Crummy Groups w/ Excellent S.D.'s?

65shootmoor

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This keeps coming to my attention and I'm sure we've all seen it. If this is covered elsewhere, please link it or tell me. The short of it is you get an awesome group with marginal/crap deviation, then fire a wider group (maybe slightly wider or a lot) with stellar S.D. What gives? Any consciences on the larger group/better s.d. sample being more about user technique/ability/error/etc or is it a fluke?

I've tended to side with the S.D. when selecting load parameters and chalk the grouping up to my abilities.
 

Sheldon N

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I've seen it on many occasions with different guns. I usually go with the smaller group. I'd take a 1/4 MOA gun with an SD of 6 and an ES of 16 over a 3/4 MOA gun with and SD of 2 and ES of 8 anyday.

Now if you're talking about SD's in the teens or higher then it's a different story.
 

65shootmoor

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I've seen it on many occasions with different guns. I usually go with the smaller group. I'd take a 1/4 MOA gun with an SD of 6 and an ES of 16 over a 3/4 MOA gun with and SD of 2 and ES of 8 anyday.

Now if you're talking about SD's in the teens or higher then it's a different story.
I sort of was, at least a wider margin. Say, a 2 S.D. versus 9-10, what would you pick then?

The most recent example I would have is a sub 1/8th" (practically one hole) group with an S.D. closer to 10 and a 3/8th" group with a 1 S.D. Groups were at 100 yards, so I chalked it up to a user error and went with the low S.D.
 

Sheldon N

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The most recent example I would have is a sub 1/8th" (practically one hole) group with an S.D. closer to 10 and a 3/8th" group with a 1 S.D. Groups were at 100 yards, so I chalked it up to a user error and went with the low S.D.
I'd probably default to looking at adjacent charge weights and see what they did for velocity and POI if they were consistent. Looking for that node where the center of the group doesn't move even though charge weights change. Similar idea with velocity, looking for that flat spot where velocity doesn't change much.

I'd also want to shoot them at distance to see what they did. Just because the SD/ES is good doesn't mean they will fly perfect out far. I did some testing with different loads and different bullets earlier this week prepping for a match. I had a load that had great SD/ES (I think SD was 2?) but was only so-so for accuracy at 100 yards, maybe 3/4 MOA. Checked it against another bullet with a accurate 1/4 MOA group and decent SD/ES (SD of 6). I sent a bunch of rounds of each at 1200-1300 yards and that so-so group opened up to like 2MOA of vertical, while the other bullet shot much better, holding a nice clean waterline and hitting targets easily.

Just because it has good numbers isn't a guarantee that it shoots good at distance. I like to think of SD/ES as a warning system... if it gets up into the double digit SD or 20-30's for ES, then there's something wrong and I should check my brass prep or if I have a good node selected. Otherwise I kind of ignore it.
 

65shootmoor

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I'd probably default to looking at adjacent charge weights and see what they did for velocity and POI if they were consistent. Looking for that node where the center of the group doesn't move even though charge weights change. Similar idea with velocity, looking for that flat spot where velocity doesn't change much.

I'd also want to shoot them at distance to see what they did. Just because the SD/ES is good doesn't mean they will fly perfect out far. I did some testing with different loads and different bullets earlier this week prepping for a match. I had a load that had great SD/ES (I think SD was 2?) but was only so-so for accuracy at 100 yards, maybe 3/4 MOA. Checked it against another bullet with a accurate 1/4 MOA group and decent SD/ES (SD of 6). I sent a bunch of rounds of each at 1200-1300 yards and that so-so group opened up to like 2MOA of vertical, while the other bullet shot much better, holding a nice clean waterline and hitting targets easily.

Just because it has good numbers isn't a guarantee that it shoots good at distance. I like to think of SD/ES as a warning system... if it gets up into the double digit SD or 20-30's for ES, then there's something wrong and I should check my brass prep or if I have a good node selected. Otherwise I kind of ignore it.
To your first point on adjacent charge weights, are you checking both points or one or the other? The charges I used are only spread by 0.2th, the later being above max. I thought about splitting the difference and trying the middle. This is after I've worked up from a lower level, the data suggested it was getting better as I went up until I got to the last, over max load.

To the 2nd point, I guess no matter the S.D. and velocity, there is no substitute for shooting a target. Is that what you are suggesting? S.D., velocity, short range groups are just a guide if you are intending to shoot further?
 

