GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: imadunatic on December 31, 2016, 07:54:38 AM
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Not sure if I'm getting older, or if the steel breeches have less room to load than the stock plastic breech, but I'd like to increase the distance between the end of the bolt and the front of the pellet loading slot in the breech on both my 2240 and 2400.
I think the easiest way is to chop some material off the back of the bolt and possibly mill the cocking slot further back in the breech, but I thought I'd see what others have done (assuming I'm not the only one with this problem) before I start making chips.
Thanks,
Kevin
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Boy I'm with you on that one Kevin, My son gifted me a new 2400kt with 4x scope ;D I was also thinking If I modded the Factory bolt and extended bolt probe just a bit, To make sure the pellet was seated just in front of the port, If I would even have room to get a pellet loaded in their?? :o I was thinking also about removing some of the rear bolt also? I Hope someone will chime in on this before, I make my move Trimming her up. Jaa
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Boy I'm with you on that one Kevin, My son gifted me a new 2400kt with 4x scope ;D I was also thinking If I modded the Factory bolt and extended bolt probe just a bit, To make sure the pellet was seated just in front of the port, If I would even have room to get a pellet loaded in their?? :o I was thinking also about removing some of the rear bolt also? I Hope someone will chime in on this before, I make my move Trimming her up. Jaa
That is another concern... I have a 10" barrel and extended probe on the way for my pistol, that is definitely going to make it worse!
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I wish that Powermax still had their V Probe available, it pushes the pellet in by the skirt rather then by the center of the pellet and over the port good. There's good room for loading the pellet when the bolt is open as well.
(http://i983.photobucket.com/albums/ae312/giant056/Airguns/vectorprobe.jpg)
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Yes, you can trim approximately 1/8" off the back of the bolt to increase loading room. I'm saying 1/8" based on memory. To see precisely how much you can remove, just pull the bolt back as far as it will go and take note of how much travel remains in the cocking slot.
As already mentioned, this mod goes hand in hand with another essential mod--using an extended probe to seat the pellet skirt past the barrel port. The stock probe puts the skirt right above the port which has two negative effects. One is that it can impair accuracy by deforming the skirt when the pressure pulse hits it. The second thing is it robs power by permitting blow-by. If you don't remove some material from the back of the bolt, the extended probe leaves insufficient room for loading longer pellets such as a JSB 10.3gr.
As Wayne says, a chisel-shaped probe or a hollow probe sidesteps this issue by seating the pellet via the perimeter of the skirt. However an extended probe works well and I like that I can convert the factory probe and be up and running the same day, as compared to costly aftermarket part that takes days or weeks to arrive.
It also gives me an opportunity to add a thin neodymium magnet to the back of the bolt to keep the bolt open. Otherwise it tends to slide forward and aggravates the problem with loading pellets.
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Wayne,
I like that V-Probe. I think if I ever am finding myself turning a bolt from scratch I might try that. How does it perform energy wise? Seems like it would be pretty good flow also.
Jason,
Thanks for the detailed description and pics (with dimensions no less!). Yet again, I'm going to shamelessly copy one of your ideas..... Ordered 50 of those magnets, should be set for awhile.
Kevin
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PowerMax has their site back up for the HiPac. I jumped on their site forum and ask, { Any Chance we'll see the .22 cal V Probe back in production anytime soon?? } And their response was, { V-Probe is coming back...in the Spring. nt - Rodents' Rapture on Jan 1, 2017, 8:08 AM } I have read about these bolt prob's on other forums as well, With with others reporting Good results, But I have not seen hard Data yet on them, Sooo I will order one and try it out when they become available again. Cheers Fella's Jaa
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PowerMax has their site back up for the HiPac. I jumped on their site forum and ask, { Any Chance we'll see the .22 cal V Probe back in production anytime soon?? } And their response was, { V-Probe is coming back...in the Spring. nt - Rodents' Rapture on Jan 1, 2017, 8:08 AM } I have read about these bolt prob's on other forums as well, With with others reporting Good results, But I have not seen hard Data yet on them, Sooo I will order one and try it out when they become available again. Cheers Fella's Jaa
Wow this is very good news, I know Alex was saying something about bringing them back but wanted to get everything figured out through his machinist. They're really excellent for loading a pellet plus the fact there's no restrictions on 90 degree rounded turn of the air to the back of the pellet.
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Yes, you can trim approximately 1/8" off the back of the bolt to increase loading room.
Jason,
Modified a couple probes last night (one each in .177 and .22 for testing); you're right these are easy peasy (though I'd like to know how you do it without a lathe??? Still amazes me what you accomplish without a mill and a lathe... unless you've added to your shop lately?). I plan to have a shootout with the stock probes, discovery probes, needle probes and if I find time to make them, V probes like Wayne posted.
