Hatsan BT65 shot string, Want to tune it

[SoCalZac]

I bought a closeout .22 BT65 from Hatsan USA and got a chance to shoot/chrony it today. It is LOUD but my DonnyFL Tatsu from my AT44 quiets it down no problem. Well except for the hammer/ping. The BT65 is an awesome bench gun, very stable and it's not to bad to shoot off hand either. It is a beast shooting Barracuda match 21.14 grain at 990 FPS Avg over 30 shots. I'd Like to make it more efficient while keeping the same power. 

I did some research and apparently it has a really heavy hammer around 90 grams or so and it has hammer bounce wasting air. This video is really good but I dont have a machine shop to manufacture parts


I want to lighten the hammer, drill all ports to 11/64", plug the holes on the valve except the one that lines up with the transfer port, and make the pellet probe thinner. Does anyone sell aftermarket parts for the BT65 such as a lighter hammer and thinner pellet probe or do I just have to have a machine shop make what I need? Is it something that I can do with basic hand tools? Any suggestions are welcome.

[redlined_b16a]

#INeedABT65InMyLife

[SoCalZac]

#INeedABT65InMyLife

It's a super bargain with the Hatsan closeout sale right now. Under $300 delivered to your door.

[rsterne]

Judging by that shot string, you need to reduce the hammer strike.... A lighter hammer is one way to do that, but just reducing the preload on the hammer spring should do the trick.... You will lose a bit of velocity on the first few shots, but get a more symmetrical bell curve.... You want the velocity to start a bit low, and then increase about 3-4% to the peak, and then decline.... When you get to 4% below the peak, stop shooting and record the pressure on your gauge.... That is the pressure you should refill from.... The reduced hammer strike will use less air, so you should get more usable shots.... Your current shot string ends too low, so although you are shooting 30 shots, the last part of the string is so much slower than the first part, your POI will be dropping.... You currently have only 14 shots within a 4% ES....

Bob

[SoCalZac]

Judging by that shot string, you need to reduce the hammer strike.... A lighter hammer is one way to do that, but just reducing the preload on the hammer spring should do the trick.... You will lose a bit of velocity on the first few shots, but get a more symmetrical bell curve.... You want the velocity to start a bit low, and then increase about 3-4% to the peak, and then decline.... When you get to 4% below the peak, stop shooting and record the pressure on your gauge.... That is the pressure you should refill from.... The reduced hammer strike will use less air, so you should get more usable shots.... Your current shot string ends too low, so although you are shooting 30 shots, the last part of the string is so much slower than the first part, your POI will be dropping.... You currently have only 14 shots within a 4% ES....

Bob

Thank you I will adjust the HS tomorrow. I realized that it wasn’t tuned the best out of the box after I started reading the chrony numbers and it was just a drop and no bell curve.

[SoCalZac]

I adjusted the HS today and it made a big difference in usable shots and air usage. I turned it 1 1/2 turns out from stock. I probably should have turned it all the way in to see where it actually is and where stock was. It made the cocking easier and less crunchy so I have feeling it was probably about maxed out from the factory. I did the same 30 shot string except this time it was only from 200-125bar. vs stock which was 200-99bar and got 24 usable shots within 4% es.


I plan on blocking the holes on the valve next. How can I tell which hole lines up with the transfer port, can I just make a mark on the top of the tube when it is screwed all the way in and see which hole lines up with the mark. What if it doesn't line up perfectly?

I have seen people drill and tap the holes and fill with a screw and I have seen where someone used JB weld to block the holes. Which one would be the better/safer option? Should I drill the ports to 11/64" at the same time or do one step at a time and see what it gets me?

[brisner]

[quote ]I plan on blocking the holes on the valve next. How can I tell which hole lines up with the transfer port, can I just make a mark on the top of the tube when it is screwed all the way in and see which hole lines up with the mark. What if it doesn't line up perfectly?
[/quote]

 I'd remove the breech and barrel and look down the TP into the valve and mark it.

[rsterne]

I would stay with the first 24 shots (965-1004-965), which is within a 4% ES.... Remember, that is a big increase from the 14 shots you had originally.... It won't take anywhere near the air to fill it, either.... because you will probably be refilling at about 2000 psi (140 bar)…. ie whatever it is after 24 shots….

If you want to block some valve holes and enlarge the top one(s) you have to determine which hole is straight up when the tube is tightened into the receiver.... If you are lucky, one will be right at the top, or can be made so with a thin shim.... Drill that one out to 11/64" and plug the rest.... I used screws and epoxy.... DON'T drill and tap for too large a screw and weaken the webs between the holes, I have seen valve break there.... If you have 2 holes at the top (or rather the web between 2 holes), you can thin out the web between them a bit, angling the flow towards the top, but do so with care.... In that case you would only plug 4 holes instead of 5....

Check to make sure that all the other ports are 11/64" and that the all line up perfectly for the smoothest flow.... and good luck !!! …. I would not go any larger than 11/64" on a .22 cal or you may damage the pellets when loading them into the chamber because they will have a tendency to drop into a 3/16" barrel port....

Realize that by doing this you will gain some power, but may lose shot count.... That may mean you need a heavier pellet, as you are already on the verge of driving the Baracudas too fast.... perhaps the 25.4 gr. JSB Monsters?....