Sheldon N

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To your first point on adjacent charge weights, are you checking both points or one or the other? The charges I used are only spread by 0.2th, the later being above max. I thought about splitting the difference and trying the middle. This is after I've worked up from a lower level, the data suggested it was getting better as I went up until I got to the last, over max load.

To the 2nd point, I guess no matter the S.D. and velocity, there is no substitute for shooting a target. Is that what you are suggesting? S.D., velocity, short range groups are just a guide if you are intending to shoot further?
I shoot OCW style, usually 0.2gr increments. I'm looking at how the point of impact of the group moves as charge weights change. I want to know what the load does above and below my chosen charge.

I'm choosing charge weights that are not near "max" (not sure if you mean book max or actual pressure signs). I want a good reliable load that won't give me troubles, and I find the lower nodes are usually more predictable and forgiving.

Yes, downrange results trump everything. The only reason people even look at SD/ES is based on the assumption that faster bullets will hit high at distance and slower bullets will hit low, creating vertical spread. To a degree that's true, but because there are so many other factors at work, it's better to simply send some rounds downrange at distance and look at the performance of the group rather than trying to use the numbers to predict the results.
 

65shootmoor

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I shoot OCW style, usually 0.2gr increments. I'm looking at how the point of impact of the group moves as charge weights change. I want to know what the load does above and below my chosen charge.

I'm choosing charge weights that are not near "max" (not sure if you mean book max or actual pressure signs). I want a good reliable load that won't give me troubles, and I find the lower nodes are usually more predictable and forgiving.

Yes, downrange results trump everything. The only reason people even look at SD/ES is based on the assumption that faster bullets will hit high at distance and slower bullets will hit low, creating vertical spread. To a degree that's true, but because there are so many other factors at work, it's better to simply send some rounds downrange at distance and look at the performance of the group rather than trying to use the numbers to predict the results.
I am referring to book max, which from Hornady, doesn't mean much. It did deliver an excellent performance with no issues. What about seating depth? I've got two data points so far, one is feedable from mag, the best isn't. Thinking about parking it in the middle to see what happens.

Is there a particular testing range ratio that keeps the data relevant? Meaning is 400 yards a good/bad analog for 1200 or some other mix? I've got the shorter range local, the 2nd is 5 hours away.
 

charnicus

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This keeps coming to my attention and I'm sure we've all seen it. If this is covered elsewhere, please link it or tell me. The short of it is you get an awesome group with marginal/crap deviation, then fire a wider group (maybe slightly wider or a lot) with stellar S.D. What gives? Any consciences on the larger group/better s.d. sample being more about user technique/ability/error/etc or is it a fluke?

I've tended to side with the S.D. when selecting load parameters and chalk the grouping up to my abilities.
Choosing SD is the right answer in my opinion. Maybe with compromise. If my best groups are coming with an SD between 6-9 I’d be more pressed to take that over say a bigger group with SDs below 6. This of course could be wrong.

When this sort of thing happens to me I visit both seating depth and brass prep. Especially with new brass and resetting the neck tension. I take back out the once fired brass and shoot the better results and experiment again. Granted I’m pretty new to this and could be beyond effed in logic... haha
 

Sheldon N

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I am referring to book max, which from Hornady, doesn't mean much. It did deliver an excellent performance with no issues. What about seating depth? I've got two data points so far, one is feedable from mag, the best isn't. Thinking about parking it in the middle to see what happens.
Look into tools and approaches to find the distance of your bullet to the lands of the rifling. Measure bullet ogive rather than OAL. You don't want to jam into rifling and you want the rounds to mag feed, so that's the constraints you're working within. I typically pick powder charge first, then tune seating depth to shrink groups tighter as needed. Just testing and seeing what shoots best. In your situation it sounds like magazine length is the limit, so I would test seating depth by starting with max mag length then working shorter in 0.005 to 0.010" seating depth increments.

400 yards is not a perfect proxy for 1200 yards, but if i you can put small groups on paper at 400 then the load is likely to hold up well farther out. That would be a point where i might start to use SD/ES to pick a load... if both made similar groups at 400, both were in a good node for POI/velocity, and there was nothing else between them, I'd choose the one with better ES/SD.
 

