30BR reamer

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acdman posted this 07 November 2007

Is there a “cast bullet chamber” for the 30BR such as has been published in past issues of TFS for the .308W? Want to chamber a rifle for the 30BR and have access to a reamer used for jacketed benchrest shooting. Don't want to go forward if a CBA chamber exists that may have subtle differences. If so, who makes the reamer?

Suggetions welcome.

 

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CB posted this 07 November 2007

I'm not aware of any special cast bullet 30 BR reamer. The only difference might be in the neck diameter you choose. I run .328 necks on my 30 cal. reamers but I think .333 is more close to the norm. You might decide on a different throat because the jacketed reamer will probably have a short .3085 ball seat but I think most guys do that with a throating reamer anyway.

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CB posted this 08 November 2007

acdman,

I'm not sure what reamer other CB competitors are using?  You ought to make your decision from which brand of 'basic brass' you are going to use, REM or NORMA/LAPUA.  Some use the 7mmBR REM case and some use the 6mmBR LAPUA. There is .004” difference in brass diameter.  It seems if there is any big secrets out there it is with reamer dimensions and throats.  It seems shooters when asked say their gunsmith knows but they don't or they're just not sure or can't remember?

Pacific Tool list a chamber reamer titled '30BR REM CAST' that I think is a good average choice using 7mmBR REM as basic brass.  It has a neck diameter of .333” which is good. (I do not think CB's need thin neck walls).  It has a 'leade' of .0527” and a 1degree throat which is ok for a bore-ride bullet. (I'd prefer a 2degree for bore-ride).  This isn't carved in stone, but is what I understand and am going to build mine by unless others have something better to post....:D.....................Dan

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Tom Acheson posted this 09 November 2007

Was afraid to jump into this but here goes”¦

I have a print of a 30 BR reamer that was used by one of our local CBA BR shooters to do a few local CBA BR rifles. The neck section is .327� long and is 0.331� dia. It then tapers at 45º down to 0.310� dia. The lead is .173� long and from that point it tapers again at 45-minutes (1.5º included angle) into the rifling.

This shooter also did my XP-100 in 30 PPC for me. Here he gave me a note describing the chamber as”¦..330â€? neck, .310â€? x 45 minutes (1.5º included angle). For this gun I use an Eagan MX3-30 AR mould. If I did the math correctly, using Don's drawing of the bullet, the bullet has a taper on it of 0.527º.

And lastly, I had a reamer made for a silhouette pistol. The chambering is 30 Silhouette (a 223 case necked-up to 30 cal.). Between me and JGS we came up with the following: It has a 0.330â€? dia. neck section that is 0.300â€? long. It then tapers down at 45º to 0.310â€? dia. The “leadâ€? is 0.090â€? long where a 45-minute (1.5º included angle) starts and goes into the rifling.

All three of these examples are intended to use “bumpedâ€? bullets. Bore riders with straight bodies take a lot more oooomph in the bump die press than the tapered bullet does. It's interesting that the Eagan bullet with a 0.5º taper needs just a bit more “bumpâ€? (about ¼º!) to get the bullet shape to match the chamber.

I was coached to tap a sized and “bumped” bullet into the chamber until the proverbial “light goes awayâ€? to measure the starting seating depth. Then the bullet is removed and in an “idealâ€? condition we should see witness marks all around the leading edge of the front driving band, confirming that the bullet made the “sealâ€?. Dan needs to help me out there”¦.the end game here is to have a cone-in-a-cone bullet positioning with a loaded round that is slightly longer than the previously measured OAL (and upon bolt closing the bullet is pushed back slightly into the case) after the bolt is closed. Supposedly the cone-in-a-cone gets us as close to optimum concentricity between the bullet and the bore as we can get? Of course with the neck sizes seen above this is a project for neck-turned brass.

My somewhat confusing 2-cents on the 30 BR reamer subject...and I'm always open to correction of mis-understood “theories"!

Tom

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CB posted this 09 November 2007

Same answer as above. If you have access to a 30 BR reamer it'll work for cast.

