Impact MKII 30cal Pellet Drag Across Port

[jking]

I've can feel my 44gr JSB's dip into the brass barrel port when I cycle a pellet in. Sometime worse than other times. I've looked at it before and actually pulled the barrel out and manually push a pellet through and observed it happening. I've open up the outter side of the port minimally and don't think I ever went deep enough to contact much less increase the port size. I think I also pushed that same pellet back out and inspected and really didn't see any damage. I think I have polished that edge as well in the past with some really fine sand paper but when I was shooting yesterday I could still feel that rough hanging spot. Doesn't really seem to effect accuracy but I can't stop thinking that it probably isn't the ideal situation. I'll look at it again this evening and see if I'm missing something. My Crown in 30 doesn't feel that same way.

Has anyone else noticed the same thing?

Jimmy

Mod Edit: Moved to PCP Airguns forum

 

[2fast2furious]

Did you open up the brass port hole bigger? When I opened my brass transfer port hole larger to get more power. The pellet would tilt enough to clip the edge of the transfer port. Sometime it even get caught and jam. I had to push it back out with a rod. When you open the transfer port, do not open it wide. Must elongate in a orval shape. I had to call fx usa and order a new brass port. Costed like $38 plus shipping if I remember correctly 

 

[bandg]

I had a similar problem with a different gun-a SPA rifle. Pellets would have a very noticeable shaved area off the pellet head when loaded across the stock port and then removed. I beveled and polished the muzzle 1/2 of the circumference of the transfer port using thin strips of emory paper. Solved the problem completely on that gun but I don't know if you can gain access to do the same on yours.

 

[mtnGhost]

You can smooth it out pretty easily with 1500 grit sandpaper wrapped around a wooden dowel stick or wooden skewer. Go lightly until the burrs are gone and thr edges are smooth.

I usually polish mine with Cape Cod cloth after doing any modifications, but that's not really necessary.

 

[Airgun-hobbyist]

I did open up my port a bit large as well, so it was doing the same as your describing. I had also raduised the leading edge so it wouldn't shave off the lead or jamming, but I found that it had more to do with my modified pellet probe allowing the pellet to drop nose first. (It was worse with short slugs, every one jammed). This was because I had removed the bottom of the probe, so it was like a half moon pushing only on the top of the pellet, whereas the full circumference of the original probe pushes squarely on the back of the pellet. So I made another probe and just opened up the probe's port to match the brass transfer port, and thinned the inside diameter to allow the most air through. Now it pushes squarely again and I can load pellets and slugs again.

 

[jking]

Thanks guys, when I pull the barrel back out for another look I'll double check the inner muzzle end edge but I'm almost certain that I didn't go near the inner edge and just barely gave the outer edge any bevel. I'll check it again and if necessary try a new inlet port. I could probably get a strip of fine emery cloth to work but I'd have to pull the port off the barrel tube which won't be an issue. mtnGhost, never heard of Cape Cod cloth. Same as emery? Thanks again all, like I said it's shoot really well anyway but it'll bug me till I get it smoothed out a little better.

JK

 

[Airgun-hobbyist]

You shouldn't have to take anything apart aside from removing the barrel assembly out of the gun. If you tightly wrap the 400-600 grit wet/dry sandpaper around a small diameter Allen key, or something similar, you can use that to round the sharp corners of that drilled port easily enough by coming up through the transfer port that you already bevelled. Making that leading edge a nice polished and raduised corner should help the pellet not want to grab onto it on its way in.

 

[Guest]

Hey Jimmy to throw my $.02 in here I believe Airgun-hobbyist was on the right track at first when he brought up the subject of the pellet probe. I have fixed the same problem you are having but on several .30 Wildcats by simply replacing the pellet probe. You can't always even discern a problem by eye but it doesn't take much to damage the tip of the probe so that it is not pushing on the pellet evenly, which causes it to get skewed in the brass barrel inlet. I would recommend replacing both your pellet probe and your barrel inlet, and I would also recommend leaving the barrel inlet alone and not enlarging the transfer port hole in it. 

The small amount of extra power you receive by enlarging the transfer port hole is really not worth the aggravation and problems it can cause. And unless you enlarge the transfer port hole in the probe to match the larger transfer port hole you created in the barrel inlet you haven't accomplished a whole lot anyway. Furthermore, the design of the tip of the probe does not really lend itself to us enlarging the transfer port hole in it without the risk of damaging it, which causes pellets to enter the breech askew sometimes or all the time depending on how bad the damage is.

To prove out what I am telling you it is a simple matter to shoot some pellets over your chronograph with a modified transfer port, and then shoot some pellets over your chronograph with a standard OEM barrel inlet with an unmodified transfer port. The difference in power is negligible in my opinion... ask yourself honestly just how much difference it really makes to a rabbit if you hit it with a pellet going 30 ft/s faster or slower? Something for you to consider is that I have not modified any transfer port holes in .30 caliber barrel inlets in a long, long time due to exactly the same problem you are having.

