OCW test gone awry. Velocity all over the place!! Chrono?

[Pond James Pond]

I've just entered my data for a bunch of test loads I had. All in all, the outing has the potential for being a waste of 7 hours loading and shooting, as well as about €55 of components and range time....

I have got variations in velocity (within a given charge) that are very uncharacteristic of my OCW strings. (weights were: 44.1, 44.5, 44.9, 45.3, 45.7, 46.1, 46.6gr N140. 5 shots each). Calibre was .308, the bullet an Oryx 165gr JSP.

Today there was a breeze, but it was pretty much at 90 degrees to the trajectory.

But I have some quite large ES values (494ft/s in one case) and velocity is not rising with charge weight as normal.

I don't know if it was the cartridges that were igniting inconsistently, or the chrono was screwing up or something. I get the feeling it might be the chrono. Battery?

For example, I got lots of duplicate values: 2777ft/s at 45.3, 45.7, 46.1, 2749ft/s at 45.3 and 45.7gr.

I got values in the high 26xx's at 44.5gr and 44.9, but then again at 45.7!! Meanwhile 45.3 had every shot in the region of 27xx, except the last that came in at 2283ft/s!

My max charge only registered 3 shots of the 5 (although one ricocheted off a chrono diffuser pole!) and one of those 3 was 742ft/s....

So I can't draw many conclusions from the velocities.

Looking at the impacts, I got a fair bit of lateral spread, no doubt thanks to wind.
I also get vertical spread, but not what I'd expect: 46.6 with that ridiculous 742ft/s still managed a group just under 1"x1" with its 4 recorded hits. That slow one should not have been on paper.

45.7gr had about 0.8" vertical spread but 100ft/s ES on the Chrono.

Felt recoil also implied steadier increases than were recorded.

Based purely on the targets, I think there is an accuracy node at about 45.9gr
, and perhaps another around 44.3gr.

Despite the breeze, I feel the load development went OK, but I'd really have liked reliable velocity values.

 

[Pond James Pond]

More pics:

45.3gr

45.7gr

46.1gr

 

[Pond James Pond]

Final pictures:

46.6gr

Whole target, lower charges.

Whole target, higher charges.

Do members agree that my Chrono may be the problem and that charges around 44.3gr and 45.9gr are worth a closer look?

 

[Bart B.]

I don't think there's any statistical difference across all those groups. They're too close to the same size.

I've maintained forever that a few grains charge spread makes little difference in accuracy at short ranges. I think you just proved it.

You're shooting at 100 meters?

 

[Pond James Pond]

Yes, 100m.

I wouldn't take a windy day's shooting by a novice as solid proof of much, though!!

Meanwhile, do you agree that it seems my chrono may be giving faulty figures?

 

[Bart B.]

Yes, your chrono's probably sick or set up wrong; don't know for sure either way.

 

[1stmar]

Personally I chrono after I find the load(s) I'm interested in and I use it to validate velocity and determine sd, es etc. chronoing while shooting for groups has too much going on. I test with some cheap 22 ammo to be sure it is set up right. The hieight over the readers, sun, shade all play a role in your readings. If you hit a screen pole you likely were varying your aiming point and tge angle across the skyscreens.

 

[Pond James Pond]

Is this type of behaviour likely with a knackered battery?

If you hit a screen pole you likely were varying your aiming point and tge angle across the skyscreens.

Trajectory through the chrono was consistent throughout a given load weight, but did change when I aimed at a different charge target.

You can see the target sizes in the first posts so at 100m it was not a big change in aiming angle.

 

[1stmar]

Very possible

 

[Pond James Pond]

Typically I'd agree with the chrono measurements coming later, but I thought that if I find some decent accuracy nodes, I would have an idea of their velocities. Being a hunting round, I'd prefer higher velocity for better expansion, therefore discarding charges that were too slow.

I was hoping for 2750fps or more with decent accuracy. I'm guessing the 45.9gr node (between 45.7 and 46.1) would be close to that.

Soon I will need to load up a 15 or so of my best loads to date and see how they do at 300m.

I'll also try to zero at that distance. Should be interesting with my track record!!