65shootmoor

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Look into tools and approaches to find the distance of your bullet to the lands of the rifling. Measure bullet ogive rather than OAL. You don't want to jam into rifling and you want the rounds to mag feed, so that's the constraints you're working within. I typically pick powder charge first, then tune seating depth to shrink groups tighter as needed. Just testing and seeing what shoots best. In your situation it sounds like magazine length is the limit, so I would test seating depth by starting with max mag length then working shorter in 0.005 to 0.010" seating depth increments.

400 yards is not a perfect proxy for 1200 yards, but if i you can put small groups on paper at 400 then the load is likely to hold up well farther out. That would be a point where i might start to use SD/ES to pick a load... if both made similar groups at 400, both were in a good node for POI/velocity, and there was nothing else between them, I'd choose the one with better ES/SD.
I've got the Hornady comparator. It's just that the new A Tips are very long and pointy. It sounds like it's a juggle, with as many attributes you can cram into one load. I think I've found it.
 

65shootmoor

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Choosing SD is the right answer in my opinion. Maybe with compromise. If my best groups are coming with an SD between 6-9 I’d be more pressed to take that over say a bigger group with SDs below 6. This of course could be wrong.

When this sort of thing happens to me I visit both seating depth and brass prep. Especially with new brass and resetting the neck tension. I take back out the once fired brass and shoot the better results and experiment again. Granted I’m pretty new to this and could be beyond effed in logic... haha
I'm definitely going to try a bit more on the seating depth. Honestly, the A Tips are not proving picky on this front, so I may get mag length for free.
 

charnicus

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I'm definitely going to try a bit more on the seating depth. Honestly, the A Tips are not proving picky on this front, so I may get mag length for free.
Could be messing with your pressures if they aren’t seating consistent. I try to check every 5 rounds. Not sure how existing seating stems deal with the A tips as I have no experience with these bullets. I’ve recently switched to using Sinclair comparators. There’s a learning curve I guess as the Hornady ones seem easier to use. Sinclair’s seem to fall more on the ogive as well.
 

65shootmoor

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It's seating consistently, down to the 0.001". I have Whidden dies, the stem is bored a lot deeper than a normal stem. No marks on ogive since I polished it more after receiving.
 

65shootmoor

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Just as you said with playing around with seating depth to see what happens. Do post the findings.
I'm wondering how fine I should make the steps to test it? I've got a 0.036" gap between the first attempt that fit the mags and the last that doesn't. I was thinking about retesting the original @ 0.074" jump, the new one at its current 0.038", and drop one in right in the middle of the two, at 0.056". Anyone think I should step it smaller than 0.018"?
 

Sheldon N

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I'm wondering how fine I should make the steps to test it? I've got a 0.036" gap between the first attempt that fit the mags and the last that doesn't. I was thinking about retesting the original @ 0.074" jump, the new one at its current 0.038", and drop one in right in the middle of the two, at 0.056". Anyone think I should step it smaller than 0.018"?
I’d work from the one that works fine and go back, not longer. You don’t want clearance too tight in the mag. The mag can actually shrink in cold weather and then your ammo doesn’t fit anymore. Ask me how I know. 😀
 

padom

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I wold do a real seating depth test, ignoring mag length limitations (for now) so you can get actual data on what your barrel prefers with these bullets and your load. Load from 0.005" off to say .03 or .04 off in .005 increments. To save time and components, you can do 3rd each. Once you find the length that shoots best in your gun, you can then decide is there another length that is acceptable to you that fits in the mag if the smallest group was longer than your mag, or get mags with longer COALs like the options discussed earlier in this thread.

I guarantee you 100% you will find one or two groups that stand out from all the others size wise. Now, I state this on the condition proper load development was done and a charge was selected in the center of a node....


My 6.5 135gr A-Tips just arrived a few minutes ago. Will load up a OCW for my 6.5x47L with Varget and get testing.
 

65shootmoor

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I certainly won't be going longer. I don't mind single feeding these, especially since it worked so well and I won't be using this in PRS. I may run the range I stated above and add more shorter than the first by the same step amounts, just to see what happens. If I can get the same accuracy, shorter will definitely be better, but I'm happy to stay long and single feed otherwise. I knew my rifle was accurate, but this was the best ever.
 

