BRA Reamer Question - Long Freebore

[MikeMcCasland]

Hey Guys,

Have a reamer on order and I'm doing the usual "mind f***ing" of everything while I wait. I wanted to sanity check with those that have played with this cartridge before.

I ordered a JGS 6 BRA reamer based off a Wheeler #1, except with a .272 neck and a .150 freebore.

The intent here is to run Berger 105 Hybrids, Berger 108 BTs, Hornady 110 A-Tips, or maybe some DTACs for use at 500/600 yard F-Class matches. I figured I had a generous neck length to play with, so I wasn't really hurting anything by throating it a little deeper for the heavier bullets.

I'll be turning brass down to ~.012-.013 (however thick I can keep it, while getting 100% clean up).

Anyone see any issues with this? I'm not going to end up with the 105s seated way too far out am I? Only reason I'm asking is I've not seen anyone else talk about having freebore this far out.

Thanks,
Mike

 

[newbieshooter]

.160 freebore

Berger 109 and 108 seated to touch. Should give you a ballpark visual....

 

[MikeMcCasland]

.160 freebore

Berger 109 and 108 seated to touch.

View attachment 1226210 View attachment 1226211

Damn, that's just about perfect. Thank you.

 

[Alex Wheeler]

My longest is .180" you can still shoot 103s but they are up there a bit. Throats hardly move on these so its fine.

 

[Chuckhunter]

Mike I shoot the 103's out of my Bra and have a .125 throat and it's perfect, That extra .025 on your reamer will probably be better suited for those 108's & 109's. I have shot the 105 VLD's as well as the Hybrids so you'll have no problems with those either. Heck you'll still have plenty of bullet in the neck even if you decide to try the 103. It's the beauty of that nice long neck

 

[MikeMcCasland]

Awesome. Much appreciated guys.

 

[whatwind?]

@MikeMcCasland 6GT is gone, moving on or Re chambering to BRA?

 

[MikeMcCasland]

@MikeMcCasland 6GT is gone, moving on or Re chambering to BRA?

I've still got my GTs, and I'm going to keep shooting them till their barrels are shot out. That said, I'm going to transition to the BRA for future 6mm barrels. I plan to keep all the 6GT tooling though, so I can have another spun up whenever.

My GTs shoot pretty well for sure (I'm playing around with mine this weekend at a 600 yard match), but I feel like the BRA is probably kept in tune easier, and I want to try a 6mm that I perceive to be better suited for Varget than the GT. I've also been at matches where shooters on this forum routinely put up unbelievable (national record level) scores at 300 with their 6BRs/variants.

That's pure speculation on my part though; probably some "grass is always greener" thinking in there too.

Hard to properly articulate this, but I've had ~8-9 .308 barrels for F-T/R and all but one of them has been extremely accurate. Buy a bunch of 200-20X bullets, find the powder/primer it likes, and they'll usually be capable of winning any match you attend (at least from a mechanical accuracy perspective; shooter is a different story). I'm trying to find the 6mm that gives me that same experience/feel, and so far the 6GT hasn't been that. It's been good, and it'll shoot tight, but I feel like nodes are narrower, and I feel like it inherently doesn't put up as good a chronograph numbers as another 6mm might.

Edit: My GTs are cut off the .120fb reamer. I think things might be different with the .160 variant. The .120 has bullets too deep in the case.

It could also just be me sucking, so I guess we'll find out.

 

[whatwind?]

Got it, a 22lbs 6mm is very nice to shoot for sure, just got my first one and it’s a pleasure

 

[urbanrifleman]

Would explain how I see people shooting 6 Dasher speeds. That has got to add another grain of capacity easy. Probably more. No wonder I am seeing these crazy high loads talked about on here.

 

[Alex Wheeler]

Freebore length doesnt actually have a whole lot of bearing on max loads or speeds. The difference from my .104fb to my .180fb is hardly noticeable. Running the high node, 3000fps+ has more to do with the barrel.

 

[GlennK]

They shoot the same nodes. But the 180 fb seats very nice for a long period of time without annealing.

 

[dskogman]

You may want to start finding some other powders to try as well as Varget. H4895 is a good one. Others will chime in I’m sure

 

[MikeMcCasland]

You may want to start finding some other powders to try as well as Varget. H4895 is a good one. Others will chime in I’m sure

I've got good supply of Varget, N140, H4985, 8208, and Shooters World Precision. Hoping one of those will work.

I doubt it will play out this way, but I'd really like to get it shooting tight with SWP (and be temp stable).

