Using chronograph data to determine the best load????

[Guest]

Any tips on analyzing chronograph data to develop loads????

Of course, low ES and SD at the desired velocity are the goal, but how do you analyze the numbers and what do they tell you???

Let's say your ES is too high......do you increase or decrease the powder charge......do you change primers, do you alter seating depth.....and how do you know what to do first and which direction to go????

Same questions for SD???

I'd appreciate a nudge in the right direction if there is a comprehensive article or FAQ concerning this subject!

 

[bailey1474]

I once loaded 13 different shells for my 300 RUM each increasing by .5 gr. I was going to do a ladder w/the 240 SMKs but it was too windy that day so I just set up the chrono and fired all 13 @ 100 yds. From 83 gr to 87 gr, I only noticed about a 50 fps increase in velocity. 87.5 gr brought a 20 fps jump as did 88 gr. The jumps continued w/increasing charges. What really impressed me was that all 13 rounds went into one hole that measured .850". The group was also much smaller before I noticed the jump in velocity. As the charge increased, my group opened up a bit to the right. Not sure why, but that is what it did.

I am going to try the same thing w/my 6BR when I get it back. We'll see if this was just fluke or if it actually works!!!

 

[Bart B]

My recommendation is don't use one. A chrony will tell you which load will make a bullet win the race to the target, but not how close together they'll arrive there. I would not try to get a given velocity. The same handload will produce different velocity in each of several rifles anyway, but can be very, very accurate in all of 'em.

Years ago I was part of a group of folks testing handloads for Sierra Bullets' then new 155-gr. 30 caliber Palma bullet. New Winchester cases were primed with Federal 210M primers. We tried several powders and charge weights thrown from measures; not weighed. AA2520 ball powder had the lowest charge weight spread, lowest muzzle velocity spread and lowest chamber pressure spread. AA2520 also produced about the worst accuracy. IMR4895 had a 3/10ths charge weight spread, average muzzle velocity spread and peak pressure. IMR4895 produced the best accuracy; tested at 2.8 inches at 600 yards.

The best primer today is probably PMC ones. They don't deteriorate and start producing higher muzzle velocity spreads within a year like the others.

Change powder charge weight by no less than half a grain to check a load's accuracy. There's no way to tell if you should increase or decrease the powder charge for best accuracy if you're below maximum.

Shoot at least 20 shots per group when you think you've got a good load; anything less isn't reliable enough to be meaningful.

Full-length size your cases such that you set the shoulder back a few thousandths of an inch.

 

[green 788]

Bart is 100% correct. The target must always be the final arbiter. And since you have to shoot the bullets to chronograph them anyway, why not just put the paper out there and believe it. /ubbthreads/images/graemlins/smile.gif

Chronographs are more of a distraction to me during load development. I find a load that shoots tight via my OCW method www.clik.to/optimalchargeweight and then--and only then--do I become curious as to the velocity...

Bart... your last name wouldn't be Bobbit would it? If you're Bart Bobbit you're a wealth of knoledge...

Just wondering. /ubbthreads/images/graemlins/smile.gif

Dan

 

[Bart B]

Yes, Dan, that's me. Joined this board to sell some bullets. They're all gone now but I may hang around for a while.

 

[BountyHunter]

Disagee with Bart on this one and green 788. If you have a very accurate gun a chrono will help you find the tuning nodes for that gun. Just got to understand what it is telling you, if you don't then yes forget using one.

I use the ladder method to ID nodes by both grouping on paper and chrono results. Guess what, they normally match up, when a close powder charge range groups on a ladder it will also group very closely on velocity on the chrono. I can pick the tuning node in the MV range I want and normally pick a weight in the middle of the node to take care of any variances with temp or pressure spikes.

Green 788 OCW method works to find an acceptable load (ie .5MOA maybe in most guns) but it will not normally find the most accurate load for a really accurate gun (.25 MOA or better).

As far as PMC being the best primer for what I do not know. The equip list for matches sure do not back that up for being the most accurate across the board. The best is what works best in your gun.

F210s in most LR BR guns, RWS and even the Russian primers are the most common on the equip lists. As we test everything, we use the most accurate and I normally use F210 and RWS.

