Range Report 175 SMK unstable

[Roz762]

Hello folks. I could very much use some guidance.

Just got back from a 600yd mid range f-class competition this morning and I am thoroughly confused.

I was told by the feller pulling my target down in the pits that my bullet was key-holing on paper. At first I was convinced he must be mistaken, but then he pulled my target and showed it to me back at the firing line. Sure enough, there is an ever so slight oblong hole where each bullet hit rather than the nice little circles that are usually produced.

The key-holing was so slight, that I had never noticed it before. In fact, the gentleman who did is a pretty seasoned shooter and I was lucky enough to have him pulling my target today, otherwise this could have gone unnoticed for who knows how long.

I shot poorly by my judgement, but decent enough despite the key-holing that I was allowed to finish the match.

What I don't understand is what is causing this.

I shoot .308 175gr Sierra MK's, with 48gr of Alliant Power Pro 2000-MR behind it. My chrono shows that I'm hitting 2780 fps at the muzzle. My barrel is a 1 in 12" twist. I know my velocity is correct because my ballistic data matches the calculator. I have exactly 13 MOA dialed in for 600yds. Atmosphere was similar today as to the day the rifle was zeroed/chrono'ed. I can put this same load in one ragged hole at 100yds when we were sighting it in.

I ran the numbers through Berger's stability calculator, and if I input the data correctly, it says my round should be comfortably stable. Please, don't take my word for it, check my work. I'm definitely not incapable of mistakes.

The barrel is a Shilen select match 26" full bull with about 1500 rounds through it. No nicks/marks/deformation in the crown of the muzzle.

At first, we were convinced that our twist must be wrong since all the other variables were verifiable. I was certain that the manufacturer must have accidentally sent me 1 in 16" twist or something instead. When I got home though, I checked the twist with a cleaning rod and a tight-fitting patch. 12" on the dot every time.

I'm at a loss. What else could cause this issue? This is my 3rd competition, and 1st at mid range, and I'm frustrated as hell. I shot a 188 on the fist string, which is not horrible, but I'm certainly not satisfied with it. It's somewhat encouraging to know that some of the poor shooting could be attributable to the arrow, and not entirely to the Indian.

I was planning on switching to Bergers anyways, but rather than just throw new loads against the wall and hoping something sticks, I'd like to have a somewhat educated guess as to the cause of the issue.

Any and all input is appreciated. Thanks!

- Roz

 

[mrbig]

have you got any old targets to check,,have you just changed lots of bullets??a 12 twist 175gr load at 2780 should be good and stable as far as you could lob it in,,

 

[AZ2000]

This may upset a few of the die hard Sierra users, which I am one for my 6mm. A friend called one night and asked if I had been checking my SMK 175 Match #2275 for my .308, I said no, he suggested I check the OG before loading because he was having a problem with his loads. I did and found the OG measured from .662 to .650, .012 difference in seating depth and for my stick makes a big difference in speed. Not sure if this is the problem, but I did go through the last batch of 500 and split them into lots using .002 difference when separating them into different piles.

Have been using Lapua 175 Scenar L and have found none more than .001 or less in OG difference. .730, all bullets were measured with the standard .308 Hornady comparator and digital and analog calipers.

Not sure if this is the problem but possibly worth looking at.

AZ

 

[KYpatriot]

Bullets get more gyroscopically stable, rather than less, as they head down range. It is not likely to keyhole because of gyroscopic stability problems 600 yards from the muzzle, they would be key holing even more at 100 than 600 if it were a gyroscopic issue. Something else is going on...are the targets vertical? Is the key holing random or in the same orientation...if it is a bullet problem the orientation of the keyholes will be random, if the same then it is likely the target was canted ( not square to you) which you may not have noticed from 600 yards

 

[LSUbeatUby40]

I am at a loss..

 

[Tx_Flyboy]

There are two possible explanations:

1. Someone Cross-fired on your target (and their issues were transposed on your target)

2. There is tall grass in front of the target that caused your bullet to deflect as it hit the target...this has happened to me before although with 556 rounds.

 

[Roz762]

have you got any old targets to check,,have you just changed lots of bullets??a 12 twist 175gr load at 2780 should be good and stable as far as you could lob it in,,

Just checked some targets from when we were doing load development, and I don't see any keyholing. After they told me I was keyholing, I switched to a different box of rounds that I had loaded up at a different time, with different bullets to see if perhaps it was a bad box of bullets that I got, but the problem continued.

