243 winchester ballistics help needed

C

crout

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Long story short. I was determining my velocy for my drop chart by shooting at different distances and then putting info into JBM ballistics to work out fps.
I am using 70 gr blitzking. 200 yard zero and a 9" drop at 400 yards. I am getting like 4200+fps to get my numbers to match.
What am I doing wrong? 4200 seems high.

P.S. My first cold barrel shot was 3" low at 400. No wonder I can never hit those coyotes!!
 
Yes, that is unreasonably fast.
I recently chronoed some 75 grain hollow point, both Sierra and Speer and with the "maximum" load of H414, as shown on the Hodgdon site, 46 grains, and they averaged about 3480.
The fastest 70 grain bullet that Hodgdon's show on line is 3660, with Suprform powder. The maximum speed of the 70 grain bullet with any other powder they show is is less by a least 100 fps.
 
I use 70 gr. Nosler BT varmits on top of 42 gr. of Varget. The published velocity of that load in the Nosler manual is 3016. The fastest load they publish is 3630 using 47.5gr. H414.

The 42 gr. of Varget and the Noslers are very accurate out of my M-70 .243 i do not have a chronograph so I go by the books figures for approx velocities

So at 4200 yep thats very fast. You should be seeing some pressure signs if there actually moving at that speed.
 
Crout are your mounts positioning your scope higher than standard 1.5" usually used in Charts. Measure your exact line of sight above bore and enter the height in your ballistic software program. The drop at 4oo may be due to higher than normal mounts. Just a guess.
 
I ran numbers through a calculator as well. Even with 3800fps on that .299 BC bullet and a scope 2" high over bore, with a 200 yard zero you still get a 12.0" drop. They must be skipping along for sure . I used a 3" high scope , which I'm sure you are not using and got 11" at 400 with 3800fps!!!at the muzzle. This may sound a little of the wall, but I wonder how much heel down those things fly? Almost like they are lifting like a wing LOL. You sure you're dead on @ 200yards??, A tad high at 200, thus making a 250-260 yard zero, would be in the ball park of a 9" drop at 400 if you could achieve 3800 fps at muzzle. Amazing trajectory no matter what is going on here.
 
A chrono will give you the velocity. It strikes me you are trying to achieve a velocity based on drop figures which are at best suspect.
You might get the same results shooting into a bag of potatoes that is hung from a tree then reconstructing velocity based on the weight of the rope and potatoes times the length of the rope to the point of impact times the distance the bag moves in centimetres.

There are charts giving drop figures based on velocity and ballistic coefficient, and there are computerized calculators that give drop figures bases on the same two factors.
 
horseman2 said:
A chrono will give you the velocity. It strikes me you are trying to achieve a velocity based on drop figures which are at best suspect.
You might get the same results shooting into a bag of potatoes that is hung from a tree then reconstructing velocity based on the weight of the rope and potatoes times the length of the rope to the point of impact times the distance the bag moves in centimetres.

Hey, don't laugh at it. In the early 1900s the British military used that type of device to determine velocity of the 303 service rifle.
It was in a British military book I once had access to. A free swinging pendalum of an exact length, A pad to stop the bullet and a measuring tape that slid out and stopped at the exreme swing of the pendalum. They figured out the foot pounds of energy and marked the scale accordingly. Once they had the foot pounds of energy they just figured out how fast the bullet would have to hit the pad, in order to give that amount of energy.
I had the book early in my shooting career, when there were absolutely no chronographs available to the shooting public. The book gave precise instructions (remember, it was British) for everything, weight and length of the pendalum and even complete directions for programming the scale to read foot pounds of energy.
I came very close to trying to build one, which would have been completely feasable, but never got around to it.
Click to expand...
 
I am 2.25" from center of bore to center of scope.

and who needs a chrony? the bullet drop is what it is. therefore the velocity is what it is. I am just trying to figure out why I am getting a 4200fps read out from jbm when I "reverse engineer" my results.
if I use a chrony it may say 3600fps but that might show a 14" drop at 400yards with a 200yard zero. I am getting a 9" drop(the 2" group is actually 8-10" low of poa so 9" is a good average)

oh and what about magnum primers. will that effect anything. no pressure signs either.
 
First things first. The program that you are using is a guide only and is algorithm based using complex formulas. These formulas were derived based on testing conditions in the lab. Things like wind, atmospheric pressures, temperatures, rifle twist, condition of barrel, consistency of bullet, powder/primer/case trimming/bullet seating also can play a role too. You are relying too much on the theoretical model in the program.

