The 6PPC and Velocity Spreads

jackie schmidt

jackie schmidt

New member
I know that in 100-200 yard Benchrest, we look at extreme velocity spreads as a "non-issue". If all of the shots go in the group, who cares.

But this has always bugged me.

Sunday, a whole bunch of us were out at Tomball, tuning up for next week ends all 200 4-Gun at Denton.

I am still trying to get comfortable with the new lot of '07, so I had my 35P Chrono set up.

I got my Rail and two Sporters tuned in, good consistant "two's" and "three's at 200 yards, nice round groups, no popped shots.

But, the velocities were all over the paper. I was getting an average 3430, but some of the strings showed as high as 3460, and as low as 3415. That, in general terms, is terrible.

This almost doesn't seem possible, to shoot at a sub .200 agg level at 200, and have that much spread.

Now, I know it shouldn't matter, but it still bugs me. But, I suppose it is better than having spreads of less than 10fps, and shooting "sevens"...........jackie
 
A 40fps extreme spread (3420-3460fps) will give only about 0.170" of vertical at 200yd with a bullet having a BC=0.290. This becomes almost 5" at 600yd. That's a change of almost 10-fold in terms of MOA, which is why velocity spread matters much less in the point blank game than in the long range game. Or so says the arithmetic ... ;)

Toby Bradshaw
baywingdb@comcast.net
 
Jackie

Your chrono is showing a spread in the range of 1.0 to 1.5 percent. Just what is the accuracy potential of the instrument. 1 percent is very good. Your velocity spread just might be a lot closer than you think.
Donald
 
Jackie, this is why tuning is velocity specific. When you're tuned the slower bullets do arc higher.

al
 
Jackie, go back into the archives and search for HBC, or try to contact Henry Chiles. Part of what you are getting may be instrument error by having the screens too close together. If I remember, Henry insisted on at least 16' of screen separation.

I may be way off on the distance but hopefully someone will correct this, someone, hopefully Henry!!.
 
Jackie, go to http://www.benchrest.com/forums/showthread.php?t=60044 . This is a recent thread by Henry.
Read his text file. Seems the distance might need to be 24'. I didn't read it in detail, my eyes are still screwy.

I just printed this out and it is about 20 pages but it will be printing paper and ink well spent if you are serious about external ballistics.
You can read McCoys whole book and it will say little more than this paper by Henry. Hopefully he will make this a blog on BR.com.
 
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jackie schmidt said:
I got my Rail and two Sporters tuned in, good consistant "two's" and "three's at 200 yards, nice round groups, no popped shots.

But, the velocities were all over the paper. I was getting an average 3430, but some of the strings showed as high as 3460, and as low as 3415. That, in general terms, is terrible.

...jackie
Click to expand...
3460 fps in a 22" barrel, zero freebore for the 00's, and V133....WOW!!
 
If memory serves, the circuitry in the Oehler 35 allows for the switches to be set for a 2',4',8',and 16' spacing. But anything over 4' becomes hard to transport in my opinion and you're not going to see significant differences or improvements for our purposes with an 8' or 16' spacing.

And the destruction manual does say to set the chrono up at least 10' from the muzzle.
 
jackie schmidt said:
I know that in 100-200 yard Benchrest, we look at extreme velocity spreads as a "non-issue". If all of the shots go in the group, who cares.

But this has always bugged me.

Sunday, a whole bunch of us were out at Tomball, tuning up for next week ends all 200 4-Gun at Denton.

I am still trying to get comfortable with the new lot of '07, so I had my 35P Chrono set up.

I got my Rail and two Sporters tuned in, good consistant "two's" and "three's at 200 yards, nice round groups, no popped shots.

But, the velocities were all over the paper. I was getting an average 3430, but some of the strings showed as high as 3460, and as low as 3415. That, in general terms, is terrible.

This almost doesn't seem possible, to shoot at a sub .200 agg level at 200, and have that much spread.

Now, I know it shouldn't matter, but it still bugs me. But, I suppose it is better than having spreads of less than 10fps, and shooting "sevens"...........jackie
Click to expand...


Jackie,
I'm curious if you shot the other loads in your tuning process over the chrono? Did you have better deviations at slower velocities but the groups weren't as good? 9 times out of 10 that I've chronoed a tune session, the most accurate load had the smallest deviation or close to the smallest deviation. In other words, the accurate load usually had a standard deviation of 15 fps or less. SOmetimes I'd get a deviation around 3 or 4 but that load may not have shot as good as the load that had 7 or 8 fps deviations but 7 or 8 is still pretty darn low.

Oh, and I'm curious as to the standard deviation of the load you settled on that had an extreme spread of 45 fps.
 
First time out this spring?...

Jackie...
Certainly not trying to insult anyone's intelligence here, BUT...is this your chronograph's first time out this spring? If so, did you check your batteries? Also...do you store your skyscreens anywhere that could potentially attract moisture? If so, take a little sandpaper over the connector inserts...
Both of these items have worked wonders for me to reduce extreme spreads and standard deviations in the spring of the year after the chronograph has spent the winter in limbo...
 
Kent

No, I had it out about a month ago, I keep a new battery on hand.

We shot several other Rifles over it, shooters just wanting to confirm their velocity windows. All checked out about what we figured. Every thing with the 35P seems to be in order.

All I really use the Chrono for is to get a baseline. I know what the old 683-03 N133 shot with my standard upper end load, I figured I would just load the to about the same velocity window,and tune from there.

I wish I had done this three weeks ago, I would have discovered I was shooting the 07 way too hot. I had already determined that it is about .8 grn denser than '03, in other words, to obtain the same weight with my Hensler, I had to move the knob, (graduated in .1 grn), that much in to duplicate the weight. Since all 133's that we have tested through the years shot about the same velocity when set by weight, I made an erronous assumption that this would as well.

It doesn't. The load that I was shooting that weighed the same as the '03 went over 3500 fps. It also shot like cr-p.

So, by working withj the Chrono, I now know, (hopefully), where the true accuracy upper window is with the '07.

I consider the average velocity to now be around 3420, that is with my "zero" freebore reamer. One of the beautys of the '07 is you don't even have to slow trickle it to get it all in like I did the '03.

What I am trying to do is find that same load combo that I had with the '03, allowing me to not change the load more than a "tenth" or two one way or another, and keep the Rifle agging with the tuner.

I got sort of spoiled with that '03, which I have used for the past 4 years, with good success But, true to my usual paractice, I bought Two "hazmats worth" of the '07 a while back, and I will get it figured out, later, if not sooner.
.......jackie
 
To Jackie Schmidt............

When you say you are .2's-.3's @ 200yds,is that inches or aggregates?
Thank you very much for your thread on tuning--much appreciated. gpoldblue
 
jackie schmidt said:
I got sort of spoiled with that '03, which I have used for the past 4 years, with good success But, true to my usual paractice, I bought Two "hazmats worth" of the '07 a while back, and I will get it figured out, later, if not sooner.
.......jackie
Click to expand...

Jackie, one thing to notice about the '07, see if you get fewer unexplained fliers. One of the SE top shooters is swearing by the '07 stuff.
Says its better than the '99 v133 was.
I'm not talking about big pop-outs but the little pop-outs that defy the condition.
 
jackie sir

you may have done this already but if you want to level out your velocites change up the jam a bit. hope this helps. tim in tx
 
Tim,
Telling Jackie to adjust his jam is slightly akin to telling a surgeon to be sure his knives are sharp. ;)
 
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