Reload Muzzle Velocity and ELR

[StormHorny]

I am fairly new to reloading and am curious as to how much variance you are getting with muzzle velocities with each shot?
I am shooting Sako TRG42 338LM and using 91gr of H1000, OAL 3.68", 300gr SMK's and F215 primers in new Lapua brass. I've got 20 rounds though a Chrony Beta and have it placed about 10-12' out in front. My velocities are a low of 2713fps and a high of 2782fps. The bulk of my test shots were closer to the average speed than the high or low speeds. I averaged out my velocities for the 20 shots and went out to 400 and 600yds, plugged in my data and was getting what I would consider for my abilities decent hits every shot using Strelok.
The farther out I go, the more I realize that I need to make my reloads tighter and get my muzzle velocities more consistent.....my questions are what are your velocity +/- FPS tolerances? What do you consider the most important process in reloading to tighten the muzzle velocities to make the gap between high and low tighter?


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[Dogtown]

Indeed, the farther you shoot, the more that velocity differences accumulate into larger groups. I think an average difference of 50fps isn't too bad, but realistically most people try to cut that in half. If you're approaching 100fps difference, then you've got problems. Put more effort into uniforming your brass and weighing your powder throws more consistently. Neck tension is another one that makes a big difference, I've found, on velocity variance. Using just a standard FL sizing die isn't enough for ELR loads in my book so try a bushing FL die or neck die as it will give you more uniform neck tension, releasing the bullet more consistently, all things being equal. To figure out the correct bushing diameter, measure the neck of a loaded cartridge, then subtract 0.002" - that's the general rule of thumb, though it's wise to get a few bushing sizes to experiment with to see which one your rifle likes better. Lastly, make sure you're using a comparator to measure COAL based on ogive and not the tip of the bullet (meplat). Ogive measurements are for more consistent and you'll quickly be able to spot when the bullet hasn't been seated to the same uniform depth.

 

[StormHorny]

Thanks for the reply Dogtown. Ok, I'm not feeling so bad now because looking at the data I wrote down most of my shots are within about a 25fps range. Especially with the Hornady 285's I didn't mention in here because I plan on using the SMKs primarily. How much does temperature play into muzzle velocity? I ask that because with the same batch of reloads I shot them on 2 different days.....one day it was 46F and another day was 54F.....the 46F day velocities were approx 30fps slower. I'm assuming that is due to the powder temp being a little colder?
Like I said I am fairly new to all of this and still learning quite a lot about it as I keep reading. I've read about ogive and the lands and those were actually next on my hit list for reading up on. I've been using the RCBS Gold Medal Dies for reloading my 338 loads. The one thing I am consistently beating my head over is case trimming......I'm planning on getting a Giraud Trimmer before the end of the summer to hopefully get me more consistent length cases.


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[Dogtown]

Giraud Trimmer is excellent if you're doing larger batches of brass at a time. It's kind of pain to adjust the cutting head for different cartridges, so while more expensive, I think getting unique cutter assemblies as well as shoulder rings for each cartridge is the way to go. Trimming is easily one of the more annoying aspects of reloading, but it's very important. I still use my old school LE Wilson trimmer often though recently started playing with the WFT which seems to be a nice middle-ground solution without going back to the Giraud (mine's still CONUS in the land of 120v power).

Temperature is something you have to be aware of when calculating trajectory, but for interior ballistics it's a bit less important unless you're dealing with temperature sensitive powders. Some are more affected by temperature differences than others, which is why it's generally a good idea to keep your loads out of the sun or in a case out of direct cold. It definitely can effect the pressure curve when shooting in extremes.

 

[StormHorny]

I just watched a video on ogive and that totally explains things on why is as constantly adjusting my seating die and scratching my head as to why I had to constantly do that. Is there a particular comparator that is better than others? The video I watched had a Hornady one and that looked pretty straight forward. Price is generally not a constraint. Do it right or don't do it is kind of my motto.
Thank you for the info! It is greatly appreciated!


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