.20-223AI looking for free bore suggestions......
- Thread starter Phil
- Start date
ab_bentley
I fix stuff, sometimes....
No more than .015" with 1°30" leadBat just said that my .378 bolt is on it`s way.......
With that, i`m looking for suggestions for free bore on a reamer, .20-223AI shooting the 39 BKings.
What do you think, what would you go with if you were building one this way?
Phil.
NorCalMikie
Gold $$ Contributor
If it was me, I'd go as short as I could. Like ZERO freebore. Nothing like loading up your favorite bullet and not being able to reach the lands with as much bullet in the neck as you can get. You can always go with a longer throat but you can't go shorter without dealing with a major chamber change. Start off with the lightest bullet you'll be shooting then as the throat wears, go heavier.
Phil, my reamer is .020 FB, but I found that to be a little short for the 40 class bullets, the 39 BK specifically. Ordered a Uni-throater & increased the FB to about .050 & now it is perfect for the 39 BK. PM me for any more details as we may want to talk.
Phil
Gold $$ Contributor
I only shoot the 39BK, but my experience is same as tooter. With the original >020 FB I had difficulty seating bullets deep enough, now it is very smooth. My neck dia. is .233, which allows FF Lapua before turning a little off for a .230 loaded neck dia. By doing the FF before turning, you get a much straighter, fully formed case which gives a more uniform neck & shoulder for more consistent turning. I also use IMI brass which requires no turning with loaded neck dia. of .228.
AckleymanII
Gold $$ Contributor
It is not going to kill your accuracy to have the bullet base a tad below the shoulder neck junction, after 10 firings on that AI brass, check for doughnuts, Simply drop the bullet in the case mouth after firing...preaching to the choir here I know.
I think that it is great to have general guide lines to go buy, but I have had great luck with a lot of Wild Cats with zero freebore to .015 freebore and stuff the bullet down in the neck, ungodly accuracy. This kind of thinking is not politically correct, I know, but I did it when I did not know any better...17 AH, 17 Mach4, 17 Rem, 223 match, 223 AI, 22/250 AI, 243 Win, 243 AI, 6 Rem, and 6 AI, 7 STW. All, everyone of those barrels shot bug holes very, very quickly in load development. I was shooting light to middle weight bullets per caliber.
Sometimes, .015-.020 may help a pressure spike with medium heavy bullets...depending on the case.
That short freebore becomes a real bonus thousands of rounds later.
For instance, in the 243,243 AI, 6 AI, the 80g berger shot in a zero freebore chamber, would shoot bug holes, with very fast velocity, the bullet of course was way down the neck. I shot IMR 4064 in the 243 at 3400 fps with 26", 12T barrel, 3550 in the 243 AI, 3600 in the 6 Rem with R#19, 3800 fps with the 6 AI with Win 760, all 80g Sierra blitz or Berger 80g.
So, we are talking a 20/223 with 39g Blitz kings...zero freebore, and there is a tad bit of fudge coming off the case mouth. 1500 rounds from now, you would be glad you did use a zero freebore.
I would not argue with .015-.020 for the 39's, but no more for my likes.
55's maybe another animal on freebore. I would set the junction of the boat tail and shank of the bullet about .040 below the shoulder neck junction, and in less than 1000 rounds or the time doughnuts may form, the junction of the boat tail and shank will be above the shoulder neck junction of the case.
There may be a magic freebore for the 55g, what ever you do, don't throw away barrel life.
I think that it is great to have general guide lines to go buy, but I have had great luck with a lot of Wild Cats with zero freebore to .015 freebore and stuff the bullet down in the neck, ungodly accuracy. This kind of thinking is not politically correct, I know, but I did it when I did not know any better...17 AH, 17 Mach4, 17 Rem, 223 match, 223 AI, 22/250 AI, 243 Win, 243 AI, 6 Rem, and 6 AI, 7 STW. All, everyone of those barrels shot bug holes very, very quickly in load development. I was shooting light to middle weight bullets per caliber.
Sometimes, .015-.020 may help a pressure spike with medium heavy bullets...depending on the case.
That short freebore becomes a real bonus thousands of rounds later.
For instance, in the 243,243 AI, 6 AI, the 80g berger shot in a zero freebore chamber, would shoot bug holes, with very fast velocity, the bullet of course was way down the neck. I shot IMR 4064 in the 243 at 3400 fps with 26", 12T barrel, 3550 in the 243 AI, 3600 in the 6 Rem with R#19, 3800 fps with the 6 AI with Win 760, all 80g Sierra blitz or Berger 80g.
So, we are talking a 20/223 with 39g Blitz kings...zero freebore, and there is a tad bit of fudge coming off the case mouth. 1500 rounds from now, you would be glad you did use a zero freebore.
I would not argue with .015-.020 for the 39's, but no more for my likes.
55's maybe another animal on freebore. I would set the junction of the boat tail and shank of the bullet about .040 below the shoulder neck junction, and in less than 1000 rounds or the time doughnuts may form, the junction of the boat tail and shank will be above the shoulder neck junction of the case.
There may be a magic freebore for the 55g, what ever you do, don't throw away barrel life.
tclaunch
Silver $$ Contributor
tooter, did you notice any hard lift at the top of bolt cycle? Your reamer is quite a bit tighter at the .200" line than what I have on hand for prints, mine are minimum sammi prints from JGS, also the freebore on your reamer is the line below what you are calling it. Your print is an .046" freebore. You don`t include the 45* cone angle. This thread has been very helpful. I started one on reamer specs for the 20P, and didn`t get nearly as much help. I`m still on the fence about my build as looking at BC numbers I didn`t see anything that will hang with the 22 cal 53 gr. V-Max at .290. I do have a barrel on the way so I am going to press forward. Can anyone provide the neck diameter of the loaded round unaltered Lapua 223 case with 39 BK seated, I thank you. Looking at SmokinJoes/tooters replys I need around .046" and .050" freebore for the 39 BK. How about bushings to neck down Lapua to 20, thanks, sorry Phil I can delete and start new thread if you wish.
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Well, guess I'm uneducated regarding freebore determination. As I see it though, that .011 is unconstricted linear distance before getting to the lands. But, I yield to someone technically more astute. 
Re: bolt lift ---- no hard lift or click using Lapua, LC and IMI brass. I use a custom (non bushing) FL die for forming new cases.
Also, might check out and compare the ballistic performance of the 20 cal. .396 G1-BC Berger 55gr. to those 53gr. V-Maxs (I haven't, but am curious what you might find).
tooter
Re: bolt lift ---- no hard lift or click using Lapua, LC and IMI brass. I use a custom (non bushing) FL die for forming new cases.
Also, might check out and compare the ballistic performance of the 20 cal. .396 G1-BC Berger 55gr. to those 53gr. V-Maxs (I haven't, but am curious what you might find).
tooter
Phil
Gold $$ Contributor
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