Sierra 7mm 140 TGK bullet variation - how much is too much?

[NorthIdahoDude]

Not too long ago, I ran across a box of 140 Sierra Tipped Game Kings for the first time. I brought some home to try, and the first 10 round group in 7x57 was 0.8 MOA, with a Mean Radius of 0.25 MOA. For a redneck like me with a hunting rifle, that's pretty damn good.

A few days later, I ran across a close out special on them for what worked out to $0.24 a bullet. For a pretty accurate, high BC bullet, that I would be comfortable hunting with, that seemed like a no-brainer, so I grabbed 1k of them without a second thought.

The more I shoot them however, I keep getting flyers, and horizontally strung groups... And accuracy in the 1.6MOA range. Damnit, is this my punishment for using a small sample size to decide a bullet was pretty accurate?

I was loading up another batch today, and just for grins, did an OAL check on 10 rounds... Varied by as much as .010. WTH? Grab the comparator, and the case head to ogive measurements actually are pretty consistent...

So I grabbed 10 random bullets out of the box I had been loading from. Again, 0.010 variance in length. The base to ogive measurements again ran pretty consistent, but flipping the bullet and measuring the boat tail with the comparator again shows 0.010 variance.

So what say you guys, does that sound like maybe my root cause for weird flyers and group stringing? And does that sound like enough variance I should get on the phone with Sierra and ask for a replacements?

 

[NorthIdahoDude]

For a comparison, I just measured 20 7mm 140 grain accubonds. All 1.275 +/- .001, with 2 examples that were minus .002. So .003 oal variance, with more than half dead nuts identical (in so far as a basic set of calipers can measure).

Edit: and 10 175 ELD-X's were only .001 variance (1.586 to 1.587).

 

[HandgunHTR]

The base to ogive measurement is all that matters. How much variation there is in the plastic tip means nothing.

Do you have a chronograph? If so, what is that telling you in regards to velocity variations? If not, get one because usually "flyers" are also rounds that fall outside of the statistical confidence interval of velocity (i.e too high or too low).

How to you measure your powder charges? Are you annealing your brass?

What is your rifle setup? Optic?

So many different variables that influence accuracy.

 

[NorthIdahoDude]

The base to ogive measurement is all that matters. How much variation there is in the plastic tip means nothing.

Do you have a chronograph? If so, what is that telling you in regards to velocity variations? If not, get one because usually "flyers" are also rounds that fall outside of the statistical confidence interval of velocity (i.e too high or too low).

How to you measure your powder charges? Are you annealing your brass?

What is your rifle setup? Optic?

So many different variables that influence accuracy.

Yes to Chronograph, no, the fliers don't seem to have velocity variations outside the spectrum of what non-fliers do. I've tried different powders (N555, H4350, Varget, and Hunter) at different velocity ranges (2700 to 2880), velocity extreme spread in the high teens to low 20's with most of the things I've tried.

Powder charges individually weighed on a balance beam during load development (generally speaking, once I find a sweet spot, I just dump with a dispenser, but I'm not there yet with this one). No, I don't anneal the brass (but if that was a problem, wouldn't I see the problem with other bullets/other load work?)

Rifle is an older Tikka T3 stainless with a Shilen Match stainless barrel (not Select Match, just plain Match), 22 inch, 1:8 twist, sporter contour. Bushnell XTreme X30 4-16x44 optic - I know some like to trash-talk Bushnell, but this one (and the other one I have just like it) tracks straight and accurately in my collumator, and has proven to hold zero on several guns before this one.

My overall loading and shooting techniques I think are pretty reasonable - considering that that exact same rifle, on the exact same day, at the exact same range session, with the exact same shooter (me), will drill sub-MOA groups for as many rounds as I have patience for the barrel to cool between when using 175 ELD-X's and IMR 4831 or H4831SC (it does a bit better with the IMR than the H, but does plenty good with either).

