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FN SLP - Fill in lifter fork project


runnerguymn
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Hi guys and gals,

I bought an SLP last week and I'm working on getting it ready for 3-gun season...and I wound up mashing my thumb on the forked part of lifter on the first day I started doing loading drills. OUCH! No blood, but plenty of bruise.

I'm new-ish to shooting sports, but I've been doing metalworking for a while, so this didn't seem too tough to get done in a couple of hours. I've gotten my loading gate welded up, reassembled, and function checked and everything looks good, but I had a question for people that are more knowlegable than I.

I noted that some of the pics I've seen of others that have done this have a slot cut in the lifter ( http://www.boomershooter.com/forums/index.php?/topic/7260-must-do-mods-for-the-fn-slp-shotgun ). Is this slot for some practical purpose, or is this just from someone yanking a lifter off another model shotgun and they happen to have a slot cut in it?

I've attached a couple of pics of my lifter in progress. Yes...that is the remnants of a table knife...I couldn't find a good piece of stainless laying around that was the proper thickness. I figured it would even out the cosmic balance...remove a fork by adding a knife!

~runerguymn

post-45472-0-74975000-1358746384_thumb.j

post-45472-0-52205600-1358746392_thumb.j

post-45472-0-54204900-1358746402_thumb.j

post-45472-0-01744900-1358746410_thumb.j

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I noted that some of the pics I've seen of others that have done this have a slot cut in the lifter ( http://www.boomersho...-fn-slp-shotgun ). Is this slot for some practical purpose, or is this just from someone yanking a lifter off another model shotgun and they happen to have a slot cut in it?

The slot can be for two reasons:

1/ In the event of a double feed, you can poke a key/screwdriver/remains of a table knife :goof: in the slot and push the second round back into the mag tube.

2/ The weight removed by cutting a slot can offset the weight added by the newly welded material. This maintains the timing of the lifter, aligns the planets and brings peace to the galaxy.

Edited by SteveA
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Hrm...sounds like I'll need to chuck it up in the mill and make a couple of chips with it then. The gun is still unfired, so I figured I'd try to run a couple boxen of loads down the pipe before pulling *everything* off the receiver and trying my hand at widening the loading port with the mill. I read somewhere that customer service gets cranky when you complain about issues on a modified product. Thanks for the enlightenment Steve!

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The slot is intended to try and keep the shell centered in the lifter to remove the potential malfunctions. Some look at it as a weight issue, but I ran 2 for close to 5K rounds with no slot and no lightening holes. The SLPs can be a little tempermental until you get them all massaged out. Each SLP tends to have its own unique features. One reason that I suspect that many smiths don't want to mess with them. With the same parts the same way, James and mine ran differently and different than some of the other guns we worked on here locally. With the Versa-Max and Benellis and even the 930JMs, if it works in one, it appears it will work in all of them.

The SLP is certainly a very good shotgun. I would make small changes, one at a time and if something goes haywire, you know what to work on. If you toss a bunch of changes at them at once, you can have issues. Personally, if I had a SLP that ran what I wanted with no issues, I would not slot the lifter. I would keep an eye on the lifter (dog leg) springs and have some spares on hand just in case.

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Have you seen the lifter springs on the SLP break frequently? I thought I was going to have another episode of searchcing my dining room for a small part while trying to install that little bugger. God must really hate gunsmiths, because all the small parts I've seen in trigger groups are at the end of a spring perfectly fabricated to throw them somewhere you'll never find them.

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I hate to have to say this in my first post, but the lifter spring/extra weight thing is a myth. First, if it will feed a 1.5+ ounce load, wouldn't that be the same as adding weight to the lifter? Second, the bolt returning to battery is what forces the lifter up quickly, not the spring. You could put 10 glock springs in there, and it still would not be fast enough for the cycle time. With that said, it looks good. I still think the slot could be very handy for clearing malfunctions.

Edited by Mcfly
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I would STRONGLY recommend putting a small v cut (or similar) in that extension (front edge). You want the center of the lifter to be short of the sides at the front so that if you jam a round in without engaging the catch or the catch hangs on something and a shell pushes back into the front of the lifter it cannot detonate. It is unlikely sure, but well worth having the safety built in. Otherwise it looks good.

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casanova: I hadn't thought about getting a primer strike from the lifter, I'll have to do a little more work and figure out a shape that's not grabb-y but has some releif in the primer area. It seems like all of the lifter gate modifications I've seen have a pretty flat profile on the forward edge. Has anyone ever heard of a cascading detonation in the magazine tube from a primer strike on the lifter gate? I shudder to think of what the mop-up on such an event would look like.