65shootmoor

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I wold do a real seating depth test, ignoring mag length limitations (for now) so you can get actual data on what your barrel prefers with these bullets and your load. Load from 0.005" off to say .03 or .04 off in .005 increments. To save time and components, you can do 3rd each. Once you find the length that shoots best in your gun, you can then decide is there another length that is acceptable to you that fits in the mag if the smallest group was longer than your mag, or get mags with longer COALs like the options discussed earlier in this thread.

I guarantee you 100% you will find one or two groups that stand out from all the others size wise. Now, I state this on the condition proper load development was done and a charge was selected in the center of a node....


My 6.5 135gr A-Tips just arrived a few minutes ago. Will load up a OCW for my 6.5x47L with Varget and get testing.
I will probably do just that if these don't shoot how I like first. I would like to keep my current mags, if possible, and none of those ranges work in them now. However, if they suck, I'll start closer to the lands like you suggest and get another mag if needed. It's starting to be a tail chasing the dog since none of these I've shot so far have broken outside of 3/8 moa, most are half that.
 

padom

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I will probably do just that if these don't shoot how I like first. I would like to keep my current mags, if possible, and none of those ranges work in them now. However, if they suck, I'll start closer to the lands like you suggest and get another mag if needed. It's starting to be a tail chasing the dog since none of these I've shot so far have broken outside of 3/8 moa, most are half that.
One group is 3/8moa or half that? Or you shot 5x5's to confirm your loads and get an avg thats 3/8moa?
 

65shootmoor

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One group is 3/8moa or half that? Or you shot 5x5's to confirm your loads and get an avg thats 3/8moa?
All groups fired with this projectile (I've fired 9-10, 5 shot groups so far) have come in at or below 3/8" @ 100 yards. Half of those have maintained 3/8 moa or better @ 400. Other projectiles I commonly use, mostly 142 SMK's, have adhered to this performance as well. So far, the load is doing exactly what I want, I'm only continuing to test for fun and attempting to keep my current mags. This projectile has proved incredibly easy to work with in my rifle.
 

charnicus

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All groups fired with this projectile (I've fired 9-10, 5 shot groups so far) have come in at or below 3/8" @ 100 yards. Half of those have maintained 3/8 moa or better @ 400. Other projectiles I commonly use, mostly 142 SMK's, have adhered to this performance as well. So far, the load is doing exactly what I want, I'm only continuing to test for fun and attempting to keep my current mags. This projectile has proved incredibly easy to work with in my rifle.
That’s awesome that you’re getting the SMKs to shoot. I haven’t been so lucky with the 107s or 110s with my 6mm.
 

65shootmoor

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That’s awesome that you’re getting the SMKs to shoot. I haven’t been so lucky with the 107s or 110s with my 6mm.
It was funny how I stumbled into using them. I normally went Hornady all the time, but with the new rifle, I ordered Sierra's, Nosler's, and Hornady. When I got them, I started sorting by ogive measurements looking to see how consistent a box was. I ended up with 6 Hornady piles, 4 for Nosler, but only 2 for Sierra, one of which only had 2 bullets. 98 bullets completely the same. Now, it hasn't always held that tight, but it hasn't mattered on target. I'm sure I could get them all to shoot, but these are my babies.
 

charnicus

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It was funny how I stumbled into using them. I normally went Hornady all the time, but with the new rifle, I ordered Sierra's, Nosler's, and Hornady. When I got them, I started sorting by ogive measurements looking to see how consistent a box was. I ended up with 6 Hornady piles, 4 for Nosler, but only 2 for Sierra, one of which only had 2 bullets. 98 bullets completely the same. Now, it hasn't always held that tight, but it hasn't mattered on target. I'm sure I could get them all to shoot, but these are my babies.
I’ll have to give the 142s a look when the 6.5 SST is complete...
 

Steel head

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It was funny how I stumbled into using them. I normally went Hornady all the time, but with the new rifle, I ordered Sierra's, Nosler's, and Hornady. When I got them, I started sorting by ogive measurements looking to see how consistent a box was. I ended up with 6 Hornady piles, 4 for Nosler, but only 2 for Sierra, one of which only had 2 bullets. 98 bullets completely the same. Now, it hasn't always held that tight, but it hasn't mattered on target. I'm sure I could get them all to shoot, but these are my babies.
142SMK’s hammer in my 260.
Both the 260FGMM load and my hand loads.

I’ve had few not so hot groups loads with awesome SD’s.

I almost always can get them to shoot decent by tinkering with the seating depth.