FB for 80 grains

[JamesnTN]

guys im going to have a new reamer ground and I'd like to know what FB I need for the 80 grain bullets in a 6BR.

 

[hammerjack]

.060 will work good.

 

[geo.ulrich]

ogive would need to known first and neck length, can't really make a decision without them

 

[johara1]

James, with Barts 80 gr. BT. in the 6br imp. .060 is good....... Jim

 

[rifleman700]

This may or may not help. I just set back my 243W barrel with a minimum spec .050" FB reamer for 64-68 grain Flatbase bullets and it was perfect. So I would think that the .060" mentioned above should be about right. Barts is a BT so you may need to factor in that if you are using it and the BR has a much longer neck as you know.

 

[JamesnTN]

Thanks guys

 

[rifleman700]

Thanks guys

Correction on my post above. My reamer used was a minimum spec .020" FB. Most of the bearing surface is in the neck at .005" jam.

 

[skeetlee]

I'm shooting an 80gr FB in my grench that has a .100 free bore. Perfect combo. Lee

 

[gunsandgunsmithing]

James, for 80 grain Berger FB's, I think .080-.100" is very good. As George said, you need to know what ogive the bullets are or at least a comparable bullet to what you are planning to use. That's why I specifically stated the 80 gr Berger FB. We can split hairs all day long, but the 6BR has a long and forgiving neck length. Just make sure the base of the bullet or top of the BT doesn't quite reach the neck/shoulder junction and you should be just peachy.

It has been mentioned on here that freebore starts at the end of the chamber, but while that is true and a reamer print will show that to be so...our measurement for determining the practical freebore is from the neck/shoulder junction forward. Short necks are a lot less forgiving and simply have less room for error in calculating ideal freebore and with which bullets.

 

[johara1]

The .060 free bore works great with Barts 80 gr. bt. .020 and .054 right out of the box with 8208......... Jim

 

[rifleman700]

With the plan of only shooting an 80 grain bullet I see no need to have a freebore longer than .060". I like a short freebore so I can seat the bullet out farther as the throat erodes. If you start with a long freebore you are already giving up valuable seating depth space in the neck if jamming or at lands to begin with.

 

[Boatschool02]

All,
Need to be VERY specific when "grouping" optimum bullet freebore classes by weight. The flat back vs boat tail variable can cause relatively HUGE swings in seating depth. For example, the Berger 80 grain flat back will seat as much as 0.130" deeper than an 87 VLD-H. By all means, go with advise from experienced competitors with knowledge of the configuration in question... but recommend shying away from categorizing by weight. FWIW, I've elected to use the Base to Ogive minus Boat Tail (Zero for Flat Back) calculation when making such comparisons.
Luke

 

[gunsandgunsmithing]

All,
Need to be VERY specific when "grouping" optimum bullet freebore classes by weight. The flat back vs boat tail variable can cause relatively HUGE swings in seating depth. For example, the Berger 80 grain flat back will seat as much as 0.130" deeper than an 87 VLD-H. By all means, go with advise from experienced competitors with knowledge of the configuration in question... but recommend shying away from categorizing by weight. FWIW, I've elected to use the Base to Ogive minus Boat Tail (Zero for Flat Back) calculation when making such comparisons.
Luke

Agreed. Here's the deal...How many times have I heard people on this board recommend a zero freebore for a 68gr berger fb? Well, I have some as well as some berger 80gr fb bullets here. Guess how much longer the 80's are, base to ogive..Yep, .080". Truth is, zero freebore is as short as you can go with freebore and with a 68 berger fb, I've gone as long as .100 in a 6BR. Granted, there's not much bullet in the neck at this amount. But, add .080", and most would call it a good amount.
Like I said before, the 6BR has a long and forgiving neck length, but if I were choosing a freebore for myself, and I wanted it to be ideal, specifically for an 80gr Berger fb, I'd go and be happy with .080-.100".
Now, as has been stated, ogive and boatail vs. fb make a big difference.
There's nothing wrong with sending a dummy round to your reamer maker of choice, with your specific bullet, seated like you want. They can take it from there. You can use a comparator with a known bullet and a known freebore length, such as I've done here, then add or subtract bearing surface length to come to an appropriate number. You could use an otical comparator as well, but most of us don't have one of those. Or, you can listen to a multitude of opinions on an internet forum. Your choice.

I forgot to add another good option. That's to throat in a separate operation.

 

[AckleymanII]

Better option is to order a zero freebore reamer, throat for what ever bullet you want, bullets are changing plenty...prepare for the future.

I hate throwing away barrel life.

 

[gunsandgunsmithing]

Better option is to order a zero freebore reamer, throat for what ever bullet you want, bullets are changing plenty...prepare for the future.

I hate throwing away barrel life.

I agree, but by the time I've chased the lands .080" in a 6Br a variant, IME, the barrel is well beyond toast, anyway.

 

[rifleman700]

Agreed. Here's the deal...How many times have I heard people on this board recommend a zero freebore for a 68gr berger fb? Well, I have some as well as some berger 80gr fb bullets here. Guess how much longer the 80's are, base to ogive..Yep, .080". Truth is, zero freebore is as short as you can go with freebore and with a 68 berger fb, I've gone as long as .100 in a 6BR. Granted, there's not much bullet in the neck at this amount. But, add .080", and most would call it a good amount.
Like I said before, the 6BR has a long and forgiving neck length, but if I were choosing a freebore for myself, and I wanted it to be ideal, specifically for an 80gr Berger fb, I'd go and be happy with .080-.100".
Now, as has been stated, ogive and boatail vs. fb make a big difference.
There's nothing wrong with sending a dummy round to your reamer maker of choice, with your specific bullet, seated like you want. They can take it from there. You can use a comparator with a known bullet and a known freebore length, such as I've done here, then add or subtract bearing surface length to come to an appropriate number. You could use an otical comparator as well, but most of us don't have one of those. Or, you can listen to a multitude of opinions on an internet forum. Your choice.

I forgot to add another good option. That's to throat in a separate operation.

Ok, here is the dimensions of the bullets you used for your example.

68 Berger FB bearing surface is .302" oal is .833"
80 berger FB bearing surface is .372" oal is .913"

6BR neck length is approximately .322" on my new blue box Lapua not trimmed.

With a 80 grain berger seated where the FB is at the neck shoulder junction there will be approximately .050" of bearing surface out of neck which would leave .010" freebore and would not include the transition area from the neck to the lead. I like to use as much neck as I can especially with FB bullets and I also use the Whidden expander buttons to size the entire neck.

This may be too close for some but like I said before I like room to seat longer if needed as the throat wears.

Good discussion!!

 

[rifleman700]

My 243W mentioned above started out with a plain jane 243W saami reamer. Chambered it in a gunsmithing class around 2000. Don't even remember the freebore but the 55-68 bullets I used jumped a mile to the lands. At the 3800 round count I could not adjust the seating depth or powder charge anymore and get it to shoot. I ordered the .020" min spec reamer and set the barrel back and rechambered it with the new reamer and it now shoots better than ever - in the threes. Throat looks very good. Not sure how long it will go but so far I am very pleased. Rifle is a varmint rifle with a #7 heavy varmint select match 1-14" T Shilen barrel and I shoot Berger BR Column target bullets.