Chronograph FPS std deviation..

E

eww1350

Guest
While helping a friend develop an accurate load for his .220 Swift..we were having a devil of a time getting W-W brass to shoot under 3/4"...working with H414 and 55 grain Ballistic tips in a Shilen SS Match 14 twist...
All loading was done indoors no a/c...shooting on my private range..
While fighting the warm switchy/windy conditions...and loading three rounds at a time and hand trickling to exact weight...we decided to try some new Norma brass...and had an imidiate improvement...Now here the story gets weird...
three pieces of new Norma brass were loaded with 41.5 grains of H414 a 55 grain BT on top and a Federal 210M on bottom...
Chronograph registered 3736, 3751, then 3886..:eek:
Whoa where did that come from...so I went back loaded the same three pieces of brass all with the same components and the Chronograph registers 3731, 3844, 3877...What the H***
Why such std deviation..???
My concern is that the primers can be the only contributor to the wide std deviation...all else was identical...temperature did not increase or decrease during the two 3 shot strings...
Have you experienced this..??
Your thoughts..!!

Eddie in Texas
 
What brand Chronograph?

Obviously something is rotten in Denmark. I have never found any brasss to contribute anything to accuracy once they are straight from having been shot and gone through a Full length die. I have abandoned Lapua for RP 308 cases for my 30-44 and am getting great accuracy from them. I picked every one of them up at the range. I use to go to Wyoming to visit friends a week in the spring and fall. I use to load 500 rounds of .223's to shoot Dogs with in his Savage 112 it think it is; a heavy single shot rifle. ( this was back when the Airlines didn't care if you had ammo in your checked baggage) Once I had found a load the barrel liked I loaded every case I had picked up with the components that shot good in the rifle. The danged rifle would shoot small holes with all the bullets touching if one payed attention. This, among other experiences pretty much convinced me that brass is only a container to hold the stuff that matters.
 
If?

If you use the same brass in the same order............next time try firing the brass in reverse order.

Let us know the results.
 
Maybe I will use a second chronograph behind the first to validate it..:rolleyes:
 
It could be the chronograph. A long time ago I was shooting my dad's old Savage 99 in .300 Savage with 150 gr bullets, and getting velocities that were even crazier than the ones you're getting, 1000 fps ES. Bad chronograph was the answer.

On the other hand I wonder if you're getting inconsistent ignition due to the primers and the H414 being maybe hard to ignite. If you can get ahold of some Fed 215's or CCI 250's you might give them a try, but cut back on your powder charges if you're near the upper end with these loads with the 210M's.
 
eww1350 said:
I am using a Pro Chrono Jr....
Click to expand...

What would be the second chrony? The reason I ask is, I had several chrony's and non of them were ever consistent for me. It didn't matter if I sent arrows or bullets the velocities were inconsistent enough to drive me nuts. I then purchased a 35p from ebay it worked for a while. I had to send it to Oehler and they fixed it but while waiting I picked up a CED Millennium infra red and it worked great. I'm now tooling around with a PVM 21. Its flawless. The way I figure it, we spend thousands of $ on equipment plus 100s of hours to make these guns shoot as small as possible. With that $/time investment isn't it worth spending the money once so we have dependable instruments to record data? Anyway, two chrony's are better then one. Give it a shot!
 
Your results are not unusual. I'm not saying the chrono is not suspect, but I have had similar results on occasion with my Oehler 35 and I know it was not a chrono problem.

First off, swifts are fussy. I own one as well and tried literally 12 different powders to find something it wouldn't laugh at. When I found what it wanted, it shot quarter inch groups to high .3"s pretty routinely but I could never get the standard deviation down less than 15 fps. A lot (probably 70%) of the loads I tried had deviations in the 20 to 30 fps range.

Second, little bullets going mighty fast often don't yield small deviations no matter what you do. You can tune a gun with little bullets (bullets under 65 grains) until it's razor sharp and you can have perfect brass and perfect barrel and it won't make a difference to lower deviations. Lots of guys as of lately have been tinkering with .17 calibers, .20 calibers, and hotrod .22's and I haven't heard too many of them comment on great deviations. They usually just mention something about 4200 fps or some other blazing velocity.

