MAC1 USFT Analysis/Overview

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Made a few changes to the gun just in the last few days.....

Dressed up moderator adaptor a bit

The raw aluminum 1/2x20 adaptor for the 16mm barrel on my USFT has always bugged me a bit. So last night I dressed it up some. Removed the set screws first, then gently went over the areas I wanted black with 500 grit sandpaper, mostly to remove the oxidation and get to fresh aluminum...
www.airgunnation.com www.airgunnation.com

And that was in preparation for the short little Hugget Atom that just arrived in the mail today.
@CTairgunner1288 recently reported some decent sound reduction from the tiny Atom on a Veteran so I decided to give it a try. The main goal was reduction of overall length. I've had a 7 inch Hogan Decimeter on the gun for about 75% of it's life. The gun was just shy of 46 inches long with the Hogan, and nearly silent. The rest of the time, prior to now, it had a Donny FL Tatsu. The Tatsu had that big fat can hanging on the end look and I never loved it, and I sold the Tatsu four or five months ago.

So, threw the Atom on this evening after work and took some shots in the garage. Lol. Not very quiet compared to the Hogan. BUT, it definitely reduces the sound level to tolerable, even in a closed garage. And the big pro of the Atom is that the USFTs overall length got cut down to about 42 and 1/4 inches. That 3.5ish inches feels much smaller. I noticed it right off the bat as I put the gun into and out of the gun cabinet and walked through my gun room door jam. Heck I even got in and out of my truck to see how that worked and I don't feel like I've got a 10ft stick of schedule 40 now. So, improvement in that regard. I'll shoot it for a bit with the Atom before I come to a complete conclusion. I sure like silent, but guns that feel like shop brooms are a chore when it comes to keeping awareness of both ends......sigh, such compromises with these first world problems.
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I gotta say, the silver accent colors in the Hugget design go well with the hardware.
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I believe if I remember right, from 3 feet away , it was 10 or 11 dB difference.

I noticed on my new to me supervet it did not do as good a job and i am going to take readings to confirm that, that rifle is shooting a lot hotter than the other rifle though (same ammo 60fps faster) , I also think the rifle is mechanically louder too.

Let us kno what you think, im a big big fan of it on my sub 900fps compact.
 
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Franklink said:
It was a a bit interesting b/c there isn't 36 inches of barrel for the flagged tape to make a complete revolution. The barrel is just under 24 inches if I remember correctly. I had to do 1/4 and 1/2 revolutions (of the flagged tape) and measure distance on the cleaning rod and then do the math for full revolutions. Repeated the process a handful of times and arrived at a twist rate of 1:36 inches. Lothar does make a 1:36 polygonal .177 barrel with a 16mm OD and Tim McMurray even has them on his website, advertised as a "slow poly."

So, is the 1:36 twist rate the magic or is there something else about this barrel that makes it such an amazing shooter? I can't answer that question, but would REALLY like to figure it out.
Click to expand...

Update on two points with my USFT - partially answering your question Franklink

1) my gun is leaking more slowly now - taking an entire week vs 2 days to get to empty , it may have something to do with the following

2) I recently installed a slow poly barrel, replacing the carbine length one of unknown twist rate. My first impression was that the long range 45-55 yards shots were grouping much better. I went with this barrel on Tim's recommendation when he had my USFT for a bottle upgrade. At that time he did not have any barrels in stock so I waited about 6 months to make the change

After the initial install I had to take the barrel off again and then reinstalled it a few minutes later. Since then leak has slowed as mentioned earlier. I am guessing that I may have cinched down on an o-ring just right. I'll take the gun apart in two weeks and see what is happening and which O-rings will need replacement.
 
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SDstephan said:
Update on two points with my USFT - partially answering your question Franklink

1) my gun is leaking more slowly now - taking an entire week vs 2 days to get to empty , it may have something to do with the following

2) I recently installed a slow poly barrel, replacing the carbine length one of unknown twist rate. My first impression was that the long range 45-55 yards shots were grouping much better. I went with this barrel on Tim's recommendation when he had my USFT for a bottle upgrade. At that time he did not have any barrels in stock so I waited about 6 months to make the change

After the initial install I had to take the barrel off again and then reinstalled it a few minutes later. Since then leak has slowed as mentioned earlier. I am guessing that I may have cinched down on an o-ring just right. I'll take the gun apart in two weeks and see what is happening and which O-rings will need replacement.
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Changing the barrel out shouldn’t have any correlation with a leak. If it’s not the valve o ring, then it may be bottle.
 
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baranjhn said:
Changing the barrel out shouldn’t have any correlation with a leak. If it’s not the valve o ring, then it may be bottle.
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it's not the bottle - I've tested that separately and off the gun - I suspect that the loosening and tightening of the barrel block may have moved an o-ring, perhaps even one that wildcj5 showed in his August 20 post
 
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What is the best way to de-gas an unregulated USFT? I'm planning to change the pressure gauge to one that is easier to read (i.e., current one ranges from 0 to 3000 psi across 120 degrees of the gauge circumference, vs the new one ranging from 0 to 2000 psi across about 180 degrees).
I figure that slowly bleeding from the pressure gauge might work well, but would like to hear of others' experiences/ recommendations. I hate bugging Tim with little questions like this.
 
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Need some help - I took my USFT apart chasing the leak which I've mentioned before. I've determined it is the plug used to replace the fill nipple when the USFT was converted to a bottle gun. I kept disassembly to clean up and out of curiosity. I found a couple of the O-rings looked much those shown before, i.e. with bits carved away.

When I disassembled I failed to take pictures of the position of the regulator/mount for the bottle and the silver threaded portion that is pointed to in the picture below. The black valve / mount for the bottle cannot actually be threaded onto the gun as there is not enough thread. That leaves that area as another plenum - I suppose. My question - where is the aluminum colored collar to be positioned? And in which direction should the hard plastic o-ring be placed?

I don't have the second regulator that wildcj5 shows on his disassembled USFT.

Any insight would be appreciated
TIA

IMG_0275.jpg
 
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A quick update. Especially to wildcj5 who contacted me with insight.

I replaced one o-ring and used a heavier, much thicker plumbers Teflon tape to seal the bolt that replaced the foster fill when I had this converted to a bottle rifle. It’s been two days since a reassembled the USFT and it hasn’t lost any pressure since.

on to my second season of FT
 
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SDstephan said:
Update on two points with my USFT - partially answering your question Franklink

1) my gun is leaking more slowly now - taking an entire week vs 2 days to get to empty , it may have something to do with the following

2) I recently installed a slow poly barrel, replacing the carbine length one of unknown twist rate. My first impression was that the long range 45-55 yards shots were grouping much better. I went with this barrel on Tim's recommendation when he had my USFT for a bottle upgrade. At that time he did not have any barrels in stock so I waited about 6 months to make the change

After the initial install I had to take the barrel off again and then reinstalled it a few minutes later. Since then leak has slowed as mentioned earlier. I am guessing that I may have cinched down on an o-ring just right. I'll take the gun apart in two weeks and see what is happening and which O-rings will need replacement.
Click to expand...
Frank,

A common method of measuring twist rate is to push a cleaning rod fitted with a tight patch thru (after putting a flag of tape on back end of the rod) and counting approximate rotation degrees of the flag.

That method generally does NOT give accurate information, since the jag on the rod end normally unscrews to some degree while being pushed, yet screws back tight when withdrawn. The result is the twist rate SEEMS slower than it really is.

Pulling the rod seems much more accurate for me.

I’ve been checking barrels for several decades, and most commercial .177 airgun barrels Had rates between 1:14.5”. And 1:18”. Of course recently the LW slow twist is out, and one i’ve used measure around 1:27” or 1:28”.

LD
 
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SDstephan said:
IMG_0275.jpg
Click to expand...

for all those disassembling / reassembling their USFTs please note that the above is the incorrect arrangement of the silver 'screw-washer' and the 90 duro (white) o-ring. The white o-ring should be up against the orange body of the rifle held in place by the silver 'screw-washer'. Please note that the screw-washer should not be tightened until after the air tube has been installed to ensure that the white o-ring is not damaged.

I hope this helps.

BTW - well over 30 days without any drop in pressure
 
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I think I've learned a bit about USFT poppet/stems, i.e., the muzzle velocity is very sensitive to poppet diameter, and to a lesser extent stem length.

