I just recently purchased a chronograph. I am currently trying to work up some Nosler Accubond 300gr bullets for the 338 Lapua. My question is, what do you guys consider and acceptable muzzle velocity spread? I did a ladder test from 88.0 grains in half grain increments all the way up to 92.5 grains. With the results from that I loaded 5 rounds of 89.0, 89.5 and 91 grains and saw a spread difference from 16 fps to 23 fps. Any information you could give me would be very helpful. Thank you in advance
What do you consider acceptable muzzle velocity variation?
- Thread starter Nysios
- Start date
For me, Standard Deviation (SD) Population of ~33:
Factory ammo: SD 20-30 fps
Reloading decent: SD 15-20 fps
Reloading pretty good: SD 10-15 fps
Reloading cooking with gas: SD <10 fps
Obviously, if you're shooting at 500+ yards, you'll want the number smaller.
Chris
15 to 20 is kind of what I was thinking. However, I just downloaded a ballistics computer for my phone called 'Shooter' and it wont even accept a deviation unless it is 20 fps or less. So I figured I would ask other reloaders. Thank you for the info
If you're not shooting a string of at least 33 rounds, then statistically, all bets are off.
Most of us shoot 5, or 10 shot strings and so the numbers aren't all that great.
Those numbers above are just 'my' little standard for less than ~33 samples.
Chris
That option on the app is not what your thinking, it is in fact meaning velocity change per degree of temperature of powder.
I.e. if your ammo temp shoots 2650 @ 70 degrees and 2670 @ 90 degrees, that would be 1fps / degree.
Its variation of speed with ammo temp, not your ammo extreme spread.
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Ok well that answers that question. I thought it was asking for ES. Thank you for clearing that up for me. Chris, why is it 33 rounds for an accurate statistic?
but to awnser your question, you will acheive great results with an ES of 10 or below. from what i have seen this requires a ton of brass prep. im getting ES's of 12 or 13 in my 243AI
Well seeing as how I despise brass prep I will just try to keep under 20fps. Thank you guys for the advice!
I think for stat freaks, 33-34 is a statistically valid population. 5, or 10, not so much so.
Chris
The three-sigma rule for normal distribution for a sample size under 30 works fine for interpreting SD when chronographing loads. This basically means most values (muzzle velocity) will fall within 3 standard deviations of the mean (avg muzzzle velocity). To be precise, 69.27% will be within 1 SD, 95.45% within 2 SD's, & 99.73% within 3 SD's. So if you fired a 175gn 308 win load 1000 times at an Average MV of 2700fps and an SD of 10fps, then 997 of your shots would fall somewhere within 2,670fps & 2,730fps. Glenn Zediker, in "Handloading for Competition", says to keep SD below 12 and forget about it. Try to keep your extreme spread below 15 and you'll be good to go. However, it's not always so easy to achieve this(deburring flash holes on most brass helps a lot)It also doesn't mean a lick inside 200 yards, and maybe out to 300.
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Does this seem pretty bad... slot bigger of a spread then I was expecting, and in my 300 norma magnum im shooting
215gr Berger's
H1000 86.0gr
Lapua case
250 primer
I would like to get that spread a little closer together anyone have any tips to get some better muzzle velocity variation?
215gr Berger's
H1000 86.0gr
Lapua case
250 primer
I would like to get that spread a little closer together anyone have any tips to get some better muzzle velocity variation?
Not terrible but there is room for improvement. Annealing and sizing necks with a mandrel did it for me. My ES for 40 rounds today was 19 and SD 3.3 IIRC. I pay more attention to ES. I've had better numbers but not regularly and not by much when I chrono 30+ rounds.
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