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acdman posted this 09 November 2007

Thanks guys. Your comments helped. Talked to Kiff and ordered a reamer. Cut for Norma/Lupua brass. Neck - .331 Throat taper 2 degrees. Separate body and throating reamers.

Mike Christopher

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CB posted this 12 November 2007

acdman,

Great, good luck.   “Now, the rest of the story".

Like Tom commented about bump dies, have you're gunsmith or a buddy with a lathe make you a bump die using the chamber reamer throat section or your throater. Simple as a 450 lubrisizer die works fine, as all you'll do is knock down the 90degree front drive band to .307 or so to have matching angles. This eliminates the transition the front drive band has to make, seats the bullet fit better,and reduces upset to the rest of the bullet during that transition (less distortion / better accuracy) and.................have a blast  ;)  Dan

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CB posted this 12 November 2007

Mike,

If you're going to use a bump die you'd better have a press set up and dedicated to using it. A bump die is different than a taper die in that you'll be reforming the bullet instead of just putting a taper on the bands. Eagan, and I think Hanned, used to make taper dies but if you try any actual bumping in a 450 you better have a welder handy to fix the handle on a regular basis.

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acdman posted this 12 November 2007

Have a SAECO lube/sizer so it's strong enough. Would make a bump and/or taper die for that. We need an article, with illustrations, in TFS to help newbies may their first die. Pat? Dan?

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Tom Acheson posted this 12 November 2007

Go to the CBA website and look at the Fouling Shot Index. On page 5 (Section 21-bullets) under g. there are 22 articles listed. My rusty memory says that Ed Doonan and another shooter had back-to-back articles on the pros-cons and how to, etc. There might be some sketches involved? Or could be I'm thinking of a different subject?

Tom

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CB posted this 12 November 2007

Mike Looks like you are gonna have to dig up those old issues of the FS after all...

Another way to deal with this is to slug the throat and have Veral cut a mold to the throat.. The downside to that is you won't be able to experiment with different bullets...

What throating reamer did you order from Kiff? I can look around up here and see what I can find if you want?!

Jeff

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acdman posted this 12 November 2007

.310 x 2 deg. Think I may be OK. Thanks

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CB posted this 12 November 2007

Mike,

Just out of curiosity what twist are you going to use and what bullet?

Taper dies are relatively simple to make and Dave Kiff sells die bodies with a 1/4 hole in them that work well. I don't bump, only taper, but in either case setting a press up to hold the die will pay off in the long run and save wear and tear on your lubesizer.

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acdman posted this 12 November 2007

Lilja 1:12 3 groove. Using the Eagan MX3-30 Ardito weighing in the mid 190"s range and sized to .309

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CB posted this 13 November 2007

Ideally I would think that should work, but 2 degrees seems a bit stiff. All of mine are either 45min or 1 min included. I have a bump press for both, but I don't bump so to speak, just enough to taper to fit the throat.

I am coming back out in January toward the end of the month, I will bring you a couple of different bullets to try.

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CB posted this 14 November 2007

I have a question about the 2 degree throat too. Dan it'll probably work fine but why are you going to choose it over something else it when you put together a BR and recommend it. And why don't you think people know what throat they're using when they write it on the tech sheet?

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CB posted this 14 November 2007

pat i. wrote: I have a question about the 2 degree throat too. Dan it'll probably work fine but why are you going to choose it over something else it when you put together a BR and recommend it. And why don't you think people know what throat they're using when they write it on the tech sheet?

Well, the tech sheet doesn't get specific enough to give an idea of what the throat actually is, just an angle.  Then it doesn't specify included angle or a side angle? There isn't a clue to how deep the ball-seat is or what the diameter of the ball-seat is, or if there is a taper to the ball-seat?

I'm not sure about 2 degree, uh maybe its a a...a....a, geeee I forget, uh well my gunsmith knows I think or maybe its a secret?   :?

