Canted Spring - low velocity

[vsraja]

We need a rifle with full power at that moment. Hence we take less care about those individual parts like piston seal,spring, etc.In my experience I can feel some of the feedback or a signal which tries to alert us when they are abused. Its like some symptoms before some life threatening diseases.These parts also react in some way if they are abused beyond it’s optimum capacity.Hence these springs will bend like these, we call them as canting, if there is any unbearable preload.Can you carry 30kg rice in a bag of 10kg capacity?.This is happening to your rifle springs.The manufacturer no need to care about this as they going to happen only after sales.Some of the rifles have preload which is very near to the optimum compression capacity of that spring, imagine how that spring feels when they are further compressed while cocking. Even 39 coils will be a huge preload for an indian gun with normal stroke length.In my rifles I don’t exceed 33 coils, which is in full power.Hence if you don’t like to remove some of the huge preload, be ready with a spare spring to change at regular intervals.But I don’t need it at that much frequently.Also a right preload offers a smooth cocking with no grinding while cocking and also with full power.Also you are no longer needed to go behind some crazy brands of springs. Normally people fear of power loss while thinking about cutting some coils and hence try to install full spring.Its like killing the whole spring by fearing about the amputation.Have you seen your spring at cocked position, it says much about the preload.Even you can get consistent velocity if you have a right preload. Also I can cock and take some time to shoot without the fear of losing some power.Most of the budding airgunners blindly try to preload as much as possible and they feel good when they can compress the full spring into the receiver.My question is that, your job is done, do you think about the consequences or side-effect of your treatment.So the rule of the thumb is that we need to remove some 5 coils from the stock spring before using the gun.

[Basu]

At places harder spring yield more power but not necessarily.
Each gun may behave differently.
One needs to pick the point as to where it settles best with power and accuracy.

Basu

[Niks]

I am just wondering if that is the grouping made from a 25 yards, basically are you a beginner? Or the gun needs some tuning? Happy shooting..

[Basu]

As a beginner , one should start from 7-8 yds and increase the distance till 30 yds with open sight.
A good pellet satisfies where as a bad pellet frustrates.

Basu

[Niks]

I m planning to experiment my AR for more velocity, this is nothing for commercial purpose purely experimental, just curious if it will really work. Going through air gun pyramid i have learned two things which can increase the velocity.
1. .125 mm size of transport port give the best velocity of any pellet size of .22 .177 or .25
2. Extended length of cylinder will accumulate more air which can give higher velocity.
So, for No.1 no problem i can just drill it away. But how to increase the cylinder length?
Here, i am going to need a donor but should be same size cylinder else everything will be a waste, since i am going to cut out the cylinder from donor and fixed it to my AR. Probably 2 inches will be cut from donor and also my AR cylinder will be cut in the middle than join it with the donor and weld it, also cooking rod should be extend. It is sure, since cylinder is extended the volume of air will increase but same old spring and piston can increase the velocity? Or do i need new piston and spring to balance the extended cylinder? This is just a layman's experiment dont have any engineering knowledge anything can go wrong. Its about trail and error.

[prashantjha19]

If I were you, I would go slow on this...and in a step-by-step manner, before I dive into all that you have suggested (cutting and extending the cylinder, and all). And BTW, how on earth will you put that fancy new extended thing in a stock?? Are you also planning to get a new size stock cut out for you?

Try these first if you are intent upon increasing the SV..
1. If it is a leather seal, replace with a synthetic one. This, by itself, should give you some 5 to 7 mm increase.

2. If your piston head sits way ahead of the cocking slot front groove when cocked, get the piston head length ground /shaved off. In local Indian ARs, you can get some 5-7 mm shaved off from the piston. Will decrease weight though, which you may want to compensate by adding heavy thrust washers inside. I put #20 or 22 steel nut and they give a good snappy shot cycle.

3. Alternatively, you can get the piston rod shortened. This is more tricky than it may look. You will need to first fill in (weld) good hard metal (brass may not take you too far) in the hatch cut-out, and then regrind the filling to perfection. Normally, it gives some 10 mm of extension.

4. The final one -and this plagues all our Indian ARs - is to reduce the TP length. I do not know why all our guns have those long tunnel like TPs (some 22 mm). On a precision lathe, get the cylinder face ground from inside. The thing here is -to ensure it does not tamper with the cylinder bore size.
Do not ever bore or drill the TP as you seem to be planning. The OD is just about fine in our ARs (i.e. in the 3 mm range). It is the length that is the culprit. For a 3mm TP, the ideal length is just 5mm. An HW99s -which is one of most energy efficient AR of all times -had a barely 6mm long TP, an SV in the range of just 37cc and yet produced 12ft.lb. flat out. Compare this with our SDB Mod 27 which has similar bore and displacement specs (after I replaced the leather one with a synthetic seal). But I doubt if it's MV is anywhere near that of HW99...despite being a deadly smooth shooter with all the tuning I have done. Why? The only culprit I can think of is the TP.

In any case, I do not think any more than 10 mm increase in SV would be practically viable in a standard Indian AR. And in fact, if you can manage only this much, you will have a terrific shooter. All the best!

