|
|
May 30th, 2007
There’s been some controversy surrounding the “ideal” 6mm bullet diameter. This is compounded by the fact that 6mm match barrels are available with both .236″ and .237″ land diameters. It has become quite clear to us that bullet diameter is an important variable to consider when choosing the best projectile for your particular barrel. Some barrels prefer “fat” bullets while other barrels prefer “skinny” bullets.
Jason Baney recently took the time to measure 12 different sets of 6mm Match Bullets, including a couple different lots of the same bullet design. Interestingly, Jason did measure the “old” Berger 105 VLD, the “new” Berger 105 VLD (first lot from the new die), and the “new, improved” Berger 105 VLD from the new die, after it was polished. Ten (10) Bullets were measured per type. Each bullet was measured three times (3X) around the largest circumference, normally where a pressure ring would be located (some bullets have a pronounced pressure ring, others do not).
Download this CHART as an MS Word Document.
Columns one and two of the chart show the smallest and largest bullet diameters measured for each 10-bullet sample. The third column shows the extreme spread over each 10-bullet set. Note, these numbers are NOT averages, but represent the “low” and “high” diameters for each set. (FYI: Jason noted that while the Lapua Scenars measured very consistently the earlier 2005 “JEVDAK” lot had noticeably smaller meplats than the current 2007 lot.) A Mitutoyo Micrometer was used, zero-checked for each bullet.
May 27th, 2007
For the past year, Forum member John Skowron (John708) has been campaigning a 6BRX, built by Nat Lambeth (RustyStud). You’ll find the full history of John’s 6BRX project in this Forum Thread. With this rifle, John was the overall 1000-yard winner at Butner in February 2007.
The 6mm BRX is based on the 6mm BR cartridge. The shoulder is moved forward, but the shoulder angle and case taper is the same as the parent cartridge. This way you can use standard dies for most purposes (although it is a good idea to have a custom full-length die so you can size the entire case body). Many of our readers have been interested in the 6mm Improved (BRX, Dasher etc.), but they’ve wondered about case durability and barrel life. John has answers for those questions:
6BRX Case Life
Case life running the Berger 105s at 3000+ fps is 14-15 reloads. Brass was discarded when the primer pockets became too loose. The 6BRX brass OAL after fireforming is 1.56″. Max OAL for the 6BRX is 1.58″. The brass never stretched enough to require trimming before discard. Anouther plus for the 6BRX and Lapua brass.
By the way don’t even bother with Remington-brand 6BR brass. The primer pockets were so loose after my standard fire-forming load I had to trash all the cases. Stick with the good stuff, Lapua.
6BRX Barrel Life
I now have 2570 rds through my 6mm BRX. I was just at the range today doing an accuracy test. I shot two 10-shot groups at 100 yards, one with 105gr Bergers, and the other with 107gr Sierras. Both were identical 0.44″ groups. Not bad for a rifle with 2500+ rounds through it.
Achieving this barrel life goal pretty much completes my 6mm BRX project. I’m now shooting a cartridge that has the same or better barrel life than the 260 Rem, it’s more accurate, with essentially equal wind drift. I’ll continue to post updates on barrel life. I think this barrel will last for another several hundred rounds.
Heavier Bullets
As far as shooting the DTAC 115s goes, I’ve temporarily abandoned that effort. The 105 Bergers, running 3050-3100 fps, give up very little wind drift to the 115s running at 2900-2950 fps. You might potentially get 3000 fps with the 115s using H4350 and throating the chamber to seat the bullets out. But since I very happy with the 105s and the way they’re performing at long range, I’m not going to change for now. [Editor’s Note: The Berger 105s in John’s latest reports were lot #559, from Berger’s new die.]
May 25th, 2007
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 both leave the necks with enough neck tension (more than .001″) that 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.
