Extreme spread?

[Bill Daniel]

What causes variations in velocity?
Same lot brass, same prep, same bullet, same powder, powder measured to less than 0.1 grain, same primer, same day.
First shot 1785 fps, second 1859, third 1840, forth 1853, fifth 1806, sixth1797, seventh 1806, eighth 1833, ninth 1858, tenth 1844. Measured with Chrony Beta 12 feet from muzzle. Henry 010 45-70.
Thanks
All the best,
Bill

[cdoc42]

Is it traceable to the Chrony and the change in background light seen between true blue sky and gray if a cloud blocks the sun in different shots?

I've gotten crazy velocity changes on days like this, particularly with large caliber handgun bullets that reflect more light from the sun.

Even with sunscreens, it depends on where the sun is at that time of the day. If anywhere but directly overhead, reflection on the bullet can change the velocity reading.

Of course, it would be worse if you didn't take all the perfectionist precautions, but it just proves nothing is 100% but death and taxes.

[marchboom]

When you find the answer to that question let me know.

Neck tension has something to do with it. Barrel cleanliness does too.

I just don't understand it when the ES is drastic.

[hounddawg]

great question, I wish I knew. Same powder and primer weighed to within a few milligrams in cases prepared at the same time and one load weight will be all over the place velocity wise yet bump that load up a tenth of a grain it will smooth out bump it two more and once again it will have major fluctuations. Every precision reloader has seen flat spots in the load velocity curve, yet no one has ever been able to explain why as far as I know

[T. O'Heir]

Everything causes variations in velocity. Starting with the loads found in manuals being averages of those tested. However, none of it is anything to worry about. The only thing that matters is the consistency of accuracy.

[Don Fischer]

Well weight the case's, they are all different. Something I finally figured out about extreme spread is it doesn't matter. What matter's is how well the rifle shoot the load! I had a cast load in my 30-06 that had an extreme spread of over 100 fps, great shooting load!Go figure!

[Unclenick]

I've seen velocity vary 80 fps just between having powder over the primer or down over the bullet when it is fired. That was with 30-06 1964 National Match ammunition (about 83% case fill). So you have to tip the gun to get the powder in exactly the same place every time or use a slightly compressed load so the powder gets locked in place.

Several other factors affect it. Fouling building up in the bore can change it. The temperature of the gun can change it. Variable crimp and irregular brass internal volume can affect it. But the biggest single factor in reducing velocity spread, after powder position, seems to be the primer. If the primer is not seated optimally you get more variation than if you do not seat it properly. Sometimes significantly more. Some loads like some primers better than others, so it can be worth trying more than one brand and trying both standard and magnum primers to see what works best. Irregular crimping will also contribute variation.

Optimum primer seating will mean reconsolidating it. The primer's primary consolidation is its assembly at the factory. Reconsolidation takes that further during seating. The primer anvil feet need to kiss the bottom of the primer pocket and then the primer needs to be pushed three thousandths further, according to two different sources of information on it, one being Federal (for large primers; they like 0.002" for their small primers) and the other being Naval Ordnance at Indian Head whose recommendation is in the 1982 and later versions of the McDonnell Douglas report MD A0514, which you can find declassified online.

There are tools for measuring this accurately, but for most handloaders, the most important thing is to be aware primers seated that way are seated hard. It isn't easy to squeeze them that much. The K&M Primer Gage Tool will measure reconsolidation for you directly on a case-by-case, primer-by-primer basis, but it's another cost and it is slow going to use and I only use mine for long range match loads and precision load development. Short of a tool like that, if you seat until you feel the anvil feet just touch down at the bottom of the pocket and then measure the primer height and seat harder until you measure an additional -0.003" deeper primer cup bottom, you will quickly learn the feel of getting there. The depth probe on your caliper or a depth micrometer with a narrow enough rod will make the measurement for you. The caliper is a bit awkward without a depth measuring attachment that gives it a wider base (there is a $10 one at CDCO under Measuring/Calipers and Attachments at the bottom of the page).

