.308 Win 220gr vs. 175gr SMK for Long Range Target

[robrob]

I have looked around the internet for info on 220gr .308 SMK for long range target shooting but mostly it says it uses too much case capacity and lowers muzzle velocity too much.

I generated QuickLOAD propellant tables for the 175 and 220gr SMK from a .308 Win using 62,000psi as max pressure (.308 SAAMI), 2.8" COL from a 24" 1:10 twist barrel and used the highest velocity from the tables for each bullet.

I realize QuickLOAD data isn't gospel but it should do a pretty good job to compare these two loads. One load is "Dangerous" and the other is "Near Maximum" so I know these aren't loads we'd actually use but I'm using the data as an equalizer between the two loads so we can compare exterior ballistics. The key is both loads are QuickLOAD max velocity loads.

175gr SMK Max Muzzle Velocity 2800fps


220gr SMK Max Muzzle Velocity 2503fps


I then used the fastest muzzle velocity from the two propellant tables to generate range cards using Hornady's very accurate 4DOF ballistic calculator & G7 BCs to compare long range performance.

1000 yards

175gr SMK at 2800 fps MV
1236 fps @ 1000 yards (104 fps slower)
593.5 ft-lbs retained energy
9.67 milliradian (33.24 moa) come up
2.99 milliradian (10.28 moa) 10 mph cross-wind (24% more drift)

220gr SMK at 2503 fps MV
1340 fps at 1000 yards (8% faster)
877.0 ft-lb retained energy
10.46 milliradian (35.96 moa) come up
2.42 milliradian (8.32 moa) 10 mph cross-wind

At 1000 yards the 220gr SMK is 8% faster and the 175gr SMK gives us 24% more wind drift and spin drift.

The 220gr MatchKing is stable from a 1:10 twist barrel with a gyroscopic stability (Sg) of 1.64 at the muzzle (1.5 is minimum for stable long range flight). If the barrel twist rate was 1:12 the Sg would be unstable at 1.14 so at least a 1:10 twist barrel is needed for .308 220gr bullets at long range.

The 220gr SMK was 297 fps slower than the 175 at the muzzle.

For target shooting we know range so bullet drop isn't as critical as wind drift. The range cards show the big 220gr stays supersonic about 100 yards farther down range. The 175gr give us 24% more wind drift and spin drift at 1000 yards and beyond.

Has anyone tried a hot Reloader 17 load with 220gr SMK for 1000 yards or longer?


Photo by robrob. All rights reserved

[Jim Watson]

I'll ask my LR friend what he is using in .308 these days. I know he was strong on the Berger 185 gr Juggernaught at one time. I never got past 175 SMK or 155 Scenar myself.

[Rimfire5]

I suggest you try the 175 Sierra Tipped Match King and 195 Sierra Tipped Match King.
They have a high ballistic coefficient and more importantly to me, they shoot incredibly accurately in my two .308 bolt actions when they are loaded out about 0.060 longer O.A.L. than their SMK brothers to accommodate the added polymer tip.

[Unclenick]

Robrob,

I had to edit your post. Please read the board policy on posting copyrighted materials. We do have permission from Ed Dillon at NECO (QuickLOAD's distributor and U.S. copyright licensee and rights controller) to put up occasional QL results, so I have left the first two frames up.

I put in the 1000 yard results you had in the tables. That will be enough for a long range shooter to get some idea what's happening.

You seem to have picked up a misconception about gyroscopic stability factor. By definition, the stability break-even value is 1.00. Any number greater than that is also stable and anything less that 1.00 is unstable. But just any degree of stability isn't automatically optimal. Spinning a little faster reduces epicyclic yawing over the range, improving BC a little and settling the bullet and narrowing group size. Spinning too much faster increases wobble due to any mass asymmetry that may exist and increases the velocity of any lateral drift due to an off-bore-axis center of mass, as from the bullet being slightly cocked in the bore. Some authorities suggest a value of around 1.5 is optimal. Others think 1.4 is. Still others estimate 1.7 is. Long ago, a Sierra ballistic tech told me to figure anything from 1.3 to 3.0 was fine for "hunting accuracy", and 1.4 to 1.7 was best for extreme target accuracy.

