Dirtdigger
Regular
- Location
- Vancouver Island, B.C.
How much deviation in fps can one expect when measuring velocity at the bore, and 10-15' out? Just averages.
Thanks, Derek
Thanks, Derek
Muzzle velocity
- Thread starter Dirtdigger
- Start date
I've found that the higher the vel., the higher the SD, quite often 100fps or more. Properly loaded Black Powder cartridges can yield very low SD in the 5-10fps. range. I've also found that the load with the lowest SD does not always yield the best accuracy.
Northman999
CGN Ultra frequent flyer
- Location
- Southern Yukon
I usually get about (+/-) 10-15 fps FPS difference bewtween shots with most of my loads.
Generally find that the less SD the more accurate - obvious enough, but gotta do it to find out. Most of my best hunting loads eventually wind up less than 15 fps extreme spread, if I was paying attention. As far as measuring at the muzzle, I've never tried - pretty sure the larger caliber stuff and "pushed" loads would probably disassemble my Chrony for me. Blast off my .45-70 is pretty severe, so I measure closer to 15 ft from the muzzle.
For reference, my last two loads of my target round (175smk, 44.5gr of Varget in .308 in federal brass, assembled with Lyman reloading gear and lee dies) had extreme velocity spreads of 20 & 23fps and standard deviation of 5.5 and 9.5.
It shoots .7-.3 groups depending on me.
All figures measured 10' from the muzzle.
It shoots .7-.3 groups depending on me.
All figures measured 10' from the muzzle.
Dirtdigger
Regular
- Location
- Vancouver Island, B.C.
Good luck measuring velocity at the muzzle with a cheap chrony...
My answer to the question is 0
Stopped after I blew the screens off.
Inquiring minds and all.
If you are asking how much does velocity drop between muzzle and 15', we don't really know, because other than air rifles, we can't set chrony that close to the muzzle. So called muzzle velocites are always measured 2 or 3 yards from the muzzle.
If you are asking about how much extreme spread can you expect, I would say 50 fps for mediocre ammo, under 25 fps for good ammo and under 10 for very, very good ammo - 10 shot tests.
The Chrony factory is about 20 miles from here. They come to my range from time to time to test their product. I guess they change part suppliers from time to time or develop new models.
They mount a series of Chronies on a long board and fire a shot through all of them at one time. The centre position is a fancy Ohler. How accurate are they?
Well, we have to define accuracy. Assuming the Ohler is accurate, each Chrony I have observed is within 20 fps of the Ohler reading. That is good enough for any purpose.
But what we want to do, usually, is not know the excact speed of a bullet, but the exact difference from shot to shot. The Chrony is very good at that. It has a very high clock speed, so measures 5ps variations very well.
Two hints. The Chrony folds. Make sure it is fully extended when using it. Otherwise the screens are not vertical and velocites will read too fast.
When you shoot across a Chrony (and maybe other makes, too) it is important to shoot across the exact same place. That is, you should ahve something on the otehr side to aim at. If you shoot at various angles, that can cause a 10 to 15 fps variation, all by itself.
If you are asking about how much extreme spread can you expect, I would say 50 fps for mediocre ammo, under 25 fps for good ammo and under 10 for very, very good ammo - 10 shot tests.
The Chrony factory is about 20 miles from here. They come to my range from time to time to test their product. I guess they change part suppliers from time to time or develop new models.
They mount a series of Chronies on a long board and fire a shot through all of them at one time. The centre position is a fancy Ohler. How accurate are they?
Well, we have to define accuracy. Assuming the Ohler is accurate, each Chrony I have observed is within 20 fps of the Ohler reading. That is good enough for any purpose.
But what we want to do, usually, is not know the excact speed of a bullet, but the exact difference from shot to shot. The Chrony is very good at that. It has a very high clock speed, so measures 5ps variations very well.
Two hints. The Chrony folds. Make sure it is fully extended when using it. Otherwise the screens are not vertical and velocites will read too fast.
When you shoot across a Chrony (and maybe other makes, too) it is important to shoot across the exact same place. That is, you should ahve something on the otehr side to aim at. If you shoot at various angles, that can cause a 10 to 15 fps variation, all by itself.
They mount a series of Chronies on a long board and fire a shot through all of them at one time. The centre position is a fancy Ohler. How accurate are they?
QUOTE]
Jim, how many can you get with one shot?
I stopped counting after I shot the 7th Chrony, but it took several years to run up that many kills.
The problem is testing target rifles with 20X scopes. I could not see the Chrony rods well enough and shot the Chrony.
Worst time was when I set the Chrony up in front of my rail gun, mounted on a concrete bench. First shot blew it away. No idea how I did that.
But when I set it up at 100 yards, to get downrange velocity, I have never so much as scratched one.
I have since solved the problem. My new scopes will focus fairly close and I aim at a aiming mark so shots are consistent and clear the Chrony.
Chrony leave them behind after each test, so I got lots of them.
BTW, it is a good idea to tape a spare battery inside the Chrony, becasue if the battery dies at he range you are SOL without a new one.
The problem is testing target rifles with 20X scopes. I could not see the Chrony rods well enough and shot the Chrony.
Worst time was when I set the Chrony up in front of my rail gun, mounted on a concrete bench. First shot blew it away. No idea how I did that.
But when I set it up at 100 yards, to get downrange velocity, I have never so much as scratched one.
I have since solved the problem. My new scopes will focus fairly close and I aim at a aiming mark so shots are consistent and clear the Chrony.
Chrony leave them behind after each test, so I got lots of them.
BTW, it is a good idea to tape a spare battery inside the Chrony, becasue if the battery dies at he range you are SOL without a new one.
Yes. Most are tests of proposed new parts or suppliers. Not the sort of thing he woudl want to sell. Besides, Peter is a nice guy and it is his way of saying "thank you" for my help and the use of my range facilities.
Have not seen him for a few years. Hope he is ok...
Have not seen him for a few years. Hope he is ok...
Only 7? Surely that must be a Canadian Record
I've only shot one and that was due to a hangfire with a shotgun slug. Did you know if you hit one of the wires with a 1 oz 12 ga slug the chrony will spin around on the tripod like a helicopter blade.
I've only shot one and that was due to a hangfire with a shotgun slug. Did you know if you hit one of the wires with a 1 oz 12 ga slug the chrony will spin around on the tripod like a helicopter blade.
