6MM Dasher freebore math for Berger VLD bullets

[DmitriyS]

Hello shooters,

I’m all new for custom guns and I think I might be making a mistake, when calculating freeborn for my 6MM Dasher PRS gun.
I’m planning to use two bullets :
1. 6 mm 115 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24430), Base to Ogive 0.678, boat tail length 0.216
2. 6 mm 105 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24429(, Base to Ogive 0.619, boat tail length 0.216.

I use neck length 0.241 in my math
I do not want to jam my bullets into rifling.

Berger recommends load development with jump around 0.13.

If I use a full neck length to seat a bullet (boat tail below neck-case junction), it gives me freebore length of 0.351 for the first bullet, and 0.292 for a second bullet. If want to use more room in a neck for powder and use only 0.121 of neck(half bullet diameter) it gives me 0.385 for free bore for the first bullet and 0.334 for a second bullet.

I searched this forum and net and I do not see anyone using freebore in this range (0.385-0.292). Usually it is no more than 0.150

Please tell me, where I’m doing my math wrong ? What freebore should I use for these two VLD bullets ?

Thanks
Dmitriy

 

[Dave M.]

Hello shooters,

I’m all new for custom guns and I think I might be making a mistake, when calculating freeborn for my 6MM Dasher PRS gun.
I’m planning to use two bullets :
1. 6 mm 115 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24430), Base to Ogive 0.678, boat tail length 0.216
2. 6 mm 105 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24429(, Base to Ogive 0.619, boat tail length 0.216.

I use neck length 0.241 in my math
I do not want to jam my bullets into rifling.

Berger recommends load development with jump around 0.13.

If I use a full neck length to seat a bullet (boat tail below neck-case junction), it gives me freebore length of 0.351 for the first bullet, and 0.292 for a second bullet. If want to use more room in a neck for powder and use only 0.121 of neck(half bullet diameter) it gives me 0.385 for free bore for the first bullet and 0.334 for a second bullet.

I searched this forum and net and I do not see anyone using freebore in this range (0.385-0.292). Usually it is no more than 0.150

Please tell me, where I’m doing my math wrong ? What freebore should I use for these two VLD bullets ?

Thanks
Dmitriy

I think you misunderstood and are misusing the term freebore. The freebore on your rifle is fixed and is likely in the .150” range. Your freebore in your rifle barrel does not change from bullet to bullet. I fail to understand what you are describing.
dave

 

[DmitriyS]

I understand that I suck at explaining things. I want to find freebore for a custom reamer ( I guess). I want to be able to shoot Berger VLD bullets in 105-115 grain interval. I want to be able to adjust bullet jump for these two particular bullets. Thats all.

 

[Capt. Oblivious]

I would guess probably around .104" or maybe .125" for the 115s. Personally id choose one bullet to start with and go from there. The 105s will do everything you need

 

[Whitehunter]

I have a .135 free-bore and it works on 105 VLD, 105 Hybrids and 107 Sierra.

 

[Mulligan]

Hello shooters,

I’m all new for custom guns and I think I might be making a mistake, when calculating freeborn for my 6MM Dasher PRS gun.
I’m planning to use two bullets :
1. 6 mm 115 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24430), Base to Ogive 0.678, boat tail length 0.216
2. 6 mm 105 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24429(, Base to Ogive 0.619, boat tail length 0.216.

I use neck length 0.241 in my math
I do not want to jam my bullets into rifling.

Berger recommends load development with jump around 0.13.

If I use a full neck length to seat a bullet (boat tail below neck-case junction), it gives me freebore length of 0.351 for the first bullet, and 0.292 for a second bullet. If want to use more room in a neck for powder and use only 0.121 of neck(half bullet diameter) it gives me 0.385 for free bore for the first bullet and 0.334 for a second bullet.

I searched this forum and net and I do not see anyone using freebore in this range (0.385-0.292). Usually it is no more than 0.150

Please tell me, where I’m doing my math wrong ? What freebore should I use for these two VLD bullets ?

