Compare BC values between .223 and .308

[ego235]

I've heard many people say that upto a certain distance the trajectory between a .223 round and .308 are similar. That distance of course depends on muzzle velocity and BC value of the bullet. However generally the .223 starts out faster but loses speed due to a lower BC and that is why the .308 catches up.

Some heavier .233 bullets have decent BC, 80 grain Berger VLD (.445). Compared to a lighter .308 bullet of almost identical BC, for example 155 grain Nosler HPBT (.450) or 55 grain A-MAX (.435), if you shot these at the SAME velocity around 2,700fps, would there be almost no difference in trajectory and be impacted by wind in nearly the same way between the .223 and .308 bullets?

I currently have a Remington 700 5R in .223. I only shoot upto 385m now but will be moving next year and get access to longer ranges of 600 and possibly 1000 yards. My rifle has a 1:9 twist and shoots .69 grain SMKs very well. I only buy factory ammo currently but am thinking of either rebarreling (cheaper option) to 1:8 or 1:7.7 and start reloading my own heavier 80 grainers or buy a new gun entirely in either .308 or 6.5 CM.

So...if the 80 grain bullets will perform as well as the lighter .308s I might just decide to stick with my 5R. Altho I understand the .308 also has a nice assortment of heavier bullets made for long distance with BC values the .223 cannot match.

 

[SporterII]

I too have a 5r and shoot the 69. It does very well and can tell you re barreling your now very well shooting rifle will ruin what you have and not get you where you want to go.
Time for a second rifle.

 

[DocB]

ego,

69 gr. SMK works out to 800 well with a 1/9 twist. If you want to go to 1k, use 80 gr. bullets 1/8 minimum twist. You should look for a minimum of 2900 and faster would be better.

HTH,
DocB

 

[ego235]

Thanks guys, the information is very helpful. I think I will stick with my 5R and not change out the barrel. At the moment it only has about 1,200 rounds fired so it has plenty of life left.

So how about the other part of my question? Will two projectiles regardless of caliber and bullet weight, if they have the same BC and muzzle velocity, will they perform exactly the same in terms of drop and impact from wind? Like if they can theoretically design a .17 caliber to match a .338 to have the same BC...will they fly the same?

 

[BC 6.8]

Thanks guys, the information is very helpful. I think I will stick with my 5R and not change out the barrel. At the moment it only has about 1,200 rounds fired so it has plenty of life left.

So how about the other part of my question? Will two projectiles regardless of caliber and bullet weight, if they have the same BC and muzzle velocity, will they perform exactly the same in terms of drop and impact from wind? Like if they can theoretically design a .17 caliber to match a .338 to have the same BC...will they fly the same?

According to the ballistics calculators, if a bullet has the same initial velocity and the same BC then they will have the same flight path. I used JBM ballistics calculator and compared the .224 Sierra 80 gr and the .308 Sierra 155 gr Palma (2155) bullets. If you launch both bullets at 2900 fps the drop is within 0.5" at 600 yds and within 4.5" at 1000 yds and windage is about 0.6" different at 600 yds and 2.6" different at 1000 yds with a 10 mph crosswind. So the flight path would be within 1 click on a 1/4 MOA scope at 600 yds and 2 clicks at 1000.

 

[holdoff]

Ballistics charts are math in a graph.

When observed in the wild, heavier bullets always seem to work better. In calm mornings, .223 Rem works wonderful, until just that bit of wind starts up, then the .308 of similar BC seems to be a little more foregiving.

And most of us would be lucky to say we just have to contend with a cross wind. The heavier bullets best the lighter ones when shooting through winds that change directions once or more before arrival to the target.

German Salazar did some great testing of this comparing .308 projectiles. Check his site: The rifleman's journal.

Sent from my 6.5 Creedmoor @ 2750 f.p.s.

 

[ego235]

This is the part which is somewhat confusing. I agree with the math, and it shows this on my ballistics calculator as well, that same BC and muzzle velocity should mean equal flight path regardless of caliber or weight. But I do hear people argue holdoff's point as well, that in practice, more seem to choose heavier bullet, in this case, 155 gr Palma .308 bullets over the 80 gr Sierra .224 bullets.

If theoretically there should be no difference, why would they prefer the heavier bullet? Wouldn't it just cost more (ie. materials), be less comfortable to shoot due to increased recoil and cause the barrel to heat up faster?

One reason I think which I've read from some reloaders is that sometimes published BC figures aren't always accurate. Hornady being one of those companies ie. the heavier 75 grain BTHP (.395) and A-MAX (.435) was an example they gave. I can see how that would support holdoff's point that if the .224 rounds figures were exaggerated, then the equivalent BC .308 round on paper may indeed perform better. Is this a valid point?

