CMP 853 Wow! and huh?

[dukja]

Just got a CMP 853 with MC stock.  It was much heavier than my expectation.  I was used to 880 even with a 4x30 scope.    I wonder if CMP weight down 853 or not?

This 853 can take quite some cleaning and oiling.  The sponge ring was quite dry.  After clean down and put a cheap scope coming from 880 (just for a quick test), I shoot it with some Crosman Premier pointed pellet.  And I was shocked!!  It takes no effort to make 1-hole group at 10m.  So easy!!  In comparison, my 880 was really struggling and can only match it on a good day.  Wow!!

However, I did notice that upon firing the scope (4x15 Daisy scope) seems to shift down. Huh??  It is not due to pellet kick but a very consistent "sinking down" motion for about 1 mil dot distance.  It presents in every shot.  And my left hand touching the pump lever can feel that the lever is also moving forward at the same time.

I would appreciate if anyone has experience such thing and may let me know if it is an issue or not.  Thanks a lot!!

[ac12]

If you think the wood stock is heavy, try the plastic stock of the 953.
I replaced the wood stock of my 853 with a plastic 953 stock to get the additional weight.
In target shooting, weight is your friend.

I shoot my 953 and 853 with diopter sights, so cannot comment on your experience with the scope.  However, while there isn't a recoil shock from shooting, there is a shock when you charge the rifle (from the lever snapping shut).

I think your 853 probably has the trigger mod, since you can shoot that well.
Otherwise the stock x53 trigger 'stinks.'

[dukja]

Thanks a lot for the reply!  The weight is actually more at the forearm or maybe the muzzle weight.  The stock is actually not too heavy to me so it is more muzzle heavy when I got it.

As for the scope mount "sinking" motion, that may be hard to detect with the 5988 type of rear sight.  I am using the same fore and rear sight in my 499B.  However, my under-corrected eye (need new glasses until insurance allows) cannot see 10m target without magnification. 

However, my first detection of the shift is from my left hand supporting the forearm.  My palm can feel the motion/shift upon firing.  It is not from the shock of firing mechanism. My current theory is that the cocking shift "something" inside the receiver and the firing relax "it" down.  I'll try to call CMP before working on it.

The trigger may be modified already since it is pretty light and crispy.  Comparing to my other guns, the trigger performance is about:
modded 880 <<< modded 1377 << (mod?) 853 < 499B

I'll appreciate it if someone can share about the "shifting" concern.  Thanks!

[ac12]

When you fire, the only thing moving is the trigger mechanism, the hammer and the valve opening.  Nothing in the forearm should be moving. 

I looked at my 953, and the only thing that I can think of is the latch for the charging handle.  If it does not lockup, then the charging handle can move about more than one would like it to.

The other thought is that the receiver is not seated SOLIDLY in the stock.
Check the rear screw.
Be careful as the receiver is pot metal, NOT steel.  So tightening it too much could strip the threads.

[dukja]

Thanks a lot for the idea.  It seems not only the scope mount move, but also the pumping lever.  So if one use the "Olympic style" skeleton support and use the bottom of the lever to sit on the top of fist, he/she will feel such movement as well.

I have found one post at Targettalk
http://www.targettalk.org/viewtopic.php?t=42586
mention exactly the thing I feel.  Here is quote:

When shooting standing, my son places his support hand directly in front of the trigger guard and under the pump lever handle. He stated that the "gun moves when it shoots" this way causing him to question his shot call.

I've shot it a bit too with this hold and the gun does move over the handle after the trigger break.

Interestingly, this movement seems to happen after the pellet leave the muzzle, since it does not affect the accuracy.  I still got one-hole group with RWS Superdome very consistently.

I have call CMP and Tom suggest me to tight down some screws.  I tightened the one after trigger guard and two (on both sides) of the forearm.  However, it does not help.  Also, if I only cock the hammer and pull the trigger, there is no such movement.  The gun has to be pumped to feel the effect.

I'll try to disassemble the gun when I have a chance to do so.  But from what I can see from the maintenance PPT, I have no clue at this moment.

[ac12]

The charging lever is NOT FIRMLY held to the rifle. 
Both of mine have side-to-side play in the lockup.  But that has not bothered me.

