TargetTalk

Gwhite wrote: ↑Sun Nov 22, 2020 10:32 pmI'd be very curious to see a copy of Larry's "Benelli Guide". Can you scan it? This is the first I've heard of its existence, despite having bought lots of Benelli parts from him & visited his shop countless times.

I've got better than that! I have electronic copies that DeAnna sent me ages ago. I'll post them soon - in a new thread because this one isn't about oiling top rounds any more. ;)

Thanks! That would be great! I'm sure there are plenty of others who would benefit as well.

Well, I don't think the buffer is the issue. I brushed the chamber out with a .25 caliber brush less than 150 rounds ago, and I had three malfunctions tonight in 80 rounds, using my daughter's relatively new LGI buffer.

I took it home and took the bolt apart and cleaned off all of the slightly thicker oil I tried recently. I re-lubricated it with Rem Oil and will try again tomorrow.

What's weird is that it went 1100 rounds after modifying the extractor and using Rim Fire Blend to clean the chamber. After that torture test, I cleaned it with Rim Fire Blend again, but my borescope showed that there was still some carbon in the chamber & throat. I tried two different carbon cleaners, JB bore paste and Flitz metal polish. That got rid of the vast majority of the carbon, but now it's acting like the chamber is somehow too clean. Several times the bolt has come back far enough to cock the hammer, but not enough to eject, and then the bolt has closed with a fired case in the chamber.

I suppose it's possible that the case is coming out so easily that the pressure can't build up enough. If that's happening, I may be able to find a slightly stiffer recoil spring. Benelli has used a very wide range of springs over the years, so it can't be super sensitive to that.

Is a bad ammunition batch ruled out? I know mine to like the hot stuff better.

Common here to see model 41 shooters do it as brought up before.

Bob

VonKasta wrote: ↑Wed Nov 25, 2020 3:06 pm Is a bad ammunition batch ruled out? I know mine to like the hot stuff better.

It's the same lot I shot 1100 rounds in it early this fall without any maintenance (not even oil), with NO malfunctions.

I'm beginning to suspect the recoil spring (largely because I've tried almost everything else...). I had a couple more failures this morning, and took it apart for cleaning. The bolt & breech faces were a lot dirtier than I expected for having fired less than 400 rounds. I've seen that before from a weak recoil spring.

I measured the spring, and it is a bit shorter than average (113 mm vs ~ 117.5 mm). It had 60.75 turns of 0.68 mm diameter wire. That is a pretty common turns count, but the wire diameter is a bit lower than average (0.70 mm). The spring constant (force/distance) increases as the 4th power of the wire diameter, so that small difference is a about an 11% drop in force. The outside of the wire was also shiny from wear (although I didn't notice any actual flat spots). None of the parameters are outside what I've measured in the past, but they all tilt in the direction of a weak spring.

I have a spreadsheet I set up with data on 20 different Benelli .22 springs. It calculates the force holding the bolt closed and fully open for each spring. This one comes in at 2.74 pounds closed, where the average is 3.31 pounds.

I'll pop in a stiffer one, and see what happens. The only two new spares I have are really strong (~ 4 pound bolt closed force). I have wondered if they might actually be for the .32 pistol. I also have some used ones that were taken out of service for unknown reasons, and I should have one with some life left in it that is in between somewhere.

Larry's instructions suggest to replace the spring if the buffer looks "beat up". Yours sounds like a good plan.

I've got a 4 pounder installed, and it definitely feels stiffer. I doubt my wife will let me sneak out & test fire it on Thanksgiving, but I'll report back once I have a chance to see how it behaves.

It's interesting that you mention the buffer. I'll have to take a photo the next time I have it apart. The bulk of the damage is a very tidy circular cut where the buffer has tried to extrude itself into the hole in the back of the bolt.

The new recoil spring is noticeably stiffer when dry firing. I practiced 80 rounds with Aguila SV with a hitch. I was prepared for problems from the super heavy spring, but it fed & cycled just fine. The pistol had been thoroughly cleaned & oiled beforehand, so even with the old spring, I wouldn't have expected trouble. Ejection may have been a little more consistent in terms of where the cases landed.

The stiffer springs should actually reduce fouling by allowing higher temperatures & pressure before the bolt opens, so in theory, it should run longer before it needs a bath again.

I will try another 80 rounds in a few days & see how it goes.

So by "4 pounder", you mean the bolt closes with 4 pounds of force, or the spring k factor is 4 lb/in?

I have one brand new recoil spring, I'll be able to check it if that will help.

