105 AMax to 1200 yards

[WDL]

I'm planning a 243 wssm build and want to shoot the 105 AMax out to 1200 yards. 900' elevation, 75 degrees air temp.
Questions:
In order to keep pressure down and also be able to shoot lighter bullets on occasion, what is the minimum twist I can use?
What muzzle velocity is needed to stay above trans-sonic to 1200 yards?

 

[BobinNC]

Re: 105 AMax to 1200 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CamoWildcat</div><div class="ubbcode-body">I'm planning a 243 wssm build and want to shoot the 105 AMax out to 1200 yards. 900' elevation, 75 degrees air temp.
Questions:
In order to keep pressure down and also be able to shoot lighter bullets on occasion, what is the minimum twist I can use?
What muzzle velocity is needed to stay above trans-sonic to 1200 yards?
</div></div>

Minimum FPS to stay trans-sonic @ 1200 yds is 2900 FPS (just barely @ 1118 FPS @ 1.2 Kyds). Using the Miller stability formula, @ 2900 FPS the minimum twist is 1-8.7 for a 105 gr bullet 1.229" OAL (105 A-Max stable @ 1.329) at your stated temp.

I'd like to see stability numbers greater than 1.400, in that case you would need no less than 1-8.4" twist @ 2900 FPS or increase velocity to 3000 FPS and a 1-8.5" twist will also work.

IMHO and YMMV

Those numbers are all cutting things very close.

 

[WDL]

Re: 105 AMax to 1200 yards

Thanks, BobinNC.
I think I will be able to run about 3200 FPS at the muzzle (28" barrel). I have a spreaadsheet ballistic calculator and when I input 1300 FPS as a "break velocity", it tells me I need 3232 FPS MV to reach 1200 yards.
I'm leaning toward a twist of 8.5 as a compromise and your numbers support my thoughts.

 

[WDL]

Re: 105 AMax to 1200 yards

BTW, my spreadsheet bullet stability calculator says I need a 7.3 twist to hit a SF of 1.3 with a MV of 3200 FPS.
I think I need a new calculator. What are you using to calculate bullet stability?

 

[vprtoad]

Re: 105 AMax to 1200 yards

I'm planning a 243 wssm build and want to shoot the 105 AMax out to 1200 yards. 900' elevation, 75 degrees air temp.
Questions:
In order to keep pressure down and also be able to shoot lighter bullets on occasion, what is the minimum twist I can use?
What muzzle velocity is needed to stay above trans-sonic to 1200 yards?

Camo,

I have done it with 1 in 8 6br and a 1 in 8 twst. .243 to 1200 yards
One was right around 2900 the other 3000 fps
You should have no problem

 

[BobinNC]

Re: 105 AMax to 1200 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CamoWildcat</div><div class="ubbcode-body">BTW, my spreadsheet bullet stability calculator says I need a 7.3 twist to hit a SF of 1.3 with a MV of 3200 FPS.
I think I need a new calculator. What are you using to calculate bullet stability? </div></div>

I use JBM for both: I used Litz g7 calc. for the BC.

When I used your temp, altitude, and 2900 FPS, I got the following:

1200 YDS Drop -12.3 MILS -42.4 MOA 1118.3 FPS

Speed of sound is listed as 1113.0 FPS so it's very close.

I used JBM's Miller Stability Calculator, found here:

JBM Calculations - Stability

Using this calculator, anything over 1.300 is green (stable). I prefer 1.400 as my minimum. I kept trying different #'s until I got into the green.

Bob

 

[vprtoad]

Re: 105 AMax to 1200 yards

I just know it works because I have done it.

I think you should have no problem

 

[WDL]

Re: 105 AMax to 1200 yards

Thanks, Guys. Appreciate the info.

 

[rymart]

Re: 105 AMax to 1200 yards

FWIW. I have a 1:9.25 twist in my 243. I run 105 gr AMax to 1000 yards without issue. Haven't tried running them further.

MV is 3100 fps. Elevation is 6200 feet.

 

[Quickdraw40]

Re: 105 AMax to 1200 yards

115s, 1:8

 

[Shooter21]

Re: 105 AMax to 1200 yards

28" barrel, 1:8, run 115 DTACs at 3000 fps +/- and never look back. yes 105 AMAX will work too even at 2900 or less, just takes more up to get there

 

[WDL]

Re: 105 AMax to 1200 yards

I'm thinking I may get a little better than 3200 fps out of a 243 wssm. Hornady says I would only have to go up 25.1 MOA for 3200 fps, but I think it will be a tad more than that.

 

[Rob01]

Re: 105 AMax to 1200 yards

Stick with the 8.5 twist. Should work just fine. A 7.5 twist can blow the 105s up at less velocity than you are looking at. Don't ask me how I know

 

[beretta989]

Re: 105 AMax to 1200 yards

I run 105s at 2850 In my 6 dasher 26' barrel 1-8 twist Krieger. It can shoot sub 2 inch 5 shoot groups at 600yds on a nice day. Shoots the hell out of Berger 108s as well.

 

[shoot4fun]

Re: 105 AMax to 1200 yards

"I run 105s at 2850 In my 6 dasher 26' barrel 1-8 twist Krieger. It can shoot sub 2 inch 5 shoot groups on a nice day."

If you are talking about groups at 100 yards, I'm sorry.
If your talking about groups at 1000 yards well, I'm sorry there too.
You will surely generate the wrath with that statement.
Maybe you could teach classes for 1000 yard BR (world record 1.43" has held up since 2002). David Tubb may be looking for a "how to" as well. They can't do that on "a nice day".

 

[shoot4fun]

Re: 105 AMax to 1200 yards

Edit appreciated.
I hope you use your nice days wisely because that is a match winning rifle.
The Dasher is a very good round. I have shot it in competition a few times and it really does well at 600.

 

[esorensen]

Re: 105 AMax to 1200 yards

105 VLD's are very stable out of my 10 twist .243. 117 DTAC's are not stable, however. I haven't tried the 105 AMAX.

 

[WDL]

Re: 105 AMax to 1200 yards

Hmmm, I just picked up a 31" 8 twist Kreiger at Bruno's today.
Guess I won't have any trouble stabilizing 105s. I visited with Walt Berger after picking up the barrel. He said his 108s were easier to group since they weren't VLDs like the 105s. So I might try them.