Trying to compute the muzzle velocity with my Chronograph set at about 10' from barrel. I'm shooting 270 wsm and was expecting 3000 fps and chronographed at 2840 average. 8 shots.

Would it drop off that much from 10feet?

Nope. The difference would be about 8 feet per second.

If you velocity came out where you expected, you wouldn't need a chronograph. Now you know why the are called de-liars.

you might wanna set that chrony out a bit further to avoid bad reading from muzzle blast.

I brought in the first Oehler 33 chrono to be seen at the range way back in the bad old days...I would test anyones loads for the data, but it only took a few readings way below what was "supposed to be..." to make me start packing iron, then stop altogether.

All it takes is a couple round from a 24" 264 Win and velocities a 270 Win beats all the time to make some folks see red concerning their favorite shooter.

It's not so bad now that chonos have been out for 40 odd years and they are cheap to boot...EVERYONE should have one...but people still have expectations...step on one of those things and be ready to go head to head...you can see that all over the net on forums of all kinds.

A chrono is just a timer and the clock can be off a few ticks very easily...my Beta Chrony is ~100 fs faster than my Oehler 33...that's set up one behind the other to get two reading at the same time. No matter where the chrony is, it's always faster.

Wasbeeman is right...step back a bit more...you can get strange readings from gas pressure, low batteries, COLD batteries, where the sun is located, with and without the sunscreens, light reflecting off the bullet, from ammo uniformity or actually UN-uniformity...etc.

Set the screens parallel, then perpendicular to the sun and try a few shots...the chrono is just a piece of machinery so don't take it as gospel.

I was doing some 444M load testing today and kept getting one high reading with one case...I weighed it and it was 5 gr heavier than the other 3 cases so the internal volume was slightly less...theoretically speaking...but enough difference somewhere to be 100 fs faster than the rest.

Lots of things can influence chrono readings, so let your targets talk to you more than the chrono...uniform, repeatable groups are better indicators of the "measure of central tendancy" value than any single or multiple velocity number.

Luck

If I have doubts about the reading I always
first move the chrony out anoyher 8-10 feet.
as the man sez muzzle blast can fool it.

It's been said, if you have a favorite hunting load, dependable and effective, never chrono it.
Another hoot is to look at some of the old ammo ads, back before every kid on the block had a Chrony, and you'll see some pretty optimistic velocity claims.

I find most loads are below book. I find a load that I like shoots well run it across the crony to find out the down range balistics.

If I want faster or bigger I buy a bigger faster cailber. I don't plan on making my 06 into a 300 mag ect.

Thanks Fellas. Yes the muzzle blast was knocking the plastic blades a flyin...

But as P dog says, I was trying to get the chrono readings to predict down range accuracy on the subtensions of the scope.

Ok, Before you cap on me, I know, I need to shoot at those ranges...

But this is part of the fun,,,guessing correctly...

quote:

Originally posted by p dog shooter:
I find most loads are below book. I find a load that I like shoots well run it across the crony to find out the down range balistics.

If I want faster or bigger I buy a bigger faster cailber. I don't plan on making my 06 into a 300 mag ect.

garyn, muzzle blast usually makes your reading higher, not lower. Temperature and other things will affect it as well. Chrony the same load a few times at different temps. It can be a real eye opener.

I haven't done this but a lot of shooters will "calibrate" their chronograph with a .22LR using the same ammo and gun everytime. 5 shots to average from the .22 to see if it reads the same as last time.

quote:

Originally posted by garyn:
Trying to compute the muzzle velocity with my Chronograph set at about 10' from barrel. I'm shooting 270 wsm and was expecting 3000 fps and chronographed at 2840 average. 8 shots.

Would it drop off that much from 10feet?

garyn:
I too have a .270 WSM and chrono my loads. Firstly, I'd agree that your chrono is too close for reliable use. I always set it at a measured 5 yards (15 ft.) from the muzzle and have never had a problem.
Addressing your anemic readings, I think it's possible to get readings such as that regardless of the info listed in your load manual. I've also found that Quickload can give rather wild predictions from what I've actually come up with. I've even recorded unexpectedly low velocities from some factory ammo I've run thru my rifle. Offhand, something like 150 or 200 fps under the velocity listed on the box.
My recommendation is to move your chrono to at least 5 yds. and perhaps put some clear tape over the sensors to protect them from dust, dirt, debris, etc. Although I use 150 gr. bullets exclusively, I correct velocity back to the muzzle and with a 150 gr. bullet, MV usually comes out to about 11 fps more than what the chrono records.
In reality, guess I'm just too anal about it.
Good luck.
Bear in Fairbanks

Yes, move the start screen to 15' from the muzzle with a magnum type cartridge. Better yet use that same distance for all testing to maintain correct comparative data.

The use of a .22LR rifle that you will always keep and a brick or two of quality match ammo is an excellent "reference" ammo/rifle that can be used to check the chronographs readings if something is suspect.

