GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: FuzzyGrub on January 01, 2019, 11:33:42 AM
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Over the years, have always wanted to a 25 cal prod conversion. For many different reasons, over that time frame, always found an excuse not to do it. It was probably the hardest when Travis built a number of 25 cal mini-rods. ;) Now that I have three long tube (7/8" OD) guns, it is just natural that they be different calibers. After allot of contemplation, decided that the newest entry in the collection, will become the "donor".
Here is the baseline starting point: My Fortitude Break-down and mod thread: https://www.gatewaytoairguns.org/GTA/index.php?topic=150000.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=150000.0)
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The goal for this project is a 25 cal light-weight Mrod. Power level and shot count should be equal to my original oem synrod. 16 shots at 40FPE 2-3% Es.
Many of you are familiar with the tuning work done by GTA members for Mrods, ie the 40/40 club. 40 shots at 40fpe. While I never made it to the club, I did achieve 32 shots at 40fpe. Doing the plenum and air tube volume calculations, it equals 1/2 of the Mrods. ie 16 shots should be achievable, as long as the porting and other factors can be kept to the same.
The biggest challenge, for me, will probably be the breech/bolt modifications needed. Spent a good deal of time thinking about that yesterday. ie workout the major stumbling blocks, before starting. I know, what fun is in that? Don't worry, there is always something you will find on the way, regardless of planning. :)
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Sounds like a fun project! Well I think you can get a .25 TJs in .4375 OD which would make it easier for getting a barrel in it. The bolt though can't help there
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The major consideration:
1) Machine the 1/2" barrel to 7/16"?
2) Bore the breech from 7/16" to 1/2"?
3) Combination of both, stepped approach?
I eliminated item 1 primarily from a strength and rigidity aspect, ie the other two options were superior. This also played into the magazine solution, which I will discuss further down.
Item 3, was the front runner, because I thought I had to stop prior to the breech screws. ie the spacing is such that going to 1/2" will break into those screw passage ways. It would also require taking the mag end of the barrel to 7/16" which again, gets into the mag issue.
That leads us to, option 2, bore out the whole barrel length to 1/2". The only mod to the barrel, will be a small notch on each side, where those two mounting screws are located. On the Fortitude, that is parallel to the TP.
A 25 cal Magazine:
I first looked at modifying a Mrod 22 mag to make it a 25. The standard 177/22 mag is deep enough for the 25g JSBs. I thought I could take the clear outer plate and carousal from a 25 cal mag and install in the black casing of the 22. Yes, I would have to enlarge the exit hole and make the carousal thinner, but seemed doable. What I found though, was the 25 cal mag is slightly larger ID. The carousal OD would need to be reduced, and then each of the 8 pellet slots, would need to get deeper. Other geometry concerns, like the ramp up to the exit hole and the groove that the pellet nose rides in, would challenge my Dremel skills.
Decided that keeping a stock Mrod 25 cal mag, but machining the breech for the wider mag, would be easier. ie about 0.100" has to come off of the back of the slot. I also checked, that there was just about 0.100" with the bolt in cocked position to allow for the wider mag. Might have to tweak the tip of the bolt probe(0.010").
Speaking of the bolt, I have found some stainless tubing to install on the bolt to get to the 25 cal diameter. This requires a little more work on the breech to accommodate that.
That's about it for now. The real mods will not start for a couple of weeks, and will document the process and the successes and any failures.
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Sounds like a fun project! Well I think you can get a .25 TJs in .4375 OD which would make it easier for getting a barrel in it. The bolt though can't help there
Thx Dillon. I didn't know that TJ had the smaller OD 25 cal barrels. A 25 GM barrel is already on the way, though. Plan is to sleeve a 22 bolt with SS tubing and epoxy.
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Sounds like a fun project! Well I think you can get a .25 TJs in .4375 OD which would make it easier for getting a barrel in it. The bolt though can't help there
Thx Dillon. I didn't know that TJ had the smaller OD 25 cal barrels. A 25 GM barrel is already on the way, though. Plan is to sleeve a 22 bolt with SS tubing and epoxy.
The MRod barrel makes it easier, assuming you are going to reuse the existing chamber and breech o-ring. This will be a very cool build.
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John,
The easiest thing to do is turn barrel to fit breech. Your gonna love having the .25 cal Fortitude. I still have my .25 mini-rod from Travis, she's in beast mode with the SS valve installed!
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John,
The easiest thing to do is turn barrel to fit breech. Your gonna love having the .25 cal Fortitude. I still have my .25 mini-rod from Travis, she's in beast mode with the SS valve installed!
Randy,
Does it use the standard Mrod 25 mag? I think with a Prod breech, it would need only 0.50" off the back, but also need to cut the slot deeper. maybe a bushing on the barrel so it snaps in?
Another way to look at it: If I mess up the breech, it is probably less than the cost of a barrel. ;)
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John,
Standard mag, no bushing required for the mag. The mag does fit loose in breech but it doesn't fall out!
Also, you'll need to cut a bolt probe slot in the mag facing the bolt for clearance & turn the end of the barrel to fit the factory air stripper if you are going to use factory shroud.
mini-rod breech dims
.704 wide & .839 deep. Hard to measure with scope installed.
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Thx again, Randy. I already have the 25 cal shroud mount and shroud spacer/stripper. Those parts are reasonable from crosman.
I'm not sure what you mean about the slot in the back, but also notice the bolt only has a "stub" sleeve on it. Which means I'm probably not aware of an issue with sleeving the full length of the 0.22 diameter portion of the bolt.
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John,
The easiest thing to do is turn barrel to fit breech. Your gonna love having the .25 cal Fortitude. I still have my .25 mini-rod from Travis, she's in beast mode with the SS valve installed!
Randy,
Does it use the standard Mrod 25 mag? I think with a Prod breech, it would need only 0.50" off the back, but also need to cut the slot deeper. maybe a bushing on the barrel so it snaps in?