I have USFT 150, an unregulated hunter setup, with the original guts built in 2011. I had a leak through the valve and accidently sheared off part of the valve stem when reassembling. Tim did not have replacement poppet/stems so I did a quick repair and also looked for other sources for poppets. As of today, I got some from Motorhead and from Tim when his supply was replenished. Although my repaired poppet/stem was working well, delivering 800 FPS with FX 13.4, I was getting a bit more ES and SD than I was hoping for and tried one of the new Mac1 poppet/stems. FPS dropped to 650 FPS and stayed there even after reinstalling it a couple of times. I tried a couple of Motorhead's and got 750 FPS and 817 FPS.

I measured each poppet/stem. Values are poppet diameter, combined poppet/stem length, length of stem extending beyond the valve cover when the reservoir is filled, and any extension of stem above valve cover when reservoir is empty and my thumbnail pushes the stem into the valve head. All values are in inches, using a Mitutoyo caliber; measured each value a few times. All 5-shot average FPS data uses same reservoir pressure, hammer spring tension, and transfer restrictor setting.

Values are:
1) 817 FPS. 0.273 poppet diameter, 1.313 length, 0.150 extension, 0.0 extension
2) 804 FPS. 0.275 , 1.289 , 0.125 , 0.0
3) 750 FPS. 0.280 , 1.285 , 0.155 , 0.0
4) 650 FPS, 0.280 , 1.360 , 0.183 , 0.084

Poppet diameter is the biggest driver of FPS change when stems aren't too long. I suspect Tim includes poppet diameter adjustment in his tunings. (He recommends a 0.285 diameter for <12 fpe, 0.280 for <20 fpe. But I can't get to 20 fpe with a 0.280 diameter poppet)

The #2 poppet/stem had a very short stem. This is my home-fixed one using purchased 2mm rods and the original poppet. I suspect the lower velocity is from not pressing the poppet down into the valve enough.

The #4 poppet/stem came with a long stem that doesn't get pushed all the way to the valve head. So during a shot, the valve spring gets fully compressed and maybe causes a fast reclosure of the valve when using this unit.

What amazes me the most is how small the differences in diameters are. (All the poppets seemed to be consistently round as I rotated them to check diameters). I wonder if the ideal poppet diameter varies from gun to gun, based on tiny differences in valve head geometries.

If anyone has suggestions on the best way to sand down the diameter of a poppet to raise FPS somewhat, I'm all ears. And of course, let me know if you have had different experiences or am full of crap in my assessment.
 
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From the last little paragraph on this post....https://www.airgunnation.com/threads/mac1-usft-analysis-overview.1044226/post-1047847

"Tim sent a note with my gun that says, "0.2fpe per 0.001" diameter of valve head." I'm not sure if he meant the valve stem can be reduced by 0.001" to gain 0.2fpe or if the outer diameter of the delrin has to be reduced by that much to gain 0.2fpe. My gun is going to stay at its just under 20fpe power level so I won't every be testing out this theory, just thought I'd include it for any interested parties. "

I've got a spare poppet that Tim supplied with my gun and I'll try to remember to measure it and provide you the dimensions when I'm not at work. I've never had that spare poppet in the gun so don't know what fpe it produces, but it might be interesting to compare specs at least.
 
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As a little bit of an update....I never reported on the last time I shot the USFT at a match. It was at the AZ state ft match in September of 2022.

I only shot Saturday, and scored 55/56 that day on the "red" course. The single miss was an offhand shot, otherwise the good ole USFT went 48/48 on the bumbag shots, 4/4 on the kneelers, and 3/4 on the offhand. Of the other shooters that shot the same course that day, the next highest score was a 49/56 (Lauren Parsons). On Sunday one of the Hunter class shooters (Kent) shot a 53/56 on the "red" course, the next highest overall score on the "red" course, to my 55/56,

The USFT is a dang good gun. As accurate as anything I've had the privilege to shoot (even if it's funny-looking).

(Shared more as a flex of what the USFT is capable of than being boastful of my abilities. As I've stated elsewhere, the couple of times I've lent this out to "newbies" they've also scored very high.)
 
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