 

[Bart B.]

I don't think any group represents an accuracy node. Their sizes are what several 5-shot groups will be with the same powder charge. If you think otherwise, shoot five or six 5-shot groups with one charge weight of your choice.

 

[AllenJ]

I'm with 1stmar on this, I always chronograph after I find the loads I like. That helps keep me from chasing velocities over accuracy.

As for your OCW test I like what I'm seeing from your "Whole Target" photos. It appears to me that you entire load spread is in the 3" or so area, pretty good for a hunting rifle with powder amounts ranging over 2.5 grains (maybe Bart is onto something about charge weights!) in my opinion.

As for chronographs I've stated my opinion a few times, I don't trust mine and I always confirm/correct what it's telling me by shooting 300 yards groups and measuring drop. Most chronos are dependent on light and when shooting outdoors that is a hard to control. My next chrono is going to be the Magneto Speed so I can eliminate that problem.

 

[Pond James Pond]

It appears to me that you entire load spread is in the 3" or so area, pretty good for a hunting rifle with powder amounts ranging over 2.5 grains (maybe Bart is onto something about charge weights!) in my opinion.

The rifle is in fact very capable. A far more successful OCW investigation gave me a load that managed sub-MOA with a 8-shot group: one ragged hole!!

So it can deliver very accurate shots. Admittedly, this is a hunting bullet not a target/LR bullet, but I was hoping for better outcomes. I think the wind did not help.

Had it been calm day, I'm sure those groups would have closed up on the horizontal plane.

IN any case, I have to start somewhere with this load if I am to hunt with it...

So I may as well load some at 45.9 and see how they do under better conditions and at longer distances too.

 

[bfoosh006]

I'm sorry , did I miss the rifle and load info ?

I'm guessing .308 ?

If you could share that info, that would help.

There are all sorts of reasons a reload might be "spastic".

Even if the primers are not fully seated.

 

[Pond James Pond]

Yep, .308 cal, 165gr bullet. OP edited to include this.

Yes, I suppose any number of things could influence the gun's performance, but the difference is that previously it has not given results like that.

 

[hooligan1]

Pond ole boy, was the bto (base to ojive) measurement the same all across that board?

Take the charge you feel like was best, load five rounds at .010 off lands, and do the exact same at .030, then .050, and .090 and .130.,,
See if those groups wont close some with one of those jump measurements, when you get a group you like, load ten and prove it. It works for me and its easier than shooting round robin..After I shoot ten at the chosen jump and I like the results, I will add powder until my velocity opens group, then go back to the last charge that shot the way you want, then move group to center of bullseye....

 

[Pond James Pond]

Well, I seated them all at about 0.035" of the lands, if I recall.

I've found seating depth can change a little from bullet to bullet and the ogive was such that I could load them out of the case to the point where they'd still fit in the mag and yet be touching the lands, so I decided to seat a tad deeper to avoid a OAL variation leading to a pressure spike.

 

[oldpapps]

Mr. Pond,

From your descriptions of the actions/reading from your chronograph, I would hazard a guess that it was the problem.
If that is correct, why?
Start with checking the battery and or replacing it, also check all connections.
You stated there was some wind, wind in it's self would have no effect but what was the clouds doing? Changing the lighting conditions would have some effects.
When I have a question about my chronograph, I will run a few .22RF over it to see if they read suitably. that about the only reason I ever shoot .22s.
Best part is you now have a valid reason to load and test again .

Load with care and enjoy,

OSOK

 

[243winxb]

N140 165gr Norma Oryx JSP flat base bullets- 308 win.

http://www.vihtavuori.com/en/reloading-data/rifle-reloading/-308-winchester.html Different Bullet = Different Pressure. Your bullet is not listed, but by the looks of the maximum powder charges, you may be starting at maximum?? Is the base of the bullet at the neck/shoulder junction? Or maybe seated to long trying to reach the rifling?

 

[Bart B.]

James, do you think every charge weight's groups will always be what they are even if you shot five 5-shot groups with each? What are the odds for a given charge weight producing groups the same size respectively as those shown?