The Ruger 10/22 is and has been my bread and butter firearm that I have suppressed over many years.
In New Zealand most Gunsmiths have threaded the muzzles for a muzzle can. This type of suppressor requires sub-sonic ammo, but the 10/22 was designed for the high velocity ammo. Hence it may not cycle reliably out of the box with sub-sonic ammo. This is were I had to design a porting or a gas bleed off system that would reduce the velocity of high velocity ammo, and still cycle the semi-auto action 100%.
 
  This is a Muzzle Can fitted by means of a 1/2" x 20tpi thread.
 
  Above a full suppressed Ruger 10/22
 
  The new "Silent Stalker" fitted on a Ruger 10/22 with a Volquartsen carbon fibre barrel.
This model screws onto the 11/16 x 20 tpi muzzle thread. No modification required to the rifle.
Sound Signature of a fully suppressed integral barrel model.
The "Silent Stalker" was designed for the 223 Rem. 32mm Ali tube, 150mm in front of the barrel & weighs 400 grams.
Seals on the rear of the tube to the barrel by means of 2 "O" Rings. No porting required.
 

The following Article was sourced from the English Mag. GUN MART. September 2002, page138. 
Please note that the Author of the following article didn't test the rifle with the ammo that it was built for. 
ie. 22 Hi-Velocity ammo that has a muzzle velocity of 1280 ft/sec. This is the common HV hollow point ammo that out of the box the Ruger 10/22 cycles 100%. That's why the manufacture ports the barrel so that the rifle will cycle 100% and reduce the velocity to below the speed of sound. Stinger at 1400ft/sec will leave the muzzle supersonic.
 
KEEPING IT QUIET. 
Our resident expert on silencers, Bruce Potts, tests a Ruger 10/22 rifle, fully sound moderatored by 
PES Suppressors.
 
Everone is familiar with the prolific Ruger 10/22 arguably the best selling 22 rimfire rifle in the world, and because of it's phenomenal success there are hundreds of aftermarket accessories to enhance the little rifle's performance.
 
Nevertheless, I must be the only man on the planet not to have shot one until a month ago. I have never liked semi-auto, despite owning a ratty BSA Armatic, but when I picked up a PES version of the 10/22 from JMS Contracts, I had to redress my views somewhat. OK, this is certainly no ordinary 10/22 and in fact that it sported a fully silenced barrel is the only reason I really looked in the first place. But having traipsed around the fields with it over the past month I have grown very fond of it.
 
Most 10/22 owner buy a new gun then throw half of it away and add custom parts to get it to shoot anything half decent. 
The model I was testing had a standard trigger mechanism, but sported the very tacile and ergonomic (and lets face it- cheap) Hogue over moulded rubber stock. The other non-standard feature was the fully silenced barrel that from first glance looked like a heavy 'varmint/target' style barrel. But on closer inspection you could make out a thin line slightly forward of the chamber area that marked where the shroud and the barrel joined.
 

 
Construction
 
Total length of the PES suppressor from front of the receiver to the muzzle is 17.5 inches of which 15.75 inches is shroud. By twisting the shroud clockwise, it can be unscrewed from the barrel beneath, revealing the barrel porting and the step muzzle to aid location for the front end. Barrel length is 13.5 inches from the receiver and is turned to a diameter of 0.5 inch. There are 16 x 1mm holes spaced around the barrel circumference, with two sets of holes being slightly staggered forward of the others to give an even bleeding off of the gases. All the machining is first class with well cut thread and precise holes, all in all very well engineered. The shroud itself contains four standard baffles in a series at the muzzle end, these are held in place by a knurled cap and can be easily removed for cleaning, There is also a blast baffle that deflects gases back down the inner surface of the shroud and this has mesh wire filler for the remainder of it's length. This helps to dissipate gases further, especially the gases emanating from the 16 bleed ports. It's a wonderfully effective system that sounds complicated but is easily maintained and largely trouble free- just check for rusting in case condensation as the rifle is brought from outside to indoors. 
The rest of the rifle is pure 10/22...i.e. sloppy! a single extractor was never enough, the action is noisy, and the trigger pull and lock time are how can we put it... leisurely. However, help is at hand in the shape of Roger from South Yorkshire Shooting Supplies who supplied the Hogue stock. Most standard problems can be ironed out by fitting custom parts but as a complete package the rifle shot very well.
 
