Eliminating the Floating Barrel/Shroud on Mrod

[venxxxxx]

I did just that the other week when I accidently ordered the wrong rings size 7/8id and it fitted nicely inside the barrel band. Btw, it would help too if you put an extra oring to keep the baffles tight from shifting.

[Ribbonstone]

So it's not strapped down with the o-ring, still free to slide in and out from linear expansion. Radial expansion would be minimal as the barrel band is pretty much over the tube end/fill end cap.

If free floating works for you, use it.  If a connected band works, use that. I can't really make a blanket statement that one is "better" than the other, just that on an individual basis one will suit that gun better than the other.

[Frank in Fairfield]

Good idea.
Went to Home Depot.
The rings are about $1.75 for 10 in the plumbing dept.
I took off the clamp, rolled on a ring to almost where it would end up, then put the clamp back on and pushed the ring to its final location.
Rolled in a second ring and pushed them into the clamp with toothpick as suggested.
Then, I wrapped a piece of playing card around the barrel and smoothed out the insertion.
I did this on my .22 and the .177 both of which are zeroed at 20 yards.
The .22 shot about 2 inches high and 1 inch right after installation.
The .177 shot about 3 inches right after installation.
I re-zeroed the scopes.
I think I can see a difference.
Can't hurt anything to try it out.
I know Scott used tape inside the clamp and a little silicone to slide it on the barrel.
Same result.

Good luck.

[RayK]

Hi Tri-Ron and other airgunners.

As you know, I've been struggling with this issue but discussing it on the Marauder Air Forum.

The point is, it still is semi-free floating, but it is now constrained in two dimmensions (up/down, side/side).  It can still move independent of the air tube front/back (with the length).

Neil Clague started this idea over on the Crosman/Benjamin Yellow forum by making solid parts out of aluminum. He believes the o-rings allow too much movement too, but I like your idea and  I will try it out later this week.

I tried making just the outer spacers this weekend out of aluminum tube that was nearly the right size.  They make a clear improvement on both my 25 M-rod and my 22 M-rod.  I also made one for my P-rod, but did not notice much change yet - perhaps because the barrel is so short maybe it is not an issue with the P-rod. I'm still not sure why, but maybe it is only an issue for some Marauders.  I did try the spacer with both shroud 1/4 turn loose and fully tight.  I got more consistent groups with the shroud tight.

I mostly shoot at a minimum of 30 to a max of 50 yards and I use high magnification scopes 21X or 24X.  What I have noticed with my M-rods is whenever I clean the barrel, the POI changes.  As I'm shooting my guns, the POI may change a tiny bit then it will move back to where it was set.  Whenever I transport my guns in a good gun case, the POI always changes a very small amount.  I use good scope mounts (BKL) and good scopes (I've bought quite a few to try out) and have eliminated the scope and rings as a possible source of the issue.

I am very careful never to handle the barrel/shroud (except when cleaning) and never to lean the barrel as some have mentioned in other posts, so that is not the issue.  When I do accuracy testing, I use a solid rest and tether my airgun to a large tank in the sweet spot of its fill range.

I'm still in the testing phase.  I will try your o-rings first, but I also ordered one of Neil Clague's solid aluminum set.  He said he can't get to them for a while because he is swamped making LDCs.

Ray

[mtsheron70]

Tried this and results were not so good.  So until I have a real deviation will keep her a free floater.  But thanks for the write up.

[Fur-n-dirt]

If I'm not mistaken, the reason for the floating barrel is to separate the barrel from the air tube. As the tube is pressurized, it will expand slightly and may move in one direction or the other. As you shoot, you release this pressure and the tube contracts slightly, and once again, may move in one direction or the other. My question is this. If the barrel and shroud are now "attached" to the moving tube, would this not also cause a shift in POI as you shoot? In other words, are you jumping from the frying pan to the fire?

For those of you who have tried the above fix, have you now noticed an improvement in how the gun maintains a steady POI, or are you seeing shifts regardless?

Michael,
You may be correct, in that the reason for the floating design, would be to allow for any air tube expansion.
 (Yes pressurized air tubes DO expand on some degree).

 Of course, the amount of expansion depends on many things.
 These can include, total volume, total length, materials, methods of construction, temperature, and ambient pressure.
 
Example- A DC-10 / MD-11 aircraft "Grows" as much as 4" in length, between sitting on the ground, and flying at altitude.
 (ever wonder why aircraft develop cracks in their structures over time ?... it's not ONLY because of vibrations).

Naturally, the air tubes on our airguns would see VERY little expansion comparatively,... yet it would be, or could be enough to be measurable, and therefore of enough concern in design, to allow for it.

I think that the O-rings would allow for any minuite growth of the air tube, and still hold it steady to protect from any side pressures of forces that might cause the POI to be effected.

I'm hoping to do a multi-day test soon. I may even do a controlled test, with one rifle being "un-modified", (the control),  and the other rifle to be the variable test subject.

