For many monolithic bullets, the faster twist rate is a benefit. It will improve bullet expansion. I've seen 55gr GMX in .223 expand to 0.75" in 1:8 or faster twist. Expansion was significantly less in 1:11. Same situation with improved expansion with the 110 TTSX in .270 compared with 1:10 and 1:11.25 twist.

I chose 1:7 twist for my 300 BO because the .308 bullet rpm at 1800 fps was similar to a .308 bullet launched at 2800-3000 fps that impacted at 800 yards. Suitable for bullet performance testing.

What bullet weight and velocity are running out of your 1-7" twist Blackout?

125 MKZ at 2100 fps with aa1680. I should get faster with Little Gun but have not tried it yet. Running subs up to 210 AB Long Range.

This replacement barrel has 0.1” less freebore and I’ve lost 100 FPS.

I forgot to mention that. Freebore has a lot to do with accuracy, velocity and pressures, especially with these smaller cartridges...

Tell me about it! I have 0.050" variation in freebore across three 6.8mm. My 20" has 0.035" more than the 18" and barely has more velocity than the 18". However, adjust my handloads to take advantage of the extra freebore and its a hot-rod. The 12.5" has 0.015" less than the 18" and shoots most loads hot without much velocity loss but I have to watch the primers when the temps warm up.

Then this new 300 BO barrel made the 6.8s seem like triplets when I had 0.1" shorter freebore. I couldn't believe it and it really hurt performance on the heavier supersonic bullets - well all the supersonic loads.

turns out a 0.001" wear in a reamer can result in 0.017" freebore variation.

Well....... I just sold my 30X357 "baby rifle"


Looking at the brighter side of life, I have a Shilen Select Match grade stainless steel barrel blank that is a 1.200" straight tube, .30 caliber with a 1-8" twist rate, that I have literally tried to give away for the past 5 years, and nobody wanted it. So now, I'm going to take this barrel blank and use it to build a T/C Contender barrel...

I have a Super 14" Contender barrel in 223 that I can cut back to around 3 1/2" in length, and bore, ream and thread it, and use it for my barrel stub...

I'll start building this barrel on Monday, and post pictures of it after I get it finished. It will take me a couple of days to get it finished, since paying customers come first, so this new barrel will get worked on between other jobs at hand...

Ok....... what barrel length do I go with? Muzzle brake? Throat length? What bullet weight to set this up for? What else?

Deer Sniper wrote:

What else?

.30 cal but what cartridge?

I'm sorry slimjim, I will chamber it to my 30X357 magnum...

Deer Sniper wrote:

Well....... I just sold my 30X357 "baby rifle" Looking at the brighter side of life, I have a Shilen Select Match grade stainless steel barrel blank that is a 1.200" straight tube, .30 caliber with a 1-8" twist rate, that I have literally tried to give away for the past 5 years, and nobody wanted it. So now, I'm going to take this barrel blank and use it to build a T/C Contender barrel... I have a Super 14" Contender barrel in 223 that I can cut back to around 3 1/2" in length, and bore, ream and thread it, and use it for my barrel stub... I'll start building this barrel on Monday, and post pictures of it after I get it finished. It will take me a couple of days to get it finished, since paying customers come first, so this new barrel will get worked on between other jobs at hand... Ok....... what barrel length do I go with? Muzzle brake? Throat length? What bullet weight to set this up for? What else?

Oohhh...more gun porn for us to drool over. I’m really looking forward to this one...I love the TC Contender platform.

125grn bullet weight......25" barrel and no muzzle break.... can add one later if think its needed. longer barrel should help with velocity???? and being that far away from ears maybe no brake needed. projectiles the nosler ballistic tip (surely one of your rifles might like them) cause I can buy factory 2nds which are discolored for less than a $ a pill or 125grn sierra flat nose designed for .30/30 as Ive been very impressed with how they both kill in the x39mm.

Elvis,

I'm thinking totally the opposite!

This gun will be more for sub-sonic loads than anything else, BUT it will have one "fast" load!

I'm thinking about an 18" barrel plus a muzzle brake, which will make the overall barrel length 19 1/2"...

Picture this: barrel diameter 1.200" full length / barrel stubbed to a T/C Contender / 1.00" diameter muzzle brake / pillar bedded forend painted black to match the black synthetic butt stock...

A Weaver style base will be attached to the larger diameter barrel?!?! unless I leave the barrel stub long enough for a "short" mount, that might allow for the mounting of a small red dot sight???

Decisions, decisions, decisions...

Fast load - 125 MKZ

Can you flute the barrel?

Yes, I can flute the barrel, and I am actually considering it...

Wow David, that is sounding like it is going to be one great gun mate...can’t wait to see it finished.