Chrono has me baffled

[Sarge]

I went to the range again today and did some chrono work. All of my velocities were much lower than my last session.

First, using Titegroup will my velocities go up or down with hotter temps outside? Last session was 65 today was almost 90 and humid. Nothing I had loaded and been using all summer made 125pf today. Last time 4.0 TG with 124 MG made 127+ so I upped it to 4.1 to put in more cushion and it made 124pf today.

3.5 TG and a MG 147 did not make 125 either. Last time 3.4 just made 125pf.

All oal's are the same at 1.14. So as I said I am baffled. Is it temp? If that is the case how can I stockpile ammo if I don't know what the weather will be like when I shoot it?

Also, it looks like 3.6 TG is max published for 147? Is it that hard to make pf with TG?

Or is there another explanation for all of this?

[BritinUSA]

Could be temperature, humidity or chrono variance:

From the CED web-site:

Chronograph Results and variables that effect readings…….

The spread between the existing brands of chronographs on the market today is aprx. 8.0%. This has a lot to do with the quality of the sensors & components used, the distance in which the sensors are spaced apart, and the firmware design of the product itself.

Here's a test you can try, set up the chrono and run some rounds over it, switch it all off, take it apart, set it up again and see if you get the same results.

[BlackBuzzard]

Bullet weight makes big difference in my results.

I can make minor with 3.2 g TG using a 147 grain Barrys bullet - 9mm.......but its uncomfortably close at 129 PF with Glock 34.

For a steel load with same pistol, I get 1000 FPS with 115g MG and 3.8 g of TG........this load does not make minor PF - its for steel only.

Lighter bullet and more powder, but still only 115PF........took my by surprise, but its true.

The steel load all I wanted was the 1000 fps....PF be damned.

BB

[boz1911]

If your shots are not parallel to the sensors this will decrease velocities. It takes longer for the bullet to travel the distance over the sensors. If your using a CED chrono, make sure the sensors are all the way on the bar.

[TM262]

If your shots are not parallel to the sensors this will decrease velocities. It takes longer for the bullet to travel the distance over the sensors. If your using a CED chrono, make sure the sensors are all the way on the bar.

Make sure the sensors are tightly secured and not in direct sunlight too.

[larry cazes]

All oal's are the same at 1.14. So as I said I am baffled. Is it temp? If that is the case how can I stockpile ammo if I don't know what the weather will be like when I shoot it?

Also, it looks like 3.6 TG is max published for 147? Is it that hard to make pf with TG?

Or is there another explanation for all of this?

The variance most likely is temperature related if all else is constant. This variance is why a lot of folks load with a 5-7pf buffer. For my 38 super open loads I load to 172pf minimum. If you don't feel comfortable doing that with TG then switch to a slower powder.

[kamikaze1a]

I once saw a guy shooting over a Chrony. I watched as he attached the tripod to the Chrony, and then opened up the Chrony. The way he attached the tripod kept the Chrony from opening up fully and chorno'd his loads for an upcoming shoot. At the match, he failed to meet Major and got minor scoring. I think that because his Chrony was not opened fully, that positioned the sensor closer together and read fast...

And this one happened to me. I was chrono'ing a new revolver for the first time. After a few shots, the display averaged about 400fps when it should have been over 600. I checked my setup and realized that my chrono was not level. I adjusted the tripod and the velocity went up to almost 700. It did not make any sense to me as both sensors are on the same plane. I never have tried testing with the chrono angled again but I now make sure my chorno is level.

Edited August 9, 2009 by kamikaze1a

[Pat Miles]

I had a bizarre chrono session about a month ago. Chronoed some rounds from a large batch of 40 for my Limited gun. Shot rounds from this same batch on a previous chrono session (172 PF). This time I'm seeing 500 fps with a PF of 54! Shot two five shot strings with same results. Wondering if the chrono or battery was TU I whip out the open gun and immediately shoot two five shot strings with a PF of 172 which is normal for the Open gun and loads.WTF! Three days later I shoot some of the SAME batch of 40 over the same chrono and I'm back to 171+ PF. Back to normal.

I have NO clue what was going on at the earlier session. Need to drop the powder a couple of tenths on the 40 load.

CYa,

Pat

[SA Friday]

1. TG is temp sensitive. The hotter it gets, the higher the velocity.

2. LIGHT is a huge factor depending on chrono set up. Cloudy day vs sunny day will equal different readings with the same load.

3. Shooting too close to the chrono will give misleading readings, I've had both too fast and too slow from this. Set up at least 10 feet away and if still goofy, try 15 or 20 feet.

What gun are you testing out of, and what is the barrel length?

[G-ManBart]

Or is there another explanation for all of this?

A couple of things could be going on. How many rounds per string did you fire to get your average velocity last time? How many this time? Are you using mixed brass or sorted by headstamp? Were the lighting conditions the same? Was it the same batch of ammo?

If you aren't shooting 10-20 rounds per string you may not be getting a true average. I like to run two 20-round strings one right after the other. I shoot 20, record the results, reload the mag and repeat.

