Thread: Published vs actual load variations.

So I may have opened Pandora's Box by getting a hold of a chronograph.

I set myself up for an OCW test this morning and went out with loads for my 7mm Rem Mag. Powder is H4831SC and bullet is 162gr ELD-X over CCI mag primers and Norma brass. Rifle is a T3 with 23.5" barrel and T2 brake.

I ran a couple of shots through to ensure I was on target for testing and to get the chrony set up and ensure it was working.

Started with a load at 62gr and went up to 65gr which is 1gr over advertised max load in Hodgdon data. Hodgdon suggests that a similar rifle should be producing 2731FPS with 60gr of powder; I'm getting 2550FPS with 62gr. Moving to the max side, at 64gr Hodgdon reckons I should see around 2870FPS and I'm getting just shy of 2800 with 65gr of powder which is over max recommended load. I see no pressure signs at all on the 65gr cases.

Anyone else see deviations like this? Anything I should be looking for?

They normally specify the barrel length, twist etc that the load was created for. How different is your configuration from their benchmark configuration?

My barrel is 1/2" shorter with a brake. Other than that the rifling is the same, 1:9.5.

Barrels vary in speed. Ammunition producers are mostly optimistic. Never seen faster results coming out of my rifles than shown on the box. 100-200fps isn't surprising to me.

So far as reloading is concerned, there is always variation there as well...

Cheers, I can take a bit of speed discrepancy here and there. Just looking for thoughts on loading over max advertised load and still about 100fps off of advertised velocity. Like I noted above, I'm seeing no pressure signs at all and when I loaded to 65gr I went up a node and had 3 rounds touching. Thinks I'll have a play and work my way up in 0.5 gr increments until I see some pressure signs.

You can get quite different velocities from rifle to rifle, I had two 6mmBR rifles same action same barrel maker match chambers with different reamers,
Same load one rifle was 50 fps faster than the other accuracy was the same so was the SD and ES shot both out to 1000 yrds both would shoot possibles
Don't worry about it try some different powders you may find one that gives better performance

All Chronographs aren't created equal either, some times shields on/off can make quite a difference.
Best thing it to shoot , chrony ,make a chart using the Bc and obtained average speed , and the Bc of the 162gr Hornady has probably been examined closely and won't be far off ,then shoot out in stages out past a least 500yrs, more if you can at a big target and note where the bullet lands each time, this will tell you whether you have speed discrepancies .
you can then fiddle with the speed/ Bc in a program untill they match, it's not quite as simple as that but you'll see what I mean.

It does seem a little on the slow side - my 7x64 runs at similar pace, but as long as it shoots ok it’s likely plenty fast enough. A 162gr flies a fair way with those sort of numbers...

I run 162 gr A-Max in my 7 mm Mag and 65grs of AR2213 SC for 2955 fps in a standard Rem 24 inch barrel. Looks as if your load of 64grs at 2800 Fps is ok and 65 grs should be at 2850- 2870 fps which in a 23.5 inch barrel is good. As stated already rifles even of the same type and barrel length can shoot 100- 200 fps slower and in some cases faster.

AR 2217 might be worth a try if you want a bit more speed, worth a try.

This is how I roll for any rifle in any caliber for non subsonic ammo.

1 Load up from minimum data or if there is no data for the chambering use some common sense from similar chamberings data....-08 06 size cases 1 grain steps are good,223 or smaller 1 grain steps are way to big go 0.2gr.

Seated at max mag length or just touching the lands(for a hunting rifle) load one shot from min to a good 3-4gr over max....fire each wearing safety glasses of course taking particular note of recoil and force required to lift the bolt and retract the bolt and any stamping/shaving of brass from the case head.
The point at which you find very stiff bolt lift/stamping on the case head being shaved off is over maximum! dont fire anymore !
Back off a grain at least from here(in a 08/06 sized case) and thats max.
Now you know where maximum is and it only cost you 4-7 shots and you can load a few at various charges around and under max to test for accuracy.

I have ADI reloading books going back to the days of "NOAH" the max charges have dropped off by 5-10% with some cartridges since the early loads. Now use their max load as starting load and never had a problem.

Just consider temperature when developing a load, if you go close or above maximum in an average temperature day it may be "hot" load when the temperature goes up… Been reloading for 7mm Rem Mag for a bit and learned that fast burning rates are better with light projectiles, try slower burn rates with the 162gr+ projectiles, Hodgdon H1000, retumbo, ADI2217 or ADI2225, i average about 3100 out of a 24" barrel without compromise.
I hope it helps a bit…

Mac

My chrony can be +- 70 fps. So don't get to hung up on it until you have validated the speed as per Jakewires post.

In this photo you can see 4 different chronographs that was shifted in positions (excepted the magbetospeed) for velocity comparison, they are 2X ProChrono, one CED thing and the magnetospeed, velocity variation was about 50ft/s if I am correct. @greghud may confirm the results.

Cheers

Mac