Another way to look at it: If I mess up the breech, it is probably less than the cost of a barrel. ;)
I like the idea of opening up the breech and using standard MRod mags, fitting snugly vs. loosely. Loose fitting mags can in some cases contribute to accuracy problems,
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John,
The .25 cal mag will need a slot cut in it for the bolt probe clearance. See photo of mag. The .22 cal bolt doesn't seat far enough back for the Mrod mag to be placed in/out the breech without the slot in the mag.
I'm not sure why Travis did a short sleeve on the .22 cal bolt? My sleeve is about .328 long, looking inside of the Prod breech I dont see any potential clearance & fit for longer sleeves.
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I have no issues with accuracy, when I do my part with shots at 100yards are fun.
You could make up a barrel sleeve to mag to remove loose fitting mags, make sure it's removable.
The only thing that is loose is at the .437 barrel to .5 OD mag. You're looking at less than 0.0315 total of clearance side to side when inserting the bolt into the mag, the mag aligns with the bolt and inserts the pellet/slug into the bore. I'm not a bolt slamming kinda guy without any thought of alignment nor did you say or imply that.
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Ok, I see the slot now. :)
I'll have to take more careful measurements the next time I have the Fortitude breech off.
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FuzzyGrub,
I am thinking in the dark here, but some questions will help me make my point:
1. Do the Marauder and Fortitude have the same barrel axis to mag rotation axis, center to center distance?
2. Do the Marauder and Fortitude have the same barrel center to mag floor plate (bottom surface that rests on receiver slot) distance?
If not, you may have to play some games to line pellets up so they feed straight from the mag into the barrel. One option would be to modify .22 Fortitude mags. This seems fiddly to me; so this is my proposal:
If my project, I would try really hard to use Marauder .25 cal mags, rather than modify .22 mags. Due to my lack of knowledge about the Fortitude, I can envision the possibility of needing the barrel axis to be higher in the receiver to accommodate the Marauder mag. Here is where your barrel OD or frame ID change question becomes interesting:
If the answer to the Marauder and Fortitude questions #1 above is that the Marauder dimensions are larger, then could the Fortitude receiver ID be opened up to .5", while simultaneously eliminating the offset between barrel axis and Marauder mag?
In other words, rather than opening the Fortitude receiver barrel hole perfectly concentric, drift the center (upwards?) to enable the receiver to use the standard Marauder mag. Now, the top of the Fortitude receiver may be too thin to do this, but my goal is just to plant the idea, for you to ponder.
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The only thing that is loose is at the .437 barrel to .5 OD mag.
I would think that having the mag self align with the barrel OD is part of aligning the pellet with the chamber. This minimizes damage to the pellet, necessary to maximizes potential accuracy. As such, I think that the mag should match the barrel OD snugly (or flats machined onto it at the rear).
The question remains; what would it take to use Marauder .25 cal mags in a Fortitude? If the barrel channel need to be opened to .5", then that provides an opportunity to fine tune the resultant mag to barrel axis alignment.
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The only thing that is loose is at the .437 barrel to .5 OD mag.
I would think that having the mag self align with the barrel OD is part of aligning the pellet with the chamber. This minimizes damage to the pellet, necessary to maximizes potential accuracy. As such, I think that the mag should match the barrel OD snugly (or flats machined onto it at the rear).
The question remains; what would it take to use Marauder .25 cal mags in a Fortitude? If the barrel channel need to be opened to .5", then that provides an opportunity to fine tune the resultant mag to barrel axis alignment.
I know that on my Gauntlet .25, when using .25 Mrod magazines i have accuracy issues. The Gauntlet .25 barrel is 11mm (7/16) so it's basically the same circumstances described here. The main difference between Gauntlet and Mrod .25 magazines is barrel diameter. I will say my Gauntlet could use a bit of clean up work in the breech/lead of the barrel so it's not unrealistic to think that with an appropriately massaged breech/lead these accuracy issues may not exist.
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The Fortitude uses the Mrod 177/22 magazines. So those centers and offsets are the same. It appears that the 25 mrod mags are centered the same. I opened and edge aligned both and the looked down the pellet exit holes were aligned. Also measured the bottom of mag to bottom of barrel slot.
177 mag = 0.170", 25 mag = 0.140", the 0.030 diff is from the barrel radius diff.
So, think I'm ok there.
FWIW: The Mrod style mags have a recess for the barrel diameter and the mag "snaps in" and aligns to the barrel. The mag slot cut into the breech, keeps the mag from creating angles, that could cause pellet deformation on loading.
I also did a more careful measurement on how far back the Fortitude bolt probe is recessed when fully cocked. It measured 0.075", so given the 0.100" difference, I would need to do the slotted mag. Thanks for posting that pic, Randy. It made me check more precisely. :)
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I had the Fortitude breech off, and checked the OD of bolt probe hole, and it will accommodate the larger 1/4" bolt sleeve without modification. As far as sleeving the 22 Prod bolt, I'm down to choosing between:
1) Smoothbore seamless SS: https://www.mcmaster.com/89895k719 (https://www.mcmaster.com/89895k719)
2) Precision (tighter tolerance) welded (and smoothed) SS: https://www.mcmaster.com/6100k345 (https://www.mcmaster.com/6100k345)
While probably not needed, considering sleeving the probe for better pellet loading: https://www.mcmaster.com/6100k191 (https://www.mcmaster.com/6100k191)
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Is there any reason to use stainless as opposed to brass? The brass may be easier to work with.
I am curious as I have never done this before, and will likely be modding a .22 bolt for use in a .25 in the near future.
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Is there any reason to use stainless as opposed to brass? The brass may be easier to work with.
I am curious as I have never done this before, and will likely be modding a .22 bolt for use in a .25 in the near future.
The SS was the only option I found that had a thin enough wall. at least at McMaster-Carr.
Update: OK, see some under "structural tubing" that may work.