Well, that heavy one will recoil more noticably and be more prone to create recoil moments that cause shooter hold-induced errors to be greater (increases the need for position and hold consistency). Barrel vibration will be greater so load tuning will be more important. It may or may not shoot as accurately for you. But once you have the loads tuned, then you will have some idea what the usable performance ratio actually looks like as compared to the theoretical maximum. But that does give you the idea there is something perhaps worth chasing down.

[robrob]

I got the Sg of 1.5 for stability from Bryan Litz, the Berger bullets stability calculator and Bison Bullets.

A graphic on the Berger Bullets stability calculator states, "A stability factor of 1.5 or greater ensures adequate stability.":

https://bergerbullets.com/twist-rate-calculator/

And from Bison Bullets stability calculator page:

"Update - 10/4/14
While the above recommendations are still applicable at short range, there is a section in Bryan Litz's new book, Modern Advancements in Long Range Shooting, that details his experiments with drag and stability. He presents a compelling argument that there is a slight increase in drag when Sg falls below approximately 1.5. Noting that, I now think it prudent to use at least a 1.5 stability factor for long range shooting, where the slight decrease in drag is more important than the slightly decreased accuracy from over-spinning the bullet."

https://bisonballistics.com/articles/bullet-stability

So new data on stability has bumped the line up to an Sg of 1.5 or greater.

[Bart B.]

If a 24" barrel with a SAAMI spec chamber is used with 220 grain SMK bullets, you will probably need a 1:9 twist for decent accuracy in cool temperatures.

[robrob]

Bart, the admin deleted the range card that shows the 220gr with an Sg of 1.64 out of a 24" 1:10 barrel but that was at 70 F.

EDIT: I just ran the numbers and the Sg at 30 F is 1.53 so it's getting close.

[robrob]

@unclenick, why did you delete the 4DOF range cards? I don't see anything on the Hornady webpage about the output being copyrighted.

For that matter I don't see anything on the QuickLOAD output that says anything about the output being copyrighted. I can understand the program being copyrighted but the output?

[hounddawg]

Buy 100 of each and see which shoots the best. It's not like you're going to burn out the barrel on a .308. Just thinking about shooting 75 rounds of that 220 in a match makes my shoulder hurt

[Pathfinder45]

If there's a moral to this story, I'd say that you really can't make a 30-'06 out of a 308. If you want 30-'06 performance, go buy one. On the other hand, you can certainly down-load the '06....



.

[robrob]

I'm definitely going to give 220gr SMK and Reloader 17 a try and see how it compares to my current 175gr SMK load. I'm also going to try Reloader 17 with the 175gr SMK.

[Mobuck]

.308 can barely push a 190 grain fast enough to maintain supersonic for longer ranges. 220 would be even worse.

[robrob]

For a 12lb rifle the recoil energy of the 220gr SMK load is 1.5lb higher than the 175gr for an 11% increase.

[robrob]

Mobuck, using Hornady's very accurate 4DOF ballistics calculator and the SMKs' G7 BC, it shows the 220gr staying supersonic 100 yards farther downrange than the 175. The 175gr SMK gives us 24% more wind drift at 1000 yards and beyond.

[robrob]

To summarize the first post: At 1000 yards and beyond the 220gr SMK is at least 8% faster and the 175gr SMK gives us 24% more wind drift and spin drift.

I used Hornady's very accurate 4DOF ballistics calculator and G7 BCs to generate the range cards for down range comparison. Unless QuickLOAD is way off here the 220gr SMK & Reloader 17 in the .308 is worth investigating.

[Bart B.]

Originally Posted by robrob

Bart, the admin deleted the range card that shows the 220gr with an Sg of 1.64 out of a 24" 1:10 barrel but that was at 70 F.

EDIT: I just ran the numbers and the Sg at 30 F is 1.53 so it's getting close.

You are correct. I must have mistyped in numbers checking it out.

[Bart B.]

Originally Posted by Mobuck

.308 can barely push a 190 grain fast enough to maintain supersonic for longer ranges. 220 would be even worse.

