The cost of being bored.

[Geoff555]

Hi. Being bored with being in lockdown then I thought it would be a good idea to clean and check the air rifles over. Re sealed the Daystate that had a very slow leak and then looked at the BSA Ultra, some time ago I had fitted a long air tube, as it was a too long way to walk from car park at the range to the outside bench rest position. ( Bad hips etc. ) so anything to cut the number of journeys was good.
Now the report from the muzzle was always very loud so I thought that as it has a very short barrel then may be it was wasting air ?? Raided the piggy bank and bought a barrel blank, machined it to fit and gave it a try, it's some 6" or so longer than standard ( when I can get to my ruler I can measure it later.) .
Result 13.9 ft-lbs. up from the 11.1 it was set at originally.
Had to fit a weaker spring to trim it back to 11.2.
When I am permitted to get to the range then it will be interesting to see what happens.
Thanks for reading.
Cheers all.
Geoff.

[Biker_Bob]

The Devil makes work for idle hands.....

I'd run a string over your chrono. You might find that the weaker spring accentuates the power curve.
Obviously it's much more technically involved but reducing the transfer port size and keeping the original hammer spring would probably give a flatter characteristic.

[TopDog]

Yes please, do let us know what the details are; all data is useful.

I did some tests a while ago using a springer which showed that the result you may expect from an increase in barrel length from 12" top 18" (about what you may be experiencing) would result in an increase in MV from 95% to 100% (ME increase from 90% to 100%). It is useful to look at the effects as far as PCPs are concerned since the rise in pressure is quite different from that in a springer (my passion!).

http://freepdfhosting.com/66fba9c8c2.pdf

Hope it all helps.

Stay safe and well.

atvb
David

[Harley_Steve]

That happened to me when I changed my S410 from a carbine to a classic. It was shooting at 11.4, when I changed the the barrel to the classic it went to 14 ft/lbs plus.
It's now shooting 10.65 grain Barracuda Match pellets at 11.7 ft/lbs and JSB 8.44 grain pellets at 11.5 ft/lbs, and I now get lots more shots per fill having changed the air reservoir as well.

[TopDog]

The Devil makes work for idle hands.....

I'd run a string over your chrono. You might find that the weaker spring accentuates the power curve.
Obviously it's much more technically involved but reducing the transfer port size and keeping the original hammer spring would probably give a flatter characteristic.

Good point Bob but not for the faint hearted! However, Power Curve determination is relatively simple!

I must get back to some MV versus barrel length investigations myself, since I only did springers!

atvb
David

[Geoff555]

Hello a bit of an update. When I first got the Ultra then the accuracy was not in question but the bolt had a lot of 'free play' before it compressed the spring, it was also very hard to pull.
Got a set of 4 springs and a different hammer, 2 long springs - 1 hard and 1 soft, 2 short springs - 1 hard and 1 soft.
The hammers were a light one and a heavy one.
These were obtained from XTX wich are now unfortunitly gone.
Fitted a long soft spring and a light hammer which gave an easier pull on the bolt and a 11.1 ft-lbs.
The short hard spring that was fitted, being sloppy, tended to shift position which led to a varyation in ft-lbs. This is the conclusion I came to?.
The barrel was 12" long and the new one 19" long. Now playing about with various combinations now, of a light hammer and soft spring Then we are at 11.2 to 11.5 ft-lbs, this will change when the barrel has more than a dozen pellets through it.
The pellets were straight out of the tin and what I had handy. AA diabolo field. 8 gn. 4.52.
Living in a flat with no garden then limited as regards noise, if careful, then I may be able to fire 5 pellets now and then. The range is closed and as yet I don't know when it will re-open.
When I know more then I will hopefully be back, next year?
Thank you all for your interest.
Kind regards and keep safe.
Geoff.

[Geoff555]

Hello, just a bit more to 'bore' you with, continuing to go through the bits and pieces, I found a S200 cylinder that was very rusted and scrap that I had forgotten about, it had a Huma regulator that was fine and rekitted. This had the same thread as the BSA and didn't need a hole drilled in the cylinder.
It was set at 105 bar. trying it gave a 14+ ft/lbs. OOPS. Set it to 90 bar and it made little difference.
OK started at the other end of the scale 50 bar and that gave 10.4 ft/lbs. Raised to approx 63 bar ( a bit above 60 bar. on the scale.) and now 11.2 ft/lbs. with very little variation.
I think this is about this for now. Shot count should be pretty good now, I hope.
On with a AGS which I think ( in my opinion anyway) is horrible.
Cheers.
Geoff.