FN 5.7x28mm reloading

[Badgersmilk]

Happened to see this while looking for Mauser parts just now.

http://www.buymilsurp.com/fn-fiveseven-10-round-magazine-extension-convert-20-to-a-30-rnds-p-4933.html

Nice!

[Fatman]

Just a thought in passing - if the gun starts to extract the casing  prematurely, would the resultant loss of contact between the casing neck and chamber (thin case is now unsupported) result in this problem?  Could you get a hold of a new or stronger recoil spring and try a round or two?

[Badgersmilk]

I'd say you could remove the recoil spring completely and it wouldnt cause a case stretch.  It wouldnt load the next round...  But it wouldnt have anything to do with ejection of a spent case or its condition.  The case is not being supported by the chamber correctly in order for it to stretch.  I'd say if the chamber were to long or not sized correctly he wouldnt be getting the cases out of the gun at all.  They'd likely stretch to fit the improper chamber, then jam in there (assuming the gun didnt blow up of course ).

As I understand it:  The instant a round is fired the brass swells in the chamber holding the case in place and sealing gasses from blowing back around the sides of the cartridge (in your face).  After that SHORT fraction of a second the slight swelling that occured from firing pressure contracts again (not 100%, but almost back to original size making "fire formed" brass that now matches the chamber size) allowing remaining "reduced" pressure to "blow back" the case and bolt / slide.  No springs involved other than the one that pushed the firing pin into the primer.  The case is stretching because the chamber is not supporting it properly.  The fact that the neck is shrinking, and the body is growing is whats weird!  DOES make it sound like the chamber is to long.  If the gun were slam firing, or firing out of battery before the locking lug engaged the head of the case would at least be swelled or cracked if not blown off.

My guess: 1. loads are to hot (every manufacture of anything for this round warns people its very sensitive due to size)  or  2. to much oil in gun / on ammunition (shouldnt really shorten the neck though) 3.  If not 1 or 2, he needs to send the gun back to FN before it blows up.  Its modified or broke.

We still dont know when he's measuring the brass.  If its after he put it in a die.  This speculation is all wasted.

Just my .02 worth. 

We havent heard back at all...  Stay tuned for a "FiveseveN blows up" video on youtube!

[brandons]

I'd say you could remove the recoil spring completely and it wouldnt cause a case stretch.  It wouldnt load the next round...  But it wouldnt have anything to do with ejection of a spent case or its condition.  The case is not being supported by the chamber correctly in order for it to stretch.  I'd say if the chamber were to long or not sized correctly he wouldnt be getting the cases out of the gun at all.  They'd likely stretch to fit the improper chamber, then jam in there (assuming the gun didnt blow up of course ).

As I understand it:  The instant a round is fired the brass swells in the chamber holding the case in place and sealing gasses from blowing back around the sides of the cartridge (in your face).  After that SHORT fraction of a second the slight swelling that occured from firing pressure contracts again (not 100%, but almost back to original size making "fire formed" brass that now matches the chamber size) allowing remaining "reduced" pressure to "blow back" the case and bolt / slide.  No springs involved other than the one that pushed the firing pin into the primer.  The case is stretching because the chamber is not supporting it properly.  The fact that the neck is shrinking, and the body is growing is whats weird!  DOES make it sound like the chamber is to long.  If the gun were slam firing, or firing out of battery before the locking lug engaged the head of the case would at least be swelled or cracked if not blown off.

My guess: 1. loads are to hot (every manufacture of anything for this round warns people its very sensitive due to size)  or  2. to much oil in gun / on ammunition (shouldnt really shorten the neck though) 3.  If not 1 or 2, he needs to send the gun back to FN before it blows up.  Its modified or broke.

We still dont know when he's measuring the brass.  If its after he put it in a die.  This speculation is all wasted.

Just my .02 worth. 

We havent heard back at all...  Stay tuned for a "FiveseveN blows up" video on youtube!

Im measuring after I shoot and after i put in dies my dies well not size this casing at all shoot gun and the try to resize it it dont do anything but size the neck. I have talked to 3 people who have this gun and there brass does it to.RCBS dies will not work but i dont want to reload until I find out why factory ammo is bulging the shoulder up.Im contacting FN today and send it back

[Badgersmilk]

"Im contacting FN today and send it back"

Good choice!  I think its a COOL gun.  But, fingers dont grow back once blown off!

[Sponsor]

[mac969]

the shoulder moving back is common in blowback guns with shoulders on the cartridge.Especially on the fn type guns. You can only reload the brass about three times before the cases fail. Also do not polish them,clean them with simple green or something like that. They have a special coating on them that let them cycle thru the p-90 mags(its like a varnish).

[mac969]

I have a upper for my AR-15 called a AR-57 and i got a longer buffer spring and tuned it to the round I shoot and the shoulder hardly even moves now. You should be able to do the same thing for the pistol or the ps-90. The ar-57 is a blowback operated upper not gas operated like the original uppers for the AR.