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John,
You could sleeve the barrel with .5 OD x .032 wall tubing may be about 0.09 long to get better barrel to mag alignment?
Sleeving the bolt, Brass or SS wouldn't matter. Brass is easier to work with.
I don't see a need to sleeve the probe for better pellet loading.
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Is there any reason to use stainless as opposed to brass? The brass may be easier to work with.
I am curious as I have never done this before, and will likely be modding a .22 bolt for use in a .25 in the near future.
The SS was the only option I found that had a thin enough wall. at least at McMaster-Carr.
Understood I see you are needing .010 vs .014 wall. This is helpful for me to think about my project. I may be tempted to turn the probe down with fine sandpaper and go for a tight press fit...
For future reference, I buy all of my k&s brass hobby tubing through Amazon prime, typically cheaper than Mcmaster.
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Actually, that SS tube may be too loose with the nominal 0.010" gap. Good catch. This one is probably too tight and would require some bolt machining: https://www.mcmaster.com/6100k191 (https://www.mcmaster.com/6100k191)
Here are the two I found in brass:
Bolt: https://www.mcmaster.com/8859k24 (https://www.mcmaster.com/8859k24)
Probe: https://www.mcmaster.com/8859k21 (https://www.mcmaster.com/8859k21)
I prefer McMC for researching the specs. On Amazon, it depends on the particular seller what is listed. The brass are much cheaper than the SS. Do you know if there is a inner welded seam on brass? or is it smooth, ie drawn?
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John,
You could sleeve the barrel with .5 OD x .032 wall tubing may be about 0.09 long to get better barrel to mag alignment?
Sleeving the bolt, Brass or SS wouldn't matter. Brass is easier to work with.
I don't see a need to sleeve the probe for better pellet loading.
At this time, until I find there would be an issue, plan to bore the breech through the full 1/2" and just notch the barrel at those mounting screws. That would allow the barrel to still be useable on a Mrod, if things change in the future.
I agree with you on the bolt probe, but it seams like it would be easy to do, and wouldn't make it worse. I'll probably order the tube and make final decision latter.
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Actually, that SS tube may be too loose with the nominal 0.010" gap. Good catch. This one is probably too tight and would require some bolt machining: https://www.mcmaster.com/6100k191 (https://www.mcmaster.com/6100k191)
Here are the two I found in brass:
Bolt: https://www.mcmaster.com/8859k24 (https://www.mcmaster.com/8859k24)
Probe: https://www.mcmaster.com/8859k21 (https://www.mcmaster.com/8859k21)
I prefer McMC for researching the specs. On Amazon, it depends on the particular seller what is listed. The brass are much cheaper than the SS. Do you know if there is a inner welded seam on brass? or is it smooth, ie drawn?
Understood and agreed on specs. I try to use manufacturers websites, in this case k&s and then find the part number on amazon.
K&S is smooth, I use it for Cobra valve chambers and orings seal perfectly....
K & S PRECISION METALS 8131 1/4 x... https://www.amazon.com/dp/B002NJ5B78?ref=yo_pop_ma_swf (https://www.amazon.com/dp/B002NJ5B78?ref=yo_pop_ma_swf)
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Understood and agreed on specs. I try to use manufacturers websites, in this case k&s and then find the part number on amazon.
K&S is smooth, I use it for Cobra valve chambers and orings seal perfectly....
K & S PRECISION METALS 8131 1/4 x... https://www.amazon.com/dp/B002NJ5B78?ref=yo_pop_ma_swf (https://www.amazon.com/dp/B002NJ5B78?ref=yo_pop_ma_swf)
Thx, yea had to go to K&S site for the tube thickness verification to part number.
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You convinced me, went with brass. :)
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You convinced me, went with brass. :)
Brass is so easy to work with... I chuck it in my cordless drill and cut it with a sharp tubing cutter. Spin the tube fast with the drill, while gently tightening the cutter. Cuts very clean with virtually no deformation/compression
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You convinced me, went with brass. :)
Brass is so easy to work with... I chuck it in my cordless drill and cut it with a sharp tubing cutter. Spin the tube fast with the drill, while gently tightening the cutter. Cuts very clean with virtually no deformation/compression
Thx. I've made safeties from brass rod before and that was easy enough. Also purchased tubing to repair valves for poppet stem wear. I haven't needed it yet.
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You convinced me, went with brass. :)
You did yourself a favor. 304 SS work hardens like crazy and can bring machining operations to a standstill.
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The barrel will be here today. Plenum just shipped out from the Netherlands.
And just received notice that the McMasterCarr order will arrive today! I went with them because I had other items on the list (fittings, gauges, etc), that I didn't want to try to find on Amazon. The tubing itself was half the price of Amazon, but that does not include shipping. MC doesn't provide the shipping cost till after, which is rather annoying.
FWIW: MC shipping was $8.25, which puts Amazon Prime at the slightly better bargain, if you were just ordering the brass tubes. Getting it in one day was a nice surprise.
Anyway, looks like I will be test fitting the bolt this weekend. :)
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Even though ordered from MC with no brand indicated, but did have tolerance specs, what was delivered was the K&S #8131 and #8128. Both will slide over their bolt locations without an interference fit. Both will need epoxy. The OD's were spot on, given my caliper measuring capability.
The latest version of miniature 0-4K gauge not thrilled with. The numbering has gotten smaller, and the needle range is less than the prior one. See below.
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I cleaned the 25 cal barrel and pushed half a dozen pellets through. The choke on this 25 GM barrel is VERY tight. It takes some effort to push the pellets through. It is much tighter than the two other GM barrels I have. Does not sound promising. I will have to install it on one of my Mrods to see what the accuracy is.
FWIW: The new 177 Mrod barrel has a TP burr that sliced off a good sliver of the pellet tail.
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Even though ordered from MC with no brand indicated, but did have tolerance specs, what was delivered was the K&S #8131 and #8128. Both will slide over their bolt locations without an interference fit. Both will need epoxy. The OD's were spot on, given my caliper measuring capability.
