I was working on developing a load for the 36 grain Barnes Varmint Grenade (Condor lead free zone) in my AR type rifle and had some strange results.

I was working up loads using BLC-2 and started at 26 grains working up in half grain increments.

At 26 grains my 5 shot group shot into just under 1 MOA.
At 26.5 grains it shot about .75".
At 27 grains it shot 1" group.
Then at 27.5 grains it shot 2.5+" group.
Then at 28 grains it shot back down to a 3/4" group.
At 28.5 grains it shot a 3/4" groups again.

I repeated an almost identical pattern with the second group of reloads. I've never seen that big of a variation in one incremental jump. Any ideas?

I have to agree.....variation of group size is not usually that pronounced....but look at it on the bright side....It means you should recreate the testing in 1/4 grain increments.....as it seems your rifle is quite sensitive to this load variation.

Are you saying that both times you got a large group at 27.5 grains? If so, that's strange.

As for the 0.75 to 1 inch groups, I wouldn't call a 0.25 inch difference significant.

At ½ grain intervals you can’t always see the barrel harmonics change incrementally. If you did the same test at .3 grain changes you could watch your groups grow and shrink as your load hit a harmonic node (sweet spot) and than moved off that node and moved on to the next node at higher velocity. My experience has shown me that most quality barrels have at least a couple of sweet spots in their barrel timing. I have also seen a number of good barrels that have a “anti-sweet spot”. The group will blow all to hell then start settling down again very quickly.

I don’t waste a minute of time worrying about the anti- nodes, maybe you shouldn't either.

Yes, the large group was repeated at 27.5 grains. The second time through with the same loads had all of the different charge weights shooting between 1" down to about 5/8" until I shot that 27.5 grain load where it opened up again to over 2" and the groups went back down again at 28 amd 28.5 grains.

I've been reloading for 28 years and I've never had one charge weight vary group size that much.

I usually start my loads in 1/2 grain increments until I find a "sweet spot". I then work around that weight in .2 grain increments and then I fine tune the seating depth.

Sounds like a classic case of the "scatter node"

quote:

(Read later about the "scatter node" which is the point
at which the bullets are being released from the bore
when the shock wave is at the muzzle. I call this area
the "scatter node" because it will produce a scattered group,
throwing flyers at random. This is the most
inopportune point of all for bullet release, the scatter node area
can be easily seen during an OCW test, and generally 1 to 2
powder graduations above the scatter node charge will have
you right in the OCW zone. The existence of the scatter node
is the main reason the conventional ladder (Audette) test often fails
to yield useful results).

HC is gonna kill me for bringing OCW and Dan Newberry into this!

But things have been kinda dull around here and we need some entertainment.

Good luck with your problem.

quote:

Originally posted by woods:
Sounds like a classic case of the "scatter node"

quote:

(Read later about the "scatter node" which is the point
at which the bullets are being released from the bore
when the shock wave is at the muzzle. I call this area
the "scatter node" because it will produce a scattered group,
throwing flyers at random. This is the most
inopportune point of all for bullet release, the scatter node area
can be easily seen during an OCW test, and generally 1 to 2
powder graduations above the scatter node charge will have
you right in the OCW zone. The existence of the scatter node
is the main reason the conventional ladder (Audette) test often fails
to yield useful results).

HC is gonna kill me for bringing OCW and Dan Newberry into this!

But things have been kinda dull around here and we need some entertainment.

Interesting theory, I've had the occasional issue with the Ladder method where one load combination throws the ladder out of whack. Maybe that's the issue.

Well, scatter node is what I was thinking, but I wasn't gonna open the door on that one. This could get interesting before it is all said and done.

i wonder if it is the bbl's vibrations hitting the end of the bbl and starting back just as the bullet gets to the end of the bbl.
causing a "shockwave".
i bet most people see this and back their load down. figuring that they have hit/passed the sweet spot.
and by going furtheer up, the wave has come back down the bbl enough for it to not show by the bllet passing through it far enough back from the muzzle.
this might be where the 21-1/4" bbl length come from in the "warehose" tests.

Not weird at all. It's the change in harmonics of your barrel with the different loads. There are several points of repeatable accuracy nodes in any barrel.

quote:

Originally posted by Fjold:
...Then at 27.5 grains it shot 2.5+" group....I repeated an almost identical pattern with the second group of reloads. I've never seen that big of a variation in one incremental jump.

Hey Fjold, I was first going to suggest it might have just been an out of balance Bullet, but to get a repeat the second time around lowers the probability of that considerably.

Scatter Node = an incorrect use of the english language and the phenomenon in general. There is no Node at the crossover point of the Figure " 8 " that the muzzle is making due to the barrel vibrations. The Nodes occur on the ends(Apogee and Perigee) of the Harmonic cycle.

At the crossover, the muzzle is moving at it's fastest speed during the cycle. The minor differences in each load and the changing bore condition will cause the Group to be at it's widest condition when this occurs.
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I do not see it mentioned, but it appears to be a 223Rem. When I Develop Loads for a Case of that Volume, I use a smaller change in the amount of powder than 0.5gr. I typically use something in the 0.2gr-0.3gr area. Similar to what Mick mentioned.
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Hey DJ, If you are out there, I thought of you and totally "reworded" what I had to say about the scatter node. I may need to go throw-up.

I can live with "incorrect use of the english language", I'm from Texas and get accused of that all the time.

But I do think whatever it is called, and wherever exactly it is in the harmonics of the barrel, the phenomenon does exist. It may not be extremely apparent in all rifles and loads, but it is in some. Also, I am with HC on using .3 grain increments for ladder/OCW testing in the smaller cases such as a .223, and I go up to .4 in medium bores.

Assuming that is a .223 or similar, smal1 changes, like half a grain, make a pretty big difference.

Frank,

I have also had weird results using BLC-2 powder in 223. It is a good powder to get high velocity, but I never could get several rifles and different bullets to work in well with BLC-2. You have a few loads that look promising, though.

Chad