(http://i.imgur.com/zZNz4OF.jpg?1)
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Nice, I'm glad to hear it went well.
No, just a simple drill press, hand drill, and files is about it :)
If you get inspired to run a comparison test of different probe types, I would love to see your results. But I think if you do some searching, you will find the effects on velocity will scale pretty similarly based on the effective cross-sectional area between the valve exhaust and the base of the pellet...whether it's a pin probe, a hollow probe, a chisel, scoop, or whatever. It seems logical that angling and radiusing things in an attempt to channel the air toward the pellet would result in better flow but people smarter than I have pointed out that the air flow is still almost entirely turbulent (not laminar) due both to the nature of the upstream flow through the valve and due to the fact the valve is not open for long enough for air flow to achieve any sort of stable, steady state flow characteristic.
In other words, if the goal is to get the highest velocity, the focus is on making the probe as small as possible rather than making it a particular shape.
With that said, I do have a slight preference toward hollow probes because they seat all pellets to the same depth since they push at the perimeter of the skirt. Also, compared to a pin probe, it leaves slightly more room for loading a pellet.
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Problem with solid bolt probes is that they push the pellet in from the center. So they push them in from inside the hollow skirt. So how deep the hollow skirt desides how deely they are chambered. So a solid proble has to be long enough to get the rear edge of a deep hollow skirt to be ahead of the barrel port.
Think one of the reasons Crosman probes come so short is that they use Crosman pellets as their guide; Crosman pellets have a very shallow hollow skirt.
Hollow probe pushes a pellet in from the edges of the pellet base, so pretty much any pellet (solid base to the deepest hollow base) is going to be pushed in so that the base is ahead of the barrel port.
I will give you that a small diameter solid probe will have the largest air path and that solid probes are a bit more restrictive.
Shortening the rear of the bolt helps a bit with a long solid probe. There is a limit to that; take off too much and the bolt won't be able to get the strriker far enough back to catch the sear. Can estimate how much you can gain by pulling the bolt back HARD...mark the distance..and let it ease back foraard until the saer is firmly caught by the sear...mark that. The distance between marks is as MAX you could shorten the rear of the bolt (and I'd add in a little bit more to allow the sear to catch evenly).
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All points well noted, especially the turbulent flow comment; I've never thought about it on that level, but it's good food for thought. I think one of my measures for the test also need to be ease of use. Since I've never used one, I think I'm looking most forward to trying out the V nose style because none of my guns have anything close to that.
Ironically, almost everything I gained by removing material from the back of the probe, I lost when I added the needle point.... My everyday driver for the 2240 and 2400 are stock disco probes, which are only about .050" shorter at the probe than these needle style, so the extra room will still help.
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Problem with solid bolt probes is that they push the pellet in from the center. So they push them in from inside the hollow skirt. So how deep the hollow skirt desides how deely they are chambered. So a solid proble has to be long enough to get the rear edge of a deep hollow skirt to be ahead of the barrel port.
Think one of the reasons Crosman probes come so short is that they use Crosman pellets as their guide; Crosman pellets have a very shallow hollow skirt.
Hollow probe pushes a pellet in from the edges of the pellet base, so pretty much any pellet (solid base to the deepest hollow base) is going to be pushed in so that the base is ahead of the barrel port.
And the flow-though probe bolt will (or can) be shorter that an extended pin probe that consistently pushes the pellet pass the TP. Mellon has the shortest flow-through probe bolt. But any can be modified to minimal length or modified to the V form, either of which always positions all pellets to the same depth past the TP.
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http://i6.photobucket.com/albums/y212/Larry59/Extended%20Bolt/01-ExtendedCockingBolts.jpg (http://i6.photobucket.com/albums/y212/Larry59/Extended%20Bolt/01-ExtendedCockingBolts.jpg)
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This design of a 22XX hollow probe intrigues me because of the self center of the pellet and the full air flow.
http://s160.photobucket.com/user/BobPratl/media/2240%20hollow%20bolt_1.jpg.html (http://s160.photobucket.com/user/BobPratl/media/2240%20hollow%20bolt_1.jpg.html)
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Yep, and Exactly what Crosman used years ago. ;)
Knife
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Good point Bob. I'll have to make up a couple flow throughs for testing once I get my drill blank stock in. Need to wrap up a couple other projects first, I have too many going at once!
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Good point Bob. I'll have to make up a couple flow throughs for testing once I get my drill blank stock in. Need to wrap up a couple other projects first, I have too many going at once!
Tell me about it, I got totally confused with so many UNFINISHED projects that I had to go to the dollar store and purchase a dozen large plastic boxes to put each unfinished project in them because I had them spread through my shop. How I have to find a place to put the boxes. Bob