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  #1  
Old 07-06-2011, 11:33 AM
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Default Choosing Bullet Weights, specifically for long distance shooting

What is the science/reasoning behind choosing one weight over another, specifically for long distance shooting.

178gr SMK in .308 at 2800fps at 1000 yards drops 533 inches.
168gr SMK in .308 at 29002840fps at 1000 yards drops 347 inches.

Chose the one with less drop? Why?

Edit:
500 inches seemed a lot so I went back to my calculator and double checked my figures. I had the BC wrong. I was using .3 when it should be .5. Now the drop is more in line with 330 inches of drop.

Making the choice easy now. I didnt realize BC makes such a difference.

Last edited by joelogic; 07-06-2011 at 10:07 PM..
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Old 07-06-2011, 11:52 AM
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External ballistics... mostly.

Ballistic coefficient and velocity are your keys to the kingdom for the most part. The higher the BC the easier it is for the bullet to slip through the air (lower drag). Drag works at both ends. Velocity is all about covering X amount of ground in X amount of time. You need a bullet that's got a high enough BC to retain enough velocity to carry its butt out to whatever yardage your target is liable to be inside of.

100fps of muzzle velocity isn't usually that big a deal but when the distances get really extreme then it's definitely a factor.

Bullet weight is related to how fast you can drive that bullet. So you need the ammo recipe for X range to account for bullet velocity, distance, BC and the performance you can get out of the case at whatever pressure is safe with the bullet in question. A 30-06 will drive the bullet faster by a few 100fps so the drop at 1000yrds will be considerably less with either bullet.

Last edited by r3dn3ck; 07-06-2011 at 12:04 PM..
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Old 07-06-2011, 12:33 PM
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the 168SMK won't get you to 1000 yards reliably. this is from personal experience and from others. it's a known fact for years. some say Sierra designed it for out to 600 yards. You should be able to search for it.

I onced shot 10 rounds at a 1,000 yard target out of a 10" twist 26" barrell and only3 or 4 rounds landed on the 11"x11" target. the rest landed 3 to 6 feet all around the target. with the 175SMK all 11 rounds landed in 11"x7" area on the target.

Velocity for the 168smk was 2900fps at 1800 feet altitude. it was hot and blew the primers out of the brass. the 178smk was running at around 2760fps.
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Old 07-06-2011, 12:58 PM
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Quote:
Originally Posted by huckberry668 View Post
the 168SMK won't get you to 1000 yards reliably. this is from personal experience and from others. it's a known fact for years. some say Sierra designed it for out to 600 yards. You should be able to search for it.

I onced shot 10 rounds at a 1,000 yard target out of a 10" twist 26" barrell and only3 or 4 rounds landed on the 11"x11" target. the rest landed 3 to 6 feet all around the target. with the 175SMK all 11 rounds landed in 11"x7" area on the target.

Velocity for the 168smk was 2900fps at 1800 feet altitude. it was hot and blew the primers out of the brass. the 178smk was running at around 2760fps.
This!

For 1000 yards use the 175SMK OR the 155gr Amax with varget and cci primers are the 1000 yard champs.

168gr are made for consistent groups no farther than 600 yards.


I'm still fine tuning my 175gr smk load. For the 155 gr you want a some what hot load to get high velocities to make it out there. If you don't top the velocities it tends to get wild around 800 yards
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Old 07-06-2011, 1:45 PM
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Quote:
Originally Posted by joelogic View Post
What is the science/reasoning behind choosing one weight over another, specifically for long distance shooting.

178gr SMK in .308 at 2800fps at 1000 yards drops 533 inches.
168gr SMK in .308 at 2900fps at 1000 yards drops 347 inches.

Chose the one with less drop? Why?
If the loads are consistent the drop will be consistent and you can adjust for it. The most difficult part is the wind deflection. A heavier, more efficient bullet will be pushed around by the wind less. I would run the 175 SMKs.

Isn't the 178 the A-Max or is there a 178 SMK?
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Old 07-06-2011, 1:53 PM
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I thought they were SMK's but the package tag says 178gr HPBT with no brand info. Scale confirms they are 178gr. I will double check

Edit:
500 inches seemed a lot so I went back to my calculator and double checked my figures. I had the BC wrong. I was using .3 when it should be .5. Now the drop is more in line with 330 inches of drop.

