First day with new BRA, w/ some issues.

[seafury]

Hey guys,

Recently finished building my new 6mm BRA and brought it out to my local range to test fire and fire form some brass. Ran into some issues I was hoping y’all could help me with. The build specs are as follows.

Impact 737r
Bartlein 24” 1/7 M24
MPA BA comp
BnA Tacsport Pro
Vortex RZR gen 2
Sphur 4006 (I think)

The barrel was chambered and installed on the action by a reputable smith and I haven’t messed with it aside from installing in the MPA.

So I set off for the range to find a fire forming recipe. The ammo was as follows.

Virgin Lapua 6mm BR brass (no prep, straight from the box to prime/powder/bullet)
108 gr ELD-M loaded to .010 jump (This will be addressed later)
BR-4 Primer
Varget (tested charges from 29.0g - 29.9g in .1 increments, 5 shots each)

Here was the big issue. I had an exactly 50% fail to fire rate. Upon inspection of the primers, they had all been struck. The cases which FTF were evenly dispersed amongst the various powder charges. Each group of five of the different charge weights had at least 2 FTF’s.

The first thing I thought of was this is fire forming and the brass does not fit exactly in the chamber, possibly allowing for the Brass to move forward away from the firing pin. I’m not a 6mm BRA guru but reading various forums I was under the impression that 6mmBR and 6mmBRA share the same base to Neck/shoulder junction dimension. I believe I also read BRA should have a .004 crush fit but I could be misremembering.

The first potential solution I came up with is loading the bullets to a jam instead of .010 jump for fire forming. That said, I’m unsure of what measurement I should load the jam to, .005?, .010? I’ve heard of guys shooting fire forming loads in matches. Anyone shooting them in PRS matches with bullets loaded to jam? Worried about ejecting a live round and leaving the bullet in the barrel.

Any other suggestions on what may be going wrong?

As a side note, the barrel looks like it will be a shooter and the BRA ran flawlessly with stock Magpul AICS mags. Really happy with that.

Thanks guys!

 

[Steel head]

People used to do false shoulders to prevent that.
Almost surely your firing pin is knocking the rim past the extractor as there’s nothing restraining forward movement.

Other than the false shoulder you’re forced to jam bullets.
I’d just jam them good in a relaxed non competitive atmosphere.
You want a well restrained case anyways so your shoulder blows out and minimizing wall stretch.

 

[seafury]

How much jam would you say?

 

[Steel head]

How much jam would you say?

Not that it matters but five to ten thou will certainly work

 

[Sheldon N]

Are you getting a crush fit on virgin brass when you close the bolt? If not then jam the bullets 30 thou so you get a nice firm bolt close. Might also try Federal 205 primers since they have a softer cup and are easier to ignite.

 

[just browsing]

Just one thing to note on “jam-forming.”

While it’s fine and a proven process to jam bullets into the lands when FFing cases, in my experience it’s also harder on brass. I don’t own a BRA so it may be different with less shoulder difference compared to its parent case, but I’ve gone through this with 2 Dashers and a 6mm Comet, and I’ve noticed that case life is considerably improved when using false shoulders.

False shoulders essentially create a “weak point” and promote case growth towards the front of the chamber, whereas jam-forming can have a tendency to allow the case to stretch in the wrong areas (namely walls, webs, and or head area). It is an extra step initially but I believe you more than make up for it on the backend in terms of longevity. I’ve also found false shouldered FF loads to be much more consistent as you’re able to load your bullets to whatever length you want.

Either way, it sounds like the issue has been addressed and should be taken care of with some new FF loads. Good luck.

 

[vietvet_al]

I always use a primer with a softer cup when fire forming. I've had this problem before when using CCI 450s. Try some CCI 400s.

 

[Steel head]

Just one thing to note on “jam-forming.”

While it’s fine and a proven process to jam bullets into the lands when FFing cases, in my experience it’s also harder on brass. I don’t own a BRA so it may be different with less shoulder difference compared to its parent case, but I’ve gone through this with 2 Dashers and a 6mm Comet, and I’ve noticed that case life is considerably improved when using false shoulders.

False shoulders essentially create a “weak point” and promote case growth towards the front of the chamber, whereas jam-forming can have a tendency to allow the case to stretch in the wrong areas (namely walls, webs, and or head area). It is an extra step initially but I believe you more than make up for it on the backend in terms of longevity. I’ve also found false shouldered FF loads to be much more consistent as you’re able to load your bullets to whatever length you want.

Either way, it sounds like the issue has been addressed and should be taken care of with some new FF loads. Good luck.

I 100% agreed that the false shoulder is the best method.

The use of CCI400 is actually really good idea if jamming

 

[seafury]

Are you getting a crush fit on virgin brass when you close the bolt? If not then jam the bullets 30 thou so you get a nice firm bolt close. Might also try Federal 205 primers since they have a softer cup and are easier to ignite.

I’m not noticing substantial resistance on bolt close. I marked the neck/shoulder junction of a piece of new brass with a sharpie, chambered it, and noticed it did seem to be making contact in that area so I was led to believe all was well. I suppose whatever contact is being made is insufficient to hold the brass in place during fireing or is doing so on an inconsistent basis.

Thanks for the replies fellas! I will be looking into the false shoulder method and CCI 400 primers.

 

[MuleyTime]

If your local range is nearby, I would suggest changing to Fed 205's and go test. I've had 2 BRA's and experienced this, but since I started FF'ing with 205's I haven't had one issue. Once FF'ed you should be able to go back to your preferred primer.

 

[Sheldon N]

Thanks for the replies fellas! I will be looking into the false shoulder method and CCI 400 primers.

Don't false shoulder a 6BRA, if you aren't getting a firm bolt close your headspace is likely still within a couple thousandths of the brass length anyway so just a softer primer and a firmly jammed bullet and you will be good to go. No worries about case stretch with the BRA since the chamber essentially constrains the case anyway at the neck/shoulder junction.

Like Muleytime suggested you might even get good FF just by switching primers to 205's.

 

[seafury]

Just to follow up on this thread. Headed back to the range for more fire forming. Using virgin Lapua brass and CCI 400 primers, I had a 100% ignition rate using a .005” and .010” JAM. Funny enough, I had 1 FTF on a round which had already been fire formed. That one had a BR-4 primer. Guess I’ll have to keep my eye on those in the future.

Thanks again for all the suggestions.

 

[Steel head]

Just to follow up on this thread. Headed back to the range for more fire forming. Using virgin Lapua brass and CCI 400 primers, I had a 100% ignition rate using a .005” and .010” JAM. Funny enough, I had 1 FTF on a round which had already been fire formed. That one had a BR-4 primer. Guess I’ll have to keep my eye on those in the future.

Thanks again for all the suggestions.

Good to hear.

 

[jsthntn247]

Most smith's set the headspace a few thou short of a br so it has a crush fit. Like you found, using a softer primer and a jam should work.

 

[918v]

Check your trigger hanger (if it has one) to make sure it’s oriented correctly. If not, the firing pin may not be cocked back far enough.

 

[flyright]

A new bra always takes a little getting used to...