Anyone ever seen a shot string like this?

[nchunter182]

Working up a load for my 280 Ackley using the 168VLD seated to the lands (3.513" COL) over H4831SC. Loaded one round each of 55-60.5gr in .5gr increments to find max load. Ended up at 2982fps and the attached target shows the results. Never seen a string like this as the shots started high and to the left and went down and to the right as velocity increased. Puzzled as to the results but encouraged that the last five shots grouped as they did.
Any thoughts?
Jay

 

[parker300]

I had that with an encore in 270 ended up changing the baces from the 2 piece aluminum to one piece steel and it fixed the problem

 

[FearNoWind]

100 yards? Is this off a bench? From a rest or sand bags? Bedded action? Assuming that the last five shots are the five lowest in the circle it appears you're close to the node for that powder charge/OAL combination. Any reason you started so close to the lands in developing the load you're looking for?

 

[nchunter182]

Yes, this is 100yds. Started at the lands to find max pressure and can back off from the lands to fine tune the groups. Didn't want to run into an overpressure if I build a max load at say -.050" from the lands and then moved up to the lands.
Jay

 

[FearNoWind]

... Didn't want to run into an overpressure if I build a max load at say -.050" from the lands and then moved up to the lands.
Jay

I think I understand your approach and it looks like you'll be able to tighten up the group with a little more experimentation. Now, of course, the only seating depth adjustment you have left is to move back from the lands and if you don't find a better node with that process you're either stuck with the results you currently have or back to adjusting powder weights to bring everything in balance.
Please understand that I'm not intending to criticize your approach to load development, but for other shooters who might be new to reloading and want to work on a load - I'd suggest starting about .020 off the lands and finding your best group/muzzle velocity combination and then working forward and back (say two or three rounds .006 closer and two or three .006 farther from the lands) to see where that charge balances with the seating depth.

 

[Mikecr]

Why would you build up to max pressure 50thou off -and then move seating into lands,, anyway?
It almost seems that max pressure point is more important to you than accuracy.

Was the bore fully fouled and at stable temp for all shots?
What was the shot rate?

 

[royinidaho]

What you are seeing in the posted group is not unusual, at least around my place.

With each rifle with which that type of group appears the cause was different.

With one rifle the easier solution was to work around your last 5 shots changing this and that until consistency over time occurred. Primers and powder charge weight were the significant variables. Consistency over time let me know, I think :roll eyes:, bedding was good.

Another rifle required rebedding to bring it around. Rebedded the action didn't help, even with adding pillars. Satisfaction was attained when 3 or so inches of the barrel was bedded.

Oh, and sometimes it was simply driver error…..

The short version is to keep messing around keeping good records and you'll gett'r figured out.

 

[stomp442]

The cause of poi change could be as simple as the barrel harmonics changing as velocity increases. When tuning a load we are not only finding the most consitent load we are also finding the point where barrel vibrations are also as consistent as possible so that the bullet exits the barrel as near to the same point during the barrels flexing while firing.

 

[BrentM]

The cause of poi change could be as simple as the barrel harmonics changing as velocity increases. When tuning a load we are not only finding the most consitent load we are also finding the point where barrel vibrations are also as consistent as possible so that the bullet exits the barrel as near to the same point during the barrels flexing while firing.

This is my experience as well. POI only represents where the bullet left the barrel during the vibration wave. Could be anywhere and it does not represent anything in my mind as far as accuracy. Like you I test for max pressure and then build a load off a safe charge weight using a seating depth test. However, I tend to test charge weights at .010 off the lands.

 

[nchunter182]

I've been trying to understand the mechanics of why the string would go low and right. Barrel harmonics would certainly be a factor and I guess I never considered that there would be left/right as well us up/down movement. I wanted to make sure there wasn't some underlying cause that needed to be corrected in order to get the best consistency. Thanks to all who suggested this.

This first pass at loading the VLD in this gun was to find just what powder charge and velocity I could safely load to. Since starting at or very close to the lands would produce the most pressure, that is where I started. After re-reading the sticky on loading Berger VLD bullets on top of this topic, I probably should have started .010" off to avoid the possibility of sticking a bullet in the lands. With the data I have gathered so far, I'll try shooting groups at the last five powder charges that all grouped together. If I'm not happy with the groups, then try the seating depth step changes suggested in the sticky. At least I will be working away from the lands and not have to worry about increasing pressure.
Jay

 

[BrentM]

I am not sure I would bother with 5 powder charges. For example I find max, primer flattening, ejector marks, and back off about .5 grains. I shoot that powder weight and test seating depth. Almost always I find a node that works well. I just broke in my new barrel and have 37 rounds through the tube now. I have 3 workable loads within that test field. At 100 yards I have 5/8th, 3/8th, and bug hole. Clearly I choose the bug hole. This particular load is with a magnum primer vs a large rifle and the charge weight is .5 under where I started seeing signs of pressure. I tested at .010 for pressure and accuracy, then jumped to .100 since I have had good luck with bergers at that distance. I worked backward, to .075, and .050. .050 put the first two literally in the same hole, next one oblonged the hole. DONE. I did the same thing with a large rifle primer and shot .010 for pressure. Got a 5/8th group. Moved to seating depth test .5 grains under pressure signs. At .075 3/8th group. Clearly I can fine tune from here and have not tested .05 or .025 yet.

My point is to demonstrate that it is probably not necesary to test that many powder charges unless you are ladder testing.

 

[trebark]

Can I suggest to you that you try H1000. Like you, I have a (now my nephew's) 280. He shoots the 168berger hybrids. We started out with H4831SC and got good results but then tried H1000 and WOW...great results in accuracy and ES.

 

[nchunter182]

trebark,
Can I ask what primers you were using with the H1000? I have a bunch of H1000 and several differnt type and brands of primers. I've been partial to the 215M with the H1000 in larger capacity cases.
Jay.

 

[trebark]

trebark,
Can I ask what primers you were using with the H1000? I have a bunch of H1000 and several differnt type and brands of primers. I've been partial to the 215M with the H1000 in larger capacity cases.
Jay.

The load that shoots well in nephew's 280 is 168berger hybrid, 60grains H1000 lit by Winchester Large Rifle Primer (WLR) all loaded to mag length (3.34"). I happen to use that primer because I don't use it for my other rifles. It worked out that this combination produces 2850fps (24" barrel) and an ES of 15.

If I hadn't hit it on the first try, I also have Fed210, Fed210M, CCI BR2 and Fiocchi primers on the shelf that I would have tried in an attempt to get the ES down. In some discussions I've had with some knowledgable people, I am told that you can use standard primers for loads up to ~66grains of powder.