Resources Tuning the Piatt/Thomas

[Troy Bakel]

Shifted to shooting indoors so time to tune the .177 Piatt/Thomas. I may be the 3rd or even 4th owner and the rifle may not have even been shot before l purchased it, as such, I had no idea what FPE it was jetted for.

Turns out it was jetted for 12 FPE. Adjusted the hammer spring CCW from 12 o'clock to 7 o'clock dropping the FPE from 13.9 to 11.6 using the Baracuda FT 9.57 gr 4.51 mm pellets.

If you give the regulator 10 seconds between shots the FPE stays between 11.4 and 11.6 (tested over 100 shots).

As for accuracy - it is a Thomas - cut the 9 ring every time on the USA/NRA 5O ft Target at 20 yards.

I want to thank Mike for an awesome design and beautiful machining and finish work, Will Piatt for assembling and smithing the rifle, and Rod for the final range set up. You three made it possible for me to own and shoot one kick ass rifle.

 

[igolfat8]

Congrats. Looks like an awesome rifle. Please post some target pics when you have a chance.

 

[BC]

Hey Troy, nice gun. Tuning wise the old way Mike slowed the speed down was NOT by hammer spring tension, but by tuning port screw lengths. He would have a tuning port screw (the 8/32 or 10/32 in the swinging breech arm) for each benchrest class. IE; lv, hv, etc. Once the hammer tension spring tension was set, the tuning port screw does the rest. So, that takes some time and a hand file, dremel tool or bench grinder, and a hand full of screws that are slightly longer than what you need them, because you will be grinding them down little by little to get to the speeds you want for each class. I am sure Mike N. or Rod as you mentioned above, may chime in with further info. Old school method, and it may still apply on his new guns?, was to turn the tuning port screw back out enough, until it provided no restriction. Shoot pellets over the chrono and screw in hammer tension until it hits top speed, whatever that may be. Once there, back it off an 1/8 turn at a time until you lose about 20-30 fps velocity. At that point the hammer tension is set and max velocity your gun will be able to shoot (depending on reg pressure) . Then, screw the tuning port screw back in til its tight (this would be your original screw thats already ground to length). Whatever that speed is, if it works, can be set slower with a longer screw, or sped back up with a shorter screw. You will have to spend time and pellets over the chrono to get it right, but its easy to do. Then keep your TP screws separated so you know which one is for whatever class. Hope that helps....im sure someone else will chime in, but this is how I have always tuned my FT Thomas and helped other tune theirs.................... BC

 

[nervoustrig]

The approach described by BC is valid. Minor correction that the restrictor is a #6-32.

Attached is a 1-page procedure I drafted up a while back...again, it's pretty much what BC described above. And a template for recording your hammer spring adjustment.

View attachment Thomas tuning instructions.pdf

View attachment hammer spring and jet template.pdf

 

[BC]

The approach described by BC is valid. Minor correction that the restrictor is a #6-32.

Attached is a 1-page procedure I drafted up a while back...again, it's pretty much what BC described above. And a template for recording your hammer spring adjustment.

View attachment 419591

View attachment 419592

those are great procedure write ups......thanks alot.....BC
and thanks for reconfirming my recollection of the procedures......

 

[Perle]

Will passed away in 2022

 

[cavedweller]

Shifted to shooting indoors so time to tune the .177 Piatt/Thomas. I may be the 3rd or even 4th owner and the rifle may not have even been shot before l purchased it, as such, I had no idea what FPE it was jetted for.

Turns out it was jetted for 12 FPE. Adjusted the hammer spring CCW from 12 o'clock to 7 o'clock dropping the FPE from 13.9 to 11.6 using the Baracuda FT 9.57 gr 4.51 mm pellets.

If you give the regulator 10 seconds between shots the FPE stays between 11.4 and 11.6 (tested over 100 shots).

As for accuracy - it is a Thomas - cut the 9 ring every time on the USA/NRA 5O ft Target at 20 yards.

