8.6 Blackout

[Enfield577]

Hi Gents,
Not been about on here for a while but as a bit of background have built a great many cans here in New Zealand (so no ATF issues here). We have just started playing with 8.6 and solid copper Maker projectiles running subsonic, I built an over barrel K baffle can with my 7 of my standard 9mm (10mm bore) baffles and whilst it is super quiet it seems to be badly effecting grouping at around 7" at 100 yards.

Now everything is well machined and nicely concentric (I have built over 100 cans) and the baffles are CNC machined, so anyone got any experience with 8.6 and the Maker projectiles.

Thanks

[mr fixit]

I have no idea on the 8.6 but wanted to tell you I'm glad to see you back around. Always enjoyed the information you brought to the forum.

[Enfield577]

I have no idea on the 8.6 but wanted to tell you I'm glad to see you back around. Always enjoyed the information you brought to the forum.

Thanks for that, I have been doing lots so will try to work out how to post photos again and put some stuff up....Cheers

[hangman]

That grouping makes no sense - even if the bullets lack concentricity.

Have you chrono'd the rounds?

What results do you get shooting the same bullets/loads in an unsuppressed gun? or removing the suppressor from that one?
How does it manage "factory loads"?

[Capt. Link.]

Hey guy nice to see you post. I know your work is above reproach so lets cut to the chase. The chances are the bore passage is to tight. Open up the muzzle cap and if that dose not work the baffles are next.

[Enfield577]

That grouping makes no sense - even if the bullets lack concentricity.

Have you chrono'd the rounds?

What results do you get shooting the same bullets/loads in an unsuppressed gun? or removing the suppressor from that one?
How does it manage "factory loads"?

Yea a lot more looking into this now, Chrono around 980 and pretty consistent.

We have since tried another gun (from this batch of barrels) with and without the can and best is 3 1/2 group, so now looking more deeply at the barrel, there were new barrel blanks imported from US. I have to try to measure the bore later today.

Thanks

[Enfield577]

Hey guy nice to see you post. I know your work is above reproach so lets cut to the chase. The chances are the bore passage is to tight. Open up the muzzle cap and if that dose not work the baffles are next.

Hi Mate,
We must catch up by email again.

Read in conjunction with reply to other chap above.

Yep I tried opening out the bore, was 0.040" clear, went to 0.060", helped very slightly, strangely we also had some other weird results, we switched to another gun and get straight strings of shots around 3 1/2" long....my can giving vertical string and a B&T can giving horizontal string.

So the mystery goes on.

[Turbotaz]

have you considered possibly
an overbore that may be too tight for 8.6 sized bullets (what is a maker bullet?)
in combination with
a substantial level of barrel whip?
heavy ass 8.6 slugs spinning 1in3 has got to subject the barrel to lots of forces.

just my initial thoughts.

[Enfield577]

have you considered possibly
an overbore that may be too tight for 8.6 sized bullets (what is a maker bullet?)
in combination with
a substantial level of barrel whip?
heavy ass 8.6 slugs spinning 1in3 has got to subject the barrel to lots of forces.

just my initial thoughts.

Thanks for the reply, yes lots to think about and being looked at, current thoughts are that the bore might be a little too large for these bullets but as I say lots being looked at.

Cheers

[Turbotaz]

Now I’m super curious about that 8.6 slug gnarly twist rate and barrel whip in general.
Has there ever been such a fast and heavy twist and slug before this new cartridge?!

Now i need
Hi speed camera
8.6 gun
6.5 gun
338 gun
…..

[hangman]

Yep I tried opening out the bore, was 0.040" clear, went to 0.060", helped very slightly, strangely we also had some other weird results, we switched to another gun and get straight strings of shots around 3 1/2" long....my can giving vertical string and a B&T can giving horizontal string.

So the mystery goes on.

Weird. Here's a thought - can you time either can with shims to rotate it 90 degrees? That might eliminate the difference in strings-orientation.

As to the forces on the barrel, I am getting ~1.5 MOA groups with suppressed 458 SOCOM in 1/14 twist, with my loads of 350gr subsonics (14.0gr of HS-6 and 2.07" OAL) from a 10.5" barrel. In terms of raw energy, should be similar enough to what you're shooting. And, if I'm not mistaken, the 8.6 is SUPPOSED to be more accurate.

The more I think about it, the more I think baffle "grazes" or "kisses"... Have you done any more testing this week?

[Enfield577]

Yea it was my thoughts as well to make shims to time the can at different angles.

Anyway the guys have done more testing and been in touch with the US barrel maker, it seems that changing the projectile seating depth has had a hugely beneficial effect.

Tomorrow they are dropping and want me to make some changes to the suppressor (cut the rear reflex length down as they now have a better stock)

So let see how it goes.

Cheers

[hangman]

That's good news.

For my 458 SOCOM loads, now I'm wondering if my testing various COL from 2.05 to 2.11 was more about pressures or the jump to the lands...