Thanks
Dmitriyb

.130” is a lot of jump for a dasher. I interpet the Berger VLD seating reccommendations to try as much as, not build your rifle around some really big number. A 105 VLD normally shoots good within .015” either side of touch and about .045” jump. Now this is from my experiance, your mileage may vary…….
Dan Dowling, the father of the Dasher has two reamers he currently uses, the .104” and a .110”. I am not sure he has cut many barrels with the .110”, the .104” does the heavy lifting in his shop. I have burned up a lot of barrels chambered with the .104” FB reamer and it just works. I have a .150” FB reamer and it works great….. but after testing it in 4 or 5 barrels, it is no better in my opinion than the .104” that Richard Schatz used to set some records.

I hope this helps
CW

 

[sofarfrome]

The first question I have for you is what twist rate will you be using? Unless it is a 1:7.5 twist you will be limited to the 105gr VLDs. Frankly, I would choose the 1:7 twist for the VLDs.

I am in the process of building a no neck turn 6BR and I plan on using 105gr VLDs in a 1:8 twist barrel. Generally I would go with the 0.104" free bore reamer. However, I am going to seat the bullet where I want in a couple of dummy rounds and provide them to my gunsmith. He will cut the free bore based on those rounds.

 

[DmitriyS]

Twist rate is 1:7.25

 

[Alex Wheeler]

You cant use the same freebore for both of those bullets, there will have to be a trade off. My Dasher reamers are .140 for the 103-105 grain bullets. I go to .180 for the 115.

 

[Bill Norris]

I load both of those bullets for my 243AI with .060 free bore and 1 - 7.5 Tw. without any issues. Plenty of room for jump without jam.

 

[Dave M.]

The first question I have for you is what twist rate will you be using? Unless it is a 1:7.5 twist you will be limited to the 105gr VLDs. Frankly, I would choose the 1:7 twist for the VLDs.

I am in the process of building a no neck turn 6BR and I plan on using 105gr VLDs in a 1:8 twist barrel. Generally I would go with the 0.104" free bore reamer. However, I am going to seat the bullet where I want in a couple of dummy rounds and provide them to my gunsmith. He will cut the free bore based on those rounds.

The 105, 108 and 109g shoot awesome from my 6 dasher 1:8 twist. I’ve considered trying a 1:7.5 or even 1:7 barrel; but the 1:8 just keeps hammering. I shot a 596-30X with it on Saturday.

 

[sofarfrome]

The 105, 108 and 109g shoot awesome from my 6 dasher 1:8 twist. I’ve considered trying a 1:7.5 or even 1:7 barrel; but the 1:8 just keeps hammering. I shot a 596-30X with it on Saturday.

The 115 berger VLDs will be challenging in the dasher with an 8tw. They may even shoot well out to a couple hundred yards. Beyond that I believe bullet dispersion on paper will not get the desired results.

 

[sofarfrome]

Twist rate is 1:7.25

That should work well for the 115s. If it was me I would go with a 0.104" free bore and the 105vlds. You can always increase the free bore simply by running an appropriately sized reamer a little deeper. It is a little more work to go backwards.

 

[Dave M.]

The 115 berger VLDs will be challenging in the dasher with an 8tw. They may even shoot well out to a couple hundred yards. Beyond that I believe bullet dispersion on paper will not get the desired results.

Agree 100%. I honestly wouldn’t shoot anything heavier than the 109’s from the 1:8 twist dasher.

