[JoeCool]

I wanted to put the Mcarbo kit in, because the trigger pull was too heavy, in an M500 that I got not too long ago. I was only going to put the trigger spring in because, I figured the hammer spring was strong enough, but after shooting it a bit with the standard springs, I got a light hammer fall about 1 in 50 with the standard springs, so when I installed the Mcarbo kit, I put both hammer and trigger springs in. The replacement seems to be better, but I still have got an occasional light hammer fall even with the new Mcarbo spring which is obviously heavier than the standard.

My read on the situation is you are better off with the replacement spring, but the problem can still appear at times, and my guess is that it is not an optimal design of hammer. That is not too unusual, quite a few shotguns have less than a perfect design of hammer, like for example the Winchester SX1, and some Browning O/U seem to have a light fall on the hammer of one of its barrels, bottom was it?

My Remington V3 gets an occasional light fall, maybe one in 200. One of the better designs in my opinion is the Rem 1100 and 870 triggers, but I have even managed an occasional light fall on one of these, like maybe one in a thousand.

Then also it is possible that something other than the spring is the culprit, like maybe a shell not fully seating in chamber, or maybe a loose barrel that leaves the barrel slightly forward of optimum position, all in all if it only screws up one in a 100, I would just live with it, while trying to see that everything is clean and in position, and let more time pass. It might even be inconsistently made primers, who knows? It is not a perfect world.

 

[JoeCool]

Putting the original back in does not make sense to me. My original had more failures than the Mcarbo replacement. The Mcarbo replacement hammer spring is stronger, giving heavier hammer fall.
If it misfires with the Mcarbo, it is even more likely to do so with the original. Of course I could be missing something, but like I said it does not make sense to me.

 

[JoeCool]

If a hull has a thin rim like many WWAA hulls you can get failures to fire.

That makes sense to me, I think my failures what very few I had with the Mcarbo spring was with Winchester ammo. Also I suspect that a slightly deep rim cut in the chamber could cause the same problem, and possibly a slightly deep primer seating, also a slightly short firing pin. Like I said, its not a perfect world.

 

[JoeCool]

One thing nice about changing the hammer spring back in, is that it is easy. While you have both springs out, you might try compressing them. When you do, I suspect you will find the Mcarbo hammer spring is stronger, which means it is going to hit harder. Generally speaking when you have light hammer falls, making them hit harder is the solution, so you may or may not decide to put the original back in at this point. It would be interesting to me to know which one is stronger. In my case, the Mcarbo hammer spring was stronger. The Mcarbo trigger spring is weaker, in order to give a lighter hammer fall. Changing the trigger spring can be a real bugger, if you let things come apart, but at least you won't have that problem with the hammer spring if the procedures are similar to the M500.

The Mossberg trigger is a pretty good simple design, but it does have the shortcoming that it has that long tang on the rear and this makes you have to use a stock that allows that long tang clearance in order to remove trigger group for cleaning. Other than that they did a pretty good job on the design. At least this is true on the M500. I assume the M88 is pretty much the same except for the safety.

Also, Mcarbo says they have a lifetime warranty on this trigger kit, so if your present spring has got weaker, I suppose they will replace it.

 

[JoeCool]

Just speculating here, thinking out loud. If 590 has dual springs, what does that tell you? The 590 is a more robust model 500, made more for military and police, the trigger housing is aluminum, not plastic for example. So why do they put two springs on the hammer in this more robust model? First guess off the top is they probably were trying to eliminate light hammer fall more positively. If they never had light hammer falls in the M500 they probably would have stuck with just one spring in the 590 also. Case in point, the original SX1 had dual hammer springs, why, I would bet they had light hammer falls in their prototype giving fail to fire so went to dual springs in the production model. That was the stage one trigger. Later they went with a heavier spring and just used one, that was the stage two trigger. But, light hammer falls is a pretty common SX1 problem, I experienced it on about 3 out of 6 that I owned. Also there are heavier aftermarket hammer springs available for it, and I put those in mine that I owned.

Therefore it would be very easy to believe the Mossberg trigger, has experienced enough light hammer falls often enough that someone like Mcarbo made a heavier spring for the same reason. It might feel lighter, but that is because it is longer, compressed to the same cocked length you can bet that it is giving more force than the standard spring. So you got to test both springs to the cocked length and see what force is needed. Then too, you could buy two 590 springs and use those like the 590 does. It will be interesting to see how you eventually decipher the problem and how you solve it. I suppose you could test the force it takes to cock the hammer, maybe cock it by placing the hammer on a scale and push on it until it cocks, then install the other spring and make the same measure. Or you could just shoot the gun and see if it works often enough to make you happy as is.

 

[JoeCool]

My problem is I want 100% ignition. The thing is I can't find the 590a1 dual spring anywhere for sale, nor can I find a schematic for the a1, just the regular 590 which has the single spring.
Another thing I noticed while messing around with the gun last night is that the firing pin spring is SUPER strong. I couldn't even push it enough with my thumb to make it protrude from the bolt face.

You impress me as excellent at diagnosing with those thoughts. The SX1 also had problems with the firing pin spring being too strong, and maybe was partially responsible for the fairly common light hammer falls on that gun. The solution on SX1 is that most gunsmiths that specialize in the SX1 routinely cut 3/8 inch off the firing pin spring when installing a new one. You may have some sort of similar problem, spring too strong, maybe a burr or dirt on firing pin or its's channel. With your skill level, I think you will run it down shortly.