The latest version of miniature 0-4K gauge not thrilled with. The numbering has gotten smaller, and the needle range is less than the prior one. See below.
Looks like it is coming together. On the tight barrel, while I've never done it, I've read where others have been very successful when starting with a tight barrel and polishing it out to size. Though it will be extra work, I bet you will end up with great results.
Another note.... where applicable, that tubing solders very well when using flux and a micro torch.
On the gauges.... that is a sore subject for me. I have a pile of micro gauges that didn't match what I thought I ordered....
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Are you looking for shooting slugs or pellets the .25 GM barrel?
on .177 barrel, can you clean up the burr without to much trouble?
On a side note, I got to shoot the mini-rod yesterday, it likes the .25 JSB heavy MKII's. the wind was light to gusty and pushing the pellets around up to 3". My barrel doesn't like the slugs so it is going to get the choke removed and see how it does then.
Also pulled out the Prod .177 shooting 21gr slugs - 850fps at 100 yards, (2 3/16" groups) I cannot wait to get on some rabbits or g-squirrels with it with low wind. I have a better long range scope for it an Aeon 6-24x 50 SF that is going to get mounted before my next outing as long as I can get it sighted in first at long range.
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I cut my first tubing for the bolt. It is about 1/16" too long and will fix that. I did not have any issue just using a standard tubing cutter and going slow. I did insert the back end of a #2 drill up to within 1/8" of the cut, for tube support.
Looking at the 22 bolt probe, it fits the 25 cal JSB pellet well. It is about the same diameter as the flat of the pellet. The 0.156" tubing has to push on the conical edges of the tail of the pellet. For now, not going to sleeve the probe end.
The rear breech hole was too tight for the sleeved bolt. I had to open it up a little with a 17/64" drill.
That did expose a possible problem with going with the standard Mrod mag. About 0.090-0.095" has to come off the back. That will leave only 0.025-0.030" before breaking into the larger channel. That would be a really thin wall. I'll have to do more thinking about the mag solution.
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The barrel will be for pellet shooting only. My experience with 177 and 22 cal with tight chokes, has not been positive. This is by far the tightest choked barrel I have ever had. It would take allot of polishing to get it where it needs to be. I'll still test it in the Mrod and see. I might return to crosman for exchange.
Yep, NP fixing the 177 barrel TP burr. Typical crosman. ;)
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The good news is you can test GM barrel in another gun before machining it!
As for using factory mag, opening up the breech could be the best choice in the long run IMO.
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I can't get a good picture of the pellet, but the whole circumference of the pellet head is being resized by pushing though the choke. I'll leave that testing for tomorrow. I have too many parts laying around already. ::)
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Well, so far, the accuracy is showing much better than I would have expected. :-[ In my 10yd basement range it is hole in hole, and what I would expect from the 25 GM barrel. The fps is down about 60fps, but can't say that is the choke. This is a reg,ed gun with 0.187 ports, but the barrel port is stock, since I might be returning it. The wind is too strong and gusty, to test at any further distances or check for spiraling.
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The major thing that this whole build relied upon, was the boring of the breech from 7/16" to 1/2". I had never done this and had not seen others describe how to before. The key to "my" process was a step drill. See below. It has 1/16" increments with 1/2" as the last step. My thought was that the 7/16" would be the pilot for the 1/2" step. There is about 1/2" length of the 7/16" diameter. That 7/16" step is a tight fit though.
Having only 1 Fortitude breech, and crosman hasn't released the schematic yet, did a small test on a Prod breech. I have a 17" LW barrel that was machined for the shorter Mrod breech. Instead of machining the barrel, decided to do a 1/2" test bore. Seemed to work fine. :)
Note: The LW barrel is 0.470" and will add a brass sleeve. I'm starting to really like this brass tubing.
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Now, I did this on my small bench top drill press. It was lacking in enough height adjustment to do this in a few steps. I had to reposition and re-align numerous times. A full size drill press would have been much better. The breech was aligned using the 7/16" drill, and needed a couple of short extension for the step drill. The step drill was too long to do the full depth, or it would damage the back side of the breech. I used a 1/2" to do the final inch or so.
NOTE: One thing I forgot to mention: Using the step drill for a piloting drill, requires taking the cutting edge off of the piloting step. For this case, I took a file to the 7/16" dia step edges. I also put some oil in the breech hole. The point is, you want it to follow the existing hole and not try to cut its own path.
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You're a braver man then I, from my old machine shop days it tells me to bore it out the breech using a 4 jaw chuck in a lathe to keep the barrel to breech aligment correct. You did it in a drill press, congrats.
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We all have our series of operations that best equipped for and most comfortable with. Very nice demonstration here.
I will likely have to increase breech size sometime in the near future, thanks for sharing the unibit idea.
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from my old machine shop days it tells me to bore it out the breech using a 4 jaw chuck in a lathe to keep the barrel to breech aligment correct.
Yea, if I had one of those..... ;) I thought this was worth a try. So far, don't think I need to call David, to bail me out. :)
The proof will be once I scope it up. But, already eyeing some other prods, such as my 2201 pistol. :)
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I just had to do it. Launched the first dozen pellets through her. :) Be it with the existing porting and only going 650fps.
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Impressive substitution of skill, improvisation and determination; over a lack of equipment.
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I just had to do it. Launched the first dozen pellets through her. :) Be it with the existing porting and only going 650fps.
Not a bad place to start.
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After allot of thought about how I could do the mods, decided to go with modify the mag, for now. Machining the breech would have been tedious with only files, blocks/sandpaper, and likely to slip and scratch/gouge something in the process. Keeping nice and square and even measuring would be rather difficult. Machining the breech is the better answer, but will send that out to have a pro do it, sometime in the future. I will probably have them add the two mounting holes so it could be installed on a Prod, too.