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McFly: I was a little skeptical about the spring/timing argument as well. Given the extremely short cycle times, the amount of spring force required to move the mass of lifter+shell upward would be so strong that you probably wouldn't be able to budge it with your thumb which would render the design useless (or at the very least quite likely to remove a finger or two). It seemed to me that all the spring action was there to do is return the lifter down to the firing cycle start position after the user loaded a round into the magazine. The rest of the action's motion seemed to be based on the inertia of the bolt.

I was really surprised at the very short throw of the piston system on the SLP. After stripping everything down, it looks like the design relies on the first 3/4" or so of the bolt travel to impart a little inertia and then transfer that energy to the return spring housed in the stock. I can understand where they're worried about larger loads imparting a pretty substantial velocity on the bolt and causing damage to either the return spring or the rear of the receiver (or deforming part of the trigger group/lifter system) if the incorrect gas piston assembly is installed. Is a short piston cycle common in shotgun actions?

I know it's supposed to be quick, dirty, and sloppy, but it does give one a bit more appreciation for the controlled round feeding of a good bolt action. Since this is the first shotgun I've ever owned, this is all pretty new to me. Is there an analog to the Winchester 70 controlled round feeding system in the shotgun world or an action that doesn't rely on glorified moving funnels to try to blindly stuff a shell into the breach? it seems like cycling most shotgun actions upside down would really do a number on the loading gate type system (not that I'm advocating a batman style 3-gun training approach...although video would be quite entertaining if anyone has tried).

Edited by runnerguymn
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McFly: I was a little skeptical about the spring/timing argument as well. Given the extremely short cycle times, the amount of spring force required to move the mass of lifter+shell upward would be so strong that you probably wouldn't be able to budge it with your thumb which would render the design useless (or at the very least quite likely to remove a finger or two). It seemed to me that all the spring action was there to do is return the lifter down to the firing cycle start position after the user loaded a round into the magazine. The rest of the action's motion seemed to be based on the inertia of the bolt.

I was really surprised at the very short throw of the piston system on the SLP. After stripping everything down, it looks like the design relies on the first 3/4" or so of the bolt travel to impart a little inertia and then transfer that energy to the return spring housed in the stock. I can understand where they're worried about larger loads imparting a pretty substantial velocity on the bolt and causing damage to either the return spring or the rear of the receiver (or deforming part of the trigger group/lifter system) if the incorrect gas piston assembly is installed. Is a short piston cycle common in shotgun actions?

I know it's supposed to be quick, dirty, and sloppy, but it does give one a bit more appreciation for the controlled round feeding of a good bolt action. Since this is the first shotgun I've ever owned, this is all pretty new to me. Is there an analog to the Winchester 70 controlled round feeding system in the shotgun world or an action that doesn't rely on glorified moving funnels to try to blindly stuff a shell into the breach? it seems like cycling most shotgun actions upside down would really do a number on the loading gate type system (not that I'm advocating a batman style 3-gun training approach...although video would be quite entertaining if anyone has tried).

The lifter spring in question, has 2 functions. It holds the lifter down to allow shells to feed on top of the lifter. (Also to allow loading the magazine) The hidden function, is the articulating pawl that engages the slot in the bottom of the bolt that actually raises the lifter. The function of the pawl is not dependant on the weight of the lifter. If the pawl had enough spring to function with a factory lifter, it will function with a modified lifter. Any time you have a part of a machine modified without verifying fit and function, you are asking for problems. Most all modified lifter issues are directly related to the modified shape placing the shell in the wrong location/angle.

The gas system is a short throw, because the gas system does not cycle the action. The gas system just unlocks the bolt at the correct time, then the remaining pressure in the barrel continues to cycle the bolt. The heavy piston delays the unlocking of the bolt a little longer so the pressure can drop down from the heavier load. The lighter piston does the opposite. It unlocks the bolt a little earlier to give it a little extra pressure to cycle the bolt. In theory, with excellent engineering, the force from the gas system on the bolt should be the same with both pistons (when used with the proper load).

If anything, it gives me more appreciation for competent gunsmiths, that actually fit parts, rather than hack a single part up, then ship it off hoping it will work. I'm not certain what you mean by shooting a self loading shotgun upside down, but the shotgun would not know the difference. The only difference would be the effect of gravity on the shell its self. The fact that the shell if forced out by a spring, then held in the lifter by spring tension, then forced to the top of the action by the bolt acting on the lifter, and the hump on the lifter holding it to wards the inside of the chamber, and the bolt forcing the shell to the chamber..... what could possibly go wrong?

Edited by Mcfly
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