"Any Interest in 6mm? - Build Thread"

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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#91 Post by rsterne »

I swapped the 6 mm upper onto the unregulated gun tonight and filled it to its MSWP of 4200 psi.... I set the SSG to just a whisker of gap and fired one shot to settle things, topped it up and fired two shots with the 73.4 gr. bullets.... 1028 & 1029 fps (173 FPE).... Then I did something I have just been dying to try ever since I came up with the idea of building a 6mm.... I loaded up a 1.8 gr. Airsoft BB, topped it up to 4200 psi and took a bead through the Chrony.... 2093 fps.... repeated it.... 2097 fps.... once more.... 2087 fps.... That gives a three shot average of 2092 fps (17.5 FPE) with a basic PCP, just shooting very light ammo.... No special equipment, just a standard SS style valve, porting that turns through 180 deg., and a rifled 29" barrel that is a poor fit on the BB.... it will actually roll out the muzzle if you hold it pointing downwards.... Running air at room temperature (the pressure in the 300 cc reservoir dropped ~ 250 psi each shot), not Helium.... Lloyd still holds the record at 2162 fps.... but he better be looking over his shoulder.... :twisted:

Bob
Last edited by rsterne on Fri Mar 23, 2018 9:57 pm, edited 1 time in total.
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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wesb2007
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Re: "Any Interest in 6mm? - Build Thread"

#92 Post by wesb2007 »

That must have been fun! [emoji5]

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FRANK
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Re: "Any Interest in 6mm? - Build Thread"

#93 Post by FRANK »

And to say not to long ago they told us the max for airguns was 1600fps that physics calculation made it that.
Custom Design by ME PCP/HPA Air Carbine 10-50X60 Scope My 2018 FT Open
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#94 Post by rsterne »

Fun & LOUD !!!

There was about 70 gr. of HPA in the barrel for those shots.... nearly as much as the lead bullet.... and nearly 40 times the weight of the plastic BB.... :roll:

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#95 Post by rsterne »

Although I plan on running the .257 barrel on the unregulated gun, while I had the upper removed to try the 6 mm on it, I thought I would try the .257 upper on the regulated lower.... It had a slight leak in the transfer port area, but I did my testing anyways.... Here are the results for the 73.5 gr. Lyman 257420 at 2800 psi....

Image

At 5% below the maximum velocity I was at 894 fps (130 FPE) at 8 turns of gap on the SSG, and the efficiency was 1.17 FPE/CI.... While that is similar to what I was getting on my .257 Hayabusa, it was a little below the 1.28 FPE/CI I got on the previous testing, which I attribute to the leak.... I was either losing a bit of velocity (likely), using more air (unlikely), or both.... but no question it would affect the FPE/CI either way.... If I was going to set this gun up as a regulated .257 I would likely bump up the setpoint pressure to 2900-3000 psi, although that may not be necessary with the 66 gr. HP version I have of this bullet, it might well shoot better at this pressure....

This pretty much completes the basic testing of these two guns.... I am extremely pleased with the results for both power and efficiency.... The plan is to put the 6 mm upper back on the 2800 psi regulated gun and run the .257 barrel on the unregulated version, and tethered it at 3800, but tune it for a few shots off tether.... All I hope now is that the snow disappears before the Motel gets too busy so that I have a chance to see how they shoot....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#96 Post by rsterne »

Although this thread goes back to before COVID, I wasn't even sure if it was on the CAF.... well, it is, and it's back for your viewing pleasure.... These guns all shoot as good as they look!.... However, never satisfied, I got two smaller calibre barrels in .172 cal and .224 cal.... Below are the additions....

Bob
Last edited by rsterne on Tue Feb 04, 2025 1:06 am, edited 1 time in total.
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#97 Post by rsterne »

Last year I built two PCPs, a 6mm regulated and a .257 cal unregulated.... This year I have a .172 cal barrel for the 6mm and a .224 cal barrel for the .257.... They are both TJ's with a 14mm OD and a 9" twist, and I have the same 14mm ID x 20m OD Carbon Fibre Sleeves for them as I used on last years builds.... Here are the two rifles I am starting with.... The 6 mm is regulated at 2800 psi, with the 165 cc plenum made from 2024-T3 with a 0.095" wall, fed from a 500 cc 4500 psi Carbon Fibre bottle.... It is tuned for 125 FPE with bullets from 61-73 gr.... with a maximum of 136 FPE....allows easy adjustment of the velocity without changing the hammer strike or pressure.... Since that capability is built into the receivers, it will also be available in the two new calibers.... This means I can leave the guns tuned for the larger calibers, and just choke up the porting if necessary....