So, I starting with the standard 25 cal mag, and basically make it as thin as a standard 177/22 mag. That involves sanding the black outer case and the inner revolver wheel. I have the rough sanding done to both, and within 0.010" of where they need to be. I should complete the finish sanding, massaging, and testing this evening. This seems well within my capabilities, but is time consuming. Will post pictures and specs this evening.
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I look forward to seeing the pics. I may go that route on the next one.
I wondered about fitting the .25 wheel into a .22 mag???
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Mag Modification:
The 25 cal Mrod black shell is 0.570” wide and needs to go down to 0.470" of the standard 177/22 mag. I flat sanded it using 80 grit to do most of the work.
Procedure:
•10 CW circles
•10 CCW circles
•Rotate 180 degrees
•10 CW circles
•10 CCW circles
•Measure with calipers
•Adj as necessary
•Repeat until 0.005” above final spec
•Drop to 320 grit to final spec
•Polishing 400 then, 600 grit
Note 1: The dimple that holds the mag open for the 1st pellet is eliminated
Note 2: Epoxy fill is used in protrusion to prevent hollow out
Note 3: the thicker material at the protrusion would often be wider than the rim. The “adj as necessary” required some extra pressure on that end to equal out.
Note 4: Before going to 400 grit, break the sharp edge around the inside.
The 25 cal revolver cartridge is 0.450" wide and needs to be sanded down to 0.350". I used same process as above, but did not find that any adj was needed. There are 6 tabs on the inside of the revolver that need to be sanded down flush. These are spring stand-offs that are not needed for a thinner mag. I used snippers and exacto knife to eliminate them.
There will still be some of the brass left for the center screw. The sand flashing can be pushed through with small brad, then screw should thread in.
The clear face-plate was not modified.
The barrel side of the mag was not modified outside of epoxy fill.
Spring and screw unmodified.
Other good mod info on mags: https://www.airgunnation.com/topic/umarex-gauntlet-tweaking-the-magazine/ (https://www.airgunnation.com/topic/umarex-gauntlet-tweaking-the-magazine/) Another good video from Hajimoto
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Getting closer. I assume due to available plenum/storage you are designing this around 25gr ammo? If so then no need to ever worry about modifying the breech?
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Getting closer. I assume due to available plenum/storage you are designing this around 25gr ammo? If so then no need to ever worry about modifying the breech?
Yes, the 25g ammo and 40ish fpe, and a 16 shot targeted count. Heavier ammo to go with higher power, would be better to use a different platform. That said, I just tried some 34g MKII in it, and cycles fine.
I am going to find a way to add that cover locking nub back. Maybe a tiny brass brad.
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Valve Plans:
•Open exhaust to 0.187”
•Open poppet pocket to 0.230”
•Change to mrod/prod poppet
•Possible mod of inlet washer
•Possible change to conical spring
•Deepen trigger assy 3rd screw relief
Plenum has landed on the east coast and should be here soon.
SS washer for plenum to plenum interface, ľ” OD sanded the OD to fit easily in air tube
Other to dos:
•Set reg to 2kpsi
•Make 0.187” Poly TP
•Barrel: modify flat and add shroud mount flat
•Bolt: final bevel check on brass sleeve and seal
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That's surprising to see 34gr fit and cycle. Very cool!
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I did find a small brass brad and cut the head off, and then rounded it off using a drill as a lathe and shaping with sandpaper. Drilled a hole thru the clear cover using a drill bit that was 0.005" smaller diameter than the brad. Using that as the pilot, drilled the hole in the epoxy. Simply pressed the brad in place.
In the second picture, the pellets are the 34g JSB MkII's. You can see they sit a few thousands below the top of the revolver wheel.
The mag snaps in, nice and secure. :)
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I haven't looked very close, but I assume you have. What prevented you from using a thinned .25 wheel in a modded .22 body?
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I haven't looked very close, but I assume you have. What prevented you from using a thinned .25 wheel in a modded .22 body?
The 22 body is designed to snap in to a 7/16" dia barrel, not the 1/2" GM. You could machine the barrel end down, though. The 22 is also a slightly small inner diameter of the black case, that may have caused some mods to each of the pellet slots in the revolver. The circular channel where the pellet head rides looks slightly different. I'm not sure if those last two items are real issues, or just worry beads. The 22 exit hole has to be enlarged, but in an offset way with the loading ramp.
Basically, I thought using a single 25 mag was easier with less risk, and didn't expend two different mags.
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I haven't looked very close, but I assume you have. What prevented you from using a thinned .25 wheel in a modded .22 body?
The 22 body is designed to snap in to a 7/16" dia barrel, not the 1/2" GM. You could machine the barrel end down, though. The 22 is also a slightly small inner diameter of the black case, that may have caused some mods to each of the pellet slots in the revolver. The circular channel where the pellet head rides looks slightly different. I'm not sure if those last two items are real issues, or just worry beads. The 22 exit hole has to be enlarged, but in an offset way with the loading ramp.
Basically, I thought using a single 25 mag was easier with less risk, and didn't expend two different mags.
Perfect explanation, thank you very much.
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Impressive work, John
I love seeing crafty engineering performed by means of commonplace tools, patience, and a good set of steady hands.
Probably saved more than a few dollars, too :)
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Impressive work, John
I love seeing crafty engineering performed by means of commonplace tools, patience, and a good set of steady hands.
Probably saved more than a few dollars, too :)
Thx.
This project has been going well, so far. The one advantage to crosman is, easy access to replacement parts when you mess one up.
If it wasn't a hobby and counted my time, probably one of the more expensive mags out there. ;0
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I discussed with Rod (GTA member rsmn), the possibilities of a single shot tray. That is looking promising. He has been able to quickly make custom ones for me, such as a 177 prod one. He is very good to work with and highly recommend him. :)
So, I'm probably going to make one more mag and not send it out in the future for machining. The machining would make it convenient for mag replacement in the future, though. vs spending a couple hours modifying one, now that I know how to do it. My experience with the crosman mags, is mostly they just need cleaning and readjusting the screw. sometimes the spring.