Thirdly, H414 probably isn't the best powder for trying to achieve small deviations. Why? Because it is so temperature sensitive that one day it might be very uniform and giving good accuracy and the next, it goes all to h%&$ in a handbasket.

Standard deviations change with the load. You can plot the sweet spots of efficient powder combustion simply by watching the deviations as you run a ladder of charge weights starting with mild loads and working up to max loads. Sometimes the best 100 yard accuracy comes from loads with big deviations. Sometimes it is best with small deviations. But all it takes to change it is .3 grains of powder!

If you want to really have an eye opener, chamber up a fast twist barrel (8") for a 220 swift and shoot 80 grain bullets through it. Deviations will be quite easy to get small. Heavy bullet, slower burning powder, and expansion ratios change and it's like having a totally different caliber.
 
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Pete Wass said:
Obviously something is rotten in Denmark. I have never found any brasss to contribute anything to accuracy once they are straight from having been shot and gone through a Full length die. I have abandoned Lapua for RP 308 cases for my 30-44 and am getting great accuracy from them. I picked every one of them up at the range. I use to go to Wyoming to visit friends a week in the spring and fall. I use to load 500 rounds of .223's to shoot Dogs with in his Savage 112 it think it is; a heavy single shot rifle. ( this was back when the Airlines didn't care if you had ammo in your checked baggage) Once I had found a load the barrel liked I loaded every case I had picked up with the components that shot good in the rifle. The danged rifle would shoot small holes with all the bullets touching if one payed attention. This, among other experiences pretty much convinced me that brass is only a container to hold the stuff that matters.
Click to expand...


Pete,
Who was the guy who said, "brass is the fountain from which all accuracy flows"? He was a pretty smart guy and a lot of what he said is considered gun scripture.
 
Maybe it was caused by sun glint off...

your bullets passing thru the screens. This can cause spurious velocity readings as the timer in the screen windows doesn't pick up the bullet accurately. Try coating the bullets with a black Magic Marker and then shoot them thru the chrono. This has cured the problem you described on several occasions for me.

Jim
 
goodgrouper said:
Your results are not unusual. I'm not saying the chrono is not suspect, but I have had similar results on occasion with my Oehler 35 and I know it was not a chrono problem.

First off, swifts are fussy. I own one as well and tried literally 12 different powders to find something it wouldn't laugh at. When I found what it wanted, it shot quarter inch groups to high .3"s pretty routinely but I could never get the standard deviation down less than 15 fps. A lot (probably 70%) of the loads I tried had deviations in the 20 to 30 fps range.

Second, little bullets going mighty fast often don't yield small deviations no matter what you do. You can tune a gun with little bullets (bullets under 65 grains) until it's razor sharp and you can have perfect brass and perfect barrel and it won't make a difference to lower deviations. Lots of guys as of lately have been tinkering with .17 calibers, .20 calibers, and hotrod .22's and I haven't heard too many of them comment on great deviations. They usually just mention something about 4200 fps or some other blazing velocity.

Thirdly, H414 probably isn't the best powder for trying to achieve small deviations. Why? Because it is so temperature sensitive that one day it might be very uniform and giving good accuracy and the next, it goes all to h%&$ in a handbasket.

Standard deviations change with the load. You can plot the sweet spots of efficient powder combustion simply by watching the deviations as you run a ladder of charge weights starting with mild loads and working up to max loads. Sometimes the best 100 yard accuracy comes from loads with big deviations. Sometimes it is best with small deviations. But all it takes to change it is .3 grains of powder!

If you want to really have an eye opener, chamber up a fast twist barrel (8") for a 220 swift and shoot 80 grain bullets through it. Deviations will be quite easy to get small. Heavy bullet, slower burning powder, and expansion ratios change and it's like having a totally different caliber.
Click to expand...

My experience coincides with goodgrouper's. (except the fast twist which I've not tried) I've had something like 20 Swifts and worn out at least a dozen barrels in this caliber.

You might want to try 3031, 4064, maybe VV140 (if there is any) or some other powders that you might think are "too fast" for this case. Going the other way 4350 can be good. The "new" short cut version oughta be better than the old. You might try that with 55s and a 60 grain bullet too. A 1-14 twist will stabilize a 60 with a good stiff load.

I'd just shoot 3 shot groups to begin with and when I found something good then chrono that and work with it to see if I can meet the velocity goal.
 
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