DPMS LR260 Chamber Specs

ctimgo

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Aug 21, 2012
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I just got a new DPMS LR260 and can't find the chamber dimensions anywhere. Would they be SAAMI standard? The rounds I am loading will have a neck diameter of .294 when loaded (243Winchester brass necked up). I know that the SAAMI chamber minimum for a 260REM is .298 so as long as the camber is SAAMI I will be good. I would assume that DPMS would use SAAMI but when it comes to playing with things that do doom I like to be sure.
 

mtwarych

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Aug 16, 2013
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Stevensville MT
This will be no help to you, but, My GII hunter in 308 has a tight chamber.
If I don't use small base dies, the rounds will not chamber. Maybe you could cast your chamber.
 

Canadian Bushman

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Fire a factory round in the rifle and measure. Easiest method and it will get you withing a few tenths to a few thou.

If you need more precise measurements, do as the previous poster suggested and use cerrosafe to cast the chamber.

Most factory rifles are well within saami spec.
 

shortgrass

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You are always much better off necking down, than necking up. Necking up thins the neck walls and after seating a bullet may leave you with more than generous neck clearances. Cast the chamber. Mic your loaded rds.
 

ctimgo

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Ok I got some factory ammo and the neck measures .291. I know that the brass will be pinned to the walls of the chamber during firing but how much will the brass snap back after expanding during firing? If I know this then I can make a educated guess as to the chamber neck measurement when I measure the fired round.
 

Canadian Bushman

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Ok I got some factory ammo and the neck measures .291. I know that the brass will be pinned to the walls of the chamber during firing but how much will the brass snap back after expanding during firing? If I know this then I can make a educated guess as to the chamber neck measurement when I measure the fired round.
It depends on the hardness, thickness, and distance the brass has to expand to meet the chamber. Usually it springs back .0005-.003" on the diameter.

.001-.002 is a practical assumption.
 

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