SDB 45 Classic tuning

[Basu]

I was repeatedly telling that SDB requires serious tuning for superlative performance.
I had decided to go with objective of Smooth effortless cocking , easy trigger action and accuracy.
Following products I used to do the tuning :
1) Cherokee 35 spring ( free length 26.4 cms taken,stock spring was 31 cms)
2) Synthetic TTI piston seal
3) TTI Moly & lube
4) Matching OD spring guide
5) One 2 mm thrust washer for piston head
6) 2 piston inner sleeves made from Coke pet bottle
The guns internals and spring was having sproradic rusting.
Used 400 grit to remove all dust/rust from receiver and gave a nice polish to piston bearing area.
I also gave a shining to the spring, both internally and externally.
The trigger is also given a nice polish so that it disengages easily.
Finally I washed every component with kerosene oil and mopped then with soft cloth.
2 sleeves were pushed inside the piston to prevent lateral vibration.
Piston was pushed into the receiver and a bit of Moly was given only on bearing area.
Spring was covered with spring lube and the guide was given a thin coat of moly.
A bit of moly used on piston sear and also on trigger blade.
Then the entire assembling was done .
It is seen that with TTI seal , its swept volume has increased to 44.35 CC.

Testing

1)Cocking became effortless with no scraping sound whatsoever ( approx 9 kgs)


2)Velocity – MSRH-14.0 grns- 453-483 Fps, earlier 495- 553 fps
MSFH- 14.3 grns-433 Fps
NE -10.5 grns-583-608 Fps,earlier 607-625 Fps.
Aimco pointed10.5 grns-548- 583 Fps
Aimco RH-11.6 grns-566-587 Fps,earlier 605- 635 Fps.

All above datas are of cronoconnect Samsung Tab 2

Extreme spread found to have gone higher, guess it is due to the new spring only.

3) Vibration-----MSRH-14.0 grns-3.8 Richter, earlier -4.3 Richter
Aimco-11.6 grns-4.3 Richter, earlier -5.2,5.3 Richter

Tremendous improvement in vibration being observed.

Accuracy
SDB was very accurate from beginning. Now the consistency have improved quite a bit .
I can hit a 3” wide bamboo at a distance of 27 Mtrs repeatedly.
At 10 Mts , a tooth paste cap can be hit with a little support almost regularly.

Trigger

Trigger, 1st slides and then breaks crisply.It is no more issue now.

Sound

SDB 45 Classic is a very quiet gun and it has become even more quiet .
( 74 decibals , 5 mtrs away from muzzle by Sound meter lite android application )

My objective to have a gun with reasonable accuracy, power and smoothness, is totally fulfilled.


Basu

[brihacharan]

Hi Basu,
> Great work on Tuning
> Wish to know where have you exactly inserted the coke pet material on to the piston?
> Normally these thrust bearings are put at the fore end & rear end of the piston by cutting a groove on the piston surface - is that what you've done?
> Frankly with what you have done you should be getting an fps of 550 to 575 (with 14gr pellets) which should give the AR smoothness, less vibration & good accuracy!
> BTW - if you are solely using the SDB45 for plinking / target shooting then - better stick to Round Heads & Flat heads.
Happy Shooting
Briha

[Basu]

Dear Briha,
The sleeves were cut to proper sizes to fit inside wall of the piston,leaving the slot.The top most sleeve's end is cut & folded to anchor on the base of piston top.A thrust washer is put through the sear rod that held the sleeve at its place. This washer also helps spring to take easy torque.
MSRH does not fit well but MSFH sits well at breech.
This gun gave maximum velocity of 635 fps with 11.6 grms AimcoRH, clocking 10.38 fpe.
I do not think this gun can deliver in excess of 10.5 fpe any day.
Hitting 3" wide bamboo with local pellets at 27 mts with peep sight ,is clear indication of its accuracy .
Extreme spread found to be higher than earlier.To reduce that the spring was scragged for an hour.Hope ES will be further narrowed down after firing 500-1000 shots.
I must mention that quietness is outstanding feature of SDB 45.

Basu

[brihacharan]

Hi Som,
> Thanks for the clarity in answering my queries
> Agree with you 100% that accuracy & shooting pleasure scores over velocity
< Enjoy your shooting!!!!
Briha
PS: My only concern is that the folded portion of the piston sleeve should not tear with the piston's impact after say ...100 to 200 shots, thus fouling the piston interior to cause interference of the spring's movement ... Your Opinion please.

[FN-Five-Seven]

I am a novice when it comes to Air Rifle / Air gun tuning , so this is my understanding .

Installing the aftermarket spring (Cherokee 35 spring of length 26.4 cms as opposed stock spring was 31 cms) reduced the FPS of the pellet . Hence the accuracy of the rifle increased . Also the use of better lubricants made the rifle quieter and the vibrations has reduced . In what did the nylon/ synthetic piston seal contributed to the overall performance of the rifle as opposed to the leather seal ?

