I’m at a fork in the road...

Shot 110 gr Sierra Pro Hunters in my 270 Win yesterday. Factory Ruger American, Winchester brass, Fed 215 primers, and Rl 17 from 55.5-61 gr, moving in 1/2 gr increments and 3 rounds per load. Had some pretty impressive groups and some pretty impressive ES/SD’s.... unfortunately not on the same loads. I know I’m not an accomplished shooter, so this makes me skeptical regarding my groups (when my numbers are good). On the other hand, all powder is measured in an RCBS chargemaster, and I’ve read here that between the given margin of error with this scale and the “rounding up” I could be off 1.4 gr (I’m not currently double checking wts on a 2nd scale). Also, I’m not alway convinced my Caldwell chronograph is reliable...I’ve gotten readings at <1000 FPS up to almost 4800 FPS. This makes me skeptical of my numbers (when groups are good)...in my shoes, would you explore the better groups or the better numbers? Thanks.

 

What's on paper is my approach.
Get a second scale to verify

 

Explore the better groups and see if you can make them repeat. Accuracy wins.

 

My suspicion would be the CM.
Have you added the McDonalds straw mod or a bushing sleeve to the dispense tube ?
OR done any of the dispense mode mods ?

I own one too and yes they can drop clumps of powder (depends on type) if you don't do any mods to them.
A rock solid bench is also necessary for repeatability.

 

As Yogi used to say "when you come to a fork in the road...take it!
Sorry, I just had to.

 

trust your target, your vel, #s are no way right ,your way off on both ends. maybe borrow a crono if you need #s .keep shooting and have fun. dave

 

You are always going to wonder and guess if ur equipment is not accurate. Trust your groups but get reliable scale and chrono or you will always wonder. Also if equipment isnt accurate what says you will repeat next time out.

 

It's always great to see a load that yields a tiny sd number, sometimes those loads will come around for group with tiny changes in seating depth, primer change, or neck tension adjustment... however sometines certain bullet, gun, powder combinations dont play well together. I've had loads that would print small groups and have an sd around 20, all because of a can of worms known as, positive compensation. Me personally I like to chase tuning a load with low sd. All data is good data you can always loop back and try another direction. As long as you're in an "accuracy node" you should have some leeway in powder charge. However the spotty chrono numbers can be alarming, if your work up is based solely on velocity differentials.
Beef

 

well I was thinking....ALWAYS take the Right fork.

 

That's good, but the definitive answer is:

". . . take it!."

 

I do F class and twenty shot groups so I am more concerned about the CEP numbers than SD's and ES's. They give you a better idea how a load shoots on target rather than on paper. Most of the time the SD's and ES numbers are good indicators of how well a load will perform but my 300 yard load for my .223 does .6 MOA ten shot groups and 1.0 to .75 twenty shot groups with a SD of 40 and a ES in the triple digits. Most of the 20 shots are within .5 MOA and all I have to do is get it centered. You can't always tell, one or two outliers can screw up a SD or ES even with a large sample size

CEP stands for circular error probable and gives you a good indicator of how well you, the rifle, and the ammo perform together

https://en.wikipedia.org/wiki/Circular_error_probable

 

My Chargemaster doesn't vary by that much. Occasional throws (maybe 1 in 5) to perhaps 3 tenths heavy (it's rarely on the light side); seldom (maybe 1 in 15 or 20) that may be up to a half a grain off. All my charges are double-checked on a scientific scale (accurate to .01 grain per the product description, though it displays in .02 gn increments.)

IMO, the tale on the target is the one you want to chase. The best numbers in the world don't mean a thing if the shots don't go where you want them to.

 

OP, you are probably too close to your chrono screens. Put them 10' farther away from your muzzle to avoid erratic readings. Barlow

 

.1 gr is quite a bit on my beam scale

 

I actually havent heard of that before, thank you for teaching me something jimsc

 

grab this https://ontargetshooting.com/ then do four sets of five shot groups without any scope adjustment then overlay the point data from the four targets into one using a software program and you can get a good idea if how much potential a load has

this is a example of two powder weights see how weight tolerant a load is. These are only 3 shot groups for this test, next step was to do 10 shot groups with the the 23.4 load. Notice the data window at the lower left corner. That CEP 95% # lets me know that there is a good chance my groups will be sub MOA at that distance even if my powder charge is off by .1 gns either way. I used 23.5 group as the sighters, a scope adjustment was made

 

Leave the chronograph at home.

 

IMO, .1 grain deviation in powder weight is white noise. It’s a deer rifle. Not a 1000 yard bench gun.

If the target look good and the load repeats then all is good.

 

Yes of course 270 Winchester

Excellent point..
J

 

Like Jim said, get a 2nd scale.