Last edited by joelogic; 07-06-2011 at 1:56 PM..
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Old 07-06-2011, 2:22 PM
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Quote:
Originally Posted by joelogic View Post
I thought they were SMK's but the package tag says 178gr HPBT with no brand info. Scale confirms they are 178gr. I will double check

Edit:
500 inches seemed a lot so I went back to my calculator and double checked my figures. I had the BC wrong. I was using .3 when it should be .5. Now the drop is more in line with 330 inches of drop.
There are 178 grain .308 dia bullets but I don't know of a 178 SMK. It may be a Hornady 178 Match or 178 A-Max.
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Old 07-06-2011, 3:09 PM
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B.C. are as far as I know whatever the company that make the bullet says they are.

I use Berger 155.5 Palma bullets and shoot to 800 yards without problem. Rifle is TRG-22 with 26" barrel. That is greatest distance at our range so have not been able to shoot 1000 yards.

Berger uses two different numbers when dealing with BC. A G7 standard and I think a G1 Standard. The Ballistic guy at Berger, Bryan Litz, wrote a recent article about BC. I'm sure it can be found on the Berger website.
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Old 07-06-2011, 3:39 PM
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Quote:
Originally Posted by joelogic View Post
What is the science/reasoning behind choosing one weight over another, specifically for long distance shooting.

178gr SMK in .308 at 2800fps at 1000 yards drops 533 inches.
168gr SMK in .308 at 2900fps at 1000 yards drops 347 inches.

Chose the one with less drop? Why?

Edit:
500 inches seemed a lot so I went back to my calculator and double checked my figures. I had the BC wrong. I was using .3 when it should be .5. Now the drop is more in line with 330 inches of drop.

Making the choice easy now. I didnt realize BC makes such a difference.
To be honest that's the worst say to make a decision..... I personally think your going to regret not going with the 175smk load for 1000. And bullet drop doesn't mean anything. That's why your scope has adjustments and ping range shooting isn't just about bullet drop it's about ballistics and how the bullet reacts to winds pressure everything comes into play and bullets are shaped differently with different dimensions and the 175smk has some pretty good ballistics for 1000 yards for the 308 round. But your money your time your choice.


And go ask this over at snipershide.com you'll get a ling more feed back and pretty much be told what I'm telling you. Those guys know their stuff about long range shooting.


And if your too lazy to sign up for SH pm bigbamboo on here he's another big name on SH and has taught me a lot of what I know and is the guy to see and talk to about long range shooting.
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Old 07-06-2011, 4:03 PM
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Another thing to look for in your calculations is the trans-sonic window. This is the point when your bullets will begin to enter a less stable phase of the trajectory and POI patterns grow rapidly. A high BC tends to mitigate this a bit, but not entirely. So if you're engaging at 1000 yards you'll ideally want a bullet that stays supersonic at that distance. Bear in mind "supersonic" is relative to environmental conditions, so it will vary a bit depending on where/when you're shooting.
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Old 07-06-2011, 5:19 PM
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When I said the choice was easy I meant for the 175's. Since that's what everyone recommends and drop is more in line with 168's anyway.

I loaded up 100 rounds of the 178's and will dial in my scope tonight so I will be ready for next weekends clinic.

Most of this confusion comes from me not being clear on the BC of a bullet. Up until this point I was only concerned with fps.
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Old 07-06-2011, 6:04 PM
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Are you shooting a 300 WM? Because the velocities you give are awfully high for a .308.
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Old 07-06-2011, 6:50 PM
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I just stopped to read Joe's post & not make a smart aleck remark......
I did it Joe!
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Old 07-06-2011, 7:05 PM
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Quote:
Originally Posted by Pthfndr View Post
Are you shooting a 300 WM? Because the velocities you give are awfully high for a .308.
That's the question I had too.....168's doing 2900fps.....155's do it but I wouldn't think 168's can be pushed that fast (safely) from a 308win rifle. Maybe I'm wrong
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Old 07-06-2011, 8:07 PM
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I don't use weight as the determining factor for selecting bullets. I use the ballistic coefficient, the ability to stay supersonic over the range being shot and practical accuracy in my rifle.

