Federal Terminal ascent required twist rates

[FEENIX]

Berger twist calculator not work for tipped and mono bullets.

Did you plug in the right information?

Below is Cayuga 117 bullet information (https://patriotvalleyarms.com/cayuga-hunting-projectiles/)

Length: 1.365"
Optimal Freebore: 0.160"-0.210"
G1 BC average = 0.580*
G7 BC average = 0.282*

*The average BC was measured using 7tw 5R rifled barrels and being shot at approximately 2970fps. Different rifling geometry and muzzle velocity will affect the BC in a nominal manner.

257 cal Cayuga 117 requires a 1:8tw barrel.

... when plugged into Berger's SG calculator...

As you can see, it does work if the right information is plugged in.

 

[Mikecr]

It worked in that case but the stability of the 117 from 1:8tw would actually be higher than Berger's 1.40sg result (where tipped).

 

[FEENIX]

It worked in that case but the stability of the 117 from 1:8tw would actually be higher than Berger's 1.40sg result (where tipped).

So I do not misconstrue your statement. Are you saying if the Cayuga 117 is a tipped design, the SG would be higher than 1.40? If that is the case, yes, I agree that the SG would be higher.

Altitude is your friend comes to SG when it. If I ran the same numbers in #15:

- Range altitude of ~3333' SG = 1.58
- Average hunting altitude of 5500' SG = 1.72

 

[257Tony]

They are showing the .308, 175 grain bullet is only .787" long, Gotta be wrong. That's the same length as a 110 Speer HP.

 

[Laguna Freak]

So I do not misconstrue your statement. Are you saying if the Cayuga 117 is a tipped design, the SG would be higher than 1.40? If that is the case, yes, I agree that the SG would be higher.

Altitude is your friend comes to SG when it. If I ran the same numbers in #15:

- Range altitude of ~3333' SG = 1.58
- Average hunting altitude of 5500' SG = 1.72

The issues I've found with Berger's stability calculator are:

1) no factor for bullet c.g. when comparing plastic tipped bullets to non-tipped. I assume because Berger makes zero tipped bullets

2) Berger attempts to use some sort of proprietary calculus in their elevation or altitude coefficient. Which, in my opinion, is bound to be less accurate than using actual barometric pressure and air temperature. Because their coefficient must assume a standardized pressure and temperature at the input altitude/elevation.

I'm sure Berger has their economic motivations. They are in the business of selling bullets. And they are fine bullets, no doubt.

I prefer the JBM Ballistics stability calculator because of the measurable inputs it requires for the above referenced "Berger deficiencies". IMO.

 

[Laguna Freak]

They are showing the .308, 175 grain bullet is only .787" long, Gotta be wrong. That's the same length as a 110 Speer HP.

View attachment 271550

Gotta be a typo. The 200 gr TA shows 1.622" long. And for competitive reference the 180 Swift Scirocco II shows 1.435" long with a much less pronounced boat tail than the TA

 

[Swamplord]

 

[257Tony]

Looks like the TA bullets are almost exactly the same length as the Barnes LRX of the same weight.

 

[Swamplord]

and this is what the 175 gr Terminal Ascent bullet looks like ....
after leaving muzzle at 3350 fps & going through a moose at 100 yards

 

[Mikecr]

Are you saying if the Cayuga 117 is a tipped design, the SG would be higher than 1.40? If that is the case, yes, I agree that the SG would be higher.

Yes. For a given weight-length with a plastic tipped bullet, more of the mass is in perimeter.
This, generating higher gyroscopic forces than a same weight-length non-tipped.
It is often surprising (to me) what twist you can get away with using tipped bullets.

I also agree with you about altitude (lower air density) being our friend.

 

[Swamplord]

Those of you who wanted to try the Federal Terminal Ascent can get the 30 cal 175 gr from Midway right now via the "factory overrun" discounted sale at $59.99 per hundred pcs, last fall they were $42.99 per box of 50 pcs and Midway has jacked the price up to $69.99 per box, so the 100 pc bulk unmarked box sale is kind of a deal, limit 2 per customer

Factory Overrun 30 Cal (308 Diameter) Bullets 175 Grain Bonded Polymer

MidwayUSA has just made a huge purchase of Factory Overrun bullets and we are passing the savings to our customers. Overrun bullets are bulk-packaged,...

www.midwayusa.com

 

[Swamplord]

Midway also have the 200 gr 30 cal Terminal Ascent bullets sold as hollow point factory seconds at $59.99 per 100 pcs

Factory Second 30 Cal (308 Diameter) Bullets 200 Grain Bonded Hollow

MidwayUSA has just made a huge purchase of blemished bullets and we are passing the savings to our customers. Blemished bullets are bulk-packaged,...

www.midwayusa.com

 

[General RE LEE]

Those of you who wanted to try the Federal Terminal Ascent can get the 30 cal 175 gr from Midway right now via the "factory overrun" discounted sale at $59.99 per hundred pcs, last fall they were $42.99 per box of 50 pcs and Midway has jacked the price up to $69.99 per box, so the 100 pc bulk unmarked box sale is kind of a deal, limit 2 per customer

Factory Overrun 30 Cal (308 Diameter) Bullets 175 Grain Bonded Polymer

MidwayUSA has just made a huge purchase of Factory Overrun bullets and we are passing the savings to our customers. Overrun bullets are bulk-packaged,...

www.midwayusa.com

View attachment 271762

I scored these last night. My Tikka .308 likes the Federal Terminal Ascent factory ammo and I kept the nickel brass so I can load up a bunch of these with Accurate 4064 powder.

 

[General RE LEE]

Those of you who wanted to try the Federal Terminal Ascent can get the 30 cal 175 gr from Midway right now via the "factory overrun" discounted sale at $59.99 per hundred pcs, last fall they were $42.99 per box of 50 pcs and Midway has jacked the price up to $69.99 per box, so the 100 pc bulk unmarked box sale is kind of a deal, limit 2 per customer

Factory Overrun 30 Cal (308 Diameter) Bullets 175 Grain Bonded Polymer

MidwayUSA has just made a huge purchase of Factory Overrun bullets and we are passing the savings to our customers. Overrun bullets are bulk-packaged,...

www.midwayusa.com

View attachment 271762

***PSA***

I ordered these and when they showed up they were not the Terminal Ascents, they were the short lived Edge TLRs. I went on Midway and other folks that received their order also noted they were the Edge TLRs. It appears Midway used the Terminal Ascent stock pic and specifications for this item but is shipping out the Edge TLR. I'm returning my order.