POI shift by breech plug
I was just reading this thread about tophat clearance possibly causing POI shift
http://talonairgun.com/forum/viewtopic.php?t=1396
I think I have found a cause of POI shift in my Condor that I overlooked before.
My tophat is still at the factory setting of 0.093″, and when I close the breech plug and lock the plug to the left, my POI shifts to the left. If I lock the plug to the right, the POI shifts to the right. I have found that my breech knob rubs on the frame when I lock the breech plug, similar to camming a bolt action shut, and seems to impart some sideways force on the breech of the barrel.
I did some testing today, and found if I do not rotate the breech plug to lock it, my group sizes got very small with no flyers.
I shot this way with my chronograph, and saw very little variation in FPS. I checked to see if my breech plug was blown foreward after the shot and it was not. It seems to me, that locking the breech plug is unecessary.
I have developed a habit of just pulling the plug knob straight back onto the tophat just before releasing the safety. Shot after shot, velocity was very similar, and the accuracy of my gun has increased greatly.
I have been having great consistency with my tophat set like this, and using rubber washers to limit tophat travel giving me excellent shot to shot velocity. So I dont want to mess with the tophat setting. I figure if it works for me I wont mess with it.
Just thought yall might want to hear about it though. Could possibly be causing others similar problems.
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Bodhisdad and WOK, I don’t think the POI shift is caused by the tophat binding to the bolt/breech, or because of upwards or sideways pressure to the barrel. I checked that already. Like I mentioned in the previous post, upon firing, the air pressure within the breech will cause the bolt to thrust forward (it happens very fast you can’t tell just by looking at it). I’m sure this happens with all the AF rifles. And when this happens, the bolt will hit the frame with a significant amount of force, thus perhaps causing some movement the moment of a shot, which in turn will cause POI shift. Try putting your finger next to the knob (or in front of it) or lightly touch it and fire your gun (with a pellet loaded) in a safe direction and you’ll see what I mean. It happens too fast to be seen, but you can feel the force by doing as I recommended.
Cheers!
Could happen. Do this. Put your tank in and look down the barrel. Towards the top hat.
What do you see? Is the top hat in alignment with the barrel? Or is it higher lower or to one side?
It the top hat is not in alignment with the barrel as you close the bolt on it, it will cause the bolt to tilt and apply pressure to the barrel that should not be there.
I have my 18″ barrel in and want to do a string/s with Blodnob’s valve. I’ll experiment with this as well today. Could very well be, but why would it have an affect? Unless there was some binding issue, like the tophat being to far out and locking the brech left or right is putting pressure on the brech end of the barrel. When it comes to AF rigs one can’t rule anything out though. I’ll see what i come up with today.
You know, it might very well be that shifting the cocking knob left or right will really do change POI. I noticed that my Condor SS’s POI remains unaltered when the cocking knob position is kept centered and not set to the left or right notch. On close inspection upon firing, I placed my finger just next to the knob when in the left or right position and there is a considerable amount of force that is generated to the frame. The knob actually bounces towards the frame and I strongly believe that such force creates some movement just right when the bolt slams onto the tophat. I discovered that my POI will either go left or right depending on the knob position. But when I center the knob, whereas when it bounces against the tophat, it would thrust forward right towards the open space the bolt glides into (when cocking it), thus not imparting any force or impact to any part of the frame. I’ve done some extensive testing today, and I believe that this might very well be a reason to shifting POI with some rifles. Additionally, I believe that if it takes just little travel from a shot, the knob is more likely to slam onto the frame with more force due to less travel backwards (making it hit the frame faster when bouncing forward), thus making POI shift much more drastic if it is locked onto the left or right notch. Because of this, I now leave my cocking knob centered, where it will bounce into the open space. And my POI is consistenly dead-on.
Because of your problem and what i’ve seen with newer talon tophat threads i’ve invested some thought into this issue. Your problem is somewhat unique. While the talon valve stem seems to be universal. In the tanks that have been through my hands or the guys i’ve correspond with concerning the valve mod 1 problem seems to reaccure. That is after they reinstall the valve and go to adjust the tophat the furthest they can get it set down to is .070. While i’ve found .067 to be a optimum tophat setting for my rig when i had a stock valve in it.
Now to reduce the the clearance one can in the case of the talon valve 1. cut some more threads on the stem (not easy) 2. shim the base to reduce travel easy. Or and this is my brainy idea 3. adjust the valve spring retainer. That is unscrew the retainer to reduce the travel of the tophat. In the case of a talon valve 1 revolution of the rtainer should do the job. With the addition of a thread locker the retainer would stay in position. This i think is a option for you. One could also load the threads of the retainer with teflon tape and screw it back in to a predetermened position. I believe when you go to lock her down your adding a little flex, which is all it takes. If my stem was as bad as you say yours is. Send e-mail or call AF and discuss a replacement. If the grub screws are through the walls of the stem you could at some point collapse the valve, you wouldn’t be the first. my .02
Hi Bod,
I went with 90° on the grip mount because thats the only way I could get the TC grip to work before, and I already had the gun modded to make it work.
