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June 1st, 2009

New 6BR: Love at First Group

Many Forum members are putting together their first custom or semi-custom precision rifle this season. These folks often ask us, “What kind of accuracy can I expect from my first 6mmBR?” Of course there are no guarantees, but a 6BR with a good custom barrel, good chambering job, and a nice bag-riding stock should be able to shoot well under half-MOA (1/2″ at 100 yards), maybe even approach quarter-MOA. Forum member Eric (aka Exercion) provided this interesting report on his new 6BR:

Love at First Group by Eric
Well, I took my new stick to the range for the first time today. It features a Savage single shot target action in RBLP configuration, 28″ Broughton 5C barrel, Sharp Shooter Supply Dogtracker stock with adjustable buttplate, and Nightforce scope.

Now, I have never owned a 6mmBR before, but from reading here and seeing them in action I decided to build one. Its main purpose in life is mid-range F-Class shooting, mainly at 600 yards, and if the winds are favorable, at 1,000. (I already have a 6.5 for “normal” conditions.) I am most grateful for all the info here, and especially the load data. I picked Reloder 15 under the 107gr SMKs for my first loads, starting at 29.0 grains, and proceeding in half grain increments to 30.0 grains. Jumped the bullets 0.015″. Ran the Lapua brass through the neck-sizer bushing die, and was concerned at the force needed to pull the expander button through the virgin brass necks but figured this was a once per case deal to round them out for initial loading. When I measured the runout on the loaded rounds, I was appalled as they had more wobble than anything I personally loaded before, but I kept reminding myself that this was the fireform/chronograph/scope and gun trial stage.

Three Shots in 0.335″ Edge to Edge
So off to the range this morning. No wind here at the house, so life was good … until I got to the range and the wind started to blow. So I set up everything, leveled the gun in the bags, leveled the scope to the gun, made sure the bore was in the center of the chronograph and bore-sighted. First couple of rounds were off to the right, so I moved the scope over 5 MOA and fired another shot, hit paper with it, so I shot 2 more and stopped because I couldn’t tell what was happening. A walk down to the hundred yard berm revealed a nice hole that measures 0.335″ at its absolute widest edge to edge! That’s the smallest 3-shot group I’ve ever fired with anything. I am so in love!

Savage 6BR

SDs Improve with Heavier Charge and Run-out Disappears
I kept going ’til I worked my way through my first 100 rounds.Given the conditions, I was more interested in the chrony numbers than group, (though 20-shot strings yielded nice quarter-sized holes) and found that as my charges got heavier the SD was coming down (the 30 grain load gave me an SD of 9). I can’t wait to see what will happen with some load tinkering, as well as bullet trials (have Bergers, Hornady A-Maxs, and Lapua Scenars waiting for the next trip). Also, as I had hoped, fire-forming “cured” the run-out problem. I ran the fired but un-sized cases over my concentricity tool and saw less than 0.001 runout on the necks now.

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June 1st, 2009

Expander Mandrels — Not Just for Neck-Turning

Lapua brass is so good that you’ll be tempted to just load and shoot, if you have a “no-turn” chamber. However, some minimal case prep will ensure more uniform neck tension. This will produce better accuracy, more consistent bullet seating, and lower Extreme Spread and Standard Deviation (ES/SD). Lapua brass, particularly 6BR, 6.5×47, .243 Win and .308 Win comes from the factory with tighter-than-optimal necks. Before you seat bullets, at a minimum, you should inside chamfer the case mouths, after running an expander mandrel down the necks.

The expander mandrels from both Sinclair and K&M will leave the necks with enough neck tension (more than .001″) so you can then seat bullets without another operation. Put a bit of lube on the mandrel before running it down the necks — but remove any lube that gets inside the necks before seating bullets.

Sinclair Expander Tool Mandrel

Both Sinclair and K&M Tools make a die body specifically to hold expander mandrels. Sinclair’s Generation II Expander Die Body (item 05-3000, shown above) completely captures the mandrel within the die so the mandrel cannot pull out. An O-ring in the die cap allows the mandrel to float a bit and find its own center within the case neck. This $24.95 unit fits caliber-specific expander mandrels (item E-XX, $8.75) which measure approximately .001″ less than bullet diameter for each caliber. Once you run the Sinclair expander mandrel down the necks of Lapua brass, after you account for brass spring-back, you’ll have about .002″ neck tension. This will make the process of seating bullets go much more smoothly, and you will also iron out any dents in the case mouths. Once the case mouths are all expanded, and uniformly round, then do your inside neck chamfering/deburring. The same expander mandrels can be used to “neck-up” smaller diameter brass, or prepare brass for neck-turning.

Forum member Mike Crawford adds: “These expanders can also reduce runout from offset seating. Prior to bullet seating, expand the sized necks to force thickness variance outward. With the Sinclair system, the necks will springback fine, and will not be pulled out of center. This leaves plenty of tension, and bullets seated more centered. I do this, even with turned necks, to get improved seating.”

Mandrels vs. Expander Balls on Decapping Rods
If you haven’t acquired an appropriate expander mandrel for your brass, but you DO have a full-length sizing die with an expander ball, this will also function to “iron out” the necks and reduce tension. However, using a die with an expander ball will work the necks more — since you first size them down, then the ball expands them up again. Typically (but not always), run-out is worse when using an expander ball vs. an expander mandrel.

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