OK guys, I'm a newbie to this forum who needs a little help with a reloading question. I've been reloading for quite a while, almost exclusively for hunting rifles for me and the kids. Our collective arsenal is heavy on 243's, 270's, and 7mm Rem Mags.

I recently bought a PACT chronograph and have gradually learned to get consistent readings with it.

My question - my concern - is that my measured velocities often fall well short of the "book" values, sometimes by 200-300 fps. I can understand lower velocities for the 243's where my barrels are 20-22 inches. But it seems to be particularly true of the 7mm Rem Mags with 24-26 inch barrels

What is this telling me? Is the velocity a good indicator of chamber pressure for that particular rifle? Can I safely increase the powder charge until the velocity approaches the book value?

Can you give an example of how many grains of powder you are using in comparison to what is listed as MAX load in the manual. And which manual are you using? What kind of powders - IMR 4831, RL 22 ???

It always comes down to all rifles & barrels are different. Remember the results in the manual are from ONE barrel/receiver only (would be nice if they avg. like 5). Sometimes my results w/ a cart. are below, equal to or greater than the manual (oh yeah, which manual??), even taking bbl. length into consideration. Having a chrono. is both a curse & a blessing. Just start low & work up, it's always been that way & always will be the safest.
BTW, I find Speer's manual to be very close to what I get. Barnes is totally off for anything but their bullets, Nosler seems to run a bit high & Hornady a bit low, JMO.

quote:

Is the velocity a good indicator of chamber pressure for that particular rifle?

For many cartridges the factory rounds are loaded to SAAMI max and they're good at trying to maximize performance.....so in most cases when you reach factory published velocities you can have some confidence you have also reached SAAMI max pressures.....not always true but it's one of the pieces of data we use to "guess" where we are.

quote:

Can I safely increase the powder charge until the velocity approaches the book value?

Absolutely not..... All other pressure signs must be taken into account.

Welcome to the Insanity, Hornhunter.
200-300 fps slower in a high powered rifle isn't that important. Ask a deer.
Like fred said,a chrony is a blessing and a curse.
If you really want to drive yourself crazy,get yourself a concentricity gauge.

The biggest reason you are not seeing the same velocities on your chronograph that you see in the loading manuals is due to the barrels being tested.

Most all loading manual creators and gun manufacturers use special test barrels. They are generally long and have minimal dimensions.
They of course give high velocities.

The 7mm Rem Mag is one of the worst examples in creation. There is so much variation in velocities that are possible in 7mm Rem Mag barrels that it is scary!

To answer your other question, yes, you can use velocity to approximate pressures. Believe me, if you are getting higher velocties than the loading manual shows, your pressures are TOO HIGH!!! (In most cases)

I guess the point is that every rifle is a different story. I have owned two rifles now that required loads that were above any listed maximum to reach expected velocities. I shot them a lot and never had a problem, but I sure cannot suggest anyone else do that!!!

R F

I'm a engineer by trade and the differences in the different manuals bothered me. So I set up a spread sheet, entered the load-velocity data from 5 sources (Sierra, Nosler, Speer, Barnes, Hodgdon), then averaged and curve fitted the maximum load and velocity. I generally start 2 grains below this averaged maximum and work up in 0.5 grain increments. The "book" values below are my averaged values.

R-P case, Fed 215 primer, 150 gr. Rem PSP seated 0.050" off lands
Powder____Load,gr.__Book Vel._Meas Vel.__Diff.
IMR 4350___62.5______3039______2785______-254
IMR 4831___63.5______3048______2744______-304
RL-19______64.5______3075______2743______-332

This is for an older Savage 110 rifle. My load for two other 7mm Rem Mags (150 gr bullet, 63.0 gr. of IMR 4350) is reasonably close to the "book" value, within 50 fps.

Every gun I own shoots slower than published velocities with both factory loads and handloads.

I've owned a chronograph for over 20 years and I have never had a load exceed the specs listed in any reloading manual that I've tried or any factory load ballistics and I've never come close to what others get on the internet.

I blame it on living in California because we have so much dirt in the air it must slow the bullets down.

There is a small correction from instrumental to actual muzzle velocity. It's about 15 fps.

It's winter now and maybe your temperature is less than the lab standard.

Guys, I appreciate your input. Let me summarize where I am now.

There is a lot of variation in the published load data for the 7mm Rem Mag so the upper limits are a little fuzzy.

Velocity probably is a reasonable indicator of chamber pressure. Consider it a better upper limit than the maximum powder weight.

As you increase powder weight, what you're really looking for, as a limit, is any indication of excessive pressure:
a) bolt hard to open.
b) primer too flat or bulged around the firing pin.
c) bright marks on the case head.
d) what else?

Also look for soot around the primer. And if your action blows up I would suggest reducing your load as well.

I've found that the Lee books give pretty accurate data velocity wise, and they are the cheapest.

Good Luck!

Reloader

I think you're last post answered your own question. An older rifle that's been fired alot, will have the throat erroded quite a bit. This becomes "freebore" & reduces vel. Weatherby chambers their rifles w/ freebore & allows a bit more powder to get vel. up.

quote:

d) what else?

Adding gunpowder obeys the law of deminishing returns. If every .5 grain increase of powder, beginning with the starting load,, yields an increase of, say, 50fps and then your next .5 grain increase yields NO increase in speed, you just passed MAX for that rifle.

I only have one rifle that meets book velocity...Browning model of 1885 in 22-250 Rem. And that's cause it's got a 28" barrel.