Hatsan Flash transfer port advise

[dcmeyer]

This is a .25 Flash that shoots JSB King's at 850 avg and KH MKII at 760.

I would like to get the KH MKII's a bit faster but nothing crazy.

The barrel port is at .185, the receiver block is .145 and the valve is .153. As I said I'm not trying to go crazy just optimize as much as possible. I'm thinking I will match the .185 of the barrel considering the opening is already very close to the o-rings and the hole in the receiver to access the passage is only .190 - .193 where the threads are. That would give me just enough to wrap some tape around the bit to protect the threads to drill the receiver.

Is this a reasonable plan?

Any input is greatly appreciated. 

[screwwork]

0.185 dia ports for the valve exhaust & transfer port will help with airflow, then the restriction would be at the valve, valve throat & poppet diameters.   I don't have a Flash to be able to say yeah I did this or that though.

[dcmeyer]

I'm wondering if being a bit more conservative might be wise because it does have a small cylinder, once the receiver is drilled I can't go back. I don't mind a lower shot count but I would still like to get 17-20 good shots. Right now I can get 25 at 40fpe.

[screwwork]

Say you opened up the ports to 0.185 and got 50fpe for 17 to 20 shots, you can always back off the hammer spring tension to get back to 40fpe.
it will breathe better using less hammer force and better shot strings at 40fpe? 

[rsterne]

First of all, I have never seen a Flash.... My opinion is, that if you have a 40-50 FPE gun, stay with the Kings, the Heavies are not necessary and the trajectory will disappoint by comparison.... I currently have two .25 cal regulated PCPs, and the 52 FPE one shoots Kings and the 70 FPE on shoots the Heavies....

Bringing all the ports up to 3/16", and making sure that the throat area (after subtracting the stem) is at least as large, should give you the power to drive the Heavies, depending on barrel length and pressure.... My AT44-S10 Long (with that size porting) shoots them at 960 fps, but only for 1 mag. (9 shots)….

Bob

[dcmeyer]

Thank you Bob. Not sure I can get the 3/16 past the threaded access but I may just go for a moderate increase and match everything up. I can always go bigger, but not smaller once it's done

[dcmeyer]

Transfer port is now 11/64, all starting from 200 BAR ending at 150 for the JSB Kings the other 2 ending just slightly below that. I'm happy with the power and will likely leave it where it is with the exception of tuning the hammer spring. One thing I noticed having it apart and pushing the pellets/slugs down the barrel is the NSA .250 slugs are VERY tight in the Flash barrel and required quite a bit of force to push pass the choked part. Maybe because there is much more contact in the barrel but I was surprised how tight they were. JSB's and other took very moderate force to push through.

JSB Kings

1   870
2   880
3   882
4   875
5   878
6   883
7   881
8   883
9   891
10   893
11   892
12   877
13   885
14   877
15   875
16   880
17   869
18   866
19   855
20   847

JSB KH MKII

1   754
2   757
3   769
4   780
5   776
6   781
7   789
8   785
9   787
10   791
11   784
12   783
13   785
14   784
15   784
16   786
17   780
18   781
19   771
20   768

NSA Dimple Point FB 34gn

1   709
2   710
3   722
4   730
5   730
6   733
7   739
8   738
9   747
10   747
11   740
12   743
13   754
14   745
15   746
16   748
17   741
18   748
19   743
20   733

[rsterne]

It is common for slugs to be harder to chamber because of their increased bearing length.... The solution is usually to taper the leade more.... or cut a longer chamber....

Bob

[dcmeyer]

It is common for slugs to be harder to chamber because of their increased bearing length.... The solution is usually to taper the leade more.... or cut a longer chamber....

Bob

I likely won't be trying to tune this for the slugs, I will try them one more time but it likes the JSB's so much I think I'm staying with them. It also shoots Polymags, GTO's and pretty much anything JSB very well.

Curious if you thing the Hammer spring could benefit from a slightly harder strike based on these numbers?

Thanks again for your input! Thanks to your advise I have made my first PCP quite a good shooter and now looking to expand my collection 

[K.O.]

well there is a way to a longer barrel, maybe...

If below vid has the right sizes...

it involves sleeving with .5" O.D. .43 I.D. tubing and then turning back down... then re-opening t-port and o-ring grooves... also any grub dimples...but can it be done that way leave very little thickness...

But here is a much simpler fix...

Shrink tube.. bet it would be about perfect and seal well with a tight fit also...

So that would give  you a 23" Barrel for a good boost with the opened porting over the 17.7" especially with heavy pellets and such...

[K.O.]

Me I am crazy enough that I might try a Maximus 26" barrel sleeved up, except for the breech area which would be shrink tube... the Max barrel is 7/16(.4375)it  fits in the .5" O.D.  4.3 I.D. 6064 t6 aluminum tube perfectly... they have brass, stainless, and mild steel tube also...

https://www.onlinemetals.com/en/buy/round-tube

[dcmeyer]

Me I am crazy enough that I might try a Maximus 26" barrel sleeved up, except for the breech area which would be shrink tube... the Max barrel is 7/16(.4375)it  fits in the .5" O.D.  4.3 I.D. 6064 t6 aluminum tube perfectly... they have brass, stainless, and mild steel tube also...

https://www.onlinemetals.com/en/buy/round-tube

Not sure how we got on to this 

[rsterne]

David, for the King Heavies you could use a bit more hammer strike.... for the Kings, slightly less.... That is if you want a 4% ES on your tunes....

Bob

[dcmeyer]

My opinion is, that if you have a 40-50 FPE gun, stay with the Kings, the Heavies are not necessary and the trajectory will disappoint by comparison.

Bob

I was reading back through and this caught me a bit off guard, I was assuming the Heavies would buck the wind better at longer distances and that's what I want to focus on, the 75-100 yard range.  Could you clarify because in my thinking it's easier to compensate for distance than wind.