Still shorter than all that, just try seating the primers hard in the first place and see if your velocity standard deviation doesn't go down (compare SD's and not Extreme Spreads, as the latter occasionally include outliers that are large, and the SD calculation mitigates the influence of outliers on your final number).

"There is some debate about how deeply primers should be seated. I don’t pretend to have all the answers about this, but I have experimented with seating primers to different depths and seeing what happens on the chronograph and target paper, and so far I’ve obtained my best results seating them hard, pushing them in past the point where the anvil can be felt hitting the bottom of the pocket. Doing this, I can almost always get velocity standard deviations of less than 10 feet per second, even with magnum cartridges and long-bodied standards on the ’06 case, and I haven’t been able to accomplish that seating primers to lesser depths."

Dan Hackett
Precision Shooting Reloading Guide, Precision Shooting Inc., Pub. (R.I.P.), Manchester, CT, 1995, p. 271.

[Bill Daniel]

Thanks to all!
The day was over cast. The crimp with the Lee factory crimp. Primers seated with RCBS UNIVERSAL. The case is trimed short to accommodate the Hornady 325 grain FTX bullet making the case fill to the bullet base.
The bottom line it shoots accurately from field position for me so I will stay happy.
All the best,
Bill

[hounddawg]

My .223's 80 gn load is all over the place velocity wise, I am talking mid 50's or better ES. Shoot it at 300 and it shoots well under a MOA with ten shot groups, try it at 600 and it looks like a shotgun pattern because velocity affects the vertical point of impact as you go farther out.

If you are a short range shooter don't sweat it

[gwpercle]

Everything should be exact and perfectly consistent with no variations.....
But in real life it doesn't work that way...reloading is anything but an exact science.
Have no idea why....it just is. I don't pay any attention to ES , I shoot for accuracy and most times accuracy has nothing to do with ES but some want you to think ES is an extremely important thing....it's not .
Gary

[McDowell300]

I've heard that changing the backstop(shoulder pressure catching recoil) can effect the velocity. For example a difference between shooting off the shoulder standing on a bench in a lead sled. Your shoulder moving back with the recoil in theory would produce a lower velocity then the rifle in the sled. Again I've heard this but I haven't tested it. My tests since then have been for load development and have been shooting off a sled to take as much me variance out of the equation. If it was a 45-70 Henry I'm guessing theres a bit off recoil your dealing with if your shooting offhand. Just my thoughs.
Dave

[McDowell300]

Dang spell corrector

[std7mag]

Contrary to Mr. O'Heir...
With your 45-70, or shooting distances of say 300 yards, extreme spread and standard deviation are not as important.

Shoot 500+ yards and low ES/SD are extremely important. Especially for a match shooter.

[hounddawg]

a 50 fps ES at 1000 yards can be the difference between a x and a 8 ring point of impact. mathematical fact not opinion

[cdoc42]

Following Unclenick's post, how many of us who search for a low ES clean the primer pockets every time we reload? Doesn't the accumulated soot change the ability to seat a primer as described?

[ms6852]

Some people weigh the brass but this in itself is not enough. You have to measure the internal dimensions of the brass cartridge by volume using water . External dimensions can vary but if you measure the volume per case this could help reproduce the same pressures and possibly help lessen the deviation. Also one of the most important factors is how you hold you mouth open every time you shoot. In reality I personally do not worry to much about the velocity variance as I do about the grouping

[44 AMP]

great question, I wish I knew. Same powder and primer weighed to within a few milligrams in cases prepared at the same time and one load weight will be all over the place velocity wise yet bump that load up a tenth of a grain it will smooth out bump it two more and once again it will have major fluctuations. Every precision reloader has seen flat spots in the load velocity curve, yet no one has ever been able to explain why as far as I know

Along with all the other things mentioned, this touches on yet another factor, and that is pressure and powder burning. First, everything that has an effect on the volume the powder has to burn in affects the pressure, and that includes the powder, itself.

