I just got a chrony and used it over the weekend and found that the first round fire was slower than the others in the string. The happened with two rifles and on two different days. Please educate me on the cause of this.

temperature, fouling.

Please elaborate a little. I assumed the temperature change was part of it but did not know technically what all was involved. In one rifle the velocities increased an average of 35 fps faster after the first shot. It is a carbon varmint barrel. The other rifle increased 100 Fps and it was a stainless barrel. The bullets were Barnes TSX in both.

Thanks

Actually, my experience is more the opposite -- velocity for first shot or two will often be greater than the rest. Ditto the pressure as measured by a strain gage.

I can only think of two variables -- temperature and barrel fouling. As chamber temperature rises, pressures and velocities may go up, if the powder is temperature sensitive. As barrel fouling changes, well, it's hard to predict how that will affect velocity, except that it can. I shoot mostly cast bullets which can be very sensitive to barrel condition.

35 fps is not necessarily a statistically significant difference. If you are only seeing a 35 fps spread, you're doing OK.

Thanks, I guess I will not worry about it since I could not see a difference on the target. I was just new using a chrony and was puzzled at what I saw.

the first shot does not count.
the first shot will calibrate the chrony.
I shoot a all fowler shots on string one and actual velocities on the others.

Hey Dwight, I see you are in Florida where the Humidity is "almost" as bad as the Carolinas.

If by chance you happen to clean your rifle real well and lightly lube the bore to protect it everytime you take it outside(like I do), then the very first shot has the bullet riding through a "slick" tube. This slightly reduces the Pressure due to less "friction or drag" and it has always been a bit slower for me.

That may or may not be the situation depending on if you clean and lube it after every trip to the Range.

Even though I'm aware of this situation, I still do all my hunting with a pristine clean and lightly lubed bore. I just don't need the "pits" created by leaving the bore filthy.

Best of luck to you.

My 8x57 Mauser has a pattern of low velocity (-25 fps) on first shot - Other rifles I load for do not.

HOT CORE,
I moved from Charlotte down to Daytona Beach a few years ago. I clean everything spotless after I leave the range and then run an oiled patch down the barrel and then I follow it with a dry patch so that I do not have too much lube in the barrel. I even clean them at the range after about 15 rounds.

Somebody mentioned on another post that chronys were not very consistent ,i have one and i always seem to get alot of variation in velocities .So iam not sure if chronys are just like that ?? or velocities are just generally haphazard

quote:

Originally posted by Dwight:
HOT CORE,
I moved from Charlotte down to Daytona Beach a few years ago. I clean everything spotless after I leave the range and then run an oiled patch down the barrel and then I follow it with a dry patch so that I do not have too much lube in the barrel. I even clean them at the range after about 15 rounds.

Hey Dwight, That is more than likely it then.

You should be able to prove it to yourself by going to the Range real early and shooting the rifle 2-3 times, then set it aside. Won't even need the chronograph set up yet.

Shoot some other rifles, have a biscuit(or two) and enjoy yourself.

Then when a few hours pass, try chronographing the Loads and you will "probably" find them doing just what you expect without the "low" initial shots.
---

You and I treat our barrels just the same. I use a Moly Grease to lube mine and dust it with Moly Powder to burnish the Moly back in that I remove during cleaning. And I then follow up with a clean patch to remove any excess lube too. "We" will never have the "pits" that some of these folks have and just aren't aware of.

I used a chronograph a good bit over the years and though they do generally measure a bullets Velocity, that is all they do. I don't waste my time with them much anymore, but I can see where people enjoy using them.

Best of luck to you.

quote:

Originally posted by velodog:
Somebody mentioned on another post that chronys were not very consistent ,i have one and i always seem to get alot of variation in velocities .So iam not sure if chronys are just like that ?? or velocities are just generally haphazard

Velo,

I use a Shooting Chrony Alpha Master (about $130). Its very consistent and accurate if shot is placed thru center.

It will on occasion give some poor reading like 990 fps on a 2800+ load if shot is placed too close to legs or if shot crosses thru at to much angle.

I always buy a box of factory loads as close to the reload I'm working up. Shoot it thru the chrono as a standard to work toward. All factory loads from 22 match to 270s have come close to listed velocity. Strings can be very consistent with a 5 shot coefficient of variation (CV) down around 0.3% on 22 match ammo and target 270 reloads.

If the barrel is very clean, it is common for them to read low and pretty inconsistent until it's properly fouled. If you're not letting the barrel completely cool between rounds velocity and pressure will go up. Fire about five, then load one in the chamber and let it set and soak up the heat from the chamber, then fire it and watch the velocity go up 100 fps. This will prove that most of it is temperature. I have a .220 AI Swift that will go about 3750 fps with the 1st shot out of a clean barrel, then will take four shots to come up to 4000 fps, then stay there. It's not the chronograph, I have two an old Oehler and a Chrony, both give good readings, except the Oehler is a bit better in low light.

Thanks for all the comments. I don't think I will lose any sleep over the chrony. Tight groups at near max loads are much more important than velocity data. Heart and lungs don't care if the bullet is going 2700 or 3000 when it hits.
I satisfied my curiosity with the speed of my old 160 gr bullets in the 7mm08 of 2400. I switched to 140 TSX and Varget and jumped to 2800 in a 20 inch barrel. I can't do much better.

quote:

Originally posted by Dwight:
... Tight groups at near max loads are much more important than velocity data. Heart and lungs don't care if the bullet is going 2700 or 3000 when it hits. ...

Yes indeed.

Let us know how the TSX bullets do for you. I've yet to see a negative report on one. Did see where one killed a Cow on the off-side of the Bull because of a pass-through, but that was not a "bullet problem".

Good hunting and clean 1-shot kills.

Do you shoot at stricklands, we shoot every Thursday morning, see ya there. Our chrony seems to registar low on the first shot.

I shoot at the Titusville Range on weekends when I shoot.