Author Topic: Just got a chrono - surprised at the velocity variations - what is normal? (Read 1885 times)

tacotime · « **on:** January 31, 2011, 05:12:59 AM »

Just got a chrono, tested some 45-70 handloads and was surprised by the velocity variations within a carefully loaded batch of ammo. Uniform trim, deburred, clean cases, same primers, same minimal crimp, same seating depth, each charge measured on digital scale by hand, hornady 350gr, 3031 or 4064, about 70 degrees temp.

Speeds ran for example 1629, 1644, 1668, 1687. Other batch 1566, 1600, 1602, 1683.

Are variations to this degree normal even with a consistent load? Or what is approximate normal variation on consistent loads?

Thanks.

necchi · « **Reply #1 on:** January 31, 2011, 05:42:07 AM »

, Yup that's pretty normal.
Unless you get into benchrest stuff and ALL the tiny variables having an Exteme Spread of 50-100fps is common.

The goal is to lower the ES and Standard deviation and that's as simple (or complicated) as changing powder.

I'm just a common everyday kinda loader for hunting/off the shelf factory guns and I'm happy with ammo that's more accurate than factory stuff for my guns. It's nice to have a chrony so I can actually use the ballistic programs out there, but I haven't reached the point of beating myself up trying to get that perfect spread. (yet)

AtlLaw · « **Reply #2 on:** January 31, 2011, 05:57:51 AM »

Hummmm, $:-\$ lessee here...

example #1: ave. velocity 1657 fps w/ave. deviation of 20.5
example #2: ave. velocity 1613 fps w/ave. deviation of 35.25

For me, those ave. deviation #'s are kinda high. I start looking for a reason when the ave. deviation starts to exceed the teens.

In both of your examples, both your high and low vel. #'s (extream spread) are way above or below your median velocities. Or is it "mean velocities"

Whatever, the numbers in the middle!

If accuracy was bad I would be trying to figure out why. If not, who cares!?

Quote from: necchi on January 31, 2011, 05:42:07 AM

The goal is to lower the ES and Standard deviation ...

Yup! What necchi said!

Except I use average deviations instead of standard deviations. $:-\$ I can figger AD in my head but I can't even remember the formula for SD!

necchi · « **Reply #3 on:** January 31, 2011, 06:38:18 AM »

That Standard Devition forumla is 1 complicated mess, useing terminal numbers that an average calculator won't even read.
I cheat,

http://easycalculation.com/statistics/standard-deviation.php
Just plug in the numbers with a comma (,) between them an click. "Presto, AbraCadabra"

drdougrx · « **Reply #4 on:** January 31, 2011, 09:55:19 AM »

The Evil Chronograph!!!!!

Makes you crazy....I'm a pharmacist. No one weighs powder better than me (just kidding...just a phrase for effect)....actually....very few people are taught to weigh powders as well as we are. Having said that, my average Sd is generally (but not always) about 17...which means that 65% of all of my loads will chronograph 17fps above or below the mean of may group. Or if I shoot 10 shots and the mean velocity for the string is 2000fps, 65% of my shots will fall into the velocity range of 1983fps - 2017fps. That's 1 Sd from the mean...2Sd from the mean (in this case 34fps) means that 95% of all my shots will fly between 1966-2034fps.

My point is this...Sd is a measure of consistency, not accuracy. Consistant loads MAY be more accurate but not necessarily. Even if you measure all of your variables as closely as possible, you may still get an inaccurate load, or, in your case an accurate load even with variation. Would be nice not to get variation, but I can't imagine that happens....so don't sweat it....chronograph be d*mn*d.....

tacotime · « **Reply #5 on:** January 31, 2011, 11:35:18 AM »

Well true but it still is surprising that with what should be matched and consistently loaded ammo, there is that much variation. The wider of these two batches had one deviation over 4.3% above the average. Sounds like a lot from consistently made cartridges.

Old Syko · « **Reply #6 on:** January 31, 2011, 01:24:21 PM »

Tacotime, sounds to me like you're getting a lesson on precision and consistency. What most of us consider to be precise is actually not as precise as we would like to think and there are more variables than we want to admit. As an example you could possibly make a slightly heavier or lighter crimp on these same loads and change everything in a big way. Maybe use a different powder, primer, bullet, or even a different lot of cases and you would see major changes for the better or worse. Learn to use the chronograph like you use load manuals. It's only a guide and your results may be nowhere close to someone else's. Trust your targets since they are the proof of your work and use the graph as just another tool. Do otherwise and you'll never win.

BTW, run some factory ammo over the graph sometime for a real eye opener.

Catfish · « **Reply #7 on:** January 31, 2011, 02:27:35 PM »

I agree with what everone has said. BUT, I bought 500 pieces of 6.5-284 Norma brass a while back and the guy I bought it from had a .338 Lapua imp. and he had a load for it that was getting an ES of 3 fps, not SD but ES. He has shot a 3 in. group with it at 1,000 yrds. I was very impressed to say the least.

squirrellluck · « **Reply #8 on:** January 31, 2011, 02:51:35 PM »

On a side note. Take the crony out and shoot it

Nothing drastic just nick it. It is gonna happen anyway so you might as well get it over with

tacotime · « **Reply #9 on:** February 01, 2011, 04:44:26 AM »

Funny.

