Beretta AL 391 FT Eject

[jrhines]

Bump this to smithing if you like,,,
A client brought me his pet Urika 20 ga, would not spit the empty hull out of the port. I gave it a good cleaning including full detail strip of the recoil spring & tube. Re-lubed, assembled and it ran 100+ rounds flawlessly. Over the years he had run in excess of 10,000 rounds through the gun without changing the spring, so I said let's replace it. He agreed, I replaced the spring with what I was assured was a new factory spring, wich I measured at just an inch plus longer than the old spring. No worries, those springs do shorten with use. The gun would not eject the spent hull. I called MGW (where I got the spring), Cole and Brownell's trying to find the specs on the spring (coils/inch, wire diameter, spring constant and relaxed length). All agreed the 17 1/8" for the new spring was correct but no one had a clue as to the spring constant or the other specs. I used my Trigger Scan to measure both springs, the old was 2 lbs and the new spring was a bit above 3 lbs. I reinstalled the old spring and am awaiting a range report now.
Anybody got any info on what these springs should measure? I was told (by two of the vendors) that they install these all the time and they work "just fine".

 

[PJR]

I have a new Beretta recoil spring for a 391. Here are the measurments of mine.

Relaxed length: 17-1/4"
Spring diameter: .5"
Wire diameter is .0455"
Six coils per inch

FWIW, my 12 gauge has far more than 10,000 through it and works fine. My 20 gauge is around 2,500 and also works perfectly.

 

[orphanedcowboy]

Did you clean the gas ports and disassemble the gas valve and spring assembly and clean them as well?

 

[jmr40]

It is possible to reassemble that gun incorrectly. It has been a while since I owned one, but I did it once after breaking it down to clean. Everything seemed to work right. It would cycle by hand just fine, but I put one part in backwards and the gas would not work the action until I figured it out and turned things around. Drove me crazy for a while.

Might not be the issue here, but worth checking especially if it suddenly starting causing problems after working fine.

 

[CD8226]

My brother has a 12 gauge and the same thing happened to it. It was assembled incorrectly. Was just an expensive single shot til we figured out the problem. Reversing the gas port cleared the problem. Hope this helps.

 

[jrhines]

PJR - Thanks for the data, mine is .042 wire, 4-1/2 coils/inch. Same length. Are both the 20 & 12 ga the same? MGW sells the same spring for both. The 1-1/2 coil per inch increase in yours would make a "lighter" spring, but by how much. Any guess at the spring constant of yours or can you measure it?
OC - Yes, a detail strip and clean means just that, everything apart (forend cap, gas cylinder, piston, everything).
CD - I don't understand "Reversing the gas port cleared the problem". What gas port did you reverse? Here is a link to an exploded 391 drawing for ref.

http://www.berettaservices.com/Modu...es/PDF Esplosi Arma Parti Speciali/eal391.pdf

This is a spring problem, the old one works, the new one does not work. The vendors say it does, but it doesn't in this particular gun??? Increasing the spring constant by 50% would not be an issue? The free length of the old spring is 16" and stuffing it into the recoil tube means you have to compress it about 4". At 2 lbs/inch, that's 8 lbs. The bolt recoils about 3-1/2 inches, so that's another 7 lbs, or a total of 15lbs. The new spring is 17" so you have to compress it about 5". At 3 lbs/inch, that's 15 lbs, plus the same 3-1/2" for bolt travel is 10-1/2 lbs, for a total of 25-1/2 lbs. That is a 70% increase in required recoil to get the bolt back to the ejector.
What am I missing??
Still waiting on the range report.

 

[PJR]

PJR - Thanks for the data, mine is .042 wire, 4-1/2 coils/inch. Same length. Are both the 20 & 12 ga the same? MGW sells the same spring for both. The 1-1/2 coil per inch increase in yours would make a "lighter" spring, but by how much. Any guess at the spring constant of yours or can you measure it?

Sorry. No idea what the spring constant is and I've got no way to measure it. As far as I know Beretta uses the same recoil spring for the 390 and 391 in both gauges.