Velocity increase after 260rds?

[JC0352]

Hey everyone,
I’d like to see if anybody has a barrel speed up AFTER having about 250 or more rounds through it. I’ve seen most people say between 150-200.

I’m at 260 rounds on a Bartlein 6.5cm, and it’s been consistently around 2700fps with my load. On Sunday I was 4/10ths high at 800 and over the top of the target at 1,000 using previous actual dope from similar conditions. I would’ve shot more over a chrono but I need my remaining rounds for a match this weekend. I fired 3 rounds with my magnetospeed to start the day and they were 2718, 2720, 2703.

 

[Fig]

It can certainly keep accelerating to (and even past) 300 rounds. The 150-200 is just rule of thumb, but how many rounds it takes to settle in will be different for every barrel and vary between cartridges. That said, you should be recording atmospheric conditions to rule that out. You would be surprised how much a change in the air can cause.

 

[bab029]

And don't forget the "lights up sights up" adage.

Bright light (i.e. Mirage) can cause low hits, on the order of 3-4 tenths in my experience.

More specifically, the target appears lower than it is, so you shoot low. I didn't believe it til I experienced it at least three different times.

But yeah, barrels speed up. Just keep tracking your DOPE and atmospherics to understand whats going on.

 

[JC0352]

I was just curious because most threads I’ve come across indicate I’ve put enough rounds down the tube to have the speed level off...

I’ll have to look at my data book to compare conditions. Hot as hell with humidity to boot, but no clue as to the difference in pressure.

This local PRs-type match coming up this Saturday won’t go past 700, so I think I’ll be okay. The next batch of ammo I have loaded up, I’ll chrono it again and dope the rifle again and see where I’m at.

 

[prcomte]

Was your ammo setting out in the sun?

 

[b6graham]

well i wouldn't say your velocity really changed a whole lot, 10FPS is minimal

but i would look at the atmospherics for the POI change

 

[JC0352]

Was your ammo setting out in the sun?

Negative

It wasn’t chambered until I was ready to fire, as well.

 

[MACHTECH]

Carbon ring starting to form causing the pressure to rise??? I have seen it forming in my Creedmoor after 200 rounds.

 

[JC0352]

Carbon ring starting to form causing the pressure to rise??? I have seen it forming in my Creedmoor after 200 rounds.

Necks are relatively clean, no sticky bolt, no ejector marks.

 

[RobertB]

Doesn't sound like it sped up. Id think lighting conditions, mirage, or zero shift

 

[JC0352]

Thanks! I’d confirmed zero that morning. Need to read up on these effects from lightning...

 

[snarkscarbine]

Sounds well within the scope of "normal."

 

[mdmp5]

And don't forget the "lights up sights up" adage.

This is something I learned about not too long ago and it does cause otherwise unexplainable impact variations between range sessions

 

[bab029]

It's just light refraction. Just like a straw in a glass of water is visually displaced. I'm not aware of any field-expedient calculation. Much like wind, but more subtly, intuition is the goal. That comes from experience, both with your gear and about your shooting areas.

 

[JC0352]

One more factor to consider... Thanks all!

I guess I’d get bored if there wasn’t something to work on.

 

[bab029]

Don't stress over it. If you see low hits, correct up. Don't do what I did my first match and hammer 8 rounds into the dirt under the target because the mirage was too bad to call your own misses. lol

Put differently, don't shoot the same miss twice. In some ways, the bullet is the best indicator of wind and other variables, but trusting the bullet to tell you these things requires a lot of confidence in your gear and fundamentals.

 

[JC0352]

I appreciate it. I was missing high in this case, though. Trying to recall the lighting conditions, my range faces north and I was there from 7:30 to around 11. Sun to my right and rising, no cloud cover.

 

[JC0352]

These were my hits at 800, aiming at the orange

 

[SporterII]

I did this at 100 the other day. Light. 1.5 min @ 6:00. Same target. Higher sun.

 

[BWB]

In my experience shooting INTO the sun (West) in the evening, my impacts will be .3 MIL high at 900 yards. Shooting the exact same setup the next morning with sun at my back, NUTS on.

I have done this 3 different times and lost sleep over it, the sun/light WILL affect your POI or more so where you think you're aiming. My experiences have all been shooting HIGH, not low.

 

[JC0352]

So a little follow up, only one shot per charge weight but I think my barrel has sped up a little at around the 300 round mark. Going off of this, I’ll continue with 42.5gr of H4350

 

[b6graham]

big node from 41.4-42gr

i still think you could go up another grain or so

 

[JC0352]

I wanted to be over 2700 which I don’t believe is a big ask for a Creedmor. The node between 42.4-42.6 was an Sd of 6 the last time I’d checked.

 

[ophious]

Maybe I missed it, but what bullet are you using? Also length of barrel? I'm right around there too on a new bartlein with 42.5gn H350. I'm using 139gn Scenars averaging around 2777. It appears that it's increasing as well. Been getting into the 2800's same load. I'm assuming the difference might be temp, neck tension etc. Using the exact same rounds out of a worn in barrel, I'm seeing around 2850. I would imagine as the lands wear in there will be less friction against the projectile and you would see your speeds increase marginally.

 

[b6graham]

I wanted to be over 2700 which I don’t believe is a big ask for a Creedmor. The node between 42.4-42.6 was an Sd of 6 the last time I’d checked.

the factory 140 and 147 eldm hover around 2700 from a 24" barrel, and theyre not hot at all

 

[JC0352]

Maybe I missed it, but what bullet are you using? Also length of barrel? I'm right around there too on a new bartlein with 42.5gn H350. I'm using 139gn Scenars averaging around 2777. It appears that it's increasing as well. Been getting into the 2800's same load. I'm assuming the difference might be temp, neck tension etc. Using the exact same rounds out of a worn in barrel, I'm seeing around 2850. I would imagine as the lands wear in there will be less friction against the projectile and you would see your speeds increase marginally.

I’m using 140 ELD-Ms, 24” Bartlein 8 twist.

 

[JC0352]

the factory 140 and 147 eldm hover around 2700 from a 24" barrel, and theyre not hot at all

Yep that’s about what I think I was getting with their factory stuff.

The ones I posted above are handloads my dad worked up for me with the ELD bullets.