Thanks for the perspective.

I did shoot the Rem 405 factory round listed at 1330fps through two Ruger #3 guns and the chrono showed 1089 and 1199! Geez! But oddly they were about where expected on the target!

Do we expect Ruger #3 guns to show lower velocities? They were showing faster than the manuals on smaller than listed charges on my handloads.

calvon · « **Reply #10 on:** February 01, 2011, 06:36:45 AM »

Everyone who posts here has a computer and there are myriad spreadsheets for every computer. I've made a very simple spreadsheet which calculates max, min, spread, and SD. All I have to do is enter the velocities which I record in pencil on a printed copy of the spreadsheet page. Then I punch those data into the spreadsheet when I get home. Here's a sample of a spreadsheet that I made and use in iWork on a Mac. I'm no computer whiz. All I did was follow a few simple instructions in a book.

drdougrx · « **Reply #11 on:** February 01, 2011, 08:56:11 AM »

Squirrell is sooo right...shoot it now...why wait!

Catfish....an Es of 3...holy crap!! Love to know how he does it ....

gypsyman · « **Reply #12 on:** February 01, 2011, 01:47:16 PM »

Catfish, don't know who that fella you bought brass from, but, if he's serious about a 3'' group @ 1000yds. He should go shoot some benchrest match's. Not sure the weight class of the gun he's shooting, but the last time I noticed, a 1000yd record was a little over 4''. And that was confirmed and sanctioned.
How many beers had this guy had when you talked with him?

If he's like some of the guys at gun shows, I've heard stories of 2'' groups off hand with a pistol at 200yds. YEA RIGHT!!. We all know that you and me can do that, I just won't swear to it on a bible about you!! See ya this weekend at Lima. gypsyman

FW Conch · « **Reply #13 on:** February 02, 2011, 05:56:36 AM »

tacotime, like many of the rest of us who reload, you are suffering from "excessive/compulsive" syndrone! If you see a doctor soon enough it may be cureable, but I doubt it. Just kidding-but not completly

. Some things that you could do that you didn't mention is, uniform primer pockets, ream flash holes, weigh & sort cases, weigh & sort bullets,etc.,etc.,etc. Rather or not any of it will make any difference or not is unknown. If you really value you sanity, don,t nick the crono-"nuke" it

!

There are many classes & catagories in 1,000 yd shooting. One record I heard in the last year was 3.3" for a 10 shot group. That was done with what I call a "shooting machine", not a rifle.

I will ask you the same question I ask myself-when it comes time to take the shot @"bucky buck", will I be able to forget all this c#*P?

Good Luck-Good Shooting-& Maybe we should start an encounter group $:-\$ ?-Jim

tacotime · « **Reply #14 on:** February 02, 2011, 10:06:35 AM »

Good advice. Thanks. I'll take the chrono with a grain of salt, but see if I can close the spreads. Starting with matching the bullet and case weights, since that's easy. The primer pockets were cleaned and the holes look good and round... some of that brass was new too.

Old Syko · « **Reply #15 on:** February 02, 2011, 10:23:22 AM »

Although it has nothing to do with the OPs thread, there are a number of different classes in 1000yd shooting. Here is one example.

Old Syko · « **Reply #16 on:** February 02, 2011, 10:25:14 AM »

No matter if you call it a rifle or "shooting machine" it is impressive.

FW Conch · « **Reply #17 on:** February 02, 2011, 02:44:30 PM »

That 50 is a big "RIFLE". The "insturment" that set the record I mentioned above had a water cooled barrel, complete with circulator system. It is mounted on a machined platform that is infinately adjustable & has no stock whatsoever. The shooter sits behind it, twisting dials to get on target & fires it with a remote triggering device.

But your right- "its all impressive"! Especially when you consider that if Lee Rasmussen could have put 5 more in that spread, he would have "beat the machine"!

JustaShooter · « **Reply #18 on:** February 02, 2011, 02:47:22 PM »

And they don't have to be big monsters like that either:

That was done with a rifle like this one (not the exact one, but this type):

Just a Shooter

tacotime · « **Reply #19 on:** February 03, 2011, 03:36:34 AM »

Just, since that setup apparently works, clue me in on what handloading techniques make this possible. And what powder, primer and bullet? Seems like I should be able to mimic some of your methods and get a pretty good group at 100 yards!

Old Syko · « **Reply #20 on:** February 03, 2011, 10:25:12 AM »

Quote from: tacotime on February 03, 2011, 03:36:34 AM

Just, since that setup apparently works, clue me in on what handloading techniques make this possible. And what powder, primer and bullet? Seems like I should be able to mimic some of your methods and get a pretty good group at 100 yards!

