RTI Reducing FPS (on RTI Priest -> Prophet conversion)

[elbeau]

I've got a .22 RTI Priest to Prophet Conversion that's slinging pellets a lil' fast (920 FPS at 90 on the reg), resulting in lighter pellets becoming unstable & spiraling.
Here's the question - what's the most air-efficient way to reduce the FPS? I'm going for a low-power tune to minimize pass throughs.
Is reducing the transfer hole at the bottom of the barrel by adding a drilled grub screw like they do in the EU more air-efficient than a lighter spring?
From what I've read, it seems that adjusting both may be necessary to achieve the best balance, but I wanted to see if anyone here could add any insight.

What I've tried/checked:

• There's no hammer spring guide/weight to remove - it is only the hammer & the spring. ID on the hammer cavity for the spring is about 9.5mm.
• Can't turn the hammer spring any lower without reg creep & a high FPS deviation on my first shot if the gun has been resting.
• Can't turn the reg down any lower than 90 without the screw losing engagement.
• I'm hunting iguanas w/Hades 15.89 & trying to minimize pass- throughs since I'm in the city, so going with a heavier pellet doesn't fit this case.

Thanks!

 

[tnt68]

I have a RTI Priest2 4,5/.177 in low power configuration, <5.5ftlbs/7,5Joule, with the original fixed 125bar regulator.
I have a Competition Electronics Procrono DLX and I found the right diameter of the reduction on the transfer port by testing different diameters for the hole(in my case about 1,1mm).
In my case, the Priest2, is difficult to find the proper M7 screw and, before having some from RTI to be drilled, I made some by myself using a more common Vespa M7 bolt.
In the picture there is the RTI 24Joule reduction for 4,5mm and a couple of mine.

 

[elbeau]

I have a RTI Priest2 4,5/.177 in low power configuration, <5.5ftlbs/7,5Joule, with the original fixed 125bar regulator.
I have a Competition Electronics Procrono DLX and I found the right diameter of the reduction on the transfer port by testing different diameters for the hole(in my case about 1,1mm).
In my case, the Priest2, is difficult to find the proper M7 screw and, before having some from RTI to be drilled, I made some by myself using a more common Vespa M7 bolt.
In the picture there is the RTI 24Joule reduction for 4,5mm and a couple of mine.

View attachment 432171

Thanks for the reply. So you are using the stock spring and just adjusted the transfer port size.
How do you feel it affects air efficiency?
and
What reduction in FPS did you achieve?

 

[tnt68]

I left all stock but the tranfer port reduction and the velocity is 165m/s-541FPS with JSB Exact 0,547g/8.44gr corresponding to 7,5Joule.
The efficiency is great with well over 350 shots per fill of the 320cc aluminium bottle @300 bar but since that I prefer not to fill over 250 bar.
With so a low power the best results I found with JSB Exact, Exact Express, AirArms 0,547g/8.44gr, RWS Field Target, RWS R10 Match.
My usual zeroing is at 20m/21.87Yards(for ratting) or 25m/27.34Yards(for targeting),is very consistent till 35m/38Yards and on the limit at 50m/54.7Yards.

 

[jcmammut]

I've got a .22 RTI Priest to Prophet Conversion that's slinging pellets a lil' fast (920 FPS at 90 on the reg), resulting in lighter pellets becoming unstable & spiraling.
Here's the question - what's the most air-efficient way to reduce the FPS? I'm going for a low-power tune to minimize pass throughs.
Is reducing the transfer hole at the bottom of the barrel by adding a drilled grub screw like they do in the EU more air-efficient than a lighter spring?
From what I've read, it seems that adjusting both may be necessary to achieve the best balance, but I wanted to see if anyone here could add any insight.

What I've tried/checked:

• There's no hammer spring guide/weight to remove - it is only the hammer & the spring. ID on the hammer cavity for the spring is about 9.5mm.
• Can't turn the hammer spring any lower without reg creep & a high FPS deviation on my first shot if the gun has been resting.
• Can't turn the reg down any lower than 90 without the screw losing engagement.
• I'm hunting iguanas w/Hades 15.89 & trying to minimize pass- throughs since I'm in the city, so going with a heavier pellet doesn't fit this case.

Thanks!

Have you thought about reducing the volume of the plenum?

 

[Joedirt199]

Hammer spring should not have any effect on reg creep. Need to get the reg creep sorted out and while you are in there, you could pull a belville washer out of the reg stack so the reg can adjust lower. Then I would cut one coil off the spring as it comes sprung too strong for low power tunes. The vented grub screw will be hard to find unless RTI sends you some and let you drill them out yourself. It is some oddball 7mm size and hard to find.

