How to approach enlarging porting on an airgun barrel?

Jump to latest Follow Reply
MrP

MrP

Member
Apr 29, 2020
1,767
1,103
New Lebanon, NY, USA
Hello there, hoping to draw on some of the wisdom and experience of this group…

I have a kral empire xs, I am enjoying this air gun. At some point I want to try opening up some of the porting. Don’t need to, I just want to give it a try.

I thought I’d start with the ports that flow air into the barrel. My guess is that expanding and contouring these holes could improve flow a bit. On one level it sees very simple but I want to be sure I have things straight.

I have a dremel tool and a drill press at the moment. I have a set of variously shaped carbide tips - ball, cone, cylinder, round-ended cylinder, etc. but these might be overkill?

I would appreciate any suggestions you may have as to tools or techniques available to the layman.

Thank you
 
You must remember that the porting on an unregulated gun is its regulator. That’s why unregulated guns have smaller porting than a regulated gun. A gun with a reg can run wide open porting for its caliber because the reg setting will only let it use a certain amount of air. Getting crazy with a material removing device can make things get strange with your bell curve and fill pressures. You can wind up with some impressive velocities but a horrible shot curve.
 
  • Like
Reactions: Sdcarlee, Spinach, MrP and 3 others
Upvote 1
Looked over my notes on my XS. I worked in concert with Troy when I was messing with the gun. I relied on him to keep me on the unregulated ship because I always bail off an hop on a regulated raft. He was doing a .25 but we both got where we needed to go and I’m happy I stayed unregulated. Since you are focused on porting, here’s the deal with it. You can go 11/64” on that .22 and not screw up the gun. But, that’s only 1/64” bigger than factory. So don’t expect exciting chronograph numbers. The good chronograph numbers come when you do the other mods I talked about before. Also, when or if you try to go up 1/64” on your porting, you have to be careful how you do it on the valve. I didn’t plunge straight down into it. You go in from the top but stop. Then angle away from the poppet. The valve exhaust port will sorta resemble a down spout on a house. Not a chimney. Like I said before, no one mod on this gun is worth a crap. When you do them all, the gun wakes up.
 
  • Like
Reactions: Airgnr_Ind and MrP
Upvote 0
I got a reply from Troy, and he said he doesn’t have a way to get parts. I figured that would be the case when I ordered the gun since I had to order from krale.

If there is any other person / vendor to contact about kral airguns please let me know.

vetmx I hear you and won’t dig into this if I can’t find replacement parts. I’m not determined to do the porting, but I definitely want to understand how people go about the job, preferred tools

I would want to be able to have spares for the barrel, spring, and valve stem at least before risking a non-reversible modification. I don’t know how these hold up but I know of a couple of guns where increased power puts enough stress on the valve and parts can bend part of the stem on one platform or break the plastic part on another.
 
Upvote 0
I would just go in and clean the port on the barrel to make it smooth, and make sure it is aligned with the transfer porting. My first gen Empire X with the offset port had really rough machining in the barrel and transfer port. I cleaned mine up as best I could with a small ball cutter in a rotary tool, chambered the barrel port a little in the breach to stop shaving pellets, and left it there. Turned the hammer spring up to get a decent velocity with the more common heavier pellets, and stopped. I don't need power from it, getting around 40 foot pounds. If I need more, I have a Pitbull regulated Bulldog in 357.

I also used rubber abrasive cutters to polish my work, only reliable place I found to get then was McMaster Carr.
 
  • Like
Reactions: Sdcarlee and MrP
Upvote 0
I've found that porting (not siply drilling the poets bigger) gives the percentage of speed for the work done (free power) because it makes the air flow more efficient, the same reason as to why we port and polish automotive engine heads. From doing my own porting, here's my advice:

go slow and steady, use good lighting and a large magnifying glass,

study automotive race engine porting for flow characteristics and follow that logic (for example, smaller ports can have more velocity, and don't do anything to the port like make it too large that may stall the airflow),

if opening up the ports, slope the factory drilled holes so the air not have to make sharp 90° turns,

when starting on a new port job, simply blend and radius the sharp factory drilled corners first and then re-assemble and test the flow and shot to shot consistency.

