September 27th, 2014

Great Resource for Firearms History and Technical Information

Forum Member Roy B. has found a website with scores of well-researched articles about guns and shooting. The Firearms History Blog features a wide variety of posts on myriad subjects, from early black powder firearms to modern match rifles. You’ll find tons of information on gun design, barrel-making, action types, and firearms testing equipment. To access hundreds of articles, click on the Firearm History Blog Archive Menu on the left side. Click the navigation arrows to access monthly collections one by one. Some of the best articles are from 2010, so be sure to check those archives too! Here are some of our favorites:

Testing Firearms: Measuring Chamber Pressure
(Comment: Crusher Gauges were used through until the 1960s, when cheap Piezo-electric tranducers became available.)

Crusher Gauge Pressure Test

Barrel Making: Making a Modern Steel Barrel (Two Parts)
(Comment: Barrel drilling process explained — interesting process.)

Metal Treatments: Ferritic Nitrocarburizing/Melonite/Tenifer
(Comment: Meloniting creates a super-hard surface layer; this has been used to extend barrel life.)

Barrel Making: Forming Rifling with Electric Discharge Machining (EDM)
(Comment: This advanced EDM method can also be used to cut chambers.)

History of Gun Cleaning Methods/Solvents
(Comment: Old-timers used some pretty weird concoctions such as “Rangoon Oil”.)

History and Engineering of Sound Suppressors (Two Parts)
(Comment: Interesting cut-away illustrations of suppressor baffles.)

Utility Firearms: Powder-Activated Tools
(Comment: There are construction tools that use gunpowder to drive fasteners into steel and concrete.)

Testing Firearms: History of Proof Testing (Two Parts)
(Comment: Fascinating article, worth a read.)

Proof Test

More Interesting Articles on RVB Precision Website
These and other articles on the Firearms History Blog will give you many interesting hours of reading — Enjoy! And while you’re cruising the web, definitely check out Roy’s own RVB Precision website. It features many interesting DIY gun and reloading projects, such as Fabricating a 17 HMR Bore Guide, Building a Swivel-Top Varminting Bench, and Fabricating a Unertl-type Scope Mount.

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September 27th, 2014

Mid-Sized Cartridge Comparison

We are often asked “what’s the difference between the 6×47 Swiss Match, the 6XC, and the 6.5×47 Lapua necked down to 6mm?” All three cartridges have 30° shoulders and fit a .308-sized boltface. However, alone among the three, the 6mm-6.5×47 has a small primer pocket and small flash hole. The 6×47 Swiss Match (made by RUAG), and the 6XC (produced by Norma), have a large primer pocket and large flash hole, just like a .308 Winchester.

Forum member DesertLefty has provided a line-up photo, with 6mmBR and .260 Rem cases provided for comparison. As you can see, the three mid-sized cases (6x47SM, 6.5×47 Lapua, and 6XC) are very similar.

6mm Cartridge Comparison

The Swiss Match has the longest neck, while the 6XC enjoys the highest capacity. But performance is very similar among the three cartridges (with the 6.5×47 necked down to 6mm), and the same powders, particularly H4350, IMR 4007SSC, and N160 work well in the 6×47 SM, the 6XC, and the 6-6.5×47 Lapua. Alliant Reloder 17, slightly faster than H4350 but with a flatter (less “peaky”) burn curve, could also prove a good choice for both the 6XC and 6mm-6.5×47.

6XC vs. 6-6.5×47
Often the question is posed “Which is better, the 6XC or 6mm-6.5×47″. The correct answer seems to be “it depends”. Current batches of Norma-made 6XC brass are very good, while certain lots of 6.5×47 Lapua brass have somewhat disappointing neckwall uniformity, demanding neck-turning for best accuracy. Overall, however, the two cases (6mm-6.5×47 and 6XC) are nearly identical in performance. Some shooters believe the Lapua brass holds up better under full-power loads. On the other hand, Norma 6XC brass from DavidTubb.com is a bit less expensive than 6.5×47 brass.

The parent 6.5×47 Lapua case is rated at 63,090 psi, while the new CIP rating for the 6XC is 63,844 psi (4400 BAR). Though the 6mm-6.5×47 has slightly less powder capacity than the 6XC, max velocities with 105-108gr bullets are quite similar. However, you should not substitute loads from the 6XC directly to the 6mm-6.5×47 or vice-versa. Because of the different case capacities and primer sizes, you should work up loads separately for each cartridge.

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