Acceptable or "normal" variation in velocity?

[bullet225ho]

Hey folks,

I finally got to use my chronograph that I got for Christmas last year.

I worked up some 44mag loads for a new 77/44.

I sighted in with some pre-loaded 240grn xtp over 22gr of ww296. I had a bunch of these left over from last year and thought I'd sight in with these.

I chronoed every shot. I was very surprised to see the difference in velocity of each shot.

I shot 11 shots to sight in and had velocities from 1681 all the way up to 1804 !!! what the heck? Thats over 112fps variance???

Now these two where extreme hi and extreme low for the string of 11. If I take those two out the range went from 1692 to 1794 the other 7 being between 1745-1770.

At any rate,

I shot some factory ww 240grn silver box ammo and velocity was 1821-1834 between 4 rounds.


I shot my test loads after sight in and

I shot 5 different loads (three rounds each) and none of them where more than 40fps different.

Here's the crazy one. I had a box of old factory WW 250 partition golds that I shot a string of 7 rounds to fine tune (and just to see how they shot) They shot the most accurate of any loads I had, however....lowest was 1664fps and highest was 1763? that's 99fps difference in 7rds.

What's normal variation? will velocity pick up on a hot barrel? do I need to wait a certain time between shots to get accurate velocity?

One thing I do know is this chronograph is going to be addictive.

 

[Rclark]

Should be less than 70 Extreme Spread (ES). What primer? 296/h110 likes the Magnum Primer. If you used a standard primer, I can see the ES being way out there.

I don't use 296, but with 4227 I found the same problem for example (138 vs 69):

20.0g IMR 4227 255g SWC CCI-300 _911fps 35 SD 138 ES, 30 shots
20.0g IMR 4227 255g SWC CCI-350 1030fps 18 SD 69 ES, 29 shots

 

[bullet225ho]

I'm using Winchester WLP primers for these loads.

Box states for magnum or standard loads?

Is there a better alternative? I'm trying to work up loads for 265 flat nose and 225 FTX to shoot out of my 77/44.

 

[Chuck 100 yd]

I have not looked up your load but the slow burning powders do burn better and give smallest extreame spreads when loaded at or near maximum. Often another half grain will show a big difference in E.S. . Also those loads like a firm crimp to hold the bullet back untill pressures start to rise promoting a better burn. Dont be afraid to warm up that load but follow the recipe with components, don't experiment with components unless you can find them in a load manual from a trusted company.

 

[Rick Courtright]

Hi,

I first started chronographing with shotshells in the early '80s. Rather than use absolute figures, I used percentages, based on the average for the load being tested. And in testing factory ammo vs handloads, it was VERY seldom that someone's handloads turned in BETTER numbers than the factory did, though they could often match them.

One of my customers, who'd done some work with then Hercules Powder Co., and I compared a lot of numbers from our matching Oehler 33s to come up with our own idea of what was a good load. Remembering that Sd is a statistical calculation, which I might be able to draw on the board and then again might not, let's just stick with the numbers it gives us for now rather than try to 'splain it at the risk of getting it wrong. We concluded if the Sd was at or below 1% of the average, the load could be called "excellent." So, if we had a load which averaged 1200 fps, 1% would be 12 fps, meaning an Sd of 12 should produce really, really good results. However, that figure wasn't realistic on a regular basis, especially with handloads.

For most purposes, though, we found that a 2% figure (can guess where most factory ammo came in?) could be counted on to produce perfect "real life" results on the firing line (in other words, a miss couldn't be blamed on the ammo!) So that same 1200 fps load running at an Sd of 24 fps was "just fine" on the line. In real life, perfectly good to excellent results were obtainable with ammo running 3% to 4%, and for some uses, even 5% Sds. Of course, it's hardly news that shotguns offer a lot more wiggle room on target than rifles and handguns.

In my own metallic loading and chronographing, I've found that same 2% figure produces pretty much "perfect" ammo for my purposes, with 3% being more realistic. Meaning a 2500 fps load with an Sd of 75 is both easily obtainable and generally shoots ok, for me, while reducing that to 50 (if and when possible/practical) oughta give real good results.

Now, this is all academic: until one actually pulls the trigger and sees the result, nothing's carved in stone! And a lot of times the results are much better than the numbers on paper suggest they should be... or as folks love to say, YMMV!

Rick C

 

[contender]

I've owned & used a chrono for a long time. It's just another tool to assist you in determining what your reloads are doing & hopefully helping you make better AND safer ammo.
There is not exact formula for all calibers & the velocity variations.
But,,, what we should strive for is consistency when loading ammo.
There are many different factors & variations in ammo, calibers, powders, primers, bullet tension, bullet weight, the firearm itself, etc to where we should use a chrono to assist us in determining what each gun does with specific ammo.
However, good reloading practices, that follow the best uses for a a particular load, will most often have lower velocity spreads, and very consistent numbers. And the funny part, it can also not be an accurate load while being very consistent.

Look at the powder, primer, bullet & how you load, and apply it to the particular firearm to be used.
A longer barrel, means you may want to use a slower burning powder. Bullet tension & depth in each case causes pressure AND velocity spikes. Uniform case length, and equal bullet depth & tension does have an effect.
And how you assemble the ammo can have an effect. How much powder in each case has a factor, especially depending upon the burn rate. Faster burning powder is more sensitive to variations of powder than a slower burning one.

