Should I enlarge my 13xx transfer port?

[Airgunnr88]

I'm wondering how advantageous this mod is for a gun with a stock valve and piston.  I don't want to go the flat top route, because of the increased wear on the pump mechanism.  I know that compressed air already flows easier than co2, so there is less to be gained with the pumpers.

It seems that the Boss Buddy enlarged transfer port from Alchemy Airwerks is generally considered the best replacement.  If I remember correctly, the hole is enlarged to .158".  They claim 25% increased flow.  My plan is to use my stock tp and drill it out to .156" (with a 5/32 drill bit, closest I could find to .158" with a common size bit).  I have a drill press, and I'm reasonably confident that I can drill it without making a pig's ear of it.

I also just got a Baker aluminum breech, which comes with a probe that is slightly longer and skinnier than stock, so that should theoretically increase the flow as well.

Another thing I'm wondering is if I enlarge my tp, should I also enlarge the hole in the barrel to the same size?

Is it worth doing, or should I just leave it alone?  Or should I forego drilling it myself and just get the Boss Buddy, which seems to have more improvements than just a bigger hole?  Any advice from those with experience on the subject would be appreciated.

[Airgunnr88]

Don't all chime in at once, now.   

I put my aluminum breech on today.  The transfer port was looking tinier than I remembered it.  I decided to leave it as it is for now, and at least shoot it with the new breech and bolt probe first.  I'll have another opportunity to take it apart when I get my new barrel band and pivot pin.

[Back_Roads]

 I use the ice maker tubing TP in my 13xx guns. cheap and I have a lifetime supply.

[Airgunnr88]

I use the ice maker tubing TP in my 13xx guns. cheap and I have a lifetime supply.

I forgot about that trick, thanks for reminding me.  1/4" outside diameter?  What length do you cut it to, or just eyeball it about as long as the stock transfer port?

[Back_Roads]

 It is a custom fit, bevel one end of the tube to create a press fit, make sure your ends are cut square.
 https://www.gatewaytoairguns.org/GTA/index.php?topic=113659.0

[Psipumper]

Is it .22 or.177 cal. ?

[Airgunnr88]

Is it .22 or.177 cal. ?

.22, started as a 1322.  Currently has a 10" barrel but about to upgrade it to 14", if that makes a difference.

[Psipumper]

Most leave it unchanged in .177 caliber.
.170” diameter would be ideal in most cases for the .22 version. I have not done mine yet. The “ice maker tubing “ mod is used commonly to go larger. I don’t know the exact size of that tubing or details .?

Should be some info on a GTA search.

Charles

[Airgunnr88]

I have a few 3d printed TPs, i can send you 2 to play around with sizing before you buy or drill your oem one open.

Cool, I will take you up on that.  Sending a PM.

[moorepower]

I would like to see some back to back numbers comparing the two. Hard to believe it makes much if any difference on a stock gun.

[Tom Tucker]

I've done it on a stock gun.  5/32" transfer port and barrel port.  457fps @ 10 pumps before, 457fps @ 10 pumps after 

On a gun that is already shooting, say, 600fps, this mod will add another 10 or so.

[Airgunnr88]

I've done it on a stock gun.  5/32" transfer port and barrel port.  457fps @ 10 pumps before, 457fps @ 10 pumps after 

On a gun that is already shooting, say, 600fps, this mod will add another 10 or so.

You probably saved me some trouble and money, since I don't plan on doing any other power mods to the valve or piston.  I chickened out on drilling mine, anyway.  I looked at my tp and I looked at my 5/32 drill bit, and I figured I'd be making tinfoil out of the walls of tp.

[happymecanic]

Hi Jim,

I've used the bigger TP mod, along with matching ports sizes and lighter valve spring, to help in a case of retained air. It also helped with the pumping effort. I started playing with the valve spring preload, and was able to lightly reduce the hammer spring tension, while still dumping all the air, so cocking effort was reduced a bit. I call these ''efficiency mods'', the best is that they're free  . You can also mirror polish your probe' tip, and check how far exactly it pushes the pellet past the TP. If it pushes it way past the TP, you can file it down a bit so the edge of the pellet skirt is just pushed past the TP edge. Have fun!

[Psipumper]

The larger size will show more gains with a longer barrel when flow is more important.
Really not an easy mod because the barrel needs a .250” spot face machined to do it right.
I would be surprised to see no gain even with the short barrel .

[rsterne]

In .177 cal, leave it alone (they are 0.140" stock).... For a .22 cal,, you can easily drill it to 5/32" (which is the same ID as most icemaker tubing)…. I have successfully drilled them out to 0.166" (go one number drill at a time past 5/32"), but there is no point unless you drill the valve exhaust port, and the barrel port, out to match.... The barrel port is only 0.134" (both calibers), so that is the biggest restriction anyways.... If you work on the barrel port, be anal about deburring it on the bore side or you will ruin your accuracy.... Also, you will have to thin out the bolt probe to gain what you did with the 0.166" porting.... Watch the length, or the pellet will end up blocking the barrel port, particularly if it has a deep base cavity….

Bob

[Tom Tucker]

The larger size will show more gains with a longer barrel when flow is more important.
Really not an easy mod because the barrel needs a .250” spot face machined to do it right.
I would be surprised to see no gain even with the short barrel .

I was surprised that there was no gain.  What I did on that particular gun (wife's gun ) was JB-weld the barrel, transfer port, and breech together as one unit.  Then I drilled it and deburred it.  I figured I would gain something just from having a perfect seal, but nope, didn't even gain 1fps.  Then I gave it a solid brass piston, valve mods, and an extended probe, and the gun shoots around 530fps on 10 pumps.