David Tubb shot 250 grain HPMK bullets from his 308 at 1000 yards with great success. 2150 fps out the barrel

The most accurate 1000 yard match load for 30 caliber service rifles was 44 grains of IMR4320 under Sierra 190's in an M118 7.62 primed case shot in Garands' 24" 1:12 twist barrels. Easily tested sub MOA at 1000 leaving about 2580 to 2600 fps.

48 grains of IMR4350 under Sierra 200 HPMK's was popular in 308 Win bolt guns for 1000 yard matches. 2500 fps or so at the muzzle. Easily tested 2/3 MOA at 1000; as good as benchrest rigs.

[Unclenick]

Robrob,

A good read is attorney Brad Templeton's article, 10 Big Myths About Copyright Explained. The first myth on his list is:

1) "If it doesn't have a copyright notice, it's not copyrighted."
This was true in the past, but today almost all major nations follow the Berne copyright convention. For example, in the USA, almost everything created privately and originally after April 1, 1989, is copyrighted and protected, whether it has a notice or not. The default you should assume for other people's works is that they are copyrighted and may not be copied unless you know otherwise.

Templeton explains later that all web content is included in that automatic copyright protection.

So, if you want to post those tables you need to contact Hornady and ask them if it's OK to post those screen shots on forums. If so, you then need to indicate in your posting of them that you have their permission when you put up the post and keep a copy of the email or whatever permission you got as we may ask you for it for our records to protect the board.


Regarding stability factor, none of the sources you cite contradict what I said. Litz says drag is higher when the bullet stability factor is below 1.5, which is another way of saying the measured BC will be lower, which is how I put it. What Litz does NOT say is that the bullet will tumble (become unstable) below 1.5. It will not do that until it gets below 1.0. What Berger said about 1.5 being necessary for "adequate" stability has to be taken with perspective regarding what they mean by "adequate". Clearly, with their citation of Litz, they mean adequate to maximize trajectory and not that a bullet would be unstable at 1.2 or any other number between 1.0 and 1.5.

Eugene Stoner would have disagreed with Berger's number. He wanted the military to go from a 12" twist in the M16 to a 14" twist to get the stability factor down nearer to 1. He didn't care about long range accuracy in a gun and ammunition combination with 350-yard effective range. He wanted the bullet to tumble when it hit a human target, and minimizing stability would ensure the bullet was still yawing when it got there. That yaw would cause it to turn and tumble when it struck a more viscous (than air) medium. So his definition of "adequate" was just not to tumble immediately after departing the muzzle.

An interesting thing to understand is that angular (rotational) velocity drops off due to surface friction with air in the direction of rotation. That is much less drag than the bullet nose experiences, so angular velocity drops off much more slowly than forward velocity does as a bullet flies downrange. This means the gyroscopic stability factor increases as the bullet goes downrange. That's what was vexing Stoner. The M16 rounds tumbled just fine when they hit a target up close, but far enough away they were they settled out and would just make pencil holes. He was trying to get them to tumble further out.

Harold Vaughn was the source of the 1.4 stability factor recommendation. He was head aeroballistician at Sandia National Laboratories, and so was even more credentialed in the discipline than Litz is. He got to his 1.4 number as a compromise, but to understand his adequacy criteria you need to know two things: First, he was not a varmint hunter. He was a Big 5 Boone and Crocket listee who hunted the plains out west and who was interested in accuracy out to 350 yards. He was not sending Berger VLD's to 1000 yards, so a small increase in drag would not be a major concern for him. Second, his experiments started in the 1950's. This meant he had experience with bullets that were not made as precisely as they are today and so minimizing in-flight wobble and lateral drift by not spinning an eccentric mass faster than was absolutely necessary was a bigger consideration for him than it would be for someone today. Thus, he was more prone to err on the slower side of spin than Litz would feel the need to be.

