180gn 7mm = 30 cal??

[Tim N]

Hi All
Just curious as to the equivalent of 7mm 180 BER @ 2850f/s in 30 cal?
215 or 230 BER
If someone could show the formula too
Thanks

[Tim L]

For a quick look id go with Energy = mass x velocity x velocity Use si units to give you the muzzle energy in joules.
Multiply that by the bullet bc on the 7 mm then transpose the formula to find the necessary velocity for the 308 bullets.
There's probably a more accurate formula but this is relatively simple.
Alternatively punch the 7mm figures into applied ballistics at 1000 yds then match the drop with the 308.

[AlanF]

Tim N,

You need to define the question further. Are you looking for the 30 cal Berger with the closest wind deflection from the same muzzle velocity as the 7mm 180 VLD? Or maybe its from the same muzzle energy? Or is it just the closest in terms of sectional density? All of those can be calculated, but I'd prefer to do just one .

Alan

[williada]

Done late, hope I didn't stuff up. Just a general comparison.

[Tim N]

Hi All,
Thanks for the replys,
If i read your first chart correctly showing wind drift, it says a 30 cal 215gn @ 2600 f/s will drift 3'' more at 1000yd than a 7mm 180 @ 2850 f/s??
So if it was pushed a little faster it would be equal.... can you work out how much?
Next question would be is there much increase in recoil from the 7mm 180 to 30 cal in a 10 kg rifle at these velocity's?
AND would there be an increase in expected barrel life if used at these velocity's?
Alan it was wind deflection I wanted, unless the other things you mention have an influence as well for the above.
Just "kicking tyres" at the moment.

[AlanF]

Tim,

The first table shows what velocities (and more importantly muzzle energies) you need to get equivalent wind deflection with the 30 cal projectiles (to the 7mm 180 VLD at 2850fps). As you can see the 230gn requires less ME than the 215gn, but is still significantly more than the 7mm.

The second table shows what deflection can be achieved with a ME of 3500 ft-lb, which may become the practical limit in future. It shows that virtually any 7mm target projectile will outperform the Berger 30 Cal VLDs in terms of deflection for a given ME. I often use 168VLDs and 175SMKs, and as you can see they outperform the 30 cals by this measure. The best on paper is the 7mm hybrid, but I have my doubts about its published BC advantage over the VLD. In ladder testing prior to the FCWC 2013, I interlaced the Berger VLDs and hybrids, and in terms of powder charge vs bullet drop the hybrid was only slightly better.

Regarding recoil, you can get a reasonable idea from ME, but powder charge has a significant effect as well. As for barrel life, they say the 300 WSM is good, but you'd have to ask someone who's been using one for a long time.

[Tim N]

Hi Alan,
You have given the parameters I need.
The 7mm still looks best.

[Norm]

Alan has nailed it.
When limited to 3500 ft'lbs energy limit the 7mm has it over the .30 cal pills.
The other problem with the .30 cal pills is the bullet drop. Its larger and you ES will result in more vertical grouping with the .30 cal.

However if you forget about the ME limit and run a big .30 cal at a velocity where it has similar bullet drop to a 7mm pill. Then the .30 cal bullet will show a significant reduction in wind drift over the 7mm bullet. Recoil will be larger however.

My pet .300 NSM is shooting 230gn Berger Hybrids at 2960 fps with 85gn AR2225 and I find it a lot of fun to shoot. Recoil in a 10kg rifle is ok but I would only bring it out to play on days when the conditions were suitable and on a range where it was permitted.

[williada]

Good work Alan and Norm. The previous graphs only showed common loads that people tend to use for accuracy, not so much the big bangers and didn't answer Tim's question as I felt others showed how. Norm made a good point about the energy restrictions. There may be a radial advantage of the 30 cal where terrain is a factor in compressing atmosphere over mounds etc discussed in a post way back compared to a VLD in certain conditions in that it is less inclined to move off a line and not quickly re-orient itself to wind flow like a VLD. The drop factor can be limited or enhanced by the type of tune. These factors tend to be trade offs.

Below are the graphs based on Alan's calculations which were the basis of your question Tim.

[williada]

Perhaps some FTR boys could give us some pet loads for 30 cal so the comparisons are better based on accuracy rather than a perceived speed and energy. Anyway I have put some more plots in, one set showing the performance based on energy limits and the other set showing a perceived accurate group with the 180 grn and the limit imposed for 215 and 230 grn .30 cals.

[Norm]

Interesting charts Dave.
I wonder what they would look like with the 230gn Hybrid at 2960fps...

[williada]

[AlanF]

Dave,

Could you add some sort of graph showing the state of Norm's shoulder? And perhaps another which measures the blood pressure of the RO?

Alan.

[Norm]

Dave,

Could you add some sort of graph showing the state of Norm's shoulder? And perhaps another which measures the blood pressure of the RO?

Alan.

I will give you a go at it Alan and you can see how you like the recoil.
I think you will be able to handle it. Especially after you have been working out with that 34" dumbbell.

[williada]

Sadly, I think I will have to part with my 30/378 reamer and dies.

I will be left to the following, of colouring in the picture below with my pencils now I can't shoot anymore.