Corrected FPS?

[husky300]

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?

 

[azsugarbear]

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.

 

[husky300]

Darn the bad luck that's disappointing, oh well thanks for you help.

 

[D.ID]

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.

 

[husky300]

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?

 

[D.ID]

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.

 

[husky300]

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

 

[D.ID]

The one in the menu bar at the top of this page.

 

[husky300]

Like I said I'm new here and cant wait till my new computer arrives so I don't have to do this over my phone. But thank you very very much for your help now it is up to me to pull the trigger to pull the trigger correctly.

 

[MontanaRifleman]

Agree with previous advise...

Also, you will need,

Accurate zero point

Accurate Scope height

Would recommend shooting at least 3 shot groups every 200-300 yds beyond zero point out to 800-900 yds, the farther the better and you will be validating actual drops in the process. IMO, 600 yards doesn't cut it unless your not going to shoot beyond 600 yds.

Make sure there is no cant in your rifle and your scope is properly mounted. Any cant in rifle will throw your shots off. the longer the distance, the greater the error.

Good shooting,

Mark

 

[husky300]

Thank you for that advice I do indeed want to shoot past 600 yards however I do not have a way to accurately determine that type of range past 600 yards that is why I want to have the most accurate ballistic projections as possible I still do no do not trust myself to range with that much accuracy using m mil mil dots to develop a good data book. But if i can consistently plug numbers into my calculator that give me the correct dope from 100-600 i can use that information to refine my range estimation.

 

[MontanaRifleman]

Thank you for that advice I do indeed want to shoot past 600 yards however I do not have a way to accurately determine that type of range past 600 yards that is why I want to have the most accurate ballistic projections as possible I still do no do not trust myself to range with that much accuracy using m mil mil dots to develop a good data book. But if i can consistently plug numbers into my calculator that give me the correct dope from 100-600 i can use that information to refine my range estimation.

Another requirement - no sense setting yourself up for LR if you don't have a range finder. I currently use a Leica. I set up my shooting spot and them walk out with targets and range back to the shooting spot if I want even 100 yd increments.

Make sure you put an anti-cant level on your scope. It will be an eye opener the first time you use it.

 

[husky300]

I do have a Leopold range finder but its only good for about 450 on my neighbors horse. And 550 on a house you guys know the deal. I do have a Vortex scope level and will start saving for a longer range finder. Until then I intend to refine my loads hence my starting at 600 and under. Baby steps, baby steps. Witch is sad as I used to go 9 of 10 at 500 with irons in the Marines. But a KD course is much different than unknown distance first shot accuracy with no wind flags.
Any other recommendations on 800yd non reflective tgt range finders?

 

[MontanaRifleman]

A google shows the Leica 1000 going for about $600 and the 1600's going for about $650 and the 1600's have baro pressure, temp and angle of shot. Strongly recommend the 1600 for the extra $50. Put a watch on Ebay and check these forums and you can get a good used one for a good price.