[Niks]

Thanks for your valuable suggestion, i dont have a problem to get a new size stock. Like you said i already changed the piston seal with a synthetic one also added a 20mm nut as washer, i think it shoot around 400 to 500 fps, since i don't have a chronograph to measure don't know exactly. Here, I forgot to mention this before about my AR, its 1hp 35 model .22 manufacturer claim it can shoot 500 fps with .22 model and 600 fps with.177model but want to see if it can reach 800 to 900 fps.
Your suggestion about cutting the piston and welding hatch cut-out, i even thought of that earlier but it could decrease the piston weight and affect the balance so i dropped the idea.
I was also wondering about the long lenght of TP but didn't realise to bore, that's a good valuable suggestion for future but as for now i don't think i can achieve desire velocity with few mm.
Its an old gun i dont mind if i have to scrap it at the end, but just want to know wether there is any hope in my project.

[Niks]

Thanks for your valuable suggestion. Here i forgot to mention my AR, it's 1hp 35 model .22, manufacturer claim it can shoot 500 fps and with .177 it can shoot around 600 fps. I think my AR shoots somewhere around 400 to 500 fps as assume by the force it penetrates wooden boards, i don't have chronograph to measure it. I did a few modification like you have said, putting 20 mm nut as washer, change leather seal with synthetic but this thing will not achieve my desire velocity which i am thinking about 800 to 900 fps.
I don't have problem getting a new size stock.
Where as, i also thought of cutting the piston and welding hatch cut-out, but this will lower the weight of piston and could seriously affect the balance so i dropped this idea.
I was also checking the TP and was wondering why it has a long tunnel, your suggestion of boring has given me an idea which i didn't thought of, this could be a valuable suggestion for future but as of now a few mm will not give me enough power.
Well, it is an old AR i don't mind scraping at the end, only thing is, do you think it will work? If there is any positive response i might want to go ahead. Forgetting to mention i already drill my TP with a .120mm couldn't find .125 mm drill bit. I dont there was much difference between and after drill, while drilling i notice that hole was of cone shape, drill bit just cut a few mm and just fell inside so inside it was bigger.
I submitted a similar post earlier but it did not went through hope it won't be double posted.

[prashantjha19]

Since you say you have thought through everything, you will be good going ahead with your experiment. Do let us (and also the manufacturers) know of your achievements though). I for one know for sure that whoever was or has been behind designing the basic prototypes for the various Indian AR models, ought to have been a thoroughbred designer, and has incorporated the checks (for Power and MV over-enthusiasts, i.e.) very intelligently.

And BTW, did the addition of your 20 mm nut (which you say you installed) affect balance? If you could really feel it, yyou should be participating in ISSF competitions. Why waste time with the Indian ARs! And in case it didn't, then none of the alterations I suggested for the piston will. Try those out. It may be advisable to do things hahan-on rather than just staying put with convenient assumptions. As they are, airguns are known to be counter-intutive by their very nature.
Regards,
Prashant

[narach93]

I fully agree with you, dear Prashantji. With a desire of getting more MV ,I have added 2 thick cut bearings (made by vortek) having total thickness of 6mm, resulted in failure of cocking of my diana 54. Only local made AR can accomodate 20mm preload !!

[vsraja]

SDB air rifles are powerful than other indian counterparts especially ihp 35 is due to shorter transfer port.In ihp 35 the long transfer port helps to maintain its low power.Breach loading side lever or under lever air rifles have much less of transfer port length.A long transfer port not only affects power but also ruin the piston seal due to unnecessary pressure on it for a long time at the end of shot cycle.It creates a need to change the piston seal more often than SDB.

[Niks]

@prashant, thinking twice, i took your advice and went for boring the cylinder to shorten the TP since it is giving double advantages, like shortening the TP as well creating more length of the cylinder unfortunately the lathe technician has no such bit to cut deep inside, and also due some work have to leave my station for few days. Once i get back i will try one thing or the other and post the details result with pictures.

[prashantjha19]

Grreat! It sure will be an interesting project, and worth waiting for. We will await your revert on this.
Just be overly cautious about about all potential affectations to the cylinder bore at the TP end. Must only let an old and trusted lathe technician handle your cylinder. Also, pls do not shorten the length of TP beyond 7mm. Regards,
Prashant

[prashantjha19]

Dear Niks, You forced me into researching the topic further; and having spent sometime mulling over the various possible options, I have second thoughts on my last suggestion (where I suggested to bore the cylinder further long).
I think (and this is also because you say you have already drilled the TP hole wider) - you should first test the gun with the wider TP -all other variables being same. Note the behaviour and MV.

Second step: DO not extend the stroke....Instead look to shorten it. For this you can add correctly sized spacers over the piston head + file and move further down the hatchline of the piston rod. Both of these are reversible, so you will not have to regret any of it even if this experiment does not work out to your taste.
I am suggesting to shorten the stroke not because it is the current fad internationally (of course a short stroke has its own advantages for shootability and accuracy), but because a wider TP is known to best complement a short stroke AR. And there are logical scientific reasons for this.

In case the results do not amuse you, you can always go ahead extending the stroke. But since you are on the project, I thought you might as well want to experience the magic of short stroking. I for one have found it worth doing, and have tuned one of my local ARs (it is a Can-On .22 cal with a surprisingly thin TP which I drilled and reamed, and then short stroked the mechanicals). It now whispers when it shoots; you can shoot this heavy gun with one hand (that is how quick and vibe free it has become) and of course the power output is better than before. It earlier matched my SDB 45 Classic. I now find it makes deeper dents and holes.

Regards,
Prashant

[targetpoint]

Dear Krishnan.adhikari1
Hope your Gennex has already passed the breaking in period.Wish to see the grouping at present state so you can do by bench rest at 10 and 15m.
Thanks.