30 BR advise

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  • Last Post 05 July 2014
Longone posted this 16 February 2014

OK so I'm sitting here in the North East and have had enough of the snow and dream of warmer days. In that dream is a 30 BR build and I need some advise on reamer, neck turning the brass and expanding the necks.  So if there is one or ten of you 30 BR guys that would like to chime in and get me started with this project I would like to hear from you.   Longone 

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mike0841 posted this 16 February 2014

Longone,

I built a 30BR on a Savage target action.  Below are the tools I used.

For the reamer call Pacific Tool & Gauge and ask for their .30 BR Robinette reamer.  (Remember I chambered for cast bullets so the throat is .310 with a 1deg taper.  The reamer has a .330 neck which gives you a good base to neck turn. Mine are turned to .0095 which with a .310 sized bullet gives me a .329 finished size leaving .001 clearance (If you are going to use jacketed you will need a .308 throat and PT&G can also supply that).

The best brass is Lapua 6mm BR Norma.  I use the K&M Shooting 6mm - .30 expander and have lost only four of 500 cases to neck splitting while expanding.  I trim to 1.510 before turning. 

Mike CBA Webmaster in training.

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Longone posted this 16 February 2014

Mike,

That is what I was planning to build it on as well. I have Lapua 6mm BR brass but what I was thinking about doing was having a reamer made that was a no neck turn and with a throat that would keep the base of the bullet from being below the neck. I'm no machinist and have not a clue how to go about this. I will be using a bore riding design so it will need to engage the lands but selecting a bullet might be a crap shoot. What twist and length barrel did you settle on?

Longone

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muley posted this 16 February 2014

I agree with Mike, you may want to consider Accurate molds # 31-225H in their catalog. it is a bore ride and a very good mold. cast about 212gr in lino or 225 in WW. what twist barrel are you contemplating?  Jim

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billwnr posted this 16 February 2014

Why have such thin brass. Lapua runs about .0145 and there's no reason to cut it down to less than .010 so why not run .014 per side and go with a thicker chamber.

I would also have the throating reamer also used for either a bump die or a tapered sizer.

My preference would be to own the throating so it would be repeatable should new barrels or dies/sizers be needed.

I have a rifle that was set up for the bullet diameter and a .009 thick neck. After cutting all the brass off the neck I was left with a question of the wisdom of doing so.

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Longone posted this 17 February 2014

For me it's a question of keeping things straight forward. Cleaning up the necks with a neck turner is one thing but I can't see the need to follow what the jacketed crowd is doing as far as going with a real thin neck. Pressures are certain to be different with lead bullets, and if using a Wilson die with bushings that can be controlled at that stage. I'm leaning towards just getting the neck of the reamer to accept std. gold box brass and like billwnr says having a throater to adjust for the bullet. As far as twist goes I would lean to a 10 or 11 twist so it could handle the longer heavier bullets or the lighter 165 grain class.

Longone

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billwnr posted this 17 February 2014

You wouldn't have a problem with a twist rate between 11 and 14. I've shot with competitors using guns in that range. For some reason I haven't seen anyone use less than 11. Sounds strange as there's a lot of production guns in use that have the 10 inch twist.

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Longone posted this 17 February 2014

Probably me but when I ran the numbers a 12 or slower was not going to work. I have had some 12” twist over the years that were absolute hammers with jacketed bullets. My concern is obviously the velocity with lead bullets. I have looked in the match results and see a 12” is about the slowest but most are using 11".

Longone

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billwnr posted this 17 February 2014

Which bullet are you using?

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Longone posted this 17 February 2014

I have molds for RCBS 165 Sil. 180SP, 200 Sil. Lyman 311299, 311284, and NOE 311299.

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billwnr posted this 17 February 2014

Any of those bullets will shoot with the twists I called out. I'm using a 12 as I wasn't bold enough to try an 11. If you want a faster twist.... then try it.  You fill find that bullet fit of the throat is more critical than picking a twist rate between 1 in 10 to 1 in 14 inches.

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Longone posted this 17 February 2014

billwnr wrote: Which bullet are you using?
How about your bullet of choice?   Longone

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billwnr posted this 17 February 2014

I use an NEI 72A.... or 73A which approximates the 311299 in a 12 inch twist barrel. Another I use is the Lyman 311649 (if I have the number right).

One bullet I squish in a bump die to match the chamber. The other I had a reamer cut to bullet dimensions and angles.

The bullet that is sized in the bump die shoots smaller groups. That's why I surmise bullet fit is more important. For my same bullet length competitors have shot well with 11 ,12 and 14 inch twist barrels.

