Home Forums Reloading Big Game Rifles weird chrono reading

I was developing some loads for my newly barreled 7mmRem Mag and got some weird/inconsistent readings on the chrono.

It is an X-Caliber 25" 1:9 and was shooting with a SiCo Harvester 30cal suppressor.

Powder RL22
Rem 9 1/2 Mag Primers
Winchester 1x shot brass
Nosler 160gr Partitions COAL 3.27" (not jammed)

First afternoon I shot at 144yds, off a bench
Loads were 63, 64gr, 65, 66 and 67, basically pressure and velocity testing.
Readings
63 - 2970
64 - 3033
65 - 3063
66 - No read
66.5 - No read
67 - No read
This last 3 I assumed error, then realized it may have been too dark for chrono (Chrony Alpha). Besides 63 and 66gr, that may have been my mistake, rounds stacked on top of each other, with vertical stringing. To me those were relaticely accurate speeds

Following day I loaded for a 405yd Audette (first time doing this)
Shooting prone and chrony at 5yd, on floor (not sure if this caused weird numbers, cause all of these where strange). All of these were round robin, but on same POI, minus the 63gr that were on 10" gong to confirm calculated dope (1.6mils at 405yd was still a bit low)

63 - 3083, Err, 3111
64 - 3220, 3204, 3245 (chamber may have been hot for last)
65 - 3227, 3286, 3333 (chamber hot for last)
65.5 - 3319
66 - 3348
66.5 - 3264, 3382

On shot each at same POI, revealed a potential clusters, though I am not clear on the 66.5/67 landing point (and this may negate the whole ladder test). I am not that experience shooting prone of bipod either, bu velocities still got me puzzled.
These velocities were over 200fps over the ones the previous day.
This is a new barrel (had only 10 shots thru it before, 1 factory round of Fed Premium with 160gr Partitions, and 9 reloads of 160 Sierra GMK 160g with 63 gr RL22 on a metal gong), but I don't believe the gain in speed should be that much from 1 day to other and after 16 shots.


Any input on how to proceed? I am thinking loading for OCW groups from 64.8, 55.1, 55.4, 55.7 and 66. Shoot at 200 to decrease possible variables, or keep the longer distance?
Reality is I could probably load 65gr and call it good for hunting inside 400yd (which would be a looooong stretch for Texas piney forests)

First question is how are you resizing your brass? Also, not to bust balls, but you are 4 grains over book max on the 160 gr Nosler load with that powder. If you are in fact running those speeds, you are pushing the limits. Nosler lists a max of 63 grains at a velocity of 3,058 fps. That is with a 24" barrel, so you should expect another 40 fps over their book max. Also, Nosler suggests an OAL of 3.290", so I'm wondering if your chamber throat was cut short? How far off the lands are you running?

With just about every 7 Rem Mag I have worked with 64-67 grains of 22 with a LR Mag primer makes about 3050-3100. If you're up over 3100FPS it's hot and chances are you'd have locked up your gun if you were really getting 3200 with a 160 in a 7 Rem. Not sure about your ladder tests, as I don't do them myself, but I'd load 63-66 grains in 1/2 grain increments and see where your velocity settles and try that. If the gun isn't bent, it'll shoot well in that charge range. 22 is a weird powder and lot to lot variations have driven me nuts over the years, but it is really good once you get it dialed in.

As to the weird readings, I have had the experience of weird readings that I assumed was because the chrono was too close to the muzzle and was reading gas. When I moved it 10 ft from the muzzle, things became much more consistent. This with my Oehler.

BSA - Brass was shot x1 in test barrel. I neck sized and it chambered easily. I had other pieces of brass fired in my previous barrel and those were much tighter/wouldn't close. Those will be FL sized for future use.
Re: charges. If you look at first day velocity reads, they seem to be on par with book. None of the loads had any traditional signs of pressure on either day. No primer flow/flattening, no ejector marks and easy to work bolt.
I'll check lands again, I should've been far out 20thou, as it is for hunting and I don't like to jam, but chamber could be short.
What puzzles me is discrepancy of speeds between 1 day and next.

Scotty - same action, different barrel as previous 7RM, I had worked up to 66gr no issues on that one, but this is new barrel. I was expecting velocities around 3000fps, as I got the first afternoon. and really puzzled by 200fps difference.
I plan to reshoot groups with 64-66, based on tjw first day rssults, as long as there are no pressure signs and the velocities resemble book and not the 3200 fos range.

Blacktailer, the chrono was 15ft out both days. First day on tripod in the afternoon, second day was 2pm. shooting prone and chrono prompted on box.
It only showed Err 1 shot.
Not sure which velocities to believe

Sponxx, you sound like an educated handloader and know what you are doing. I'm wondering if some interference with the chrono had something to do with it. Some are affected by clouds and bright sunlight. I get err on my pro chrono from time to time, but generally it seems to be pretty accurate. Sounds like a chrono issue though..

I have used a Chrony before, and found one day that it had gotten hung up on something on the tripod and was not fully opened, only by a very small amout.............

Given the velocities it would not take much shortening of the distance between sky screens to effect velocity readings...............

When I used my PACT it would sometimes give erroneous readings if I was shooting something with higher muzzle blast and figured the shock wave was affecting the readings. A bright sun at mid day or later in the day with the sun shining directly into the slots of the skyscreens would give either false readings or no reading at all.

