FPS when reloading

[armyguy209]

Ok so this might be a dumb question but now that I have my new Magnetospeed chrono I am curious. I know that when reloading certain FPS corresponds with each bullet weight and per each charge weight. Now when reloading you want to see how accurate your loads are by looking at the data in the manual. So for example a 55gr jacket bullet under 23.0 grains of H335 should have a velocity of 3018 FPS in my lee manual.

So when reloading .223 is there a certain FPS that I am trying to hit? I loaded up some 55gr zmax yesterday and they were like 700 FPS under the manual data. I know my powder drops had to of been inaccurate because the varied quite a bit, unless I was using my chrono wrong which I might of been. I am going to hand load and double weigh next time just to be sure.

Another question is how many FPS does barrel length actually effect the bullet by? They don't list which rifle length they were shooting out of in the lee manual but in some of my other manuals they do list it and it is usually 20"+. So out of a 20" barrel per se, if a bullet is marked as traveling at 3100 FPS out of a 20" barrel, how fast would that same bullet travel out of a 16" barrel and a 14.7" barrel? I know the twist rate of a barrel also makes a difference but I am curious of how much? Say the same bullet out of a 16" 1in7 twist vs a 16" 1in9 twist?

I am just trying to wrap my head around this.

[Intimid8tor]

All the manuals are starting points and in some cases maxes. Reading your cases and tailoring the round to the specific firearm if you are going for accuracy is the key.

[BajaJames83]

Generally its about 100 fps for 1" of barrel length lost.

[afrancke]

Here are your priorities:

1) safe pressure (including a margin below "max" if you are using a temperature sensitive powder)

2) accuracy node - a powder charge amount that yields the least impact scatter

3) speed - reducing time of flight to target improves accuracy at longer distances (because wind and gravity have less time to operate on the bullet and therefore aiming errors' effects are lessened)

The fps in the load guides is useful to try to match in order to ensure goal #1 is met; you know that if you duplicate the load given, you will stay within a safe pressure range. You will have to do some adjustment if you have a different barrel length than was tested (and typically for rifle loads the manuals use pretty long barrels). Even with this info, you will also want to watch your brass carefully for pressure signs.

All that said, you are hunting for the fastest accuracy node for your rifle at the end of the day, not trying just to duplicate whatever load the manual said was best or fastest.

[armyguy209]

Well it was weird yesterday because my loads were showing way off on the FPS side. Like I said though, there could have been a few reasons that affected it but I was happy with the groupings at 100 yards with 22.4 grains(if that is what it even was) with a 55gr Zmax. Not bad at 100 yards being that the bullseye on these is about the size of a quarter.

The 4 smaller targets are mine. The first one(21.6) I started messing with my eotech after I was done so I added a few extra holes, but the original three were decent(one bullseye, one close to bulls eye, and one down and left). They were 2505 FPS and 2399 FPS. The second one on top was the 22.4 and my best group, but the Magnetospeed showed my FPS way off. They were 2721 FPS and 2378 FPS. Although they weren't near the 2900-3000 FPS as stated in the manual, they were my best group and I was happy with them. They cycled the rifle and had no signs of pressure(but none of the loads did) as Hornady uses pretty conservative loads vs other manuals. The third and fourth were 23.5gr and 24.0 gr. The magnetospeed stopped working for some reason so I didn't get to see what those were pushing. I am going to load 5 of each next time strictly for measuring FPS. I will just put them in a block, and use my Chargemaster 1500 to dispense the powder so that there is no way of being different. I found yesterday after I had loaded them that the power die had some oil or something inside of it that was collecting all of the powder, which I think had an affect on my loads.

[JagerDog]

All true, but....something is likely wrong if the variance from published is 700 fps. 10% difference can be attributed to a variety of factors.

[DSMeyer]

One thing to remember is that all measurements from load data books are from a bolt gun. Some data reference from a 20" or a 24" barrel. You will have a fairly large drop of velocity when using a semi auto rifle as the forming pressure curve gets bled down for action cycling.

I get a 350fps change between the same loaded rounds from my 30-06 bolt gun to my 30-06 semi auto both have the same barrel legnth.

['ol shooter]

The measurements are done in lab quality test barrels, you are unlikely to be able to duplicate the results. The best group that measures fairly consistent on the Chrono is what you should be after, IMO.

[smalltime]

Same bullet with 25gr H335 & CCI 41 primer, LC Brass averaged 2948 from my 16" 1/7 spikes upper. Got best accuracy with 26.5gr Varget, 10 shots averaged 2916, SD 15