Four pounds is the calculated force holding the bolt closed.

For the curious, I've attached my spreadsheet. I've got data on about 20 springs from various pistols, spare springs & used springs I've collected over the years. If you got a spare handy and wan to measure it, I can add it to the collection. Counting turns accurately is a pain in the neck, so I made up a gauge:
The biggest two variations in force I've found are from the number of turns, and the wire diameter. The latter doesn't change value a lot, but the force changes non-linearly due to the 4th power effect the diameter has. The spring I removed has a wire diameter of 0.68 mm, where the average value is ~ 0.70 mm. The spring I'm using now has 0.71 mm wire. That produces almost a 20% increase in force.

The number of turns I've run into seems to indicate a design change at some point. There are a bunch that are around 50 turns, but the bulk of them are closer to 60 turns

The lengths are moderately consistent, and tend to run between 110 mm & 120 mm. I don't know how much of the variation is just from age.

I shoot a Benelli MP95, close to the original poster's MP90. I used to place a tiny bit of Pro Shot CLP on the first round every other mag, or once every 10 shots. Then I decided to try what Larry Carter always said, keep the chamber clean! That helped a lot, but it seemed to only last 60-70 rounds. So, I changed ammo from "waxed bullets" such as CCI-SV to the thinner "oiled bullets" such as SK Pistol Match. Haven't had a problem since. Using oiled bullets and brushing the chamber with a .25 bronze brush every 20 rounds and I no longer have to add that drop of oil. Matter of fact, just a few weeks ago I shot in a .22 only 2700 Bullseye match (270 rounds) and did not have a failure of any kind.

I fired another 80 rounds today with the heavy recoils spring. Round #53 trapped the case lengthwise between the bolt & the breech:
I had cleaned it 133 rounds before the jam, when I changed the spring. I've seen this type of jam a few times since I re-ground the extractor, and I have to wonder if the change in extractor tip angle is tossing them up more. I also seem to be getting more rounds visibly going straight up, or worse, bouncing off my head. What I don't know is if these jams are from the case just popping up several mm & getting caught, or if they are leaving the pistol & falling back down into the action. I've had at leas two instances where the case is trapped lengthwise but backwards, which is hard to do if the case never left the breech area.

In any event, I don't think the jam is related to the recoil spring change, and the other types of jams I was getting before that change have gone away (so far). I will continue testing...

That is so weird. Never seen brass in that orientation on mine. And, without a scope riding above the breech to bounce it back down!

Mine throws brass at my forehead too, and never alibis these days. Personally I think the stiffer spring is a mistake, but I'm totally interested in the results.

One observation - yours has the older MP90 square bolt. Mine is the somewhat newer one with the top corners knocked off. It's somewhat lighter. Relevant?

Who knows?

I have a suspicion that they may have lightened up the bolt and possibly the springs when rapid fire went to .22 LR. People immediately started looking for the lowest recoil ammo they could find that still met specs. I wouldn't be surprised if Benelli tweaked a few things to make the pistols cycle well with the feebler ammo.

I installed the stiffer recoil springs and gave it a good cleaning 380 rounds ago. The only malfunction since was the one odd trapped brass after 133 rounds, which I think was a random case falling back into the action. After 260 rounds, I had a league match and brushed the chamber before sustained fire, but didn't do any additional maintenance.

Before the stiffer recoil springs were installed, it wouldn't go more than about 100 rounds before it would have a failure, The vast majority were after the last shot in a magazine. The bolt wouldn't come back far enough to eject, and it would close with the fired case in the chamber. These were often in sustained fire. Based on some recent experience with a MatchGun MG2, I think the chamber was heating up enough that it expanded slightly, and that allowed the bolt to come back before adequate pressure had built up. It may also be that the rapid firing softened up fouling in the chamber, making it easier for the case to slide back. The weak recoil springs make things worse, and pushed it over the edge. This problem also got worse after I had done a super thorough job of cleaning the chamber.

Bottom line: The stiffer recoil springs are a success.

I will continue testing it, but I have another league match this week, and will give it a good cleaning this afternoon.

As promised a while ago, here is a picture of my buffer:
The large circle is from the hole in the bolt, and the smaller circle is from the hole in the recoil spring guide tube. Aside from the circular marks, it's not in that bad shape. I've replaced several that had major chunks broken out.

It's definitely a rubbery material, and not one of the harder plastic ones from LGI. I know some people have had issues with the Benelli buffers, but I wonder if they improved them over time. This might be a newer one.