20x47 Lapua..

[Pilgrim]

Tim

You sure about that those JBM calculations?

[coyotelatrans]

I think he posted MOA and not actual inches for drop or wind drift.

[Tim Anderson]

drop and correction both M.O.A.

[Pilgrim]

Even so, the calculations do not work. On the moon, maybe.

[coyotelatrans]

Pilgram is right on this one, didn't pay much attention until I ran it myself!!!!! The JBM program is way off real num,bers of this load!!!!

[Tim Anderson]

[quoteEven so, the calculations do not work. On the moon, maybe.][/quote]

Why don't they work???
If all the proper info is put into the formula it will put you on fur most times.. This same info is used to calculate bullet drop for the Kenton dial and i have no problem hitting my targets out to 800 yds.. I've even noticed you don't have to have the exact info to make it work so the bullet hits its mark...
I took a young man out shooting a few years ago, he has never fired a center fire before just shotguns and 22 L.R. mainly and he never dreamed he could hit a target past 100 yds either. I set the 17 Pred up on the shooting bench for him and gave a few pointers.. I then turned the Kenton BDC dial to 500 yds with no windage adjustments and said fire away... After he shot five rounds we went to go look at the target.. I'll let the pic. speak for the Kenton dial and this young shooters ability..

[Tim Anderson]

Pilgram is right on this one, didn't pay much attention until I ran it myself!!!!! The JBM program is way off real num,bers of this load!!!!

LOL... The loads listed above was just an example. I did'nt compute bar. pressure, altitude or any other varibles. I just threw in the bullet weights and BC and used a vel. close to each other and left everything else zero... If i would of put everything in it would still have the same outcome from the 3 cartridges listed.

[coyotelatrans]

Tim it is stating like 189" of drop at 1,000 yards That is a bc .195 G7 and 3,800 fps with a 55 grain bullet, JBM must have issues but try it in another program those numbers are off. That little 55 grain bullet would need a BC of over .400 or more to get those kinds of numbers.

[Tim Anderson]

What calculator are you useing?? I tried a few others and they where with-in 1" except for the one provided by Hornady which was close to what you have..



P.S. I got this from another ballistics site and this is what they had to say about JBM ballistics..

(The world renowned JBM Ballistics computer is now powering all of Ballistic's computations. JBM is used by world-class shooters everywhere to deliver some of the most precise calculations. This great ballistics computer is now available in the palm of your hand and simpler to use than ever. ))

So with that i would have to say maybe youre ballistics program is off, but can't say for sure since i don't know what it is...

P.S. I did some more searching on ballistic programs, it seems the one provided by some hunting sites are all very simular with same results but at the same time they don't go into exacts like the JBM program does so i guess the only way to find out which is right is to actually go out and shoot at a few targets and see which program comes the closest.. I'm going to go look at my Kenton dials and see what they have for bullet drop correction since i know they are on..

[Tim Anderson]

Here is a JBM calculation for a 17 cal, 30 gr, woodchuck bullet at 3800 fps, elavation at 1322 at 32 degrees.

Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
0 -1.5 *** 0.0 *** 3814.9 3.510 969.3 0.000 0.0 ***
100 -0.0 -0.0 0.8 0.8 3390.2 3.119 765.5 0.083 0.0 0.0
200 -1.5 -0.7 3.6 1.7 3006.5 2.766 602.0 0.177 0.0 0.0
300 -6.9 -2.2 8.4 2.7 2655.6 2.443 469.7 0.284 0.0 0.0
400 -17.3 -4.1 15.8 3.8 2331.5 2.145 362.0 0.404 0.0 0.0
500 -34.1 -6.5 26.2 5.0 2030.8 1.868 274.7 0.542 0.0 0.0
600 -59.4 -9.5 40.4 6.4 1754.0 1.614 204.9 0.701 0.0 0.0
700 -96.1 -13.1 59.0 8.1 1505.4 1.385 150.9 0.886 0.0 0.0
800 -148.2 -17.7 83.1 9.9 1292.8 1.189 111.3 1.101 0.0 0.0
900 -221.3 -23.5 113.1 12.0 1127.2 1.037 84.6 1.351 0.0 0.0
1000 -321.7 -30.7 148.8 14.2 1014.6 0.933 68.6 1.632 0.0 0.0

I checked with my Kenton dial set up for the 30 gr. gold and found that there are 52 clicks required for correction at 700 yds. Since chart is MOA you need to devide 52 by 4 (clicks) and you will come up with 13 MOA. The chart shows 13.1, close enough for minute of coyote>>>

[Tim Anderson]

I was out burning up some fire-form loads yesterday and thought i would show you how well the Kenton dial works and how easey to use.. all i did was dial in the elavation and no windage corrections where made.. Shooting was done with my little 17 pred. shooting a 30 gr. gold bullet.. here is a short clip ...

[Tim Anderson]

The sizeing die and bushings finally showed up and still waiting on the seater die and a 20.cal trimmer pilot.. I got 100 rounds of lapua brass necked down to 20 cal. and found that my 22-250 ackley seater die would work for seating the bullets for the time being.. I did'nt want to use up my good Berger bullets on fire-forming loads so i picked up a box of 40 gr. V-maxs to use for that.. I got a load figured out useing Ram-shot big-game and the 40 gr. bullets and loaded up some brass.. i fired the first round and inspected the primer and also took a few measurements of the brass webb area and everything looked good so i fired a couple rounds through the Chrono-graph and got a vel. of 3750.. Good enough for fire-forming..
I tested fired and also cleaned the barrel for break in every five shots and fired 3 five shots groups and also worked on fire-forming some new brass for the 17 Pred.. Everything looks good so far, except i need to take the rifle over to the gunsmith and have him adjust the trigger for me its a little on the heavey side. I have one more session today of fire-forming and will have 50 rds ready for testing the bergers and working up to a good hunting load . hopefully i can get all this done by this week so i can also get it tested out to 6-700 yds a see if i have to order a Kenton dial or if one i use for the ackley will work..
I also had a little time to apply a camo finish to the rifle to help break it up some when hunting.

[bucksnbears]

Tim, any up dates on this rifle??

[Tim Anderson]

At the moument I'm shooting the 40 gr. V-max with it, with vel around 3850 fps. I well work up the load to a higher vel. later on.. Any way called in coyotes shot in center of chest or broadside in shoulder or rib cage area I'm just getting one hole in nothing out and dead right there.. Hits to high to the back bone or to far back are simular to a 22-250 wound, messey.. I got one coyote that was way out there last week, range finder would'nt pick up the distance. Buddy of mine offered to walk out and pick it up for me and also stepped off the distance. It was a good poke..LOL
I still like the 17 pred. more due to the fact that it don't tare them up on a baddy placed shot..

[Tim Anderson]

Picked up a nice double today with the 20x47 L.....