Opinions on Repeating a good Load , ES, SD , Velocity, Grouping

[Lindsey]

This has happened a few times. Find a good load one year, go back the next and it isn't a great load anymore.

BUT the loads I am working on now both in .260 and 7mm Rem Mag I got Great groupings with Low ES ....4 days ago. I load the exact same loads so I am shooting in the same location with the same weather, same everything that I can think of and the groupings have doubled in size. The velocity also changed. On the .260 Still have an ES of 12 but 28fps slower. On the 7 an ES from 7 is now 23 and velocity 16fps slower.
Any Ideas of why? So frustrating.
Thanks for any help.

 

[Capt RB]

If it is single based powder loaded last year it will degrade.

 

[Lindsey]

That could makes sense on the loads from last year if it is single based. How do I know if RL16 is single or double?. RL-26 is what I recently shot and all shots were from the original bottle just purchased. And I'm sure many will say then the error is the shooter but I am doing the best I can to do everything the same including how I am shooting.

 

[LongBomber]

What chrony are you using? May expalin the velocity shift.
Were your temps exactly the same on the two eange trips?

 

[Lindsey]

ProChrono Digital . Placed at Same distance and leveled. Temps are less than 5 degrees apart. I have lab radar. Looks easy to use. Have been out with couple different people and haven't been able to get that to work.

 

[Capt RB]

That could makes sense on the loads from last year if it is single based. How do I know if RL16 is single or double?. RL-26 is what I recently shot and all shots were from the original bottle just purchased. And I'm sure many will say then the error is the shooter but I am doing the best I can to do everything the same including how I am shooting.

As far as I know all Reloder powders are double based. Not is not to say that there is a bit of degradation but as a rule they are better for long term storage.

 

[Greyfox]

How many rounds have your barrels seen? Whether factory or custom, I have found that I generally takes as many as 200 rounds to stabilize velocity and accuracy.
Using optical chronographs, it not uncommon for subtle differences in lighting to alter results. As to the group size changes you describe, I would confirm these changes with one or more shooting sessions.

 

[Lindsey]

The 7mm Rem Mag has more than 200 rounds. The .260 Has around 220 rounds through it. I know the chronograph is a cheaper one (which I was I was so excited for Lab Radar... until nobody can get it to work! Online videos...it looks so easy. Looks like I need to keep working at it)

 

[JTB]

Grouping sizes fluctuate a little on me also. I have always contributed it to the wind changes, barrel condition and maybe I am a little off my game. Early morning always seems to produce the best groupings as no heat waves to blur the target and minimal wind. That being said I always work up my hunting loads immediately prior to going out to make sure they are grouping well. When I am comfortable with grouping size I leave the barrel in the same condition it was when I finished working up the loads. Normally they group best for me after about 10 rounds through a cleaned barrel but they are all a little different. One thing that helps me is to run a ladder test to find where the stable velocity range is. Normally you will find charges within about 1 grain range to produce similar velocities and POI. I try to stay in the middle of that range to give me that margin of error to work with. If the powder charge or temperature varies slightly I won't be as likely to see the POI change.

 

[snox801]

That's why I don't put to much weight on ladder tests. I know it is a part of the work but I also have the same thing. I now use a magneto speed as it's very accurate. I find pressure then back off a bit and see what the sd is. Part of it is me not being able to shoot the same group each time. So my best group may not be the best load.
I had velocity differences with my f1 also.

 

[ralphjunius]

Your sample size may be too small. How many rounds was your previous calculations based upon?

 

[Rudolph Ferdinand]

I've been handloading for 30 years and I just got into this thing called, "PRECISION Reloading". The old years days, I would find a good powder for the cartridge and loaded it up and off to the range I go for accuracy testing...not anymore. With SD/ES numbers and group sizes, we want it every day, and it just isn't going to happen. Atmospheric pressures aren't consistent...change but how much does affect that powder...second grade powders we used not the same, like, companies like Hornady or Remington uses. I built an AR-10 in 6.5 CM and here is all the factory manufactured ammo I used trying to find a load (factory) for it; Hornady 140 grain BTHP (200 rounds), Federal Premium 130 gr. Gold Medal Berger, and Norma Match 130 gr. and Hornady Match 140 ELD, and Hornady's American Gunner 140 gr. HPBT. All the Hornady ammo worked at first as long as the temperature is above 65...not enough atmospheric pressure? I have tested loads one week but the next, the load, isn't doing anything, like the week before and it is above 65. So, I am just going to shoot my guns and enjoy the day! The AR-10 build cost me with including the scope $2600-$3000. Puzzled! By-the-way, all non-Hornady ammo would shoot.

 

[ShtrRdy]

I've also had this same velocity change happen in the past. Recently I learned something about my current "Jeckle & Hyde" velocity. After I had arrived at a load that would generally group well, I decided to try the 10 round Satterlee test. I loaded up a series of shots spaced 0.2 grain apart. What I discovered is the powder charge I had chosen for my load was in an unstable velocity node. It was a velocity flat spot but the center velocity actually dropped in the middle and then came up again on the next step. ( I used a magnetospeed )

There was another velocity flat spot in the series so I'm currently trying it out. On three different occasions I've loaded some rounds, gone out to the range, and measured velocity and shot a couple groups. The average velocity from each of those three outings is within 5 fps of each other, and all the SD are single digit.

 

[Lindsey]

Your sample size may be too small. How many rounds was your previous calculations based upon?

I am shooting 4 shots for testing.