Fully Suppressed 
The advantage of a full shroud sound suppression system should be obvious to all. Most rifles that have a standard moderator attached to the front of the barrel suffer from that all too familiar problem - unwieldy length, causing the rifle to feel front heavy. At one time the only way around this was to shorten the barrel, then re-cut a thread at the muzzle for a screw on moderator. Having a rifle with a full- length silencer that shrouds the entire barrel allows the rifle to stay the same length and, more importantly, handling is unchanged. 
How much noise reduction you get depends on many factors, but certainly a gun with a full length shroud moderator offers the best noise level reduction available. In fact there is only so much noise you can reduce before the noise of the action and firing mechanism becomes louder. At this point, "total" sound suppression is at it's limit. 
Needless to say this is exactly the category into which the PES 10/22 falls, total suppression - all you hear is the noise of the bolt slamming back and forth when your using sub-sonic ammo. In fact, the PES system is so efficient that even standard 1250fps velocity ammo is reduced to almost the same level. How can this be? How come you you don't get the supersonic crack associated with standard ammo? Well, not only is the barrel fully shrouded with a convention baffle stack up front, but as mentioned before, there's also a series of 16 precision cut holes that port the barrel just in front of the chamber area. 
This porting bleeds off gases shortly after ignition and as the bullets passes each hole around the barrel circumference a little gas is bled off into the shroud. The result is that there is a small reduction of overall velocity as the bullets passes up the barrel. This means that a sub-sonic round starting at 1050fps will be reduced to a velocity of approx 910fps at the muzzle. Ok, there's no real advantage there, as sub-sonics are quiet anyway, but at this level they are even quieter and the combination of the huge shroud expansion chamber coupled to the stack of convention baffles up front make for a phenomenally quiet rifle. The only disadvantage is that certain sub-sonic ammo does not cycle an un-tuned 10/22 action all that well. Some makes do, but the majority wil not. When running standard velocity ammo through the rifle, say Elley EPS at 1085fps, there is a reduction of 140fps to a figure of 945fps, well below sub-sonic noise level and the rifle is again totally quiet, yet the semi-auto action functions far better with the initial extra 'oomph' from the standard velocity ammo. The only disadvantage is that most standard ammo is target grade and uses a a solid head, not designed to expand on game, and so over penetration and ricochets are a distinct possibility. This might be Ok in New Zealand - where PES suppressors come from - with all it's acreage, but it could prove dangerous in the UK.
 
However, when you step up to High Velocity (HV) ammo the noise level is reduction is still excellent, because you are suppressing all the expanding gases and eliminating the muzzle blast noise. The porting reduces the muzzle velocity to sub-sonic level. This type of ammo comes more readily in hollow point and is the preferred option.
 

 
Ammuntion 
I tested a wide range of subsonic ammo- Eley, Winchester, CCI, Lapua, PMC and RWS as well as some CCI CB Longs - to check for accuracy, reliabilty in feeding and noise levels. 
The most accurate by far were Eley - no surprise there then, as they are my favourite anyway. They shot 0.25-0.35 inch groups at 30 yards and feeding or cycling the action was 100%. Next best were the RWS that shot slightly larger groups, not much, but with the lower velocity averaged failed to cycle 50% of the time. All the others were much of a muchness really, with cheap old PMC shooting quite well, but still having function problems. I know a lot of people use Winchester but this particular rifle did not like them - accuracy was poor and functioning was iffy to say the least. I'll stick to the Elley subsonic. I was quite surprised that Lapua shot poorly, as this usually shoots nearly as well as Elley, but every rifle has individual preferences and another 10/22 will probably shoot this array of ammo differently anyway. Always check your own particular rifle to ascertain what ammo suits it best. 
As for standard velocity ammo, I used Elley EPS and Remington Target, as that was all I had at the time. Both shot the same in terms of accuracy and velocity, and cycling of the action was flawless. However, both are solid nose projectile and so this rather negates their use against live quarry. 
High Velocity ammo was confined to Stinger and Elley Scorpion, as I do not usually use HV ammo. However, both shot very well with 0.5 inch groups, and that extra poke ensured trouble free functioning. For those who require that extra yardage from your gun then these would seem the logical choice. But the real interest obviously was the noise reduction of this suppressed rifle over a standard model.
   
    
 
Sound Results 
Ambient background was about 50-53 dB and un-silenced Elley subsonic recorded 104.5 dB. Using the same Eley ammo in the fully suppressed 10/22 rifle by PES gave a diminutive reading of 87.3 dB. That's a 17.2dB reduction in noise level, which, considering that sound level reduction is logarithmic, is superb. To put this into context, a standard Sako rifle with a conventional silencer system attached via a muzzle thread gave a good account of itself at 93.5 dB, which is a good reduction in noise, but nowhere near as good as the PES suppressed rifle. The High Velocity tests showed un-silenced Stingers gave a reading of 119.0dB and fully silenced 105.5 dB, a very good 13.5 dB reduction with High Velocity ammo nearly bring it down to subsonic level un-silenced, now that is very good. (To give a correct comparison the HV test shooting was into straw bale to stop the sonic crack).
 

 
Conclusions
I took this little rifle out on many occasions and unexpectedly fell in love with its lightweight and superb handling. Every shot from the rifle went where I aimed it and don't those rabbits know it! It was so quiet that all you could hear was the action bolt slapping back and forth and that was quite noisy.
Functioning was flawless and the stealth of operation had many bunnies running toads me as the Elley Subsonics struck their buddy. This is because the sound of the bullet strike on the target had them running in the opposite direction. That fairly illustrates the advantages of having a suppressed rifle of any sort, as your goal is to fool your quarry and as the PES suppressed rifle works a treat, in fact, it has got to be the quietest rimfire I've ever shot.
 
For further information on PES moderators, contact Julian at JMS Contracts on 01273-846470 or fax 01273- 841397, mobile on 07771-962121 or e-mail at julian@savory.free-online.co.uk