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Very Hot Topic (More than 25 Replies) Standard deviation vs. spread on velocities (Read 21599 times)
Domino81
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Standard deviation vs. spread on velocities
Oct 14th, 2018 at 5:11am
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Hi, I am Dominik, It's my first post on this forum so having the occasion I wanted to simply say hello. 

I am shooting oryginal Black Powder Maynard Sporting Rifle 35-30 that I bought some time ago and reanimated. It has 26'' barrel pretty good bore that allows me to believe I could be shooting some good 100 meters groups. I see the potential in this rifle as It happens often that 4-5 shots out of 10 shot string are in less than an inch grouping.. 

Unfortunately as I try to find a good load, there is something strange on the chrono that I cannot understand and as I presume it might have something to do with the group sizes. The Spread is almost every time over 50 with a double digit Standard Deviation. 

In the same time I wanted to ask about Standard Deviation and how does it differ from Spread read on My Chronograph. 

I weigh every charge to 0,1 grain. Bullets are +/- 1 grain. 

What may be primary sources of a large spread? As I presume it should be no more than 15-20 and it might have a devastating influence on the accuracy. 

Also, what are the velocities I should be aiming for?

Dominik.
  
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frnkeore
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Re: Standard deviation vs. spread on velocities
Reply #1 - Oct 14th, 2018 at 8:30am
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Welcome to the forum, Dominik.

Yes, 50 fps is to much. You didn't give us the load or bullet weight you are shooting. Is it black powder or smokeless? If smokeless, what powder are you using? Some powders burn better than others, at our lower pressures. BP, depending on the brand, will burn a bit different and will also foul the bore differently.

Please give us the powder, weight and velocity, also the bullet weight and whether your shooting breech seated or fixed ammunition.

Not many people shoot your caliber so, much of what we say, especially about smokeless loads, will have to be speculation but, I do have a rifle that should be close. It's a 35 caliber on the 357 Maximum case but, I have only shot it breech seated, with smokeless.

Frank
« Last Edit: Oct 14th, 2018 at 10:05am by frnkeore »  

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MartiniBelgian
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Re: Standard deviation vs. spread on velocities
Reply #2 - Oct 14th, 2018 at 8:34am
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Sound like fouling management issues, or a bullet that is not seated correctly in a fireformed case.  More details would be helpful though.  Bullet weight, alloy, fouling management, dimensions,...
  
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frnkeore
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Re: Standard deviation vs. spread on velocities
Reply #3 - Oct 14th, 2018 at 10:08am
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One thing that I forgot to ask is, are your groups stringing mostly vertical or are they horizontal or both? 

Frank
  

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gunlaker
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Re: Standard deviation vs. spread on velocities
Reply #4 - Oct 14th, 2018 at 10:24am
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One further thing to be aware of.  Some chronographs are easily confused by the wads and debris coming out of the muzzle of a rifle shooting black powder.  I sold my Shooting Times Chrony and switched to a Magnetospeed for that reason.

I don't shoot that cartridge, but generally all of my various black powder rifle loads are between 1150 and 1420 fps.   Ten shot standard deviations of 5 fps are easy to achieve.  Getting below 4 fps SD takes more effort. Often large SD's are not a function of the load, but a function of your fouling management.  An inconsistent bore condition will easily take a 3 fps SD load and make it a 6 fps SD.

I don't pay as much attention to extreme spread as I do to SD, but I'd say that ten shot extreme spreads of 15 fps should be easy to achieve.  Extreme spreads of 10 fps or less are possible but require more effort.

Often you can get big changes by switching primer types.

Chris.
  
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Domino81
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Re: Standard deviation vs. spread on velocities
Reply #5 - Oct 14th, 2018 at 10:29am
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Yes, sorry, sure, should have provided more details. I shoot Black Powder Only. I was trying from 26 to 32 grs in 1,5Fg and 2Fg. I always pour the powder using 24 inch drop tube. 

Barrel has 1:28 twist. I shoot 200 grs nose bore riding design (Accurate Moulds) Band .001 larger than the bore (slugs at .369). Bullets are made from 8BHN alloy. 

Bullets are not sized, pan lubed with SPG. 

I clean after each shot, Felt cleaner with cleaning compound and then dry patch. Problems are still there. 

Velocities that I am noting are between 1100 Fps (26grs CH4) to 1300 (32 grs CH2). I get the same kind of spread in all loads that I test. 

The Spread has a tendency increase if I compress. 

I tried both: 
- fixed ammo with fire formed cases neck sized so that cases can hold the bullet and then bullet hand loaded into the case. Necks sized so that there is a sure hold for the bullet, but no crimping. If I do not size the necks, inner diameter is 8 thousands of an inch larger than the bullet. Simply original cases had thicker walls than 38-55 cases that I shortened and adopted to this obsolete caliber.
- Breech seating 1/8 inch ahead of case, case full of powder. Also different granulations. On 37 grs of FFFg gives max velocities of 1350 Average Fps. the same kind of spread unfortunately. 

That would suggest ignition issues? I started thinking that 26 inch barrel is maybe too short to burn that kind of powder amounts? 

I also do have an observation, that compression increases spread - that would probably point over to ignition issues..

My Maynard is a percussion breach loader, so I ignite the powder with a 6mm RWS Musket cap...

Schuetzendave, are you putting the Wad from the primer side or from the powder side?
  