 

[JoeCool]

Good thoughts, Uly.

 

[JoeCool]

Well, it certainly sounds as if the spring is way too heavy. A really easy thing to try is replace the spring with something weaker and try it. If you have a supply of generic springs available you could cut one of proper diameter to length and give it a try. If you have nothing available, then you can cut some off the original, or buy a replacement spring, compare it to the one that is in question, and then maybe try to make one from either of those two springs by cutting off some length if it needs to be cut to get it to where you think it is light enough. You want it heavy enough to retract the pin and keep it back, but not so heavy as restrict the force to the primer. Sounds like maybe I should check my firing pin spring also.

If you do a lot of fooling around with guns you might want to get this:
https://www.brownells.com/gunsmith-tool ... ?rrec=true
or this:
https://www.brownells.com/gunsmith-tool ... ?rrec=true

 

[JoeCool]

It might tell you something test firing with a primed case, might as well try it. Be sure you don't leave a wad in the barrel after any testing you do.

I took mine apart to inspect everything. While it was apart, I cobbled up a weaker firing pin spring. I test fired with a couple primed cases and it seemed to function. I will take it out and shoot it about a hundred targets and see how that goes. One thing I discovered working on the M500, an 870 Remington is a lot easier to take apart and put back together.

I was getting an occasional light strike, maybe as often as 1 in 50 maybe as far apart as 1 in 100. What will the test firing show? Who knows?

 

[JoeCool]

It looks like mine is fixed. To review, I cobbled up a slightly weaker firing pin spring, that by wildass guess is about half as strong as the original. Installed it, tested with primed cases, and it gave really deep dented primers. Today I shot 100 targets, using factory STS, Estate, Winchester universal, and reloads with Noble sport 688 primers. All primers were deeply dented, no puny looking dimples at all. All 100 fired. It would appear from this that the overly strong firing pin spring was the culprit in my gun. By the way, it still has the Mcarbo springs in the trigger. I might shoot it again tomorrow and the day after, but maybe not, as it appears to me to be entirely cured, and I usually shoot a Rem V3 at targets these days.

I still have the original firing pin spring set aside, but from my experience that spring will NEVER go back in my gun unless I take a coil off of it. I think taking one coil off and giving it an overall length of just 1/16 inch less than standard will probably do wonders at making the gun more reliable on firing, just my wildass guess.

Mcarbo maybe should include a new firing pin spring in their trigger package. Actually they could probably eliminate the new hammer spring if they put in a reasonable firing pin spring then maybe that stronger hammer spring would not be at all needed. I got fail to fire with the stock and replacement Mcarbo hammer springs, but more missfires with the standard spring, like maybe one in 25-50.

 

[JoeCool]

Interesting that your gun is fixed. Let us know if your gun keeps running well or if it has any more trouble. I might end up sending mine in to the factory simply because it's going to cost me quite a bit just to shoot enough ammo to get a decent sample size.

Yes cost of testing does come in, both in money and time. All things considered, older guns not even using a firing pin spring, time to remove spring and cut off a coil, cost of new spring if you screw up the old one, time and cost to pack and ship stuff to Mossberg, it would appear to me the idea of just cutting off a coil on the old spring is a very low risk and low cost way to go.

I might test mine some more, but maybe not. It was miss firing often enough that it would show up anytime I took it out and fired at least 50 rounds, so going through 100 with no problems and ALL primers being well dented convinces me the firing pin spring was the problem. That could be in error, for some unknown reason. That is the thing about the unknown, you just don't know it.

I do have another bolt coming in the mail. Someone had an unused bolt assembly complete with the plate that it sits on at a really low price on ebay so I bought it. Because I now have an extra bolt assembly coming I might put that one in and try it, also check strength on the firing pin spring on that one. In any event I took one coil off that original firing pin spring that I had set aside, so I have a spare spring that is definitely weaker than the original and it is the spring that gave seems to have given the problem while it was at original length and strength.

So the inspiration might hit me to check this all out further, but maybe not. I intend to go on vacation starting next Tuesday and that could keep me from checking it out some more at least for some time, but who knows?

 

[JoeCool]

Update, my new bolt assembly arrived. This gave me something to test against with my modified one with the cobbled up weaker firing pin spring.

I primed two empty cases.

I fired one in my modified weak spring old bolt assembly.

Then I switched out the bolts and test fired with the new bolt and strong regular firing pin spring.

The difference in the primer strike was huge. The one with the weaker spring had a dent twice as big as the one did with the standard spring.

This tells the whole tale for me. Now I have to take that new bolt out, and put the one back in that gives deep primer strikes.

For me this is case closed. I believe Uly hit the cause when he covered the fact of the overly strong firing pin spring.

 

[JoeCool]

Vast difference in those springs. I would not be surprised if the newer, longer one would work better with a little cut off it. If you load some primers in empty cases and try firing them, you will get a very good indication of the difference in the strength of the primer hit.

 

[JoeCool]

Well, now you have a spare spring and you can chop one a little and still have the other unmodified. Sounds like you should be in business now. Time will tell.