This is why you have a chronograph. Now you actually know where you are at, not wild guessing. I haven't loaded .280's, but I'd say your .243 loads are typical. they will go 2900-3000 with a 100 grain bullet however. My brother had some .243 55-grain loads he was shooting coyotes with, book said they were 3900 fps, they went 3580 over my chronograph. On the same day my .220 AI loads were going 3991 fps.

Thanks for all of the responses....

Tailgunner- Your post sounds like it is right up my alley. I believe that I have headspace issues with this rifle (bulged primers with moderate loads and no signs other signs of pressure), and accuracy is not good. I don't know if my gunsmith has time to pull the barrel and headspace it before I go out west, (I'll need time to work up some loads), but I will call him on Tuesday.

Thanks

Jasper243

I have tested Shooting Chronys by lining two up, and shooting through both. From the average difference between the two, you can calculate the random error in the system. It is only a few fps.

As long as it is a sunny day, or if the clouds are thin enough that you can see the shadow of your tripod, your readings will be very consistent, and probably very accurate.

If you leave the skyscreens in place as the clouds thicken, you will get low readings.

Some published reloading info is wildly optimistic. Some of that may be out and out fabrication, but mostly it is because tests are ordinarily done with chambers cut to minimum specs. The smaller chamber yields higher pressures and velocities. That ensures that most any real life chamber will produce lower, safer pressures, and also lower MV's.

Generally, I have been able to duplicate Hodgdon MV's in my rifles. They do tend to specify long COL's, so you have to watch that, too. Also, Hornady bullets have quite a different shape than Speer and Sierra. That will make a difference in how long a COL you can have without touching the lands.

Extreme powders do produce lower temperature coefficients, IN SOME CASES. In other cases, they are just as temperature sensitive as other powders. In my Mosin M39 (a bit smaller case than the '06), IMR4350 and H4350 have practically identical temperature coefficients. In my 308, Varget gives me zero tempco. In my 223, it is less temperature stable than "white box" mil type ammo. Their ads considerably overstate the virtue of their product.

Tailgunner

I would like to hear the details of your chamber change.

What cartage?

Is the chamber a standard or a mininum?

finished neck size?

any other details that could help me?

thanks

bglenn

The manufacturers of the Chrony line of chronographs quote an accuracy to within 0.5% of actual velocity, with shot to shot repeatability likely to be much better than this.
These are really in the budget price range too, especially their lower range products, way less than 100 bucks.

Steve is, of course, correct. a lot of published data is very "optimistic", especially what's being published today vs years ago. Just remember that what is a maximum load in one rifle may be way under, or way over, what is maximum in another.

These little cheapie chronographs are just as accurate as a lot of the expensive ones! Try firing some .22 rimfire stuff over your screens. i'll bet it'll be very close to published figures! For example, my Beta model Shooting Chrony gives the same readings as my Oehler, and is a lot easier and faster to set up when I get to the range!

Shilen 1-12 barrel #5 conture origionly finished at 26". Fitted to a MK-X receiver.
I spec'd a minimum SAMMI 30-06 chamber, with a .3085 cylinder throat (the only non-standard feature).
The first smith (a true plumber, that was recogmended by a Moddy on another board) cut the chamber off-center and to deep (dropped closed on a NO-GO, and almost closed on a FIELD) and the throat to .3125 (he also seated the barrel to the front of receiver, not the "C" ring, and than only hand tight).
it worked for the first 50 rounds than went south fast. At 250 rounds I gave up on it, and turned it over to my regular gunsmith. He first took a chamber cast and found the above errors. Also that the rifling had started eroding already (probably due to the gases blowing past the bullet).
To streighten everything out (and get past the dammage) he had to remove almost 1 inch off the chamber end. Chamber is now centered and at minimum SAMMI Spec. He did not run a seperate throater in, as he knows that I only use 1 bullet weight in that rifle, which leaves me with .043 jump to the lands with .040 mag well clearance. Neck is "Min. standard", but all my brass for that rifle is match prepped.
Smith #2 cuts and casts a dummy chamber with every reamer he gets (Dave Manson is his prefered maker now, used to be Clymers when Dave was still there) to make sure that they CUT to minimum SAMMI spec, or customers spec on a custom reamer, (if not he returns them for correction/replacment) his standard headspace spec is 0.0000 to +0.0005 (unless he's building a dedicated brush/swamp beater than he goes to +0.003, still well under SAMMI NO-GO spec).
Sorry I don't have all the numbers in front of me anymore (wife cleaned up my desk for me ).

Tailgunner
Thanks for the information.
bglenn