Apparently, a number of years ago, 50 BMG was banned in France. A French gun builder by the name of Eric Danis (company name is Dantec, whence DTC came from) came up with the idea of trimming down the brass, fireforming it to expand it to more or less the original case capacity, and thus requiring only a new barrel in order to get comparable performance out of a non-50-BMG gun using all the same other parts as its BMG counterparts. His involvement with the US implementation of 510 DTC was, unfortunately, tangential. The Americans forged ahead with incorrect specifications, and as a result we have a separate standard.
The differences between 510 DTC (Europ) and 50 DTC EDM
When 50 BMG bans started hitting the USA, some enterprising individuals looked at what happened when the same bans took place in France. The result was the decision to start chambering rifles designed for 50 BMG in 510 DTC, which is a European (French, actually) specification designed to bypass the ban on rifles which fire the military 50 BMG round. That was the plan.
Apparently, things went wrong when some folks got the chamber specs wrong when designing reamers (basically, the fancy drill bits which cut the chamber into a rifle barrel) - these reamers were the 'JGS' reamer and 'Mason/EDM' reamer. While subtly different, field reports claim that both reamers will interchange ammunition, however the Manson reamer seems to have won out in the battle. The chamber spec differences from 510 DTC Europ were discovered well after rifles with chambers based on those reamers were already "in the wild".
In any event, rather than throw away everything that had been done so far and orphan the rifles already in customers' hands, the various American companies took advantage of this to correct some public misperceptions and solidify a new standard. The misperception arose from the National Firearms Act's assertion that any rifle with a bore over .50" is a destructive device. While 510 DTC uses the same projectiles as 50 BMG, the barrel diameter is .510" if your measurement includes the space within the grooves in the rifle, and .50" if your measurement does not. For NFA purposes, the latter measurement is used and the 510 DTC Europ is identical in diameter to the 50 BMG (and 50 DTC-EDM for that matter). Thus, 510 DTC Europ is not a destructive device, but the question keeps coming up from the folks who actually think about the NFA. They resolved this matter by calling the new chamber standard 50 DTC.
For purposes of this article, please consider all 50 DTC references to be references to 50 DTC-EDM. Any reference to the European chamber specifications will refer to the round as 510 DTC Europ.
Practical Implications of the DTC-EDM vs Europ chambers
This section written thanks to Dave Manson's info
The Europa spec has a larger radius (sloping area) on the neck/shoulder junction of the case than the DTC-EDM spec. This means that the Europa has a gentler slope to its curves than the DTC-EDM case. As a result, a DTC-Europa chambered rifle can shoot any DTC-spec round, while a DTC-EDM chambered rifle can only shoot DTC-EDM spec rounds (not Europa). Dave Manson produces reamers in both the DTC-EDM and DTC-Europa specs, and strongly recommends that anyone considering building a new line of rifles, use the DTC-Europa spec in the hopes of eventually mostly re-unifying the standard.
Why a Radius Matters
A radius, in the context of chamber specs, is generally only found at the neck and shoulder dimensions. The radius can be summarized as using a sloping contour in place of a sharp angle. Most bottle-necked brass has a radius at the shoulder and neck. The reasons radiused shoulders and necks are desirable over sharp angles are twofold.
Brass with sharp corners is much harder to form, than brass with radiused corners.
Mass produced resizing dies are almost never perfectly in sync with a chamber's dimensions. Every time a piece of brass is fired, it is fire-formed and expanded to match the dimensions of the chamber it was fired in. A resizing die's job is to push it back into its original dimension. A piece of brass which is resized every time it's fired, from a sharp angle to a radiused shoulder and back, will weaken and probably fail with fewer loadings than a radiused piece of brass which is being reshaped less.
That having been said, usually radiuses (or lack thereof) at the junction of body and shoulder don't cause problems.
Technical Explaination (what's above was a summary for the average reader)
The only functional difference between DTC-EDM and Europ chambers, is the presence of a .250" radius at the neck/shoulder junction on the Europa, compared to a very small radius at the same point on the EDM version. If the radius at the neck/shoulder of the cartridge is larger than the corresponding radius in the chamber, the round will not seat against the shoulder and can prevent the action from going into battery. If the radius of the chamber is larger than than that of the case at the neck/shoulder junction, and all other dimensions are compatible, the round will chamber properly. Both chamber specs call out a maximum radius at this point, which means that the chamber can have a sharp corner and still be in spec. Specifying a maximum radius at this point simply allows for a reasonable amount of wear to the reamer cutting the chamber. The case will likely never have a radius at this point smaller than the chamber, and should therefore never experience interference at the body/shoulder junction.