Also is the aftermarket spring ( Cherokee 35 ) , the sythetic pistol seal , lubes etc available in Calcutta or are they needed to be ordered from Target Tune India online ?

F-N-Five-Seven

[Basu]

Dear Briha,
You raised a very relevant point.
I also wondered whether pet bottle material would be
able to withstand the transverse vibration, imparted by
spring.
Before hand , I had used the same in my other two guns
and both of them have gone past 4000 shots without any
sound or problem.Having experinced that this time also I went for the same stuff.

Dear FN- Five-seven,
Cherokee 35 spring is available almost all Gun Shops here in Kolkata.
My gamble was that how much of its to be removed to get best shooting pleasure.
Moly, lube and piston seal are to be sourced from Target Tune India only.
I do not think they have any agent in Kolkata so far.
This tuning is done with many aftermarket products, all have contributed in their own way.
Main effect of seal found to increase the swept volume to 44.35 cc
and with much shorter spring it could able to deliver velocity of 608 Fps as against 635 Fps.
A lose in velocity was on the card, but it is only 27 fps but the gain
in overall performance is phenomenal.

Basu

[brihacharan]

Dear Briha,
You raised a very relevant point.
I also wondered whether pet bottle material would be
able to withstand the transverse vibration, imparted by
spring.
Before hand , I had used the same in my other two guns
and both of them have gone past 4000 shots without any
sound or problem.Having experinced that this time also I went for the same stuff.

Dear FN- Five-seven,
Cherokee 35 spring is available almost all Gun Shops here in Kolkata.
My gamble was that how much of its to be removed to get best shooting pleasure.
Moly, lube and piston seal are to be sourced from Target Tune India only.
I do not think they have any agent in Kolkata so far.
This tuning is done with many aftermarket products, all have contributed in their own way.
Main effect of seal found to increase the swept volume to 44.35 cc
and with much shorter spring it could able to deliver velocity of 608 Fps as against 635 Fps.
A lose in velocity was on the card, but it is only 27 fps but the gain
in overall performance is phenomenal.
Basu

Thank you Basu
Briha

[captrakshitsharma]

Pics?

[Basu]

The pics for parts are not taken.
Yet if you want to see the rifle please see the thread "SDB air Rifle"
under airgun section .


Basu

[Basu]

Just an update.
After the tuning, unfortunately the Cherokee spring broke and I resorted to stock spring after removing one coil.
Velocities as follow :
MSRH- 480 fps
AimcoRH- 600 fps
Aimco pointed- 550 fps
NE- 615 fps
Maximum energy output is 9.6 ft lbs with AimcoRH.
My considered opinion is that SDB 45 can not be asked more to deliver.
All above datas are of Cronoconnect in conjunction with audacity.

Basu

[bennedose]

Basu my SDB 50 felt so sick after a Cherokee spring transplant that I cut off 6 rings. After that it is sweet and smooth and delivers about 480 fps wih light (700 to 750 mg) pellets.Most important it regained its accuracy which was lost after spring change. It remains accurate up to 25 meters at least.

[Basu]

As per my experience Cherokee 35 is the worst suited spring for Deshi gun if used total free length.
With that, one can hit every where except centre.
It rattles the gun so much that all nuts and bolts fall off.
My choice always have been Cherokee 27.
You did the right thing by removing 6 coils.
Since you have leather piston seal so 480 fps is good.
Had you ured synthetic seal ,some 40 fps is on the card.
Accuracy and smoothness is most important, I totally agree.

Basu

[harshvardhan]

Whatever spring you use...please provide front and back washer in both the ends of spring ,
also give a very good polish to both the ends,so that the spring can take the torque smoothly

A good spring not talks in terms of velocity.it talks in the form of standard deviation...
I am getting 530-545 fps in Aimco Round head by using only 30 coils Cherokke Spring..
And absolutely no effort for cocking...Butter smooth trigger..and accuracy.sometimes even i Cant believe....
I think the spring is of 38.5 coils...so i have removed 8.5 coils....
Short spring ensures less vibration area and if one wants to increase power..than it can be
achieved by adding pre load at back of the spring...

[brihacharan]

Whatever spring you use...please provide front and back washer in both the ends of spring ,
also give a very good polish to both the ends,so that the spring can take the torque smoothly

A good spring not talks in terms of velocity.it talks in the form of standard deviation...
I am getting 530-545 fps in Aimco Round head by using only 30 coils Cherokke Spring..
And absolutely no effort for cocking...Butter smmoth trigger..and accuracy.sometimes even i Cant believe....

Whatever spring you use...please provide front and back washer in both the ends of spring ,
also give a very good polish to both the ends,so that the spring can take the torque smoothly

> You are very right Harsh...Torque being a tangential force can cause 'eccentricity' in the spring's travel - resulting in vibration.
> Those innocent looking washers do play an important part in minimizing 'standard deviation'
Briha