[dukja]

No, I was not referring to the side-to-side motion, but an upward movement synchronized very precisely with the trigger break.  I have looked the photos in the 853 repair PPT again.  Now it seems to me that the movement should be between the internal gun and the wood stock.

Maybe the internal was not hold rigidly with the stock by screw due to the gap between screw holes on the stock and the screw size.  The screw at the back of trigger guard may not be enough the hold the internal and stock together.  So the firing of the valve move the internal up against the wood stock.

I'll try to disassemble the gun tonight.

[ac12]

The fit of the receiver/trigger housing into the stock may indeed not be tight.
Using some paper or brass shim might work to tighten up the receiver into the stock.

Take a look at the bottom of the receiver and the matching part of the stock.  And along the bottom of the inside of the stock.  There may be flashing or wood that is sticking up, preventing the receiver from seating well in the stock.

Again, be very careful on tightening the receiver screw, behind the trigger.
I was looking at some repair pics.  It appears that the rear screw is held by 2 parts; 2 metal fingers from the receiver on the right, and  on the left by 1 opposing plastic finger from the right side plastic receiver cover.   The 3 fingers squeeze in on the screw.  If it strips, replacing the plastic receiver cover might fix it.  But without disassembling my rifle I can't tell which part is threaded; the 2 receiver fingers or the plastic cover finger.  My parts diagram does not show the cover by itself, so I do not know if you can order just the plastic cover.

I could be that the threading is already partially stripped, causing the movement.

The design does not lend itself to solidly tightening down the receiver.

[dukja]

I disassembled the gun and immediately identify something that may or may not be the source of problem (see photo):
* The long screws fastened the internal gun to the wood stock has been bent.  I can see that under some tension, the screw will turn and make the internal gun shift inside the stock.  This is my main suspicion.  Looks like I need the parts 853-7.

* The "barrel seal" according to the Repair PPT (slide 22) is missing, which is the spacer between barrel and the valve body/frame.  This may affect the barrel stability.

* I also found out there is an gap between the abutment of the barrel and the valve body.  I am not sure if that matter.

I'll contact Tom at CMP to see if I can get some replacement parts from them.  Any comments on those observations are welcomed!

[dukja]

I got the new screw set from Daisy and put them on.  They do not solve the problem completely, but they did change the behavior.  I now conclude that the shifting or movement is probably due to the age of the screw holes on the stock.  They have been somehow enlarged, which compromised the tight fit between inner gun and the stock.  Also, the screw may have been reach the end of thread at the nut due to the flexing of the stock.  I'll try to find some washer small enough to fit in to see if that will help.

O-ring problem:
Also, in the process I realized the pump tube has quite sharp edges.  The "U-shape" cut-out actually chips off the O-ring gradually.  I can see a visible damage on the o-ring already.  Some internet page mentioned the 19x1.5mm O-ring from NAPA.  But mine measured as 24x2.5mm.  I did find an almost exact O-ring from NAPA.  The part number is 116.  I smoothed out the edges of pump tube and replace the O-ring.  The chrony data shows that the velocity has increased from about 440 fps to 490 fps.  And the O-ring is now safe from the razor edge.   

Pellet test:
I was pretty happy with RWS Superdome.  After I did all the fixing, I tried Superdome, Meisterkugeln, Crosman pointed, and Gamo Match.  I was pleased to find out that 853 is not too pellet sensitive.  All of them are doing well.  Due to my benched stability, I cannot clearly say which one is the clear winner.  However, I think even the low cost Crosman Pointed and Gamo Match may be sufficient for my standing offhand practice.  And I also tried some reused H&N Baracuda Green.  They actually group not too shabby at all.  I am really excited about this since I may get another one to use these lead-free pellet indoor in the Summer time!

Conclusion:
While the CMP 853 is certain a low-cost solution, it is not trouble free.  Some may have the luck to get a descent one.  Others may find that they need to spend time working on it.  Now I am thinking either join some CMP affiliated club in order to purchase a new 853, or I just wait for the 753 with synthetic stock (cheaper) available.  These 8/753 are fine air rifle to keep.

[dukja]

After I added some washers to the long screws, the whole gun gain much more solidified feeling.  However, there is still some minor movement that can be seen via scope.  The amount is reduced a lot.  And if I use skeletal support holding on the pump lever, there seems to be even less movement.

