New QB79 velocity report

[adam h]

Just received my new QB79 from Archer Airguns yesterday.  Chronied it with some Beeman Silver Arrows (17.1 gr) tonight.  Here's what she did:
494
509
511
514
500

505 average.

This is bone stock.  I'm planning on doing some mods and wanted to take a "before" reading first.  Great product and quick delivery, Archer!

[SDale]

High 600's to mid 700's are possible with a good port & polish. Also eliminating the piercing pin and opening up the valve inlet works very well too!

[adam h]

551
535
541
566
548

548 average.

I gained about 40 fps from stock.  I followed most of the Charliedatuna guide.  I did the minor bolt mod, barrel to breach mod, tapered the valve stem and turned down the hammer pin to match the valve stem.  Strange thing is that after my 5 official chronied shots, I shot a few more and got one that read 580!  Some jump!  What would cause such a jump?  The following shots came back to around the others, but it does seem like I gained some velocity as I was shooting, could it need to "break in" to reach max velocity?

[ribbonstone]

A little bit of a break in.  Any time there is metal sliding on metal (the hammer and spring guide mostly) they are going to wear in  a bit.  Can also figure about 2fps per degree of temperature change...so if shooting 550 @ 68 degrees, will be near 575 @ 80 degrees.

[SDale]

Yup... you're gonna need some break-in time.Things will smooth up and mate after a tin or so of pellets and you should gain a bit of velocity.

That jump may have been from the valve sticking juuuuuuust s tad. Once it wears in ans smooths out, you should be around 550-560 consistently.

Another thing you may want to do is pull out the felt pad & screen in the valve for a little more flow. Also polish up the flow path. No porting needed. Just a good polishing. You'd be surprised at the gain from that alone!

[adam h]

I forgot to mention that I did remove the filter and screen.  I didn't really polish much, so I'll have to go back and do that.  I also didn't drill holes in the aluminum main body or notch the washer.  Maybe someone can explain it to me, I don't understand how doing this helps.  Isn't the pressure already beyond that point before you pull the trigger?

[SDale]

Yes, you're right about the pressure already being there, but remember. Pressure rapidly drops unless there's flow to support it.

Notching the washer helps the flow of more gas. It's like having an air tank dump 1 cubic foot of air at once through a 1 inch hole, and an identical set-up dumping air through a 2 inch hole. The second will have greater volume due to the increased flow. That's the idea behind notching the washer.