Tikka 22-250 1:8 88eldm Stability?

[Castle Rock]

The 80’s group amazing in my factory 18” Tikka 223. I’ve shot them out to 900 yards. The problem is that the BC drops way off for me. To use them effectively, I’d have to have two separate ballistic profiles, one for >500 and one for <500. I’m pretty sure that the 1/8 twist rate is the root cause of this. The 75’s however will use one profile out to the same distance with no seeming drop off in BC.

That’s interesting, what velocity are you getting and what’s your drop at 900?

 

[djauofd]

So Castle Rock makes a good point. Basically the the gyroscopic effect on a bullet is about moving the center of mass al9ng and axis. The problem is that in standard profiles, the additional length is lead filled brass. In reality, the tip projection is solid nylon plastics. The plastic megaplant weighs only 15% of what solid brass would be. So, while the overall length of the bullet increases by approximately 0.135". It's affect on the center of mass is only marginal. So if you carry across a linear projection, all things being equal, not purely scientific because we don't know the total mass of a bullet tip if it was brass , a quick SWAG is that it only affect mass by 25%of the length of the plastic tip . So .135" (25%) becomes or .03375". Which means you are subtracting .101" off the measured length of the bullet. For the 88gr ELDM's the overall is 1.242 , using 1.141 as an overall now brings SF to 1.36. For the 80 grain ELDM, the overall goes from 1.155 to 1.054" So that takes the SF from 1.21 to 1.58, making the 80 gr ELD M completely stable Whereas the 88 gr ELD M will be stable with a slight possible wobble, which could affect the BC of the bullet slightly. Which you would only notice at extreme ranges.

Thanks for making me do the exercise. Something to be considered when doing calculations for stability factor using bullet overall lengths when considering plastic tipped bullets. That being said, I think I will get some 88 ELD M's and see what kind of performance I can get out of them with the 223's using the Shell tech cases. Based upon projected velocity of 2,795 out of a 20" barrel , at sea level, the 88's are transonic out to 1,120 yds. For the 80 gr ELD M's using 2,900 fps, it is transonic to 1,060 yds. Both of which are absolutely insane from a standard 223 rem round out of a 20" gas gun.

Every day is a learning event.

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[wind gypsy]

The 80’s group amazing in my factory 18” Tikka 223. I’ve shot them out to 900 yards. The problem is that the BC drops way off for me. To use them effectively, I’d have to have two separate ballistic profiles, one for >500 and one for <500. I’m pretty sure that the 1/8 twist rate is the root cause of this. The 75’s however will use one profile out to the same distance with no seeming drop off in BC.

What BCs do you use for sub 500 and over 500 on the 80s? I wouldn't think it would be that far off that you couldn't use the lower BC at sub 500 too?

 

[SouthPaw]

80gr eldm shoot well in my factory tikka .223. Hornady BC has worked fine to transonic.

 

[tallbuchholz]

10-shot group at 100 yards with the copper creek 88s in .22-250 from this week. 30mph winds so I definitely wasn't my best. They don't group as well as the 75s or some 55s in my gun but that's plenty good for me.

 

[djauofd]

So I got my 88 ELDM 's last week and loaded the up for my 20" AR 15. loaded long for single feed at 2.495, lands were 2.505". Using Shell tech 80,000 psi casings. AR Comp ladder 23.5 gr thru 25.9 gr .3 grr increments. Top speed was 2,943 fps, the case heads are clean, no smearing of case heads at all. Primers were getting flat, but at 25.9 gr, there was significant catering. At 25.6, was just starting. So, I would think the max load should be 25.6 gr.. belocity was roughly 2,930 fps. Pretty crazy stuff. The rifle cycled perfectly, a tiny hair over gassed ejection right at 3 o'clock. It has an adjustable gas block, so I'll shut it down a touch. The carbine buffer is 5.3 oz and it uses a blue spinco spring.

Sighted in at 25 yds , bullets showed no sign of tumbling , nice tight holes. According to Strelock at sea level 59 deg, with a 10 mph crosswind in mills, 5.98 mills drop, 1.92 drift. Transsonic at 1,190 yds super sonic to 1,300 yds . At 1,000 yds velocity, 1,453.8 fps with 453 ft lbs of energy. Using my previous set assumptions, stability factor 1.38.


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[B_Reynolds_AK]

What BCs do you use for sub 500 and over 500 on the 80s? I wouldn't think it would be that far off that you couldn't use the lower BC at sub 500 too?

Eh, I don’t know exactly. Changed the ballistic profiles on my Revic app, so couldn’t say exactly. I know that it was significant, whereas the 75’s don’t drop off at all for me.

I did just receive an 18” PVA 223 1/7 twist .100 fb barrel, but don’t plan on spinning it on anytime soon as the 75’s are such hammers with the factory barrel, which I only discovered after having ordered the PVA.

 

[Schmo]

So Castle Rock makes a good point. Basically the the gyroscopic effect on a bullet is about moving the center of mass al9ng and axis. The problem is that in standard profiles, the additional length is lead filled brass. In reality, the tip projection is solid nylon plastics. The plastic megaplant weighs only 15% of what solid brass would be. So, while the overall length of the bullet increases by approximately 0.135". It's affect on the center of mass is only marginal. So if you carry across a linear projection, all things being equal, not purely scientific because we don't know the total mass of a bullet tip if it was brass , a quick SWAG is that it only affect mass by 25%of the length of the plastic tip . So .135" (25%) becomes or .03375". Which means you are subtracting .101" off the measured length of the bullet. For the 88gr ELDM's the overall is 1.242 , using 1.141 as an overall now brings SF to 1.36. For the 80 grain ELDM, the overall goes from 1.155 to 1.054" So that takes the SF from 1.21 to 1.58, making the 80 gr ELD M completely stable Whereas the 88 gr ELD M will be stable with a slight possible wobble, which could affect the BC of the bullet slightly. Which you would only notice at extreme ranges.