All reloading manuals provide pretty good estimates of the muzzle velocities of their bullet with a specific charge of powder. What you are doing, is to attempt to back calculate (the hard way, i might add) your velocities based on bullet drop. If you want absolute certainty of your velocities - buy a chronograph.

Using your method to determine velocity is kinda like guessing the speed of the vehicle in front of you on a highway using a stop watch and timing his travel between two power poles 500 meters in front of you. When you could instead, just keep up with him and use your speedometer as your reference.

I shoot a 243 and use Nosler 70 grain bullets exclusively. I worked up a load based on muzzle velocities using the nosler manual and use 335 powder. It's a tack driver and the load is very consistent. I then shoot to determine the average drop of my load at different distances and plot my curve on that basis, not the other way around.
 
sobo4303 said:
First things first. The program that you are using is a guide only and is algorithm based using complex formulas. These formulas were derived based on testing conditions in the lab. Things like wind, atmospheric pressures, temperatures, rifle twist, condition of barrel, consistency of bullet, powder/primer/case trimming/bullet seating also can play a role too. You are relying too much on the theoretical model in the program.

All reloading manuals provide pretty good estimates of the muzzle velocities of their bullet with a specific charge of powder. What you are doing, is to attempt to back calculate (the hard way, i might add) your velocities based on bullet drop. If you want absolute certainty of your velocities - buy a chronograph.

Using your method to determine velocity is kinda like guessing the speed of the vehicle in front of you on a highway using a stop watch and timing his travel between two power poles 500 meters in front of you. When you could instead, just keep up with him and use your speedometer as your reference.

I shoot a 243 and use Nosler 70 grain bullets exclusively. I worked up a load based on muzzle velocities using the nosler manual and use 335 powder. It's a tack driver and the load is very consistent. I then shoot to determine the average drop of my load at different distances and plot my curve on that basis, not the other way around.
Click to expand...

Just to make certain, what is your powder charge? Since 4200 appears high and the Nosler book using H335 shows less than 3500 at their max. The Nosler accuracy load is using the lowest charge and suggesting a velocity of 3200.

Since the height above bore appears excessive, are you using the formula: 1/2 bolt diameter + distance from top of bolt to bottom of scope tube + 1/2 scope diameter = bore to line of sight. Most of mine measure in the 1.5 - 1.65. The 1.65 is using a Model 700 with medium rings and a 30 mm scope tube.

I was not laughing using my Sack of Potatoes comparison but emphasizing the need for precise measurements to determine velocity.
 
using h380. 44.1g cci mag primer which might give me 3450fps(just a guess)
which equals a 16" drop at 400 yards with a 200 yard zero.
I would need a 300 yard zero to get my 9" drop at 400 yards.
 
That bullet has a BC of .310. Your above figures would appear to be accurate. What figures are you using to get your bore to line of sight measurements?
 
horseman2 said:
Just to make certain, what is your powder charge? Since 4200 appears high and the Nosler book using H335 shows less than 3500 at their max. The Nosler accuracy load is using the lowest charge and suggesting a velocity of 3200.
Click to expand...

My powder charge was the resultant of a couple of weeks worth of load testing for my rifle; is 37.3 which is just over 3,400 fps. Why is it that I feel like I am being corrected?? I never made any suggestions nor representations of velocities of 4,200 fps. I do know that my drop at 300 yards is pretty minimal (about 5" - 0 sighted in 1" high at 100 yards) compared to other loads and bullets I am familiar with. When using a calculator, it should be about 9". So much for accurate formulas.
 
sobo4303 said:
I do know that my drop at 300 yards is pretty minimal (about 5" - 0 sighted in 1" high at 100 yards) compared to other loads and bullets I am familiar with.
Click to expand...

I'm not far off you sobo, about 5.5" drop @ 300yrds with factory Hornady 75gr HP's out of my Sav 10 Brush.
 
If you know the drop at a few different ranges and you have accurately measured scope height from the bore. Start adjusting the BC of the bullet along with the muzzle velocity to make the numbers line up with your real world drops.
"true" the software to the real world results.
JMO
 
Just the way you hold your rifle can account for 5 inches or more @ 400 yds. To use the formulas with any degree of accuracy you need to have a huge sample over a variety of barometric conditions and light conditions. Just a change of lighting can change 400 mtr group position by as much as 8". Any good silhouette shooter will tell you how much difference light, and temp changes can change their sight settings out to 500 mtrs using the same rifle and load. Hence the need for a chronograph.
 
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