Basu wrote:Dear Prashant,
Hope it is quite a few months since you bought Sport.
Factually that is my most favoured AR among SDBs.
Wish to hear a general assessment after some use.
Basu
Dear Basu Da,
Thank you for nudging me on to take on Sport yet again!
First things first….It now seems to me that you were absolutely right when you had advised me during the last tune up to settle with a spring length of round 245mm (I had gone for 255mm, if you recall!). We will soon see why!
Second, ….I had noted somewhere in the original post in this thread that the SDB folks seem to have kind of finally arrived (that is, in terms of getting the knack of designing fine shooting air rifles….). And my new experience with Sport ….and the fact that the new spring SDB has installed in Sport is a softer and longer spring only testifies to that!
For the benefit of our readers, here’s a little update on the last tune of my Sport. I persisted with the old stock spring (My gun had the old 3.16mm wire spring). With the new seal, in a freshly setup new action, it gave one of the snuggest and solid shot cycles…dishing out 10.3 to 12.8 fpe of ME with various pellets. Almost all Precipell pellets and the lighter GECO were among the most accurate, too. The energy efficiency ranged between 30 to 38%. Noting it all on a public forum here, I feel relieved that one of our well-received members had personally tested the gun at a local shooting range in this tune and had given it full marks!
And now the climax! …….
For the last several weeks (by when the gun would have shot some 300 pellets or so…), I noticed some erratic behaviour, in that its accuracy sometimes ended to get whimsical. I first attributed it to myself –it could be anything…a shaky pair of hands, tentative state of mind, and what not! Nonetheless, But I was becoming suspicious. Got buy with projects on other rifles, and Sport took a back seat. Your query got me back to it. And when most folks were busy with Holi, I got busy with my trademark accuracy testing (old-fashioned style, some would say…but it is spot on!)….and here is proof of its whimsical accuracy behaviour. Put simply, the gun in this stiff tune has become highly hold sensitive!
IMG_20190321_141129-A.jpg
Watch the groups carefully! I use three grips to conclusively ascertain the exact state of hold sensitivity of a rifle in any given state of tune – Rested-Unrestrained, Rested-Guided and Rested-Restrained (which is akin to the field shooting hold)! In this case, only two grips got the writings clear on the wall.
In the current tune, the gun is accurate …ONLY IF YOU CAN RESTRAIN ITS RECOIL…AND IN EXACTLY THE SAME MANNER EVERYTIME! In a typical unrestrained state (which is somewhat akin to what we know as the Artillery hold), it is going nuts!
My experience is that it is only due to the seal setting in nicely! Of course, that is the sign of a good quality seal! No questions about that. To add to it, SDB cylinders have always had a fine hone inside…so all I hear during cocking is just the hiss of the seal…no gurgle, whistle or anything ever! Now, the reduction of friction between the seal and the cylinder wall during the bedding-in increased the piston velocity significantly….leading to very high initial recoil acceleration. The resultant significantly high peak pressure did not all convert to pellet driving pulse (because ME didn’t go up!). So where was all that extra pressure going? ….In driving the piston bounce! Most of it is getting used to both advance and accelerate the piston bounce….leading to a very high secondary recoil, the surge. That is something, an average shooter like me can not handle…and hence the high hold sensitivity! The fact that it has to generate this high ME with just 78mm of stroke only compounds the problem.
IMG_20190321_141208-A.jpg
Now look at this other photo…. Grouping by a Sport stable mate, again from SDB……same distance, same pellet, same holds. A sweet shooting rifle must be the least sensitive to hold. Look at how the POI drops in the restrained hold!
Let’s look at the Sport’s current behaviour from another perspective ….this 3.2 kg full rifle has a 299 gms piston assembly (piston and part spring weights) hurtling inside to generate recoil. At 10.6:1, the ratio is maddening for any break barrel, let alone for a light springer like the Sport! For comparison, look at the TX200 – A similar weight piston (actually 5 grams less) and a much lighter spring (than this 114 grams resized spring I currently have in my Sport) does the job is a whopping 4.5kg rifle….taking the ratio up to over 16:1. Nominal recoil displacement on Sport is 7.5mm (the TX has it in the 4mm range). How’s that for a spin!
No wonder, I have already readied up a lighter piston to test. But this is another project. Also, this will be set up at 85-86mm stroke….my lowest stroke of my taste personally. I would also request SDB to try this stroke length out in Sport …to give similar ME but with a softer shot cycle!
IMG_20190320_175911-A.jpg
IMG_20190320_180208-A.jpg
And you were always right, Basu da, in advising me to keep this light Sport in the 10.5-11FPE range. That is where it shoots at its powerful and sweet best!
For now, I will first go by your advice….i.e. either cut or collapse two coils of this spring, or use the new 2.9mm Sport spring that SDB is using currently. Will report back again!
The gun remains as sweet as ever. Final words….A stiffly set up light springer is a must have for all those who love shooting…..because shooting it every now and then will keep you disciplined and your technique intact, and not let you become complacent about correct hold, grip, trigger action, follow through, and all! And I love my Sport for that the most….of course, its trademark “punch” is inescapable!
Happy Holi and Happy shooting!
Prashant
Added in 6 minutes 31 seconds:
sagar 12345 wrote:still date sport hold nicely, breach o ring hold nicely. power wise sport deliver same power like new out of box.i enjoyed it lot.now since i am using club elite & genex more but when ever i want to take long shot for plikling i prefer sport.i still not found any suitable pellet for sport so i am searching somewhat heavy pellet like 9 to 10 grain round head from gsmith for both sport & huricaine air riffles.
Dear Sagar Ji,
I have found that the Precipells (all of them) shoot terrifically accurate in my Sport. You may already have tried those out by now though. if not, it would be worth. Second, I always found the G Smith ones way too oversized for the SDB breech.
I would also suggest you try the Marvellous Shot pellets. The round head lot I ordered shoots reasonably accurate in both Precihole and SDB barrels. They do not match the Precipells but are a good cheaper option for daily plinking.
Regards,
Prashant