I am getting a reamer for six BR to run 68 grain Bullets I know that the throat length needs to be short . how would you determine if your throat was too short ? checking to make sure the bullet is above the donut? Or is there some other standard practice where you want to position the bullet in relation to the neck for Accuracy?
Reamer question
- Thread starter kawsam62s
- Start date
You can't really go too short for 68's in that long BR neck. Best way to establish amount of needed freebore for a reamer is to seat your desired bullet into a dummy round, where you want it..and send it to your reamer maker. For your setup, between 0 and about .060 works very well but that long neck is very forgiving. With any flatbase I can remember, you could go as long as the common .104 freebore. Ideally, around .030 but the longer freebore is more versatile. I'd go about .095 or so for that because it'll work with such a wide array of bullet weight/lengths, up to the 105 class but you won't have a lot of bullet in the neck with most 68's. It doesn't take much.
swd
Silver $$ Contributor
I have a .060” reamer and even with flat base 65’s there’s not a lot bullet in the neck. I’d go zero to .020”.
NorCalMikie
Gold $$ Contributor
jackieschmidt
Gold $$ Contributor
I have a .060 as well, for short range bullets in the 65/68 grain, a .020 would be ideal, especially with boat tails.
Expected ogives? It's tough to infer ogive info from a reamer print with so many bullet designs and jacket lengths, bt's vs fb's etc. Someone may be able to be of help if you have a more specific question, though. What are you looking to do?
I was wandering if the lead or throat dimensions would predict a ojive location for any 6mm bullet?
So if you had a print you would be able to assume we’re the ojive would be located for a dummy round.
AlNyhus
Silver $$ Contributor
The throat (leade) angle also makes a difference as to where the base ends up in the neck. Excellent 6mm BR bullets are made on both the .790 and .825 length and that 13 twist will like them both. Keep that in mind when pondering free bore length so you don't end up either locked into one jacket length or sacrificing powder capacity (up the neck). For the .790's, .060 would certainly be the outer limit I'd want even with a 1 degree throat angle. Half of that would be a good number.
Another thing is free bore diameter. Nothing good comes from having that dimension being too snug. The 'standard' is .0005 over groove diameter but remember that reamer makers work to a tolerance. Consider specifying the critical dimensions as 'not less' or 'not more' than what you want it to be.
Another thing is free bore diameter. Nothing good comes from having that dimension being too snug. The 'standard' is .0005 over groove diameter but remember that reamer makers work to a tolerance. Consider specifying the critical dimensions as 'not less' or 'not more' than what you want it to be.
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LVLAaron
Gold $$ Contributor
Life lesson right there. A 600-40x gun can turn into a shotgun incredibly quickly with a tiny bit of carbon buildup.
Edd
Gold $$ Contributor
If you are locating the ojive at bore diameter, the above reamer is .237" at about 1.690" and it is .236" at about 1.709".
.AlNyhus
Silver $$ Contributor
Bullets are pretty tolerant of being swaged down through the free bore section. Right up to the point where they aren't. I'm not sure where that point is as I've never gone that tight. Stan and I went as far as .0007 over the groove diameter with the .30's with no loss of accuracy. I can't imagine that .0008 or even .001 over would be like falling off the edge of a cliff but who knows? I do know that a new 30BR reamer I have coming isn't as snug as I would have specd some years ago.
I don't work with the long bullet stuff but a spit ball hunch is that they might be a little snottier than a shorter bullet in a tight free bore?
Edd
Gold $$ Contributor
LVLAaron
Gold $$ Contributor
Possibly. I was shooting 105's. Had a perfectly tuned 6GT open gun with 100 rounds on it. Won a match. Cleaned it like I normally would... Next match, half way through, shotgun pattern. Took it home, looked at it.. freebore area totally black. I was a bit desperate at the time to make it work. Ended up giving the reamer a half turn by hand... back to being a tack driver.
I'll spec a reamer for that one and the freebore will be a half thou larger than normal.
urbanrifleman
Site $$ Sponsor
Nailed it.
Zero freebore in 6br with 300 thou long neck for 68s. Can't be too short with 68s.
urbanrifleman
Site $$ Sponsor
It's pretty amazing to see over the years of all these posts, 10-15 years ago everybody was trying to get everything tighter and tighter because that would make it shoot better. Now it's going the other direction.
AlNyhus
Silver $$ Contributor
That's called evolution.
In extreme accuracy shooting (real Benchrest), tweaking one area often leads to rethinking another area. And then another. Pretty soon you've come full circle built upon the incrementals of each change adding up to new total that's better. Or maybe not. You don't know until you try it and find out.
Take a look at neck clearance in SR Benchrest. While it's now standard proceedure to run a bit more clearance, shooters got there by tweaks made to neck tension, understanding what different powers like, working with boat tailed bullets, etc.
So we can't just look at neck clearance....in and of itself... and make the leap that since BR shooters run .003 neck clearance that neck clearance doesn't matter and start hanging .010-.011 total on every reamer. Doesn't work like that.
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