Your friend, Chuck

 

[jking]

I had a chance to pull the barrel and looks things over again. After pulling the barrel I slowly pushed a few pellets through the brass port fitting and into the SS adapter piece while watching it from underneath. Surprisingly but good news, zero tips. The first resistance I felt though was when the pellet enters the SS adapter and the back edge of the pellet skirt sticks at that point requiring extra effort to push it forward. Once it reaches the liner and into the liner it's smooth and consistent as expected. Not sure why I said the pellet was tipping in the opening post, maybe a different barrel and caliber in the past. I was thinking that I hadn't altered the inner barrel port dimensions and that's exactly the way I found it upon inspection. Just a very slight taper to the outer edge. Looks like abandoned that project at the time. 

I did notice something that didn't look right and might be part of the bumps in the road while loading a pellet. There is a substantial gap between where the end of the SS adapter male end butts up to the brass port. I'm guessing 3/32" and could possibly cause the bearing edge of a pellet to drop into that gap. Externally I noticed also that the O-ring gap groove made when screwing the two pieces together was wider than what it probably should be. Before reassembly I polished the inner edges of the brass port and the inleade to the SS adapter. Upon re-assembly I used a little heat to see if it might screw together further but it didn't.

All back together using a K&L single shot loader the pellet loading felt better but still not 100%. Here's another fly in the butter.. Just loading with fingers which isn't easy the pellet would load with almost no hic-cups most of the time, smooth as can be. I'm thinking now that the little hangup spots is most likely the widest part of the skirt and the gap made by the SS adapter fit. 

Could someone shooting a 30cal take a look at that connection and gap on yours and let me know what you find? I have another brass port ordered as well. Wondering too if I made a delrin washer to fit precisely might help.

Jking

 

[Airgun-hobbyist]

I was ripping mine apart last night to do some mods and found that the pellets are doing the same thing at this point of barrel entry as well. The gap inside is there too, but it's only about .005" and just appears to be a radius to the end of the barrel. They are "hanging up" as they enter the barrel there because they are sizing themselves to the bore from what I could tell. The pellets would easily back out with the cleaning rod and have smooth bore marks on the skirt from squeezed entry, and if I reloaded the pellet it wouldn't have the same resistance as it initially had. 

What's odd is the "timing" of pellet probe action doesn't seat them that far into the barrel, (to size them into the breech), even if adjusting the rod and probe all the way in it would not push a pellet this far into the breech.

Because of the action's cocking stroke (even with everything timed just right for clearance and a new longer pellet probe to seat the pellet further in the breech) there is no way to seat the pellet into the barrel breech. My next experiment will be seating them deeper manually to see if it changes FPS. Then I'm going to bevel the breech there so the pellet doesn't initially contact the barrel so abruptly.

 

[Guest]

Ok, now I know what is going on with your gun let me tell you what I do about it...

On every one of these guns with the STX barrel system I heat up the brass barrel inlet and remove it. With the barrel inlet off, you can see the barrel liner inside the silver adapter, and see if it is set too far in...if it is too far in the pellets encounter the steel adapter before they do the leade into the barrel liner. This is wrong! To correct this problem I simply adjust the silver threaded piece at the muzzle (with the barrel inlet off) until the barrel liner protrudes out of the silver adapter just a hair. Then when you screw the brass barrel inlet back on and snug up the threaded piece at the muzzle, the pellets will now enter the leade into the barrel liner first, rather than the silver adapter.

When I perform this procedure I always remove the barrel liner completely and clean the factory preservative out of it. Then using 1200 & 1500 wet/dry paper I polish the leade into the rear of the barrel liner, and polish the crown on the front of the liner, to remove any burrs or machining imperfections. I use the paper wet so that it polishes these two surfaces to a mirror like shine. Then I polish the inside of the brass barrel inlet to remove any burrs that may be located inside where the transfer port hole was created. At this point I push a few pellets through the liner with a cleaning rod and inspect them...then if necessary I polish the bore with patches on my cleaning rod saturated with extra fine valve lapping compound...I repeat if necessary. Finally I clean the liner with hot water followed by denatured alcohol.

This is the point where I reinstall the barrel liner into the barrel tube. If you look inside the front of the brass barrel inlet you will see a shoulder machined for the barrel liner & silver adapter to butt up against. Just make sure the liner protrudes just a hair past the silver adapter so the leade into the liner is the only thing the pellet encounters. To do everything I have described here should not take you more than about 30 minutes. The last thing I do when I am finished with all this is index the barrel liner while shooting groups to find the sweet spot that gives me the absolute best accuracy. Hope this helps you with your problem Jimmy.

 

[jking]

Chuck I think I'm following you. For some reason I thought the liner ran up against a shoulder inside the SS adapter but what your saying is that the liner can pass all the way through through the SS adapter if you wanted it too? Question, If you kept screwing in the on the liner retention nut/screw at the muzzle what would keep the liner from traveling too far? It always feels like the liner bottoms out inside the ss adapter.

