Minimus Maximus

[datilD]

As a follow-up to my Marauder woes thread https://www.gatewaytoairguns.org/GTA/index.php?topic=128060.0, I decided to start a thread to document the building of a lower power Maximus.  My goal is to have a quiet shooter, with a long, flat, quasi-regulated shot string.

I received my .22 Maximus on June 29.  The first thing that I noticed was that it was shipped in the retail packaging, without an outer box.  The second thing that I noticed was that there was a large hole in the box about where the bolt would be.  When I got the box open, I confirmed that the bolt did make the hole, and the bolt handle was bent to the point where it could not cock the AG.  After several attempts, I was able to get it cocked, but it was a struggle.  A call to Crosman customer support, and a replacement bolt and handle were on their way.  In the meantime, I installed a custom bolt and handle from a project 1322.  It may end up staying on the Maximus.






Having the barrel loose from the tube, I noticed that the valve and transfer port are anodized red.  Nice!  This anodization will eliminate any potential issues with corrosion/oxidization of bare aluminum.  I ordered a few Challenger transfer ports (CH20009-026) to make a smaller transfer port to get the velocity down in the 650 - 700 fps range, giving me about 13 - 15 fpe.  Plenty of power for chipmunk and paper. 

To get the proper port size, I ordered three wire gauge drill bits from ebay to experiment with; #42 (.0935), #43 (.089) and #44 (.086).  I figure that I'll start with a smaller, or mid size transfer port and run some strings over the Chrony.  If I don't like the results, I can drill them out larger.  Looking at a chart that Bob (rsterne) posted a while back, the smaller transfer ports really flatten the shot curve and increase shot count.  He commented that a 0.090 transfer port would provide about 700 fps.  The #43 drill bit should be about right on.  I mounted a transfer port in my lathe, and drilled it to .089".  This is going to be my baseline, and I'll decide if I need to make any changes after a good string over the chrony. 

While I was on the lathe, I figured that I would make a depinger.  After some internet research, I decided on a dam type depinger which is basically a cup with a hole, held in place with an o-ring.  I made it out of Delrin, and drilled a single 3/16" hole in the center.  If I don't like the results, I can always get a Hill depinger in the future.

The stock Maximus trigger is too stiff, even after changing out the spring.  I ordered a Marauder Gen. 1 trigger assembly (1763A105) and a Challenger trigger guard (CH2009-031).  The trigger arrived broken, and I had to place another call to customer service.  I sent pictures of the break, and they are sending me a replacement trigger (not the entire assembly).  I"ll swap it for the broken trigger this week.



The hole closest to the front of the trigger is the perfect location to mount the trigger guard.  I used a 10-32 tap to thread the hole.  A 10-32 3/8" allen screw is a about the right length.  I had to cut a 1/2" screw to size, because I couldn't find anything shorter.  The hole in the Challenger trigger guard is just right for the 10-32 screw.  I love it when things work out like that.




After getting the trigger guard installed on the Mrod trigger assembly, it was time to modify the Maximus stock.  I measured the opening by eye, aligning the trigger with the mounting holes and marking the stock with a Sharpie.  I used a mini hack saw to cut the stock to my marks, keeping the saw parallel to the existing opening.  Once I reached the marks, I cut perpendicular to the opening to make a relief for removing the piece.  A pair of pliers made it easy to snap off the piece of plastic.  It took two cuts to achieve proper clearance.  I used a flat file and small triangular file to clean up the saw marks, and even the opening.  The results are very close to a stock looking opening.  A little fine grit sandpaper, and the cut marks won't show at all.




I finally got my replacement trigger from Crosman and installed it last night.  The trigger pull is really stiff, and I will need to read up on adjusting the pull weight.  Edit:  Found a Tom Gaylord post about adjusting the Mrod trigger.  Simple and easy!


My DIY depinger and polished Maximus hammer.  I got some lathe time on Saturday, and made the depinger.  It is white Delrin, or Nylon.  The red o-ring is a #015 silicone o-ring from a flashlight project.  (My other hobby is building and modifying high end flashlights.)  I polished the hammer with some wet/dry sand paper and Flitz metal polish.  The hammer had some grooves from machining that were too deep to remove with polishing.  I am not going to mess with it now, but a lighter weight hammer is on the wish list.  I will either modify a stock Max/Disco hammer, or build one from Delrin and brass, adding a stroke adjuster.