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CB posted this 14 November 2007

Really no reason to get upset. I choose the taper to match the bullet length I plan on using, faster twists shallower angles so the longer bullets will be resting in the taper instead of having to cut a real long ball seat. This whole taper thing is just like a Morse taper on machine tools and the more the bullet's being held by the tapered portion of the throat the better I think. I wrote a post that told you the approx. length of commonly used tapers and Joe B. expanded on it. 1 and 1 1/2 incl seem to be the norm so I just wondered why you suggested 2.

I don't know what you mean by knowing if there's a taper to the ball seat. If it was tapered it wouldn't be a ball seat.

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CB posted this 14 November 2007

pat i. wrote: I have a question about the 2 degree throat too. Dan it'll probably work fine but why are you going to choose it over something else it when you put together a BR and recommend it. And why don't you think people know what throat they're using when they write it on the tech sheet?

Well I don't have a gunsmith so he don't know either, but I've been gathering my notes. First of all I'm talking about bore-ride cast bullets such as; RCBS165, Lee 180 & 200gr, Lyman 311299, 311290, 311679, 311284, MX4 and etc. These CB's have an average base/nose ratio of about 27/73 percent including loading just past the gas check. With 73 percent of the nose bore-ride section supported in the lands, that is the most important to competition accuracy. The average bore-ride length in .838".

Using cotangent calculations the actual length of the 1.5 degree throat is .3820” and the 2 degree is .2865” which still isn't an abrupt angle. That's about a 33% difference of the junction of the angle and bore, giving more land support to the nose. As the angle wears under competition use, the 2 degree will also be easier to chase than a longer 1.5 or 1 degree throat. The sketch below is not to scale, but gives an illustration of the differences in land support with the vertical lines at the junctions of the angle and bore. The top 2 degree sketch has the 33% more land contact than a 1.5 or 1 degree throat. That larger gap on the nose does make a difference towards poor accuracy as I have found in my Savage and halfa dozen other rifles I shoot in competition.  Long throat angles are not friendly to bore-ride bullets, tho there is nothing wrong with the 1.5 degree, this why I'd rather have a 2 degree throat.

:}

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CB posted this 15 November 2007

But now add a bump or taper die into the equation and what happens to the front of the bullet? On a short bullet like the 165 Sil and a 1 1/2 degree taper you can just kiss the bore ride where it meets the ogive and the first band but with the 2 degrees you'll only be adding to the unsupported length up front which doesn't do anything for guidance. Add bullet length and the problem gets worse with a taper or you have to run a long ball seat if you bump. Using the 165 sil as an example the bore ride length is about .380 long, the same as a 1 1/2 degree taper, with a for the sake of argument .225 ogive. You can taper or bump it in a degree and a half die to kiss the front band and the spot up front and you still end up with a .225 plus a smidgen ogive. Now if you taper it in a 2 degree die to kiss the front band you have to add almost .100 to the ogive so you have .335 of unsupported bullet riding up there (almost 32% of oal) instead of .225 (21% of oal).

An .838 average bore ride sounds a little long to me. Assuming even a short ogive of .225 you're at 1.060 which is as long as a 165 Sil to begin with without even adding the bands and grooves on other bullets.

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Tom Acheson posted this 15 November 2007

Pat,

Thinking about Dan's sketches”¦.maybe a wrinkle here or maybe not. I had a chance to play with the Redding Comparator die. It sure revealed the variance in commercial jacketed bullets as to where, relative to the base of the bullet, the ogive starts. If we set our bullet seating die-up using one example bullet, there WILL be other assembled loads with the bullet's ogive in different locations of the chamber after we close the bolt. Can't be avoided. Using cast bullets we may have more confidence that “ogive driftâ€? will be less. Do you think it's fair to speculate that bumping the bullet helps minimize this drift? But then we have the nose-pour moulds and the sprue cut-off area at the bullet tip. This small irregularity is going let our ogive drift a bit also, no matter how consistently positioned the ogive is on the bullet. So”¦has anyone ever tried to use the Sinclair meplat trimmer on cast bullets? Or is this interest in ogive location in the chambered round all about nothing?

Tom

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