Density Altitude, Muzzle Velocity and Load Development

[fvalmostthere]

Struggling to figure this all out, new to using a kestrel just got a 5700 with link for Christmas and every time I go shoot my DA has been pretty different and my muzzle velocities have been all over the place.

I had settled of 44.4gr of H4350 AND 123 SCENARS that I was averaging about 3045fps this fall. Because I kept track of all the other environmentals I calculated Density Altitude to about -200 and 200 the 2 days I tested and decided on that load.

This past week I got new brass (same hornady brass just different lot number) and with a kestrel given DA of about -1000 I was averaging 3066fps with the same load on new unfired brass.

Today I had a DA of -2000 (also crazy windy) and I had a average of 3000fps with the old lot of fired brass, 3014fps with new unfired brass and 3021fps with new once fired brass.

So I can see the difference in brass is about 20fps and I understand that.
The change in MV seems extreme, however I know the DA changed drastically.

I guess my question is what do i do with this information? Will my velocity consistency(node) that I found at 3046 remain the same at a lower velocity and different DA?
Im guessing i should tweek my new brass load to have the same MV as the old brass load?

Any information would be a great help!

 

[Bandit320]

-2000 feet density altitude? That almost sounds impossible unless you are shooting at the bottom of a mine shaft. What were your environmental conditions?

 

[fvalmostthere]

150 ft elevation, 30deg Fahrenheit, 30%humidty. 30.10hg. 2.4deg dew point

 

[Bandit320]

Wow, I would never have thought it could be that low. I wouldn’t think that DA would effect velocity that much, since it’s basically measured at the muzzle. Down range ballistics would be another matter. I’ll be interested in what you figure out.

 

[Inifinty]

Wow, I would never have thought it could be that low. I wouldn’t think that DA would effect velocity that much, since it’s basically measured at the muzzle. Down range ballistics would be another matter. I’ll be interested in what you figure out.

Right, atmospherics shouldn’t effect muzzle velocity much but ambient temperature can effect powder temps and some powders are more temp sensitive to others.

 

[AIAW]

Struggling to figure this all out, new to using a kestrel just got a 5700 with link for Christmas and every time I go shoot my DA has been pretty different and my muzzle velocities have been all over the place.

I had settled of 44.4gr of H4350 AND 123 SCENARS that I was averaging about 3045fps this fall. Because I kept track of all the other environmentals I calculated Density Altitude to about -200 and 200 the 2 days I tested and decided on that load.

This past week I got new brass (same hornady brass just different lot number) and with a kestrel given DA of about -1000 I was averaging 3066fps with the same load on new unfired brass.

Today I had a DA of -2000 (also crazy windy) and I had a average of 3000fps with the old lot of fired brass, 3014fps with new unfired brass and 3021fps with new once fired brass.

So I can see the difference in brass is about 20fps and I understand that.
The change in MV seems extreme, however I know the DA changed drastically.

I guess my question is what do i do with this information? Will my velocity consistency(node) that I found at 3046 remain the same at a lower velocity and different DA?
Im guessing i should tweek my new brass load to have the same MV as the old brass load?

Any information would be a great help!

You've got a problem somewhere else in the load/process. It's not DA that would cause this. Ambient temperature affecting powder, sure. Not DA, not at the muzzle.

Ahh, I refreshed the page and MTN beat me to it.

Typical stuff to check here. Check dies, check for bullet seating consistency, charge consistency, etc.

Did you record ES and SD information from your chrono results?

 

[fvalmostthere]

I’m running h4350 which I thought wasn’t suppose to be to temperature sensitive. I load in an insulated but unheated garage in Maine, so it is pretty cold in there, but not freezing, I have a water bottle on the bench that proves that haha.

I did just switch from a lee powder thrower and Frankfort scale l to a charge master, but I cross measured the first couple batches to make sure they were the same. I also switched from measuring coal to using a comparator and measuring to the ogive. I also switched from a plastic stock to mpa chassis. Not sure if any of these could have this effect. The temperature was around 30 today but with windchill was down closer to zero....