While expensive to obtain today, Vaughn's book, Rifle Accuracy Facts, includes some nice output plots from a 6 DOF trajectory program he wrote. They show the coning motion of a bullet tip from initial yaw spirals outward when the stability factor is less than 1, continuing to increase the bullet's angle off the trajectory until the bullet sides catch so much air that it tumbles. When the stability factor is greater than 1.0, the path of the bullet nose spirals inward until it settles at an equilibrium point at the yaw of repose. Spinning faster settles it in fewer cycles. Right at 1.0, if that could be maintained as a constant value in flight, the spiral neither grows nor shrinks, but just continues. That would keep some part of the bullet profile exposed to the airstream and increase drag to maximum (minimize the measured BC).

If you want the most technically detailed resource on the topic of ballistic projectile stability, get a copy of the 2nd edition of the late Robert L. McCoy's book, Modern Exterior Ballistics. He walks you through all the terminology of factors affecting a bullet's flight and the math. His McGyro program was a gyroscopic stability estimator a little less simplified than Don Miller's modified Greenhill approach (the one on the JBM site). You can access it in the calculators at Geoffrey Kolbe's site, which gives you graphs of the initial stability factor with respect to barrel twist rates, but you need more bullet details to use it than the JBM estimator does.

[robrob]

For long range target shooting I highly recommend going with Litz's 1.5 Sg minimum to minimize lag time and wind drift. See Litz's Applied Ballistics For Long-Range Shooting, chapter 10, Bullet Stability for more info.

It turns out that 210 and 220gr SMK are popular with British Commonwealth Match Rifle 1000M .308 shooters.

[hounddawg]

pretty popular in US also

Best Ever — 1000-Yard Records Set at 2018 F-Class Nationals

[robrob]

Thanks hounddawg,

From the article:

In the F-TR class, two men, Ray Gross (Team McMillan) and Mike Plunkett, both set a new pending 1000-yard record with a 200-16X score.

Ray, along with the vast majority of other F-TR competitors, was shooting a .308 Win. His load included Berger 220X bullets, in Lapua brass, with Vihtavuori N140 powder and CCI 450 bullet. Ray’s rifle features a 28″ Bartlein Heavy Palma barrel, mated to a Kelbly Panda action in McMillan stock. Up front was a Phoenix bipod with lowering bracket. The scope was a Nightforce NXS 8-32x56mm.

[Bart B.]

Originally Posted by Pathfinder45

If there's a moral to this story, I'd say that you really can't make a 30-'06 out of a 308. If you want 30-'06 performance, go buy one. On the other hand, you can certainly down-load the '06.....

The reason 308's are favored over the 30-06 for long range target shooting is their 30+% smaller test groups is worth a 4% increase in wind drift caused by 100 fps lower muzzle velocity. That began back in the early 1960's.

You can add 4 inches to 308 barrel lengths to shoot at 30-06 velocities.

[Jim Watson]

And .308 is all you get for Palma and F/T-R. Unless you want to really stretch a .223 which I chased without much success for a while.

[T. O'Heir]

A 220 is too long for the .308 Win.
Use a 175 or 178 grain match bullet for distances past 600 yards. Both will use the same data. Three grains won't matter.
A 190 is really best for .300 Win Mag match rifles. Knew a guy who regularly won DCRA(our version of the NRA but without the political clout) 1,000 yard 'sniper' matches. The Win M70A receivered rifle weighed 17.5 pounds. It's original stock lives on my .243 deer rifle.
"...all you get for Palma..." Or .223, but it's a 155 grain bullet only in .308 Palma. And the rifles weigh in at 14 or 15 pounds and are single shots.
F-T/R is .223 or .308 only with a max rifle weight of 18 pounds. Bipods and adjustable rests are allowed.
F Class is a totally different game. It's basically any rifle, any sights, any caliber .35 and under. One of the many such games available.
There's something for everybody so try as many as you can before spending a pile of money.
"..."If it doesn't have a copyright notice, it's not copyrighted."..." Be really interesting to watch that trial. Traffic court would still be way more entertaining and it's free. Much better if you're not there at the request of the Crown or State though.
1,000px × 1,110px is too big anyway.

[Bart B.]

Originally Posted by T. O'Heir

A 220 is too long for the .308 Win.

Read post 17.