Hornady Manufacturing Company :: Bullets :: Rifle :: Choose by Caliber :: .224 22 CAL :: 22 Cal .224 75 gr A-MAX®
Hornady Manufacturing Company :: Bullets :: Rifle :: Choose by Caliber :: .224 22 CAL :: 22 Cal .224 75 gr BTHP

Below is a post which somewhat touches on the questions I raised, but did not go much into detail.
http://www.snipershide.com/shooting...16397-75gr-224-vs168gr-308-out-700-yards.html

 

[SporterII]

I offer 75 amax at 2870, 35 min. to a 12" plate at 1000. 95 degrees, sea level.
Two days ago. 100 yd zero, 35 min by Night force. 32.7 by Hornady ballistic comp.
My chrono, their bc., or the calc?

 

[damoncali]

If theoretically there should be no difference, why would they prefer the heavier bullet? Wouldn't it just cost more (ie. materials), be less comfortable to shoot due to increased recoil and cause the barrel to heat up faster? [/url]

Weight is built into the BC already. If two bullets truly have the same BC, the lighter one is preferable. It will be faster (assuming same case) and deflect less in the wind. That rarely happens. People like heavy bullets because they tend to have high BC's. This is why you get arguments about the 6mm 107SMK's and the 115 DTAC's (which are basically just long 107's). You get a little BC, but you lose velocity with the 115's. So it depends on what wins in the particular rifle being used. Throw in that people don't always believe BC's (the DTAC's were somewhat famously overstated for example, manufacturers don't use the same standards, and the cynical might say that there is an incentive to inflate them), and you get differing opinions. But you're right - BC and velocity are all that matter.

 

[damoncali]

If theoretically there should be no difference, why would they prefer the heavier bullet? Wouldn't it just cost more (ie. materials), be less comfortable to shoot due to increased recoil and cause the barrel to heat up faster? [/url]

Weight is built into the BC already. If two bullets truly have the same BC, the lighter one is preferable. It will be faster (assuming same case) and deflect less in the wind. That rarely happens. People like heavy bullets because they tend to have high BC's. This is why you get arguments about the 6mm 107SMK's and the 115 DTAC's (which are basically just long 107's). You get a little BC, but you lose velocity with the 115's. So it depends on what wins in the particular rifle being used. Throw in that people don't always believe BC's (the DTAC's were somewhat famously overstated for example, manufacturers don't use the same standards, and the cynical might say that there is an incentive to inflate them), and you get differing opinions. But you're right - BC and velocity are all that matter.

 

[scotharr]

My experience is that the 223REM competes as an equal to the 308WIN out to 800 yards or so. This is with a 30" barrel shooting 80 gr A-Maxes at close to 3000fps. At 1K my 223REM falls apart and the 308WIN does notifceably better. 800 yards and in though: the 223REM is awesome.

However, a 1:9 twist is not going to handle any 80 grain bullet well: a 1:7.7 is ideal in my book.

 

[ego235]

That is the twist I was thinking of getting, but 30" is kind of unwieldy...how much velocity lost going with something like 24"? Will that still be okay at 800?

It is good to know about the BC being the equaling factor given muzzle velocity is the same. The purpose of this post was obviously not to say that .223 is as good as .308 at long range. Only that I wanted to see if heavier .223 bullets could match lighter and mid weight .308s to a certain distance and it seems like that is possible.

I've been shooting for a while and have been looking forward to getting into reloading in the near future. When I move next year I'll have the room and longer distances at the range to try things out. I will finish up my remaining few hundred 69 SMKs and then perhaps getting a new heavier profile barrel with faster 7.7 twist. I enjoy shooting my heavier .223 rifle (16+ lbs) as it allows me to see my bullet trace and not lose sight picture, similar to a rimfire. I've shot a couple .308s and was not able to see the bullet land which was a little bit of a bummer.

 

[BoilerUP]

I have a 22" 223AI and run 80gr A-Max @ 2890fps.

At 1000yd, a 30cal 175gr Matchking @ 2675fps matches it in the wind but the 223AI is still 26.7" flatter.

 

[holdoff]

Hi again,

I found the article I had read in the distant past, link below. While it is a comparison of .30 cal bullets, it does substantiate the point that heavier is better. Again, as others have mentioned, the .223 with a 80gr bullet at > 2900fps barely keeps up with a 175 SMK with a initial MV of around 250 fps less.

The bottom line is that we do our shooting in the real world, and ballistics tables are fun to play with, BUT at days end we have to consider what sacrifices we are willing to make in favor of the lighter bullet. Heavier bullets make it easier in the wind, which is the real environmental that makes us miss the most.


The Rifleman's Journal: Ballistics - Heavy Bullets