Weird chronograph readings

[watkibe]

I had some chrono results today that are hard to believe. In my Savage 111 338 Win. Mag. I shot 2 bullets, 2 loads each. For the 215 gr bullet I got average velocities of 3347 and 3490 fps. For the 225 gr bullet, the results were 3193 and 3367 fps. If these were the real velocities, the 338 Lapua would be unnecessary ! I was expecting 2700-2900 fps for 215gr and 2600-2700 fps for the 225gr.  The extreme spreads were under 100fps, and the SDs were all under 65fps. If the data was flaky, I would expect more variation.

What makes it weird is that just before I shot the 338, I chronographed 41 and 44 loads. I got about 1100fps for Unique loads and 1400-1500fps for H110 loads; in other words, expected velocities. After the 338, I shot my 223. Velocities were about 3200fps, again as expected.

I can't explain the high 338 velocities, and it bothers me because I worry that pressures were high too, even though the primers looked OK and extraction was normal.

[LaOtto222]

Back off your powder - your pressures are most likely too high - even though you had no pressure "signs". I have a 223 that I developed a load for, this was before I had a chronograph. Every thing looked good and felt good. I was under .3 grains from Max and it shot great. No sticky cases, no cratered or pierced  primers, no excessive stretching. I shot this load for over a year with no problems. Then I got a chronograph, so naturally I wanted to know how fast I was pushing the 50 grain bullets at. Almost 3700 fps I backed off 2 full grains and then got about 3380 fps - more in line with what I should be getting. Trust your chronograph - after all you were getting expected velocities out of your other guns; so why would the chronograph give you bad readings for the 338? Good Luck and Good Shooting

[Lone Star]

Those velocities are simply too high not to show excessive pressure signs - if they were accurate.  The .338 has a much greater (64% greater) internal cross sectional area than a little .223, so a high-pressure .338 load will lock up the action due to bolt thrust while a .223 would not do so at the same high pressure.

That is SIX HUNDRED FPS above manual velocities!  Yes, there are "fast" barrels - but not that fast, something is wrong.  How far away are the chrono screens?  Muzzle blast - which is much higher than the other pussycat cartridges you fired - could be causing erratic readings.   Fire a few factory loads with the chrono in the same position and see what you get before you faint from worry.


.

[MZ5]

I agree with Lone Star.  This isn't simply over-pressure rounds resulting in high velocities; the numbers just aren't reasonable for it to be that.

[stimpylu32]

Yesterday must have been the day for strange readings , mine was showing a load of 6g of Bullseye @ 850 FPS and the same gun with 25g of H110 going 200 FPS slower , I moved the Chrono out another 10 feet and the speed went up to 1600 FPS with the H110 loads .

So that tells me that the placement of the Chrono will make a BIG differance in the same gun and even more with another .

stimpy

[John R.]

Check your battery. When my chrony starts giving weird readings with known loads, I change the battery. It immediatly goes back to reading correctly.

[watkibe]

Thanks for the input, guys ! The Chrony was in the same position for all my shooting, so it could have just been too close. The 338 does have considerable muzzle blast: the first time I shot it, it knocked the poor Chrony over ! I was afraid I shot it, but it was just the blast. BTW, the batteries are new...

[Luckyducker]

I don't know what firearm you have chambered in 41Mag, but my Ruger Blackhawk in that caliber shoots a 210 JSP at 1335 ft/sec with 20.5 grains of H110 and that is a pretty hot load.  Also when I had my 338RUM I was shooting a hot load of H1000 under a 225 grain Hornady Spitzer and chronographed those at 3200 ft/sec.  I truly think your load is OK but your chronograph is in lala land.  Maybe you could borrow somebody else machine and see what numbers it gives you.

[Autorim]

IMHO, it's a chrono problem. They can be very light sensitive and battery sensitive.

[billy_56081]

It very well could be to close to the muzzle. What it may be picking up as a the bullet may be powder particles going past the skyscreens.

[LaOtto222]

I always set mine up about as far out as possible - so I never gave it a thought...that it might be too close. I learned early that muzzle blast can effect readings, even a 223. So set it back up and move it out as far as possible and see if you get the same readings. As suggested if you can, shoot some factory loads over it for comparison. Just because there are no signs, does not mean it isn't over pressure. Good Luck and Good Shooting

[Lloyd Smale]

the problem is your chrony. Ive had two and for the most part there junk. they just arent accurate enough to use to work up max loads with. I ran into the same thing with my second one. (first one went tits up after 6 months). i was shooting a ruger 1b in 280 using a 145 speer grand slam with a load that should have been giving me about 2900 fps. It was giving me readings around 3100. I at first thought maybe the 26 inch barrel had majicaly made my b into a 7mag but i took the loads and gun to my buddys and shot them over his ohler and low and behold 2850 was the average. I sent that one back to the factory and it came back (after a 30 dollar charge) reading the same as before. I tossed it to the side and bought a pact. Ran the same ammo across the pact and guess what? 2850. I contacted chorny again and told the guy on the phone and he said theyd be happy to look at it again. FOR 30 MORE DOLLARS! I told him in not to nice words to forget it. Id have 60 bucks into fixing it and i could buy a new one for that! YOud never get me in a million years to recomend or buy another. Sure its nice to have a chronograph on the market that the masses can afford but to me if its not reliable and accurate you might as well not have one. You can get a pact that even has a printer on it for 200 and considering most guys on here are avid enough shooters to own a multitude of guns and that 200 dollars is about a 1/3 of the price of a new rifle id say that if you want a chronograph to save your money for a couple more months and buy a good one.

[jhalcott]

  I had an Oehler give me a 3300 fps reading from a RUGER SUPER BLACK HAWK!!!?? When I called the factory and explained my shooting position, they said it was a shock wave reading. Only one 3300 fps reading,the rest were in the normal range. After that I always had the chrono screens 20 to 30 feet in front of the muzzle and the rest of the machine on a separate table.