" If you look inside the front of the brass barrel inlet you will see a shoulder machined for the barrel liner & silver adapter to butt up against". Does your SS adapter butt up against that brass shoulder? See mine don't by probably 3/32". I'd like to clarify if these two surfaces actually butt up against each other.

Jimmy

Duh, forgot I could look at my 25cal Impact barrel system. There is no gap to speak of between the brass shoulder and the SS adapter end which results in a lot better O-ring groove as well. I think now to solve the problem I just need to figure out why the 30cal is not screwing together all the way. Here is the 25cal make-up..

JK

 

[jking]

Ok, here we go again. Pulled the barrel back off and discovered what Chuck was talking about. I sure didn't realize that the liner could pass all the way through the SS adapter. Another thing that I discovered was what I thought was the shoulder in the the brass port and a "gap" was not correct. What I was seeing was just a machining mark that made it appear that there was a gap. So what I did then was work the inleade leading edge over again and enlarged it hopefully a little. Seems to have hopefully fixed my issue. Will be able to tell more tomorrow. Funny how these things go.....

Jking

 

[Guest]

Ok Jimmy, we are almost there so let me try to explain it using your picture there... On the old SmoothTwist barrels the leade in to the barrel itself butted up against that stopping point (shoulder) inside the brass inlet, so that the pellet started right into the barrel and could not do otherwise. Now we want to accomplish the same thing with the STX barrel liner system...we want to make sure the tip of the barrel liner itself is up against that shoulder inside the brass thimble. To make sure of that just remove the liner lock nut off the muzzle; and remove the brass barrel inlet from the other end; then you will see that you can push the liner right on through the stainless adapter.

You will also discover that you can push the breech end of the liner into the stainless steel adapter a little way so that the head of the pellets encounter the edges of that adapter before they can get started into the barrel liner itself, because the adapter will butt up against the shoulder in the brass inlet with the liner up inside the adapter. To prove this to yourself just remove the liner and set it aside and screw the barrel inlet all the way onto the stainless adapter until it bottoms out on the shoulder in there. You don't want your pellets to enter the adapter first...you want them to enter into the liner first...even if we are only talking about a few thousandths.

So, with the liner sticking out of the stainless adapter a little bit, screw on the brass barrel inlet until it stops...so that the first thing butted up against the shoulder inside the barrel inlet is the liner; then install the liner lock nut at the muzzle and just tighten it a hair past snug...don't over tighten it or you can bend the liner like a banana. This guarantees that your pellets enter straight into the barrel liner first as they are being pushed through the brass barrel inlet by the probe.

I polish the leade into the barrel liner by putting a small piece of sand paper over the tip of a sharp pencil that is in my Makita, or for .30 cal. I sometimes use a piece of sand paper on the tip of one of those cone shaped stone things in my Dremel Tool kit. What I achieve is to make the leade into the barrel liner sort of cone shaped and smoother than a baby's bottom so the pellets slide in with the greatest of ease. I do this with the liner out of the black tube and with the barrel inlet off of course. I figure I have it about right when I can start a pellet into the liner with my thumb and finger and push it into the liner just past the skirt of the pellet with the tip of my finger without hardly even trying. Sometimes I have to wrap some sandpaper around a small wood dowel and using my Makita I smooth out the first inch or so of the inside of the liner. The point is that I don't want my pellets to have to "find" their way into the liner...I want them to leap in there easy peasy and be on their way.

This is one of the things I do to give the rifle a fighting chance to be accurate...and you know what I mean by accurate.

 

[jking]

Thanks Chuck, that's where I left it this evening. I was also able to push a pellet just inside the liner with my finger now that I opened up and polished that liner edge microscopically. I cycled a few pellets using that K&L when I finished and it felt really good now. Like I said the liner was butted up to the brass port but I didn't recognize it due to the false image the machining mark was throwing at me. Thanks again for the help, much appreciated.

Jimmy

 

[Guest]

My pleasure sir.

 

[ribbeschoer]

i was reading this very interesting topic, i am interested in the single shot loader made by K&L, can i establish that the single shot loader is not hitting/touching the brass barrel inlet? (sure i can adjust the barrel placement a little so there is no contact between the two.. ) i have an impact mk1, is it necassary to remove the small rubber "balls" to place the Single shot loader? ( sorry the last question is a little off topic) 

 

[jking]

I can't answer your question on the rubber balls but the K&L does not contact the brass inlet piece. As in the photo, there is a groove cut into the housing of the K&L. There is also adequate gap between the pellet holder and the end of the the brass inlet and the tubing that holds the pellet is some sort of rubber.

Jking

 

[ribbeschoer]

I can't answer your question on the rubber balls but the K&L does not contact the brass inlet piece. As in the photo, there is a groove cut into the housing of the K&L. There is also adequate gap between the pellet holder and the end of the the brass inlet and the tubing that holds the pellet is some sort of rubber.

Jking

Thank you so much Jimmy for your re-post and illustrated it with photos of the SS! it is really appreciated!