Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Hunting > The Basics, Starting Out


Reply

Corrected FPS?

 
LinkBack Thread Tools Display Modes
  #1  
Old 12-28-2012, 11:08 PM
Junior Member
 
Join Date: Dec 2012
Posts: 11
Corrected FPS?

I am new to this forum and currently posting from my phone so my search ability is limited so if this has has already been answered I apologise in advance and please post a link or where I could find it.

Now that I have given my poor disclosure I'm looking to find a way to determine my correct FPS. Of my particular load from my 308 that I like to load up. I have never Chronograph the round and have no access to 1 however im inclined to believe that with my reloading data my BC and length of barrel i should be in the ball park. That said I want to start pushing out to 800yds.

So lets say i shoot a perfect group at 100yds to give me a good zero, then i shoot at 600-700yds using the given MOA adjustment from a good ballistic calculator. Is there a way to take the projected results and actual results and backtrack that to my starting muzzle velocity?
Reply With Quote
  #2  
Old 12-29-2012, 04:13 AM
Gold Member
 
Join Date: Sep 2005
Location: Central AZ
Posts: 930
Re: Corrected FPS?

In theory, the answer would be yes. By zeroing at 100 yds and then shooting a second group at 600, you would learn/confirm the number of MOA or Mils (whichever you are using) necessary for dialing up. By inputting your bullet BC and other external conditions into some ballistic software, you could back into an estimated muzzle velocity through trial and error.

In reality, the answer isn't always that simple. There are so many variables that go into calculating a "ballistic blueprint" of what your bullet is actually doing in its flight. For example, some bullet mfgs overstate the BC of their bullet. Your software has no way of knowing this. It simply takes for granted that the BC input by you is accurate. So when you begin to "play" with various muzzle velocities to arrive at the correct MOA dial up, your velocity will be artificially low. The truth could very well be that your bullet is traveling faster than your assumed muzzle velocity and the faulty BC number is the culprit instead.

The same goes for elevation, temp, G1 BC vs. the more accurate G7 BC, etc. Your software assumes that all these measurements are correct. It's always better to confirm all your data and then tweak or message the software. One final caution, not all Chrony's are accurate either. :-)
Reply With Quote
  #3  
Old 12-29-2012, 12:09 PM
Junior Member
 
Join Date: Dec 2012
Posts: 11
Re: Corrected FPS?

Darn the bad luck that's disappointing, oh well thanks for you help.
Reply With Quote
  #4  
Old 12-29-2012, 07:19 PM
Gold Member
 
Join Date: Dec 2008
Location: Boise IDAHO
Posts: 838
Re: Corrected FPS?

If your bullet's bc has bean thoroughly researched and confirmed you can nail it on the head. In fact I quit using my chronograph all together because data established by confirmed bc, noted conditions and real world trajectory cycled threw Jbm or g7 calculators is more reliable than the chronographs. Gravity does not lie. Many of the most common long range bullets have bean very extensively researched. Most hunting bullet manufacturers pull a number out of there * but most real long range bullets have some good numbers or have had some serious corrective research done.
Reply With Quote
  #5  
Old 12-29-2012, 07:56 PM
Junior Member
 
Join Date: Dec 2012
Posts: 11
Re: Corrected FPS?

Okay just when I have given up hope I have a glimmer of chance show up.
So if I am confident in my BC you are saying that would work?
What would that formula look like?
I will tell you my thought process of how I would do this that might give you guys a better idea of my thought process. .

transpose data on to a full sheet of plywood from a ballistic chart for my given velocity and range give to me from my ballistic calculator taking into a effect the ballistic coefficient and barometric pressure. Then I would shoot a good 100 yd zero. back myself off as far as my range finder will let me (about 550+ yds). Adjust my scope according to my calculator and shoot another group. Now go down range and take my elevation measurement
Take the difference and start plugging FPS until my calculator numbers match my measurements. Of courses i would verify at say 300 to make sure of my calculations.

Basically the more I'm actually thinking about this the more I'm actually trying to fudge my calculator into giving me wrong data but data that matches my loads?
Reply With Quote
  #6  
Old 12-29-2012, 08:27 PM
Gold Member
 
Join Date: Dec 2008
Location: Boise IDAHO
Posts: 838
Re: Corrected FPS?

If and it is a big IF your bc and your atmospheric data is accurate, you check to make sure your scope is tracking the proper distance (1moa is really moving 1moa) use a good proven calculator: you are not getting wrong data, your adjusting estimated data to match the reality, your simply adjusting your estimation till it is real at which point it will match...................... If you note your known data (everything but fps), check your tracking for adjustment reality and then zero at 100yrds, move out to the farthest distance that is practical and shoot a group of three based on your swag, then go to the target and measure with a measuring tape the real difference, calculate scope adjustment needed for a dead center hit. Go back to the line, make the adjustment and fire 3 and go prove your were ware you should be on the target. Go into the g7 calculator and enter your known data. Select trajectory validation and enter the range and adjustment it really took to get a center hit at that range under those conditions...........it will give you your muzzle velocity. All having already bean proven, run the calculator based on that fps, print it off and go confirm at other distances.
Reply With Quote
  #7  
Old 12-29-2012, 08:39 PM
Junior Member
 
Join Date: Dec 2012
Posts: 11
Re: Corrected FPS?

What calculator are you using that has trajectory validation? I've never heard of a calculator that does that if there is 1 I'm interested in knowing what brand or software:-)
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes



All times are GMT -5. The time now is 04:39 PM.


Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC