Sierra Bullet Availability

[smk]

I have had a hard time finding Sierra 7mm 168 MK lately. I called Sierra today and the nice lady told me "Oh yeah, we are out of them and aren't scheduled to make any more until June 9th, but it might really be later than that. We have too many other bullets ahead of them on the schedule we need to make first" I guess these aren't real important bullets to Sierra, so I am considering switching to the 162 Hornady SST at 2500 fps. Any thoughts on that bullet at that velocity for Rams?

[DanDeMan]

smk,

The 162 Hornady AMax is an excellent bullet and will shoot even in a 9-twist barrel.  Launched at 2,400 to 2,500 fps it will do an excellent job on the rams.  It has a substantially higher BC than the 168 Sierra MK.  The 162 AMax would be my first choice for a 9-twist barrel.

[smk]

Thanks. I'll give the A-Max a try. I was hesitant to use it since I have a 1 in 9.5"  twist and Hornady recommends an 8 for this bullet. That's why I was considering the SST instead. Do you think the Amax will work with a 9.5" twist or is 1 in 9 as slow as you can go with this bullet?

[DanDeMan]

smk,

The 7mm 162 AMax has a Stability Factor of about 1.5 at 2,400 fps out of a 9-twist barrel.  That is the usual design spec for most gun designers.  However, a 9.5-twist will produce a stability factor of about 1.348, still stable but in cold, dry conditions one might find a bit of bullet yaw (wobble).

If you are interested in testing to see if the AMax will work, just shoot some groups at 500 meters using heavy corrugated cardboard as a target backer.  Also, the colder and dryer, the better will be the prediction in the conditions you shoot matches.

After shooting the groups look at the holes through the cardboard.  If they are all perfectly round with no elliptical component you are good to go.  It should be said that even if a barrel maker lists a barrel at a certain twist, I've seen plus/minus variation of 1/2 inch about the spec.  Since you are on the marginal side, if your barrel is on the slow side of the specified twist you might find that the bullet produces elliptical holes.  When a bullet produces elliptical holes that also means your actual in-flight BC is much lower than would be the case if the bullet was optimally stable.

I've had extremely accurate 500 meter loads that had Stability Factors in the 1.4 range so give it a go and let us know how it works out.  Also, a careful measurement of your actual twist would add more important information to the discussion.

[DanDeMan]

smk,

As a further data point, the 155-grain SMK in 6.5mm was shot in 8-twist barrels up to 2,700 fps at 500 meters.  At that MV the Stability Factor (SF) is about 1.132.  By definition any SF above 1.0 means the bullet is statically stable at Standard Sea Level Atmosphere air density.

Static Stability means that the gyroscopic effect is sufficient to make the bullet point into the apparent wind force that is the vector sum of its forward speed and the atmospheric wind.  Dynamic Stability means that the yaw induced as a result of bullet launch from the muzzle will damp out with time, that is, the bullet "goes to sleep."

But, the 155 SMK in 6.5mm launched out of an 8-twist barrel produced flyers at 500 meters.  I could never get it to shoot reliably at the ram line.  A few bullets would tend to group and then, OUCH, major flyer.  On the other hand, out of my 6.5mm Swedish Mauser (7.5-twist) when launched at 2,550 fps the same bullet is devastatingly accurate and reliable at the ram line and has failed to ring a ram, if my memory serves me well.

There are several reprobates…errr...shooters…that read this site that have seen the Swed's affect on rams with the 155 SMK's on the nastiest rams in CA: Swiss Rifle Club, Coalinga and Modesto Rifle Club HP silhouette range in the Sierra Foothills.  Maybe they can chime in about how well that bullet works on rams out of the appropriate twist barrel.  I believe that Sierra no longer makes that bullet, bummer.  I do have a 160-grain, 6.5mm bullet design that will be stable out of an 8-twist barrel at 2,500 fps and have a higher BC than the 142 SMK's but the cost of custom dies is more than I'm willing to spring for at this time.  And, getting jackets long enough is also a problem.

[nomad]

For some reason, I feel another one of 'those' headaches coming on...

[Jason]

I guess it's just different strokes for different folks, then. I get all excited when I see Dan post anything more than a paragraph or two. I grab something to drink and settle in for a good read. Of course, that's probably just the engineer in me coming out.  :grin:

[nomad]

Jason,

1. Daniel and I go way back and I consider him a friend.
2. I have nothing but admiration and respect for his detailed investigation of those parts of the shooting game that most people won't even consider thinking about and I try hard to learn from them.
3. ALL his posts are longer than a couple of paragraphs!  :roll:
4. What I posted was a joke.
5. Please don't tell him about what I said in section 2 above.  :wink:

[shootingpaul]

Hi Dan,
well I dont thing that you got your typing fingers warmed up yet - so here it comes:
Lapua 139 scenar 6.5 -  I just love them!, I was shooting sierra 142 and left way too many rams, ever since switching to the Lapua my day has been not the same since, latelly ,dough, I left some rams - i think that my barrel is wearring down and velocity is lower with the same round - so maybe have to crank it up a notch...
whats your take on the 139s? I found them shooting relatively flat with good hitting/knock out  power - vel about 2750 fps.
I think that he Lapua has harder bullet which will transfer energy better to the target - thus getting it fall down, Sierra has a softer bullet - beeter for paper punching but not our steel game
Thanks
Pawel

[DanDeMan]

Yo Nomad,

Now you've gone and done it.  Your #2 statement is forcing me to donate all of my shooting caps to Goodwill as they are all now too small.  I'll be asking for donations to purchase some XXL caps soon.

For those of you that don't really know The Nomad, he's really not a Texan.  He may try to fake it now and again, but the truth of the matter is he's a Mainer, yes I said Mainer.  And, you know what they say about those from the People's Republic of Maine, "You can take the boy out of Maine, but you can't take the Maine out of the boy :-D

[Feez]

Also, a careful measurement of your actual twist would add more important information to the discussion.

Do you have any tips on how to do that?

And are you suggesting that twist rates aren't always consistent ... say from one brand to another ... or even in rifles otherwise identical.

I guess what I'm asking is, if my rifle's owners manual says it has a 1 in X twist - can I trust that?

[DanDeMan]

Pawel,

You are right on target about the 139 Lapua Scenar bullet.  It is quite a bit tougher than the 142 SMK and will therefore have a longer dwell time on rams which means they go over better than when using the MK.

From testing and talking to a lot of shooters, the 139 Scenar seems to perform best between 2,750 and 2,825 fps.  I shoot them at 2,775 fps out of my 6.5mm TKS and 2,825 fps out of the 260 Hunter.  Both of those MV's are in the optimum range, but the other reason those loads are shot is because they are very accurate in my rifles.

The solution to 6.5mm ram ringing is a long, flat-based bullet with 15 caliber radius ogive and meplat in the 0.15 caliber range.  Such a bullet will be about 1.475" long, weigh about 165 grains and have a 2,700 fps BC in the 0.680 range compared to the Scenar and MK BC of about 0.580 at the same MV.  If I ever get around to having the dies made, $3,000 plus other equipment expenses, they will flat-out be the ultimate ram killers.

[nomad]

As many of 'us' Texans say to All Y'all:

I wasn't born here but I got here as quick as I could! lol

[longgun]

Hi Dan,  Last year I started playing around with 123 gr Lapua bullets for shooting at the ram line.  With velocity of 2650 f/s they are pretty reliable.   In addition I have found that the 130 gr Norma bullets are even better and are probably the most accurate of all the factory bullets.  I was loading them at 2650 f/s and haven't lost a ram with them,  however I didn't hit a lot either but the hits all went down.   The Norma bullets are a little more costly,  but shooting the 123 lapua & 130 gr normas are like shooting a little "pop gun".  don

[Jason]

The solution to 6.5mm ram ringing is a long, flat-based bullet ...

Dan,

If you have time, could you elaborate a bit more on why a flat-based bullet is better for longer range shooting like this? I'm putting off highpower silhouette for another year or two so I can concentrate on smallbore, but I'm trying to learn as much about it as I can before I start building a highpower rifle. My limited experience with loading for hunting and paper punching didn't show much accuracy difference between flat base and boattail bullets, and the boattails are definitely easier to get started while seating. If anything, I thought the boattails would come out ahead in accuracy and ballistics once you get beyond a couple hundred yards. What little I remember about aerodynamics from my engineering classes in college point toward less drag on the boattails, too. What am I missing?

Thanks!

[DanDeMan]

Nomad, get out your BIG bottle of Advil as this is about a 600 milligram post :-D

Jason, this is a 3 beer read and cogitation exercise

As with any engineering optimization problem we must first state the givens.  The givens in this optimization exercise are that we are constrained to an 8-twist, 6.5mm barrel that is capable of launching a 139-grain bullet to at least 2,825 fps and 2,600 fps for a 165-grain bullet.  The 139-grain bullet at 2,825 fps will be our baseline for comparison of BC, and terminal momentum, the best parameter to compare ram knock-down when coupled with bullet toughness and dwell-time.  Bullet toughness can be measured using a simple smashing pendulum.  Dwell-time would be far more difficult, but we can roughly estimate it relatively using bullet length.

Let’s first start with a discussion of bullet drag and bullet weight; and how they contribute to BC, which allows us to compare bullets of any caliber or design for wind deflection characteristics and terminal momentum at a given MV.

The place to start this discussion is with the BC equation.

BC = Sectional Density / Bullet Drag Coefficient

Sectional Density = Bullet Weight in lbs / caliber squared

So you can see by inspection of the two above equations; as bullet weight goes up for a given caliber so does BC for a given drag coefficient.  Therefore, we can conclude that the 165-grain bullet will have a higher sectional density than the 139-grain bullet.

Now, we have the bullet drag coefficient to deal with.  Contrary to popular belief, boattails DO NOT produce the highest BC possible for a given twist/caliber combination.  I know that sounds like heresy, but physics is physics and “Ya can’t deny the laws of physics, captain!” as Scotty on Star Trek would say.  For a given bullet length, nose design and alloy density, a boattail will produce a higher BC compared to a flat-based bullet, but that is not what we want when it comes to knocking over rams and driving down recoil by shooting a 6.5mm bullet.

So, what gives and what the heck is DanDeMan talking about now?  One optimization trade-off driver in the bullet design process is we must have sufficient bullet stability.  Boattails reduce bullet stability due to the smaller base diameter when compared to a flat-based bullet for a given caliber.  Base drag contributes to bullet stability while the smaller the base diameter from boattail designs, the less stable the bullet will be and therefore the shorter and lighter it must be for sufficient stability at a given MV.  With a boattail, that reduced base drag, which is a function of base diameter, decreases overall drag, but at the same time it decreases stability.  That means for a given twist we can have a longer, heavier bullet if it has a flat-base.  The increased base-drag of the flat-based bullet is more than off-set by the increased length of the bullet, length of the nose ogive and increased weight.  For ram-slamming that is the direction we want to go.

Now, let’s run some computer simulations to estimate the difference in terminal momentum and wind deflection at the ram line for the 139 Lapua Scenar, the best commercially available 6.5mm ram bullet IMHO, to the proposed Ram-slammer flat-based bullet.  We are going to use the same calculated recoil (11.4 ft-lbs) for both loads to make the comparison fair; well not quite fair, but more acceptable to most.  We’ll discuss more on that issue at the end of the post.  That means the 139-grain Scenar will be going 2,825 fps at the muzzle and the 165-grain Ram-slammer will launch at about 2,550 fps.

139 Scenar Ram Line Performance:
MV = 2,825 fps
Terminal Velocity = 1,971 fps
Terminal Momentum = 1.22 ft-lbs
Wind Deflection from 10 mph 9 o’clock wind = 2.2 MOA

165 Ram-slammer Ram Line Performance:
MV = 2,550 fps
Terminal Velocity = 1866 fps
Terminal Momentum = 1.37 ft-lbs
Wind Deflection from 10 mph 9 o’clock wind = 2.1 MOA

As you can see from the above estimates, based on computer simulations, the flat-based Ram-slammer bullet will deliver 1.37 ft-lbs compared to the 139 Scenar’s of 1.22 at the ram line.  Dwell time is in favor of the Ram-slammer at 1.475” long compared to the 1.388” length for the Scenar.  Also, it should be said that the perceived recoil of the Ram-slammer load will be lower due to its reduced impulse force which is a function of slower acceleration due to its increased mass compared to the Scenar.

Both bullets will be equally stable out of an 8-twist barrel but the Ram-slammer will have lower felt recoil.  While this is subjective, I’ve shot enough over the years to know this is a real benefit in minimizing the build-up of score robbing flinch.  This load will have more of a softer push compared to the crack-like felt recoil from the 139 Scenar load.  And, the Ram-slammer will have about 12% more ram knock-down just based on the delta in terminal momentum.  The difference in dwell time, that is a function of bullet length, will make at least as much of a difference.  For example the 155 SMK Long-range bullet is softer than the Scenar, yet at 2,550 fps it is much more devastating on rams than the Scenar at 2,825 fps.  That delta in ram performance is difficult to quantify other than by shooting thousands of rounds of each load and seeing the results over time.  Finally, the Ram-slammer bullet has a slight edge in wind deflection, but nothing worthy of all the time, money and effort to manufacture said bullet.

The real Ram-slammer benefit is in ram knock-down performance which will far exceed the calculated delta in terminal momentum at the ram line.  My estimate, based on years of shooting HP rams is that if you ring 10 out of 100 rams with the 139 Scenar launched at 2,825 fps you will only loose 1 ram per hundred with the proposed Ram-slammer bullet launched at 2,550 fps.

If one is serious about their HP silhouette performance, that is not a trivial increase in performance.  And, if you shoot places like El Paso or New Braunfals, TX or a few of the ranges in CA, you are looking at serious performance enhancement.  Based on stories from the guys and gals that suffered through the last TX state championships down at El Paso, if shooting a 6.5mm, such a proposed bullet would have made one heck of a difference in one’s final score.

But, there is always an 8-twist 7mmBR launching a 175 SMK……..

[Jason]

Ok, that wasn't nearly as complicated as I was expecting it to be. Let me see if I can sum it up. The flat base of the bullet does indeed cause more drag than a boattail, but it also greatly increases the stability. That increased stability lets us shoot a longer, heavier bullet with a given twist that we can use to increase terminal momentum and dwell time on the ram without an increase in recoil. In fact, even though the actual recoil is the same with the longer heavier bullet, the fact that it's being launched slower gives less perceived recoil, which increases functional accuracy due to reduced flinch over an extended shooting session like a silhouette match. Simple enough...

... but what about just using a 7.5 twist instead of being constrained to 8?  :grin:

[Jason]

One more question.. I'm trying to work through the actual physics of the impact between the bullet and the ram, and I keep coming back to the hardness of the bullet making a huge difference. I'm envisioning hitting a billiard ball (very hard surface, like the ram) with either a beanbag or another billiard ball. Even though a beanbag and a billiard ball of the same weight and speed would have the same momentum on impact, the billiard ball would cause a much greater acceleration of the impacted target than the beanbag, wouldn't it? By the same token, a very hard bullet would cause much greater acceleration of the ram in the direction of the bullet's travel, which should result in a much higher chance of it being knocked from the stand. For practical purposes, though, are we constrained to just balancing the greater mass of the lead (usuall in the core of the bullet) versus the toughness of the copper jacket (thicker jacket = less room for higher mass of lead), or are there other alloys available to get both toughness and mass? Maybe we need rifle bullets made out of the alloy they use for Hevi-shot or something.

[DanDeMan]

Jason,

I’d characterize the alloys’ (jacket and core) mechanical properties of bullet toughness as compressive strength and not “hardness.”  We can make very hard bullets but some of them would be poor performers when knocking over 50 lbs of ram steel is the objective.  Such a bullet would be called frangible.

Yes, we want tough bullets to better topple the rams which will increase bullet dwell time as well as transfer more momentum.

Yes, the billiard ball would transfer more knock-down due to it being an elastic collision verses an inelastic collision for the beanbag given that both weigh the same and are traveling at the same velocity upon impact.

A simple way to think about this is that the momentum of the beanbag before the collision is equal to the momentum of the beanbag and ram after the collision.  Since we are assuming an inelastic collision for the beanbag, the bag and ram would move backward together.  However, for the billiard ball collision with the ram (we’re assuming that it doesn’t shatter) the ball will bounce backwards in the opposite direction of initial impact travel if the travel is perpendicular to the surface of the ram upon impact.  That means the ram absorbs the momentum from the impact of the ball, just like the beanbag, but the ball bounces off in the opposite direction so that momentum is added to the initially transferred momentum, think ram pushing on the ball and equal and opposite reaction.  I know it “sounds crazy”, but an elastic collision transfers more momentum to a stationary object (the ram) than an inelastic collision where the beanbag moves in the direction of the ram meaning it sticks to the ram and they both fall over together.

But, the best we are going to do, because no bullet we are likely to shoot in HP silhouette will bounce off a ram, is a bullet that is tough enough to increase dwell time as much as possible.  If the bullet was too tough it would punch right through the ram.  A 50 BMG AP round would probably leave a ram standing but with a sizable round hole through it.  So, we want a bullet constructed so it takes longer to totally blow the bullet up upon impact with the ram.  I’ve worked with cast bullets that will actually bounce backwards off of a ram without blowing up.  They knock over the rams better than when a softer lead alloy is used even though the softer alloy casts a bullet that weighs more.

Years ago much testing was done by this poster to determine optimum core alloy for ram slamming.  The most common metal used to “toughen” lead is antimony, but antimony also reduces the density of the core alloy.  Lead has a density of 11.34 gr/cc and antimony’s is 6.697 gr/cc.  Above about 11% antimony the alloy becomes frangible and the increase in compressive strength diminishes per percentage increase from 1% to 11 %.  About optimum with respect to increased compressive strength and high alloy density is right at 3% antimony.  The copper-zinc jacket material is an industry standard at 95% Cu and 5% Zn.  One custom bullet manufacturer has used 30 cal jackets to make 6.5mm bullets by swaging down the jackets to increase their thickness.  These thicker jacketed bullets do knock down the rams better than bullets made with standard jackets.

[Leadlauncher]

Dan,
Re cast bullets for Ram slamming. I was thinking about trying this out & developing a load with a 6.5, 7mm08 or .30 cal sact bullet. Do you think that cast bullets are accurate enough, or am I just wasting my time & should just stick with jacketed bullets?
kind regards

[DanDeMan]

Leadlauncher,

The BC of any 6.5mm, 7mm or 30 cal bullet cast from commercial molds is so low as to make the difficult job of hitting a turkey or ram when the wind is up a painfull proposition.  I'd not go there.

[B_Koes]

Dan,

I've read your posts about bullet composition with great interest.  In fact, I've had debates with guys about the effects of bullet "toughness" on target knockdown ability.

First, you're mixing kinetic energy and momentum when you talk about momentum and elasticity of collisions.  Momentum is conserved according to Mr. Newton so in my mind the only variable regarding knockdown power is how much of the bullet fragments (in terms of weight) in a vector other than directly toward the target.  We know this happens because we've seen the bullet splatter on a target.  I wonder if there is a quantifyable difference in knockdown power of similar momentum bullets (measured at the target) and the diameter of the bullet splatter??  Thoughts???

Bret

[DanDeMan]

Bret,

Could you please point out where I’m confusing kinetic energy and momentum?  I did use incorrect dimensions in a previous post for momentum; “ft-lbs” when it should have been “lb-s.”

Of course momentum is conserved, as was discussed, maybe not clearly, in a preceding post.  Draw a collision diagram of the billiard ball and ram collision.  You will find that if we define the positive direction as the direction the billiard ball is traveling just before collision, it is traveling in the negative direction after the collision and that post collision momentum must be added to the momentum of the falling ram.  In the inelastic collision of the bean bag and ram the bean bag continues to travel in the positive direction so its post collision momentum is NOT added to the ram’s momentum.  That is why an elastic collision transfers more ram knock-down that an inelastic one.