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Getting a little bit of time today:
- Adjusted reg to higher pressure, hopefully close to 2Kpsi (still awaiting plenum)
- Opened valve exhaust to 0.187"
- Opened poppet pocket to 0.230"
- Main valve body is 0.560" ID, nothing left to get there
- Installed Mrod/Prod poppet
- Found a conical spring that should work, but need to mod retaining washer or make new one. The opening in the retainer is only 1/4" OD, so want to go to 3/8"
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The plenum finally arrived today. See below for the latest stack up of parts to go back in the tube. Still need the gauge to see the set-point, but will be able to see if I can hit the 40fpe mark, before pulling the gauge back out.
Rod has shipped out the semi-custom shot tray and should have that by the end of the week.
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The plenum finally arrived today. See below for the latest stack up of parts to go back in the tube. Still need the gauge to see the set-point, but will be able to see if I can hit the 40fpe mark, before pulling the gauge back out.
Rod has shipped out the semi-custom shot tray and should have that by the end of the week.
That is a whole lot of plenum!!!!
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It looks like I'm in the ballpark. :) One half turn on the reg adjustment does equal 500 psi. It was right at the 2k psi per fill gauge.
I got 16 shots at and just under my power range, but in my haste to make a TP, it is leaking.
Mag is cycling fine.
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Your plan is coming together nicely.
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Your plan is coming together nicely.
Thx. I am missing a 25 cal shroud mount, so will need to put in a order with crosman. Need to go thru a list of Mrod 22 parts, to see what is needed to complete that gun.
I need to pick up some modeling clay so I can figure out the right TP length.
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Received the SS tray from Rod. Fit tight, works nice. :)
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Looks good. I like the high vis orange, should make it harder to lose trays.
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Looks good. I like the high vis orange, should make it harder to lose trays.
I generally only use them for testing, and mainly on the indoor range. The orange allows me to easily see that it is installed in the gun and gives good visibility of the pellet when in the channel. Rod does have multiple color choices.
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I must admit I really haven't paid much attention to the Fortitude---I don't have a need for yet another 7/8 tube, long rifle in my airsenal. So I have intentionally not paid much attention. Yesterday I finally watched Southern Gunner's lengthy review and now I understand the attraction. It is magazine fed and it is LIGHT!!! Plus being a crosman spare parts, mod parts, modding methods are known and readily available.
You've created an ultralight, MAGAZINE FED, rifle with Mrod like power. I get it now. 15+ shots of 40fpe out of a very lightweight package. it is almost screaming for a double tube kit---if it wouldn't take away from the gun's best quality of being lightweight.
I have my own version in QB78 form that I may drop a .25 upper on if only to test. It is the SS Cothran tubed gun in my profile pic. It is set up with an in tube Huma.
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I understand the attraction. It is magazine fed and it is LIGHT!!! Plus being a crosman spare parts, mod parts, modding methods are known and readily available.
You got it! :)
I actually built very similar guns prior to release of Fortitude. A good number of years ago, built one with a custom air tube from MM. And before the Fortitude was announced, built one from a Maximus tube. That one looks so close to the Fortitude, I'd swear they got the idea from me. ;)
Actually, for a 177 or 22 I'd wish the were 4" shorter, ie carbine length.
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Actually, for a 177 or 22 I'd wish the were 4" shorter, ie carbine length.
40" overall would be perfect!
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John, I have a huma plenum question.
I need a plenum for my qb78 double. It needs to have an outside oring on one end, a face/flange oring on the other. Without a gauge hole. Prod/disco diameter.
Do you know which plenum to order? Thanks in advance.
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John, I have a huma plenum question.
I need a plenum for my qb78 double. It needs to have an outside oring on one end, a face/flange oring on the other. Without a gauge hole. Prod/disco diameter.
Do you know which plenum to order? Thanks in advance.
All of the Huma plenums for Prod, Maximus, and Disco, have face seals on both ends. None have provisions for a gauge or the outer o-ring like on a gauge block. They seal against the valve or gauge block. The disco one sitting on my bench, also states it fits Artemis PR900W / Diana Stormrider. I suspect that huma does not sell one in that diameter that does what you want. :(
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I have been working on a better sealing TP: https://www.gatewaytoairguns.org/GTA/index.php?topic=153928.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=153928.0)
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I did a test string with the new TP. Now getting 16 shots at average of 882fps. The poly TP must have been leaking more than I thought.
Also, this was the first time shooting the 25 cal with the shroud back on. Nice and quiet. :)
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I did a test string with the new TP. Now getting 16 shots at average of 882fps. The poly TP must have been leaking more than I thought.
Also, this was the first time shooting the 25 cal with the shroud back on. Nice and quiet. :)
You exceeded your goal by just a bit, great job.
Thanks for the info on plenum extensions.
Do you know the lengths of the Prod and Disco extensions? I could make one work by inserting a Prod gauge port on the valve end, with only one oring, towards the valve. the issue is I currently don't have anything for a face/flange type oring to seal against. The gauge port would provide that.
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The Disco/Maximus is 2", while the Prod is 1.25". I think it estimated out at 5cc per inch. I have a prod gauge block somewhere in the drawer, if you need the length of that.
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The Disco/Maximus is 2", while the Prod is 1.25". I think it estimated out at 5cc per inch. I have a prod gauge block somewhere in the drawer, if you need the length of that.
Thanks for the info. Length on the Prod gauge block won't matter. I seem to recall it being just over 1". Now that I have the extra capacity of the double tube I may just go with the Disco plenum and add it to what I've got now, which is around 15 or so cc I believe.
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I have been chasing a persistent slow leak. I ignored it for a while, because was tearing it back down, during the tuning process. The leak was coming from the trigger assy hole, so it had to be something with my plenum spacer. Initially, I thought I didn't get a good seal with the brass plug with the epoxy, but found I was taking a small chunk of the o-ring out as it passed the gauge hole and trigger hole. Deburred these holes again, and put extra care in depressing the O-rings as they were pushed past the subject area. Still leaked.