I think it would also be interesting to see if other members here could do the same testing and compare results.
(all from a bench rest position, of course)

May I suggest you do the sentivity on one rifle since one rifle will not preform exactly the same as the other.   Really looking forward to checking out the results.

[Fur-n-dirt]

What is the greater evil?   Constraining the barrel on the end drastically changes the dynamic response of the barrel.   The Crosman engineers indended for the barrel to be free floating so, the structural modes would be like a tail wagging, constrained on one end only.  However, if you throw a metal shim sandwiched between the barrel guard, its constraining an additional point on the OTHER side, so the barrel FLEXES differently during the shot.  In this case, the fundamental mode is drastically different and the barrel could flex in an inaccurate manner.   

I am not a gun designer, but it seems that a free floating barrel is better based on firearm experience.  HOWEVER, if the shroud design is such that it causes the barrel to reside in a different position over time due to bumping, gravity, etc..  than it could be better to constrain for POI; however, it would make sense the group diameter could increase.  And POI could slightly change with reduced pressure...

Another idea..   An oring is NOT the same as a aluminum bushing.  An oring is like a spring, if soft enough, it will have less influence as a boundary condition (includes damping) and barrel can still act like "free floating"  versus the aluminum bushing...  If the oring helps position the barrel for "repeatibility" and still generates an approximate "free floating" boundary condition, this might be the best solution..

Hobby foam, oring of various durometers, and metal bushings could very well produce drastically different results..

Just depends on the dynamics...  lots of testing necessary to determine which is better..

I can tell folks are getting pretty excited about the possibility of reducing groups.. I hope it helps...

[Motorhead]

My cure on "NEWER" rifles utilizing the larger clearance barrel supports, is slide off the support and REMOVE the I.D. o-ring.  Then using 1/16" hobby foam ( One side adhesive ) line the I.D. of support with a strip cut to width and length.  End result looks like this  pending color of foam used being it comes in MANY 



Older rifles with the smaller supports, replacing o-ring with a 1/16" x 1"o.d o-ring closes the gap to zero making a nice firm fit eliminating wiggle. 

Excuse me but.... Huh?? Adhesive,colored Hobby foam ??  - What and where please !

1/16" thick 8x10 sheet of Hobby / Craft foam cut to fit I.D. of support 

[Fur-n-dirt]

Hi Tri-Ron and other airgunners.

As you know, I've been struggling with this issue but discussing it on the Marauder Air Forum.

The point is, it still is semi-free floating, but it is now constrained in two dimmensions (up/down, side/side).  It can still move independent of the air tube front/back (with the length).

Neil Clague started this idea over on the Crosman/Benjamin Yellow forum by making solid parts out of aluminum. He believes the o-rings allow too much movement too, but I like your idea and  I will try it out later this week.

I tried making just the outer spacers this weekend out of aluminum tube that was nearly the right size.  They make a clear improvement on both my 25 M-rod and my 22 M-rod.  I also made one for my P-rod, but did not notice much change yet - perhaps because the barrel is so short maybe it is not an issue with the P-rod. I'm still not sure why, but maybe it is only an issue for some Marauders.  I did try the spacer with both shroud 1/4 turn loose and fully tight.  I got more consistent groups with the shroud tight.

I mostly shoot at a minimum of 30 to a max of 50 yards and I use high magnification scopes 21X or 24X.  What I have noticed with my M-rods is whenever I clean the barrel, the POI changes.  As I'm shooting my guns, the POI may change a tiny bit then it will move back to where it was set.  Whenever I transport my guns in a good gun case, the POI always changes a very small amount.  I use good scope mounts (BKL) and good scopes (I've bought quite a few to try out) and have eliminated the scope and rings as a possible source of the issue.

I am very careful never to handle the barrel/shroud (except when cleaning) and never to lean the barrel as some have mentioned in other posts, so that is not the issue.  When I do accuracy testing, I use a solid rest and tether my airgun to a large tank in the sweet spot of its fill range.

I'm still in the testing phase.  I will try your o-rings first, but I also ordered one of Neil Clague's solid aluminum set.  He said he can't get to them for a while because he is swamped making LDCs.

Ray

If a person wanted to test the sensitivity; why not use some "wood" shims to jam between the shroud barrel and barrel guard at three points?   This material is much stiffer than rubber...  and could be very quick.. of course its not permanent..

[joel w]

I think where I went wrong was when the POI shifted after the mod install, I adjusted the scope to the new POI instead of adjusting the o-rings or barrel band to bring the barrel back to zero where it was when it was free floating. 

Shooting with a slightly curved or unrelaxed barrel..

[Motorhead]

I think where I went wrong was when the POI shifted after the mod install, I adjusted the scope to the new POI instead of adjusting the o-rings or barrel band to bring the barrel back to zero where it was when it was free floating. 

Shooting with a slightly curved or unrelaxed barrel..

Indeed, have a material in the gap, barrels is going to be stiff too rotate within support and settle back into it's natural position.
So ... some purposeful alignment to get barrel re-centered over air tube before tightening support set screws is required.