Mixed headstamps can cause a reasonable amount of swing. I've seen several PF difference between two different brands of .40 brass (Starline and Win, with Win being higher). You could have had an artificially high number last time and a true number this time, an artificially high number last time and an artificially low number this time or a true number last time and an artificially low number this time....all just with mixed brass and/or not enough shots per string.

Try to get an overcast day or setup the chrono in the shade...even some cardboard taped to the sky screen uprights will work.

Lastly, work up a load that will give you a consistent 135PF averaged on multiple days. Going sub-minor means you're shooting for fun...which is NO fun. You won't notice the difference between that and a 130PF load so there's really no reason not to do so. R,

[Aircooled6racer]

Hello: The temp is your undoing. What I did was do your normal load with Tite Group and put 10-20 in a plastic bag and put them in a cooler with some ice. Then shoot the outside temp loads over the chrono and then try the cooler ones. My results showed a difference of 6000 and went from 171PF to just barely 165 in a 40. I have also noticed that the bullets will fool the chrono sometimes. I actually took a Sharpie and painted the bullet to get good readings on a very sunny day. It worked I chronoed the same loads a week later and got the same readings. I load all my 9mm Production loads to 131PF so that they won't go sub minor even if it snows Hope this helps. Thanks, Eric

[Singlestack]

I'll add one more thing. A .1g change in charge weight is not a valid change.

[ebg3]

My PACT chrono instructions say a "bright overcast day" is the best time to chrono. I have seen wierd results over the years when the sun is at different angles to the chrono.

[BayouSlide]

In my experience (probably temps from high 90s to low 60s), Titegroup has never varied too much for me, maybe a PF difference of 1 - 3, but I don't load at the limits of minor.

I and my G34 are MUCH more comfortable with a PF around 135+.

Curtis

Edited August 9, 2009 by BayouSlide

[Sarge]

Thanks for all the replies. Most of the points brought up were in at least some small way applicable. The gun is an M&P PRO 5". I always shoot several 10 shot strings. The light was more or less the same as last time I chrono'd, only the temp was drastically different. .1 grain changes have made a difference in the past and as I noted I WAS making power factor before and only wanted to goose it a little for some breathing room. I can't see adding more than .1 at a time until I get where I want to be with pf. The main problem is that pf went way down after adding .1. I do know the chrono was tilted forward and not level and am thinking this might have been the culprit. Again, thanks for the ideas and I will get out again this week and try again.

[Singlestack]

The reason .1 change is not valid is by the time you add up the tolerences between the powder measure, scale, repeatability, chrono you might not have made a change.

[Sarge]

The reason .1 change is not valid is by the time you add up the tolerences between the powder measure, scale, repeatability, chrono you might not have made a change.

I understand your point and agree with it. But that does not change the fact that my velocity dropped as much as it did and that is what I am curious about the most.

[G-ManBart]

The reason .1 change is not valid is by the time you add up the tolerences between the powder measure, scale, repeatability, chrono you might not have made a change.

I understand your point and agree with it. But that does not change the fact that my velocity dropped as much as it did and that is what I am curious about the most.

I forgot to ask if it was the same lot of powder from the previous chrono session? That can and will make a big difference sometimes. R,

[Sarge]

The reason .1 change is not valid is by the time you add up the tolerences between the powder measure, scale, repeatability, chrono you might not have made a change.

I understand your point and agree with it. But that does not change the fact that my velocity dropped as much as it did and that is what I am curious about the most.

I forgot to ask if it was the same lot of powder from the previous chrono session? That can and will make a big difference sometimes. R,

Yes it is.

[Singlestack]

Voodoo

[HSMITH]

This is precisely why I stopped using TiteGroup, that and it recoils a lot harder than other powders that are more consistent.

[Sarge]

This is precisely why I stopped using TiteGroup, that and it recoils a lot harder than other powders that are more consistent.

Such as?

[ormondopen]

This is precisely why I stopped using TiteGroup, that and it recoils a lot harder than other powders that are more consistent.

Such as?

N320, pricey but extremely consistant

[Sarge]

No luck today either. I have pm'd a few reliable sources but thought I would throw it all out here to see if somebody picks up on something.

I did/tried all the recommendations since my last attempt. Nothing helped. These are my results from today.

124 MG CMJ 4.2 TG 1.12, 1.13 and 1.14 mixed brass. All pf'd just over 127.

147 MG CMJ 3.6 TG same three oal's. All pf'd just over 128.

I know Mixed brass can have an effect but I am no where near where I should be with these loads right??

My crimp is .376 same as my factory ammo. My SD's are good. (only 6 with the 147's)

147 group was outstanding @22 yards(10 shots in 3" with 8 being under 2". The 124's were all over the place though. I think 10" was the best they did.

My concerns are that these loads are max published and to get 135pf I am going to have to go much higher.

Is this just a bad combo for my gun? Should I switch to 320 and moly's? What combinations can anyone recommend. I am shooting Ohio in October and I need to get this figured out soon.

Thanks.