I'm not worried about drop, that's always constant shot to shot because gravity's the same and always works. Worry about the wind drift. Wind varies all the time. Many times it will change multiple different directions and strengths over a 1,000 yard range.
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Old 07-06-2011, 9:47 PM
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I am shooting a .308 and speed is a bit fast because the primers are flattening out a bit. I will dial my loads down.

What are the usual expected speeds for 168gr and 175gr bullets?

Seems WC846 is hotter than BLC-2 which is the data Hi-tech recommends.

BLC-2 168gr Min 44.0 FPS 2569 39,400 CUP Max 47.0 FPS 2754
WC846 168gr 46gr FPS 2861

BLC-2 175gr Min 43.0 FPS 2517 39,200 CUP Max 46.0 FPS 2706
WC846 175gr 45gr 2840.

Last edited by joelogic; 07-06-2011 at 10:06 PM..
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Old 07-06-2011, 11:25 PM
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In pretty much any caliber the heavier a bullet is the higher it's BC will be. Heavier bullets are longer because they have more material in a fixed diameter. This increases SD (Sectional Density) and this increases BC (if the bullet shape is correct). This is why VLD's in any caliber are always at the heavy end of the available bullet weights. Their long tapered shape is why they fly so far, so well.

There are 3 BC drag models to choose from. If you use flat based bullets, use G1, regular boat-tails use G5 and heavy VLD's use G7 drag model.

If the Mfgr doesn't supply G5 or G7 BC info you will need to calculate it. G5 is usually about 62-63% of the Mfgr's BC1 and G7 about 50%. Example, mfgr BC1 = .362 - G5 corrected = .229 - G7 corrected = .181

Last edited by GeoffLinder; 07-06-2011 at 11:28 PM..
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Old 07-06-2011, 11:48 PM
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Geoff on my reloading I have been doing 62 and 69 grain.. My thinking was it will shoot good in my Mini 14 and ok in the Kel tec and my Ar style rifles... Yes no maybe?
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Old 07-07-2011, 5:37 AM
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Quote:
Originally Posted by ronas View Post
The Ballistic guy at Berger, Bryan Litz, wrote a recent article about BC. I'm sure it can be found on the Berger website.
Article? The guy wrote a 500+ page book on ballistics two years ago. It's a must read.
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Old 07-07-2011, 9:09 AM
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Quote:
Article?
Here's a May 16, 2011 article he wrote. Form Factors: A Useful Analysis Tool
Link below.

http://02b0516.netsolhost.com/blog1/?p=186
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Old 07-07-2011, 10:09 AM
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Quote:
Originally Posted by Pthfndr View Post
Are you shooting a 300 WM? Because the velocities you give are awfully high for a .308.
This is exactly what I was thinking...

I haven't chrono'd my SMK 168 load yet but judging by the drop out past 500 yards, it should be up around 2500-2550.
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Old 07-07-2011, 10:17 AM
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44gr of varget 168gr bullet gets me 2700+ on the Chrony, it was set 15 feet in front of the muzzle.
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Old 07-08-2011, 11:48 AM
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Quote:
Originally Posted by joelogic View Post
I am shooting a .308 and speed is a bit fast because the primers are flattening out a bit. I will dial my loads down.

What are the usual expected speeds for 168gr and 175gr bullets?

Seems WC846 is hotter than BLC-2 which is the data Hi-tech recommends.

BLC-2 168gr Min 44.0 FPS 2569 39,400 CUP Max 47.0 FPS 2754
WC846 168gr 46gr FPS 2861

BLC-2 175gr Min 43.0 FPS 2517 39,200 CUP Max 46.0 FPS 2706
WC846 175gr 45gr 2840.

Flattened primers are an indication of pressure, but don't necessarily mean that you're too hot. This is where the chronograph comes in real handy. Mine are definitely flat and even slightly mushroomed at nominal velocities. Depends on who's primer your using.

Also, I don't know about WC846, but BLC-2 is one you have to watch out with. The hotter the day is, the hotter the load becomes. This is pretty typical of ball powders in general.
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Old 07-11-2011, 11:57 PM
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Those speeds are measured from your gun? What barrel length? Lots of shooters use the 175 smk, 178 amax, or 155 scenars for a reason. They work.
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