[joel w]

Indeed, have a material in the gap, barrels is going to be stiff too rotate within support and settle back into it's natural position.
So ... some purposeful alignment to get barrel re-centered over air tube before tightening support set screws is required.

So I finally got some .25 pellets in and got to do some testing this morning.  I started with the shroud and air stripper off.  I zero'ed the scope and then put the air stripper on and re-shot and noticed a POI shift to the right about 1/2" at 51 yards. My air stripper is modified with three large elongated holes tapering to the back. I had randomly installed it with 2 holes on the left side and one hole on the right. So I rotated the air stripper so I had one hole on the top and two holes on the bottom to the left and right.  Shooting again my POI was now just a bit high, but re-centered.  (if your air stripper is stock, ignore this part)
 
Now, I installed the shroud, baffles, o-ring and end cap.  This dropped the POI back to where it was with a naked barrel.   From here I installed the o-rings into the barrel band but no matter what I did, my groups were all over the place ranging from 2" -1.5" groups at 51 yards with  25.4g JSB kings.

With the o-rings removed and now back to a free floating barrel my groups dropped to just over .780" or nickel size.
Here is 8 shots at 51 yards in some mild wind.  (more like .845 than .810, I goofed)


5 more shots at 51 yards 20 mins later.  A small POI shift but i think temp has something to do with it.


At 10yds (i said 20yds earlier, my bad) with 5 shots,  there is one single clean pellet sized hole. 


For my Mrod at least, I will stick with a free floating barrel for now.  Maybe try another scope to rule this one out.

[Frank in Fairfield]

Yepper

[Gertrude]

well I am finally going to be able to do some shooting this coming weekend.
Will be heading out to a buddies place in Temecula on friday night or early saturday morning, coming home sunday evening.
I am looking forward to testing out the O-ring idea on both mine and Camerons .22 Mrods.
we will be shooting at various distances, and possibly out past 100 yds.
Hoping for good weather and no wind.

[Frank in Fairfield]

well I am finally going to be able to do some shooting this coming weekend.
Will be heading out to a buddies place in Temecula on friday night or early saturday morning, coming home sunday evening.
I am looking forward to testing out the O-ring idea on both mine and Camerons .22 Mrods.
we will be shooting at various distances, and possibly out past 100 yds.
Hoping for good weather and no wind.

Temecula...No wind? Good Luck. I took the rings out and all is good.

[trinket]

I have never had my POI change from day to day or week to week on my Marauder. Gene said it already but a lot of people do not handle their guns good.

I never grab my Barrel/shroud when handling, I do not lean my barrel or shroud on anything! I have seen plenty of youtube videos of people leaning their Barrel/shrouds on trees, picking their guns up by the shroud, poking dead animals with their gun. etc.

Basically a lot of people are not taking care handling the gun....(I totally trust the free float, I have accidentally bumped the barrel a couple times and it still held zero..... When putting my gun away in the closet it stands up against the wall balancing on the scope turret,butt pad and bi-pod ...3 points of contact none of them the barrel.

Sperho...all the barrel bands have an O-ring....

++++++1

[Scott Endler]

From here I installed the o-rings into the barrel band but no matter what I did, my groups were all over the place ranging from 2" -1.5" groups at 51 yards with  25.4g JSB kings.

With the o-rings removed and now back to a free floating barrel my groups dropped to just over .780" or nickel size.
For my Mrod at least, I will stick with a free floating barrel for now.  Maybe try another scope to rule this one out.

Thanks. Finally some good target shooting to test the theorizing. It makes no sense technically to couple the muzzle end of the barrel/ shroud to the air tube which is subject to differing amounts of expansion from varying air pressure and also from shifting from pressure from different holds on the foregrip. This is the big problem with the Airforce SS rifles accuracy since the barrel is mounted to the shroud at both ends and the foregrip is mounted to the shroud following a fairly flexible frame. The best groups from any air rifle with a long barrel would probably be with the shroud removed. But it is worth it to have something really quiet.
.
If the barrel of a Marauder is really that wiggly in the receiver then the fix has to down at that area. Keep in mind when discussing .22 Marauders that they are notorious for pellet fussy, loose bores, outright bent barrels, and mediocre group sizes.

[Ribbonstone]

Barrel is not hog-tied to the inside of the shroud, so the expansion/contraction aspects should be covered by that "slip fit".

Certainly wouldn't bother trying the shroud o-ring trick on a gun that shoots great and has a stable POI, but evidently not all of them are so blessed.  It's an easy mod that is easily reversed, so worth trying on problem guns.

Would also pay attention to the fixation of the shroud at the rear.

[cooter472]

Man o man did I stir the wrong pot of beans

[Frank in Fairfield]

Man o man did I stir the wrong pot of beans

Yep.
That was last year Tim.
As I wrote in your other post, I have since put the rings back in and I them. I was witness to Scott cleaning the course at the Diablo Range in Concord, CA with his rifle set up with the hobby tape. In fact, I was the scorekeeper and target re-setter. Very impressive performance....