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10/20/2017 1:01:18 AM
9/22/2017 12:11:25 AM
Posted: 8/22/2005 5:57:11 AM EDT
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
Link Posted: 8/22/2005 8:03:46 AM EDT
[Last Edit: 8/22/2005 8:05:38 AM EDT by j3_]
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.
Link Posted: 8/22/2005 4:01:14 PM EDT
.032 to .038 is spec.

Not really rocket science since all you need to do is chuck the FP in a drill by the ass end, and use 400 sand paper to round and shorten the protrusion to the needed distance out the face of the bolt.
Link Posted: 8/22/2005 4:53:05 PM EDT
[Last Edit: 8/22/2005 4:54:28 PM EDT by j3_]
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
Link Posted: 8/22/2005 5:16:10 PM EDT
[Last Edit: 8/22/2005 5:37:34 PM EDT by Dano523]
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 to wipe your ass as toilet paper. The problem is that as a whole, very few non-Colt/FN parts are held to any kind of standards, and for the most part, you end up tweaking the parts to get them to work as a complete unit.

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.
Link Posted: 8/22/2005 6:44:00 PM EDT
If you had some hot rounds that popped a couple primers, the tip of the firing pin will become eroded by the hot gasses and that rough tip could cause more popped primers on normal loads. Try swapping pins. They are only like $7.
Link Posted: 8/22/2005 9:08:18 PM EDT
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
Link Posted: 8/22/2005 10:29:17 PM EDT
[Last Edit: 8/22/2005 10:29:53 PM EDT by Tweak]
Link Posted: 8/23/2005 8:35:12 AM EDT
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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