Image

The .257 is unregulated with a MSWP of 4300 psi, but I plan to run it at 3800 psi, the same as I am currently in .257.... It has a 300 cc 2024-T3 reservoir with a 0.120" wall.... It is tuned for 165 FPE with 80-92 gr. bullets, and peaks at 201 FPE....

Image

Both guns have my own version of the SS Valve, and MDS hammers with an 11 lb/in. spring and are very easy to cock.... They are both fitted with harmonic tuning weights on the muzzle, which I plan to fit to the new barrels as well.... The receivers are interchangeable on the lower assemblies.... If you want to read about the original builds, you can do so here.... Before you ask, I have not yet done any accuracy testing of either gun, the Motel prevents me from doing any shooting in the summer, so serious testing will have to wait until 2021, after we retire.... ::)

https://www.gatewaytoairguns.org/GTA/in ... pic=128036.

When the new barrels are fitted I will have four calibers, and all can be shot regulated at 2800 psi or unregulated at 3800.... although I plan mostly to use the .172 regulated and the .224 unregulated.... I currently only have one bullet for each caliber, I have a HP version of the 27 gr. NOE 172-26 which weighs 24.7 gr.... and the FN version of the NOE 225-61 which weighs 61 gr.... I have already made chamber reamers and cut the chambers in the TJs barrels, you can see what that process was like in this thread....

https://www.gatewaytoairguns.org/GTA/in ... c=154242.0

Today I got a good start on fitting the new barrels.... I made two new bolts and loading trays, one in each caliber.... Here they are, along with the bullets....

Image

I made the receivers with a 1/2" bore for the bolt and barrel, so it is pretty easy to change calibers by making the above parts.... The loading tray is fastened into the receiver with a single flat-head 4-40 screw.... The receiver is shown below, you can see the threaded hole for that 4-40 screw in the loading bay in the upper receiver....

Image

The receiver is only notched out for loading on the right.... leaving the left side full height for increased rigidity.... They are both equipped with a velocity adjusting screw on the back which pushes a steel pin forward to prevent the bolt from being fully retracted in the J-slot.... This allows easy adjustment of the velocity without changing the hammer strike or pressure.... Since that capability is built into the receivers, it will also be available in the two new calibers.... This means I can leave the guns tuned for the larger calibers, and just choke up the porting if I have too much power.... The next step will be to machine the barrels to fit the receivers, and machine the barrel ports, transfer port recesses, and grooves for the O-rings to seal the breech....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#98 Post by rsterne »

Today I worked on the breech end of the barrels.... First I machined the O-ring grooves, checking as I went to make sure I got the groove the proper depth to get a nice sliding fit on the bolt.... I used a #009 O-ring on the .224 cal and a 4 mm ID x 6.4 mm OD x 1.2 mm CS O-ring on the .172 cal.... I had to grind down the internal grooving tool I had made previously for that CS Metric O-ring as it was too large in diameter to fit inside the tiny bore.... These were time-consuming to make, but went well and I am pleased with the results....

Image

I also laid out and machined the barrel ports and the 3/8" flats for the transfer ports to seal against.... Both barrel ports are oblong to get full bore area without exceeding 80% of the caliber for the width of the port.... The .224 cal port is 0.176" wide and 0.27" long, and the .172 cal port is 0.136" wide and 0.26" long at the boreline…. Both start at 0.257" at the transfer port face, to match up to the transfer port ID, and are blended from round to oblong within the thickness of the barrel wall....

