Puzzled about chronograph

[WBY MAG MAN]

Hello again all, I recently picked up A chronograph, it's A Prochrono Digital. My question or problem is, how do you tell if this thing is working right! Some of my test's are reading very closely to advertised speck's ( Nosler,Speer,P.O. Ackley,Hodgden). While others are off A country mile.(Lyman, Barnes#3,Alliant) Along With many factory load's. I am doing every test the same and I am not saying the later 3 and factory's are not right! But I am getting as much as 150-200fps on some of these load's, is that normal ? I am shooting 3 to 5 shot's and averaging them out. I would say 97% reading low 3% high (guessing on this). I don't no if I got A bum unit, or they are just that far off!! ANY help or prior experience with this would be greatly appreciated as I am lost here...Shoot well...Shoot often...Shoot safe.... Thank's....Jerry

[zonie]

I have an older Pact model 1 that I have been using for 14-15 years  and never had any problems with it that was not my fault.  Of course you have to read the directions and follow them.  My Pact doesnt like overcast days  and I have to position it correctly so the sensors pick-up the shade of the bullet when passing thru.  I have used mine for pellet guns, arrows, shotguns, rifles and pistols and all worked fine.  As far as velocity is concerned,  you just learned a good lesson,  advertized velocity's are just that and does not mean that you will be getting those speeds,  on the flip side I have gotten higher than expected velocity's in some rifles,  each rifle is onto themselves, some may have tight chambers and built more pressure/velocity some may not, barrel length plays a part, etc.  I suspect  with out knowing your exact set-up, your chronograph is probably right.  150-200 fps is not out of the realm,  If they were shooting 300 fps slower in a BBL of say 22 " and their test figures were using a 26 " BBL,  I would raise an eye.  The big manufacturers use specific guidelines when testing, Temp, altitude , test guns, etc. all these  effect  bullet velocity.  When I first started using mine I asked the same questions, then I corrected velocity by using different loads etc.  that's what's cool about a chronograph.  Honestly I couldn't be with out one anymore, but I have been known to be a perfectionist.  The only real way of knowing if your unit is correct is either send it back or test it against another chronograph.  good luck

[Oregon Jim]

A chronograph also showed large variations in my bullet velocity, so much so that there was no way that I could have shot decent groups. Simply put, I didn't believe it. I am extremely finicky about accuracy in my reloading and could not believe there would be so much difference from round to round.

After asking everyone I know about this I have concluded that either the chronograph was not very accurate, or I was shooting too from close to the chronograph. I suggest that you move your chronograph another ten feet or so farther away from the chronograph just in case the muzzle blast is affecting the unit.

[dubyam]

Velocity variation will tend to show accuracy issues at longer ranges than 100yds, as the time of flight is so short to 100yds (especially for Weatherby rounds!) that it often doesn't factor in to point of impact.

As for the chrono readings the original poster was speaking about, I'm with zonie.  It's very likely an issue with the loads, not the chronograph.  I've shot a variety of guns across my chrony, and a PACT Professional, and have even used both concurrently to double check.  Velocities were very close or exactly the same, so I believe both chronographs are reading true.  For many rifles I work with, I've had variations against the published data.  That is compounded by the overly optimistic data reported in many of the most recent manuals which show the same or increased velocities with lower powder charges than previous editions of the same manual.  As Scotty said, "I canno' defy the laws of physics, Captain!"  Chronographs are one of the most useful and necessary tools for a handloader, and yet considered a luxury item by many loaders.  Velocity is the one thing that is most directly proportional to pressure, and thus an invaluable indicator of what's really happening in your rifle.

There's a reason we call chronographs 'de-liars'...

[Chip]

Your chrono is probably reading correctly.  While working up a load for a 270 WSM I shoot a few to see what combo had the best and most consistant velocity figuring those would probably group the best. Well when i went out and checked the groups at 100 yards guess what?  I was wrong.  Now in my wifes 7-08 the velocity from shot to shot in a string was really low a couple of feet per second and it shot like gangbusters.  I think it depends on the gun the way the stock is bedded and barrel vibration as much as consistant velocity.  I think you'll find that loads that shoot well exhibit a low extreme spread but you'll also find that there are loads with low extreme spread that don't shoot for crap.  It's a wonder handloaders don't all have eye twitches   

[WBY MAG MAN]

Thanks again gent's, I knew you guy's would be A big help!!! I went back out today, backed up my result's on my gun shop owner's crono side by side with mine. Result's were all with in 20fps. It was A perfect day to try many different test! A big cloud would roll over, different result, either slower or error read out.Brought out the "BIG GUN" 338-378 put crono at muzzle, again error read out,I believe do to extreme muzzle blast as one of you mentioned, moved it out 10 feet, got A consistent 3360 to3370 read out. Just what it's supposed to be. I also have 3- 7mm mag's, 1 Remington, 1 Winchester, 1 Ruger I borrowed all with 24" barrel's. I shot same load in all, and as you all said every one had A different read out with 107fps spread between them! Ruger and Win. were close at 16fps average apart and Rem. 91fps faster!! Talk about education time!!! Now on to the 30-378. I was out last Tuesday and dialed it in, out to 300yrd's from 100 where I had to quit the week before do to lack of hand load's. I had no crono, just A lead sled and good scope. The target is in "MY TROPHY ROOM" A couple clik's on the scope and I was touching 4 bullet's 1" high at 314yrd's, according to my book these are supposed to be at 3420fps. They are actually averaging 3456 after 10 shot's across the crono!! I was wondering why it started out shooting high? not that this is bad but I to am A bit of A perfectionist and assumed these book's, crono's, etc were more exact than they are.(to many year's building Winston Cup cars). With you guy's wisdom I now know these are are all just tool's to set up some guide line's for my own hand load's. If I want to know exactly where my bullet's are dropping to, then I must load for and shoot the different distances and do the math and not rely on published data selling hype so you / I will buy "THERE COMPONENT"S"...... I again thank you all for your insight and wisdom...Shoot well...Shoot often... Shoot safe.. Jerry

