medium range shooting

[rsc1960]

ok lads,

 

been asked this question on a few occasions but I can't answer it,

 

what would work best for a max range of 600 yards.

 

1 bullet velocity over bullet weight for stability.

 

2 bullet weight for stability over bullet velocity.

 

the 2 rifles are a 6mmbr 252 barrel with a 1/9 the next is a semi custom 243 with a 1/8 25" barrel.

 

bullets used would be, 115 detac in the br and the 70gr noslers in the 243. ?

 

your thoughts

 

cheers

 

RSC

[gbal]

I'm not quite sure what you mean by 'stability'-neither combination mentioned is likely to even approach transonic issues at 600y. Given the barrel has a suitable for bullet weight twist,let's have a basic look.

 

The best guide is the very familiar BC (Balistic Coefficient) of the bullet,essentially a measure of how much drag the bullet is subject too-it reduces with velocity,and thus indirectly with weight,and reduced length,to a lesser degree.BC is also a function of bullet design-tangent/secant ogive,Ballistic tip,etc)

 

Detailed technicalities aside,for fairly fast medium bore cartridges like 6BR and 243,(even more so for the very fast small bores-20,224 etc),then performance (less bullet drop,and less bullet driftin wind) comes from velocity in the first 300 yards or so (approximately),but thereafter BC is 'THE" factor,andd increasingly the better BC bullet will be superior in drop/drift terms.

Of course,within strict limits,velocity can be increased,but then again,there are some bullets with higher BC,though neither of these main factors are unlimited !

"accuracy'-"hit probability" is a better term-tends to be helped by reduced drift,as there is less wind judging error,the serious limiter to longer range performance,given ranging lasers. "terminal effect" is more a function of retained energy-heavier bullet favoured-and bullet construction matched to quarry.

And '"accuracy" can be subject to an individual rifles preferencesin bullets-can only try and see.

 

So,at any distance,velocity at a safe level,which also gives near maximum accuracy,AND as high a bullet BC as is available for yur purpose,are the recipe. As distance increases,beyond about 300 yards, then the BC is the more important bullet characteristic.

 

A look at any detailed cartridge performance guide shows all this fairly clearly-velocity cannot compensate for poor BC,as velocity begins to drop off.BC of coursedoes notmean a magic bullet,just a bettter one.

Some of the hot varmint bullets shows this -eg the lovely little 17 rem-very fast-has a dismal BC very light bullets,and struggles beyond 300y. Slow twist 224s likewise-they cannot 'stabilise' the heavier better BC bullets that fast twist barrels can,so have similary reduced effective range in comparson. N0 224 is really a 1000y number( yes I know) but a slow twist 55 g one is a non starter-well it starts ok,it's more a non-finisher for serious use.

 

You did say 600y. Further is essentially the same,max safe velocity and especially max BC bullets-there's a reason Berger's do well.

For 300 max sort of distances,preferably less,IF something of a 'point and shoot'-is wanted,better described as 'no vertical/horiz (wind) adjustment; (or minilmal hold over),then velocity may suffice-you don't need an 80g 224 bullet to hit a fox 150y away,indeed there are better lighter bullets for that.

 

The 243 has been 'held back' by the non availability of fast twist factory rifles,and limited very high BC bullets (Dtac are fine).That is changing.But there isn't always the ideal bullet etc actually available-despite what seems a huge choice,when all the desired features get factored in.6BR has a better bullet choice,but limited factory rifle options.

 

OK,I think that's the basics for a reply.

 

"Velocity is for Xmas,BC is for life" ....if you're a bullet :-)

 

gbal

[rsc1960]

Thank you so much,

 

Better bc for me too,not just for Xmas

 

Regards and thank you for your time and your response

 

RSC

[Laurie]

If I read you correctly, you plan 115gn DTACs in a 6BR with a 1 in 9 twist barrel for 600 yards targets. You'll hit a barn door (maybe!) at 100 yards and nothing you aim at 600 except by sheer fluke. A 9-inch twist rate simply doesn't stabilise this bullet. 1 in 7.5" is usually recommended, 1 in 7.8" is optimum and 1 in 8.7" is the theoretical slowest twist rate, but would likely prove unsatisfactory particularly at 6BR velocities.

 

If you've transposed the two cartridges / barrels and the bullets in your initial post, the reverse transposition is fine assuming that the 243 is 'throated' for the long DTAC projectile. The 243 also has the boiler room capacity to give the 115gn a worthwhile MV too.

 

Assuming this is a theoretical 'which is better' type question, there is no comparison between the pair in terms of external ballistics for 600 yard shooting except in trajectory where they are pretty similar.

 

Assuming shortish barrel sporting rifles giving a 70gn Nosler Ballistic Tip 3,200 fps in the BR and the 115 DTAC 2,700 fps in a 243, they both need around 14-MOA elevation on the sights over a 100 yard zero - 87 inches for the DTAC and 88 for the Ballistic Tip and MRT levels are close at 30-33 inches. (At short distances, the lighter bullet would have a marginally flatter trajectory than the DTAC.)

 

In every other external ballistics measure, the DTAC wins by a huge margin. 1,838 fps retained velocity at 600 compared to 1,444 fps for the 70 despite starting out 500 fps slower at the muzzle; 13.1 inches windage in a 10 mph 90-deg crosswind against 24.6".