Ok, I'm starting to think either my Chrono is super slow or there are weather conditions that cause a chrono to read slow.

My last range day had my 7mm RMag shooting 300 fps slower than factory...I suppose that's possible but, seriously, 300 fps??

As an aside, it was a moderately overcast day but not threatening rain. I have a "shooting chrony" chronograph.

What really annoyed me is that the fps spread seemed normal. But a 140gr. Nosler AB from the Nosler Custom shop chrono'ed 2850-2900 with listed velocity around 3250.

Rifle is a Merkel K1 24" bbl.

Thoughts?

Did you take the diffusers off? You are supposed too when conditiond are cloudy.

Just becasue the rifle Nosler shot was at 2850 doesn't mean your rifle will have the same velocities. Shoot a couple more loads over your chronograph you may have a slow barrel. Chamber reaming and barrel dimensions play into figuring velocity and pressure.

Back off another 10 feet. somtimes a large
charge of slow powder will change the reading
due to muzzle blast. A change in distance will
check on that.

Not only are published velocities optimistic but measured in a test barrel. Real rifles, especially shorter barreled hunting ones, seldom shoot what the mfg says. 300 fps is a non factor. My opinion.

check your screen spacing

I would check the chrono with a different rifle and different caliber just to check the FPS on how close it is with factory. or even check it with a bow & arrow.

I check mine with 22 target ammo out of a pistol.

Lower then book vel is nothing new.

How do you know the factory vel is correct if your hand loads are incorrect.

Find another crono and compare the two

Good suggestions guys. I'll put a few to the test.

My testing gun for the Chrony has always been a very old Daisy BB gun. Works like a charm to both check if the Chrony is seeing the bullet and if it is showing correct speeds.

Novi, couple of thoughts.

If you don't get a Shooting Crony all the way open, they may read fast, but not slow....

Right now, it's the winter. Low temperatures will reduce velocities. The difference between 70 degrees and freezing is often around 100 fps.

Many other factors can effect velocity. Barrel length, chamber size, throat erosion, ect. Consequently a 300 fps variation between your rifle and published stats is not unusual. Unless you can conclusivly prove it's wrong, I'll belive my chronograph over the published data.

quote:

Originally posted by Antelope Sniper:
Novi, couple of thoughts.

If you don't get a Shooting Crony all the way open, they may read fast, but not slow....

Right now, it's the winter. Low temperatures will reduce velocities. The difference between 70 degrees and freezing is often around 100 fps.

Many other factors can effect velocity. Barrel length, chamber size, throat erosion, ect. Consequently a 300 fps variation between your rifle and published stats is not unusual. Unless you can conclusivly prove it's wrong, I'll belive my chronograph over the published data.

+1

I know many people want to believe their factory rifle is shooting their rounds at "advertised" velocities. But very rarely does this happen, or even close. The makers want you to give them your money. And are willing to "fudge" (lie) to you about what you are getting.
This is what drives the advertising business.

muck

I have had 3 of them; they either work or they don't; I have never seen one work consistently slow or fast. One got hit by a "friend" and it was very consistent after that; always read zeros.

quote:

have had 3 of them; they either work or they don't; I have never seen one work consistently slow or fast. One got hit by a "friend" and it was very consistent after that; always read zeros.

There are 2 type of people who own chronos those who have shot them and those who will.

quote:

Originally posted by Fury01:
My testing gun for the Chrony has always been a very old Daisy BB gun. Works like a charm to both check if the Chrony is seeing the bullet and if it is showing correct speeds.

Over 40 years ago Dr. Ken Oehler personally demonstrated his chronograph test rifle for me -- a Daisy BB gun. He said that particular BB gun was consistent at 300 fps, IIRC. I think Daisy has weakened them a little since then and most are clocking around 275 fps now.

quote:

Originally posted by Stonecreek:

quote:

Originally posted by Fury01:
My testing gun for the Chrony has always been a very old Daisy BB gun. Works like a charm to both check if the Chrony is seeing the bullet and if it is showing correct speeds.

Over 40 years ago Dr. Ken Oehler personally demonstrated his chronograph test rifle for me -- a Daisy BB gun. He said that particular BB gun was consistent at 300 fps, IIRC. I think Daisy has weakened them a little since then and most are clocking around 275 fps now.

Don't tell me,... and then Dr Ken shot the chrony...

Get a magneto and you don't have to worry about set up weather etc just put it on your gun and shoot it takes 30 seconds. Great device

Be sure the bullet path and the chrony are parallel or level.

It is not uncommon for loads to exhibit considerable variation in velocity from rifle to rifle. I use an Oehler chrony, and have a great load for 180 grain noslers in 30.05 that always produces velocities variations in the 10 fps range (SD).
I've shot this load in 4 differnt model 70 featherweights, and recorded variations up to 250 fps between rifles with this same load. Each rifle shot a very small sd, but some barrels are fast, while others are slow. Trusting a published factory velocity in your rifle without testing is nothing more than widhful thinking. I've learned to trust the chrony unless multiple rifles with a known history start producing wild readings.
Bill

quote:

Originally posted by mike_elmer:

quote:

Originally posted by Stonecreek:

quote:

Originally posted by Fury01:
My testing gun for the Chrony has always been a very old Daisy BB gun. Works like a charm to both check if the Chrony is seeing the bullet and if it is showing correct speeds.

Over 40 years ago Dr. Ken Oehler personally demonstrated his chronograph test rifle for me -- a Daisy BB gun. He said that particular BB gun was consistent at 300 fps, IIRC. I think Daisy has weakened them a little since then and most are clocking around 275 fps now.

Don't tell me,... and then Dr Ken shot the chrony...

With an Oehler, only the screens are downrange, not the chronograph itself. But back then, the challenge was to shoot the 2"x4" paper screen and not hit the screen holder! But now that I think of it, I'm not sure how much penetrating the first paper screen might have slowed the BB.

Two things come to mind.

1) I have never seen so much variation in velocity as with various 7 Rem Mags.Some are fast and many make a 30-06 look like a speed demon. I don't doubt that yours could be as slow as its showing. Velocity changes as large as your seeing will show up in your drops so its easy to confirm. Or try another chronograph.

2)Shooting chronys have been on my hate list for many years. 3 of us each had one and they were lucky to read within a couple hundred of each other.
I've also seen Chronys give consistant readings that were 300-400 fps too fast, then inexpicably return to sanity an hour later. We eventually wrote that off to changing light conditions. A quick and frustration free way of fixing the problem was buying a CED.