Project 7 LR

[Shadow292]

First post on here
I throated my Christensen mesa long range an additional .185 with the goal of increased velocity with heavy 7 bullets. I've seen other have success but with powders that i haven't found available since the build. Like H1000 and N565 .
Bullets tested are 190 bergers and 175 eldx.
I have been using Magpro since the rifle was new cuz I can get it.
It produces decent velocities but I cant verify accuracy due to rapid excessive carbon build up at the throat entrance AKA carbon ring.
I first discovered this issue soon after thoating it.
I fired about 300 rounds prior without issues but after throating the issue came on immediately.
I know I can try other powders but was wandering if I could solve it with deeper seating or increased neck tension.
I have 8lbs of magpro and other than the carbon the results are great.

 

[DJ Fergus]

What is the parent case? What's your barrel length? What primers are you using?

 

[Shadow292]

7mm rem mag parent case is 375 H&H.
useing CCI 250 LRM primers

 

[DJ Fergus]

Ok, I didn't realize it's a 7mm rem mag. I've shot 7mm rem mag extensively but I've never used magpro. Magpro seems like it would be just about perfect for what you are doing. I don't hear many folks who run into carbon ring issues with the 7mm rem mag. I use cci 250s as well with no issues. What is your barrel length?

 

[Shadow292]

26in 416R 1:9
I didnt experience the feed resistance of the carbon ring till I throated it.
But I'd shot 300 or so magpro rounds out of it prior to the throat reaming.
So I'm not sure if it accumulated through that whole time or started right after I throated it. I didnt know about carbon rings till I learned it the hard way.
So I bought a bore scope and cleaned it out 100% clean steel. Then loaded 40 rounds all with magpro and got through about 20 of them and the carbon fouling in the throat was back to the point I was jamming the rounds into battery again. I got home and cleaned it again and that's where I'm at now.
I'm leaning towards the bullet only occupying the neck of the case to being the issue like the charge goes off and the bullet is instantly clear of the case before the powder case fully ignite resulting in the throat acting as part of the case for the burning to take place if that makes any sense. If that is what's happening and I can delay the bullet leaving the neck just a bit by either seating it deeper....which was the purpose of throating it in the first place.....or increasing neck tension which may or may not make enough of a difference in this case.
The worst case scenario is changing powders and starting from scratch.
But I'm getting excellent velocity with the magpro and I have a bunch of it.
So I want to eliminate all other possibilities before moving to a different powder

 

[DJ Fergus]

I'm no expert on why carbon rings develop. I do have some ideas but won't claim them as hard facts. I had a rifle that developed carbon rings past the neck & into the throat, along with above normal carbon buildup on the muzzle face & in the muzzle brake. This was with powders that didn't exhibit carbon build up in any of the other rifles I had. I believe that I wasn't getting a good complete burn. When carbon builds quickly in the throat, it leads me to believe that too much powder that's not completely burning as it should is getting excessively pushed into the throat area way before the bullet itself is getting started down the bore. This statement is very wordy, sorry for that but that's the only way I knew how to explain my theory. This theory could be completely wrong..... I'm welcome to ideas if anyone has a better explanation.

 

[Shadow292]

My light neck tension and only seating the bullet in the neck would could allow the bullet to pass through the freebore prior to a large charge to fully burn as you stated.
I have 7828 and H4831 I can try both are faster powders. But those are for my 270. Lol
Btw 7828 and 140 TSX works great in a 270 win
Thankyou for your thoughts

 

[DJ Fergus]

My first assumption of carbon excessively building is that the powder is too slow of a burn rate but I'm not 100% convinced that this is always the case. I'm thinking that my particular problem may have had something to do with the throat size having excessive diameter. Maybe giving a chance for an excessive amount of partially burnt powder to pass around the bullet into the bore as the bullet starts to travel to the lands. This is just a theory.

 

[Shadow292]

 

[Taylorbok]

Is the carbon in the neck/throat area or in the lead?
what is your brass length?

 

[Shadow292]

Before and after
Carbon interference at the start of the freebore not in the neck section. BTW CLR ROCKS!!!

Case trim 2.49

 

[Shadow292]

After cleaning I fired 20 more rounds and started having to jam into battery again. So I stopped, went home and cleaned it again and that's where I'm at now.

 

[Taylorbok]

it looks like it might be propagating from the neck junction. stick a piece of brass down there and post another pic with the Teslong.
If the chamber has an abnormally long neck maybe the extra freebore is causing the carbon to build up. you might have to let your brass grow a fair amount to seal the chamber better. which is gonna be a PITA if you can only fire 20 rounds at a time.

I wish I could see a picture of the brass in there with the carbon build up.

 

[Shadow292]

I will post a pic of my brass with a clean freebore tonight