Both Sinclair and K&M Tools make a die body specifically to hold expander mandrels. The Sinclair version, item NT-EXP, is shown below. This $17.90 unit fits caliber-specific expander mandrels ($7.95) 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. Note: an alternative to this procedure is to full-length size every case with an expander ball in place, prior to loading. That works too, but many reloaders may prefer to simply expand the necks, when using Lapua brass.
May 22nd, 2007
Larry Medler has come up with another smart little invention–a simple, inexpensive Empty Chamber Indicator for rimfire rifles. It is made from a section of plastic “weed-wacker” line and a wooden ball from a hobby shop.
Larry explains: “At all Highpower rifle matches, silhouette matches, and other shooting events I have attended, Open Bore Indicators (OBI), or what are now called Empty Chamber Indicators (ECI) have been mandatory. The NRA’s yellow ECI for Highpower rifles is easy to use and has been well-received by the shooters. However, I have not seen ECIs used much for smallbore matches. In fact I had not seen a truely workable ECI for 22 rimfire rifles–until I visited Michigan’s Washtenaw Sportsman’s Club where I saw juniors using ECIs for their 17 Caliber Air Rifles. Someone at the club made the empty chamber indicators by attaching an 8″ piece of weed wacker line to a 1″-diameter wooden ball, painted bright yellow. I now make similar ECIs for the 22 rimfire silhouette matches I run.”
Construction Method: First, drill a 7/64” diameter hole all the way through the 1″-diameter wooden ball. Then enlarge half of that 1″-long hole using a 13/64” diameter drill. Next insert an 8″ piece of heavy duty (0.095″ diameter) weed wacker line through the ball, leaving about 2″ on the side with the bigger-diameter hole. Then, with the short end of the line, fold over the last half-inch so the line is doubled-over on itself. Then slide the line into the ball, stuffing the doubled-over section through the 13/64″ (large) hole. Finally, pull the longer end of the line until the doubled-over section is flush with the outside of the ball. This gives you a sturdy line attachment without messy adhesives. When the assembly’s complete, hold the ECI by the tail and dip the ball in yellow paint. If you’re making more than one ECI, you can drill horizontal holes in a spare block of wood and use that as a drying rack.
May 13th, 2007
 Among the many helpful and FREE services offered by Sierra Bullets, is the “X-Ring” Technical Newsletter. With contributions by bullet designers and Sierra’s team of tech experts, the X-Ring provides some great info on bullets and general reloading matters.
Here are Questions answered by Sierra’s Carroll Pilant in the X-Ring.
Q. [Why do] some cases chamber easily, while others you almost have to crush them into the chamber when they are all the same batch of cases and all been full length sized?
A. The expander ball is pulling the neck / shoulder area up as it pulls out of the case. It usually squeaks as it comes out. Cure–Lube the inside of the case neck better, or slightly decrease the diameter of the expander ball ( about .003 under bullet diameter at the most ) and polish or both.
Q. I have a rifle that has a long throat and it doesn’t shoot boat tail bullets very well at all.
A. Try a flat-base bullet. They will often shoot better in a long throated or a worn throat gun than the boat tail bullets.
Q. Why do my case necks have a lot of smoke residue all the way down the case neck?
A. This usually comes from a mild load that doesn’t have enough pressure to seal the case neck against the chamber wall or the case necks have work hardened and aren’t sealing. Cure–Bump the powder charge up if it is a mild load; and, if the case necks have work hardened, either anneal the brass or replace it with new.
And here are some of Carroll’s Reloading Tips:
● When using a collet style case trimmer, try to tighten the collet down equally each time to keep lengths uniform. If you tighten it down hard, the case will be longer than one you tighten down lightly.
● A little lube on the pilot and cutter on a case trimmer every few cases will help keep it from trying to gall in the case mouth and helps keep the blades sharp and cutting smoothly. It makes trimming an easier task.
● Just because two bullets weigh the same doesn’t mean they can be loaded the same. The amount of bearing surface can vary drastically.