I think I finally found it. The plenum spacer was made from a special gauge block that was given to me. On this bock, the 113 o-ring grooves had a depth of 0.600". Comparing to the Fortitude gauge block which read 0.590". Checked the Prod and a Maximus block, and found the same 0.590". This was making the O-rings tighter than needed and was enough that I kept scalping the O-rings.
So, made a new plenum spacer from the Fortitude one. It is exactly the same length as my "special" one, so the spacers all stood the same. Note that the Fortitude gauge block is not flat. If you plan on sealing a huma plenum against it, it would need to be flat sanded. I'm going to keep using the Prod gauge block, seeing how I have enough air volume to meet my goal. I drilled out the main passage to 3/8". Filed down the top of the brass plug to get it to fit below the surface. Epoxied it last night and installed this AM. So far, so good.
My original spacer on the left, Fortitude one on right.
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I have been chasing a persistent slow leak. I ignored it for a while, because was tearing it back down, during the tuning process. The leak was coming from the trigger assy hole, so it had to be something with my plenum spacer. Initially, I thought I didn't get a good seal with the brass plug with the epoxy, but found I was taking a small chunk of the o-ring out as it passed the gauge hole and trigger hole. Deburred these holes again, and put extra care in depressing the O-rings as they were pushed past the subject area. Still leaked.
I think I finally found it. The plenum spacer was made from a special gauge block that was given to me. On this bock, the 113 o-ring grooves had a depth of 0.600". Comparing to the Fortitude gauge block which read 0.590". Checked the Prod and a Maximus block, and found the same 0.590". This was making the O-rings tighter than needed and was enough that I kept scalping the O-rings.
So, made a new plenum spacer from the Fortitude one. It is exactly the same length as my "special" one, so the spacers all stood the same. Note that the Fortitude gauge block is not flat. If you plan on sealing a huma plenum against it, it would need to be flat sanded. I'm going to keep using the Prod gauge block, seeing how I have enough air volume to meet my goal. I drilled out the main passage to 3/8". Filed down the top of the brass plug to get it to fit below the surface. Epoxied it last night and installed this AM. So far, so good.
My original spacer on the left, Fortitude one on right.
I am planning to use a Prod gauge block, thanks for the heads up.
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FWIW: While I was able to fix my leak at the plenum ext, still have a slow leak unable to locate. I couldn't find it with suds/foam and did a couple of re-o-ring and re-taped the foster. Kicking my ^&*. ;) Need to go to full submerge on air tube.
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FWIW: While I was able to fix my leak at the plenum ext, still have a slow leak unable to locate. I couldn't find it with suds/foam and did a couple of re-o-ring and re-taped the foster. Kicking my ^&*. ;) Need to go to full submerge on air tube.
Some leaks are tough..... My Huma QB78 needs a reg rebuild, ever so slight leak out of the vent that persists after 2 teardown/oring replacements.
BTW, I finally used my GM .25 barrel. Some time ago I had ordered the parts to make a complete spare barreled action for my P15. Now I have .25 and .22 barreled actions but only have one stock LOL... I found the GM barrel to have a very tight choke, very much like what you found in this thread. I worked on it a bit with bore paste and that helped some but it is still pretty tight. I still have to thread the muzzle, when I tear down for that I plan to spend some more time working on the choke.
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I got a Boyd's AT-ONE stock that will fit my three long tube prod/fortitudes, from a GTA member. I tried it on my 25 cal Fortitude. :)
It joins a Blaster, Varmint Thumbhole, and syn stocks.
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I picked this back up, after a long hiatus. I was plagued by a slow leak that I couldn't find, via aersol leak detector on all the possible locations. I gave the air tube a warm water bath, and was able to quickly find it. It is leaking from the gauge vent hole. Which is not uncommon, but I had been hitting the back side of the gauge, and this one was on the outer perimeter. :-[ This was a new gauge from MC, too. Anyway, glad to find it. All along I was worried that it was coming out the reg vent, which could mean anywhere within my large stack of parts for the plenum.
Going to fix the stock lug. A couple of members have pointed me to Lloyd's article: https://www.gatewaytoairguns.org/GTA/index.php?topic=41405.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=41405.0) and have discussed their success using it. I had something more elaborate and more problem prone in mind.
The barrel for this, came from my Mrod, and was replaced with a new one. That turned out to be a crosman barrel, while this one is GM. This is going back in the Mrod, and a new crosman barrel will be ordered on Monday. The original replacement went into the 25 Liberty project. None of the modifications to the barrel, up to this point, effected its use in a Mrod. I do plan to machine the front edge of the barrel to 7/16" from the 1/2", so that it will be able to use the stock Seneca Aspen 25 mags. Making one custom mag was fun, making a few more, just seemed like work. ;)
The hammer in the Fortitude (same as Disco/Maximus) has allot of material between the face and back of spring pocket. Going to drill a pocket and add some peek to reduce some of the mechanical noise.
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Ordered the 25 Mrod barrel, current price is $62.30
I was able to get the CS rep to look up a Fortitude air tube, since mine is scratched up from all the times assembled/disassembled, only $24.24
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Ordered the 25 Mrod barrel, current price is $62.30
I swear that is what I heard, but the email invoice shows: Barrel, .25 cal. 2563-001 $46.73
I was able to get the CS rep to look up a Fortitude air tube, since mine is scratched up from all the times assembled/disassembled, only $24.24
Price correction: Barrel, .25 cal. 2563-001 $46.73
Air Tube: ME-013 $24.25
Barrel Band: ME-008 $6.35
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Dare I say Crosman's parts are reasonably priced (yes, free would be nice, but that is not realistic).
I see the Crosman .25 barrels is a lot cheaper than what they sold the GM barrel for a year or so ago. That was $75, if I recall.
