How much difference does it make if I place my chronograph about 10' from the muzzle vs 5'? I am talking bullets in the 3000-3500 fps range.
Thanks

It depends on the bullet, the atmosphere, etc. Basically, probably not a lot. Maybe around 15fps? Pull up a ballistics app like JBM or something and experiment. A low BC bullet looses speed faster than one with a high BC. Same with more dense air....

Thanks

I'd be careful about anything closer than about 10'. Muzz;e blast could cause problems.

Nothing whatsoever!

JBM says that my 6.5x284 load has a corrected muzzle velocity difference of 2.8 fps when comparing chronograph readings from 10' in front of the muzzle to 5'.

Muzzle blast gives erratic reading if very close!

Wait til you let a 500Nitro off at that distance

Don't ask me how I know

Go to http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi and you can calculate the velocity of any bullet at any distance.

I usually put the center of my Oehler screens, which are four feet apart, at about 10 feet from the muzzle. This is far enough to eliminate interference from muzzle blast. If the velocity average is, say, 3069 fps, then I round it up slightly for recording the muzzle velocity as something like 3075 fps. Close enough for gov't work.

I have used a Chrony since they were first sold and I have never, ever pondered the difference between the velocity at the muzzle and the Chrony set at 10ft. Exactly what is the purpose of that?

quote:

Originally posted by wasbeeman:
I have used a Chrony since they were first sold and I have never, ever pondered the difference between the velocity at the muzzle and the Chrony set at 10ft. Exactly what is the purpose of that?

Exactly.

Variation between shots in the string will more than the difference you might see.

From a practical point, nothing at all.

I stopped using chrony when started to shoot .500 S&W. At least ~7 yards or meters was distance it started to measure. Now using Labradar.

well, at 10ft you MIGHT get good readings - 15-20 is better -- at 5', you likely will get the screens blown off and erratic shooting ....

add 2 fps if you like -

my lab radar obviates the risk of erratic due to blown off and over sensors

Thanks again guys. I was shooting a gun and getting readings that I thought were 150 fps too slow. I had my chrono about 10 feet from the muzzle. I was wondering if that distance would give much lower readings.
You guys have answered my question, thanks.

My chronograph is always set up 10' from my muzzle, whether I'm shooting my 22.250 AI at 4,300 fps or my 458 Win Mag at 2,200 fps

you could extrapolate at zero -- shoot 5 at 10', and 5 at 20' -- find the difference, and add to the 10' reading .. it'll be close enough ...

low price chronos have been making liars of reloading books for decades

i personally feel that there's a few VERY important reloading tools

quality scale
micrometer
chrono

are three of the best ones

I shoot through my Oehler 35p at 10 feet from the muzzle. Do yourself a favor and buy a Magnetospeed. It is relatively cheap and is the only chrono I have ever found that rivals the Oehler 35P in accuracy. No need to worry about setting up a chrony perfectly. No need to worry about light. No need to leave the shooting bench. Can even be used at indoor ranges. Easily packs for travel. I still have the Oehler, but it rarely gets used.

I have checked my Magnetospeed MVs out to 1500 yards on a couple a calibers and found the chrono to be right on the money.

Brian Litz conducted probably the most extensive testing of shooting chronographs ever performed, and the Magnetospeed was the top performer for accuracy.

The Magnetospeed and the 35P are the ONLY chronos I trust. MOST chronographs that shooters use are nowhere near accurate enough to be trusted, and you are wasting countless hours and countless loading supplies shooting through them.

My best friend bought a labradar last year, but has had some issues with that, especially while at a crowded range.

With a good chrono, you can easily find accuracy nodes without even shooting groups (I frequently just shoot into a hillsde with my magnetospeed attached). And a good chronograph is the ONLY way that you are going to get your reloading practices under control and get the lowest ES possible.

If I had a unit like the Shooting Chrony, Super Chrony, Pact, or PVM; I would just shoot ladder tests and not even bother using the Chrono. Mater of fact, Litz found the PVM-21 and super chrony to be so bad, that it was misreading on average 78fps off of true MV and was showing extreme spreads as high as 48fps (when it was actually 3). You are never going to properly dial in a long range ballistic solution with those numbers.

I just bought a magnetospeed. Best purchase this year. Easy to use, easy to set up, easy everything. No need to worry about shooting low and killing it.

Interesting. I have proofed my Chrony against some of the higher priced units and it has always been dead on. Not bad considering the unit is 25-30 years old.
How do you determine an accuracy node by merely shooting into the side of a hill without any idea of where the bullets are hitting?
Also interesting that you and Desert Dog became new members just in time to tell us what a hot item the magnospeed is.

quote:

I have proofed my Chrony against some of the higher priced units and it has always been dead on.

+1

quote:

Originally posted by wasbeeman:
Interesting. I have proofed my Chrony against some of the higher priced units and it has always been dead on. Not bad considering the unit is 25-30 years old.
How do you determine an accuracy node by merely shooting into the side of a hill without any idea of where the bullets are hitting?
Also interesting that you and Desert Dog became new members just in time to tell us what a hot item the magnospeed is.

If you were not proofing it against a properly set up Oehler or verifying ballistic solutions at the supersonic limit, then both units are likely off (just not enough to really matter at a couple hundred yards).

Using a Chrony only to find accuracy nodes has become a very popular method. Check out some of the videos that Scott Satterlee does.
https://www.youtube.com/watch?v=ACyfeeBHVOA

Here is an example of an accuracy node I found using ONLY my magnetospedd while firing into a dirt hillside at 50 yards;


I chose the 42.3gr load because it was right in the flat spot and had a super low ES. Loaded up a small batch, and shot this for my first group:


This method works and saves a lot of ammo. It is basically a ladder test, without shooting a target. BUTTTTT, you MUST have a very good chrono set up PROPERLY to make it work.

Link to the Brian Litz Chrono testing from his book "Modern Advancements in Long-Range Shooting":
http://www.appliedballisticsll...ronographChapter.pdf

I have always added 10 fps and put my Oehler 35 screens 10' from the muzzle. I have only used my Labradar a few times but I like it. At a crowded range you just turn down the sensitivity. I also like not having to shut down the range to set it up.

I could never use a Magnetospeed because it will effect groups sizes and POI by being attached to the muzzle. It's important to measure velocity WHILE developing a load. Often, the chronograph is the first sign of high pressure, and often you get great groups with poor extreme spreads--meaning it's not a good load. I want to see that while I am developing a load, not after the fact.

quote:

Originally posted by INTJ:
I could never use a Magnetospeed because it will effect groups sizes and POI by being attached to the muzzle. It's important to measure velocity WHILE developing a load. Often, the chronograph is the first sign of high pressure, and often you get great groups with poor extreme spreads--meaning it's not a good load. I want to see that while I am developing a load, not after the fact.

All true. THE MS does change POI, but The Magnetospeed works so well for me because I don't shoot for groups while finding accuracy nodes (too much human err involved to be reliable). I shoot into a hillside without aiming and graph chrono readings to find my accuracy nodes, then shoot for groups and play with seating depth later if needed without the magnetospeed. The magnetospeed is just so small, accurate in all conditions, easy to set up, and cheap in price.

Shooting for groups during initial load development will introduce human err into the equation and mask real data.

My first two chrono's were Chrony's.
I learned quick two things.
Anytime the whole works is in front of the muzzle it means they're trying to sell more of 'em for those of us that shoot them up.

I had unburned powder grains go thru the thin plastic screen and ruin it. The next one I let a friend shoot and he hit a wire, wrecking that one.

After that I decided: Replace the wires with wood dowels, 40" piece for a dime will make five sticks. Cut a piece of 1/4" clear plastic to put in front of the screen. This goes for any brand or model that uses metal wire legs and those with the whole unit in front.
I also had a b/p patch hit a screen too.

Just some experience to share is all. Do it your way, don't matter to me.

George

I use an Oehler M33 Chronotach, and have for over 35 years. If I ever can, I will go to an M35. It will solve all of the problems I have with the M33.
(I guess that's why the M35 was built in the first place)
The only thing I can visualize is shooting the computor. I've shot the screens, diffusers, supports and cables, and they were easily fixed, sometimes replaced, sometimes repaired.
If I were to shoot the computor, it would be because something else was wrong. If you've ever seen an M33 or M35 used, you'd know what I mean, lol.
My M33 has the Skyscreens set up with a 5' spread, and the first screen at 5', giving an instrumental velocity distance of 7 1/2'.
I've never had any problems caused by distance, the only ones were caused by angle of sun, or brightness.
Early on, there were difficulties from putting the computor too near the muzzle, especially with handguns. It was quite interesting to see 3500-4000fps readings from a .41 Magnum with 210gr bullets, lol.
The largest rifle I use now is either a .300WinMag or a .375/348 Improved, and neither give erratic readings from powder effects, or vibration. I have reshot some of the loads a week, month or year later with no variation in velocities.
The difference in velocity readings from 7 1/2' to 15' or 20' instrumental, though calculable would be of no value to any other calculation.
Have fun,
Gene

for the magnetospeed users:

is there an appreciable accuracy difference between the sporter model and the V3?

I've had 6 or so different chron's. MS was accurate however did not like the shift in impact as I like to shoot for accuracy as well when working up loads. Oehler 35P is very accurate. I have two of them set up on the same 48" rail and they both read right on the money. But pain to set up. Now that I have a lab radar I don't see me using anything else. Just too simple to set up and cool that it will give you readings at multiple distances.