6mm BR Freebore - Help please

[wildcat284]

Hey guys,

I would like to run projectiles from 70gr to 107gr in my 6mm BR project rifle. All the advice I'm getting from here is to run with a freebore of .073.

I'm getting my barrel from Tru Flite here in New Zealand, and I have been told that the 0.73 freebore is too short, I need to be looking at .200 or slightly more for the 105/107gr VLD's to achieve full case capacity & decent velocities.

arrgh what do I do!!!!!

I am considering having my rifle built as a switch barrel with 1 barrel in 1:12 and the other in 1:8 twist, then set up the freebore to suit.

Regards,

Michael.

 

[dreever]

.200 freebore for VLD's is way to much! With the 105 Berger VLD I doubt you'd have much in the case, and I guarantee with the 95 VLD you would not be in the case at all if you were trying to get into the lands.
My opinion if you want to use bullets from 66-107's stick with an .060 freebore to be into the lands with all bullets. The exceptions are the new flat base heavy bullets like the BIB 95's, there you need at least an .080 to get up out of the neck shoulder junction.

Why don't you do this. Have it chambered at .060 try it, if you need more freebore any smith with a throater can give you more.
If you start out big like .200 you can't put it back and your screwed.


Sure if you seat the bullet way out in the neck you gain case capacity with less pressure for more velocity. BUT, BUT, BUT, what happens when the throat wears? And believe me starting with that first shot it's only going to go one way. If you only want 900-1000 round barrel life due to a lengthened throat that's one thing, but personally I'd like to be able to chase the lands for a bit more than that.

Danny

 

[jb1000br]

.113 FB will allow you to seat the 115 DTAC JUST ahead of the donut area.

JB

 

[DJD58]

.200 is too much unless you are going to use some BIB heavy flat base bullets.

I'm curious as to whether they have a reamer for the Lapua brass there at Trueflite.

If it is for the old 1.52 case length it would make more sense to have that much freebore.

But it is too much for anything standard bullet wise.

 

[Forum Boss]

Different smiths and different reamer-makers measure freebore in different ways. If you're using a PT&G or JGS reamer, something in the .090 to .110 range should work well for your application.

Best thing is to load up a dummy round with the bottom of the 105/107 bearing surface about .070 up from the neck-shoulder junction. That should give you good case capacity and you should still have enough neck for some of the lighter bullets, but maybe not the Berger 95gr VLD. It has an extremely short bearing surface.

I have a friend with a 6BR that was throated for the 115 DTAC. He his shooting the 105gr Berger VLDs very well, but he's got just the minimum amount of shank in the neck. In hindsight, a shorter throat probably would have been better.

 

[wildcat284]

Thankyou all very much for your input. Honestly, some of the rubbish I hear down in this part of the world from people who think that they know it all drives me to desperation sometimes.

What has bugged me about this is the fact that i have sent Mr Blenkarne at True Flite the article on the Savage / Pac Nor 6mm BR,article in Gun of the week, No.36) where Dave Kiff designed a .073 freebore especially for people with my sort of project in mind, and he completely ignored it. Ironic when you consider Trueflite state that they use reamers from Pacific whom they consider the best in the world.

I'm going to email Mr Blenkarne and let him know that Dave Kiff recommends the .073 freebore.

Otherwise, I'll go to another manufacturer. Thats the beauty about choice.

Regards,

Michael.

 

[Forum Boss]

The .073 freebore was set up specifically to put the Lapua loaded ammo right at the lands. The factory-loaded 105s measure 2.330" OAL.

Most guys, with the 105s, are running COAL of 2.350" or longer. A 0.090 Freebore, measured PT&G style, will give you a bit more speed with the heavies and still have enough neck for the 70s. If you want to shoot the really short bullets, then a .070 or so freebore is in order.

 

[wildcat284]

Ok guys an update.

A fellow New Zealand shooter & gunsmith saw my original post on here and emailed me. He has a 6mmBR reamer set up for Lapua brass,not Norma) and 2 freebore lengths - .060 & .070.

I think that based on what Jackie Schmidt recommended to me,I had also placed a post about this on Benchrest Central), plus another couple of shooters as well I'm going for a .060 freebore. I'd be looking at shooting in the heavies the 105gr Berger VLD and I had a part box of 95gr Berger VLD's given to me. Jackie really likes the 105gr Berger VLD alot.

I had also thought about the 105gr A-Max. With a .060 freebore how far does the base of the bullet sit in the case when it touches the lands?

Regards,

Michael.

 

[expiper]

Yours ??? is a lil difficult to answer...you havent said your trim length...that is what determins how much of the shank of the bullet is in your particular case....what really matters is how far is the bearing surface is from the donut..going on what my particular reamers give me...I would "guess" that you would have .270" of jam....generally with the cases trimmed to 1.550" ..and that is aprox ..030" from the donut...hope that makes sense!! Roger

 

[chris308]

I sent in a dummy round to PT&G with a Sierra 107 seated so the boat tail/bearing surface junction is about halfway up the neck.The reamer says .134 freebore.How does that look to you guys? I plan on shooting only the 107/105`s.thanks chris

 

[dreever]

Chris,

With that freebore you'll pretty much rule out any of the VLD's because you won't be in the case if you try to touch the lands.

Danny

 

[Forum Boss]

My friend John Southwick has a Freebore about that long on his 6BR. We were really worried that it was a big mistake, but so far it has worked with Berger 105 VLDs seated about .010" in. Pretty marginal in terms of shank in the neck.

I think if you stick with something in the .090-.100" range you'll be happier.

 

[dreever]

One thing about this freebore question that you have to consider is throat wear. When that chamber is brand spanking new .XXX freebore might be perfect for that XXX bullet you plan to use, but as that throat begins to wear and you have to chase those lands by seating that bullet further and further out perhaps that long .XXX freebore wasn't such a good idea.

If you have plenty of bucks, and don't care how long a barrel lasts, and are just concerned with getting that ultimate accuracy/velocity combination right now, by all means do what you have to do.

On the other hand, it may pay you to go with a little less freebore initially, giving up some velocity, and after 1000-1200 rounds if your throat has moved say .030 you'll still be into the lands with the bullet further up the neck to compensate for throat wear.

With this in mind, I'd personally recommend going with a freebore initially in the .060-.090 range since considering $450 for a barrel job, I'd like to get as much mileage as I can before re-barreling.

Danny

 

[chris308]

with the .134 free bore,the loaded aol is right at 2.400 with a sierra 107.I set a 107 next to the dummy round and the pressure ring is 3/4 the way down the neck.Should i send the reamer back to pt&g and have them grind some off? The rifle has not been chambered yet.....chris