Thanks for making me do the exercise. Something to be considered when doing calculations for stability factor using bullet overall lengths when considering plastic tipped bullets. That being said, I think I will get some 88 ELD M's and see what kind of performance I can get out of them with the 223's using the Shell tech cases. Based upon projected velocity of 2,795 out of a 20" barrel , at sea level, the 88's are transonic out to 1,120 yds. For the 80 gr ELD M's using 2,900 fps, it is transonic to 1,060 yds. Both of which are absolutely insane from a standard 223 rem round out of a 20" gas gun.

Every day is a learning event.

Or instead of doing all these mental gymnastics, just pull up 4DOF, input altitude, twist, and velocity, and it’ll give you the stability factor.

 

[cq0302]

I know there’s guys with a lot of success getting the 88 to stabilize in a 22cm in tikka 1:8 barrels

What about the slower velocities of the 22-250? Berger and Hornaday apps say it’s a no go.

Elevation at about 3k for practice, 7-10k for hunting. I was getting 3050-3100 fps with the 75ELDM with a 20” barrel but would like to shoot a higher BC larger bullet


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I’ve had good luck at 100yds getting .75” groups with staball 6.5 and n560. No indication of instability but will take them to 900 and report back. I have had tremendous success with the Berger 85.5 and 38.2 gr n560 out to 1000+

 

[Jordan Smith]

Sorry I was wrong that 1.2 was for a 80 gr ELD m , For the 88 gr ELD M the Stability factor is only like 1.06 That is at sea level. Although atmospher does not change the stability factor. `This is at roughly 2,900 fps for the 80 gr and 2,790 fps for the 88 gr bullets. I have been playting with shell tech cases in 223. You can get an extra 200 fps out of them., and have been toying with the idea odf getting a 1-7 twist barrel to shoot the 80 gr and 88 ge ELD M's Getting like 2950 fps with 77 gr RDF's out od a 20" BHW barrel. but it is a 1-8 twist . Ideally Stability factor (which is not affect by atmosphere) should be at 1.4 or higher, below this the bullet can wobble and affect the ballistic coieficient, and acuracy to full fledges sideways wad cutters. So stabilizing an 88 gr bullet is a virtual act of God, anything temperature, speed, seating depth load changed can set it off. Just like a top that is wobbeling once it starts it will goi in and out of hamonic. Not good.

You've said that a couple of times, and it's simply not true. Atmospheric conditions certainly affect air density, and air density affects stability.

Ideally, an SG of 1.5 or higher is generally the goal to achieve super-stability and maximize the BC value.

 

[djauofd]

Yes you are correct.


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[Castle Rock]

air density affects stability.

Hey Jordan, that’s new to me, I would appreciate any more information or a link to such please

 

[Jordan Smith]

Hey Jordan, that’s new to me, I would appreciate any more information or a link to such please

Sure, no problem.

Gyroscopic stabilization overcomes perturbations and asymmetries where the center of pressure of the projectile is in front of its center of mass. If you fired a bullet in a perfect vacuum, flying perfectly straight (ignoring any perturbation caused by the expanding gas as the bullet leaves the muzzle), it would remain straight even if it wasn't rotating at all. The reason that the scenario changes in atmosphere is because of drag forces imparted by the air on the bullet. Those drag forces are highest at the front of the bullet, while the majority of the mass, and therefore inertia, is located at the rear of the bullet. The natural tendency is for the bullet to swap ends because the "lighter" end of the bullet gets pushed around by drag more than does the "heavy" end. By spinning the bullet and imparting angular momentum, the bullet resists this "end-swapping" force, since a certain amount of overturning torque is required to destabilize the bullet (for a stable bullet, this torque threshold is more than the torque generated by the drag force).

Now, drag force is a function of the density of the medium through which the object is travelling. If you've ever tried wakeboarding, you'll know that when you're in the water and the boat is trying to pull you up, it requires a fair bit of effort to keep the wakeboard in front of you and get up out of the water, even though you're not going very fast at the beginning. This is because your center of pressure is out in front, close to the wakeboard, while your center of mass is rearward, somewhere near the center of your body, combined with the density of the water through which you're trying to plow. You can imagine that if you were doing the same thing in air, instead of in water, you'd have to go a lot faster to feel the same force trying to push your wakeboard behind you and pull you on your face (i.e., overturning torque). That's because air is much less dense than water.

The same thing applies to bullets. The more dense the air, the more overturning torque is applied to the bullet by the drag force, and the more angular momentum the bullet requires to overcome that torque. So you have to spin the bullet faster to maintain the same stability. In external ballistics, the entire reason that we care about atmospheric quantities, such as pressure, humidity, temperature, and derivative quantities like density altitude, is because they allow us to quantify air density, which affects not only stability, but the bullet's trajectory (both elevation and windage), as well.

Bryan Litz has discussed this in his book Modern Advancements to Long Range Shooting. You can find more info here: https://bergerbullets.com/the-state-of-the-art-in-rifle-bullet-stability/

 

[Castle Rock]

Thanks for that great explanation, I wasn’t seeing the forest for the trees.