 

[Roz762]

Bullets get more gyroscopically stable, rather than less, as they head down range. It is not likely to keyhole because of gyroscopic stability problems 600 yards from the muzzle, they would be key holing even more at 100 than 600 if it were a gyroscopic issue. Something else is going on...are the targets vertical? Is the key holing random or in the same orientation...if it is a bullet problem the orientation of the keyholes will be random, if the same then it is likely the target was canted ( not square to you) which you may not have noticed from 600 yards

I didn't notice any real pattern to the keyholing (i.e., being oriented in a certain direction). Also there are two separate shooters shooting on the same target, not simultaneously. I score his target while he shoots and then we switch and he goes down in the pits and scores my target while I shoot. He didn't seem to have any issues with keyholing on the target so I don't think it was the orientation of the target itself. For some reason it seems to be limited to my rifle and my load when I'm shooting nobody else had the issue.

 

[0311 Hesco]

Bullets get more gyroscopically stable, rather than less, as they head down range.

Oh no. Not this again. lol

Are you by chance using a concentricity guage on the rounds? Lets measure all aspects of the arrow before we exclude anything.

 

[Deadshot2]

Something else is going on...are the targets vertical? Is the key holing random or in the same orientation...if it is a bullet problem the orientation of the keyholes will be random, if the same then it is likely the target was canted ( not square to you) which you may not have noticed from 600 yards

To be precise, the target should be at right angle to the bullet path. At 600 yards, the bullet is on a downward path and for the target to be struck square it should be slightly canted away from the shooter.

If one wants to see if it's keyholing or just a bullet not striking square, Put several layers of cardboard behind the target then examine the path of the bullet hole. A bullet diameter hole through an inch or so of cardboard, with a downward path from front to rear, means no keyhole . A ragged or oblong hole would be self explanatory.

 

[Roz762]

Oh no. Not this again. lol

Are you by chance using a concentricity guage on the rounds? Lets measure all aspects of the arrow before we exclude anything.

I used to use it religiously, but I found that my bullet seating die tends to seat the round pretty concentric. So I use it occasionally to make sure nothing has de-railed.

 

[ksthomas]

Roz,
Assuming everything is just as you describe it, these bullets are going to be stable, no question. Makes me wonder if something you may have overlooked, isn't quite what you've described. You don't mention what type of barrel you're using, but that's the first thing I'd check. Cut rifled or buttoned? If it's a button barrel, it's not at all uncommon to see them vary a half inch (or more) from their stated twist. In otherwords, that 1x12" may actually be anything from a 1x11.5" to a 1x12.5" . . . or slower. If it is indeed on the slow side, load combinations that may appear "stable" when calculated on paper, may just give marginal results in real-world firings. First thing I'd check, just to make sure the barrel is at most a 1x12" twist. Bit of a crap shoot where buttoned barrels are concerned, as the error can go in either direction.

 

[damoncali]

Double check your twist (and bullets - you never know) before getting into any of the more esoteric voodoo. They should be stable enough not to notice any yaw.

 

[TommyAtkins]

Maybe I missed it if it has been mentioned already, if so forgive me. Is it possible that your bullets are OVER-stableized? If they are hitting normally at 1000yards, maybe at 600 yards they are not following the arc and are hitting nose-up?

 

[0311 Hesco]

Roz,
Assuming everything is just as you describe it, these bullets are going to be stable, no question. Makes me wonder if something you may have overlooked, isn't quite what you've described. You don't mention what type of barrel you're using, but that's the first thing I'd check. Cut rifled or buttoned? If it's a button barrel, it's not at all uncommon to see them vary a half inch (or more) from their stated twist. In otherwords, that 1x12" may actually be anything from a 1x11.5" to a 1x12.5" . . . or slower. If it is indeed on the slow side, load combinations that may appear "stable" when calculated on paper, may just give marginal results in real-world firings. First thing I'd check, just to make sure the barrel is at most a 1x12" twist. Bit of a crap shoot where buttoned barrels are concerned, as the error can go in either direction.

So you're saying that a half inch twist difference can/will make 175s keyhole at 600?

 

[0311 Hesco]

Maybe I missed it if it has been mentioned already, if so forgive me. Is it possible that your bullets are OVER-stableized? If they are hitting normally at 1000yards, maybe at 600 yards they are not following the arc and are hitting nose-up?

What arc are you talking about?

 

[TommyAtkins]

When the bullet leaves the barrel it travels in an arc to the target. When the bullet is properly stable, the attitude (verticle angle) of the bullet follows this arc. If the bullet is over-stabilized it will maintain the angle it was fired at even though gravity pulls it down, giving it a "nose up" attitude. At short range (100 yards) the tragectory is pretty flat, at 600 yards there is 78" of drop (13min), if the bullet is not pointed in the direction of travel (downward) it will produce a keyhole coming down from 78".

 

[0311 Hesco]

If the bullet is not perpendicular to the target it won't make a concentric hole. I have never heard of over-stabilization affecting the the "attitude" of the bullet. Please list a reference on where you're getting this stuff.

