Shooting vs. Ballistics Cal.

[65Whelen]

I've done very little long range shooting so when I found myself deer hunting on a stand with 400yrs of shooting I went to a ballistics calculator. My Grendel is set-up for hunting the big woods of northern WI. Due to unforseen circumstances the second half of deer hunting was in the central farmlands.

I have my Grendel zeroed at 50yrs, which gives me 1.5" high at 100yrs and 3.5" low at 200yrs. This I have shot at the range. So now my discrepancy, I wanted to find out the estimated drop at 300 & 400yds. Using Hoernady's ballistic calculator, I enter my fps and all other info and the numbers don't match up. To get the numbers to jive I have to add in an additional 272fps.

I chronographed my load at 2128fps using the MagnedoSpeed chronograph. To match my range results I need to input 2400fps. Anyone seen similar results or maybe it's the chronograph?

[acourvil]

If you are using a budget chrony, you can easily have 100fps or more variation between the reading and the actual, but 300fps seems unlikely to be all data error. However, a combination of having your zero a little off, data error (both fps and BC) and failure to account for environmental changes could get you there. And of course, it's certainly possible that part of the variation is your technique, e.g., if you zeroed in one position with a stable rest, your field shooting position could be causing part of the vertical difference.

[LRRPF52]

I've done very little long range shooting so when I found myself deer hunting on a stand with 400yrs of shooting I went to a ballistics calculator. My Grendel is set-up for hunting the big woods of northern WI. Due to unforseen circumstances the second half of deer hunting was in the central farmlands.

I have my Grendel zeroed at 50yrs, which gives me 1.5" high at 100yrs and 3.5" low at 200yrs. This I have shot at the range. So now my discrepancy, I wanted to find out the estimated drop at 300 & 400yds. Using Hoernady's ballistic calculator, I enter my fps and all other info and the numbers don't match up. To get the numbers to jive I have to add in an additional 272fps.

I chronographed my load at 2128fps using the MagnedoSpeed chronograph. To match my range results I need to input 2400fps. Anyone seen similar results or maybe it's the chronograph?

What are your numbers?

Barrel length
Bullet
2128fps is really slow, unless you're using a pistol/SBR, 140gr, or just a really mild load with the lighter bullets and normal barrel lengths.

What program are you using?
Does it have input data for BC, and did the decimal get entered?
Did you enter the barometric pressure with the decimal in the correct place?

I was entering BC data at the range a few months ago, and somehow the decimal kept getting skipped when I entered barometric pressure, so the numbers were way off like yours.

[Drillboss]

I saw pretty good results using MagnetoSpeed velocity and then the ShootersCalculator.com ballistics.

http://www.shooterscalculator.com/ballistic-trajectory-chart.php?pl=%5BPreset+Name%5D&presets=&df=G1&bc=.51&bw=123&vi=2500&zr=100&sh=1.5&sa=0&ws=10&wa=90&ssb=on&cr=1000&ss=25&chartColumns=Range~yd%3BElevation~in%3BElevation~MOA~FBFFF5%3BElevation~MIL%3BWindage~in%3BWindage~MOA~FBFFF5%3BWindage~MIL%3BTime~s%3BEnergy~ft.lbf%3BVel%5Bx%2By%5D~ft%2Fs&lbl=&submitst=+Create+Chart+

I was zeroed a couple inches high at 100 yds, resulting in an effective 200 yard zero. At the range, it was pretty much spot on at 100, 200, and 300 by dialing the scope according to the ballistic table.

[65Whelen]

My numbers:
14.5 Sabre barrel
Hornady 129 SST, B.C. .485
no barometric pressure was asked by the Hornady ballistic calculator.

[JASmith]

My numbers:
14.5 Sabre barrel
Hornady 129 SST, B.C. .485
no barometric pressure was asked by the Hornady ballistic calculator.

We don't yet know enough of your load data. e. g., powder, weigh, and OAL to see if your chamber is merely slow or you are using less than a max charge weight.

Having said, that, it is really difficult to get enough velocity with that bullet to make it an interesting long range item. The exception is the "Gee Whiz!" feeling one gets when connecting.

Have you considered a lighter bullet that will yield a flatter trajectory at the expense of some wind drift?

[65Whelen]

We don't yet know enough of your load data. e. g., powder, weigh, and OAL to see if your chamber is merely slow or you are using less than a max charge weight.

Having said, that, it is really difficult to get enough velocity with that bullet to make it an interesting long range item. The exception is the "Gee Whiz!" feeling one gets when connecting.

Have you considered a lighter bullet that will yield a flatter trajectory at the expense of some wind drift?

My load:
25.9g of XBR-8208
COL 2.245 (max COL for the 129 SST in this barrel is 2.255)
Hornady brass
CCI-450
I don't really understand how the specific load is relavent, FPS is FPS, isn't it? Enlighten me, always willing to learn. As I said, not a lot of experience with long range shooting. And for the record, I would not have tried a shot longer than 250yds and I had very nice 10pt at 450yds. The "gee whiz" factor is tempting.
I developed this load for short range. Obviously, I need to work up a load with a lighter bullet and a lot more velocity in case I find myself in a similar situation.

[Drillboss]

I looked at ShootersCalculator with your data yesterday and saw similar results. Got to thinking about it again today and did some what-ifs.

With 2128 fps muzzle velocity, a 2.75" sight height, and a 150 yard zero, it predicted 0.31" high at 50 yards, 1.28" high at 100 and 3.71" low at 200. Those numbers seem reasonably close to what you're seeing at the range.

[biodsl]

Whelen...I just plugged some data into JBM. I set the zero at 100 yards 1.5 inches high. This shows a trajectory that is .5 inches high at 50 yards, 3.6 inches low at 200 yards. Seems to me that this pretty much jives with what you're seeing in the field. 300 yards is -19.3 inches, 350 is -31.7 and 400 yards is -47.5.

FYI - My Hornady manual shows a max charge of 26.2 XBR moves a 129 grain bullet at 2300 fps out of an 18" barrel. Considering your barrel length and load I think your velocity is in the ballpark.

[LRRPF52]

If you plug in the Litz BC for the 129gr SST, it is higher at .495 G1, .247 G7, but that won't change your numbers noticeably at close ranges.

Hornady lists a max load of 26.2gr of 8208XBR under any of their 129gr cup and core bullets in 6.5 Grendel.

I would look at CFE and LVR if you want more speed, because you could likely get a 129gr to 2300fps from a 14.5" with either of those.

Expansion on the SST stops at 1800fps.

What's your optic height?

With your current speed, you will have expansion just out a little past 200yds.

If you use LVR or CFE and get up to 2300fps, you will have expansion out to 315yds and a flatter trajectory.

[JASmith]

...I don't really understand how the specific load is relavent, FPS is FPS, isn't it? Enlighten me, always willing to learn...

The post by LLRPF52 illustrates the "why" -- you can safely get a significant increase in velocity by using a difference velocity.

That is is important because your velocity drops below the nominal 1800 fps threshold expansion velocity at about 200 yards using the default weather conditions in JBM.

Even if you can get "only" to 2250 fps with an alternative powder, that max ethical range might get extended to about 275 yards.