A day with a high overcast worked the best of all.

That chronograph isn't that highly regarded and I'd suspect the changing light from one day to the next had something to do with it.

Also, how hot was it? I gave up on RL22 a long time ago because it's temp heat sensitive, I watched my velocities climb over 300 fps out of a 7mm rem mag one day over the course of about 20 shots on a pretty warm Mississippi afternoon. I now use H1000 and get a lot less temperature sensitivity. I've seen various degrees of temp sensitivity over the years but have seen nothing as bad as RL22. That was a while ago and maybe they've reformulated it since. I don't use the stuff for anything any more.

A couple of things with chronos. Yes you can't get muzzle blast to close to chrono causing errors and misreadings. Also sunny vs cloudy days make a difference. Cloudy days have the best results for me not using diffusers. Cloudy days give me the most accurate readings. On sunny days you can get shadows from the bullet across the chrono. So on sunny days I use different methods to block all shadows. I'll use the diffusers on sunny days. This seems to work well for me.

Adams

I had written a response a couple days ago, and it disappeared. I know that my Alpha chrony is not top of the line and light can cause false readings.
I was surprised that there was a 200fps difference from one day to next. I thought that light shifts would give false or Errors, not consistent solid readings (only 1 shot missed).



This above may the reason, as it was open and prompted on a box, not locked on tripod.

Temp wasn't much different from 1 afternoon to following day, hot both days, low 80s one day to mid-high 80s the following, so I dont think RL22 temp sensitivity would be a problem. I have shot that same lot powder at higher temps in the previous barrel (different loads)

I do not think muzzle blast is culprit, as chrono was 15ft away both days, and shot through suppressor, unless shooting prone and closer to floor causes gases to expand differently?

I will retry this weekend, loading in 0.5gr increments from 64,5 upwards as long as velocities are in the 2900-3000fps and no pressure signs appear.

When a chronograph is reading between two eyes,a lot of things can happen.Let me try to explain it in a simple way.Let's say the distance between the two eyes is exactly 12".When the first eye sees the bullet and the second eye sees it is exactly 12",you with have an accurate reading.Let's say you have a bullet actually traveling 3000fps and the eye is not properly picking up the bullet at the right time,it could be like 11 15\16" giving you that high velocity reading.Just a fraction being off at 3000fps is going to give you a false reading.I learned this one morning at the range.The way it was set up I was shooting east towards a rising sun.I start early one morning recording my velocities with the sun still behind the 30ft berm.About one hour later those same loads and rifles were shooting nearly 100fps difference.WTF???I was noticing a lot of variation from trip to trip with load velocity,so I decided to try something different.There was another section of range where you can shoot towards the North.My velocity readings began to be really consistent from trip to trip and my ProChrono is reading nearly the exact reading as my Magnetospeed.My conclusion to what was originally going on was the sunlight was casting a shadow on the eye boxes on my chronograph.As the sun rose higher my readings were changing too.Shooting at the other range to to North,the sunlight was not affecting my reading and they stayed the same because the eyes were seeing the light the same.My load for 160gr Accubonds with Reloader 22 is 66.0grs.I have four 7mags and all of them will shoot that load very well.There is a velocity difference between each rifle,shows that every rifle is different.The velocity range is between 3000 and 3100fps.

Here's a good one from my LabRadar

Did you get a chance to reshoot?

yep, only had one other bizarre reading in a couple of years.

What baldhunter said.

Light screens are going to be the most likely affected by environmental conditions. Sunlight, wind moving the screens/unit while perched on a tripod, etc.

The weak link in all our chrono’s is the stop-start mechanism. Doppler radar, electromagnetism, or light.

Ironically,probably the most accurate chrono available to the average guy was the first consumer chrono on the market—the Custom Chronograph that used the paper screens. That type of screen is a “absolute” start and stop of the chronograph.

If they still made the screens I’d still probably using mine…..

Scotty -
Yes, did the chance to shoot (Kind of)

I've been extremely busy this week and didn't load at home, thinking to load over at the ranch. Rushing outr I brought everything, except the press (set up on a portable Sinclair stand)

I had some leftover bullets that I didn't shoot last time due to weird "too fast" readings and setup at at 144yds
For the loads I had speeds were on par of what they should be, progressing from previous. I do believe firmly what I suspected, weird light or chrono not open enough, as has been suggested

65.5 - 3099 3096
66 - 3126, 3124
66.5 - Err2 3111, 3113
67 - 3149, 3149, 3210 (last shot was on a hotter chamber than planned)

Shot round robin and POI fairly same for all of them, but I decided to change rear bags halfway through (dumb!!), so POI shifted between 1st and 2nd shot of same charges (but almost same for each string of different charges)
I got some minor primer flow on the 67gr loads. No extractor marks or hard bolt lift, but I would call 67 max, and will try some groups with 65 - 66.5 range and see if there is one that shines clearly over the others

If it were me, I’d try to load from 64-67 grains in 1/2 grain increments. See if anything pops out at you. Chances are you’ll see something around 65-66.

Changing rear bags isn't going to "shift" POI. If it does, you have major problems..

Agree, the major problem is my hold changed, from sand bag to squeezable bag. Major problem with my technique and bipod.