Small groups but large SD

[Jayhawkhuntclub]

New bolt build in 223 Wylde. Tested 4 loads with five 3 shot groups for each load (88 eld, W760, CCI 450, 2.5" OAL, F-1 shooting chrony) at 100 yards.
The two worst loads average 0.78" and 0.62" with SDs of 26.1 and 28.8
The two best loads average 0.58 and 0.48 with SD of 49.6 and 35.7 respectively.

Very happy with group size, but obviously not with the SD.
Suggestions for bring down the SDs? Thanks!

 

[JCCinOhio]

I never had much luck with the F-1 chrony.. that may be some of the problem with your SDs..

 

[Olen_4504]

yeah that sounds like a chrono problem. i highly doubt you'd get good groups like that with SDs that large.

well... i partly take that back.

when i was starting out and shooting factory .308 ammo. i was getting SDs in the 20s and it still shot half moa.

i still think the chrono is suspect though

 

[AIAW]

You've just got to experiment with it and tune everything to match. It's most likely not your chronograph. Not saying it couldn't be, but it's unlikely.

This happens to everyone, especially at 100 yards. That small MV delta isn't going to change your group size at that distance. Factor in harmonics (OBT) and you could be in a "trash node".

You very well may need to expand your OCW testing down more or up more, or start experimenting with seating depths depending on how you like to handle your load development process.

 

[Ripdog28]

100 yards? Won’t show much. I did a ladder of 39.8grains to 42 grains over the chrono with over 150fps difference at 200 yards and every one was under 2” group without much trying for precision. What was your ES? ES and SD help with consistency at distance. Not much good at 100

 

[steve123]

First I'd start over with a temp insensitive powder otherwise you'll be weaving in and out of the node, and you better pick the low node if you stay with that powder, or you'll be blowing primers come summer.

Between 3 of those chrono's we couldn't get our dope to line up. Then we bought a Oehler and the dope made sense.

Do a ladder test at 300Y with "suggesting H4895" and don't worry about ES, just pick the tightest node, and then do a seating depth test.

Also those 88's are a great design, they fly well, though they are inconsistent in quality, if you get a flyer it's likely a bad bullet.

You are weighing vs just throwing charges, right???

 

[luv2hunt6]

Like a couple of the comments above, 100yds won't show much when it comes to POI change due to MV extremes. If you take your best load and stretch the distance out to 400,500, etc. you will see how quickly the groups vertically open up.

 

[Jayhawkhuntclub]

Yes, I'm well aware that 100 yards won't show much. I'm concerned that my high sd might result in severe vertical stringing at distance. Otherwise, I would have no reason to ask the question.
I ordered a Magnetospeed today. So next week I will either confirm my results or find out it was the chrono.
And yes, I am weighing charges. thanks

 

[AIAW]

Yes, I'm well aware that 100 yards won't show much. I'm concerned that my high sd might result in severe vertical stringing at distance. Otherwise, I would have no reason to ask the question.
I ordered a Magnetospeed today. So next week I will either confirm my results or find out it was the chrono.
And yes, I am weighing charges. thanks

Of course it would. No maybe or might about it there. We are simply going by the title of the thread. It mentions group sizes - nothing about any undesired outcomes at distance.

Sounds like you are on the right track though.

 

[OLD308]

Don't read to much into ED and SD measurements. The measurements are only relevant if done in lots matching the round count of your competition. I did a write up explaining the science of this for PRS, tactical shooters, and hunters. It got hammered my the sudo scientist, I cared not. I'm sure ill get hammered again by the same types. But as the saying goes "facts don't care about your feelings". Till someone with science behind their method provides evidence to the contrary, Ill stick to the science. I'm open to having my mind changed. An inexpensive method of checking you load development (per the groups referenced) that is much more practical is grouping at distance. If, your ability as a shooter is there, group at 200 or 300. 1 to 1.5 inch 5 shot group at 300 yards is more than accurate enough for PRS and tactical matches. Hope this helps.

 

[TheGerman]

A chrony once told me that I shot a 5.56 round at 7500 fps.

 

[black5.3]

How many rounds down the barrel? I would let the barrel settle in some too before i got a serious load worked up.

 

[Rocketvapor]

With a SD of 49.6 and 35.7fps I wonder how fast the max and how slow the min were.
If you had one round that went say 2750 and another that went 2820, an extreme spread of 80 fps (true velocity excluding Chrony errors),
how would that show up at 100yds?
Node or no node, what would the vertical component of your group size be @ 100yd?


For the 88ELD I see that velocity difference (from 2750 to 2820) contributing about 0.1 inch to your group size at 100yds. Hidden for all purposes in a half inch group. For 3 shots, one at 2750, 1 at 2785, and 1 at 2820, velocity will not be seen on paper.
Unless you are really really good

Group size is composed of several independent causes. We often just combine them and assume a half inch group at 100 will be a 1.5" group @ 300.
Where the velocity component was hidden (very small) @ 100 yds that same difference would be over an inch @ 300. Not exactly HIDDEN.
You're tossing in a potential inch into a 300yd group.

This velocity difference at 500yds has the potential to be over 3.5" in the vertical component of your group.
(don't look at 1000 yd)

0.1" @ 100yds to 3.7" @ 500yds for a 70fps spread. SDs and ESs are a good way to grade reloading efforts but the results may or may not show up @ 100yds.

 

[BLKWLFK9]

I had sub .5moa groups with factory 147 eldm PRC ammo out of my 18" custom with a 35 SD over a magnetospeed. Its possible.

 

[CanSniper]

Yea it is possible both ways. Good groups, bad sd, or bad groups low sd. I usually look for a good sd, then run seat depth test to bring the group in. Never tried the other way around. There should be sweet spots in your powder charge that has good sd. If the two fall together you nailed it. If not something is off in your combo of bullet vs powder.

 

[Jayhawkhuntclub]

UPDATE: Okay can't really say how much the chrono played into it. Now have a magnetospeed and will compare at a later date. I bought a new batch of Starline 5.56 brass and a Forster Ultra Seating die. Set the bullets 0.005" off the lands. Took advice and started over with less temp sensitive powder (Varget). Loaded 10 loads (0.1 gr increments) 3 cartridges for each load. This gave me data and groups. I found a solid node spreading from 21.7 to 22.0 grains. The sd for all 12 shots in this range was 14.7. For the 21.8 gr load the sd was 11 and for 21.9 gr the sd was 7.1. The corresponding groups were 0.235" and 0.35" respecively! And this load will keep me supersonic past 1200 yards! What a great day at the range! I've been reloading for 20 years, but shooting long range has been an education! It's a different animal for sure. Thanks for all the help!

 

[black5.3]

Sounds like your getting close.. if you feel like tinkering with it then check several different seating depths and see if the sd’s come down anymore.

 

[Herstal 12]

After testing ammo with 2 different lab radar, I have tossed my F1 chrony out, it wasn’t even close.
Hope this helps

 

[Steel head]

My favorite AR load has pretty bad ES but groups well to three hundred yards.
If your not shooting distance chasing ES is kinda silly.


It certainly could be your chrony though.

 

[deanq]

Increase your samples to at least five rounds for initial testing. That should at least give some confidence in your numbers. Then take your most accurate groups with the lowest SD and adjust seating, charge weight, etc. to lower your SD. A low SD or ES doean't do you much good if it isn't accurate in your rifle (small groups). JMHO, YMMV.