Bulging case necks with 107, 108, 112 grainers in 6BRA

[stacy]

I'm just as confused as you all are.... I've never had any experiences like this before.... And I've had some pretty extreme wildcats.... Like a .243 JRP(270 Ackley improved, necked down to .243

IS YOUR CASE NECK WALL THICKNESS .00125

 

[titus123]

Chamber Neck dia. may be the issue.

I would check chamber neck diameter and chamber length of neck as well.

Aside from Cerro safe how would I go about measuring the neck?

 

[KenOath]

Aside from Cerro safe how would I go about measuring the neck?

Start with measuring a fired case.

 

[Bill Norris]

Yes a fired case will tell u alot.

 

[mikecr]

It sounds like the longer bearing bullets seating deeper are pushing neck donut area outward (given fixed land relationship).
With this, you should see loaded neck ODs higher near neck-shoulder junction than further up the necks.
If it's a .272 chamber, and your donut is resisting chambering, then your donut thickness is leading to greater than .272.
Fired necks smoking from a .272 chamber should read around ~.2715

 

[titus123]

It sounds like the longer bearing bullets seating deeper are pushing neck donut area outward (given fixed land relationship).
With this, you should see loaded neck ODs higher near neck-shoulder junction than further up the necks.
If it's a .272 chamber, and your donut is resisting chambering, then your donut thickness is leading to greater than .272.
Fired necks smoking from a .272 chamber should read around ~.2715

These are once fired cases( Alpha munitions 6BRA brass). Though there is an odd ring that has formed since the first firing( fireformed rounds basically because the brass was 4 thousands off of headspace).

 

[Bill Norris]

. Fired cases( measured 5 at rando

These are once fired cases( Alpha munitions 6BRA brass). Though there is an odd ring that has formed since the first firing( fireformed rounds basically because the brass was 4 thousands off of headspace).

Dem. of fired cases ?

 

[PeteB]

Dem. of fired cases ?

Carbide soot the neck shoulder area, that should indicate the area of concern. It could be the neck brass or it could be a chamber issue.

 

[titus123]

Carbide soot the neck shoulder area, that should indicate the area of concern. It could be the neck brass or it could be a chamber issue.

I'll give it a shot

 

[rr1220]

what does the case neck measure on a fired unsized case?

 

[titus123]

Case measurements: fired

At the 200 line- .468
At the base of shoulder- .458
At the base of neck-. 269
At the case mouth-.269

One thing of note- every piece of fired brass has this ring around the neck, that wasn't there before fireforming.

 

[titus123]

IS YOUR CASE NECK WALL THICKNESS .00125

Yes Sir it is.

 

[mikecr]

Now size & seat your problem bullet, and measure neck base to mouth

 

[Mauser06]

Sounds like you ha e a .269 or .270" neck by the fired case?


That line looks like a bushing line. But could be from the chamber.

 

[titus123]

Sounds like you ha e a .269 or .270" neck by the fired case?


That line looks like a bushing line. But could be from the chamber.

I am using an L.E Wilson Full length bushing die, so it could well be from the bushing.

 

[bfiles]

If your measurements are accurate, it seems you have a ~.270 neck. If you can turn a few thou off the necks or have your rifle plummer open it up to at least .272, you’ll have a better time. Guys are even going as far as .274 and having success with BRA.

I have a .270 neck BRA that is fine for the first couple of firings with new unturned Lapua brass and then it starts to randomly show signs of too much pressure (sticky bolt mostly). No such problem with my .272 neck barrel or if I turn the necks a little.

I suspect what you are dealing with is a combination of a tight neck, bushing resizing leaving a slightly bigger dimension right at the neck-shoulder junction, and long bullets seated all the way down the neck. If your freebore will allow it, you could try chambering a dummy round with your long bullet seated only half way down the case neck. Chances are, it will chamber. As a solution, you could try a non bushing full length sizer that would size the neck all the way down but I don’t think that’s a long term solution.

 

[stacy]

Yes Sir it is.

I BET YOUR CHAMBER IS A .270 NK DIA

 

[AICS308]

The inside and outside of the case neck in the picture do not look like they have been chamfered. That can cause a real problem.

 

[titus123]

The case mouth looks gnarled up

This picture was taken pre trimming, post first

I BET YOUR CHAMBER IS A .270 NK DIA

That is a distinct possibility... Though, according to what I've been told, Douglas who made the barrel only uses a .272 neck.

The inside and outside of the case neck in the picture do not look like they have been chamfered. That can cause a real problem.

 

[titus123]

At this point I'm going to either have the barrel rechambered, or replace it.... There are too many unknowns with this particular barrel. And upon confirming with a smith who has 30 some years of experience, it only makes sense to approach from a different angle.... The barrel is a shooter, and I'll likely have it rechambered. But a new barrel is also a strong possibility.