Bullet selection for reloading

[Aplusseller]

Hi guys,

Newbie question.

Reloading for 308, after doing a test of the new ELD match and a Sierra bulllet, I noticed that with the same powder amount the Sierra bullet is hitting higher than the ELD match bullet at 100 yards. As far as grouping they both grouped very well.

If grouping is the same, am I better choosing the bullet that shoots higher? Or should I choose the one with higher bullet coefficient?

Thank you
Gino

[condor bravo]

What are the bullet weights? I'm assuming they are the same but if not that could be a factor. Bullet aerodynamics influence by boat tails, hollow points, jacket material and length of bearing surface can account for velocity difference even though same loading.

[Aplusseller]

175 for Sierra hpbt and 178 for the eld match

[Stats Shooter]

There are several factors that can cause a bullet to have a higher point of impact than another at 100 yards. The first and most obvious is velocity. However at that distance, the velocity difference would have to be substantial for velocity alone to cause a major Point of impact difference.

The next is barrel whip or "timing" . If the barrel is whipping up every time with bullet "A" and down with bullet "B" then poi for bullet/powder combo B will be lower, maybe even a few inches lower. This can, and does often happen even though bullet powder combo "B" is traveling faster than bullet powder combo "A".

Then there is stabilization point. A bullet may initially yaw or sort of corkscrew for several dozen yards.

The bottom line is, you should pick the most accurate bullet that accomplishes what you need it too. If you want velocity you'll need a chronograph.
And if all else is equal, choose the bullet easiest to buy.

[Aplusseller]

Thank You!!!

[T. O'Heir]

"...A bullet may initially yaw or..." A bullet will initially yaw. No maybe's about it.
The two bullets are different weights. That'll make the POI slightly different. The Sierra has slightly lower BC and sectional density too.
However, the velocity matters. The BC, not so much. Ballistic coefficients are about how a bullet travels in the air. Hornady's site has a really good explanation. In English with math subtitles.
http://www.hornady.com/ballistics-resource/external
Either of 'em have any edge in group size? That's the important part. That and the relative differences in cost. Hornady's are currently on sale at Midway.

[Don Fischer]

Only thing written in stone is that your not gonna know what will happen till you try it! What are you using the load for? If it's for target shooting, the only match bullet I've ever used has been SMK's. They have done me well eniugh I'll probably never change that. Sierra knows how to make great match bullet's! I'd also try match bullet's in a varmint rifle, shot I have! But sounds to me like this is nt a match rifle, what is it?

[Mal H]

I noticed that with the same powder amount the Sierra bullet is hitting higher than the ELD match bullet at 100 yards.

How much higher?

[PA-Joe]

How much higher it hits doesn't really matter.

If you are going to hunt with these what is the expected range of the game you are shooting at.

I normally set the point of impact at 2" high are 100 yards.

[Unclenick]

If the point of impact is significantly different, the bullets probably have a significant difference in barrel time. For example, one may have less jump to the lands, which will raise pressure, or one may stick down into the powder space further, which also raises pressure. Raised peak pressure shortens barrel time, so the bullets will then exit at points in the muzzle swing that are enough different to cause the POI shift. It doesn't tell you how they will perform after the sight setting is corrected for them, though. It does, however, hint that at least one of them is probably not at its most accurate load sweet spot with that particular powder charge, and that you need to do some load development to find where that is. Dan Newberry's OCW method is a good place to start. If you have 300 yards, you can try an Audette ladder.

[Jeffm004]

Just tested SGK 165 and Hornady SST 165s over 140 Benchmark at 200 this weekend. No discernible difference, both max mag length.

Different weights is hard. I try with a 45-70 to use lead for practice but it gets hard.

Also proved .223 77gr Hornady Black box does very well in 30 mph quartering wind. 3" better than 55 on zero at 200 - in fact, did not move off zero out of the bull, just a tad of drift to left. 20" barrel, you know, like it was designed to have.....

[Stats Shooter]

If the point of impact is significantly different, they bullets probably have a significant difference barrel time. For example, one may have less jump to the lands, which will raise pressure, or one may stick down into the powder space further, which also raises pressure. Raised peak pressure shortens barrel time, so the bullets will then exit at points in the muzzle swing that are enough different to cause the POI shift. It doesn't tell you how they will perform after the sight setting is corrected for them. It does, however, hint that at least one of them is probably not at its most accurate with that particular powder charge, and that you need to do some load development to find where that is. Dan Newberry's OCW method is a good place to start. If you have 300 yards, you can try an Audette ladder.

