6BRX imminent case seaeration while fire forming?

[limbic]

Ive got a new .236 bore barrel. I tried to use my old brass but it didn't work. I got a shiny ring on the case head area. Next I bought some new brass, Lapua, and fire formed it. I use the false shoulder technique with the bullet .020 in the lands. .267 bushing for .002 nk tension. 29.5 varget w/ 108 Berger. Well the fire formed brass also has a shiny ring. Not as bright or shiny but it is there. If you resize it and reload it the ring gets a bit more definite and will catch your fingernail if you run it over it. Any ideas?

 

[msnations]

have you checked to make sure there isn't actually some kind of rough bit in the chamber? How does the headpace on the fireformed rounds look?

-Mark

 

[rcw3]

Ive got a new .236 bore barrel. I tried to use my old brass but it didn't work. I got a shiny ring on the case head area. Next I bought some new brass, Lapua, and fire formed it. I use the false shoulder technique with the bullet .020 in the lands. .267 bushing for .002 nk tension. 29.5 varget w/ 108 Berger. Well the fire formed brass also has a shiny ring. Not as bright or shiny but it is there. If you resize it and reload it the ring gets a bit more definite and will catch your fingernail if you run it over it. Any ideas?

What's the OAL of your fire formed cases? That can be an indication of what might be happening (or not).

Robert

 

[limbic]

OAL is 1.533-1.537

My smith polished the end of the chamber. He thinks that the bright ring was from a sharp edge at the end of the chamber cutting into the case. We cut one case oPen with an end mill and the case wall looks good. The bright ring apparently is a ridge and not a dePression. We'll see tomorrow!!!

 

[rcw3]

OAL is 1.533-1.537

My smith polished the end of the chamber. He thinks that the bright ring was from a sharp edge at the end of the chamber cutting into the case. We cut one case oPen with an end mill and the case wall looks good. The bright ring apparently is a ridge and not a dePression. We'll see tomorrow!!!

Based on the OAL of your fire formed brass, it would not appear the case is stretching right in front of the web during fire forming (i.e. the "blow out" brass is coming from up in the shoulder/neck area) and that's why your cases are a good bit shorter than out of the box brass, so I suspect the bright ring is not related to a possible case separation from fire forming. I have seen situations on fire forming where the case gets pushed too deep into the chamber then fired and it sticks up in front in the chamber and the stretch happens at the back (that's not good), but then the OAL of the fired brass is typically longer than it should be (which yours is not). That is why I asked.

Robert

 

[brxbrad]

I had the same thing happen to me. I had just recieved my BRX from my smitty and started the fireforming when after about 10 rounds I experienced case head seperation. Well long story short, after many trials and tribulations, I sent the gun back for another look see. He ended up rechambering, refacing the bolt, and set the distance between the bolt and the barrel as tight as possilble. Don't waste your time and money ruinning brass . Send it back and get it fixed.

 

[limbic]

update.

I went to the range today and everything worked out pretty good. There are still some very light rings except they aren't palpable. The gun is shooting well. solid .25MOA at 200 with 105 Scenar 33.6 N550, BR4 prmer and OAL of 2.845. I'm going to get it polished down a bit more.

 

[bozo699]

limbic,
I had a problem similar to yours until I bumped my neck tension up, I am running about .005 neck tension for my first fireforming and .002 for the next firing. After the second firing there fully formed, sharp shoulders, and no ring as your mentioning, after the second firing I drop the tension to about .001, 34.5 grains of varget and 107 SMKs jammed .012 shoots awesome @ 3080 fps
Wayne.

 

[shooter63]

ill agree with bozo669 use 5th. tension &back varget off to around 30.5gr. with 107 20th in i use cow method almost all the time now works for me doesnt cost much no wear to speak of shooter63

 

[bozo699]

Shooter63,
Your right on the fireform load, I should have clarified that.
I had problems with 29.5 grains blowing the shoulder out so I bumped it up to 30.5 grains and a 105 jammed ALOT!! .040+ My 34.5 grain load was for the brx case not the 6br fire form load.
Wayne.

 

[limbic]

I've gotten my old barrel back and have used it for FF yesterday. No problems with the above recipe. No rings at all. I will probably try a bit more varget next time. I have 108 Berger boattails. The ring is less noticeable so I'll get the smith to polish it a bit more tomorrow. Also use the smallest bushing I have .266. What do y'all consider shooting "awesome ?". I'm happy with .5" five shot groups at 200. Varget may do better than the n550.

 

[bozo699]

mine is shooting .5 to .750 @ 3oo yards with the loads I mentioned before.