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Old March 16, 2011, 09:42 AM   #23
Senior Member
Join Date: July 20, 2005
Location: Indiana
Posts: 10,167
Bear in mind we're just guessing here having not had the actual rifle in our hands. Also bear in mind no-one is "having a go" at you, we're just curious to find a definite answer to what & how this happened.
Oh, I never really thought anyone was "having a go" at me, I know you're all trying to help.

2 things that come to light from your post.
Firstly that is an abnormally high incidence of incidents.
Secondly there was a change made (the spring).
I'm not overly inclined to think that the spring is the issue as this is the first incident I've had since replacing it. I actually had more slamfires before with the OE spring and I intentionally put in a much heavier spring because of it. Also, I'd shot the rifle a fair amount with Federal ammo after replacing the spring without issue.

Based on that I'd guess there is a problem somewhere within the rifle/ammunition/user chain. I don't think it is drastic, but it IS causing incidents so it probably needs fixing for your comfort & safety. Ammo with 10 FPS is very, very minor, but ammo with a different pressure curve from a different propellant may well be causing the gas to behave differently, even if the velocities are identical.
The more I think about it, I think the problem probably has to do with the ammo, gas system adjustment, or both. As I stated earlier, I did have the rifle checked by a gunsmith who seemed fairly familiar with FN-49's and he told me it was mechanically fine. An improper setting on the gas system or defective ammunition, however, wouldn't be something that he would have been able to tell unless he fired the rifle. I'm beginning to think that one needs to adjust the gas system for a specific loading and either stick just to that or readjust the gas system anytime a different ammo is used.

Either way, I'm getting rid of this rifle. Even if it is mechanically fine, I have no use for a gun that I have to be so picky about ammunition with. I feel that I can sell it in good concience since a gunsmith has given it the mechanical OK. I've also opened the gas vent all the way (this allows the least amount of gas to act against the piston) and set the plug to the grenade launching setting (this prevents semi-auto fire) so that whoever I sell it to will have to adjust the gas system for whatever ammo he decides to use.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar
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