Thoughts on Leade angles and freebore

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  • Last Post 10 December 2014
tomme boy posted this 17 November 2014

I am looking to have a new barrel for my Savage made up. I have standardized on reloading the 308win. What I am looking for is the reason for the use of what angle on the leade and the freebore.  What makes one better or worse than an other. 

Also, a parallel or a tapered freebore? 

I am looking to run my cast no faster than 2300fps MAX. I am going to use either a 1-12” or a 1-13” twist barrel. With a 0.300"x0.308” blank.

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corerf posted this 17 November 2014

This is a great question and Im looking forward to the answers. I hope someone or several will chime in and offer thorough input. Not just what works, but why. Bumping this one to the top 'cause its important!

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tomme boy posted this 18 November 2014

Do I have this in the wrong section?

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RicinYakima posted this 18 November 2014

There are no answers to your question other than opinions. We have beaten this dead horse for several years, check the “search” function. IMHO, the quality of the workmanship in chambering and throating is more important than theories about anything else. Ric

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Ed Harris posted this 18 November 2014

When John Ardito was active, he was cleaning everyone's clock with a long, gradual tapered throat with no cylindrical ball seat at all, but with a .312 major diameter at the case mouth, tapering down to. 300 over a distance of about 0.7", about 1 degree. Holding the bullet only by the GC and bottom band, bumping the bullet in a die cut with the same reamer used to throat the barrel. Small cases and a nominal caseful of RL7.

The 7.62x39 Lapua chamber is cut that way, and in a 13” or 14” twist barrel outshoots anything else I have shot in a .30 caliber. If you want to have a .30BR or. 308 Win set up that way it will shoot very well with bullets that fit.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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goodsteel posted this 02 December 2014

I'm certainly no authority on the matter, but I agree with RicinYakima. I have seen many rifles that shot extremely well and the throat designs varied all over the place. Everything from 50s vintage Marlin lever guns that had little better than a 45 degree angle going from the caseneck to the groove diameter, to well worn Mauser rifles that seemed to have a throat 2” long. The one constant was bullet fit. Fit the bullet to the throat, and fit the cartridge to the chamber and you have a place to start looking for accuracy. Bullet fit can be perfect, such as the XCB with a Morse taper style fit, or it can be like an hourglass such as you have with your current 308 (contact in two places fore and aft that rapidly come together at engrave). Regardless of how you do it, the bullet should have more influence to keep it centered in the bore, than it has to do otherwise. I cut a 2” section of barrel (never found a better use for a Remington barrel) and in one end I ream just the throat, and in the other I ream to the shoulder. I use one end to gauge bullet fit, and the other to gauge cartridge fit/seating depth. This lets you get eyeball to eyeball with bullet fitment. I stick the bullet in the throat end of the gauge and try to wiggle it. A good bullet will be rigidly held by the throat having been just lightly seated there with finger pressure. A bad bullet will pitch and yaw and wiggle around a bit. 

One thing that I pay a lot of attention to is chamber concentricity. I expect near perfection from a cast bullet rifle, and I measure with a 50 millionths indicator to make darn sure things are right. Another thing I pay attention to that is often disregarded is barrel straightness. You will not shoot as well, nor as fast, if your bullet is having to climb a wall as it traverses the barrel. It needs to be thrown straight down the barrel with no influence to depart from the way it was started. Action squareness and bedding play into this as well, because the straightest barrel in the world will be bent while the bullet is going through it if it is screwed to a canted action face, or if that action is allowed to torque in a strange manner due to bedding. Everything plays in when you're talking about shooting cast at high speeds, and the most important thing is to get a well built rifle in the first place, then match the bullet design to it.

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frnkeore posted this 02 December 2014

Well, to start with, for rifles built for target shooting, square and concentric is to be assumed to start out on even footing to be comparing chambers.

If you don't have a competent gunsmith, your just not going to get anywhere.

For cast bullets, for at least 25 years, to do well you need a gentle leade angle with (IMO) no steeper than 1 deg per side. My 30 cal reamer is 3/4 deg and my 28, 32 and 33's are 1 deg per side. I had my reamer made in 1988 by Hugh Hendricson, based on what I had learned in CBA match shooting at that time. To illustrate what difference it will make, make a fist and plung it into water slowly (shallow angle leade) and then fast (steep angle leade), slowly the water conforms and fast it speads rapidly out, deforming the water. The steeper angle also causes more forward resistance, increasing the chance of deformation over the shallow angle.

All that said, I had a chance to meet and shoot with Mel Harris, this last Stepember (my scores weren't recorded for CBA because I'm not a member), as most CBA guys know, he holds at least 15 current CBA records. We talked about throats and he uses a freebore (didn't ask if it has any taper) and a 1 deg leade. From his results, 1 deg is all that is necessary. I also think that he said he uses a .309 freebore but, I'm not completely sure on that or on the length but, it was in the .100 range.

