Mid-air fragmentation...308WIN

[Paddycakes]

Chronographing a few cartridges yesterday - had just leveled my scope and had not bore sighted it. Figured I'd kill two birds with one stone, get the scope on paper and chrono the rounds. Long story short I had mid-air fragmentation on at least one round that splattered a target set at 65 yards, could have been either the 170r flat nose at around 2200-2300 fps, or the 165gr SST at around 2600 fps. Never got the rifle on paper that I could see so unsure as to how many rounds may have prematurely fragged. Upon inspection some rounds did hit targets intact, I was also firing 168gr SMKs from 43gr to 44.6gr in a build up, max 2705 fps.
Any experience with this, simple troubleshooting? Possibility of ricochet? It has rained without stopping for three days, ground is soaked, forest floor, shooting in the rain under a lean-to. 170s were on top of 39.3gr IMR 4064 and 165s were on 43.0gr IMR 4064, CCI BR primers and Hornady and Norma neck sized brass, bushing sized at 330. Thats about all the info I've got, can't remember how far off the lans they were, but I believe it was between .002 and .005.
Rifle is a Tikka T3lite .308WIN 1:11 twist.

[Unclenick]

That's most unusual. No chance you launched a 170 at higher velocity than the .30-30 range? Nothing about your loads or velocities seems unusual. I assume you had no pressure signs. It could have been a single, defective bullet.

I would go back and refire the same loads, but use a separate target for each bullet to see if you can get another incident and this time identify the culprit. Though your twist rate should be very compatible with the bullets you are shooting, if a bullet's mass is eccentric, even a normal spin rate can make it wobble badly enough in flight to fall apart. If the jacket isn't tight on the core, you can get core striping, where the jacket slips over the core as it is accelerating in the barrel, so the core never spins up to rpm fully and the bullet exits with some space between the two. Usually this error in spin is small and this just leads to groups opening up significantly—very significantly at long range—but it could get bad enough to cause tumbling and possibly disintegration.

Very peculiar, though.

Oh, and I would weigh the individual bullets before seating them. A light bullet (off by more that a couple or three grains) is likely short some core material.

[Paddycakes]

I am going for 2500 range on the flat nose, I've heard tell it can be done effectively, although the 2200-2300 is more representative of what is does coming from a 30-30. I just saw conflicting data on the Sierra site and IMR site regarding max powder load for the 168SMK. Sierra's set 43.5 grains of 4064 as max while the IMR data sets 45.9c as the max for 4064.

[Unclenick]

Sierra tends to be more conservative (though not every time, so watch for that). Note, too, that .308 cases vary in internal capacity by brand and lot number more than any other cartridge except .300 WM. The difference between a Winchester case and a Lake City case can mean the Lake City case reaches the same pressure with about 2 grains less powder. That's enough to make a 10% pressure difference. The brand of primer can make another 5% difference. So you just have to start out by believing the low numbers and come up.

The Hodgdon data is all from a SAAMI standard pressure and velocity gun. This has a chamber carefully made to the minimum SAAMI standard dimension ±0.0005", and a standard bore at 0.308" groove diameter and with a standard bore cross-sectional area, and is 24" long within, IIRC, 0.010" inches. It's pretty specific. For powder, Hodgdon uses its reference data powder to build the loads that is right at the middle of the manufacturing tolerances. The lot you buy can have a burn rate up to ±3% different from that lot, so allow that your actual results can vary a little due to that, too. But the bottom line is that if you use Winchester brass and 205M primers, you should be able to work up to the Winchester maximum. That may not be so in some particular guns, so do the workup and watch for pressure signs is all I can advise.

Personally, I look for accuracy nodes in the shooting. To paraphrase Jack Weaver, placing a moderate speed round accurately counts for a good deal more than a super high speed miss.

[Jeffm004]

My guess is splatter from the other side coming back. It is not coming apart in the air. I promise.

[Paddycakes]

I will post a few pictures so we can visualize. The target is taped to a cardboard panel, the backdrop is soft, saturated forest humus and dirt. The lead shrapnel appears to hit the cardboard and the easy-spot target at a greatly reduced velocity, leaving some small pieces protruding from the face of the cardboard as the larger pieces pass through.

[Marco Califo]

I recently shot 36 grain Varmint Grenades at 3800-3900 range in a 1:9 twist Savage. Every shot thudded convincingly on the 100 yd steel plates.

I do not think your bullet broke up, unless, you hit a:
bird, or
bat, or
drone, or
the ground, or
golfball sized hail, or
a very big mosquito
(are you in Texas?)

[44 AMP]

Just out of curiosity what 170gr bullet were you using?

It is incredibly rare for a quality .30 bullet to come apart in flight.

Personally, I am a bit confused that you don't know which round(s) didn't hit the target. If I don't see a strike on the target (or nearby ground) I STOP and check my bore to be sure it is still clear!

Your loads seem ok, I don't have any good explanation for the bullet fragging in the air (other than a grossly defective bullet).