Bob

[SoCalZac]

I would stay with the first 24 shots (965-1004-965), which is within a 4% ES.... Remember, that is a big increase from the 14 shots you had originally.... It won't take anywhere near the air to fill it, either.... because you will probably be refilling at about 2000 psi (140 bar)…. ie whatever it is after 24 shots….

If you want to block some valve holes and enlarge the top one(s) you have to determine which hole is straight up when the tube is tightened into the receiver.... If you are lucky, one will be right at the top, or can be made so with a thin shim.... Drill that one out to 11/64" and plug the rest.... I used screws and epoxy.... DON'T drill and tap for too large a screw and weaken the webs between the holes, I have seen valve break there.... If you have 2 holes at the top (or rather the web between 2 holes), you can thin out the web between them a bit, angling the flow towards the top, but do so with care.... In that case you would only plug 4 holes instead of 5....

Check to make sure that all the other ports are 11/64" and that the all line up perfectly for the smoothest flow.... and good luck !!! …. I would not go any larger than 11/64" on a .22 cal or you may damage the pellets when loading them into the chamber because they will have a tendency to drop into a 3/16" barrel port....

Realize that by doing this you will gain some power, but may lose shot count.... That may mean you need a heavier pellet, as you are already on the verge of driving the Baracudas too fast.... perhaps the 25.4 gr. JSB Monsters?....

Bob

So if I want to stay with the Barracuda Match I shouldn’t enlarge the ports? Will blocking the extra holes on the valves give me better efficiency thereby increasing my shot count?  When I read your thread on the at44 tune I thought you had to increase your HS tension to get it back to shooting the same FPS after blocking all the holes on the valve and enlarging everything. I am basically using that as my guide to tune along with some videos on the bt65.


Thank you for your help I went back and edited my posts so it is 11/64" I don't know where I got 3/16' from maybe a video on a .25.

[rsterne]

I haven't played with a BT65, so I don't know if blocking 4 or 5 ports and opening the top one (2) would require more hammer strike or less.... Generally if you increase port size at the smallest restriction (making the gun breathe better) you will gain FPE at the same pressure, but reduce the shot count.... Think of large ports like a hot cam in an engine.... more power over a narrower range....

You can still use the Baracudas, but you might have to reduce the pressure and hammer strike if you have too much velocity setup the way you are now....

Bob

[SoCalZac]

Today I found where the valve lined up with the transfer port and of course it lines up with the web on the valve. I degased the cylinder took the valve apart and tapped the 4 holes that didn’t line up at all. I was able to use a 10-24 tap without having to drill out the holes at all. I then chamfered the two holes on either side of the web toward each other. I need to get some 10-24 x 1/4” grub screws and jb weld. I’ll plug the 4 holes I tapped and fill the groove with jb weld and see how it does.

[SoCalZac]

I was able to pickup some grub screws from HD along with JB weld today. I installed the screws and filled the groove with jb weld. Now I just need to let it set up overnight. Hopefully I’ll get a chance to chrony it tomorrow and see How it does.

[SoCalZac]

Ihad a chance to chrony the valve mod today and it wasn't quite what I expected. It up shooting a little faster and not as many shots. I filled the gun to 200 Bar last night and forgot to check the gauge before shooting so maybe the pressure dropped slightly overnight due to cooling. Not sure why blocking off the extra holes is giving a higher FPS. I am going to back the HS out another 1/2 turn and see what that gets me.

[Rallyshark]

You're going to want to bring the two holes closer together with a dremel or something.  You want to angle them, so that the area in the middle comes together with almost a knife edge.  Right now, they aren't really angling the air towards the center as much as would be ideal. 

I made a quick paint diagram to show you what I mean.  I hope that helps

[SoCalZac]

You're going to want to bring the two holes closer together with a dremel or something.  You want to angle them, so that the area in the middle comes together with almost a knife edge.  Right now, they aren't really angling the air towards the center as much as would be ideal. 

I made a quick paint diagram to show you what I mean.  I hope that helps

Thanks I’ll work on making it more angled towards the middle I was just worried about removing to much material like Bob warned about.

[Rallyshark]

You'll be fine as long as you only work inward between the two open holes.  I agree with what Bob was saying too.  That issue with weakening things usually happens when people open up all the other holes too much and cram too large of a grub screw in there making the entire valve weak.  The first AT44 valve I ever did lined up just like the one on your BT.  I had to do the same thing you're doing, because I didn't have a suitable shim at the time. 

Either way, you're on the right track

[Runefalk]

Hi. I just bought a Hatsan bt65 elite rb in cal .22 and it is a 17 joule version.
So the question is what do I need to do to get it up to full power???

[Dan H]

A simple adjust of the hammer spring can bring this gun up or down , no real need to butcher the internals on that gun ..

[Runefalk]

A simple adjust of the hammer spring can bring this gun up or down , no real need to butcher the internals on that gun ..

hi and thanks for the reply. I have adjusted the hammer all the way in but it's still shoots very slow.

[OleTomCat]

The transfer ports are probably very small as you have a reduced power gun for your countries requirements.

Modifying it for more power may put you in trouble with your local law enforcement.