You have learned that you have some variables to work with & try to reduce the velocity spread. Work slowly & with only one change at a time to see if you can improve or not.

 

[5of7]

In addition to magnum primers and loading at or near maximum pressures when using 296 or other slow-for-handgun powders, it is important to get good solid and consistent crimps.

The only way to get consistent crimps is to trim the brass so that all the brass is the same length.

When these things are done, you will find that extreme spreads will run in the 50 to 30 fps zone with SD running somewhere in the teens.

 

[Rclark]

, what we should strive for is consistency when loading ammo.

That is the other part of the equation. Components may be right, but if not consistent (powder drop usually, but mixed cases, old brass, crimp, case bullet tension, etc. are reasons too), results aren't going to be consistent. BTW, WLP fall between CCI standard and CCI magnum primers in my back to back tests.

BTW, I've never had to trim a piece of pistol brass. One step, I've never had to do, yet I feel I still get good results. My conclusion is (for me) not necessary. Rifle is different story.

For me, any load that is over 80 ES won't be used in my revolvers period. The load I use for .32 H&R Mag has ES of 14 (15 shots). For .45 Colt 40 ES (15 shots). For .44 Special 29fps ES (12 shots), etc... When I test, I always try to shot 15 shots per test. Should be at least 10. Note I compute SD, but ES to me has much more meaning. I throw out the obvious flyer. You'll find SD is roughly around a 1/3 of ES anyway. BTW, a low ES 'never' guarantees a tight group (guns can be finicky), but it will always help never hinder.

 

[bullet225ho]

Thanks for the info folks,

My reloading is what I would think to be precise. I'm trimming all cases to the same length if needed, measuring each charge prior to putting it into the case and seating at the same depth.

I'm using lee carbide dies and also the crimping die. My crimps may not be firm enough I just have it now where you can feel the pressure slightly at the bottom of the down stroke (RCBS rockchucker press)

Is there a better primer than the WLP for the 44mag out of a carbine?

 

[Jimbo357mag]

You should be able to keep your spread for 10 shots under 50 fps. I usually shoot for less than that but stuff happens. If you are getting a 100 fps spread sometimes, I would look at your process, probably measuring powder or crimp. It is easy to check the crimp on an XTP bullet. They have a deep crimp groove and you should roll the case mouth into that groove.

btw - I have never had a problem with the WLP primers.

 

[Rclark]

I use CCI-350s over WLPs for magnum powders every time. Nothing like 'testing' to see what works best for you . In fact, sometimes when I don't like what I see, I'll try a different primer to see if makes a difference. One of the 'fun' things about reloading is you can mix it up and see what happens over the chronograph ... and on the target .

 

[5of7]

You'll find SD is roughly around a 1/3 of ES anyway. BTW, a low ES 'never' guarantees a tight group (guns can be finicky), but it will always help never hinder.

True, I have noticed the same things myself. 8)

 

[bullet225ho]

Hey folks,

An update of sorts

I loaded up some more 44mag rounds today and went to the club.

I'm trying to work up a load for 265grn Jacketed Flat points for my 77/44 (got them on sale)

and also some 225grn FTX for the 77/44

I'm in Mid GA and our club is starting to see a rise in wild hog population. I'm hoping this little 77/44 will be good medicine for them.

At any rate, This is in response to my velocity spread question and taking the steps that you great folks have suggested. The new rounds were made as usual as stated earlier but this time I added what was called a "heavy" crimp with the lee crimp die (per the manual)

with the 265's I got two strings together and on the second string The chronograph showed "duplicate" which I'm assuming is pretty good. The first shot was within 4 fps of the duplicate rounds. These where also my best group with the 265's.

Antoher thing I learned about a chronograph is it quits working when the sun goes down (At least I hope that was the issue) it quit reading a little after sunset and I got no data for the 225FTX.

I'll do a search on here for these two loads for a 77/44 and add to them or start a new thread for each load.

Thanks a bunch for the input.

 

[5of7]

I have used a Pact Model 1 for about the last 25 years or so, and have found that I get the best results in an overcast day. If I place the skyscreens in direct sunlight, especially shooting 'down-sun,' if you will, the readings get a little erratic.

It is also important to keep the screens about 10 or 12 feet down range from the muzzle, otherwise the start screen will read the atmospheric disturbance created by the muzzle blast, and produce an erroneous reading----usually a very low velocity reading. 8)

 

[jsh]

I will say all of the above advice and input,is as good as it gets.
About the only thing I did not see touched on was muzzle blast. Dunno how close your chrono is, but moving it back away from the muzzle may help out some.
The very best I ever got on spreads was a 2.
That was from a 657 41 mag, cast plain base, starline virgin brass,using Long shot. This was for 25 rounds.
I actually thought my chrono was messed up. Loaded another 12 rounds and repeated it again with the same recipe, it was worse, it was a 3.

Same load in fired cases, along with some cases of unknown firings averages under 20 through out.
Dunno if I just got everything right, or the 41 mag does have magical powers. I vote for the magical powers.
Jeff