BH

 

[green 788]

The PMC's are Russian primers... FWIW. /ubbthreads/images/graemlins/smile.gif

 

[green 788]

Bart,

I've read much of your stuff over the years. As I say, you're a wealth of information. For any who haven't seen Bart's stuff, here's a page with much of his commentary on it: http://yarchive.net/gun/index.html

Dan

 

[bailey1474]

[ QUOTE ]
I use the ladder method to ID nodes by both grouping on paper and chrono results. Guess what, they normally match up, when a close powder charge range groups on a ladder it will also group very closely on velocity on the chrono. I can pick the tuning node in the MV range I want and normally pick a weight in the middle of the node to take care of any variances with temp or pressure spikes.


[/ QUOTE ]

That is exactly what I used the chrono for. I guess I could have got caught up w/velocity and took the load that was shooting almost 3000 fps, but I saw the wide node between 2830 and 2870 . I loaded 85 gr of Retumbo behind the 240 @ 2850 fps and the rifle shoots .25 MOA @ 100 yds.

I'm not sure of the group sizes @ longer ranges yet, but can tell you I nailed two consecutive milk jugs @ 950 yds and a whitetail @ 503 yds. I'm going to have to agree w/BountyHunter on this one. I believe a chrono can be used to find accuracy nodes as I did w/this rifle. Just remember that accuracy is the first priority, not speed.

 

[30-06 boy]

i have shot competitive 1000 yard benchrest.(its been a while though).but in my experience a chronograph's extreme spread will let you know if your case prep and things are in line.if not your loads will be all over(velocity).if your extreme spread is too much you might verticle string shots at long range.what are the "fella's" thoughts on this?

 

[ss7mm]

Most of the time you aren't going into load development and testing "blind". By that I mean that you usually have some idea as to what loads have been used and what velocities have been attained with those loads, and what will probably be the range in which you will find a useable powder charge.

All chambers and barrels aren't created equal. The load that gives certain results in a barrel and chamber that has most of the dimensions on the loose side will give entirely different results than the same load in a combination that has specs on the tighter side. The chronograph allows you to track the velocities and you can keep track of whether they are following the charge increases like they should.

Most people can't afford pressure testing equipment but just about everyone can afford a chronograph. Sometimes pressure signs may not show up as quickly and easily in a custom action using quality brass, but the velocity of each shot shows up each and every time a bullet goes down range.

Long range shooting would be much more difficult if done without a chronograph. Ending up with large velocity spreads and not knowing it would just drive you crazy when you start getting vertical stringing at extended ranges. Track it with the chrony and you know as soon as it starts to go south on you.

I have also found that usually the velocity results closely track the accuracy results of my load testing. I also base all of my final load decisions on the most accurate load, not the fastest load. I believe that you will find that the vast majority of the long time shooters on this site will choose the most accurate load every time, and not the fastest. Speed is just another parameter that needs to be documented and tracked.

What I'm saying is I consider the chronograph to be one more tool that gives me additional data to help me keep track of load development and testing both in cold weather and hot weather. The more data you have to make your decisions, the more accurate the decisions will be. Why would you not want every available bit of information you can get your hands on?

 

[green 788]

I think chronographs are great for helping to plot trajectories and estimate energy, but not for deciding on which load to use.

If the shots are stringing vertically at 1000 yards, it doesn't matter what the chronograph says.

And if the shots are nesting nicely at 1000 yards, it doesn't matter what the chronograph says. /ubbthreads/images/graemlins/smile.gif


Dan

 

[Bart B]

30-06 Boy, you're right. Muzzle velocity spread will cause more vertical shot stringing if it's too much. All one has to do is look at down range drop tables for your bullet at different muzzle velocities to figure this out. Example, a .30-06 with 100 fps muzzle velocity spread will have vertical stringing at 100 yards of just under 2/10ths inch. At 1000 yards it'll be almost 40 inches.

Good long range shooters will notice this without a chronograph 'cause their shots won't hold elevation.

Then there's the issue that no two people will get the same muzzle velocity with the same rifle and ammo. There can be 80 to 100 fps difference caused by how they hold the rifle.

 

[bailey1474]

[ QUOTE ]
Then there's the issue that no two people will get the same muzzle velocity with the same rifle and ammo. There can be 80 to 100 fps difference caused by how they hold the rifle.

[/ QUOTE ]

What??? I'm no expert, but how could this possibly make any difference? The same powder charge, the same primer, the same brass, the same chamber, the same bullet, and the same bbl. I'm not buying this. There is no way one person's "holding the rifle different" can make the internal ballistics of the rifle change.