I'm loading a 280 Remington with 150 grain Nosler Partition and WLR primers and IMR-4350.
I chrono my loads and find I am consistently 200-300 fps than the reloading manuals predict.
For example my last load was 54 grains of I-4350 that had a velocity of 2716 fps. Three shots show little velocity variation and scale has been checked with check weights. What am I missing?

I meant to write consistently 200-300 fps slower than the manuals.

Do you have any other experience with this barrel? What is your barrel length? Check the manual. Most report the barrel length they used for testing. If the manual lists 26", and you are using a 22", that would provide at least a partial explanation.

I run into the same thing with my 270. As stated, barrel length can account for some of it. I see this with all loads and all bullet weights. I think the manuals might be a little optimistic.

Good point Brice. The reloading manual data is for a 26" barrell and I have a 22". Not sure how much velocity will change with a shorter barrell. Sierra's max load of IMR-4350 is 54.9 grains. I could try bumping the load another grain or switch to a faster burning powder. Any thoughts?

Thanks for your input neazor91. You are likely to be right since most people don't chrony their loads. When I worked up my 300 Win Mag load (with a 26" barrel) things worked pretty close to the Nosler Manual #6 prediction.

This website estimates about 20 fps variation per inch of barrel length. http://www.ballisticards.com/faq.htm

nimrod, in a .270 I usually see close to 50 fps per inch of barrel.

In addition every component in the load can change your pressure level. I can change my velocity 200 fps by just changing the primer and brass. Sometimes these differences are negligable, other times not. In addition, the same load, in two different guns of the same barrel lenght can easily very 200 fps. Differences in chamber size, length of throat, ect...these all effect your velocity.

If the books were always right, no one would need a chronograph. They are not....and that's why we need them.

QL calls the difference for that load 114Fps. differnet case and primer can add or subtract. Also many loads are tested in a pressure barrel and probably a tighter chamber than you have.

QL calls your load to be 2806 at 57,000. I would say your reading is in the ball park. Different barrel, cases, primers, throat, powder lot etc.

Almost every one of my guns gives less velocity than the manuals say, even my 26" barreled ones.

The only exception is a 26", 3 groove, Pacnor supermatch chambered very tight in 22.250, it delivers consistently higher velocities with almost every manual load.

I love this site. Instant access to people who actually understand the issue. I'm starting to bump the pressure limit for 4350. It looks like RL22 and IMR 4831 build higher velocity with lower pressure (at least in a 26" barrel). I'll give one of them a try and give 55 grains of 4350 a shot and let you know how it goes. Thanks guys.

Nimrod, if you have a 26" tube I'd opt for a slower powder, either the RL22, or H4831sc (NOT imr4831)

i had a custom 280 built with a new douglas barell. after using and loving it for many years i boght a Oehler 35P. It just about ruined that rifle. a moderate loaded 7x57 would have beaten my 280 any day. 300fps lower from book using max loads. to find out my smith used an old reamer with a huge throat. the only way i could even approach book values with this gun are to use Max loads plus 2.5 grains of reloader 22 to get even close. those loads are safe and just fine , you would not want to fire them in a normal throat thought and must be cautious if someone used your loads. just fwiw.

quote:

It looks like RL22 and IMR 4831

If you are using the Nosler manual I've always found it VERY optimistic.

As to the 280 if I only had one powder it would be RL22. Second choice is 7828. Even in your 22" barrel.

IMHO the difference is in the throat of your rifle.
Try some factory ammo, and you'll see the same kind of velocity difference.
I run a tight throat in my -06, and am running within 10fps of what the Nosler manual predicts, with multiple powders.
After 1 rebarrel, velocities were down 250fps and a chamber cast showed a throat that was .003 over bullet diameter, after setting the barrel back 1" and re-cutting the chamber/throat the "book" velocities returned.

I wanted to thank everyone for their help and provide a little more information that may help others. Keeping everything else constant, I loaded 55 grains of IMR-4350 behind the same 150 grain Nosler Partition and got an average velocity of 2807 fps from a 22" barrel. This is well above the load max. for Nosler's manual and right at the load max. for Sierra's, which is based on a 22" barrel. This is only 100 fps less than Sierra predicts for this load and their 150 grain Game King bullet. The accuracy for four shots was pretty bad (about 3").
Switching to 140 grain Sierra Game King bullets, I produced loads with 53.0 grains and 54.5 grains of the same IMR-4350 as before. I 1/2" groups with both loads and average velocities of 2725 fps and 2841 respectively. Only about 50 fps slower than Sierra's book.

140 gr bullets should give you 3000 fps in a 22" barrel with N160 or H 4350. This is a safe 63,000 psi load.

You may get good results with N560 as well.

In my 280 Ack Imp with 24" barrel I get 3100 fps with 150 gr bullets and 3000 fps with Nosler 160 gr Accubonds - spot on Nosler manual load using N560.