This was a long day requiring a lot of concentration, so I am putting off threading the muzzle end for the harmonic tuners for another day.... Once that is done I will be able to cut the carbon fibre sleeves to length and glue them onto the barrels.... This project is moving along quite nicely.... 8)

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#99 Post by rsterne »

Today I threaded the muzzles 1/2"-20 NF to accept my harmonic tuners.... I can also use a Hatsan Air Stripper, should they become available again.... I then cut the Carbon Fibre sleeves to length.... They are 14mm ID x 20mm OD, so once installed the barrel will be over 3/4" OD.... I sanded and cleaned the barrels and the inside of the sleeves, and installed them with Loctite 638.... Here is what the muzzle looks like, without the tuner in place....

Image

After an overnight cure at room temperature, I will give them a post cure in my wife's oven at 175*F for 3 hours.... Then I can finish fitting the OD of the sleeve to the receiver and drill the 6 holes through each sleeve for the setscrews so that they bite against the steel of the barrel when installed....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#100 Post by rsterne »

The primary reason for the carbon fibre sleeve is to stiffen the barrel and improve accuracy by reducing the amplitude of barrel vibration during the shot cycle.... I will further tune out any remaining vibration with the harmonic tuner on the muzzle, which is a movable weight that will allow me to have the bullet exit from the muzzle coincide with the momentary pause of the barrel at the end of a vibration, by tuning the frequency at which the barrel vibrates....

For those who don't know about carbon fibre, it has approximately the same strength and stiffness as steel, but weighs about 1/6th the weight of steel.... The sleeves I am using on this gun are 20mm OD, while the barrel was only 14mm.... This increases the stiffness of the barrel by over 4 times.... The 28" long steel .22 cal barrel weighed 26 oz.... and the carbon sleeve weighs only 5.7 oz., for a total weight of 1.98 lbs.... If I had a steel barrel that was 20mm OD, it would weigh 3.65 lbs.... so I have saved 1.67 lbs. in weight compared to an all steel barrel of similar stiffness....

If you are building a bench rest gun, where weight is an advantage, then use an all steel barrel.... For these guns, where I used an aluminum tube to save weight, sleeving the barrel with carbon fibre is the way to go, IMO.... plus, as you say, it does look cool.... ;)

Incidently, when I was purchasing this CF tubing, I found that the manufacturer makes a 20mm ID x 30mm OD tube that would slide over the one I have.... That would increase the stiffness by 5 times over what I have now, or more than 20 times as stiff as the steel barrel alone.... yet add less than 1 lb. more weight.... Of course you would have to incorporate the receiver into the outer tube (by building it into a 20mm OD structure), like I did in my Monocoque PCP.... but what an amazing way to build a light, rigid structure.... 8)

Image

You can view the thread about that project here.... https://www.gatewaytoairguns.org/GTA/in ... opic=99759.

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#101 Post by rsterne »

Yesterday I did a post-cure on my barrel sleeves, crowned the muzzles, and lapped the bores with JB Bore Paste and then polished them with Bore Brite.... Today I turned down the breech end of the sleeves a few thou to fit into the receivers.... Once that was done, and the barrels could be slid into place, I marked and drilled the locations for the six setscrews in each barrel, fitting the .224 cal. barrel to the .257 receiver and the .172 cal. barrel to the 6mm receiver.... I use a SHCS drilled though with a 1/8" hole for a drill guide, which I install in each hole and then run the drill down to drill through the sleeve to the barrel....

Image

After marking all six holes, I then enlarge the holes with a 3/16" drill, removing all the CF to that diameter and leaving a shallow pocket in the steel of the barrel for the setscrew to bite into.... Here is what the finished barrels look like....

Image

You will notice that the O-rings are in place in the groove in the breech end of each barrel.... I checked the length of each bolt nose when retracted into the J-slot, and shortened them flush with the back of the barrel port.... They load the base of the bullet just past the front of the barrel port, then you pull it back into the lower slot to remove all obstruction to flow.... That retraction distance can be decreased with the velocity adjusting screw on the back to force the bolt nose to partially obstruct the barrel port....

After lunch, I checked everything over and fitted the .172 cal upper to the regulated lower.... The transfer port was the proper length, so I was able to take a few shots.... I didn't change the SSG adjustment from the last time I shot the 6mm, and by measurement it was set at 8 turns of gap.... Even so, those tiny 24.7 gr. bullets screamed across the Chrony at 1060-1070 fps.... What really shocked me was how quiet the gun was.... Mind you, the last few times I tested in the shop I was shooting a .357, but even so, the report was very low.... Not what you would get with some assistance from a can or shroud.... but they are illegal in Canada anyways....