I will shoot with him again in March (the Roseburg range is 90 some miles from me)and if I'm off on those figures, I'll correct it.

For the BSing experiment, you can get a throating reamer made and increase your freebore to about .190 or so, to take most all of the bands with very little pressure or maybe increase it to take the whole bullet with the GC at the start of the freebore, using just light palm pressure.

Frank

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OU812 posted this 05 December 2014

Would a bullet with no taper work? It would require a very long leade. Here is a sample of a .309 diameter bullet with very long bearing surface. Leade could be cut to .309 diameter and bullet sized to .3084. Case would grip bullet at base and gas check, with most of the bullet in leade/throat.   Or you could cut leade @.3085 diameter and size hard cast bullets using a .308 diameter RCBS type sizing die (size nose first to size and seat gas check). Bullet will spring back slightly under .3085 which would be perfect fit for free bore and throat. Should shoot jacketed pretty well also.

Larry Gibson posted this 05 December 2014

OU812

It works very well indeed. The 323471 fits the long throat of most milsurps as such.

LMG

Concealment is not cover.........

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OU812 posted this 05 December 2014

OU812 wrote: Would a bullet with no taper work? It would require a very long leade. Here is a sample of a .309 diameter bullet with very long bearing surface. Leade could be cut to .309 diameter and bullet sized to .3085. Case would grip bullet at base and gas check, with most of the bullet in leade/throat.   Or you could cut leade @.3085 diameter and size hard cast bullets using a .308 diameter RCBS type sizing die (size nose first to size and seat gas check). Bullet will spring back slightly under .3085 which would be perfect fit for free bore and throat. Should shoot jacketed pretty well also.   Or you could cut leade @.3084 diameter and size hard cast bullets using a .308 diameter RCBS type sizing die (size nose first to size and seat gas check). Bullet will spring back slightly under .3085 which would be perfect fit for free bore and throat. Should shoot jacketed pretty well also.

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OU812 posted this 05 December 2014

Here is a shorter version. Free bore may need to be  about .350 - .400” long

Ken Campbell Iowa posted this 05 December 2014

i note drawing says * secant ogive * ... wouldn't a secant be a straight taper ? sorry for trivia-police, god made me this way ... ( g ) ...

ken

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frnkeore posted this 05 December 2014

Ken,A secant ogive still has a radi but it's tangent point gets relocated in X or Y axis or both. The 225450 is a extreme example of this and the NEI 295 is a very mild example. Frank

frnkeore posted this 05 December 2014

NEI

Ken Campbell Iowa posted this 05 December 2014

thanks frank ... i'll have to absorb that ... looks like google time. reminds me of a job i got to make a grinding template with a length of 16 inches and a radius of 45 feet.

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Ken Campbell Iowa posted this 05 December 2014

fit like a morse taper ... hmmm .

always brings to mind a bullet in throat, totally locked in a perfect tapered position, ready for a perfect launch ... but i then ( years pass ) wondered just how much different throat angles support how much of the bullet. so i inculcated ::

for a groove depth of 0.004 ( one side ) here are the lengths engraved:

1/8 degree per side: 1.83 inches 1/4>>>>o.92 1/2>>>>o.46 3/4>>>>o.31 1>>>>>>o.23 2>>>>>>o.11 3>>>>>>o.08


ok, let's see ... i got a 1 inch long bullet ... 0.1 in the case ...0.1 freebore groove diameter ... 0.2 nose cone unsupported ... leaves me with 0.6 bullet to support in tapered chamber ... i need no more than 0.5 degree one side taper.

aaarrgh ... anybody wanna buy my perfectly good 3 degree throater ...0.313 to 0.297 ptg reamer ? i think i need to reorder ..wonder if a 1/8 degree would help breech seat ? no wonder we need long bore rider designs ... our 3 degree factory tapers combined with a 0.004 oversize freebore ...equals perpetual 3 moa groups. just what i shoot !!

oh wait ... Ardito told us that 20 years ago ...

ken

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OU812 posted this 05 December 2014

Thinking outside the Ardito box.

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OU812 posted this 06 December 2014

No post

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tomme boy posted this 06 December 2014

And what would you use these for?

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OU812 posted this 06 December 2014

tomme boy wrote: And what would you use these for?   To shoot in my rifle...just kidding. Higher Velocity with cast, less bullet slump, longer bearing surface. The longer leade cut in chamber would give better support.  When chambered the bullet will be jammed into rifling. The gentle 1 degree taper per side would do the sizing when bullet is launched.

I went back and checked measurements (close enough). What do you guys think? I know the tip is not pointed enough, but it is the best Accurate molds can do.  I have no ballistics software.

  I may have two different diameters cut (.309, .310) in aluminum double cavity mold

 

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OU812 posted this 06 December 2014

Kind of like this old design. Should work good with 3 groove Obermeyer rifling or any other style including 6 groove.

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