6BR vs 6BR Improved

[ChrisNam]

I plan to build a 6mm for 300, 500 and 600m F Class. I already shoot a 284 Win at 800 and 900m and am extremely satisfied. I cannot decide between a straight 6BR or an improved version,BRX or Dasher or my favourite, aslightly longer neck with 40 shoulder). Will the improved version have any significant advantage over the straight 6BR? What will be the difference in velocities? I will probably order a 28 inch, 1:8 twist Krieger or Border. I will appreciate your advice
Cheers
Chris

 

[6Dasher]

Hi,

I have a Dasher and a 6BR. The Dasher shoots the 105 scenars at up to 3150, while my 6BR goes to about 2950. There is more work required to form the Dasher, but it is an excellent cartridge. Accuracy wise I don't think there is an advantage to either of the two, but the Dasher will drive the bullets a bit faster to get some ballistical advantage at 600+.



jim

 

[Forum Boss]

I know Jim and some other guys are driving 105s/107s past 3100 fps with Dashers and BRXs, but you may find you top out at around 3030-3050. Much will depend on your barrel. Still that gives you a good 100-130 fps more than you may get from a std. 6BR. With its 40-degree shoulder, the Dasher brass is very stable once fire-formed. I just talked to Jerry Tierney who shoots a 6BR UBL, very similar to a Dasher and he says his brass hasn't stretched at all in 20 firings.

The biggest drawback to the improved is that you're burning 10% more powder so you can expect less barrel life. And with a neck that's significantly shorter, you want to make sure your freebore is set very precisely. You want to be able to get into the lands for accuracy, and still have the base of bearing surface,full diam. bullet shank) at least .030" above the neck-shoulder junction.

Bottom line--the guys who shoot the improveds seem very happy, and with the BRX you can pretty much fire-form in a match without sacrificing much accuracy. If you want the simple soluation and 2890-2930 or so is fast enough, then the basic 6BR will do the job. You can't make a bad decision either way.

 

[6Dasher]

Hi,

I can actually get the 105 up to 3230fps But that kind of shortens the life-span of the brass,4-5 firings). BTW; don't try this at home!!!!!

Moderator has some good points on the brass,neck and such). If you're interested in the Dasher, I have a set of new reamers for sale in the classifieds...

 

[sparker]

Shot my BRX prone rifle Sun. 200-16X with irons on the MR-52 target while fire forming. All 20 shots landed within a 2.25" group. The 16Xs all are in a 1.5" group. Nine of those are in a 1/2" group.It splintered 4 golf tees in that string. Two thousand rnds and it still shoots quarter minute groups.

Scott Parker

Bakersfield CA

 

[ChrisNam]

Moderator, you have already in previous responses convinced me to go with a 1:8 twist, 28 inch barrel to shoot the 107 Bergers. Jim and you now pretty much convinced me to go the Dasher route. We are however a couple of guys who want to go the same route. Will I be able to get standard dies,preferably Wilson) for the Dasher?
Jim, I see the reamer has a .060 freebore and has been set up for the 95gr bullets - will it work for 107 gr Sierra`s.
Cheers
Chris

 

[6Dasher]

Hi Chris,

Most smiths have a throat reamer so you can always set the throat to be optimal for the 107. I think the 107 just goes below the neck/shoulder junction. Not optimal, but I have no noticed a real effect with my 105 scenars which stick further down than the 107SMK's.

I hear Redding has Dasher dies... don't know if wilson is making them yet. I had a pair of dies made along with the barrel.

 

[Wild_Bill]

Hi i have just had a Dasher built i spoke with Dave at Pacific and he thought .100 thou free bore was optimum with a 107gr Sierra and it will work for a 115gr if needed. I have also got a set of 6mm Dasher dies from Redding and a Wilson seater. Redding does not make a competition Seater and Wilson does not make a seater either. It is reccomended to ream out the sleave in a Redding 6mm BR die by redding as it will give you a custom fit to your chamber. I had a 6mmBR Wilson hand seater reamed with my chamber reamer to have a perfect seater just make sure you use a chrome molly die as the stainless are supposed to be verry tough . But i dont know how it could be worse than a stainless barrel.

any way hope it helps i would try the shorter throat before changing it it might shoot like a house on fire and will give you more chance of seating out the projectile when the throat wears.

Cheers Bill
Australia

 

[Dubya]

Well, there you go! Dave Kiff told me to use .120 throat with VLDs' on my 6BRX and so for has worked out very well. Good luck with your project and have fun.
dubya.

 

[ChrisNam]

Moderator, Jim, Bill & Dubya
Thanx for the advise, but just as I thought I`ve sorted everything out, you bring up the next minefield. What freebore do you think is best for the 105-107 gr bullets? I thought I could simply use the same reamer for my 1:12 twist barrel shooting the 80gr Bergers,to br used for hunting), but it now seems as if a seperate reamer and custom dies are required, or are there an compomise?
Confused in Namibia

 

[6Dasher]

With the short neck cases like the Dasher and BRX, it can't be optimal for both the 80gr and 107gr bullets. You have to "compromise" one of the two. Look at which you want to put the most emphasis on, 107 for long range or 80gr for varminting and such. I have a 0.60 freebore,for 95VLD) and shoot 105gr and 88LD bullets as well. These two stock below the shoulder/neck junction, but they still shoot tiny groups.

 

[Forum Boss]

Jim raises a good point. But if you want a compromise freebore, consider something about .080" With this Freebore in my 6BR, the 105 Scenars' bearing surface starts about .060 above the neck-shoulder junction with the bullet .010" into lands. I have enough neck to support the 95 VLDs, going .008" into the lands,though the amount of shank in neck is pretty marginal, about .135"). Interestingly, with the .080 Freebore, my Lapua factory 105gr ammo is about .010" from the lands. So obviously this is a set-up that Lapua thinks can give pretty good accuracy.

If I was throating just for the 105s/107s I'd want a .100-115" freebore. This will let you load a little hotter. Please note that all these freebore numbers are based on Kiff's Pacific Reamer prints. Other reamer makers measure differently. But something in the .075-.080" range should be very versatile, without giving up much for the longer bullets.

 

[BountyHunter]

What seems to be the freebore needed for the 95 gr BIB FB bullets and what else will work with it?

BH

 

[Forum Boss]

Bounty Hunter,

The 95s have a pretty long bearing surface for their weight. We've loaded some test rounds, just touching the lands, and the base maybe .020-.030 above the neck-shoulder junction in a rifle with a .080 Freebore. So... we'd suggest a .100-.120" freebore, the same you'd use with the 105-107gr bullets. Basically if you have an 8-twist set for the 105s, these will shoot fine, though a 10-twist might be ideal.