MAC1 USFT Analysis/Overview

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Typical USFT tune uses lower pressure like 1300PSI with mass added to hammer yielding a longer dwell time.

I have wanted to test against higher pressure like 1600 psi with lightened hammer/heavier spring setting to net same FPS at muzzle. See if there is any change to BC massing up the hammer and reducing pressure, maybe isolating obturation effect, or amplifying irregularities in bore... ? External adjustable reg and the later hammer with threaded hole, add some bolt mass, hide out in LD's test tunnel for a couple hours, get some wisdom from the creator... sounds like a fun morning.
 
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thane said:
Typical USFT tune uses lower pressure like 1300PSI with mass added to hammer yielding a longer dwell time.

I have wanted to test against higher pressure like 1600 psi with lightened hammer/heavier spring setting to net same FPS at muzzle. See if there is any change to BC massing up the hammer and reducing pressure, maybe isolating obturation effect, or amplifying irregularities in bore... ? External adjustable reg and the later hammer with threaded hole, add some bolt mass, hide out in LD's test tunnel for a couple hours, get some wisdom from the creator... sounds like a fun morning.
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Sounds like a fun way to spend a couple hours.

If it helps with your potential project....when I bought mine Tim told me he'd set it to shoot the .177/13.43 at just shy of 20fpe. I went straight to 10.34s and was slightly over 20fpe. A VERY slight reduction of the hammer tension and fiddle with the transfer port got me to an average of about 910-920fps.

But to your point about varying hammer and hammer spring and fill pressures as a potential way to compare obturation....mine has always needed filled to 1500-1450, shooting down to 1250, and then refilling. I have no idea where my hammer spring would fall on a heavy/light scale. I do have the threaded hammer but run it with no added weight for field target. Point being that my "tune" doesn't sound like the typical tune that you've seen. And with you living where you do, you're kinda in USFT central-likely seeing a good representation of how many of them are tuned.

Bobby and I have discussed that the ideal way to investigate the obturation theory would be to be able to inspect and compare fired pellets. But specifically fired pellets that haven't been damaged or changed by the collection method.....Read something once about using pillow batting or old grocery bags in a containment vessel, like pipe, as a way to gather data on fired pellets with minimal damage from the collecting...just haven't personally tried it....yet.
 
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I have the same Tim tune, but with a bottle and reg, higher set point with lite hammer doing the same 10.34 @ 910 fps on 1450psi.

LD commonly runs lower pressure like 1250, brazes carbide to the hammer. Then he puts on his wizard hat, shoots a few shots... grinds off some carbide... shakes a dead chicken over the barrel... repeats;).

May end up with something, or just rule it out. Either way shooting at LD's ranch is fun.
 
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thane said:
I have the same Tim tune, but with a bottle and reg, higher set point with lite hammer doing the same 10.34 @ 910 fps on 1450psi.

LD commonly runs lower pressure like 1250, brazes carbide to the hammer. Then he puts on his wizard hat, shoots a few shots... grinds off some carbide... shakes a dead chicken over the barrel... repeats;).

May end up with something, or just rule it out. Either way shooting at LD's ranch is fun.
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I totally agree that LD's ranch is one hell of a good time!
Shooting in the tunnel is an experience!..Love the sounds you get when firing. It's like sound effects from Star Wars.
Don't know if he is still doing monthy BR matches..those were great too
Mike
 
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beerthief said:
For those of us not in the know , i had to look it up as it pertains to Air gun and pellets.

Obturation - Wikipedia

en.wikipedia.org en.wikipedia.org
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Yep, the USFTs unique combination of low pressure and transfer port configuration are VERY different than the standard PCP.

The big question: does that low pressure obturate the pellet differently (less?) than a blast from a typical PCP operating on a reg pressure 2x (or more) as high.

The other potentially relevant detail here is that the USFT doesn't have a transfer port cut into the side of the barrel @ 90 degrees to the direction of pellet travel, which is how the vast majority of airgun designs delivers air to the base of the pellet. So less turbulent/more laminar air? Lots of other questions to ponder, and not many answers, just the fact that USFTs are TOUGH to compete against in field target. But why?
 