Manson/EDM vs JGS reamers
According to one of Mark Serbu's posts on Serbu.com's forums, the only difference between the two reamers is the outside radius at the shoulder. The Manson reamer specification doesn't call out a radius at all, while the JGS reamer specifies a range from 0 to .125 as a radius. JGS claims that they went with zero for the radius on the machines, then stoned a very slight radius onto it by hand afterwards. So, in essence, there's no difference between the two reamers, and rounds built for the 50 DTC-EDM standard should be entirely interchangeable. This is almost an academic point, however, as it seems that nearly all the companies making 50 DTC-EDM are now using the Manson reamer. Serbu used the JGS reamer until their 12th DTC rifle, at which point they switched to Manson.
Vendors of rifles in these calibers
Bluegrass Armory is the only US-side vendor which is still considered likely to be producing rifles chambered in 510 DTC Europ, instead of 50 DTC-EDM.
Bohica Arms is a new name in the AR-15 upper assembly business, and they're selling their Bohica in 24", 30", and 36" variants, chambered in 50 DTC-EDM or 50 BMG. The author of this article happens to own the 30" model.
EDM Arms is well known for their Windrunner rifles. I'm not sure if they were the first to have chambered a rifle in 50 DTC-EDM, but they seem to have made their name stick to the spec. EDM rifle owners do have one additional source of commercially loaded ammunition to them, at prices comparable to that of loaded 50 BMG rounds.
Serbu Firearms, Inc
Serbu Firearms makes 50 BMG, and now 50 DTC rifles. According to a post made in 2006 by Mark Serbu, their chambers happen to be identical to the EDM chambers. Very early Serbu guns (pre-#12) used the JGS reamer, which is still very close to the DTC-EDM standard Mason reamer.
Safety Harbor Firearms
The Safety Harbor Firearms Inc. manufactures the SHF/R50 rifle and Ultramag 50 AR-15 upper conversion. Both are Magazine fed bolt action - 3 and 5 round mags are available. Both are available in .50 BMG or .510 Europ
Ameri-Can Enterprises, at (405) 284-6869. Ameri-Can is a licensed class 06 FFL (reloading license). He asked, when answering my questions, that I explain to my readers that his rounds are only for EDM customers and rifles. EDM bought him the tooling, barrels, and everything necessary to make the ammunition, so he feels that exclusivity is the honorable thing to do. Equipment does wear out, and putting wear and tear on EDM-bought equipment for non-EDM customers wouldn't be right. He has supplied some manufacturers with ammo for them to perform compatibility testing with, which is where reports of his ammunition working with or not working with other firearms comes from. In his loads, he uses M33 ball FMJ and Hornady A-Max projectiles exclusively. He will not load armor-piercing projectiles in this caliber. As this is an exclusively civilian caliber, it is probably a good idea to avoid making AP ammunition commercially available. For fire-form loads, Ameri-Can uses 225gr of WC-859, which is a military powder the average reloader is unlikely to have. I include its designation only for completeness's sake. I have been informed that EDM Arms will sell the ammunition to non-EDM customers.
Chris over at Bohica has made me aware of a gentleman who's getting ready to get into the reloading business for this caliber. Details when I have permission to post them.
Another individual from Calguns.net is also getting ready to get into the reloading business for this caliber. Details when I have permission to post them.
Reportedly, Mark Serbu (of Serbu Firearms) is working with a major ammunition vendor now to produce 50 DTC ammunition on a large scale.
The Right Reloading Equipment
Make sure that you've secured the correct dies for your barrel before getting into reloading for DTC. If your
The Press: Although Lee advertises that their new classic cast turret press is large enough to load 50 BMG, what they neglect to tell you is that it's not threaded for standard 50 BMG dies. I have been informed that the new Lee 'Classic Cast' press can indeed load the 50 BMG/DTC cartridges, and is actually easier to work with because the case can slide into the shellholder without having to tilt it in. Members on the Brian Enos forum have recommended the RCBS Ammomaster or Hollywood, or possibly the Rock Crusher (not Rock Chucker).
Lee Precision will custom-build DTC dies. Collet dies (seating only, no resizing) are available for $150 (as of 11/27/07), which is the cheapest die solution available provided that you aren't having to do the step of resizing BMG brass into DTC. You can also special order a full length sizing die from them. Their full-length sizers are presently based off of JGS-supplied dimensions, which may mean either 50 DTC-EDM/JGS, or 510 DTC-Europe chamber specs.
Dave Manson suggests that, for anyone considering setting up tooling to make 510 DTC, that they use the Europa-spec reamers. The reason for this is so that guns made using the reamer will accept rounds formed for either DTC-Europa or DTC-EDM. A friend pointed out that it's sort of like the reason most folks should opt for an AR-15 in 5.56mm or 223-Wylde instead of 223.
JGS Precision Tool MFG produces reamers, and apparently no dies. I'm not sure if they still make their reamers the same as they did to begin with, or if they've changed to follow more prevalent Manson reamer spec.
Given the lack of ammunition vendors for this caliber, it will be necessary to form your own brass from 50 BMG brass until such time as a vendor steps up. The procedure is:
Resize the brass using the correct dies for your chamber.