I then removed the .172 cal upper and fitted the .224 cal one.... Once again, the existing transfer port length was fine, so a took a few shots.... With the 61 gr. bullets I intend to shoot in the unregulated version the velocity was only 775 fps.... so I tried some of the 47.6 gr. Bowmans and they shot a very respectable 930 fps at the 2800 psi regulator setting I am using on this lower assembly.... That's a bit less than I was getting in my .224 cal Hayabusa with the same bullets, but that was shooting at 3000 psi.... and as I said, I never even touched the SSG gap, it was still set for whatever tune I last had for the 6mm.... The .224 was noticeably louder than the .172.... so I guess it really was that quiet.... 8)

I have a leak to chase down in the unregulated lower assembly, it was empty when I pulled the .257 upper assembly off.... The bottle on the regulated lower assembly, on the other hand, was still sitting at 3600 psi, which is about where it would have been when I put it away months ago.... In fact, I never added any air to it for todays initial testing.... I am delighted with todays results, and over the next few days I will do some proper testing to explore both the upper power limits and the efficiency of both the .172 cal. and .224 cal. uppers on the 2800 psi regulated lower assembly.... Testing the .224 (and probably the .172 as well) at 3800 psi unregulated will have to wait until I find and fix that leak.... ::)

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#102 Post by rsterne »

I tested both barrels today, first on the regulated lower at 2800 psi, and then on the unregulated lower, tethered at 3800 psi.... First, are the results regulated....

Image

The .172 cal HP maxed out at 1060 fps (61.6 FPE), and at this pressure I was not really able to dial the velocity down much.... With 8 turns of SSG gap it was still shooting 1050 fps, but it only used 300 psi from the 500 cc (30.5 CI) bottle for 10 shots, ie just 30 psi per shot.... That should mean between 50-60 shots per fill.... I can dial the velocity down by using the velocity screw on the back of the receiver.... Screwing that in 6 turns drops the velocity to 980 fps....

I used a 45.0 gr. bullet when testing the .224 cal at this pressure.... It maxed out at 1010 fps (102 FPE)…. This was more out of curiousity, because the intended use of that barrel is with a heavier bullet in the unregulated version at 3800 psi.... Here are the results at that pressure....

Image

As you can see, with the 61 gr. bullet the gun peaked at 997 fps (135 FPE), and had a normal tuning range of about 200 fps, as can be expected with an SS valve operating within its design range.... At 6 turns of gap, the velocity was 960 fps, and 5 shots averaging 125 FPE used 400 psi from the 300 cc (18.3 CI) reservoir, which works out to 1.24 FPE/CI.... This gave a short string starting from 3800 psi, with the first 4 shots within 11 fps, dropping another 11 fps on the 5th shot (less than a 3% ES)…. This means I can tether at 3800 psi and expect that kind of performance with the tether removed, which is just about perfect for my use....

I tested the .172 cal upper, just out of curiousity, at 3800 psi, and it was just shy of 1200 fps.... peaking at 1184 fps (77 FPE)…. Dialed back to the minimum practical with this valve, it was barely subsonic, at 1120 fps.... :o

So, this project ended up right where I wanted it for the .224 cal version.... The .172 cal is maybe a bit hot, I'll have to see how it shoots at 1050 fps, compared with dialed down a bit with the velocity adjuster.... If it ends up shooting better in the mid 900s, then it would be best to reduce the setpoint pressure, but since the regulated lower is shared with the 6mm barrel, and that shoots right where I want it at 2800 psi, I will just dial the velocity down by restricting the barrel port with the velocity adjuster if necessary....

I am delighted with the way this project turned out.... I now have 4 calibers interchangeable between the 2800 psi regulated lower and the 3800 psi unregulated lower.... I hope they end up as accurate as they are powerful....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!
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rsterne
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Re: "Any Interest in 6mm? - Build Thread"

#103 Post by rsterne »

I tested the .172 cal 24.7 gr. NOE HP in soap today.... It is quite spectacular at 1050 fps (60 FPE)….

Image

The penetration was 3.5", and the wound cavity is nearly as wide as the length of the bullet, at 0.45"....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!
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