6CM Freebore Question

[tbeasley]

Of the ones who are shooting the 6CM and having great results of which is everyone I read on here. What is the Freebore in your rifle's chamber?

I am shooting a 1-8 Kreiger, 28 1/4" long, 1.25 straight contour with a .100 freebore.

This is one caliber with alot of ?? with little load data and hardly none seating depths. For the people who have said they jam .040 in or .010 in, that means nothing to me if you have a shorter freebore than I do or longer. You get the point.

Here are my findings so far with my rifle:
Fireforming velocity
47.0 H-1000 2888fps 107smk
48.0 H-1000 2906fps 107smk

Formed loads
49.0 H-1000 with no neck tension 2973fps 107 smk
49.0 H-1000 with .265 bushing 3050fps 107smk
49.5 H-1000 with .265 bushing 3086fps 105 VLD
50.5 H-1000 with .265 bushing 3152fps 107smk
51.0 H-1000 with .265 bushing 3196fps 107smk

48.5 H-1000 with .265 bushing 3010fps 117 VLD

I'll post later when I get the sweet spot found with all info

 

[davidd]

The velocities you have posted seem slow to me.

28 inch Brux 1 in 8 twist barrel

50g of H-1000 in a Winchester case

FGMM primer

105 Berger Hybrid jumped .040

MV of 3,287

5.5mil/19.1moa to 1,000 yards with a DA of 5800 feet

I am seeing no signs of pressure with this load in my rifle.

 

[tbeasley]

50.0 gr H1000 with 108 Berger gives me 3050fps.
Now I may have slow reading chrono, but it's consistent when I add .5 grain charges and get steady increases.
Accuracy is very good too

 

[Dgd6mm]

tbeasley, have you searched for load info on this site? It's here, all here and then some. My 27" 6CM load is 48.7 grs. H-1000, oal is 2.860, MV is 3153 fps, 115 DTAC. Yours does sound alittle slow. I have a 30" with a load of 49 grs H-1000 takes 1 moa less at 600 yards then the 27". I know this isn't apples to apples, but this load in the 27" chronoed 3225 with a 115 DTAC.

 

[tbeasley]

Thats crazy.. I'm running a .270nk and using a .265 bushing. I bet if I step down to .263 I can get the velocity up. My chrono may just be off that much. If you look at the steady increase, the gain in velocity matches it pretty spot on. You notice the velocity increase of 80+FPS just applying neck tension. I'll report back this weekend when I go out q d shoot. The 105 Hybrids made it in.

 

[Dgd6mm]

David Bruno chambered my barrels with the same reamers dimensions that Joe has on the prints. I do similar to what Joe does. First I FF, then full lenght size with a .272 bushing, inside neck ream, then size with a .269 bushing and load. I have used a .273 also before inside neck reaming, rifle shoots just as good either way. You may want to try another chronograph.

 

[joesr]

I have shot this cartridge through several dozen barrels. Velocities change from one barrel to the next.

I always use a cut rifled barrel with .237" inside dia, 1:7.5 twist.

I will say this. You need to measure the outside dimension of you loaded round. Then you want to use a bushing 2 thousands smaller. Any more than that and you are decreasing the life of your brass.

Velocity is great, but increasing the neck tension, in most cases decreases accuracy.

The chamber's neck dia is .276. I use a .271 bushing.

Also, and I've said this before, I shoot 49.0 g of H1000 behind every bullet. I only shoot 108's and 115's Bergers.

Joe H