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which ar-15 cartridge?

rain164845 said:
Is the Fat Rat a straight neck down, or does the shoulder angle or body taper change? Who chambers that one?
My 6Rat upper was chambered by John Holliger (http://www.whiteoakprecision.com). I don't know if he still offers that chamber.

I later sent the upper to Lee Wells (http://www.accurateandreliablerifle.com) to open up the neck slightly to the 6FatRat. This was so that there would be extra clearance for the very thick-walled Laupa brass without having to turn the necks.

I can highly recommend both gunsmiths if you are interested in a 6RAT or FatRat (these chambers are very similar).

To add to ar15topgun's comments: There is a straight neck-down of the 6.5 Grendel - this would be the 6mmAR (http://www.6mmar.com), developed by Robert Whitley. The 6RAT and FatRat are necked down 6.5Grendel, with the neck moved forward and shoulder blown out to 40 degrees. The 6RAT/FatRat require fireforming the necked-down case, but it turns out that the fireforming step is trivial and not wasteful of components (powder, bullets) or your time. The fireforming rounds are very accurate and can be fired in matches, even out to 600 yards.

If you are interested in a necked-down 6.5 Grendel, you should definitely consider the 6RAT or FatRat, despite the need to fireform the cases. Essentially, all that means is that your first round in each case will have the powder capacity of the 6mmAR (the straight neck-down of the Grendel), and the subsequent rounds will have a little more powder capacity. You simply neck down the 6.5 Grendel case, leaving a collar or "false neck". Load and fire that round as usual (even in matches), and the fired case will now be a true 6RAT or FatRat case.

Also consider the 6HAGAR, especially if you are shooting XTC matches. There are advantages and disadvantages of the 6HAGAR vs the 6RAT/FatRat. Either would be a good choice.

Send PM or email if you have questions.

Randy
 

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