Here is some benched test shots at 10m.  The 1st and 2nd rings are .125" and .425" in diameter.  The Gamo Match pellet shocked me in this run of test.  Single hole!!  However, after multiple runs of tests it seems the Superdome has best consistency.

[ac12]

Try a few more wadcutter pellets.  You want as clean a cut as you can get on the target, as it makes scoring easier.

The rifle you are talking about is the 853CM, an 853 with the plastic stock from the 953.  But it seems to be discontinued.
https://www.pyramydair.com/product/daisy-avanti-853cm?m=1000

You can buy the 953 plastic stock, and put it on your 853.  That is what I did.

[dukja]

Both Gamo Match and RWS Meisterkugeln are wadcutter.  And I appreciate the clean cut.  However, after 2~3 pellets, even wadcutter can rip the target to a stage that is hard to tell.

The one I am thinking about is Daisy Match Grade Avanti 753S
https://www.pyramydair.com/product/daisy-match-grade-avanti-753s?m=144
PA still has the woodstock version.  I tends to shoot my rifle instead of staring at it so I would rather save $150 for pellets.   

And this is my CMP 853:

[JMJ in NC]

dukja,

I have a CMP 853 with the Monte Carlo stock as well. The action, barrel, and stock that you have are identical to the 753. The 753 just has a lighter barrel weight and better aperture sights. If you're shooting with a scope, there is no need to "upgrade" to the 753.

If you want to upgrade to the 753 sights, the PN's you'll need are 5996 (rear) and 5901 (front sight with barrel weight).

If you want a plastic monte carlo stock, you can buy it from Daisy (PN 138448-000) or track down a 953 (discontinued). The lighter barrel weight only is 154518-000. An old order form is attached for pricing, though some PNs might not be on there.

I upgraded my sights to the 753 version and did some other mods to make it fit me better. I shoot RWS Basic, Hobby, and Meisterkugelns exclusively. Great backyard shooter that I will be passing down to my kids.

Here's mine.



JMJ

[dukja]

Thanks a lot for the good info.  I did understand the difference of 753.  The reason to get it is that it is the ONLY new 8/753 available to the general public.  I know CMP still sell new one but I will need some club member associated with them, which I don't have any.

I would like to get a new one just to see if it is any better (in terms of the shifting/moving issue) than my current CMP used 853. 

Or anyone know another SSP as accurate as 7/853?

And I would love to use the global and aperture sight as soon as I get my new glasses next year.     I am using 5988 and a global site on my 499B for 5m shooting.  My current vision is just good enough to use that sight at 5m.   10m will be hopeless with my current glasses.   

I'll try RWS Basic and Hobby later.  Meisterkugeln is not doing any better (actually slightly worst) than Gamo Match.  Although sometimes Gamo is hard to fit in the barrel, but I was pretty surprised to its performance with such low cost.

And you got a very nice stock to look at.   

[Underdog]

To test pellets, bench rest the rifle and shoot groups of five or ten at 20 or 30 yards. That'll give a better indication what the pellets are actually doing.

[dukja]

Since my application is 10m target, so I test it at 10m rested at bench.

[Underdog]

Maybe so, but IMO the longer distance will give you a better idea which pellets are performing better. At 10 meters, just about anything will shoot ok.

[dukja]

Then it is a blessing, isn't it.  Cheap pellets are always welcomed!! 

On the other hand, "OK" is not good enough for Olympic game, right?  There is always room to be picky.     Using my previous shot photo as an example, the rest of pellets are poor.  RWS Superdome was OK, and Gamo Match is excellent. 
(But this is just one data point.  It does not mean Gamo is always better.  I have Crosman pointed group exactly like Gamo in this photo in the past)

[Underdog]

Then it is a blessing, isn't it.  Cheap pellets are always welcomed!! 

On the other hand, "OK" is not good enough for Olympic game, right?  There is always room to be picky.     Using my previous shot photo as an example, the rest of pellets are poor.  RWS Superdome was OK, and Gamo Match is excellent. 
(But this is just one data point.  It does not mean Gamo is always better.  I have Crosman pointed group exactly like Gamo in this photo in the past)

I quite agree. I like that I can shoot just about anything in my 1322, because realistically, I'm not going to be shooting 20-50 yards with it... But I'm going to test pellets regardless, and start using the best ones...