In my .338 Lapua Magnum, my load pushes a 300 gr bullet around 2750 fps. It shoots bugholes at 200 yards and is 1/2 MOA at 600....under 3/4 MOA at 1,000.

My dad gave me some .338 Nosler partitions, 225 gr and at the time I had no other .338 rifle so I loaded them up for my .338 Lapua just for the heck of it. I chose a load near the middle of the recommended MAP from the manual and loaded all 20. Obviously I didn't have enough of them to do a load development so I was just using them to foul the bore.

Anyway, the velocity of these were about 2,900 fps which again is moderate for this cartridge and bullet combo using Retumbo which is slower. However, despite being a lighter bullet traveling faster, the POI was 8" low and right of my 200 yard zero with the 300 gr bullets still going slower at the 200 yard mark. (At around the 400 yard mark the 300 gr bullets will pass the 225)

The reason for this was that I was at the optimal barrel time with the .300 gr bullet and way off with the 225 gr bullet. Again, I didn't much care and didn't do a load workup for the 225's as they were designated foulers and I only had 20, but still, the 8" low and right was not because they were slower at the POI, but because of the difference in barrel Harmonics.

Now, at the time I didn't know all this, but I do now, and if I had everything tuned properly for both of those bullets, I shouldn't see much in the way of Horizontal deflection at all, and the vertical should be within a couple inches.

[Unclenick]

Jeff,

Higher BC makes for less wind deflection because there is less drag on the bullet. Didion figured out the mechanism and published the solution in 1859. Many folks continue to mistakenly believe bullets drift in a crosswind due to the effect of that wind over time of flight (TOF) through it, though.

NRA technical guru, Wm. C. Davis, Jr. gave a good example of why that drift account for it. He pointed out that if you zero a .22 LR with 1240 fps MV at 100 yards, the TOF is about 0.273 s. The same time a bullet takes to drop a little over 14" from a stationary position. Yet a 10 mph crosswind will move the fired bullet about 5.5" to the side of zero by the time it reaches the target. Do you believe that if you drop a .22 LR bullet from a height of 14" or 15" in a 10 mph wind that it will be blown 5.5" to the side by the time it hits the ground? Intuition tells you immediately that it will be blown only a fraction of an inch and will be nowhere close to 5.5" to the side. Being blown directly by the wind is not the mechanism. Rather, it is the sideways component of the vector resulting from combining the bullet's own head wind and the crosswind that moves it off point of aim.

Didion figured the calculation out very simply. You take the TOF the bullet would have for the same range in a vacuum, where the muzzle velocity would remain constant all the way to the target, and subtract that from the actual measured TOF. The difference is a measure of the effect atmospheric drag has on the bullet. You multiply that difference in TOF by the velocity of the cross-component of the wind to learn how far the bullet will be deflected by it.

To take Davis's example of the .22 LR in a 10 mph (14.7 ft/s) crosswind, if the muzzle velocity of 1240 fps were not subject to drag, the TOF for 300 feet (100 yards) would be:

TOFvacuum = 300 ft / 1240 ft/s= 0.242 s

but actual TOF is:

TOFmeasured = 0.273 s

So, find the difference:

0.273 s - 0.242 s = 0.031 s.

Multiply that difference by the cross wind component speed (same as wind speed for a 90° crosswind)

0.031 s × 14.7 ft/s = 0.46 ft = 5.5 in

To learn the cross-component of any wind direction for that calculation, just multiply wind speed by the sine of the angle of the wind, where 0 degrees is straight ahead and the degrees go counterclockwise around you looking down. So 90° is a wind from 9:00 and 270° is wind from 3:00. A positive number moves the bullet to your right and a negative number moves your bullet to the left.

The bottom line, though, is that the higher your bullet BC, the smaller the drag effect, so the smaller the difference between the vacuum TOF and the actual TOF will be. That means less wind deflection.

[Longshot4]

If I were you I would adjust the sights.

[AllenJ]

If grouping is the same, am I better choosing the bullet that shoots higher? Or should I choose the one with higher bullet coefficient?

If grouping is the same choose the one that best fits what you are going to do, it matters not which shoots higher or lower at 100 yards. A few years ago I had to choose between the 175 SMK or the 178 Hornady Match, both shot very well out of my rifle and both were about the same price (the Hornady's were a tad cheaper at that time). I went with the higher BC Hornady's since they'll be able to shoot accurately to further distances.

[RC20]

Like he said.

Hornady tends to be lower cost and or on sale more.