Modern smokeless powder is designed to burn under pressure. Pressure that starts at atmosphere and goes up very fast. I think it entirely possible that at certain specific pressures, the powder burn rate more uniform than at others. And I think that "sweet spot" is somewhere different for virtually every combination of load components and firearms.

The other factor, already mentioned is the variability of the readings of outdoor consumer level chronographs due to shifts in natural light conditions, which can, literally change minute to minute.

Everything that goes into the round is within a range of tolerances. Tolerances that can "stack" in different ways and produce varying results. Add in more tolerances in the fit of the ammo in the gun (one big one is bullet to barrel fit, (barrel temperature also plays a part in that) there are many, many variables that, ..vary.. despite all our best efforts (and the maker's) to be as uniform as possible.

The loads with the smallest extreme spreads USUALLY shoot the most accurately, but usually isn't "always" and every gun and load combination can be almost a law unto itself about some things.

[74A95]

Originally Posted by 44 AMP

The loads with the smallest extreme spreads USUALLY shoot the most accurately, but usually isn't "always" and every gun and load combination can be almost a law unto itself about some things.

This might apply to rifles, although the Army Marksmanship Unit says that uniform velocities alone don't reliably predict accuracy.

In handguns, at least for a typical handgun at typical handgun distance, like 25 yards, there is no apparent correlation between extreme spread or velocity standard deviation and accuracy.

https://americanhandgunner.com/exclu...city-accuracy/

[std7mag]

74A95,
That would be a given from my posting stating under 300 yards.

And do you shoot a 45-70 handgun often?

[rclark]

Also note the velocities for the handgun loads in that article mentioned above. For .45 Colt mine are in the 850-950fps range. Not 1100-1300fps range of the test. Also, I shoot out to 75 yards or more, so ES would start making a difference regardless -- gravity is gravity. I guess my point is ES will never hurt accuracy and always 'could' help it. I will still look for low ES handgun loads that are accurate at all the distances I will be shooting .

[44 AMP]

And do you shoot a 45-70 handgun often?

I do. What of it??

[hounddawg]

I agree with almost everything you said UncleNick.

There are several good articles out there on primer performance, one of the best is This one by Laurie Holland.


http://www.targetshooter.co.uk/?p=1471

Since I read Hollands article I make the final step of a load a primer test like this

https://imgur.com/a/aNCjhDO

The only thing you said I disagree with are the tools sensitive to seat primers correctly. In one of his primer articles Holland expressed his fondness with the old style tray Lee. I have one as a standby but don't care for it.

Some think the magazine fed primer tools can be dangerous. Perhaps they can but with my left hand issues This is what I use most of the time these days

http://rcbs.com/Products/Priming/Too...ming-Tool.aspx

Last evening priming new Lapua cases for the first time I could feel the primer seat in two stages using that bench primer. The goal now is good enough case prep so I always get that two stage feel. Between primer feel and seating feel you can tell when a case is past it's accuracy peak

One test everyone can do no matter how they prime is just run your finger over the primed case. You want feel the primer slightly indented below the case when you run your finger over the primer. You can use the depth gage part of your caliper to see if they are uniform also if you want

[arlaunch]

If you have a load that you are trying to tune up/improve, the easiest thing can sometimes be changing primer brands and working up again.

If you are tuning a load you will notice a range where the case fill ratio is the happiest.This will net you the lowest ES's with that primer/powder combo (sometimes this correlates with your accuracy node)

It is thought that it is a powder type, primer type & bullet weight vs. case fill ratio that makes up the majority of extreme spread.

Your developed load should be in the middle of a accuracy range of at least .3 tenths. Fretting over 1 tenth variations in powder to get your load shooting is not the best load choice. Choose a different range or a different primer/powder combo.

Getting below 25 fps goes into cartridge type X vs X type case design, as well as perfect bullet release. Perfect bullet release has much to do with bench rest style case prep and chamber dimensions etc.

[GeauxTide]

The load that produces the smallest SD and ES gives the smallest groups is the one I'm looking for. Large SD and ES usually produces large groups.