MAC1 USFT Analysis/Overview

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.
Sure sounds like it is the Delrin diameter referred to in Tim's note. (And yes I now recall you had that in your excellent review that started this thread.) My #1 and #3 poppet/stems had reasonable stem lengths and 3.2 fpe difference for 0.007 diameter difference. Tim's guidance would predict a 1.4 fpe change. So fairly consistent results to his guidance.
 
Sure sounds like it is the Delrin diameter referred to in Tim's note. (And yes I now recall you had that in your excellent review that started this thread.) My #1 and #3 poppet/stems had reasonable stem lengths and 3.2 fpe difference for 0.007 diameter difference. Tim's guidance would predict a 1.4 fpe change. So fairly consistent results to his guidance.
I'll get you some specs off the spare one Tim supplied with my gun.
 
Zounds! Here's my #150. Labelled as hunter. My gun was originally #151 canted when built in 2011. I bought it last year and asked Tim for a barrel mount that would make it a hunter version, i.e., without cant. I like that the designated number changed by just "1". Maybe you didn't keep up with your copyright payments. LOL

View attachment 347638

Your USFT 151 became Hunter 150.
That now gives me a build date/year of 2011

now back to the technical discussions
 
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Tim made more than one gun with identical serial numbers if they were different model. He serialized the barrel mounting blocks rather than the receiver, so swapping from angled blocks to upright hunter typically meant a different number series (not that much attempt was made to produce the guns by model year.

As to poppet SEAT DIAMETER (the stem is the thin shaft, the valvehead is the delrin part with part guiding the return spring and the other sealing against the VALVE BODY seat face). The gun was designed at first ONLY for 20fpe field target use, and yes it was convenient to adjust power level by modifying the seat-to-valvehead overlap margin, since it was easy enough if an old gun that had remained charged for many years and had lost a little power could be restored to original power by sading the delrin seat a a few thou to bring it back to original clearance (typically they grow by settlling over a long period).

Frankly the early guns never had, nor do they need a port restrictor … yours was added later for some reason.

Now don’t believe these guns NEED smaller poppet seal diameters to shoot harder! I have a couple (still unregulated USFT’s) in .22 cal that can easily shoot well over double the 20fpe limit, and even moret, albeit they ARE modified, but the poppets are absolutely standard items with around .180+ seal dia.

The latest one Im playing with the is for long range Field Target and 100y benchrest coming up in Ashland Or. I built it 14yrs ago for 50yd BR shooting when the open class allowed 34? Fpe and it did pretty well. But now I’ve bumped it to around 50fpe in .22 with the 25.4rds. Im only getting about 30 consistent shots on a charge, Though my second gun, which holds more air, gets 50 good shots, still fairlly low preseure And. CAN shoot up t0 65fpe, but not as accurately.

So don’t sand the valve seal down, just shorten your valve return spring a little (based on you post and picture). Also, take that port restrictor screw out and grind the end flat, then put a well firring drill rod up the port and run the screw in til it touches and loctite it there.
 
For the spare poppet that was supplied with my 2018 vintage Hunter #165...


0.279" = poppet diameter
1.390 = poppet overall length
16812754506367493943765918975204.jpg
 
If your rifle has the STRANGLE screw in the loading arm ? It could be choking flow and thus output ... Check it.
It did not have the "strangle screw". I also tried the #4 poppet/stem with the "max power" loading arm you sent me that did not have a restrictor hole. I got 680 fps (13.8 fpe) with your arm. I got 670 using my original arm with restrictor backed off 1/2 turn and 650 with it backed off 3/4 turn. I might try shortening the valve return spring length of one of the spare springs you sent to see the impact that LD described. I did not think that spring would have much impact as long as it wasn't fully compressed during a shot. After reading LD's comments I wonder if the hammer spring might have weakened a bit over the years.
 
Hey guys,
I realize this is an old thread, but hoping someone can help me here. I just dug out my USFT that I bought used 10 years ago from another member, been setting in my closet for a couple of years and it's still holding air and just noticed that it doesn't have a model or serial number on it like all the other ones I have seen pictures of..
Thanks Pete
 
Hey guys,
I realize this is an old thread, but hoping someone can help me here. I just dug out my USFT that I bought used 10 years ago from another member, been setting in my closet for a couple of years and it's still holding air and just noticed that it doesn't have a model or serial number on it like all the other ones I have seen pictures of..
Thanks Pete
You got some pics and what is your question?
 
LD made 7 "Simple Simon"s before the USFTs were even a concept. They were not anodized and were hand made, so maybe a little more basic in appearance. If yours is aluminum, unfinished, it is likely one of those. Extraordinarily well made with select HW barrels, they would be great to own. Steve Schultz used one to win the US Nationals the first year they were available.
Bob
 
I love the simplicity, accuracy and the trigger is amazing. I looked it up and I had purchased it from James Brinkley who was very helpful in filling me in on changing over to be bottle fed which I never got around to doing. Have a couple of bottle fed guns and compared to this being happy at 1400 psi my 74 cuft. air tank last so much longer than using other high pressure guns.
 
I was into point blank benchrest 100 -200 yard 6 PPC for awhile and lost my private shooting range, so I saw that James had this gun for sale and it was quite change from my ole RWS Diana 48 springer which I still love by the way. And liked the fact that these PCP guns with a muffler on them are so backyard friendly. We have a cabin up in northern Michigan that I can shoot up 85 yards at and don't have to leave the property. I have to many hobbies and got out of shooting for a few years, and my brother bought me a FX M3 and I naturally got the bug again. Decided to dust off the Mac 1 and was blown away all over again! LOL gotta love the trigger on these rifles, the trigger on my 6 PPC was set at just over 1 oz. so I was used to a very light trigger feel. I don't plan on any competitive shooting at this point just some backyard fun.. Don't get me wrong, the M3 has it's place especially for those pesky chipmunks.. :)
 
might still be one of the coveted first 100 that were claimed to have specially selected barrels.
looks great, every time I see a tube version I question my decision to turn mine into a bottle gun...
LD did test a good number of the first ones in his tunnel and there was an accuracy guarantee of sorts but mine is #25 and the barrel that was on it, as well as a couple of friends barrels were far from "selected". Mine and my friend's were tested and had good groups but in the wind... quite sensitive. @Franklink's, by comparison is as good as it gets in the wind. I replaced my barrel w an LW poly and it has been a HUGE step up in shootability... maybe even close to @Franklink's.
Phenomenal rifles, regardless. If you're not competing, the wind sensitivity probably won't matter much anyway.
Not trying to rain on anyone's parade... just not sure where the "coveted" aspect comes in. Comparing mine to @Franklink's, his is MUCH more refined and his is a late version.
I have a good number of good shooters but my USFT will definitely be one of the last to go from my collection.
Bob