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Domino81
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Re: Standard deviation vs. spread on velocities
Reply #6 - Oct 14th, 2018 at 11:00am
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frnkeore wrote on Oct 14th, 2018 at 10:08am:
One thing that I forgot to ask is, are your groups stringing mostly vertical or are they horizontal or both? 

Frank


I get both unfortunately
  
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Domino81
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Re: Standard deviation vs. spread on velocities
Reply #7 - Oct 14th, 2018 at 11:03am
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gunlaker wrote on Oct 14th, 2018 at 10:24am:
One further thing to be aware of.  Some chronographs are easily confused by the wads and debris coming out of the muzzle of a rifle shooting black powder.  I sold my Shooting Times Chrony and switched to a Magnetospeed for that reason.

I don't shoot that cartridge, but generally all of my various black powder rifle loads are between 1150 and 1420 fps.   Ten shot standard deviations of 5 fps are easy to achieve.  Getting below 4 fps SD takes more effort. Often large SD's are not a function of the load, but a function of your fouling management.  An inconsistent bore condition will easily take a 3 fps SD load and make it a 6 fps SD.

I don't pay as much attention to extreme spread as I do to SD, but I'd say that ten shot extreme spreads of 15 fps should be easy to achieve.  Extreme spreads of 10 fps or less are possible but require more effort.

Often you can get big changes by switching primer types.

Chris.



I use Pro Chrono Digital
  
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frnkeore
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Re: Standard deviation vs. spread on velocities
Reply #8 - Oct 14th, 2018 at 11:08am
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Dominik,
Back 30 years ago, when I still shot muzzle loaders, regularly, percussion caps where a huge variable in accuracy and could make or break any load.

In my testing, RWS caps where the only ones that could give me any real accuracy. The only others available then, was CCI and Remington.

Also, at that time, the only powder available was GOEX. With that brand, accuracy only came with larger granulation's, FF & F. That was because of the "fine's" in the smaller granulation's. That may not be the case anymore with powders such as Swiss but, with GOEX, it played hell with the ES's. Going from FF to F in my cartridge rifles, reduced the groups by about 1/3 and that was w/o weighing and just throwing charges.

I also used LDPE, 1/16" thick wads, that helped, too.

If you use paper between the cap and powder, you could do it by installing it in your case, before charging it with powder.

Frank

« Last Edit: Oct 14th, 2018 at 11:31am by frnkeore »  

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Domino81
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Re: Standard deviation vs. spread on velocities
Reply #9 - Oct 14th, 2018 at 11:19am
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In Schuetzen Rifles Book of Ned Roberts i have read that they used a sort of priming smokeless powder charge to help ignition. Wondering whether that smokeless could be replaced with c.a. 3 grs of 4Fg.. did anyone tried that kind of priming charge on the bottom of the case?
  
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MartiniBelgian
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Re: Standard deviation vs. spread on velocities
Reply #10 - Oct 14th, 2018 at 12:25pm
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If you're using GG bullets (as I think you are), you could be overcleaning:  1 or 2 moist (not wet) patches should be enough.
Try fireformed and unsized, bullet seated into the rifling (touching).  Never mind the bullet being a bit loose in the case.
Start out  with a load requiring little or no compression, and then starting increasing your load.  Annealing your case necks might also help if you are using neck tension.  And that primer, yes, definitely a variable...  Overprimerwad  usually inside the case.
The fact that your twist limits you to a light for calibre bullet doesn't help either.
And me, I'm mainly looking to ES instead of SD  Wink
  
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JLouis
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Re: Standard deviation vs. spread on velocities
Reply #11 - Oct 14th, 2018 at 1:45pm
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I personally have found over the past seventeen years of competition and load development that the lower SD's and ES's don't always provide the best results and often times they can provide just the opposite. I have learned to go by what my targets / group sizes are telling me is the very best and no longer pay attention to the SD's and ES's they are what they are when all is said and done and they can either be on the high side or the low and they don't seem to make any difference in regards to what actually ends up shooting the very best. 

JLouis
  

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Re: Standard deviation vs. spread on velocities
Reply #12 - Oct 14th, 2018 at 10:27pm
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When I had a rifle that I couldn't quite to get to shoot straight BP, I used about 10% by weight 4227 or Reloader 7, or just enough to clear the bore of fouling, but no more than 15%. Next step was to experiment with overall cartridge length; engaging the rifling, .005", .010"  & .015" short of that. It took me half a ton of BP to discover that on my first rifle, a .38-55. Everyone told me to engage the rifling  Cry   

My Ohler 33 gave me straight BP info comparable with Gunlaker's.  When I got to where I wanted to be, the chrono data and the targets agreed. 

Not sure what my BHN was, but the bullets were mostly half wheel weights and lead or 30:1 lead tin. Be careful with the stick on wheel weights.  Many of them contain zinc and you do not want to contaminate your pot or mold with it!

Leave no stone unturned, you will get there.  Good luck & Welcome to the forum.
  

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frnkeore
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Re: Standard deviation vs. spread on velocities
Reply #13 - Oct 15th, 2018 at 2:11am
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If your load shoots like crap and has large ES, you work on your load.

If your load chrono's well with small ES and the targets are crap, you work on your rifle.

It's just a tool that can help you if, you lesson to it. It's not necessary if you can start with a proven load but, can really help if that isn't available. 

Frank
  

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Re: Standard deviation vs. spread on velocities
Reply #14 - Oct 15th, 2018 at 8:16am
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And if all that doesn’t help then work on your golf game 😀

Jack
  

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