On the breech plug, yes the plug cams against the frame, you read correctly.
Mostly the problem seems to be the little plastic sleeve on the breech bolt shaft is oval and worn out. I am going to build a breech bolt that will be sure to be unique, I just have to figure out how to do it, laff..
I swear I wake up every day with a solution and cant wait to get home from work to try it out.
BTW, I should have read your reply here before I looked at your updated thread. You answered some of my questions already, thanks!
When my Dad passed away a few years ago, he left behind a lot of woodworking tools. I ended up with most of his saws, and my oldest brother ended up with a sander setup that I just have to go out and buy. Just about everything he built went across that sander. Very cool.
Thats how we learn. A 90 degree is near impossible for the grip securing. 1/4″ through hole at the angle of the grip (mine are slightly angled 15 degrees), then a 9/16″ counter hole from the bottom i use 1.5″-2″ hex head and washer and drill till i have a 1/2″ of threads exposed for the anchor. I have mine cutout, inletted, need to cut out the skeletonized protion and i’m ready for attaching points and shaping. Made a oscillating sander out of my drill press and pvc tubing 3″ long, super glued some 60grit on and it works great. Still want my oscillating sander, but will have to wait till i sell a stock or two. Its going to work awesome, the bottom strut design adds alot of strengh
On the topic of the brech issue, are you catching part of the frame as you lock it left or right?? Which is how i read your post to begin with. Might have a solution if so, easy one.
Ok I think I got the mounting of the stock sorted. Decided to go with a pillar mounting of sorts. Glued in some thickwalled carbon tube to act as the pillars, mounted the stock, then glued the 2 halves together on the gun. (Dont worry, the stock comes off its not glued onto the rifle)
Pics of the pillars
1st half of the stock mounted, before gluing the 2nd half on.
2nd half glued and clamped.
It should be obvious this stock is very ugly and will probably stay mostly unfinished as it is a test. Gonna chalk it up as a learning experience, LOL. If it works I might sand it and finish it, but I want a better hunk of wood.
If things go well, I can have mine mounted by this weekend. None of the shaping will be done and I will probably end up with splinters, but I want to test-fire the stock ASAP.
I nearly have it glued up, I need to decide on the mounting hardware and method i.e. thru the grip is a pain in the butt, + the angle of the grip screw isnt the same as the front screw… binding a probablility.
Might have to go with a captured grip screw 90° to the frame, access hole thru front of grip maybe…
Guys,
I really like the whole idea behind the full stock on these rifles. Look forward to checking these out as you guys advance with them
The pic I posted is the center rib of he stock. It is lammed to the same thickness as the lower rail/trigger area of the gun frame.
More layers will be lammed onto it which will extend up to the rounded part of the frame. The stock will mount the same way Bodhisdads stock will, with the grip screw and the next forward screw just ahead of the safety.
Hopefully the stock will be rigid enough to not flex. This way I wouldnt be able to twist the gun frame, because I wont be touching it at all. The only original part of the gun I will be touching is the trigger.
I dont expect this stock to work as well as it could, because I am using cheapo wood. If the design is comfortable and shows promise, I will probably invest in something worthwhile. So far, it shoulders and feels pretty good.
Nice Knifemaker that .20 has some balls!
Really looking forward to seeing the 1 piece stocks you guys come up with too!
Jim.
I am so thankful that I haven’t had any of the reliability issues that some of you have had. So far. So good. I have more problems with wind here than anything else! The 18″ .22 bbl. should be here Mon, or Tuesday. (It was scheduled for Fri of course!). I hope it does well. The .20 12″ has been superb. Took a feral *** with it a few days ago. 47 paces, at night. .20 cp, 14.3 entered the bridge of the nose, exited the back of the pallet, re-entered the back of the throat, and broke the neck. Got to love it!!! Mike
I remember reading about this same poi shift on our fallen brethren site, I personally think it holds water.
adjusting the tophat so there is no binding should definitely help, but probably not cure the problem, after realizing I couldn’t “man handle” the rifle and seeing what the redwood did I’m convinced these thing are incredibly touchy to slittiest little thing out of norm.
what I do is always rotate to the right, it has become an unconches habit, I will try leaving in the center and see if anything changes and let you know what’s what
how about some info and pics of the stock you’ve started ❓
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Had no problems today with POI changes left, right or center. I do have play from the tophat to the lockout position, so i know i’m not binding or misaligned. All shooting was done from a bipod, benched to chrony my 18″ with Sean’s valve. Only had 2500psi but still got good numbers well over 900, into the 950’s and no POI changes what so ever. Indoor shooting so its not like i’m out shooting at 40+yds either. 10yds is more like it, but i was stacking them 1 on top of another.