I want to thank Mike for an awesome design and beautiful machining and finish work, Will Piatt for assembling and smithing the rifle, and Rod for the final range set up. You three made it possible for me to own and shoot one kick ass rifle.View attachment 419492

@Troy Bakel - I recognize Palmyra and that beautiful gun #124? .... and hey i have the NOTA rest that belongs under it.... Rudy from Mobile

 

[Troy Bakel]

Hey Troy, nice gun. Tuning wise the old way Mike slowed the speed down was NOT by hammer spring tension, but by tuning port screw lengths. He would have a tuning port screw (the 8/32 or 10/32 in the swinging breech arm) for each benchrest class. IE; lv, hv, etc. Once the hammer tension spring tension was set, the tuning port screw does the rest. So, that takes some time and a hand file, dremel tool or bench grinder, and a hand full of screws that are slightly longer than what you need them, because you will be grinding them down little by little to get to the speeds you want for each class. I am sure Mike N. or Rod as you mentioned above, may chime in with further info. Old school method, and it may still apply on his new guns?, was to turn the tuning port screw back out enough, until it provided no restriction. Shoot pellets over the chrono and screw in hammer tension until it hits top speed, whatever that may be. Once there, back it off an 1/8 turn at a time until you lose about 20-30 fps velocity. At that point the hammer tension is set and max velocity your gun will be able to shoot (depending on reg pressure) . Then, screw the tuning port screw back in til its tight (this would be your original screw thats already ground to length). Whatever that speed is, if it works, can be set slower with a longer screw, or sped back up with a shorter screw. You will have to spend time and pellets over the chrono to get it right, but its easy to do. Then keep your TP screws separated so you know which one is for whatever class. Hope that helps....im sure someone else will chime in, but this is how I have always tuned my FT Thomas and helped other

tune theirs.................... BC

Hey Troy, nice gun. Tuning wise the old way Mike slowed the speed down was NOT by hammer spring tension, but by tuning port screw lengths. He would have a tuning port screw (the 8/32 or 10/32 in the swinging breech arm) for each benchrest class. IE; lv, hv, etc. Once the hammer tension spring tension was set, the tuning port screw does the rest. So, that takes some time and a hand file, dremel tool or bench grinder, and a hand full of screws that are slightly longer than what you need them, because you will be grinding them down little by little to get to the speeds you want for each class. I am sure Mike N. or Rod as you mentioned above, may chime in with further info. Old school method, and it may still apply on his new guns?, was to turn the tuning port screw back out enough, until it provided no restriction. Shoot pellets over the chrono and screw in hammer tension until it hits top speed, whatever that may be. Once there, back it off an 1/8 turn at a time until you lose about 20-30 fps velocity. At that point the hammer tension is set and max velocity your gun will be able to shoot (depending on reg pressure) . Then, screw the tuning port screw back in til its tight (this would be your original screw thats already ground to length). Whatever that speed is, if it works, can be set slower with a longer screw, or sped back up with a shorter screw. You will have to spend time and pellets over the chrono to get it right, but its easy to do. Then keep your TP screws separated so you know which one is for whatever class. Hope that helps....im sure someone else will chime in, but this is how I have always tuned my FT Thomas and helped other tune theirs.................... BC

The "tuning port " screw, or "Jet screw" as I refer to it was already cut to length and very nicely ground to a fine taper. As such, I knew the rifle had been set to an FPE and all I had to do was determine that FPE and use the hammer spring tension to fine tune the FPE to pellet weight.

I am happy with 12 FPE and shooting LV so, as you can see, I got lucky and the rifle was tuned in about an hour using 6 different weights of pellets.

 

[Troy Bakel]

Will passed away in 2022

Yes I know. I am in contact with his wife and received her permission to engrave his name on the rifle.

 

[nervoustrig]

Just a friendly observation, going by the figures stated in the original post, the hammer spring adjustment produced a change from 13.9fpe -> 11.6fpe, which is about a 16% difference in energy or an 8% change in velocity. That means the hammer spring tension is not set optimally.

Given your description of how well it is shooting, I don't necessarily think you would benefit greatly from stepping through the adjustment procedure. But given the extraordinary accuracy these rifles are capable of, you may want to consider trying it when you get the opportunity.

 

[Troy Bakel]

@Troy Bakel - I recognize Palmyra and that beautiful gun #124? .... and hey i have the NOTA rest that belongs under it.... Rudy from MobileView attachment 419637View attachment 419638

@cavedweller, Hello Rudy! We shot together when you stopped buy PSA to visit Rod!

I was shooting my Rod tuned and setup USFT off of my Rod customized Targetshooters.com one piece rest.

I forgot you sold this rifle to Rod. The serial number is 0314 (my wife's birthday!!!!)

What do you know about this rifle? When I ran a dry patch through the barrel it came out spotless, a second patch with WD40 was also spotless. So unless you shot it and cleaned it I don't think you or the person you bought it from shot it.

I contacted Mrs. Piatt and she is going to research her husband's gunsmithing paperwork to find any related info on this rifle and pass it along.

 

[Troy Bakel]

Just a friendly observation, going by the figures stated in the original post, the hammer spring adjustment produced a change from 13.9fpe -> 11.6fpe, which is about a 16% difference in energy or an 8% change in velocity. That means the hammer spring tension is not set optimally.

