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.