6mm and .204 twist dilema...

[funkyon4wheels]

My name is mike, i appologise ahead of time for the extremely long post. ive been creepin around the website for a while now and was lookin for sum imput..Im wanting to build my first gun and im leaning toward a 6mm improved...i was planning on using a savage 110 long action..i know people get rem 700 "blueprinted" i was wondering if the the same applied, true up the bolt face, bolt lugs, reciever lugs, i know its a "floating bolt head" Im undecide on barrel brand/length...was thinkin bout one of the "savage drop in" barrels from shilen in 26-30" length..but my main reason for posting was regarding twist rate..ive done quite a bit of tinkering on www.jbmballistics.com and from what i understand using the miller formula 1.5 is the "optimal" stability factor...using that formula i was thinking about 87gr vmax's so to get the 1.5 stability a 1:10 would be needed...i was bored so i started puttin in numbers that are know for example..i absolutely love my .204 ruger so i put the stability numbers in. assuming 39gr blitzking (.737 long) @ 3730 out of my 1:12 twist factory 24" savage barrel..put it in the calcluator and you get a stability factor of .890!!! i just shot 1 liter bottle at 650yds with that load today!!!so now im completely confused about this "stability factor" so if sombody would please set me stright on this i would be very hapy

 

[RonAKA]

Simple solution is to just use the Berger Reference Sheet, pick out the bullets you want to shoot, and go with the fastest required twist that is recommended. If you are into low drag boat tails, you won't find any harder to stabilize than the Berger VLD's. So, if you have the spin for a VLD you have enough for just about any other boat tail bullet of the same weight.

Berger Reference Sheet

 

[jonbearman]

Its a waste of time trying to figure out the jbm ballistics calculator.It simply isnt accurate.I checked several of my rifles and none of them match to any thing. Just use shilen or bergers site.

 

[RonAKA]

I have some confidence in the calculator at the Border Barrel site below. It is based on the McGyro code, and is more sophisticated than just using weight and length. It accounts for shape and density of the bullet. The down side is that it needs dimensions that can be hard to get. What you can do if you want to refine the Berger numbers is feed the dimensions from that Berger Specification chart into the calculator, along with the recommended twist. The calculator will give you a graph of the stability vs velocity. So you can see if you agree with how conservative or not Berger has been. Berger rounds off to even increments so you may in some cases want to go a 1/2 twist slower, if you are going to a barrel maker that does half increment twists.

Border Twist Calculator

Some tips. Always enter a twist to get the graph I talked about above. I just estimate the boat tail by putting in 10 degrees.

 

[kjcpoint]

+1 for the berger reference sheet.

Kyle

 

[funkyon4wheels]

ok so what im gathering from this is forget jbm...and go with the bullet mfg/barrel makers reccomendations....thanks..now on to the savage action..does anyone know if savage still sell's just the precision target action? is it available in long action? and repeater? is "blueprinting" a savage action the same process as would be a rem700? im wanting to do this project on a budget so i was plannin on doing all the work myself..i have access to mill and lathe and a comptetent mech. engineer/machinest to run them...

 

[RonAKA]

ok so what im gathering from this is forget jbm...and go with the bullet mfg/barrel makers reccomendations....thanks..now on to the savage action..does anyone know if savage still sell's just the precision target action? is it available in long action? and repeater? is "blueprinting" a savage action the same process as would be a rem700? im wanting to do this project on a budget so i was plannin on doing all the work myself..i have access to mill and lathe and a comptetent mech. engineer/machinest to run them...

I would trust Berger recommendations. The last time I looked at Lilja's site they just based twist on bullet weight. It is a bit more complicated than that. Berger covers most bullet types. The Border Barrel site calculator is if you want to get that last bit of slow twist, and probably only if you want to go to 1/2 increments.

The Savage Target action seems to be still available but only in short action, single shot only.

http://www.savagearms.com/firearms/actions/target/

The bolt head is self aligning, but after that check with others. Installing a Savage pre chambered drop in barrel does not need much for tools. Check with Pac-Nor and Shilen for availability.