So 100% agree - lots of things affect accuracy (or more correctly, consistency), in this case I feel I've narrowed it down pretty tight to the bullet - brass, gun, primers, shooter, etc - otherwise all work pretty well together.

 

[TaperPin]

Yes to Chronograph, no, the fliers don't seem to have velocity variations outside the spectrum of what non-fliers do. I've tried different powders (N555, H4350, Varget, and Hunter) at different velocity ranges (2700 to 2880), velocity extreme spread in the high teens to low 20's with most of the things I've tried.

Powder charges individually weighed on a balance beam during load development (generally speaking, once I find a sweet spot, I just dump with a dispenser, but I'm not there yet with this one). No, I don't anneal the brass (but if that was a problem, wouldn't I see the problem with other bullets/other load work?)

Rifle is an older Tikka T3 stainless with a Shilen Match stainless barrel (not Select Match, just plain Match), 22 inch, 1:8 twist, sporter contour. Bushnell XTreme X30 4-16x44 optic - I know some like to trash-talk Bushnell, but this one (and the other one I have just like it) tracks straight and accurately in my collumator, and has proven to hold zero on several guns before this one.

My overall loading and shooting techniques I think are pretty reasonable - considering that that exact same rifle, on the exact same day, at the exact same range session, with the exact same shooter (me), will drill sub-MOA groups for as many rounds as I have patience for the barrel to cool between when using 175 ELD-X's and IMR 4831 or H4831SC (it does a bit better with the IMR than the H, but does plenty good with either).

So 100% agree - lots of things affect accuracy (or more correctly, consistency), in this case I feel I've narrowed it down pretty tight to the bullet - brass, gun, primers, shooter, etc - otherwise all work pretty well together.

When I’m curious about something like that I’ll measure some bullets, like at least five of each length to be tested, mark all around the exposed part of the longest with one color sharpie and the shortest with another color. When they are all fired at the same target, there will be a slight bit of color around the holes of the marked bullets. Shooting onto white butcher paper is an easy way to make big targets for long range and the color shows up well. Freshening up the bullet color at the range seems to help soften the dried marker and let it rub off easier, but many guys just color it at the reloading bench and call it good. You can go through the solid colors, then some will even mark bullets half and half. It’s a great technique borrowed from the competitive shooters, that really comes in handy at long range when a spotting scope can’t see the bullet holes of different loads fired at the same target.

 

[NorthIdahoDude]

So I went back and remeasured using a double comparator set up (one comp on the boat tail, one on the ogive), and still got about .003 variance, which isn't nearly so crazy seeming as .010. also weighed them, and they vary by 0.2 grains.

Running the same double comparator test on 140 Nosler ABs was near identical in terms of variance (Noslers a hair less, maybe .0025 ish, guesstimating needle between lines on the calipers).

But then running the same double comparator test on 175 ELD X's, showed .0005 variance, at most (again, making some guesses based on how close the needle was or wasn't to the exact same tick mark on the calipers).

So I don't know that really proved anything in terms of how that might or might not affect accuracy.

The overall length variations I'm seeing in the TGKs does seem to be mostly in the tip, although there are definitely is some measurable variations in the bullet beyond just the tip.

Anyway, I like the suggestion of loading up some on the extreme ends of the spectrum, and shooting them at the same Target and seeing if there is any consistency in terms of some of them having a slightly different POI. I'll try that and see what I get.

Thanks.

 

[OverInfinite]

Sounds like the real answer is what taperpin suggested. Try an experiment. Separate 30ish and load up 6 groups of 5, grouped by their lengths and see if the groups move around the target.

 

[NorthIdahoDude]

So apparently, I've been Doing It Wrong(tm) with the TGKs. These bullets apparently don't like carefully hand-weighed charges of my best powder over expensive BR primers in super-carefully prepped and weight sorted brass and only shooting for accuracy with the ones I'e checked runnout on... No, that's not the correct approach, it seems...