Here's some pics of the original Impacts ports after porting. The inside sharp corners are radiused to optimize flow and the ports are oblong and sloped as much as possible to "straiten" out the airflow.

Screenshot_20230910-224452.png


Screenshot_20230910-224332.png


Screenshot_20230910-225758.png
 
  • Like
Reactions: MrP
Upvote 0
On single hole transfer hole into bore ..... NEVER exceed @ 70% area of barrel bore to hole ratio. Doing so allows the pellet or slug to fall / tilt into the hole as it passes over it. If wanting near bore area transfer area an ELONGATED slot is a far better solution. ( narrow side to side, longer in length following bore )

Also take note : The flow threw the passages valve to barrel will be strangled by the tightest dimension the air passes threw. If the passages under the barrel are smaller, opening the barrel port won't do squat ;)
 
  • Like
Reactions: Airgun-hobbyist and MrP
Upvote 0
Remember..."big"...doesn't always mean better.
I would NOT go larger in the port in the barrel, than the transfer port area.

Keeping all of the different "holes" the same square inches will help the air move evenly and as quickly as possible.
Moving from a small hole to a large hole WILL...slow down the air speed. This isin't good for proper movement of air (or any other gas, liquid).

Mike
 
  • Like
Reactions: Airgun-hobbyist
Upvote 0
Absolutely.

The precautions are appreciated. I’ve had a classified posting looking for parts or barrels for the Empire X / XS because I would only feel comfortable doing this if I had a different barrel to work on and keep the original one as is. At some point if nothing turns up, I may try anyway. At this point the only thing I would be comfortable doing, would be smoothing out the edges and contouring the barrel port.

The idea that it doesn’t make any sense to have one large opening in a pathway that’s restricted and that enlarging one section next to a restricted one will create turbulence and energetic changes that are not involved in moving the air forward smoothly makes sense me. If at some point down the line, I have enough of an understanding of where the restrictions are on this gun, the structure of the valve, etc. then as was first suggested I might try to take it further.

I am not trying to change this into something that it isn’t - i am hoping to identify some places in the air path where the manufacturer may have taken some manufacturing short cuts to keep costs down that can be simply corrected with a little time at careful work.

Shortcuts like not deburring the barrel ports, or not contouring areas / rounding corners in the air path, etc..


I have to get the appropriate tools clear in my head. I have a set of various shaped carbide bits for a variable speed dremel type tool, they look very coarse…. I have conical felt polishing tips and two different polishing compounds but it is my understanding that this is just for surface polishing after any shaping / smoothing is done. Is there something else I should have here?

I appreciate you alll taking the time to steer me right here
 
Upvote 0
MrP said:
I have to get the appropriate tools clear in my head. I have a set of various shaped carbide bits for a variable speed dremel type tool, they look very coarse…. I have conical felt polishing tips and two different polishing compounds but it is my understanding that this is just for surface polishing after any shaping / smoothing is done. Is there something else I should have here?

I appreciate you alll taking the time to steer me right here
Click to expand...

As Greg_E mentioned above, rubberized abrasive wheels work well. I'm a gunsmith (retired) and one of the most common jobs I did was throating and polishing the feed ramp of a 1911 barrel to make it reliably feed hollow points. I used Cratex brand rubberized abrasive wheels. I'd rough the feed ramp out first with a proper size/shape carbide burr, then switch to the appropriate grit Cratex wheel or cone to blend and polish, and finish up with a high polish using a felt bob and fine polishing rouge. The same procedure should work just as well for airgun port work.

Cratex wheels are particularly useful because they both remove material and blend/polish at the same time. They come in a variety of sizes, shapes, and grits for use with a Dremel tool or similar hand held grinder. Here's a link-

CRATEX Abrasives – Rubber Abrasive Wheels Points Cones Sticks

CRATEX is the leading US manufacturer & supplier of rubber abrasives. Largest selection of grinding & polishing wheels, points, sticks and mandrels online. (800) 800-4077
www.cratex.com www.cratex.com
 
Last edited:
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu