Lows SD, bad group

[PD Gohil]

Ar15 I built 1:8 16" barrel

Come up with this load 2 years ago and it seemed to shoot well.
New Lapua brass
Fed 205 primer
23.3g AR Comp
Barnes 70g tsx
Seated @ 1.852 B2OJ
The load shot well generally between 3/4 and 1 MOA. The average velocity ran around 2763 and stdev always right around the 10 to 12 mark for each shooting session. This rifling combination have killed several critters with no problem.

Fast forward to today I had seven rounds of that original load that I shot. SD of 7.7 EXsp of 22. Avj 2792fps. However the down range results were disastrous. Group was 2.25 MOA....

So what I'm getting at with a low SD and consistent speed should it not also group well? Or do I need to know refocus on seating depth???


Thanks for the help.

PGohil
WV

 

[L.Sherm]

Forget the numbers and believe the target

 

[Coyotefurharvester]

Scope/mount or gun rest change/issue.

 

[Straightshooter1]

Ar15 I built 1:8 16" barrel

Come up with this load 2 years ago and it seemed to shoot well.
New Lapua brass
Fed 205 primer
23.3g AR Comp
Barnes 70g tsx
Seated @ 1.852 B2OJ
The load shot well generally between 3/4 and 1 MOA. The average velocity ran around 2763 and stdev always right around the 10 to 12 mark for each shooting session. This rifling combination have killed several critters with no problem.

Fast forward to today I had seven rounds of that original load that I shot. SD of 7.7 EXsp of 22. Avj 2792fps. However the down range results were disastrous. Group was 2.25 MOA....

So what I'm getting at with a low SD and consistent speed should it not also group well? Or do I need to know refocus on seating depth???


Thanks for the help.

PGohil
WV

I had the same kind of thing happen last September with my .308 RPR. I was using some AR-Comp pushing the new 177 SMK's and for a 5 round session I got an SD of 2.0 and and ES of 5, but the group ES was 1.196". This was for a set of OCW testing and this was the worst of them. Because I had some better loads, I never retested this load to see if it'd repeat. In your case, I'd suggest trying that load again and see if you get the same kind of result. What you got there might just be some kind of anomaly that's really hard to find what the cause is if it can't be duplicated.

 

[varget204]

Have you checked throat for Carbon/ Copper build up ?

 

[fkimble@charter.net]

What did the group look like? Wide, tall, all over the place? How many rounds since last cleaning? How many rounds on the barrel? Barrels speed up for a number of rounds. Maybe yours sped up enough to mess up your load?

Frank

 

[PD Gohil]

The group was slightly taller than wide offset an inch to the right from POA in randomly distributed. Did not seem like a horizontal or vertical string predominantly.
I'm probably a hundred rounds after last good cleaning and have not seen excessive copper or carbon buildup.

 

[RegionRat]

I'm probably a hundred rounds after last good cleaning and have not seen excessive copper or carbon buildup.

Unless you already know this recipe and bbl will go that far and farther.... then this may be the sign to scrub her down and test again.

Sometimes, you can get away with even more rounds than this, and other times you only get about that much. I stopped trying to determine what makes one go twice as far versus the another, but trust the test results.

Folks I trust have been able to go incredible round counts without cleaning, but that has never worked well for me and for reference I have had many years worth of full automatics, prairie dog trips, Service Rifle, etc.. to fall back on for reference.

Much depends on how much experience a shooter has with troubleshooting when it comes to higher performance issues. When experimenting, I will often suggest keeping a reliable reference ammo that you either buy or make, but more importantly is a known performance standard for high performance guns. This takes many years worth of troubleshooting to judge when a troubleshooting investigations take a focus on the gun versus the ammo (versus the shooter...).

 

[DLT]

I believe that’s a hot load. 23.2 with 69s in my wylde chambered bolt gun went through brass

 

[RegionRat]

I believe that’s a hot load. 23.2 with 69s in my wylde chambered bolt gun went through brass

I agree, it must be pretty difficult to even fit that much. Max is shown for mag length at 20.9, but even if you seat it really long.....


And that 70 TSX is really long too.

 

[PD Gohil]

I'm gonna start all over and see what results I get. This was the first cartridge I reloaded for 3 years ago. Lord knows I've learned a ton and do things a bit different now

 

[Keith Glasscock]

Velocity variation has a randomness to it. We want to ascribe low velocity variation to a good group size, but testing very large samples suggests that the two are not related at short to medium range. At longer ranges, increased velocity variation will make groups taller, but your best bet is to ignore the velocity variation on small samples unless it is huge.

 

[Rocketvapor]

"Forget the numbers and believe the target"
Was this at 100yds?
Yup, target telling you your load is crap