Crosman hollow probe build

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   With new enthusiasm I started making a couple of new hollow probes. These allow the air or CO2 to travel up and act directly into the back of the pellet. The other design factors i've included are a tapered edge that fits inside the pellet skirt and enough length that it seats the pellet past the transfer port into the breech. I tapered the edge so that it should help engage the skirt with the rifling and so create a good seal.
I will let the photos do the talking, but this is progress so far. First photo shows the main profile and O ring groove formed

Here you can see the probe halfway across the TP, and second photo shows a clear passage through probe. 

The next couple are various angles of the hollowed out probe. I still need to workout the bolt hole angle and placement so that the hole lines up with the transfer port when pushed home.

One more showing how the taper fits into the pellet skirt.

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Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 10 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1172	Post Options Post Reply Quote Pauly5 Report Post Thanks(0) Quote Reply Topic: Crosman hollow probe build Posted: 09 May 2023 at 10:11pm
	With new enthusiasm I started making a couple of new hollow probes. These allow the air or CO2 to travel up and act directly into the back of the pellet. The other design factors i've included are a tapered edge that fits inside the pellet skirt and enough length that it seats the pellet past the transfer port into the breech. I tapered the edge so that it should help engage the skirt with the rifling and so create a good seal. I will let the photos do the talking, but this is progress so far. First photo shows the main profile and O ring groove formed Here you can see the probe halfway across the TP, and second photo shows a clear passage through probe. The next couple are various angles of the hollowed out probe. I still need to workout the bolt hole angle and placement so that the hole lines up with the transfer port when pushed home. One more showing how the taper fits into the pellet skirt.

Billbobnz Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 13 Jun 2020 Location: Ashburton Status: Offline Posts: 765	Post Options Post Reply Quote Billbobnz Report Post Thanks(0) Quote Reply Posted: 10 May 2023 at 9:04am
	wow great work Paul, let use know if you get any increase of power when you test shooting it

nunga Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Forum Moderator Joined: 08 Mar 2013 Location: Pukekohe Status: Offline Posts: 824	Post Options Post Reply Quote nunga Report Post Thanks(0) Quote Reply Posted: 10 May 2023 at 10:57am
	I would be interested to see how much it cools down per shot due to the CO2 expanding at a faster rate. Looks good!
	2nd place HP springer - WFTF World Championships 2014

kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1671	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 10 May 2023 at 11:07am
	Would not the easiest way to line the hole be to make the bolt/probe minus the hole, then with the breach attached to the barrel, lock the bolt shut turn the breach and barrel upside down in a vice, aline it and with a drill press, drill it to just shy of actual circumference needed then finish it off out of breech. This to me would eliminate the need to have to work out angles, as the hole is drilled at the correct point for the locked position of the bolt. I love the tapered edge for end of probe. Assuming that pellet skirts are even and not causing a lockup against the barrel, I imagine that air/CO2 will after the initial push starting the pellet, push back causing the skirt to flare nicely with good pressure. Be keen to hear results when done. Looks like I might be ditching the extended probes I have which are awsome for your design if they work well. And of course if I can persuade you to make me a couple.

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 10 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1172	Post Options Post Reply Quote Pauly5 Report Post Thanks(0) Quote Reply Posted: 10 May 2023 at 12:32pm
	I haven't tried it on CO2 yet. Kruza, I had made one a while ago, and so I have exact measurements to follow that work for the probe tip, but I have made a hardened centre punch tool for marking the exact position of the bolt hole while the probe is in position. So this definitely works, but haven't compared it with the extended probe, but I feel both benefit over the factory probe by getting the pellet past the transfer port and have less restriction for the air/CO2 to get behind the pellet. I am going to try and make a few while I have my "flow on" if you know what I mean. Billbobnz, I reckon there is an increase, but I often forget to make notes before I start, so don't have the comparison. I have fitted one to my 362, and compared it to a brand new 362 out of the box, and from 8 pumps I am getting 13.8 fpe, and the new std gun got 12.2 fpe with the same pellets.

J-S Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Senior Member Joined: 19 Oct 2014 Location: Auckland Status: Offline Posts: 356	Post Options Post Reply Quote J-S Report Post Thanks(0) Quote Reply Posted: 10 May 2023 at 2:07pm
	Looks awesome! Could you have done the bolt handle first, close bolt firm in the breech then marked the TP hole for location?
	J S Airguns Air Arms TX200('s) Theoben Sirocco HW77 FWB 300s Webley Patriot One or two others... Current projects: Too many..

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 10 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1172	Post Options Post Reply Quote Pauly5 Report Post Thanks(0) Quote Reply Posted: 10 May 2023 at 6:53pm
	Yep, ok JS and Kruz I agree that would work too. I don't drill the hole in the probe tip, but run a small round file across it. I didn't drill it because the wall is quite thin, and I was concerned if the drill bit snagged it would pull it out of shape and bugger it up. But I could definitely mark it up that way and then form the hole. I'll do it on the next one.

kruzaroad Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 02 Jul 2022 Location: Hastings 4 now Status: Offline Posts: 1671	Post Options Post Reply Quote kruzaroad Report Post Thanks(0) Quote Reply Posted: 10 May 2023 at 6:55pm
	But if it doesn't work you welcome to give us grief for the sujestion

jwabfrog Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 12 Nov 2021 Location: Thames Status: Offline Posts: 118	Post Options Post Reply Quote jwabfrog Report Post Thanks(0) Quote Reply Posted: 11 May 2023 at 8:36am
	Awesome engineering Pauly, you obviously have a lathe? Jeweller's size or something bigger?

Pauly5 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 10 Mar 2013 Location: Titahi Bay Status: Offline Posts: 1172	Post Options Post Reply Quote Pauly5 Report Post Thanks(0) Quote Reply Posted: 11 May 2023 at 9:07am
	Yea, it's a small one from the toolshed. Often referred to as a Chinese mini lathe. I've had it a couple of years now and it's addictive learning how to set it up and use it. I'd recommend it if you're looking for another hobby. One thing I have learnt to appreciate is that tolerances are so important, and you can often make an ordinary everyday item better by reducing tolerances.