Does barrel memory effect MV?

[Jackomason]

I noticed a trend in my load development today.

I'm shooting a bolt gun 224 valkyrie and I'm loading 80gr eldms with H4895.

On 4 of the 5, 5 shot strings the first round has the highest velocity of the group and it throws my ES/SD off.

Is this just coincidence or is this common? I am using an F1 chrony so take that into consideration. Although SD/ES are correlating with group size and numbers seem realistic for the given charge.

 

[918v]

I propose that the first round in a series tends to have the highest velocity because the barrel is cool and the bore is constricted.

 

[Lowlight]

Wrong

The cold barrel is not effecting muzzle velocity and there is nothing that suggests the first shot is the highest of the group with any caliber.

Old Wives tales,

I can show a host of recordings where the first round is not the highest, for all we know he has a first-round flinch and it's a cold shooter, not a cold barrel.

If MV was tied directly to heat, they would always change, it would not end at 1, 3, 5, 7, it would just keep getting hotter the more you shoot and hence should change all day, in this case, go down because you claim colder has a higher velocity

Movement with a barrel is stress-related, which can have a heat component, but it's stress, that stress does not always push into changes with MV.

More details would be needed, but it's not related to hot or cold being in the middle there.

 

[Jackomason]

This is my chicken scratch of the test, it is just a 224 so I havent been waiting all that long between strings. I looked at some of my other data with different bullet powder combos and saw a similar trend.

It is a button barrel, and I've seen no shift because of cold bore.

In some cases that first round of the group does stand out and in others it doesnt.. well at 100 yards anyway.

Put this one on the fridge though!

 

[Jackomason]

In the case of this test 24.5 and 24.8 both showed a different POI

 

[Lowlight]

It looks weird but I would not think anything about it, sky screen stuff can be weird.

The F1 Chrony is not the greatest as it still uses sky screens, and it's on the lower end.

But because it's load development, I would not read too far into it just yet.

You can pull random images of Magnetospeed screens off Google and they are all over the place with regards to the first shot vs the rest. It's not unusual

It's' seems like it averages around 24-34fps which is pretty high, so it's hard to say cause group 5 is pretty normal. I would say, try bringing a second unrelated rifle to the range use that first and compare it. Maybe it's a cold chrony, LOL

it reads odd for sure on paper, with the flier appearing too, I don't know, button barrel, but your right its strange, however, I am still not sure it's something to sweat. At least not until you settle on a load.

 

[Dthomas3523]

What are you using to drop your powder charge?

Also, what is your brass prep routine? ES is a bit high. And it’s not always the first shot that keeps the ES fairly high.

Your 23.5 and 24.2 also had another shot in each that was within a few FPS of your first shot.

 

[Jackomason]

What are you using to drop your powder charge?

Also, what is your brass prep routine? ES is a bit high. And it’s not always the first shot that keeps the ES fairly high.

Your 23.5 and 24.2 also had another shot in each that was within a few FPS of your first shot.

Good point, this was virgin brass. Ran it over an expander then lightly hit it with the deburring tool and primed it with a hand primer.

I didnt suspect it was brass related because I saw the trend and got tunnel vision. Hmmm, could it be that virgin brass is throwing my numbers and it just so happens that its shot #1 that has a higher velocity?

 

[918v]

Please repeat the test with another chrono.

 

[Jackomason]

Please repeat the test with another chrono.

Not to be smart but if I had access to one I'd be using it. If it was the Chrono (which I'm not ruling out) then my problems would persist and I'd be able to predict it and discount it. If it's not the chrono then it should be more random and should settle out with more load development... right?

Or is it possible that there is a cold shooter aspect that has to do with recoil management? I know that can have a slight effect on MV but dont know how much.

I guess the mind set I'm in right now is to load the seating depth test for 24.8 and see what happens. If my groups can come down to 3/8" or so then I'll run it out to distance and let the bullet tell the truth.