AR 10 low velocity problem.

[tsokasn]

Hello folks!
I've been notified about low velocity on my FWB P70.
I can hear it,and so do other athletes.
The point is that I once tryed to raise the velocity by tightening the screw of the "firing pin's" spring and it had reach the max tightening position,with the velocity,measured with shooting crony,to be in the desired area.
I am going to check again if the screw got loose but if it hasn't,what must I do?
I've been told to get a harder spring...
Could that be the cure?
Thank you!

[Rover]

I'm not really familiar with your gun, but it sounds like you need a new striker spring (cheap), but sometimes you can get it too tight and it actually works to your detriment.

[tsokasn]

Good morning!
I have already tightened the spring to it's limit.
I will check it tomorrow if it has came loose.
If it hasn't,then a new spring will be ordered

[TenMetrePeter]

take out the hammer block and ensure it is dry of any oil.
Oil in there will act like treacle and kill the power as the hammer block slows.
If you think how many times per second a car engine valve spring compresses there is no need to assume the spring is to blame at this point.

[tsokasn]

Will do!!!
Thank you!!!

[rmca]

take out the hammer block and ensure it is dry of any oil.
Oil in there will act like treacle and kill the power as the hammer block slows.
If you think how many times per second a car engine valve spring compresses there is no need to assume the spring is to blame at this point.

Air guns should not be oiled inside.

TenMetrePeter
The spring analogy between a car's valve springs and those of an air rifle isn't accurate.
Valve springs compress for a fraction of a second and are quite thick and hard to compress by hand. True they compress a lot more times, but they are way more robust than a spring in an air rifle.

The striker spring on an air rifle is compressed for a much longer time, and if the rifle is left cocked, this can be days, weeks... Also, the spring is much "softer" than a valve spring.
In normal use the spring can be compressed for a minute or two at the time. This times 60 shoots plus sighters in 1:30 hours (paper targets). Then they rest for days until you pickup the gun again...

My experience with low velocity air guns is similar to Rover's. A low velocity usually indicates a week or collapsed striker spring.

Now the good news, FWB is excellent in supporting their old equipment. Use the contact form on their site and you can buy directly from them. Or contact a dealer near you.

Hope this helps

[TenMetrePeter]

What is the evidence to show that springs dont like being compressed within their working range for long periods? I cant find either metallurgical theory or empirical evidence to support this.
I dont believe springs take a "set" through being left compressed within their design range. This only happens when they are stressed near their elastic limit irrespective of the time interval, and with most compression springs they are difficult to go beyond the elastic limit at room temperature.
Just my opinion. others are available.

[Rover]

Then here are "others" opinion:

"My experience with low velocity air guns is similar to Rover's. A low velocity usually indicates a week or collapsed striker spring."

This is called experience.

Doubt it? Ask any TOZ35 FP owner how they like their striker springs.

[TenMetrePeter]

Then here are "others" opinion:

"My experience with low velocity air guns is similar to Rover's. A low velocity usually indicates a week or collapsed striker spring."

This is called experience.

Doubt it? Ask any TOZ35 FP owner how they like their striker springs.

I am not doubting thst a weak or broken spring can cause low velocity.
So can oil dirt or rust on the hammer rail.
I have experienced both in my time. No argument. The OP has two valid causes to investigate. Great.

I am saying that keeping springs compressed for a length of TIME does not do the damage. It is a total myth caused by your grandad telling you not to leave your BB gun cocked.

Springs are damaged by repeat stress fatigue, working them beyond their range, or ultra high temperatures taking out the temper. Not time.

[rmca]

I am saying that keeping springs compressed for a length of TIME does not do the damage. (...) Springs are damaged by repeat stress fatigue, working them beyond their range, or ultra high temperatures taking out the temper. Not time.

We will have to agree to disagree on this.

My experience with any sort of gun tells me otherwise.
Leave a pistol cocked from one season to the next and you'll need a new striker/hammer spring.

It is a total myth caused by your grandad telling you not to leave your BB gun cocked.

