Index for Cartridges for Long-Range Competition

[sparker]

I have put together a potentially useful formula for selecting a cartridge for prone rifles.

It is the bullets drift in minutes at 1K yds x muzzzle energy / velocity at 1K. Using the results from multiple cartridge/bullet combinations allows one to use a single value to select a cartridge/bullet combo. Lower values are favorable.

Some combos and their values:

6.5 x 47 L (130hyb.) =10.8
6BR (105hyb) =10.1
308 (155sie)=20.6
308 (185 hyb) =17.3
.223 (90vld) =8
22BR (90vld) =7.4
284 (183 sie) =10.6

Scott Parker
Bakersfield CA

 

[Cool Tool]

I have put together a potentially useful formula for selecting a cartridge for prone rifles.

It is the bullets drift in minutes at 1K yds x muzzzle energy / velocity at 1K. Using the results from multiple cartridge/bullet combinations allows one to use a single value to select a cartridge/bullet combo. Lower values are favorable.

Some combos and their values:

6.5 x 47 L (130hyb.) =10.8
6BR (105hyb) =10.1
308 (155sie)=20.6
308 (185 hyb) =17.3
.223 (90vld) =8
22BR (90vld) =7.4
284 (183 sie) =10.6

Scott Parker
Bakersfield CA

You have to shoot the wind regardless of what you choose that's on you whatever you choose.

 

[skiutah02]

That settles it then, I'm shooting my 90vlds at LR Nationals instead of my 185s.

 

[Ned Ludd]

That settles it then, I'm shooting my 90vlds at LR Nationals instead of my 185s.

I've been sayin' it all along....

 

[spclark]

Then why the heck don't we see more 22BR'S & 223's at matches I been shooting?

 

[sparker]

Then why the heck don't we see more 22BR'S & 223's at matches I been shooting?

Bob Gill likes the .223 with 90s

 

[sparker]

Ho

Then why the heck don't we see more 22BR'S & 223's at matches I been shooting?

How many 22BRs have you actually seen?

 

[sparker]

That settles it then, I'm shooting my 90vlds at LR Nationals instead of my 185s.

Considering that the LR Nationals have been won with 6mm, 6.5mm, 7mm and of course, .30 cal in all manner of cases, including Palma rifles, there are many options available which would be competitive. The index allows for one to gage what I call drift efficiency: reducing drift while minimizing the energy applied.

In the case of the .308 with 185s vs the .284 with 183s, the bullets are nearly identical in mass and the muzzle energies quite close as well. However, their respective index values are quite a bit different. This is due in great part to the efficiency difference between the two bullets. If given the choice, I'd rather shoot the .284. That said, either cartridge would be competitive.

While the 22BR has a quite low index value, the .223 is quite close to it, cheaper to load for and brass is omnipresent. That said, a 22BR with 90s could be a tough cartridge to beat.

There isn't enough difference between the 6BR with 105s and the 6.5x47 with 130s to choose one over the other. Economics and other considerations would come into play.

 

[Keith Glasscock]

Ok I'm confused.

Does the muzzle energy in the equation relate to the shoot ability of the cartridge or the monetary efficiency?

I understand the use of the 1k wind drift, but what purpose is there in the 1k velocity? I understand the need to be supersonic, but velocity in excess of that seems to make little difference.

 

[Scott Harris]

I thought April fools day was in April??? oh wait, it's prone rifles...

 

[Clavius-Walker]

How's the 17hm2 fare in that, was going to try it in f-class

 

[sparker]

Ok I'm confused.

Does the muzzle energy in the equation relate to the shoot ability of the cartridge or the monetary efficiency?

I understand the use of the 1k wind drift, but what purpose is there in the 1k velocity? I understand the need to be supersonic, but velocity in excess of that seems to make little difference.

Well Keith, the retained velocity at 1000yds goes to the efficiency of the bullet. Of course one can decrease drift by applying velocity(energy). That may not be very comfortable to shoot however. In this formula, lower energies and high ballistic efficiencies are indicated by a lower quotient value.

The main interest in achieving minimal drift with less energy goes to recoil. The attempt here with the formula is to allow shooters to evaluate cartridge /bullet combinations through a lens that includes recoil. All of the above listed combos are competitive at 1K. Not all are equally pleasant to shoot. I dont think it matters if you drop a point due to wind or drop a point due to failure to follow through. A point lost is a point lost. However, if shooting a more pleasant cartridge allows you greater focus, it might just save you that point that would otherwise be lost to the wind.

Again, the index is useful in that it magnifies differences in energies and efficiencies while allowing the shooter to look at different calibers among several that would be quite serviceable in competition. I hope this has clarified things a bit.

Scott Parker

 

[sparker]

I thought April fools day was in April??? oh wait, it's prone rifles...

Please try reading the original post in its entirety and follow up commentary.

 

[sparker]

How's the 17hm2 fare in that, was going to try it in f-class

Please try reading the original post in its entirety and follow up commentary.

 

[Keith Glasscock]

Thanks Scott,

That makes sense.

 

[spclark]

Scott I see a pattern in your numbers.

Maybe there's a practical threshhold of 10, below which there are difficult to control variables that preclude reliable performance?

That the 22BR exhibits such an attractive number yet is rarely present (I've never seen one used) due to factors that make other choices more practical? I've seen 6BR's shot at 1K yet seldom end up near the top unless conditions are benign.

 

[dennisinaz]

Yeh, that list doesn't help much with real world realities. Not sure why I would give some much credit to lack of energy.

 

[Steve Blair]

Bob Gill likes the .223 with 90s

Yes, Bob likes them for a good reason; they win for him. Greg Taylor also won the California F-TR Long Range with a .223/90, and Nebraska and Missouri State F-TR MR. It seems a competitive combination among multiple shooters and states.

 

[sparker]

Yeh, that list doesn't help much with real world realities. Not sure why I would give some much credit to lack of energy.

Again, this is not the the index for your tacticool/dress up like a sniper on Saturday shoot. It is for prone shooting, conventional NRA Long-Range. If that is not the shooting you do, the index doesn't directly apply. However, it wouldn't take rocket science to figure out how to use the index in another discipline/application involving long range shooting.

 

[sparker]

Scott I see a pattern in your numbers.

Maybe there's a practical threshhold of 10, below which there are difficult to control variables that preclude reliable performance?

That the 22BR exhibits such an attractive number yet is rarely present (I've never seen one used) due to factors that make other choices more practical? I've seen 6BR's shot at 1K yet seldom end up near the top unless conditions are benign.

I think you really need a difference of 2 or more to choose one cartridge as superior over the other. The .308 with 185s is clearly the better choice over the .308 with 155s. Having shot both from position, the recoil feels the same. The 185s do allow for more wind error. The difference is 3.3 in index values.

I need to work out more values to see if that 10ish value holds as a threshold. I did notice it as you did.

Scott