[Jeffvn]

Lots of people ask lots of questions about bullets and their BC. A picture is worth a lot of words (sometimes more than 1,000). Here are some pictures I took of the bullets that I have or will be shooting out of my various .308s and my 6.5x284. Sorry some of the images are not the best.

First are the darts that come from the 6.5x284.

In order from left to right
Sierra 142 gr., Sierra 140, JLK 140, 140 AMAX, 139 Lapua & 123 Lapua.

Next we have the.308 155 class - its easy to see why the Lapua kills teh SMK in BC

In order from left to right 142 SMK from 6.5 to show length difference, 155 Lapua, 155 Carteruccio, 155 SMK

the 175 class

In order from right to left 142 SMK from 6.5 to show length difference, then 175 JLK, 175 SMK,

the 190s

In order from left to right 142 SMK from 6.5 to show length difference, then 190 JLK, 190 SMK,

Jeffvn

 

[Jeffvn]

For thoes of you who wonder why teh 6.5x284 KILLS the .308 in long-range shooting look below. The .308 is a M118LR, with 175 SMK standard seating depth. The 6.5 x 284 is a 142 SMK seated fairly short, for magazine loading from my Neseka Tactical ADL - its a dummy round to see if it fits properly into the chamber. The picture makes it pretty clear why - more powder (66 grain capacity for the 6.5x284 versus 56 for the .308) and MUCH higher BC for the 6.5 (.600+ for the 142 SMK versus .495 for the 175 SMK)

JeffVN

 

[Cliffy]

some nice pic's I like the looks of the 6.5-284 and have thought of biulding one some day. Do you have a web sight for the JLK bullets? How much better do the 155 lapua fly over the 155 siera?

 

[Scatch Maroo]

and MUCH higher BC for the 6.5 (.600+ for the 142 SMK versus .495 for the 175 SMK)

What do the numbers .600+, .495 represent? I know the ballistic coefficiency, but is that the same as drag coefficiency? Is the BC higher simply because you can pack more gun powder into it, or because of the shape/design of the bullet itself?

Scatch "Ignore my Ignorance!" Maroo

 

[Jeffvn]

I'm not sure what "drag coefficiency" is, but I suspect its the same concept. BC is a ratio that represents how efficeint a bullet flies, the lower the number the higher the drag. The difference between the 155 SMK (.442) and the 155 Lapua (.508 - actually higher than the 175 SMK) is pretty dramatic at distance, translating into a 4 MOA difference from my Patriot (at roughly 2,850 fps) - the Lapua being flatter and faster - at 1,000 yards.

JeffVN

JLK does not have a website. (He makes them all by hand - JLK are his initials) You can get them through OK Weber and several other specialized sellers. They tend to be on the spendy side like Berger - but they fly like crazy and are heavily relied upon in the 1,000 yard F-Class TR class (.223 and .308 only)

FYI, the 142 SMK is .584
the 140 JLK is .630
the 123 Lapua is .547.

The 175 SMK is .495
the 175 JLK is .545 - equal to the 200 SMK
the 190 JLK is .602 - equal to the 220 SMK

 

[Cliffy]

Looks like I'll beswitching to lapu, now I shoot the 155 siera through my win 70 vssf with great results but if I can better that I'am laughfin. How much differnets you think the bullet drop would be between the to, 155 siera at 2950fps, and could you drive the lapu at the same vel.
Thanks Cliffy

 

[Jeffvn]

probably close to the same difference in drop at 2,950 (which is roughly what you have to drive the 155 SMK to stay supersonice at 1,000). The Lapuas will stay supersonic at 2,850 because of the higher BC. Shooting them out of a 24" tube limits my ability to drive them beyond 2,900 without significant pressure problems.

I've seen several tests on other site of the L155s by 155SMK shooters that showed significant reductions in powder (0.50 grains of Varget less for me) to reach the same pressures and velocity (the Lapua is considerably longer as you can tell in the pitcure, but I can load it out 0.200 further because of the ogive) Where it gets troublesome is if you are magazine loading the Lapua - given its length.

I run em' naked, so if you use molly, everything changes -as you already know.

JeffVN

 

[Cliffy]

I shooten naked to and out of 26' tube, seating them out might still be ok have to check mag length, my siera are 2.80 OAL now, do you know what the mag length is on a winchester?
Cliffy