Could also try some N150 if it wants something a touch slower with the heavier bullets.

Not really looking to try and compete with you Open guys; just want something low-cost, and drama free that shoots tight at 300-600.

 

[Capt. Oblivious]

I bet you will find love with N140

 

[Mark26]

Edit: I talked to JGS about how they get calculate freebores from dummy rounds that are sent in. But I don't yet have any of the Berger 105 hybrids for measuring. Does anyone know off hand what the distance is from the base of this bullet to the .241" diameter on the nose?

Also, roughly, what is the minimum amount above the neck/shoulder junction one should start so that any chasing of the lands that is necessary would always keep the base of the bullet’s bearing surface ahead of a donut that was moving forward into the neck and getting taller (smaller diameter)? And is there any loss in accuracy at larger freebores vs the ~well known .104 FB? Sorry for all the newbie questions.

_________________________________

I hate to ask a dumb question, but I'm unsure of my freebore / shank length calculation. Can someone tell me whether this is right or wrong, and where I messed up if wrong?

Using the AW 6 BRA #1 reamer print and Berger 105 hybrids as an example...

Distance from bolt face to lands in chamber = 1.570" chamber case length + .104" chamber freebore + .012" chamber transition into the freebore = 1.686".

Distance from bolt face to ogive on cartridge = 1.555" trimmed case length (per AccShoot for Lapua 6 BR brass) - shank length - .213” boat tail length (per Berger book) + .624” bullet base to ogive length (per Berger book) = 1.966" - shank length.

So when the ogive of the bullet is at the lands of the chamber, 1.686 = 1.966 - shank length, or

Shank length = 1.966-1.686 = 0.280" when the ogive of the bullet is at the lands of the chamber.

With a cartridge neck length of 1.555”-1.2378” (same neck/shoulder junction as the standard 6mm BR, 1.2378” in AccShoot) = .317", this would put the base of the bearing surface of the bullet at .317"-.28" = .037" above the neck/shoulder junction. Or, if I was planning to jump the bullets .020", then the base of the bearing surface of the bullet would be at .037" - .020" = .017" above the neck/shoulder junction.

Note also, the 6mm BR cartridge neck/shoulder junction used above, of 1.2378”, is larger than the minimum chamber neck/shoulder junction of 1.2364” from the print (???).

 

[Alex Wheeler]

Your over thinking this. The BRA throat hardly moves, you don't have to worry about chasing it. A .104 puts you well above the doughnut with almost any bullet you want to shoot. A benefit of the long neck. You can also go longer, no harm at .135-.155. To my knowledge, all the records my rifles have broken have been on the .104fb if that means anything. But a couple nationals have been won with my .135". My advice, get a proven reamer, and learn it. They are all a little different.

 

[johnnyi]

I've got good supply of Varget, N140, H4985, 8208, and Shooters World Precision. Hoping one of those will work.

I doubt it will play out this way, but I'd really like to get it shooting tight with SWP (and be temp stable).

Could also try some N150 if it wants something a touch slower with the heavier bullets.

Not really looking to try and compete with you Open guys; just want something low-cost, and drama free that shoots tight at 300-600.

If you want an easy button.... well you have one! 450's with 4895, AR Comp, 8208, Varget, N150, they will all hammer down and shoot very small at 600 fairly easily. I would go in that order of powders as those have proven to work best in our area. They all shoot small. I'm positive you will really enjoy the little BRA. Don't chase speed. just pick a nice wide node and enjoy shooting this little tack driver!

 

[MikeMcCasland]

If you want an easy button.... well you have one! 450's with 4895, AR Comp, 8208, Varget, N150, they will all hammer down and shoot very small at 600 fairly easily. I would go in that order of powders as those have proven to work best in our area. They all shoot small. I'm positive you will really enjoy the little BRA. Don't chase speed. just pick a nice wide node and enjoy shooting this little tack driver!

You're my inspiration on this, so I'm holding you personally responsible if it doesn't immediately bughole at 600.

Ordered some more components this morning too.

 

[johnnyi]

You're my inspiration on this, so I'm holding you personally responsible if it doesn't immediately bughole at 600.

Ordered some more components this morning too.

View attachment 1228060

if some how you have issues with that die. you can always call Harrels and order a die to properly size the .200 line. just in case you have any issues down there... I use a Harrels D3 Dasher die with .080 chopped off of it. I believe is a standard practice for them. So keep that up your sleeve in case your factory Bra die doesn't size enough.