Screen spacing is critical. The Chrony fold out type must be folded out to the same place at each set up. If not discrepencies are inevitable. Screens that can be moved closer or farther apart can be "calibrated" with another chronograph of known performance or with the "reference" rifle/ammo if they get moved out of calibration. Moving the start and stop screens closer together will decrease the TOF measured and increase velocity. Farther apart increases TOF and decreases velocity. It does not take much movement of screen spacing to affect a large change in velocity. The shorter the screen spacing, such as with a Chrony, the greater the increase or decrease of velocity per movement of screen spacing. If the screens are not parallel and angled outward at the top a high shot will give a slower velocity than it would if shot lower across the screens. Visa versa if the screens are angled inward.

I use a 2' screen spacing on my M35P screens and a 4' with my M43 Oehler screens. Both have been calibrated to each other and I have epoxied the screens to the tubes so they won't move. I've also set up my M11, M35P and M43 Oehlers in line and calibrated all 3 together. Velocities I get are in line with manuals that use commercial rifles, not test barrels, for the listed velocities using the same componants. A change of conditions, componants and the use of a different rifle will sometimes give appreciably different velocity results. Velocity readings from "test" barrels will almost always be higher than what you get with a factory commercial barrel. All of those should be taken into account when comparing velocity results between what you get and what is reported. I always try to use data from manuals that show test velocities from real rifles not test barrels.

I've been using Oehler chronographs since '75 and have had a lot of other chronograph owners ask to set theirs in line with the Oehler because they think the Oehler sets the standard for accuracy. I think so too.

Most all of the chronographs tested proved reliable if they were set up properly. Of those that gave readings "off" I found the spacing not correct or, in the case of Chrony's, they weren't opened so the screens were parallel.

Larry Gibson

I'll be guilty of hijacking the thread and asking another question. Seeing as how some folks with chronograph knowledge seem to be around. Several years ago I was at the range and I don't have a chronie. A fellow that was there let me use his. I was testing some cast bullets in a .243. I was getting a reading around 2900 fps but according to book it should have been around 2500fps. I also tested some jacketed bullets in the .243 and they were about as expected. The chronograph owner had several rifles and he said they were all reading as expected. Was the reading a fluke and did the cast bullet cause it?

Yeah...my 33 is real touchy about screen spacing and can be "adjusted" by sliding the screens apart or closer in ~1/4" intervals.

Here is one good example of WTF...I'm trying to get some loads worked up for a Savage Edge/Axis...most worthless POS I've ever encountered...at least mine is...the stock flexes badly on the bench just from finger on the trigger pressure and the trigger was in the 10-12# range...DON'T BUY ONE...buy the standard Sav 10/110 instead...you WON'T have to buy a $100 trigger and if you don't like the stock there are plenty aftermarket ones to go around...so far there ARE NO AFTERMARKET STOCKS FOR THE AXIS.

Anyway...I ran the last two Hornady 100 gr bullets in the box over the Beta, 54gr RL-17, seated 3.28"(I long throated the barrel), standing ~15ft away and got readings of 3993fs and 4034fs. Something TOTALLY WRONG somewhere. No pressure indicators like a case welded into the bolt which would be the case at that actual velocity. The base showed ~0.0008" expansion, primers flattened but normal for the Fed GMM. I continuously check my powder scale while using it and all the loads were individually weighed, spot on.

I loaded up 3 100 gr Speer SP with the same powder amount - 54gr RL-17, same 3 numbered cases, fired in order, I had been using for the previous 10 load sets, primer, trimmed, neckturned all the rest of the fancies.

This time I stepped back 30 ft and got 3430, 3325 and 3143...correct velocities for that COAL, bullet and load components...but still WAY too much velocity spread...more work needed

I already did a trigger job, opened up the barrel channel and bedded around the recoil lug...basically the same thing I do to all my rifles BEFORE I start load testing, PLUS all the BR work on the brass, but so far this Savage isn't showing ANY signs of squeezing down the groups beyond ~1 1/2" or so...and the 3 cases I've been using are as close as possible to each other...0.2 gr weight, neck runout 0.0005" or less, 0.0135" neck walls and I use a Redding bushing die, Redding Comp shell holder, and Forster Ultra seater...the same tools I used to produce 5 shot bughole groups with 75 Horn VM, 100 Horn and 120 Horn bullets in a Rem Sendero I got REAL stupid and traded off.

I'm going to pull off the barrel and put it on one of my other Sav La receivers and see how it works.

Sorry for going WAY OT...at least the chrono data might be of some use.

Luck

No, there is no appreciable loss of ve @ 10ft. I don't know why you expect a certain vel, all rifles are diff, I have never seen two identical rifles give identical vel. SO take the readings @ 15-20ft & then use tha as muzzle vel, close enough for even 1000yd computations.
WHen testing rifles, I set my Oehler up @ 20ft, 15ft for handguns, 10ft is too close for anything but 22lr or maybe 38sp.