View Full Version : Chronograph On Home Loads...
07-15-2011, 11:06 AM
I just received a small simple Chrony Chronograph and used it for the first time with some .38 special re-loads I just finished. All of these .38's were carefully prepared and I used a electronic weigh scale to get the powder at the same grains down to the same tenth of a grain but the results from the chronograph show some large variations in feet per second after shooting the rounds. In 25 rounds the fps ranged from 960-1209 with the vast majority around 975 feet per second. Are my re-loads that different, am I setting up the chronograph wrong, or are these cheaper chronographs that innacurate? I really don't know what I expected! Any tips would be appreciated...
07-15-2011, 11:39 AM
I had the same problem with my Chrony. Turns out that I needed to move the device about 10 feet out from the end of the muzzle to get "real" velocity, not the blast velocity.
07-15-2011, 12:07 PM
Strange you mention that, I just got done doing the same thing just yesterday. Not with a handgun but I too was getting those very odd readings. It got me thinking for a bit and then it dawned on me that the censors (1 in back and 1 in front) had to be juuuust right, I had mine on a slight angle. After that it seemed just fine, and for the remainder of the session all was ok. And I had mine at 10ft away as well. Just can't get myself to try it with the scattergun yet, don't want anything I cant control hitting the screens.
07-15-2011, 12:29 PM
I loaded these 38 specials light with 110 grain bullets and 4.6 grains of HP-38 which the charts show as a beginning load. All the casings were cleaned, sized, flared, primed, loaded with powder, bullets seated and crimped at the same time so deviation I assume is not from that aspect but who knows? From the posts so far, here and on another site, I gather I was way too close to the chronograph at 3.5 feet and muzzle blast is probably the problem. I was afraid I might shoot the chronograph at a longer distance! I'll try some more rounds this weekend with the chronograph further away. Hopefully I won't wound it in the process!!!
07-15-2011, 12:34 PM
I shoot that bullet Lee 90316 w/ 4.0 grains of Red Dot in the.38 Spl...1,012 avg FPS MV---however I find it best to use a poly filler as it lowers the spread quite a bit. Very accurate bullet/load out to 100"..the max range I shoot them for when plinking. Also shoots great in the Marlin 1894C... I like this bullet as it saves a lot of lead.
07-15-2011, 01:40 PM
Thank you for the information. You were all right in that I had the chronograph too close to the shooting bench. I moved it out about 12 feet and tried out some 30-30 Winchester loads I worked up this last week and the FPS were all very close. Thanks!!! :)
07-15-2011, 07:40 PM
3.5 feet is way close. You also will find that some loads just have large extreme spreads. And those loads may well be very accurate. Lint loads can be bad this ay as the small share isn't always ignited really consistently.
Like anything else in shooting, there is a learning curve with a chrono
07-16-2011, 03:17 PM
As you found you were measuring the bits of powder and other ejecta as well as the bullet. I set my chronograph up with a tape measure at 10 feet from the muzzle to the front of the chrono to help make more meaningful comparisons from session to session.
Measurements get flaky if the sun gets too low on my chrono.
Carefully weighed loads don't necessarily chrono with great consistency for me especially with handgun loads. I had some SR4756 give over 100 fps SDs with weighed charges. Maybe it's just me but I've read several good articles lately and a few things seemed to make a lot of sense. Take it all with a grain of salt. Most gun 'riters are ordinary people like the rest of us. One of the thoughts was that a dropped charge packs into the case more consistently when falling from a measure than when poured though a funnel from the powder scale pan. That is probably much more of an issue with nearly filled rifle cases than half filled handgun cases. Another suggestion that made a lot of sense, and this was from a benchrest perspective, was that variables in power weight from a measure are one of the smallest variables in the equation. A .2 gr variation at 40 grains is 0.5%. H4895 throws +/- .1 for me with an old Saeco measure. A .2 gr variation at 4.7 grains is a touch over 4%. With all of the other variables in handgun shooting that's probably close enough for most applications. The writer pointed out that wind, primers, temperature, shooter and a host of other variables exceeded the variable of thrown charges. Wish I could remember where I read it!
After reading and mulling over the article I've started throwing all of my .223 and .22-250 test loads rather than weighing each one. Even for 10 loads it's no slower to set up the powder measure than to trickle 10 loads. The SDs are surprisingly low, often running single digit to less than 20 fps over 5 shots. Until something surprises me I'm a believer in these ideas.
Don't believe just 'cause I wrote it but give it a try.
07-24-2011, 07:07 PM
Some really high velocity variations (extreme Spread or ES) are possible.
I have yet to figure that out as it does not seem to be "the" indicator of accuracy actually precision that one would assume.
Short distances between sky screens may well add to the variation.
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