Anyone notice first round in a string faster than the rest???

[PWS]

This happens quite a bit during my load tests.

I'll have a variety of different loads to chronograph and the first shot in a string will be faster than the rest. In addition to a speedy first shot, consecutive shots get slower. For instance, the velocities of one load tested today went 1412, 1345, 1343, 1350, 1340, 1343, 1329, 1331, 1315, 1310.

Doesn't happen every time but often enough that it's noticable and makes me wonder if it's my chronograph or there's something else going on?

Anybody else notice the same phenomenon?

[303Guy]

I've owned my chrony so long the warranty expired before I ever used it! But I will be looking out for this phenomenon the next time I do use it. Soon, I hope.

I can only speculate what might be causing it. Warming of the barrel or chamber resulting in less neck tension or less throat resistance, lowering chamber pressure maybe? What gun and caliber was it?

[milkman]

It might be happening, but I have never noticed it.
Milkman

[P.K.]

First thought's are always a cold bore. What's your slug diameter as opposed to your sized dia?

[Jack Stanley]

I've noticed it but never investigated it . Like P.K. I'd lean toward the cold bore idea but also anything that doesn't keep bore conditions the same like to much lube or not enough . Perhaps even the wrong lube for the job .

In the end it would be a long way for me to track it and I never wanted to invest that much time into it if it didn't effect the group .

Jack

[runfiverun]

yes.
it's fighting the left over congealed lube in your barell.
it generally goes high/left or low/left.
we have done some testing to make the first shot go into the group from a cold barell,it generally takes around a 4% powder reduction for this to happen.
we have been calling it the c.o.r.e. principle.
some lubes don't have as much of a tendancy to do this and generally the colder it is the more affect it has on the ones the cold does affect.

[Bwana]

yes.
it's fighting the left over congealed lube in your barell.
it generally goes high/left or low/left.
we have done some testing to make the first shot go into the group from a cold barell,it generally takes around a 4% powder reduction for this to happen.
we have been calling it the c.o.r.e. principle.
some lubes don't have as much of a tendancy to do this and generally the colder it is the more affect it has on the ones the cold does affect.

It happens with jacketed bullets also. I never shoot for group size with an unfouled barrel. And since I use moly on my jacketed rounds I don't start counting group size from my rifles until 10 or twenty rounds after a good barrel cleaning. Of course the gun is good to go for 80 to 100 rounds after that till the next cleaning.

[geargnasher]

Cold lube/fouling film = more drag =more for powder to work against=more pressure=more velocity. Been trying to kick that little problem for some time now, there are lubes that will not do that even from a clean bore if you build the lube recipe to work in a narrow temperature window.

Gear

[jbc]

Any oil in the bore before shooting?

[quilbilly]

I am going to try that "4%" concept next week at the range with a couple calibers. Interesting indeed!

[cylinderman]

I have this happen too. Some worse than others, my 357 Herrett is one of the worst. Always 60 to 80 fps faster on first shot, can even feel recoil difference.

[dbosman]

I thought the first shot was called the fouling shot, for several reasons. One of which was cleaning the bore. I didn't know it might be faster.

[PWS]

Hmmm, so it's not just my imagination! Nice to know my ragged out old Chrony is still giving good results.

I had a hunch it had something to do with fouling but never associated it with temperature. Most of my shooting is cooler ambient temps and pretty much all of my guns, pistols and rifles both, do it.

I've started to pay closer attention to fouling. Usually during a test string, all shots are fired, velocities recorded then I have look down the bore to see what kind of train wreck might be left behind. Visible powder fouling typically looks like little flakes or miniature versions of the powder before combustion. Lead and lube fouling will look like, in the dreaded form, a big smear of metal, or in a lesser form, like a shadow (tyipcally in the throat), or when it's not adhering to the barrel walls, look like loose dust (especially with Trail Boss!) or will almost look like condensation beginning to form. Recently, in a .358Win load with a 14Bhn 195gr plain base 10 gr over Universal (1350fps), there remained "droplets" of lead/lube on the rifling near the muzzle immediately after firing but they evaporated or blew away as I watched, leaving the bore looking "silky".

No doubt bullets do not form a perfect seal and all the blowby gunk that gets eroded from the bullet, whether lube or metal or even powder remnants, becomes a factor in successive shots.

I'll be curious to see what comes of the quest for the holy lube. Personally, I haven't been astute enough to notice a different POI on target but will be watching for it.

[fouronesix]

When I chronograph loads, whether they be cast or jacketed, I always start with a clean bore. I record the velocity shot string to get the mean velocity and and velocity standard deviation. I just looked at my chrony log and cannot detect the trend you described. Seems, if anything, the first shot is usually a few fps lower than the mean of the string. As far as the POI- the only general trend, with a few exceptions, is that the POI of the first shot from a clean bore is usually a little higher than the rest of the group. With some loads, out of some rifles that "fouling stabilization" of the POI may take up to 3-4 shots.

[milrifle]

The higher POI is not due to higher velocity?

[fouronesix]

The higher POI is not due to higher velocity?

Nope. I think it is more complex than that including variables like: barrel time, acceleration curve of bullet, fouling, temperature, barrel length, barrel design, barrel wall thickness, and barrel harmonics.

If there is a relationship between small differences in velocity and POI it is.. with lower velocity the barrel time of the bullet is longer- therefore the recoil has more time to raise the muzzle before the bullet exits. This is more noticeable with lower velocities and is much more noticeable in handguns. At some point downrange this effect of course is cancelled by gravity and the slower bullet's trajectory will fall below that of the faster bullet regardless of the angle of departure from the muzzle.

[Reg]

I haven't paid attention to the POI but have lots of records showing the velocity change. Dosn't seem to make a lot of difference, clean or dirty barrel. Seems to show less so with pistols, more so with rifles.
I just thought I was doing something wrong ??????

[runfiverun]

some guns shoot lower at the higher velocity.
my girls rifle will throw a 150 fps shot 1-1/2" lower.
my ar-30 will put the faster shots higher.

guns do what guns do.
with jaxketed my 7x57 ackley throws the first two shots @ 3/8's an inch higher and slightly right then the next 3-5 move down and cluster together.
they don't walk down they just move there and hold group.

[fouronesix]

Except for the possibilities I posted earlier, I think other variables would include how the barreled action is bedded and the type of stock material. I've never tallied the % of my rifles that shoot higher or lower POI for the first shot(s) but my guess is at least 75% of mine tend to shoot higher on first shot(s) out of a cold, clean barrel.

As to the bedding question- a common thing happens in many barrels that aren't free-floated. The first shot(s) still tend to go higher as with any other type bedding but if the rate of fire is such that if the barrel and stock get hotter and hotter, at some point the group tends to start stringing back upwards.

[HangFireW8]

I've noticed the first shot/fastest phenomenon many times on jacketed loads. I haven't cronographed yet with cast because a.) velocity is not a primary goal and b.) haven't had much time to do so. I'll probably get around to it.

The velocity difference may related to my previous cleaning regimen of cleaning out all fouling and leaving a very clean, dry bore. I don't clean that extreme any more, cast or jacketed, except when buying a used gun, switching from jacketed to cast, or correcting an extreme fouling situation. At a minimum I now pre-foul before shooting boolits by passing through a patch with some loob on it. While I haven't checked the first-shot velocities yet, my groups tell me this is working well.

I used to do what one poster here said, shoot at least one fouler before shooting for group. I no longer do this. I now track the first shot very carefully in relation to the rest of the group, for any gun or load, cast or jacketed, because in hunting and in life, the first shot is often the only one that matters.

HF