 

[TommyAtkins]

I used an incorrect term, it should be "Yaw". Is Bryan Litz a suitable referance?
Over-Stabilization of Bullets ? Why Is Too Much Spin a Problem? « Daily Bulletin

 

[BigMahi]

When the bullet leaves the barrel it travels in an arc to the target. When the bullet is properly stable, the attitude (verticle angle) of the bullet follows this arc. If the bullet is over-stabilized it will maintain the angle it was fired at even though gravity pulls it down, giving it a "nose up" attitude. At short range (100 yards) the tragectory is pretty flat, at 600 yards there is 78" of drop (13min), if the bullet is not pointed in the direction of travel (downward) it will produce a keyhole coming down from 78".

I know what you mean. The o-give (hollow point) is still "facing" the horizon as it descends onto the target.

0311Hesco, think of a Boeing jumbo jet landing onto the runway. The nose of the aircraft is pointed in a different direction (up to the horizon) than its target direction (down at the landing strip).

 

[TommyAtkins]

This link gives a visual to explain over stabilization.
http://www.nennstiel-ruprecht.de/bullfly/fig15.htm

 

[TommyAtkins]

Quote from Bryan Litz;
"All of the above applies to stable projectiles in supersonic flight on ‘flat fire’ trajectories. For projectiles fired at high angles (above ~10-20 degrees above the line of sight), it is possible for the bullet to not track, or trace with the trajectory. This is a common design challenge for artillery shells that are often fired on high angle trajectories. The axis of the spinning shell may be too rigid to bend with the exaggerated trajectory. In that case the shell can ‘belly flop’, or fall base first. However for small arms projectiles on flat-fire trajectories, this isn’t a problem."
At 600yards, the weapon is being aimed 13 minutes above the target, this is not a "flat fire" trajectory.

 

[BigMahi]

This link gives a visual to explain over stabilization.
http://www.nennstiel-ruprecht.de/bullfly/fig15.htm

What would be a good way for the OP to test this theory out?

I suggest taking several close range shots (100 yards) at the target. Take care NOT to group the shots and mark the entry holes. Then take a few shots every 100 yards out (200 yards, 300 yards, etc.). Measure the height of the entry holes.

If indeed the over-stabilization is the issue, the entry holes will progressively increase in size (e.g. 100 yards shots yielded perfect .30" holes, 300 yard shots yielded .32" rectangular holes, 400 yard shots yielded .35" holes, etc.).

Am I missing something?

 

[lash]

I used an incorrect term, it should be "Yaw". Is Bryan Litz a suitable referance?
Over-Stabilization of Bullets ? Why Is Too Much Spin a Problem? « Daily Bulletin

I wanted to believe your point, so went to your link and read through the whole thing. Here's what I read:

- First, it's not "Yaw" you meant but "Pitch". Bryan Litz -

yaw (rotate side to side around its axis), tilt nose-up (pitch)

- Second, you quote Bryan to discuss flat-fire trajectories, but failed to include the part where he defines them: Bryan Litz -

All of the above applies to stable projectiles in supersonic flight on ‘flat fire’ trajectories. For projectiles fired at high angles (above ~10-20 degrees above the line of sight), it is possible for the bullet to not track, or trace with the trajectory. This is a common design challenge for artillery shells that are often fired on high angle trajectories. The axis of the spinning shell may be too rigid to bend with the exaggerated trajectory. In that case the shell can ‘belly flop’, or fall base first. However for small arms projectiles on flat-fire trajectories, this isn't a problem.

So, are you saying that 13 MOA is greater than 10-20 degrees?

Edit: I didn't want to trap you or divert the conversation, so here's your answer:

A minute of arc (MOA), arcminute, or minute arc, is a unit of angular measurement equal to 1/60 of one degree.

Just so you know, I did not post to argue or pick on anyone, as I am interested in this also. I just thought that I would help to move the discussion in a direction that would be more useful to the OP. Once I read the linked article, it was evident that this wasn't (or shouldn't be) a factor in his issue.

 

[TommyAtkins]

I did not bring this up as an absolute answer, I thought it was something that should not be overlooked. I presented the reference because someone suggested I pulled this out of thin air and I wanted to show it is a real phenomena. The OP did describe the Key-holing as "ever so slight oblong hole ", this opens the range of causes. If nothing else, my reply has opened some minds and caused people to do some reading.

 

[lash]

I agree.

Hopefully, we can continue along that thought line.

 

[KYpatriot]

How about pictures, or it didn't happen...

 

[Jedbo]

Inspect your muzzle very carefully for any nicks, burrs, etc.

