey08]

Compare the bullets BCs. I dont see anything that currently has a better BC than 7mm/.284. Lots of favorite cartridges out there but the BC doesnt lie. Not sure about the big stuff like the cheytac

 

[Hamo]

I know the cheytac has a bc of around .9 to 1!!! but i think its in a totally different league than 'normal rounds' that can be chambered in common actions.

I never considered recoil to be part of it. I guess for military sniper rounds where they only need to make 1 shot can have the punishing recoil of some of the modern developments like the 338 lapua and the cheytac.

I shoot a .308 about 3 out of 4 weekends (with a steel buttplate) and find the recoil just fine. However, i usually wear a heavy leather shooting jacket with a rubber pad on the shoulder. The few times i have fired it in just a T shirt i have definately known about it, and the difference is incredible. I would not want to be doing that all day.

just looking at what the long range crowd are using, it seems like 6.5 or 7mm is probably one of the ideal balances