Given your description of how well it is shooting, I don't necessarily think you would benefit greatly from stepping through the adjustment procedure. But given the extraordinary accuracy these rifles are capable of, you may want to consider trying it when you get the opportunity.

But optimal for what pellet weight? If I return the hammer spring adjustment CW from 7:00 back to 12:00 (original setting), a 7.0 grain RWS MEISTERKLUGEN launches at 12.4 to 12.9 FPE.

When I first tested the gun as delivered, and outdoors, I 3 shot group tested at 25 yards pellets from 7.0 to 10.3 grains and the 7.0 MEISTERKLUGENs were by far the best grouping. I called Mike to find out what this rifle was jetted for and he nearly puked a lung when he heard I was shooting a 7 grain pistol wad cutter.

 

[Troy Bakel]

Just a friendly observation, going by the figures stated in the original post, the hammer spring adjustment produced a change from 13.9fpe -> 11.6fpe, which is about a 16% difference in energy or an 8% change in velocity. That means the hammer spring tension is not set optimally.

Given your description of how well it is shooting, I don't necessarily think you would benefit greatly from stepping through the adjustment procedure. But given the extraordinary accuracy these rifles are capable of, you may want to consider trying it when you get the opportunity.

One more wrinkle - the H&N Baracuda FT 9.57 gr comes in 3 diameters 4.50, 4.51, and 4.52 mm. I tested the 4.50 and 4.51 mm and when set to between 11 and 12 FPE the 4.50 grouped really bad, all three were flyers. Someone told me a Thomas was tuned to JSB 10.3 gr and at 11 to 12 FPE this pellet did not group well at all, was not the worst but far from the best.

So I agree with you, I think at 67 years old with an ICD I'll spend time on the trigger instead of the grinder.

 

[nervoustrig]

But optimal for what pellet weight? If I return the hammer spring adjustment CW from 7:00 back to 12:00 (original setting), a 7.0 grain RWS MEISTERKLUGEN launches at 12.4 to 12.9 FPE.

You are correct, to fully optimize the hammer spring tension, it needs to be done for the particular pellet you will be using. A different pellet weighing more or less will spend a different amount of time in the barrel, and will therefore benefit from more or less valve dwell (which is what is being manipulated with the hammer spring adjuster).

With that said, I’m completely onboard with your initial approach of screening different pellets. The state of tune will influence the results but as long as it’s running at approximately the right fps/fpe and isn’t wildly unbalanced (e.g. velocity ping-ponging all over the place), it’s good enough to cull out any pellets that show no promise of grouping acceptably. But once it looks like you’ve identified “the one”, it pays to get the HST and jet set up for it. The reward is more consistent performance in the face of a whole host of things that conspire to diminish your scores…temperature effects, pressure variations associated with regulator creep or linearity or refresh rate, little variations in hammer strike, etc.

 

[Perle]

Yes I know. I am in contact with his wife and received her permission to engrave his name on the rifle.

She’s a real nice lady. I was lucky to buy 2 of Wills rifles after he passed from her.

That’s cool about the name engraving

 

[thomasair]

Yes I know. I am in contact with his wife and received her permission to engrave his name on the rifle.

As part of the rules of others smithing my guns....the smith was required to engrave or stamp a distinctive identification on the bottom of the action so things could be traced to the smith.

Mike

 

[Troy Bakel]

You are correct, to fully optimize the hammer spring tension, it needs to be done for the particular pellet you will be using. A different pellet weighing more or less will spend a different amount of time in the barrel, and will therefore benefit from more or less valve dwell (which is what is being manipulated with the hammer spring adjuster).

With that said, I’m completely onboard with your initial approach of screening different pellets. The state of tune will influence the results but as long as it’s running at approximately the right fps/fpe and isn’t wildly unbalanced (e.g. velocity ping-ponging all over the place), it’s good enough to cull out any pellets that show no promise of grouping acceptably. But once it looks like you’ve identified “the one”, it pays to get the HST and jet set up for it. The reward is more consistent performance in the face of a whole host of things that conspire to diminish your scores…temperature effects, pressure variations associated with regulator creep or linearity or refresh rate, little variations in hammer strike, etc.

Just shot this target indoors at 20 yards. The sighter is 5 shots from a clean barrel. The records were shot in sequence. 4 and 10 suck because I didn't relieve the torque on the rest - the cross hairs were dead center on the POI after I sent it.

 

[SDstephan]

Adequate

 

[Troy Bakel]

Adequate

 

[SDstephan]

I guess I have the next two days to show you up. Nice shootingTroy, methinks you have the “purple dream” sorted