[Oregon Jim]

When I began shooting at longer ranges I did not have access to a chronograph, so I was forced to use the estimates from the manufacturers and reloading manuals. The longer the range I fired, the more deviation there was from the estimates, so I decided to use a different approach.

I went to a ballistic calculator and figured out what velocity matched my bullet performance at all of the distances I was shooting. The estimated velocity for my particular load was 3035 feet per second, but using my backwards method I determined that my average velocity is really a meager 3015 feet per second. Though I was unhappy with the reduced velocity, I was thrilled to have numbers that matched what I was shooting.

Again, using the ballistics calculator, but this time using the wide spread in velocity indicated by my friend’s chronograph, I determined that it would be all but impossible to shoot as accurately as I was shooting with that velocity deviation.

In the end I decided that all that was really important was matching my calculations to my bullet flight.

[WBY MAG MAN]

Oregon Jim; Your last sentence say's it all !! And I agree 100% !! I should have known this from the start. As A race car builder,I experienced the same thing. If I would have bought everything that was supposed to add 5 horsepower here 8 there etc,etc I would have had A 1200 horsepower Winston Cup car that weighed 2900lb's (impossible) instead of 825hp @ 3500lb's!!! What I plan to do now is check velocity, shoot my different ranges, and reverse engineer my bullet drop and then use that to figure true velocity and energy if the tables are right. I only use 1 load in each of my gun's so I can really get them dialed in. I play with them until I find what it like's in the caliber I want to use in it. Small gun, small animal, big, ect, ect. with 25, I cover just about all of them from 223 to 338-378. I still have the web site you gave me for the ballistics and I'm going to start there! I do appreciate all your help over the last few week's!!! Thank You again...Jerry  Shoot well...Shoot often...Shoot safe

[dubyam]

If you've built race cars, you understand that two identically prepared small blocks with the same parts, built by the same hands, in the same shop, will have different dyno runs.  There's a little 'art' in everything mechanical!

What you're doing as far as determining your actual trajectory is affectionately known as "shooting your drop chart" and is the last step in the process.  I use data and simulation to give me an idea of what I want to try to accomplish, and what loads will match that.  Then I work up the loads.  Then I shoot out my chart, because there are too many variables in place to rely on simulations.  Even the BC of the bullet is not some fixed number.  You can likely relate that to CD from your racing days - ambient temp, pressure, and humidity can all affect the actual BC, as opposed to the theoretical BC derived by software or testing.  Expect some variation in your drop (though not enough to matter in hunting situations at common ranges) due to temperature and atmospheric variations in the field.  Might be an inch difference at 400yds, might be two.  Always verify your drop chart on the range.

I'd love to hear some of your stories sometime - I used to be a huge race fan, back when I had time to watch and keep up.  Even got a face full of Goodyear a few times sitting at the end of the trioval at Talladega...but that was back when several guys were still alive and racing who are missed by the sport still.

[zonie]

Hi Jerry:  MOA is  1.047 "  @ 100 yds,  double that @ 200,  triple that  @ 300, and so on.  Most people just refer to it as 1  " @ 100 yds.  Anything under that is considered sub-moa.  To measure your group measure center to center the farthest shots,  another way to measure when all bullets are toughing  is measure outside to outside farthest shots and subtract one full bullet diameter, Your target group at  314 yds is really good,  Just shows you what a non benchrest rifle can do when loaded to it's potential.  Duby is right a lot of variables. I have always found the Speer BTSP shoot well.  I use the 85 gr BTSP in an old rem 788 in 243 which shoots wonderful, usually one ragged hole  @ 100 yds when I'm doing my part.

[Charles B]

When having problems with chronographs and lighting / spacing are good.  Fire some .22 long rifle target ammo across the screens.  This ammo will be very close to the rated speed and verify your chrono.

Check over on the 6mm BR site for free target analysis software called On Target.  Great program for the handloader.

[WBY MAG MAN]

Hello again, I have read all your post's and will check the site's you mention! zonnie, thanks for the explanation, been wondering what you guy's were talking about. dubyam, your absolutely right,  when working under Roush, of 100 engine's none of were the same!! Kinda make's you wonder about the I.R.O.C. series! They were close but could very 25 horse power depending many different aspects. As of now you guy's have me dialed pretty good. I am trying to get A rifle done every other day or so. Will let you know how its going later! Thanks again guy's...Shoot well...Shoot often... Shoot safe...Jerry

[dubyam]

Keep us posted on your results.  It's all good when you're at the range!

Roush?  I'm assuming you're located somewhere in north Michigan?  If you're down here in the good old southeast somewhere, let me know.  I'm in north Alabama, and always looking for a range partner who is as detail oriented as me.  I have CDO.  It's like OCD, but with the letters in alphabetical order, like they're supposed to be!