What I really needed to do to make them shoot good was just get annoyed with them, prime some of my crappiest brass with no prep except a trim and size (no weight sorting, no primer pocket uniform, no none of that), with my crappiest primers I'm shooting just to get rid of, and use my cheapest available powder in the right-ish burn rate (Ramshot Hunter), play with the powder dispenser till it hits about 100.5% case fill (I found out later that was 49.2 grains), use my Frankford Arsenal universal "one size fits all cartridges" seating die instead of my nice Forster benchrest die, totally ignore any thought of the distance to the lands and just load them till I have about .284 of bearing surface sunk into the case neck (2.502 comparated OAL I found out later), don't measure runout or OAL variations, and then go shoot them at the range while I'm pissed off because some dude backed into my truck in the parking lot and now I'm gonna have to play phone tag with insurance companies for a couple weeks to get my truck fixed, and I'm hot and I'm sweaty which just makes me even more pissed off... That, that, that right there, folks, is the magic process whereby to make these bullets shoot pretty good for a hunting rifle. I knocked off another 5 rounds at 200 that aren't pictured; but they held the same POI and Mean Radius - so 15 rounds total, and 5 more at 200 yard steel which I didn't measure, but all hit what appeared to be identical POI in a nice cluster) - which is a big enough sample size to have some reasonable confidence that I'm 'there', finally!!!

So, mystery solved - I should stop thinking, put away all my precision loading tools, and just set up my progressive press to spit these out as fast as I can trim brass, and call it a day...

 

[NorthIdahoDude]

So apparently, I've been Doing It Wrong(tm) with the TGKs. These bullets apparently don't like carefully hand-weighed charges of my best powder over expensive BR primers in super-carefully prepped and weight sorted brass and only shooting for accuracy with the ones I'e checked runnout on... No, that's not the correct approach, it seems...

......

So, mystery solved - I should stop thinking, put away all my precision loading tools, and just set up my progressive press to spit these out as fast as I can trim brass, and call it a day...

Son of a mother loving biscuit... so... one thing i had not mentioned above, was I had the Magnetospeed strapped to the barrel the whole time. I even went back again to the range twice more while bumping the powder charge a little bit each time, and got identically awesome results, but with ES and SD tightening up dramatically the hotter I loaded it, and I stopped when I hit what should be around 57kpsi...

So today, with exactly the same rounds from exactly the same batch/same loading session/everything as last time... but without the chronograph hanging on the barrel... oh look, shoots just like it did with every other powder all over again - just shy of 2MOA... son of a...

So, I guess it's either a) barrel harmonics that the magneto-speed was dampening, or... b) I didn't have enough sample size for the hotter load and this is just what I get at that pressure... I guess I'm back to the loading bench on this one.

 

[NorthIdahoDude]

Working on the barrel harmonic idea, I was messing around with where things are at in QuickLoad, I'm super close to one of the OBT nodes for a 22 inch barrel.

Though my personal jury is still out on if OBT is a predictable thing in that we can say '22 inch barrel. there is a node is at 1.1270' - my general experience is that there are definitely sweet spots, but they may or may not line up with the charts on what OBT time is.

So I guess I can go back and do a larger sample size of the lower charge weight load without the chrony and see what I get.

 

[NorthIdahoDude]

So, I've been back trying a bunch more with the 140 TGK's, and it remains consistently bad. I even tried one of those Limbsaver barrel tuner things (thinking that maybe if the chronoraph had dampened something that helped, it would do the same), and it didn't help anything. So, I'm back to hating on the 140 TGK's in my 7mm - I'm not sure what to do with these other than bang steel at not-overly-long ranges Sighs...

And it's not the gun, or me having a bad day - 2 groups attached, shot on the same day/same setup/same me, about 15 mins apart - the 175 ELD-X's are dead-nuts money (the one on the farthest left that isn't touching the others was a called flier, even), and the 140 TGK's are all over the place (with more horizontal than vertical stringing, consistently), with no called fliers.

Anyone with some suggestions, I'd be all ears (though I'm confident the suggestion is 'yo gun no like them, shoot something else', LOL).

Thanks,