6 Creedmoor pressure issues

[dnellans]

I went from shooting 105's at 3130FPS to 109's at 3110 FPS, the same charge weight shot best so didn't change it.

The 110's at the same charge weight were at 3115 but didn't like shooting there. ~.75moa, I had to increase the charge in the lapua cases up to 41.3gr of RL-16 to get them to shoot well (3140FP and slightly better than .5moa) but they still weren't shooting as well as the 109's for me and i didn't like running that high a charge.

so the 110's have been relegated to positional practice loads back at the lower charge weight to use them up.

One other data point since you're looking at speed - with that same load I had run these barrels at 29.5 inches initially just as an experiment and I only had about 10FPS advantage over the 26 inch length (I set them back) with same charge weights.

 

[gman47564]

looks like two things are causing your pressure problems to me... one is a carbon ring... only way i know to get it all out of there is with some jb bore paste and a nylon brush and brush the crap out of it... second as ranger188 said your bullet should fall down in a fired case... solution turn the necks.... around 3050 is a good place to run the 6creedmoor... they like to run around 3150 also but barrel life is short lived... toasted my first one in 600 rounds... at 3150...

 

[Kratos]

looks like two things are causing your pressure problems to me... one is a carbon ring... only way i know to get it all out of there is with some jb bore paste and a nylon brush and brush the crap out of it... second as ranger188 said your bullet should fall down in a fired case... solution turn the necks.... around 3050 is a good place to run the 6creedmoor... they like to run around 3150 also but barrel life is short lived... toasted my first one in 600 rounds... at 3150...

Really asking, not arguing, but: where are you guys seeing a carbon ring? I’m only seeing bare metal under the case neck in the chamber.

And I’m definitely going to try turning the necks. I only have turning stuff for 50 BMG but I have a Sinclair tool arriving tomorrow (I wanted something that would show up quickly and didn’t want to waste money if I’m going to end up getting the 21st century lathe).

 

[gman47564]

the carbon ring is that black ring in front of the case mouth... it doesnt affect the actual neck of the case. it affects the bullet ... i think if you took a sharpie and painted the bullet from the ogive to the case mouth and chambered it and then removed the round the painted part of the bullet would have scuff marks on it from the carbon ring.... think of it as restricting the lead a little... i use the 21st century lathe... does a nice job... hope this helps... im sure their folks on here that can explain the carbon ring and its effects better than i...

 

[Kratos]

I’ll try some more aggressive cleaning of that area with JB bore paste. I don’t have Iosso on hand.

 

[Kratos]

I turned necks to 0.012" and no longer had pressure signs at the same loads above. I also went after the chamber with JB bore paste, and was able to fire the rest of the loaded rounds from the original post that I'd stopped on. However, I do still get pressure and erratic velocity when pushing past ~3030 fps with any of the three bullets tested. In testing today, it shot very well with N555 pushing the 105 Hybrids at 3000, although I get soot all down the cases from incomplete sealing. I'm going to load those and see if I can get another match or two out of this barrel before it becomes scrap metal.

 

[Kratos]

This is what the brass looks like after firing. Some have soot all the way down into the extractor groove. How concerned should I be?

 

[spudgun]

I built a 6mm Creed and after putting the barrel on and checking head space I was getting some of my brass to look like that too. Not as heavy but you could see the marks down the side of the cases.

I removed the barrel and reattached it and took out .001" of headspace. My issues with smugged up brass went away.

I guess my problem was just a tad too much head space causing the shoulder not to seal tight enough and allow gas to escape down the case.

 

[JimSC]

never had soot go down that far on anything I have ever shot. Could setting the shoulder too far back cause something like that ? Just curious, not saying that is the issue

 

[Kratos]

I think it's officially toast. I'm shooting one more match with it this Sunday, but velocity is dropping like 40 fps every hundred rounds now. Time for some Dasher load development. Yes, I know, so 2019...