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Posted: 8/22/2005 5:57:11 AM EDT
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Was wondering what the dimmensions are suppose to be of an AR fp. Also, how far out it should extend when fired. Having a problem with pierced primers. Checked the end for damage and its ok. Swapped my fp out for a spare a guy had at the range the other day to try and it seemed to work without damaging the primers. Did a search and Googled with no luck. Ponchonorm |
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www.bushmaster.com/shopping/gunsmith/mmt-0005.asp Link to gauge if you want one. Thinking it might be .028 min. and .036 max protrusion but I am guessing. I had some foreign ammo made in Bosnia a while back that the primers would pierce on even with a good pin and min. protrusion. |
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Page 3 20 of the manual has the numbers. Looks like .028 min. and .036 max. www.ar15.com/content/manuals/TM9-1005-319-23.pdf |
The manual doesn't cover 7.62 ammo using hard primers, nor lightened hammer springs to reduce the trigger break under the 6lb normal pull. In regards to the semi AR-15, and the repair manual (M-16/4) there a lot of pages that could be torn out and used Simply stated, sending him out to just buy another FP, could end him up in the same position as once he started (read once that could be the correct protrusion, but the tip too sharp and punching threw the primers). Best to just have him de-sharpen the FP tip/point and see if that solves the problem. Worst case, he shortens it too much, and has to set back the stop collar a few thousands to get the correct ignition. |
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Thanks for the responses. After closer inspection of the fp with a magnifying glass i got at the dollar store, it had the slightest dimple on the end. Couldn't really see it without the glass. Chucked it up in my drill and used some Scotchbrite on it and it took the dimple away. Will try it at the range on Thurs. Will have a couple of new pins too. Ponchonorm |
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something else to check is the length of your bolt, OAL. if it's short the firing pin can protrude excessively. a thinner than normal firing pin spool will lead to the same problem. the dimple may be from the tip of the firing pin hitting the rear of the bolt face. that is usually a sign that the bolt is short or the firing pin is long. if you removed the dimple there is a good chance that the firing pin can now move farther forward thereby increasing protrusion. were you using reloads? |
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Yes i was using my own reloads. Had a thread in the Reloading forum and got some good info there. Trying some different powder for the bullet weights i'm using. Might have a slight overpressure condition. Never had the bolt apart on an AR, but will give it a try and do some measuring. Not new the AR's but new to having my own. Thanks for the info. Ponchonorm |
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