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delmarskid1 posted this 18 February 2014

My rifle as chambered with the Robinette reamer. I turn the necks to .009". Yesterday I tried the Lyman 314299 bullet. They came out at .302” across the bore riding portion and .312” on the driving bands. These fit in fired cases with out sizing and did not de-bullet on extraction. I charged the case with 18g of IMR 4198 and used Winchester small rifle primers. Hey, I use what I've got. Fifteen rounds went into 2” at 150 yards. The bullets were cast of my soft plinking what ever alloy. It was 20 degrees and a five mph quartering wind. The fellow who chambered my barrel told me of the “no turn” chamber and how to do it. He suggested running in a separate straight reamer to make the neck dimension the same as the .308. Wayne told me what the reamer was called but I don't remember. My barrel was drilled .298” and cut rifled 4 groove in a 1 in 12 twist. I was real surprised when that .302” nose went in. Soft alloy isn't such a bad idea I guess.

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Longone posted this 18 February 2014

delmarskid1, do you have means to attach a pic and measure a loaded round? Stoney Point gage? I would be curious to see how long they are. I suspect once they chambered the barrel the gunsmith went in and moved the throat forward. In the case of a “non neck turn” throat I think they use a necking reamer that throats also.   Longone

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delmarskid1 posted this 19 February 2014

Longone wrote: delmarskid1, do you have means to attach a pic and measure a loaded round? Stoney Point gage? I would be curious to see how long they are. I suspect once they chambered the barrel the gunsmith went in and moved the throat forward. In the case of a “non neck turn” throat I think they use a necking reamer that throats also.   Longone I need to get a camera, if for no other reason so that people can see what I'm trying to say. My guy did say that he could use a neck reamer. We did not do this because we wanted to see how things went with out it. I determine my loaded round lengh completely by feel. I make a dummy round and chamber it easy to see if the bolt will close with just that little bit of resistance that you get with a light case neck crimp. I extract this round and look for a shiny ring that goes completely around the foremost part of the driving band. I did spring for cerosafe and made a chamber cast. My chambers throat is .010” and I size to that or shoot a bullet as cast. I don't know if the leade is 1 degree or not. Looking at the cast it probably is. I do see rifling marks along the length of bore riding potion of the 314299 bullet.

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Longone posted this 16 March 2014

I was talking to Douglas barrels on Friday and they advised me that they now make 11” twist 30 cal barrels. I ordered one for a 308 project I have going on and will see how well it shoots once it arrives. Looking through the results pages it looks like the 11” has some following.

Longone

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TomG posted this 16 March 2014

Guys,

I've been watching this thread for some time. No doubt, there are lots of opinions on what works best for best accuracy. Look at who is winning the matches in heavy and unlimited for what twists and bullets they're using and you won't go wrong. No sense re inventing the wheel.

When I was shooting in the matches I eventually settled on a 30 BR because of the case volume and the availability of high quality Lapua brass.

Case neck thickness. 9 or 10 thous. is just fine. There is no reason to use any thicker. In face, if you seat a lino bullet in a thick neck and then remove it and examine it, you will see that it can actually size the bullet down some.

I used thin necks and all I wanted the neck to do was hold the bullet straight and push it up into the throat solidly and consistently. I set the bullets out about .020” long and let the bullet push back into the case as the bolt cammed in battery. I used tapered bullets and tapered throats. The full dia. bands on the bullet were sized to be a slight interference fit in the staight cylindrical part of the throat. This gave a tight seal and maximum guidance of the bullet as it transitioned from the case to the barrel. I throated the gun so that I only seated the bullet .2” into the case. That way the throat guided the bullet not the case neck.

Keep the neck clearance in the chamber at .001” to .000” so as to keep the bullet as central to the bore as possible.

A thin neck can help seal up the combustion gasses and give better performance. A couple of times one day, I forgot to put powder in the case. When I fired the cartridge I found that when I opened the bolt that the case neck had expanded and to seal the chamber and the primer had driven the bullet solid into the throat and made a perfect seal. The pressure was contained in the case and I could hear it release the gas as I opened the bolt. The thin neck was able to expand and seal the neck. A thick neck won't do that.

Twist:

You design the rifle around the bullet you will use. There are twist programs out there that will calculate what twist is needed. A stability factor of 1.5 is all that is needed and more is not better. At one time I campaigned a 7 BR. I had a real long bullet and it showed a stability of 1.1. It shot fine in warm weather but when it got cold the bullet was not stable. This told me that you want to go with conventional wisdom and be at a stability factor of 1.5 to 2.0 for best results with all air densities.

All bullets are imbalanced to some degree. The faster the bullet spins, the more the imbalance is aggrevated. Overspinning the bullet only makes is wobble, gyrate, nutate more, and hurts accuracy. Don't spin it any faster than it needs. A 12 twist if fine for even long lead bullets. Here's a free program that I've always used that is scientifically based and really works.

http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

Use the one called “bullet drag and twist” to get the proper stability factor at the velocity you want to use. It's always worked very well for both lead and jacketed bullet guns I've designed. Make sure you use the specific gravity of lead not that of jacketed bullets and you won't go wrong.

Just a couple of things to think about.

Tom Gray

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Longone posted this 05 July 2014

Any preference on the number of grooves, 4 or 6?  Anyone?

Longone

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