I am beginning to reload for a Compass Lake AR that I got. This rifle has a Bartlein barrel & a CLE chamber. I was checking the headspace dimensions of cases fired from that rifle and am confused with what I am seeing. Using a Hornady headspace comparator w/ the A330 bushing, the fired cases are 1.456" long. unfired cartridges are 1.458" long. How could new, unfired cartridges have a measured headspace that is longer than the fired cases?
Headspace??? Fired Cases shorter than than unfired cartridges.
- Thread starter MMH
- Start date
Blows out more in the body that can be accounted for with spring back in the shoulders? I know every gauge and chamber is different etc but my Remington brass fired measures 1.456. Compare the case bodies at the case head .2 up from the bolt face and the shoulder diameters.
0.2" above base fired case dia. is 0.373" and new is 0.374". At shoulder fired case is 0.355" & new is 0.353".
So how do I set up my FL sizing die?
The difference is probably the difference in the shoulder where your comparator touches. What kind a variations are you see between fired cases?
I would probably set it at 1.455 and see if they chamber. I suspect that they might take a time or two to reach full fired size but with an ar I wouldn’t want to risk it jamming so I would set them back just ever so slightly. Testing a batch of 5-10 with minimal sizing to see what they would do after a second firing would be a safe option if you have hundreds to process. Typically the suggestion for an ar is .003-4 from fully formed case to ensure reliable function.
Are you using the same set of calipers to measure both the fired and unaired cases? Most all digital calipers have some error in them. Using a go gauge to calibrate mine, I found that they indicated .007 short every time. I’m not sure whether this holds true for dial calipers as well.
It is possible the headspace in your chamber is a little tighter than it should be. .002" at the shoulder isn't much, and if the body and neck diameter portions of the chamber are not also undersized, dropping the bolt in an AR on those rounds will bump the shoulders back enough to chamber. Do unfired rounds eject easily? I'd expect them to be a little tight, with extra effort required to manually eject unfired rounds.
Try the same measurement on an unfired case before and after chambering it by dropping the bolt from the catch. You might be surprised at the result.
Semi-stupid thought, measure a new round. Chamber it from a magazine. Measure again. Could be a short chamber and they are resizing when you chamber them. Shorter and fatter would be odd from match chambers.
Edited to correct spell check "corrections".
Edited to correct spell check "corrections".
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