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Franklink said:
Yep, the USFTs unique combination of low pressure and transfer port configuration are VERY different than the standard PCP.

The big question: does that low pressure obturate the pellet differently (less?) than a blast from a typical PCP operating on a reg pressure 2x (or more) as high.

The other potentially relevant detail here is that the USFT doesn't have a transfer port cut into the side of the barrel @ 90 degrees to the direction of pellet travel, which is how the vast majority of airgun designs delivers air to the base of the pellet. So less turbulent/more laminar air? Lots of other questions to ponder, and not many answers, just the fact that USFTs are TOUGH to compete against in field target. But why?
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????????? i do not know ,but is each barrel timed and locked in place @ best timing ? I would assume so ,the way mine shoots .
Also , can too high of pressure create too much "seal" that would create drag ?
 
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beerthief said:
????????? i do not know ,but is each barrel timed and locked in place @ best timing ? I would assume so ,the way mine shoots .
Also , can too high of pressure create too much "seal" that would create drag ?
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The rotation of the barrel can be tested, if somebody is motivated enough to do so. And by tested I mean simply shot in various positions to see if one particular location is "best."

I supposed too much "seal" could cause excessive obturation and additional pellet/bore interaction.....but I haven't the faintest clue on what the net effect of that would be on accuracy.
 
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SDstephan said:
I was lucky enough to acquire a second MAC1.
This a 22 call Hunter, S/N 38. Definitely a first gen rifle. No more complaints about converting my USFT to a bottle gun as this is a tube gun.
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How much fpe from the new-to-you .22 tubed USFT?
I've been intrigued by the handful of USFTs in that 45ish fpe range, as .22s, that I've seen comments about from time to time.
 
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Franklink said:
The rotation of the barrel can be tested, if somebody is motivated enough to do so. And by tested I mean simply shot in various positions to see if one particular location is "best."

I supposed too much "seal" could cause excessive obturation and additional pellet/bore interaction.....but I haven't the faintest clue on what the net effect of that would be on accuracy.
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I call that indexing ?
 
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cavedweller said:
It had to happen or i would spend too much time and money at the audiologist for hearing aids - which would affect my funding for future airguns.

I added a 16mm Rowan barrel adapter 1/2" UNF - perfect fitment, though i did move the barrel band slightly aft. The basic Weihrauch .177/.22 moderator has reduced the bark to very backyard friendly. @BC thanks again.

Question for all in the know = the breech lists "MWP at 1800 psi". Is this in fact the maximum airtube fill pressure?


View attachment 423985
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BC said:
Its at Tims now being converted over. I figured I should get one just to have a 20 fpe gun. In case I head over to the bucket brigade to join you guys one of these days. haha you never know......BC
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lucky me..... now it's a bench rest queen in my lair of things i dream of shooting as i have time.
 
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cavedweller said:
lucky me..... now it's a bench rest queen in my lair of things i dream of shooting as i have time.
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When i 1st saw the Mac and LD simple simons ..i really didn't think too much on the looks
then we started shooting ...dam thing is Gorgeous..Just Gorgeous
You have a Nice one @cavedweller
Are you going to try get that 2-groove benchmark too??
Mike
 
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manabeknives said:
When i 1st saw the Mac and LD simple simons ..i really didn't think too much on the looks
then we started shooting ...dam thing is Gorgeous..Just Gorgeous
You have a Nice one @cavedweller
Are you going to try get that 2-groove benchmark too??
Mike
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forgive my ignorance = 2-groove benchmark? Mine (both of them) shoot very well, the sub 20 prefers JSB 13.4 redsigned, my only gun which likes (loves) those evil pellets.
 
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manabeknives said:
there was a small run of these barrels that was a custom order from Benchmark with 2 grooves (unknown twist)
but because of the amount of material that the button had to remove, they were too expensive to do as a custom order
don't know how many were made, but they are something else.
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Ted of Ted's holdover did a video on a friends USFT at one point. I'm vaguely remembering that THAT USFT was one of the early ones with a 2 groove Benchmark barrel.

Also vaguely remembering, but for some reason I'm thinking those 2 groove Benchmark barrels were only in .22.....anybody got more concrete info?
 
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