The point you need to realize is, no matter what combination of equipment and components someone else uses the same won't work for someone else. You can try your best to copy someone else's equipment only to fail miserably due to the most minute differences. If it was as simple as copying someone else's lead there wouldn't be any competition because everyone would have the same capabilities.

I have read that Rasmussen turned or had turned his own individual projectiles that were altered after much research with numerous chronographs. Don't hold your breath waiting for him to divulge his knowledge to the public.

tacotime · « **Reply #21 on:** February 03, 2011, 10:46:24 AM »

Yes and that point was known, but still one or two tips might help the average guy benefit with a little more consistency out of his ordinary sporting rifle and basic handloads, without costing anybody a match or a shooting record.

Richard P · « **Reply #22 on:** February 04, 2011, 09:56:37 AM »

I should take time to read all the posts, but I'll add that you really dont need to figure SD. SD will be roughly one third of ES. We would like to see as small of ES as we can get and some loads are capable of small ones.
If you arent match shooting a 100fps ES isnt going to make you look bad. Look at your mean velocity and how many shots were close to it. Was your large ES due to one shot ? Two shots ? More ? Was your accuracy on paper acceptable for the task ? How much time and material are you willing to expend to lower your ES ? Are you sure your large ES is the cause of any inaccuracy ?
Barrels vary, Bedding and barrel band influence varies. Triggers are not often helpful in shooting good groups. Barrel crowns do become damaged. Scopes are sometimes suspect or a proven trouble spot. Mount screws do loosen.
If you know the rifle/ handgun doesnt have mechanical problems you can learn a lot from a chrono. If the gun has its own problems the chrono may only prove that the ammo isnt the source of your aggravation.

JustaShooter · « **Reply #23 on:** February 04, 2011, 05:43:58 PM »

Quote from: tacotime on February 03, 2011, 03:36:34 AM

Just, since that setup apparently works, clue me in on what handloading techniques make this possible. And what powder, primer and bullet? Seems like I should be able to mimic some of your methods and get a pretty good group at 100 yards!

My methods? Um, sorry if I've given the wrong impression, I'm not nearly that good! I saw that over at Accurate Shooter's Daily Bulletin (http://bulletin.accurateshooter.com/) Lots of good info about benchrest reloading techniques over there, but unless you have a benchrest quality rifle, much of it won't do any good.

Just a Shooter (average shooter, that is)

tacotime · « **Reply #24 on:** February 07, 2011, 03:50:56 AM »

All good and fair questions and info.

I'll just creep along here, trying to eliminate suspect variables when I can and not worry too much about it if the groups are reasonable...

corbanzo · « **Reply #25 on:** February 08, 2011, 02:19:10 PM »

My spread is normally 50 fps or so, but honeslty, it doesnt matter. I just got a chronograph so i would have the information for my loading data and energy computations. After I write it down, I dont worry about it. Unless there is some crazy variation.

john keyes · « **Reply #26 on:** February 15, 2011, 12:58:21 PM »

I carried my chrono out to the range today to see what a new rifle and load were doing.

.223, assorted range brass, 24.5gr H4895, 64gr fusion, Fed 205, 2.300 OAL

in order, no fouling shot: 2961, 2865, 2918, 2867, 2945

so it looks like I've got a big spread, but the load shot under 1" at 100 with 2 out of three touching

tacotime · « **Reply #27 on:** February 17, 2011, 03:53:26 AM »

What I noticed with the 45-70 is, since this often slow-moving and stiff-recoiling round can spend considerable time in the barrel, that if there is a noticeable variation in the velocity, it will magnify the POI difference by slinging the slow round obviously higher on the target.

Shot a batch of carefully loaded rounds last weekend. Most rounds in about a 2 inch circle at about 1650 and then a round went off about 1400 and went high about 2 inches above the others, even at 50 yards.

So my theory is the same velocity variations with a fast little bullet matter much less than spreads with the big slow bullets. Can I get a witness?

james · « **Reply #28 on:** February 17, 2011, 04:58:47 AM »

My daughter and I ran a batch of .223s from min to max load using AA2230 powder and 55 gr. Rem bullets. With her shooting three shot groups of one grain increments, in a 700 Remington, the spread went from 60 fps and 3" groups at the min load to 8 fps and half inch groups with the max load. I would say you get a more consistent burn rate and constant velocity when the case is full of powder and the bullet is traveling at a higher velocity. My most accurate and most consistent velocities were actually a half gr. over max which was a compressed powder charge but it heated the barrel up quickly. I don't use that load for prairie dog shooting.
So, I'll go out on a limb and say the slower moving 45-70 would have a greater StdDev in velocity.
Also, a 50 fps variation in a 1500 fps round is twice as much as a 50 fps variation in a 3000fps bullet.

tacotime · « **Reply #29 on:** February 18, 2011, 08:27:06 AM »

Truly spoken. When folks say a 100 fps spread is not abnormal, it is as you said, twice as extreme for the bullets travelling at half the speed of the other.