ELR Barrel Twist - 7mm

[cperazza]

Putting together either a 284 JAZZ or 7 HULK for ELR.

Bullets: 180 Berger Hybrids / 195 Berger EOL
Expected Velocity: 3350 fps / 3150 fps
Barrel: Krieger #17 MTU 7T 26-28"
Action: Defiance Deviant Tactical or Stiller TAC338
Stock: McMillan XTR Adj
Trigger: Bix'n Andy TACSPORT

Currently shooting a 284 Shehane (8.5T, 27") at 2,868-2,900 for (180s) and 2,750 fps (195s).

Any advice on going with a 7T instead of the 8T/8.5T? Another alternative (since the twist rate is too fast) is chamber the 7T barrel in a 284 Shehane or another project.

 

[THEIS]

Hi,

What projectile are you planning to utilize?

Sincerely,
Theis

 

[cperazza]

Hi,

What projectile are you planning to utilize?

Sincerely,
Theis

Good catch...
Bullets: 180 Berger Hybrids / 195 Berger EOL

 

[Jeffvn]

If you running the Jazz or Hulk, the velocities you are going to run are going to be sky high. You could easily run the 8.0 and possibly even an 8.25 and hit Berger's optimum spin rates (assuming you run the 195 @ 3,200 fps). The 180s are fully stable according to Berger's spin calculator.

http://www.bergerbullets.com/twist-rate-calculator/

Jeffvn

 

[cperazza]

Jeffvn, I am with you, tracking both bullets will be stabilized with 8T or 8.25T. Bergers twist rate calculator pretty good tool. Given both bullets will be stabilized, any additional considerations going with a 7T barrel?

 

[Tjfarmer]

You should be able to stabilize the 197 Sierra, unless you want to push exotics I think 8t will do everything you want. I went 8t myself for my current build.

 

[bjay]

I think 7 little too fast..8.25 up to 195gr i think is more than enough

 

[Carolina Hill Billy]

I've had good luck with 197's in a 7.5 twist 280AI.

 

[Tjfarmer]

When I went to bergers website, 197’s at 2900-2950ish in my air was just enough with 8t.
jmackey, Do your 197’s b.c’s hold up to their numbers, are they a pain to find a sweet spot for accurate load? I found 197’s real cheap, but hate to buy a bunch if my build don’t like them

 

[Carolina Hill Billy]

When I went to bergers website, 197’s at 2900-2950ish in my air was just enough with 8t.
jmackey, Do your 197’s b.c’s hold up to their numbers, are they a pain to find a sweet spot for accurate load? I found 197’s real cheap, but hate to buy a bunch if my build don’t like them

The applied ballistic calc worked at 1000 yards with Magnetospeed velocities. That's the farthest I've shot it. I have a pretty short barrel but can get 2725 with RL26. It shot well enough after the quickload guesstimate that I didn't waste barrel life trying to tune. I'm in SC so the elevation is minimal and humidity is thick, but it certainly achieves stability. The same load has shot well from 85+ deg to a little below freezing.

 

[Tjfarmer]

Thanks, appreciate the info

 

[cperazza]

Fellas, thank you for your inputs.

284 JAZZ and 7 HULK Expected Velocity: 180 gr 3350 fps / 195 gr 3150 fps

Another alternative (since the twist rate is too fast) is chamber the 7T barrel in a 284 Shehane or another project.

 

[sandwarrior]

I shoot 180 Berger Hybrids from a 7mm-08 @ 2700 with an 8 twist and they stabilize well at that speed.

I think going much faster and you'd be tearing up bullets. So, I certainly wouldn't go a tighter twist than 1-8". At your speeds, maybe go with the 1-8.5