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Ordered the 25 Mrod barrel, current price is $62.30
I swear that is what I heard, but the email invoice shows: Barrel, .25 cal. 2563-001 $46.73
I was able to get the CS rep to look up a Fortitude air tube, since mine is scratched up from all the times assembled/disassembled, only $24.24
Price correction: Barrel, .25 cal. 2563-001 $46.73
Air Tube: ME-013 $24.25
Barrel Band: ME-008 $6.35
That's odd that they would keep the same Gen 1 part number of 2563 for the new non GM 25 cal barrel since I would think it would be easier to be able to differentiate between the two parts. But then if the GM is no longer available it likely does not matter now.
BD
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Received UPS email that the parts will be arriving tomorrow. :) So tore down the pressure tube. I will be giving the original Fortitude air tube away, just pay shipping. It has a few scars, but nothing terrible. If interested, keep eye on classifieds.
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thanks for sharing the new barrel price----that price is hard to beat for transplants/conversions. I need to pick up another for my stash.
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Well, received the parts order today. Guess what is on back order? …. yep, the barrel. ::)
At least I have the air tube and gauge to get the bottom end back together.
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Darn, too bad about the barrel. Glad to hear that it is coming together. Reading your story has made me appreciate that I have not had any major leaks other than the normal ones of cutting the o-rings during assembly.
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Darn, too bad about the barrel. Glad to hear that it is coming together. Reading your story has made me appreciate that I have not had any major leaks other than the normal ones of cutting the o-rings during assembly.
I think John (Crosman_Engineer) made improvements in G2 to minimize leaks. The G2 I received recently, doesn't have any issues with leaks. Rock solid.
Just received a UPS shipping notice. Looks like the barrel (only thing back-ordered) will be here tomorrow.
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Assembled the air tube. It did take a couple of times on the thin valve O-rings to get past the gauge and screw hole unscathed. The edges are not as sharp as Gen 1 tubes, and I didn't dress them before install. I did notice a new regulator vent hole. Gen 1 relied on the thread gap between the tube and stock lug. I pressurized to just under 2K last night, and still there this AM. :) Will keep an eye on it for next few days.
As luck would have it, the barrel is now showing a Monday delivery. ::) I'll work on the peek striker and have the complete lower assembly done before it arrives.
The regulator came for the Liberty, so now its waiting on the Fortitude. ;)
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Congrats on the no leaky! Sometimes that can be a challenge on our regulated guns (more orings and opportunities to damage them.)
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The crosman 25 cal barrel did arrive. :) Definitely a crosman, 7 lands, not GM. I pushed a few JSB's through it, and found it just like the previous, with a very tight choke. I did not find any burrs that were taking chunks out of the pellet. No visible issue with rifling. Barrel was relatively clean, too. Installed it in a mrod. Groups were single pellet hole at 10yds and consistently hitting 1" spinners at 50yds. Declared the accuracy good enough to start the machining, which voids the 30 day warrantee. Also, the leade, like the other one, chunky on probe closed.
This will go on the caveman lathe to turn down the very first 0.060" to 7/16" from 1/2", so the standard Seneca aspen 25 cal mags will fit. Otherwise, the same machining I did before:
- Side clearance for the two breech screws
- TP to 0.187"
- Smooth leade
- Flat for new shroud mount location
After 6 days, gauge hasn't budged, so declare it leak free. :)
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I have that exact same stock on mine John, same color and everything. I should be getting mine back soon. A buddy did a bunch of work on it for me. Looking forward to reading the whole thread.
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I have that exact same stock on mine John, same color and everything. I should be getting mine back soon. A buddy did a bunch of work on it for me. Looking forward to reading the whole thread.
I got it off another GTA member. It is nice and he did some minor inletting for the Mrod trigger. I do think I'm going with the varmint thumbhole, posted earlier, and use the AT-one on the re-vamped 22 Maximus prime project. The blaze orange sticks out too much for me, for field use. Fine for bench and plinking.
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I agree that orange is very vibrant. It is my wifes gun and it will be a target shooter and plinker for the most part.
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The crosman 25 cal barrel did arrive. :) Definitely a crosman, 6 lands, not GM. I pushed a few JSB's through it, and found it just like the previous, with a very tight choke. I did not find any burrs that were taking chunks out of the pellet. No visible issue with rifling. Barrel was relatively clean, too. Installed it in a mrod. Groups were single pellet hole at 10yds and consistently hitting 1" spinners at 50yds. Declared the accuracy good enough to start the machining, which voids the 30 day warrantee. Also, the leade, like the other one, chunky on probe closed.
This will go on the caveman lathe to turn down the very first 0.060" to 7/16" from 1/2", so the standard Seneca aspen 25 cal mags will fit. Otherwise, the same machining I did before:
- Side clearance for the two breech screws
- TP to 0.187"
- Smooth leade
- Flat for new shroud mount location
After 6 days, gauge hasn't budged, so declare it leak free. :)
JFYI, I counted the first land twice. ::) The crosman made 25 cal barrels only have 6 lands, compared to the GM which has 10.
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Using the caveman lathe, put the step in the breech end, for the 25 seneca mags. For doing flats, used the 1/2" shaft collars to help guide the file. That worked much better than freehand, especially on the flats for the breech screws, which just need some widening. The flat has to go on the angled part.
Mrod barrels, depending on the mechanical tolerances, can fit the Fortitude/Prod breech with no mods, but with a slight mis-alignment of the TP. If you align the barrel port, centered in the breech opening, the barrel extends a hair too far into the breech slot and the mag won't fit or is very tight. I took a few thousands off the barrel and chamfered it. The Seneca mags snap in, but not overly tight.
Assembled it back together and was nice to see the chrony reading high 860's with the 25g JSBs. Right where it was before. :)
Need to make a trigger guard, and modify the existing barrel band to add some non-rigid support, to at least prevent the shroud to air tube ringing.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=165335.0;attach=293648;image)