I am going to make a tool to polish the inside of the tube with progressively finer grits of sandpaper and follow up with the Flitz metal polish.  It should be close to a mirror finish when I get done.  Hopefully I can find some time this week, or it will have to wait for the weekend.

To be continued...

[Radrob]

Thanks for starting this thread, I'll be watching.

[anti-squirrel]

Good pictures and great verbiage.  I'm following this one.

[grimeszee]

+1

[travelbike]

Like the Challenger trigger guard on your maximus !

 I have the Euro Maximus in .177.  It came with the a very low velocity outputting at only 8.5 fpe.  Drilled the transfer port with a 2mm drill or about  .079" (stock was about .05").  Also changed the stock hammer spring with the one used on the Challenger.  Now it outputs about 790 fps on 8.3gr = 11.5 fpe.

Update us please for more inspiration on modding the Maximus.  One thing I've noticed is sometimes the chrono speed would go down maybe 10-15 fps. I feel a slight puff of air coming out of the pellet probe.  Might replace the pellet probe o ring with something thicker.

[Ribbonstone]

 May not help....but I do find having a goal helps me.

So I kind of pick a power level or shot count (or a combination of the two) to try for...pretty much the only way I figure out when to stop; opened ened goals (like "all I can get") tend to keep you modding/working for minimal gains.

Nothing really wrong with that last....if extgending a shot count from 47 to 50 or moving up from 18.1 to 18.7foot pounds  really makes your lights blink, then it's a good thing...and I've done that with some rifles I've pharted around with for years and years....but sooner or later, you just gotta blow the whistle and say "enough".

[datilD]

Like the Challenger trigger guard on your maximus !

 I have the Euro Maximus in .177.  It came with the a very low velocity outputting at only 8.5 fpe.  Drilled the transfer port with a 2mm drill or about  .079" (stock was about .05").  Also changed the stock hammer spring with the one used on the Challenger.  Now it outputs about 790 fps on 8.3gr = 11.5 fpe.

Update us please for more inspiration on modding the Maximus.  One thing I've noticed is sometimes the chrono speed would go down maybe 10-15 fps. I feel a slight puff of air coming out of the pellet probe.  Might replace the pellet probe o ring with something thicker.

I almost bought a .22 Euro, but Crosman wouldn't let me use a coupon code because it is a "custom build".  Instead, I ordered a standard .22, and a load of parts.

May not help....but I do find having a goal helps me.

So I kind of pick a power level or shot count (or a combination of the two) to try for...pretty much the only way I figure out when to stop; opened ened goals (like "all I can get") tend to keep you modding/working for minimal gains.

Nothing really wrong with that last....if extgending a shot count from 47 to 50 or moving up from 18.1 to 18.7foot pounds  really makes your lights blink, then it's a good thing...and I've done that with some rifles I've pharted around with for years and years....but sooner or later, you just gotta blow the whistle and say "enough".

I'll be saying enough, sooner than later.  I am going for 40+ semi-regulated shots at around 13-15 fpe.  The additional tweaks for improved efficiency will be after I benchmark the AG in it's current form.  Basically, I am only planning on adding an SSG, and experimenting with different springs.

[travelbike]

datilD,  can you let us know what pressure range you think your rig is the most accurate.  On my maximus, it seems to be most accurate at about 1500 to 1200 psi.  Thinking of connecting a 13ci ninja bottle at a regulated pressure via the gage port.

[Ribbonstone]

Interrested in how your Maxi turns out.

Admit...I'm a little prod of how the cheap Disco trned out (OK...cheap in the sense that for a long time, there really wasn't a less expensive PCP...today, can think of several that are less expensive).

Worked on my Disco off and on for a long-long time (with months inbetween fiddling around).

No b-staley o-rings/ no anti-bounce device...just trying to blance striker spring strength, lenght, striker weight, and transfer port. Not that there is anything "wrong" with the o-ring mod or anti-bounce systems, they just weren't around when I started and I was too deep in to double back to the beginning.


Left it here for the last couple of years.





Other than the LDC and "extra" barrel band at the rear, it looks pretty much like it did at the start.

[Hoosier Daddy]

SUBSCRIBED!

[datilD]

Ribbonstone, that is one impressive Disco!  I guess that I should expect it will take me months to get things sorted out, too.

[Ribbonstone]

Going to put this in a new thread rather than stepping on yours any more.

Truthfully, do think current versions have had some changes over the years....stringer striker spring, perhaps some valve stem changes, etc....so I don't know "jack" about the current Disco or Maxi.