 

[Spinach]

Hammer spring should not have any effect on reg creep. Need to get the reg creep sorted out and while you are in there, you could pull a belville washer out of the reg stack so the reg can adjust lower. Then I would cut one coil off the spring as it comes sprung too strong for low power tunes. The vented grub screw will be hard to find unless RTI sends you some and let you drill them out yourself. It is some oddball 7mm size and hard to find.

The priest is 6mm TP. Easy to find a grub screw.
Prophet is 7mm and P2 and 3 are 8mm .

 

[Joedirt199]

Well that should help his dilemma. I would get the reg sorted to go lower then shorten the hammer spring to accomodate for the lower pressure. Fastest way is to reduce transfer port size.

 

[tnt68]

I confirm that on my Priest2 I got new last summer there is a 7mm reduction.
I sent an email to RTI and they sent me back some of those to make more elegant that the ones I made from a 7mm Piaggio Vespa bolt.
I agree that a better way to have a proper reduction is to play with the regulator and hammer and spring, maybe as I'll have to do more deep rebuild or a regulator and bottle upgrade...
I suggest to have a look at Chairgun to see how a low power setup helps to have a better kill zone in short distances as for ratting.

 

[lbc_PSI]

Depending on the length of the barrel you could scrub a lot of velocity going from a 23” LW to a 16” CZ…assuming this is a .22 approximately 10FPS per inch If you currently have a 23” bbl with a long shroud you’ll also need a short shroud. Starts to get expensive to lower FPS if you go this route..as you might have to get a short CF bottle to clear a moderator.

 

[griffwyn]

The priest is 6mm TP. Easy to find a grub screw.
Prophet is 7mm and P2 and 3 are 8mm .

My priest 2 is 7mm grub screw

 

[Spinach]

My priest 2 is 7mm grub screw

Earlier priest is 6 mm, I've never handled a priest 2.
Thanks for the update.

 

[EPG]

I've got a .22 RTI Priest to Prophet Conversion that's slinging pellets a lil' fast (920 FPS at 90 on the reg), resulting in lighter pellets becoming unstable & spiraling.
Here's the question - what's the most air-efficient way to reduce the FPS? I'm going for a low-power tune to minimize pass throughs.
Is reducing the transfer hole at the bottom of the barrel by adding a drilled grub screw like they do in the EU more air-efficient than a lighter spring?
From what I've read, it seems that adjusting both may be necessary to achieve the best balance, but I wanted to see if anyone here could add any insight.

What I've tried/checked:

• There's no hammer spring guide/weight to remove - it is only the hammer & the spring. ID on the hammer cavity for the spring is about 9.5mm.
• Can't turn the hammer spring any lower without reg creep & a high FPS deviation on my first shot if the gun has been resting.
• Can't turn the reg down any lower than 90 without the screw losing engagement.
• I'm hunting iguanas w/Hades 15.89 & trying to minimize pass- throughs since I'm in the city, so going with a heavier pellet doesn't fit this case.

Thanks!

I’ve used this spring stock (1.5 wire thickness) to make softer than stock springs for my Prophet V1s :

Amazon.com

There is also a 1.2 wire thickness version of the same spring that I’ve used in other rifles, not tried in Prophets.

The Prophet uses these 10mm diameter springs fine. You mentioned your Priest conversion has a 9.5mm opening. Interesting that they changed that from the Prophet.

In 9mm I found this one on Amazon, but max length available is 50mm from this brand, likely too short:

Amazon.com

-Ed

 

[Ema]

Hello guys, anyone have any idea how many fps increse by adding a power plenum on a Priest2 with a 24 inches barrel ? Or it remain same power but just more shot count? Thank you !

 

[Rizz01]

Anyone think of using heavier pellets? I know those RTI guns are tuned for them.

 

[Ema]

Hello guys, I have a question: if I add a power plenum on a Priest2 .25 with a 60cm barrel how many fps I increase with 22 cc extra of air ? Or just I have same speed but more shot count ? If someone already tested and let me know thank you really !

 

[griffwyn]

The priest is 6mm TP. Easy to find a grub screw.
Prophet is 7mm and P2 and 3 are 8mm .

My priest 2 is 7mm

 

[Spinach]

My priest 2 is 7mm

The original priest was 6mm, I've never handled a priest 2.
Probably using the same block as the original Prophet.

 

[griffwyn]

The priest is 6mm TP. Easy to find a grub screw.
Prophet is 7mm and P2 and 3 are 8mm .

The prieast2 has a7mm to