Any chance you actually hit the ground and only fragments hit the target?

You did say you never got it on the paper...

[Paddycakes]

Indeed I was checking the barrel after each shot. From my vantage it did not appear (even through my spot scope) that any of the bullets had hit the paper. i also saw a few splashes from standing water off target. Upon closer inspection of the 100 yard target, I found that a number of shots were on paper, if only barely. I could not be sure which round fragmented because I fired multiple 'misses' at the same target and there was previous (handling) wear on the easy-spot target which camouflaged the shrapnel impacts until the target was more closely inspected, at which point I discovered what appears to be a number of shrapnel pieces lodged in the outside of the target.
The 170 grain is a Sierra Pro Hunter flat nose 30-30 bullet.

[Unclenick]

If you had a number of misses, was the target close enough to the ground that a miss might have shattered on a rock in front of the target and deflected up into it?

Bottom line will be the same: more targets. See if you can find the side of a large box from a big TV or a storm door or something for your target backer so you can clearly pick up the POI's of the misses on it.

[jmorris]

Only time I ever had bullets come apart due to the centrifugal force was when I combined thin jacketed .224 varmint bullets with a 1:7 twist barrel.

[wogpotter]

I've had a virtually identical experience!

I was given a box of 170 Gr (Hornady I think, it was a while back, about 20 years or so) "flat tip for 30-30" bullets. I decided to make some plinking loads for my .308 rifle by reloading them to 2450~2500 FPS velocities with WW 748 BR powder. They were fired in a Springfield Armory M1a Match (not National Match).

I started at 25 yds to get a basic zero with the new load. I could not see any bullet holes on the target so I went downrange to check. Firing, cycling, feeding, ejection & so on felt completely normal. There were a dozen or so tiny, jagged holes scattered all over the paper. Fired brass also looked 100% normal.

I came down to 15 yds The paper had a lot of scattered small jagged holes all over it.

At 10 yds the target had some round .30 bullet holes surrounded by a "spiral" of several grey streaks, mixed with small random grey splats & keyholed rounds

The only thing I can think of that explains all these things is the lead core somehow breaking down or melting (maybe a little of both?) & the jacket tumbling & fracturing because the core was spraying out somehow, changing the balance & weight & upsetting the spin stabilization, all within the first 10~15 yds.

What caused it? Dunno, I m guessing somehow .308 @ 2500 through a 1:10 twist barrel somehow over-stressed the 30-30 projectile causing internal failure followed by jacket fragmentation. Maybe its designed to be "on the edge" at 30-30 velocities, spin rates & so on for good terminal ballistics somehow?

[mikld]

I believe I would move the target closer even up to 25 yards, and fire one load at a time (various aiming point on same target, same load data, like one round at 12:00 o'clock, one at 3:00, one at 6:00, etc.). I would think if a bullet is gonna fragment it would do so in the first few yards outta the barrel...

[T. O'Heir]

"...how many rounds may have prematurely fragged..." At those velocities, none. No .308" hunting bullet will do that unless it hits something hard.
"...had not bore sighted it..." That's what you need to do first. Take out the bolt, secure the rifle so it doesn't move, look through the barrel at something about 100 yards away(light fixtures work well), then through the scope. Adjust the reticle. Or you can buy a bore sighter.

[wogpotter]

But they might not have been .308 bullets, but 30-30 ones.
As for it "never happening" how do explain my experience?

There was another very similar experience related by a 3rd shooter a few months back as well.

[Paddycakes]

T'Oheir, done and done on the bore sighting. I like to tape a flashlight with a narrow focus to the back of the action and sight it down a long dark hallway. It was a mistake not to but I had time constraints that day, which was my second error.

Unclenick, the only reason I don't believe I was hitting rocks on the ground was due to a paper spray I got prior to adjusting the scope at all, which was 18" or so high and perhaps 20" inches off center at 100 yards. After roughly adjusting the reticle at that point I was on paper, I just couldn't pick up the holes due to the wetness of the target (is my only guess). I've still got about 20 of the FN rounds to investigate, and I am starting to lean towards them as being the culprit - perhaps even something about the way they were seated using the competition seating die which has a seating cup designed specifically to cradle the 168 SMK, and perhaps the length off the lans may be a co-conspirator. We'll get to the bottom of this yet...

[Peter M. Eick]

I had a 220 swift that with the proper loads (darn hot) and light 40 grn bullets would occasionally smoke the bullet and it would fragment on the way to the target. On a calm day you could see the trace of the bullet as a sort of greyish line starting around 30 yrds out and generally ended around 80 yrds or so.

Some bullets would hit the target tumbling. We recovered a couple that had all of the lead leaked out. I presume the rifling cut the thin jacket material and the lead melted out.

On the target you would get splatter of lead, sometimes copper pieces and sometimes tumbled bullets.

My guess is something similar happened. The jacket was cut and the bullet started to tumble.