I’ve argued the issue of bullet toughness with several university professors.  Out of their lack of experience they were all of the mind that bullet toughness didn’t matter with respect to knocking over a ram.  Man, did they have their heads where the sun don’t shine.  Toughness does indeed make a substantial difference in ram knock-down performance at a given terminal momentum.  As an aside, terminal energy is not sufficiently predictive to be useful in making a decision on what caliber/MV/bullet combination will perform better at the ram line.  Terminal energy goes by the terminal velocity squared and so distorts the metric in favor of light, high velocity bullets when in fact heavy, slower bullets are far more devastating on rams.

Bullet splatter does indeed often predict knockdown.  As an example let’s use the 142 SMK and the 139 Lapua Scenar.  The 142 makes a rather large gray splash, often like someone swiped the ram with some gray paint from a spray can.  The 139 Scenar, on the other hand, usually leaves a shiny, quarter-sized mark.  The same is observed with the 107 SMK and 108 Scenar’s.  On chickens, pigs and turkeys the 108 Scenars leave a shiny dime-sized mark on the animals while the 107 SMK’s leave a gray splotch.

Years ago a test was run using a 6mm BR silhouette rifle to investigate the affects of heat treating 107-grain, 6mm SMK’s on ram knock-down performance.  The bullets were set vertically with their tips up in a specially made jig.  A number of bullets were heated at 460 F for 1 hour and then quenched in cool water.  Both heat-treated and non-heat-treated bullets were shot at rams from the bench.  The load’s MV was about 2,900 fps.  The range had new stands and rams.  The guys that put in new stands did a great job of leveling the stands so this was a very “fair” test.  The rams were new and made from T1 steel.  They were carefully setup after making sure the stand tops were free of dirt.  Ten rams were shot in the “arm pit” using the non-heat-treated bullets with only 3 going down.  Those rams were reset but this time the heat treated bullets were used.  Eight rams went down with the heat-treated bullets.  Another interesting observation was that the sound of the bullets hitting the rams was much more pronounced, louder, when the heat-treated bullets were used.

[Varn1808]

Dan,
     If I remember correctly, didn't heat treating the bullets also induce unexplained fliers?    Varn

[DanDeMan]

Yo Varn,

Yes in deed heat-treated bullets had diminished accuracy.  The unexplained flyers were from tying to shoot the 6.5mm, 155 SMK's out of an 8-twist barrel.

Even when very carefuly heat-treating bullets with enough antimony in the cores to be heat-treatable, accuracy was degraded by a factor of two or more.  If my memory servers me well, the 6mm, 107-grain SMK's shot into a sub 1/4-MOA group when using non-heat-treated bullets.  With the heat-treated bullets accuracy was in the 3/4 MOA range, quite a large decrease in accuracy.  When the 142 SMK's were heat-treated accuracy was in the MOA range with the non-heat-treated bullets producing 1/4-MOA accuracy.  All accuracy testing was done at 100 yards in clam conditions off a quality benchrest setup.

[B_Koes]

Bret,

Could you please point out where I’m confusing kinetic energy and momentum?  I did use incorrect dimensions in a previous post for momentum; “ft-lbs” when it should have been “lb-s.”

Dan,

My point is simply that elastic collisions preserve kinetic energy while inelastic collisions do not.  Momentum is preserved regardless of the elasticitiy of the collision which is why it is a better predictor of knockdown ability than kinetic energy.  If you could develop some sort of coefficent for each bullet design the transfer energy to a hard metallic target then we could use that KE number. :grin:

Before you perceive this as an attempt to refute your statements, your comments seem to fall in line with my thinking.  Whether you want to call it bullet toughness or frangibility or whatever, what matters is the ability of the bullet to hang together in such a way that the bullet fragments are directed toward the target instead of at an angle away from the point of impact (like the splatter of the SMK you describe).

Bret