rebarreling a tikka to 6 br, got a few questions

[243DH]

I have a t3 that will be rebarreled shortly. Don't plan on shooting in any stringent weight class, probably some club level matches and maybe a tac match or too thats close. They aren't run and gun, or stretch out more then 700. I have several rifles that can fill that roll. Mainly shoot steel, but some paper punching also. I have 1330 yds on my range that my creedmoor and 243 play on, thought it might be fun to try a 6 br that far out for s&g. The barrel is a 31" lv modified bruno's contour, 1.210" for 5" then tapers to .830". 4 groove .237 Krieger. Would like to get 105 hybrids to 2900 atleast, this is my 3rd br.
I have H4895 (16lbs), varget(12 lbs), and 203b(6 lbs)
105 vld hunting and 105 hybrids for bullets. Goal is to feed from ai mags, got this figured out on a savage 6 br in aics. Using same modified mag in a 243 tikka that's in a whiskey3 chassis the br feeds great into the 243 chamber . Probablt run another w3 or their new xray chassis.
Now the questions: i don't want any more weight then needed, what length for barrel to get 2900+? I have a 28"@2855 and a 26"@2890. The 28" feels like a oar but new rifle will probably be a folder, so transport won't be as bad as the old 28" fclass. Smith has a .264 and .266 reamer, also has a throater to set chamber for 105 gr freebore. He has a nk reamer also, not sure on spec. All my brs have been .271 nk and i usually clean up lapua nks to .267" to uniform them for bushing dies. Is having a tight nk any benefit in a repeater? Looks like having .010 nk thickness would get beat up with an ejector. What is the opinion of u guys on thin nks and repeaters?

 

[swed6.5]

not all barrels will have same velocities. ive found using RL 17 gave me quite a boost in velocity over RL15 that is similar to n203. 29" or 30" will do it

 

[65BR]

My former 26" 3 groove Pac-Nor 8 twist on a Ruger #1, shot 2850, using 28.5/Varget/naked Amax

 

[243DH]

Thanks guys, talked more to the smith about chamber specs. His reamer is .265", but has a nk reamer to make it .269 or .270. My minimally turned nk diameter loaded, is .267. He also has a throat reamer to set freebore to mirror my other repeater chamber. Kinda leaning towards 28" as max. Thats interesting swede, i have gotten faster velocity in 26" barrels by going from varget to H4895. I guess with the long tube it gets more burn time to use up the slower powder? I have about 20 lbs of h4350 and 7-8 lbs of imr4350 . I use them and h4831sc in 6.5 cm and 243 fast twist. Also picked up some Norma202 when my H4895 was running low. It will run whatever speed it shoots good at, that's the true goal, but i hope it is around2900. The 26" is a prefit savage, with 29.5 H4895 and 105 hybrids. It chrono's 2890, but to get drops dead on out to 1000, with DA and other atmosphere conditions entered, 2920 fps has to be used in shooter . Thanks guys

 

[swed6.5]

you will run out of room in the br case if using 4350 before desired speed is achieved if you have plenty of varget or 4895 use em.

 

[243DH]

That's kinda what i thought. Never used reloader17, is it pretty dense powder . I was thinking it was about same burn rate as h4350. I got some varget, 203b,202,&H4895. Surely one of those with a hybrid or vld-h will get some results. I have never used 202, hodgdon chart has it between H4895 and varget. On this site i have read that 202 is about viht135 burn rate. On norma's reloading data, they use both 203b&202 with the 105 class bullets. Appears that 203b is faster then the quicker burn rate 202.