Editor’s Note: This last point by Carroll is something we have to emphasize often to novice reloaders. Not only do same-weight bullets vary in bearing surface, but you can have variances in shank diameter up to .001″ among bullets of the same weight and nominal diameter. Yes there are “skinny” bullets and “fat” bullets. Obviously the fatter bullets (given similar bearing surface) create more drag in the bore and this will affect the appropriate load.
SIERRA BULLETSMITHS — 1.800.223.8799
Back Row: Robert Treece | Carroll Pilant | Rich Machholz
Front Row: Duane Siercks | Paul Box | David Brown
May 12th, 2007
A friend of ours recently took delivery of a new barrel which was chambered by a smith who had done the original build on the rifle, but who had not headspaced the barrel on the action itself this time. The smith headspaced based on his old records. Our friend happily screwed on his nice, new barrel and headed to the range. After the first few rounds, with known, safe loads, he was seeing deep craters on his primers, and then he even pierced a few primers with loads that should never have done that. Interestingly, the brass was not showing any of the other pressure signs. This was with bullets seated .015″ out of the rifling.
We were thinking maybe too much firing pin extrusion or maybe he got a hot lot of powder. Then I asked him to email me dimensions off his fired cases compared to new, Lapua brass. He emailed me that his shoulder moved 0.0105″ forward. I sent an email back saying, “hey, that must be a typo, you meant 0.0015″ right–so your shoulder moved one and a half thousandths correct?” The answer was “No, the shoulder moved over TEN thousandths forward”. Ahah. This explained some of the cratering problem in his brass. His cases were able to bounce forward enough in the chamber so that the primer material was smearing over the firing pin. And now he has brass that is “semi-improved”.
The point of the story is always check your headspace when you receive a “pre-fit” barrel, even from the smith who built the rifle. Purchase Go/No Go gauges for all your calibers. Headspace is not just an accuracy issue, it can be a safety issue. Pierced primers are bad news. The debris from the primer cup can blow into the firing pin hole or ejector recess causing a myriad of problems.
May 7th, 2007
 Remotely-mounted video monitors offer many benefits for precision shooters. With an outboard LCD monitor, one can shoot “heads up” while watching downrange conditions and wind flags. Moreover one will no longer have to struggle with ultra-critical eye relief or strain to stay centered on a tiny exit pupil (as small as 1mm on high-magnification scopes). A remote screen that displays the view from the scope has obvious advantages for disabled shooters, and for military snipers (who can stay completely concealed). Varmint hunters operating at night and in low-light can also benefit, as the image from the scope can be boosted electronically to appear much brighter on the display.
Alamo Four Star of Texas has pioneered a video display for hunters and disabled shooters, the Deros Vision System. In the pictures below, you can see the system mounted on a rifle and also placed on a Deros rifle fixture used by a disabled shooter. Priced at $995.00, the Deros Vision System is not cheap, but its benefits are obvious for special applications. We predict that, with time, major optics makers will all offer some kind of digital viewing system that can function with spotting scopes and rifle optics. The gimbaled mechanical gun fixture, sold separately, can be mounted directly to a wheelchair.
May 6th, 2007
 Are you re-barreling a BR rifle and need to know if you will still make weight? Or perhaps you are trying to select the right contour to hit an optimal carry weight for a new varmint rifle? Dan Lilja offers FREE software that will calculate barrel weight for straight contour, straight taper, and radius-tapered barrels. Dan’s software even calculates how fluting alters barrel weight.
For general info on barrel weight calculation for straight and straight tapers, read this article on Lilja’s website. Click HERE for another article explaining weight calculation with barrels that have a radiused (curved) contour section.