This is exactly what we do, when we want to "tune" a new BB gun for competition. This lowers the velocity so that the rifle jumps less. And it's done by leaving the rifle cocked for a couple of days (or weeks). (Yes, we also hold competitions with BB guns on special targets (14cmx14cm))

Hope this helps

[TenMetrePeter]

Yes we disagree. That is ok.

I would prefer to pass 100 shots thru a new gun to settle it in. Leaving a gun cocked is against our safety regime.

[tsokasn]

So,today, I managed to crony the rifle...
Average speed was 525f/s...
I then took off the hammer block and degreased it...
Yes,that is correct my friends,I degreased it...
And that's because in a previous maintenance interval,I greased the hammer pin because I thought it was correct...
Any way,got the rifle back together and did my practice.
I realised a difference in the sound but did not had the time to crony it again.
The POI was also different (from 10 to 8 ring at eleven o'clock)
It maybe my idea but I feel the rifle very "peaky"...
I will post the new crony readings
Thank's Peter and everyone who shared with me knowledge!

[tsokasn]

What is the speed that I should go for ?

[TenMetrePeter]

Glad I could help. FWB dont seem to have a figure in the manual. An 8 grain pellet at 5 ftlbs would be 530fps and 6 ftlbs is 580 fps by my calculation. An F marked German rifle would not normally exceed 6 ftlbs. (Some countries state max fps rather than ftlbs or joules which is illogical.)

By having a bone dry hammer and hammer guide/rail you will get consistency at all temperatures rather than widely variable velocities.
Depending on the design some folk reduce friction further by polishing with with metal polish. Some rub in and then rub OFF pure moly paste or drislide. It must be dry of any liquid lube on assembly.
Any talk of FWB "Special lube" does not apply to hammer mechanisms. That is for cylinder seals.

[tsokasn]

Good morning Peter.
I am in the range and just finished crony.
AS after cleaning is 583 f/s.
Is it too much?
Should I back off a bit?
This speed is with the spring being fully compressed by it' adjusting screw

[TenMetrePeter]

583 on a 7.2 grain pellet is OK - change to 8.2 pellet or over.

583 on 8.2 grain is a bit faster than the gun was certified for back in Germany. Try 550 on 8.2 but there will be a sweet spot round there somewhere.

NB I am talking 10 metres rifle.

http://www.pyramydair.com/article/What_ ... ust_2003/5

[tsokasn]

Hello again my friends.
I would like to continue here my new problem rather than open a new topic.

So August was a vacation month in shooting for my rifle.
When I got back in September.,my rifle started to loose velocity.
3 shots POI in the 10 ring and then the rest fell off the target,six o'clock...
The striker pin spring preload screw was all the way screeed in to have a 583 f/s velicity.
I thought that the spring needed replacement.
The new spring now gives the rifle's velocity a strange behaviour.
Don't know that there must be a break in period for it but velocity goes up and down (even in the same practice period)
Striker pin is free of any kind of oil,and the rifle has shot around 150 pellets with the new spring.
For example,today,I cronied the velocity at A.S 573 f/s and after about 50 pellets,I cronied it again at 630 f/s...

What do you think about that?

[tsokasn]

Update.
Came back from practice.
Yesterday,I set the velocity at A.S. 570f/s.
Today,before pracrice I measured it at 450 f/s...
I unscrewed and screwed the air cylinder and velocity rised...
Done the same again,and the velocity falled...
Then I tryed another air cylinder,from a 700 model.
With that cylinder,velocity was the same before and after practice...
What could the problem be???

[TenMetrePeter]

If you have eliminated any potential problems with hammer mechanism it is further downstream like firing valve, regulator or cylinder . You have almost proved it to be the cylinder though I am not sure how unless the check valve is bad
It needs a thorough service.

[nglitz]

"Springs are damaged by repeat stress fatigue, working them beyond their range, or ultra high temperatures taking out the temper. Not time."

The most accurate description of spring wear outside of metallurgical textbooks. Any spring that is damaged by being left normally compressed has very poor spring design or metallurgy.

Not time.