Chrony readings

sailrecovery · Post by **sailrecovery** » Tue Jan 13, 2009 9:28 pm

When you chrony your AP do you check fps close to the AP or close to the target?

RobStubbs · Post by **RobStubbs** » Wed Jan 14, 2009 3:17 am

sailrecovery wrote:When you chrony your AP do you check fps close to the AP or close to the target?

Closer to the pistol. Just make sure it's at least 2-3 foot beyond the end of the barrel (or whatever it recommends in the instructions).

Rob.

Spencer · Post by **Spencer** » Wed Jan 14, 2009 4:55 am

Out of interest, anybody know what the difference is between MV and velocity at 10m for a target pellet?

Spencer

toznerd · Post by **toznerd** » Wed Jan 14, 2009 3:31 pm

The velocity will be probably be 0 fps, depending on the backstop, (unless the pellet bounces back, and then it's a negative number!)

Sorry, I couldn't resist. Actually, I'm a bit interested in that info myself. Is there anyone here that hunts with wadcutter pellets and knows the ballistic coefficient of a .177 wadcutter? Any field target shooters out there keep track of the terminal energy of their pellets at 10m?

toznerd

Oz · Post by Oz » Wed Jan 14, 2009 5:21 pm

There was an episode of Mythbusters and some fans were complaining about measured projectile velocity according to position.

The Mythbusters believed that the difference in velocity was negligible for the point they were making. But to prove it, they chrono'd initial velocity as well as target position (on the order of 5-7 meters). The difference was insignificant.

But this should be something easy enough for a member of this forum to test I would think... I'd like to hear about 10m AP specifically.

If nobody gets to it before I do, I have a buddy with a chrono and I'll see about taking a crack at it. Hopefully someone here can do it tonight!

Spencer · Post by **Spencer** » Wed Jan 14, 2009 6:29 pm

Oz wrote:There was an episode of Mythbusters and some fans were complaining about measured projectile velocity according to position.

The Mythbusters believed that the difference in velocity was negligible for the point they were making. But to prove it, they chrono'd initial velocity as well as target position (on the order of 5-7 meters). The difference was insignificant.

But this should be something easy enough for a member of this forum to test I would think... I'd like to hear about 10m AP specifically.

If nobody gets to it before I do, I have a buddy with a chrono and I'll see about taking a crack at it. Hopefully someone here can do it tonight!

I think it would take two chronographs that are 'cross-calibrated'

Spencer

Gwhite · Post by **Gwhite** » Thu Jan 15, 2009 7:05 pm

I'm surprised nobody mentioned the Combro CB625 air gun chronograph. It straps directly to the barrel, so it's very much a "muzzle velocity" device. I've never used one, and I'm not even sure who sells them in the US. They seem to be very popular in the UK.

Oz · Post by Oz » Thu Jan 15, 2009 7:20 pm

Spencer wrote: I think it would take two chronographs that are 'cross-calibrated'

That would be an elegant solution! I was just going to take 10 shots at the muzzle -averaged, and 10 shots at the target -averaged.

RobStubbs · Post by **RobStubbs** » Fri Jan 16, 2009 3:37 am

Oz wrote:
Spencer wrote: I think it would take two chronographs that are 'cross-calibrated'
That would be an elegant solution! I was just going to take 10 shots at the muzzle -averaged, and 10 shots at the target -averaged.

Somewhat easier to do and easier than trying to find a second (and equally calibrated) chrono.

I'm surprised nobody mentioned the Combro CB625 air gun chronograph. It straps directly to the barrel, so it's very much a "muzzle velocity" device. I've never used one, and I'm not even sure who sells them in the US. They seem to be very popular in the UK.

People in my club have used them but they are at best troublesome. Most of the time they fail to register anything and are fiddly to attach to the gun. I'm sure they're pretty inacurrate as well so of limited use in reality. Suffice it to say that no-one in the club uses one now.

Rob.

David Levene · Post by **David Levene** » Fri Jan 16, 2009 4:17 am

RobStubbs wrote:
I'm surprised nobody mentioned the Combro CB625 air gun chronograph. It straps directly to the barrel, so it's very much a "muzzle velocity" device. I've never used one, and I'm not even sure who sells them in the US. They seem to be very popular in the UK.
People in my club have used them but they are at best troublesome. Most of the time they fail to register anything and are fiddly to attach to the gun. I'm sure they're pretty inacurrate as well so of limited use in reality. Suffice it to say that no-one in the club uses one now.

That's a surprise Rob. I have had one for years and, apart from a battery terminal breaking (when they sent an immediate replacement unit and LOADS of batteries as compensation) have found it to be reliable, consistent and easy to use.

I made a special bracket to fix it to my LP5 so that, with the cable attaching the unit to my laptop, I can get readings for the 5 consecutive shots easily.

For the 162EI I just remove the front sight and the supplied bracket then works fine.

As regards accuracy, I couldn't care less. I am more interested in consistency. I know that when my guns have just been serviced I get readings +/- 2fps. I also know that when the reading drops by about (an indicated) 20-30fps or the consistency deteriorates it is time to get the gun serviced. (Early excuse for the BPC Open Meeting this weekend, my 162EI is WAY down on velocity and is at the limit of adjustment. It's being serviced next week)

In the UK the price is just under £40.

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Chrony readings

Chrony readings

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