Here are the free software programs offered by Dan Lilja. Right click and “Save As”:
Straight Contour (.exe file) | Straight Contour (Excel file)
Contoured Barrels with Radius (Excel file)
April 22nd, 2007
Regular readers of this website will know that we are big fans of Wipe-Out™ from SharpShoot-R™ Precision Products. Wipe-Out™ really works, and can save countless hours of cleaning, plus reduce wear and tear on your barrels. (Click HERE for related article.) The only shortcoming of Wipe-Out™ foam cleaner is that you’ll need to wait an hour or more to get the best cleaning results. This editor’s barrels like two applications of Wipe-Out with four hours total dwell time. Terry Paul, inventor of Wipe-Out™, has come up with a solution for shooters who want the benefits of Wipe-Out™ without the extended wait time.
 Terry’s new Patch-Out™ product is a non-petroleum-based liquid solvent that is effective on carbon and copper fouling. It does the job with just 15-25 minutes of soak time in the barrel. Unlike many other solvents, it does not leave a gummy residue in your barrel, and it doesn’t have to be “neutralized” after use.
Patch-Out™, as the name indicates, is applied with wet cotton patches. You can also use a brush, but you’ll probably find that you’ll get excellent results with only minimal brushing. After applying Patch-Out™, and letting it soak for 15-25 minutes, just use a dry patch. Because Patch-Out™ has a rust inhibitor, you don’t need to follow up with oil. Patch-Out™ is also safe to leave in your barrel overnight, just like Wipe-Out™. There is some evidence that, if you use a non-petroleum-based solvent such as Patch-Out™ and no oil, you can shoot more rounds through your barrel before a stubborn carbon ring will form just ahead of the throat. This is because that carbon ring is actually created, in part, from the “burn-off” of petroleum-based solvents and lubes. Patch-Out™ will be available from major suppliers including Brownells, MidwayUSA, and Midsouth Shooters Supply.
April 20th, 2007
 Reader Richard H. just tested his new CED M2 Chronograph, one of the first units in the country. This is an all-new design with many upgrades over the previous CED Millenium model. Clock speed was boosted to 48 mHz, expanding the measurable velocity range to 7,000 fps. Memory storage has been expanded 500%. You can now have up to 500 speed readings per string (and as many as 500 strings). CED claims: “Expanded digital chip design now gives the CED M2 the ability of reading velocities at much lower light levels. On clear days, this means the ability to chronograph from early morning till almost sunset.” If this claim is true, the CED M2 would definitely out-perform rival PACT and Shooting Chrony designs in marginal light conditions.
We’ve found that, with most chronographs, the biggest problems are confusing controls and keypad sequences that are hard to remember. CED has addressed that with the new machine. The $199.00 CED M2 Chronograph features single function string removal (something we wish the Shooting Chrony had), and the M2 offers “one touch” calculation of the average of the three highest velocities in a string. Another major (and much appreciated) improvement is the addition of a USB interface. That offers simple “plug and play” compatibility with laptops and home PCs. USB connectivity will make it much easier to download Chrono data into the updated CED Data Collector software. For more info, contact Competitive Edge Dynamics, CEDHK.com, (610) 366-9752. Right now the CED M2 is back-ordered, but a new shipment is arriving in 2 weeks and M2s should be available by mid-May at Brownells and MidwayUSA.com.
Richard tells us: “I’ve been frustrated for a long time with my inability to get my extreme spreads below 30-50 fps and have wondered if my bargain-basement Chrony F-1 might be part of the problem. Well, after I got my Denver Instruments MXX-123 last month, the powder scale was no longer a credible culprit, so I went shopping for a new chrono. This is what I found. Initial results (only three 5-shot groups so far) suggest that ES with the CED M2 is only half of what the Chrony measured. In the Chrony’s defense though, it is surprisely good for something that costs less than half as much (also more convenient and more portable).” If anyone in the Sacramento, CA area has an Oehler Chrono, Richard would like to do a 3-way comparision test with the CED, Oehler, and Shooting Chrony. We’d all be interested in the results. Contact Mailbox@6mmBR.com and we’ll put you in touch with Richard.
|