 

[rotts4u]

I shoot a 105 Hybrid in my dashers and originally I used .104 freebore like many others. I got two more barrels made at two different high end Benchrest and or F class gunsmiths and I let them pick freebore this time. Both wanted longer freebore. I think one is .160 and the other is 150". I have noted that the length grew compared to my original seat depths to get closer to lands. I normally shoot ,010-.015" jump with hybrids. About the only thing I have noticed between the original 104" barrels and these is that I now have to run a little more powder to get back to the same velocity. I run 105 Hybrids at 3010-3020fps from 30" barrels. I think my next barrels will use a shorter freebore than .150-160" I dont see any accuracy difference or anything else different and I am using 1-8 twist barrels, Burx and Kreiger so far

 

[707electrician]

I am in the same boat as you. I am working on building a 6 dasher and I am trying to figure out if I should have my smith use his .135" freebore reamer, or if I should order one with a longer freebore. The reading I have done, people are using all different FB but it seems that .135ish is the longest for the most part. However, like you, when I am measuring cases with the bullet (109 hybrids) set in the case with the boat tail in the shoulder, I am getting FB measurements a lot longer than .135", it looks like I should be around .220", and that would be touching the lands. I asked Berger where they recommend seating this bullet and they told me they recommend starting at .015" off the lands and working back into the case in .015" increments. So I too, have been thinking I am doing something wrong.

 

[Mark W]

This is exactly why I like the BRA so much. The long neck is very forgiving.

 

[Ccrider]

Been down this rabbit hole. .104-.160 for up to 108gr in an 8tw barrel. For the larger bullets, you have got some pretty specific Andrew from people that actually know.

Berger gives very general recommendations that are targeted at and apply to the masses. Follow there directions until you get ready to get dialed in to benchrest accuracy standards. Then listen to the guidance from the guys in this site.

 

[darkangel_r2]

Hello shooters,

I’m all new for custom guns and I think I might be making a mistake, when calculating freeborn for my 6MM Dasher PRS gun.
I’m planning to use two bullets :
1. 6 mm 115 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24430), Base to Ogive 0.678, boat tail length 0.216
2. 6 mm 105 Grain Very Low Drag (VLD) Target Rifle Bullet (p/n 24429(, Base to Ogive 0.619, boat tail length 0.216.

I use neck length 0.241 in my math
I do not want to jam my bullets into rifling.

Berger recommends load development with jump around 0.13.

If I use a full neck length to seat a bullet (boat tail below neck-case junction), it gives me freebore length of 0.351 for the first bullet, and 0.292 for a second bullet. If want to use more room in a neck for powder and use only 0.121 of neck(half bullet diameter) it gives me 0.385 for free bore for the first bullet and 0.334 for a second bullet.

I searched this forum and net and I do not see anyone using freebore in this range (0.385-0.292). Usually it is no more than 0.150

Please tell me, where I’m doing my math wrong ? What freebore should I use for these two VLD bullets ?

Thanks
Dmitriy

bearing surface-neck length= freebore for bullet with boat tail bearing surface junction seated right at brass neck shoulder junction and ogive just touching lands.

So for your two bullets If you want both bullets seated above the neck shoulder junction on your brass and at a minimum of 1/2 caliber (.122") seated in the neck then your max freebore would be:

105 vld=.619-.216=.403"
.403-.122=.281"

And your min would be:

115 vld bearing surface=.678-.216=.462
.462-.241=.221"

So with .010"jump that would be about .23" up to a max of .29" .260" splits the difference.

I do not know if this is a good freebore for this chambering but I think that's the correct math for your criteria.

EDIT: These are numbers for freebore+ leade. So freebore alone would be .090" min to .150"max with .120" splitting the difference.

 

[timeout]

bearing surface-neck length= freebore for bullet with boat tail bearing surface junction seated right at brass neck shoulder junction and ogive just touching lands.

So for your two bullets If you want both bullets seated above the neck shoulder junction on your brass and at a minimum of 1/2 caliber (.122") seated in the neck then your max freebore would be:

105 vld=.619-.216=.403"
.403-.122=.281"

And your min would be:

115 vld bearing surface=.678-.216=.462
.462-.241=.221"

So with .010"jump that would be about .23" up to a max of .29" .260" splits the difference.

I do not know if this is a good freebore for this chambering but I think that's the correct math for your criteria.

With all due respect sir, something is not correct with your math. I shoot dashers with 105 VLD'S and you are coming up with way too much freebore. See post #9.