My normal load process is resize with a Redding type S bushing die. I run all the brass through with the button on to smooth the inside of the necks and then I run all the brass through again without it to set neck tension. Tumble the brass and then rcbs case prep machine to clean primer pocket, chamfer and debur the case mouth. I prime on a lee handheld and charge with the charge master lite and seat with a Forster ultra micrometer.

Using a magnetospeed sporter chronograph. My ES was 17 with the old lot of once fired brass, 17 with the new lot of unfired brass and 8 with the new lot of once fired brass today. That was across 3 shots of each at 44.4gr of H4350. I ran ladders of all 3 from 44.1-44.5gr with 3 rounds for each tenth. I was trying to compare across all 3 on the same day to see the difference in lots.

I took 10 shots of 44.4gr of h4350 last week with the old plastic stock and 40deg and no wind, with the new lot I fired brass and average 3066 with and ES of 58. Most shots fell in the 3060’s with the low being 3037, and a high of 3095. I’ve been using the same load process throughout all of this...

Sorry for the story book just trying to get all the info out there..

 

[just browsing]

Virgin brass can do some funky things to velocity. Especially with middle of the road brass like Hornady. Factor in different lots and you’re just compounding potential changes at that point.

Reload those cases you fired cases today using the same process/load that you settled on and compare with your older data. Remove variables one at a time until you arrive at a logical explanation.

 

[fvalmostthere]

That’s why I ran the test yesterday. The last time I shot was on virgin brass from the new lot and I averaged 3066. I reloaded that same brass and some more virgin brass from the same lot with the same reloading process and got 3014 from the virgin and 3020 from the once fired that was 3066 new.

 

[PinesAndProjectiles]

I think you have something wonky in your process. A -2000 DA will have an effect, but not 40-50fps.

We shot a match about a month ago and DA was -2200 but I never saw drops in velocity like you are.

 

[fvalmostthere]

Ran it again today and the virgin brass stayed pretty consistent at about 3022 over 20 or so shots, had a few crazy numbers pop out but overall they were repeatable. Similar conditions with about 30deg and 30% humidity and windy, another -2000da day. My once fired brass numbers were lower again with an average of 2993, but had a few really low numbers in the 2700 and 2800 range, i didnt count those in the average because they were so different. Im thinking about just taking virgin brass to my next competition, since I have an idea of what its going to do. Going to clean the barrel this week and load some more once fired and see if I can get some repeatable mv.

 

[surprise]

How long is it been since you’ve cleaned your barrel? How many rounds down between cleanings do you normally go? And what is your cleaning process? I don’t expect that you would see changes in velocity like that due to barrel condition but, with all the other things potentially going on anything is possible.

 

[fvalmostthere]

I usually try to do it every 250-300 but I think I’m at like 375-400 right now. Just trying to eliminate as many variables as possible. The temperature drop is about the biggest variable I can figure right now. They shot 3066, on a 40deg and no wind nice sunny day. They went down to 3022 on 2 days in the 20’s and very winding, wind chill was probably single digits. Would a 30ish degree temperature change make that difference?

 

[patriot07]

There is a difference between "not temperature sensitive" and "doesn't change speed at all". 20 fps isn't a huge number if the temp change was significant.

CFE223 is not temp stable at all, but I used to get swings of 100+ fps with large temp swings. So 20 fps is pretty reasonable compared to that.

 

[surprise]

I usually try to do it every 250-300 but I think I’m at like 375-400 right now. Just trying to eliminate as many variables as possible. The temperature drop is about the biggest variable I can figure right now. They shot 3066, on a 40deg and no wind nice sunny day. They went down to 3022 on 2 days in the 20’s and very winding, wind chill was probably single digits. Would a 30ish degree temperature change make that difference?

Still trying to figure all my sh!t out but from what you are saying, it makes sense that a 20 fps decrease is reasonable based on that type of overall temp change. I would expect to see a little different elevation hold numbers as well, especially at distance.