Saturday, September 13, 2014

Marauder HDD



Preparing My Gen-1 Marauder For Extreme Benchrest
This fall will be my second year at the Extreme Benchrest match in Arizona. I want to shoot better, but I also want my Benjamin Marauder to shoot better.


I Wanted More
Most airgunners would like to get “a little bit something more,” from their airguns. In this case, it is my first generation, .25 caliber Marauder. Marauders deliver a lot more then their $500 price tag suggests, delivering velocity and accuracy close to guns costing two or three times as much, but for my second year of 75 yard benchrest I wanted more.
I wanted more shots per fill from my 3000 psi dive tank, more uniformity, but not at the cost of the Marauder’s 40 foot pounds of muzzle energy.  That is a tall order, but I only wanted “a little bit more”.
This post and two more will be about what I have done to get ready for Extreme Benchrest.




Installing a Hammer De-bouncing Device
I decided to install a hammer de-bouncing device (HDD) from Airguns of Arizona. The  reports I read said that it would deliver more shots per fill as well as uniformity between shots once you shot the gun for a while to mate the HDD to your rifle’s working surfaces. The device’s designer, known on the web as Steve in NC, used steel that would take most of the wear. I also read that some airgunners had been so dissatisfied that they had removed the HDD almost as soon as they had installed it, but my friend Arimo Dave told me to shoot it for a while before making that decision.


On the Internet
After the second day of working on the installation for several hours each day,I posted this on the New Crosman Forum.
“I installed a HCC (the one from AOA) in my Gen I Marauder. It took two afternoons and three tries to get it in and operating. It may require one more time to get it adjusted and working smoothly.
I can see why some folks lose their patience, and take it out, but I had noticed that those who took it out did so promptly without shooting it in place for very long”.
The line was drawn. I wasn't happy with the installation or the results, but I would not let this sucker get the better of me without knowing the reason why.


What Happened?
On the first try, I tipped the HDD over into the space around the hammer. You have to put the gun back together before you can complete the installation, and if it goes south, or at least down there with the hammer, you get to undo all those screws and take the rifle apart again.  



Speaking of screws, I lost the short one that holds the back of the breach to the air tube. It hides under the bolt and must have fell out when I moved the breach/barrel assembly to a “safe” place. I found it after a couple of hours that Steph and I spent searching, sometimes on our knees with flashlights, AND after I had resolved to call Crosman in the morning to order several more. The little screw had been hiding in the towel I placed on my work surface to keep from losing small parts.
On the second try, I got it in, but it fit so tightly I could not cycle the bolt. It had to come out One more time. Once out, I reduced the HDD’s height by 0.005 inch. By this time, I became a pro with the short piece of tubing you have to use to keep that little block of steel from falling into the first level of Hell otherwise known as the space around the hammer.
Once things were back together, I could cycle the bolt, but things would have been easier if I turned into the Incredible Hulk. The bolt’s cycle was not smooth, and the force needed to cock the hammer was out of the question even for a slow fire match, let alone in one where rapid fire was required.


Words of Encouragement From Steve and George
Steve in NC answered my post on the New Crosman Forum. “I'm sorry you're having difficulty with HDD installation, Ron. I know it's no consolation, but that's not the usual experience. Would you mind sharing what part(s)  of the installation were problematic?”
I posted back, “The HDD binding the bolt on the cocking stroke. I had read your (Steve’s) post about the fit of the HDD in newer Gen I Marauders, so I backed off the set screw ⅛ turn and then another ⅛ turn to reduce the Device's height to 0.431 inch. That has helped a lot but the bolt is still very stiff in the last portion of the travel where the magazine indexes and the trigger is set (cocked).”


The First 100 Shots
When I set out to install the HDD, I decided that before I measured velocities or groups I would shoot 100 shots to settle the device into the gun. I had some Beeman Silver arrows that didn’t shoot well at 40 foot pounds that I could use to shoot those 100 shots. The thrill of launching them into the backstop didn’t last long. After two clips I was shooting at 50 yards at a gong made from a one foot length of 10 inch steel tubing. Without  trying to shoot a match group, the next 84 shots hit the bell.



I refilled the gun to 3000 psi before shooting the gong, The first shots were on a parr for velocity with a Red Rider bb gun, but after that the shots kept getting stronger according to the gong’s sound. One thing was sure, my Marauder was way more effecient with air then it was before. 50 shots used up 1000 psi, Before the HDD, I was getting 25 shots from the same amount of air, I got pretty excited thinking that my quest was over.
I got on the phone with George in ID who is a retired engineer and a good sounding board.
“Was it worth it Ron?” asked George referring to the time I had spent and the results I had received so far.  
“George, I shot the last 50 shots on 1000 psi without a serious shift in point of impact”. I was sold on the HDD.
Now that the 100 shots were in the background, I did some chronographing and found that the gun was getting 29 foot pounds as well as some serious valve lock at 3000 PSI. Initial velocities were as low as 296 fps, but within 20 shots that had stabilized in the 650s with 31 gr Kodiaks (29 foot pounds). It was nowhere near the 40 foot pounds I wanted. I didn’t finish this string because the first part was just too slow to be part of the solution I wanted.
The HDD had met my first goal. The gun is pretty stingy on air pressure per shot. In the best part of the string it was using up  25 PSI per shot.
Back on the phone, I told George about the low air use, but also the low velocity, and the force it still took to cock the gun.
Ever the engineer, George reminded me of that  iron clad law of physics, “You don’t get something for nothing. If you conserve air you will pay for it somewhere else,”
I groused about the force it took to cock the gun.
“Well Ron,” continued George, “ your story is taking on tone of other HDD installations that I have read about.” then he added, “Keep at it.  You are just a couple of thousands away from success”.


What next?
My Marauder had to come apart again. I used a new Arkansas stone to polish the sides of the HDD. I could not see any new wear marks on the gun or on the HDD.  I reduced the HDD’s height to 0.430. One more time I had to balance the ball bearing and steel block on the hammer and carefully set the breach/barrel assembly back on top of the air tube without disturbing the HDD or the transfer port.
About the last thing you do is put the bolt in. This time the bolt would not go in. It stopped dead at the point when the shoulder behind the pellet probe came even with the HDD. I cursed the gun, the bolt and that devilish screw that held things together but was out of reach under the bolt. Then it hit me. It wasn't the HDD’s height. It was the screw. That darn screw was tightening the breach down against the air tube, and closing the space for the block to move between the hammer and the bolt. Out came the bolt and I loosened the rear breech screw a quarter turn, Reassembled, the bolt cycled smoothly with only a little resistance from the HDD.
I posted on the New Crosman Forum that I had, “I set the hammer spring to 7 turns CW and the Hammer throw to 4 turns CW for my starting point. I chronographed 24 shots and got the following. Starting pressure was 2600 and ending was 2000.


High V: 806
Low V: 773
Average: 793 (35.5 FPE)
ES: 33
SD: 9”


Steve in NC responded, “Glad you got it sorted, Ron”.
The HDD had made the gun air stingy, as well as lowering the fill level.  I was on my way to what I wanted. Now I had to adjust for a better shot string and more power. Then shoot at 75 yards for the final preparation for Extreme Benchrest. More to come.

Ron