High velocity change throughout the day!!

[Matt_3479]

So first time taking the new build out past 100 yards. Developed a load and tested it in different temps over a couple weeks but in short sessions. Rifle is a 6mm creed pushing the 105 hybrids at 3137fps test by a magnetospeed.

To start off the day we re checked zero at 100 and point of impact was perfect. After running my dope we fired groups from 200-600yards my dope lined up beautifully. By this time it’s roughly 1:00pm starting at 8:30am this morning.

We moved back to the 1100 yards and while taking a 30-45 mins break we left the ammo and rifle on our shooting mats. My dope called for 28.33 moa for 1100. After a clean misses we spotted my second miss 2 moa high! I came down to 26 moa and was ringing steel beautifully! I switched out and spotted for a couple guys for roughly another hour while the whole time my ammo was laying in the sun. When I got back behind the rifle I was once again high!! Another 2 moa high!! I had to come down to 24 moa even and was hitting the 2moa plate, 1 moa plate, 1 moa silhouette and our deer plate with ease!! I could feel my rounds being fairly high pressure! After running the numbers it’s telling me I was slinging them at 3360fps!!! My app won’t let me do trajectory validation so that took a bit to figure out.

When i got home this evening I weighed the remaining live loads and had good consistency. I picked 5 random and pulled the bullets and re weighed my charge and all 5 were spot on! Has any one experienced this much change throughout a day of shooting?

 

[Precision Underground]

It is doubtful that you gained that much speed from hot ammo. Did mirage come up as it got hotter? Mirage can make the target appear higher in your scope and make you aim high.

 

[Dthomas3523]

Why didn’t you run them over the magneto again?

But yea, probably mirage and/or combination of shooter error and mirage.

 

[kthomas]

Sounds like it's also a new barrel - those will speed up over the course of break in, but usually no more than 80-120 fps over 100-150 rounds.

I'd say it's a combination of barrel speed up, mirage and maybe even shooter error as Dthomas3523 mentions.

 

[Hondo64d]

My guess is possibly a combination of mirage, higher DA and hot ammo, as a result of increasing ambient temperature during the day.

John

 

[Dthomas3523]

What was your environmentals or DA?

My quick calculations on phone needs negative 1000ft DA to need 28moa at 1100yds with a 105 moving at 3127.

DA would need to move from -1000 to 6000 to need 24moa

Generally speaking.

 

[Matt_3479]

Why didn’t you run them over the magneto again?

But yea, probably mirage and/or combination of shooter error and mirage.

I know I definitely did not increase velocity that much but was hoping you guys could explain it as I’ve never had a change this large before!!

Unfortunately I didn’t bring my magnetospeed with me for the shoot. I know my velocity increased slightly as towards the end of the day my rounds felt slightly high pressured but nothing brutal!

I figured the mirage and humidity played a factor with the first “increase in velocity) when it called for 28.33 and actually needed 26. But when I got back on the rifle and had to dial down again, it was getting towards the later afternoon/early evening and temps were starting to come down and there was no mirage what so ever!

Barrel had 180 rounds down it before Sunday and came home with 260 rounds down the tube.

 

[Subwrx300]

I know I definitely did not increase velocity that much but was hoping you guys could explain it as I’ve never had a change this large before!!

Unfortunately I didn’t bring my magnetospeed with me for the shoot. I know my velocity increased slightly as towards the end of the day my rounds felt slightly high pressured but nothing brutal!

I figured the mirage and humidity played a factor with the first “increase in velocity) when it called for 28.33 and actually needed 26. But when I got back on the rifle and had to dial down again, it was getting towards the later afternoon/early evening and temps were starting to come down and there was no mirage what so ever!

Barrel had 180 rounds down it before Sunday and came home with 260 rounds down the tube.

Another guy had this happen a few months back... Turned out he was shooting the wrong target and it was a about 50 yards closer than he thought.

While it's not inconceivable that you could pick up 50-100fps due to a combination of factors, 200fps seems a bit much unless everything swings in one direction.

if take it back over Chrono without cleaning and then clean it and rechrono. When in doubt, clean it out .... Might find your velocity is back to normal.

 

[Jack's Dad]

That's a super common occurance at extended ranges. I shoot in mils, but I can be +/-.5 morning to afternoon. My friends shoot moa and very commonly they're +/-2 moa. Atmospherics and ammo temp can change poi dramatically. I try to keep my ammo in the shade.

 

[Dthomas3523]

That's a super common occurance at extended ranges. I shoot in mils, but I can be +/-.5 morning to afternoon. My friends shoot moa and very commonly they're +/-2 moa. Atmospherics and ammo temp can change poi dramatically. I try to keep my ammo in the shade.

Not 4 moa as described.

 

[Matt_3479]

That's a super common occurance at extended ranges. I shoot in mils, but I can be +/-.5 morning to afternoon. My friends shoot moa and very commonly they're +/-2 moa. Atmospherics and ammo temp can change poi dramatically. I try to keep my ammo in the shade.

I’ve experienced minor difference in the past (1-1.5 moa) but not 4.

 

[patriot07]

What powder are you running? A rise in DA combined with a rise in ammo temp can have the effect you're describing. May not account for 100% of the delta, but I am 100% confident it played a role.

I ran CFE223 in my Tikka Varmint awhile back, and I would see 100-120 fps increase if I left my ammo out in the sun. That doesn't even account for DA differences, which are absolutely in play at 1100 yards.

I have no doubt mirage was affecting things as well, but gun and ammo both laying out in the sun and changing DA are all things you need to avoid (sun) or account for (DA). I keep my ammo in a cooler here in texas when it's 90+ degrees (small amount of ice in the bottom, thick towel above that, ammo above that to keep it around 60-80 degrees). And I always keep my gun in the shade when not shooting, and I have an extra towel that I soak in the ice at the bottom of my cooler that I use to cool off the barrel quickly. Barrels take forever to cool when it's 105 degrees.

 

[Steel head]

That's a super common occurance at extended ranges. I shoot in mils, but I can be +/-.5 morning to afternoon. My friends shoot moa and very commonly they're +/-2 moa. Atmospherics and ammo temp can change poi dramatically. I try to keep my ammo in the shade.

Not 4 moa as described.

I was shooting at my mile spot Sunday.

I was using almost two less Mils than any previous time.
DA was About 1000 higher than any previous time and I had a pretty substantial wind from about 150 degrees.

 

[Matt_3479]

My barrel must of sped up a little bit which seemed odd as I had 180 going into the shoot figured it had settled down. For the weeks prior i watched the barrel speed up and then what I thought had settled and finalized a load at 42.8grs of h-4350 at 3130fps which was holding in the .2’s-.3’s for 5 shot groups. When I got to the shoot Sunday I rechecked zero and fired a beautiful little 5 shot .263 to start the day. While doing load development I found 42.5grs shot really well as well, .3’s-.4’s at 3095-3100fps.

I got some time and had a few rounds left over from the shoot, so loaded up a few more of 42.8grs and a few at 42.5grs and loads averaged 3199fps and 3178fps. Groups opened up, and pressure was up. Looks like I’m going to have to drop load and see if I can find it again. 42.5grs at 3178fps was still shooting pretty good but pressure was pretty high.

 

[Dthomas3523]

I was shooting at my mile spot Sunday.

I was using almost two less Mils than any previous time.
DA was About 1000 higher than any previous time and I had a pretty substantial wind from about 150 degrees.

Big difference in 1100 and 1700+ yds