 

[0311 Hesco]

I did not bring this up as an absolute answer, I thought it was something that should not be overlooked. I presented the reference because someone suggested I pulled this out of thin air and I wanted to show it is a real phenomena. The OP did describe the Key-holing as "ever so slight oblong hole ", this opens the range of causes. If nothing else, my reply has opened some minds and caused people to do some reading.

No. Someone subtly suggested that you re-read your own "knowledge" because you are talking about things that don't happen at 600 yards. If this were even the slightest bit relevant, then why did the OP say his rifle and load was the only one doing it that day? Does your lofty physics only work sometimes? No. I appreciate the elementary lectures, but lets look at ALL the parameters that the OP gave us before we get off on spin drift, sleeper bullets, Coriolis effect, Eötvös effect, Poisson effect and anything else we can pull out of a book that sounds cool.
If it's only happening to his rifle, shooter combo, do you really think the spin of the earth divided by the moons positional tide effect subdivided by the temperature of light times purple will only effect him? C'mon dude.

If she weighs as much as a duck then she is a witch right?

 

[TommyAtkins]

This thread is getting off-track and is no longer helpful to the OP. I got into elementary subjects because you asked "What arc are you talking about?" and I provided references to explain Over stabilization because you stated "I have never heard of over-stabilization affecting the the "attitude" of the bullet". Granted, I should have wrote "pitch" instead of attitude. I think the combination of weapon, load, projectile and environmental conditions will have the same result each time which is what the OP stated to begin with. You asked "If this were even the slightest bit relevant, then why did the OP say his rifle and load was the only one doing it that day?" We don't know if there were any similar rifle/Load combinations "that day". Only that another shooter was using the same Target, thereby eliminating the angle of the target. The parameters we know: 26" Barrel, 12" twist, 2780 FPS, 13 min of drop, no Crown deformity, Target is vertical.
One discrepancy I found; When I put this load (175SMK, 2780fps, 12"twist) into Applied Ballistics, it says there should be 11 minutes of drop. The OP does not give Temp or humidity values, only that they are the same as when he Sighted-in at 100yrds. Also not given is the SD of the rounds. Maybe using a benchmark ammo like FGMM would help to eliminate ammo or environmental causes.

 

[Roz762]

OK, so after kicking this around with my dad the past couple days, we think we might have developed a plausible theory. This was partly discovered by accident as a result of cleaning the rifle after the match.

We have had this rifle for a little more than a year, and as stated previously, we estimate approx. 1500 to 2000 pills thru the barrel.

We had previously been using Hoppes with copper cleaner, thinking we were taking care of excessive copper deposits when cleaning. This isn't just plain Hoppes. It was supposed to also remove copper, but I'll get to that in a second.

Apparently, we were wrong. We recently switched to Wipe Out on a suggestion. Our first time using it on this rifle was the day before the match (a mistake in hindsight).

So here is the theory:
Wipe Out sprays in to the barrel as a foam. After some time, the foam dissipates and the solution settles as a liquid in the bottom of the barrel. We let it sit overnight and then ran a patch thru the next morning. There was significant copper build up removed by the Wipe Out that the Hoppes apparently didn't get. I mean a lot of copper. So with the solution pooling in the bottom of the barrel, more copper build up on the bottom is removed when compared to the top. Compound this with the fact that copper deposits are usually thicker towards the muzzle of the rifle since the bullet is at it's greatest speed there.

So basically, we think that the copper build up that wasn't removed on the top of the barrel near the muzzle is causing the bullet to yaw, leading to the instability issues.

It's a theory at this point, but we have been scrubbing the bejeezus out of the barrel the past few days and will be testing to see if there is any improvement.

 

[0311 Hesco]

Well it's more plausible that only-on-your-rifle physics...lol

 

[lash]

Roz, keep us posted as I'm interested to hear what you find. Yaw does seem to make more sense, since you mentioned that the mild key-holing was not consistently in the same relative location.

BTW, there is a reason why I do not suddenly clean my rifle or make any changes just before a match. If something happens, I want to know about it before I'm on the line under time and pressure. And I'm just a know-nothing newbie to all this.

 

[flounderv2]

Ive never used that powder before but 48gn seems like a lot. When was the last time you cleaned your rifle. Stranger things have happened.

 

[Roz762]

Ive never used that powder before but 48gn seems like a lot. When was the last time you cleaned your rifle. Stranger things have happened.

I used to shoot 155gr bullets with 49.5 grains behind it. There was so much powder in the case that we had to make sure our seating depth was spot on or it would compress the powder. We actually noticed it because the powder pushed the bullets back out of the case some and I couldn't chamber the round cause the bullet was in the lands. Once we corrected our issued with the load we were getting 3200 fps, with zero pressure issues, but that's a post of a different day.

As far as our theory, I'll keep yall posted on our findings.