RTI Prophet P1 .22 Efficiency & Power question?

[Scotty1]

If I’m shooting heavy pellets in my P1 (MRD’s) regularly, I add a hammer weight. Here is one for a P2.

 

[EPG]

It's a huben cricket regulator, pretty reliable one. My RTI failed and couldn't find parts locally so I machined an adapter to fit that reg into my gun.



I have no issue with pellets but with slugs, I feel that the gun is working hard to produce 55ftlbs (27 grain .22 shooting around 940-950fps). And yes, if I fill up my gun to 250, then I'll get 50 shots. But that's not the point I'm making here. Just out of curiosity why my DIY gun could bring out nearly as much power with shorter barrel (fx superior heavy 500mm) while P1 struggles with longer 600mm barrrel, heavier hammer at lower efficiency. I have a scuba tank and compressor so filling up is not really an issue, just want to optimize my gun.

Well, a P1 is a pretty simple design.

Its all about airflow. So, as others have alluded to, you can either hit the valve “harder” by using more weight in the hammer, or perhaps lighten the valve spring.

Your DIY rifle must be flowing more air - the usual reasons for that, valve opening duration, transfer port size, etc.

If you try a lighter valve spring, I’d be interested in hearing your results.

-Ed

 

[obi123]

To repeat the Gen one LR barrel is NOT designed to shoot slugs. It’s too slow of a twist rate and your attempts to make it do what it’s not engineered to do are futile.

Just to clarify, I have superior heavy liner barrel from FX 1:16 twist which I think pretty standard for some slug action. They group great, and I'm happy my P1 now, lowered velocity to around 925fps 27gr .22 slug. And the gun holds zero day in day out. And I understand that P1 was not designed for pure slug power like it's succesor so I was just wondering if I can improve it's capability. If not, then I'm happy with what P1 has already brought.

Well, a P1 is a pretty simple design.

Its all about airflow. So, as others have alluded to, you can either hit the valve “harder” by using more weight in the hammer, or perhaps lighten the valve spring.

Your DIY rifle must be flowing more air - the usual reasons for that, valve opening duration, transfer port size, etc.

If you try a lighter valve spring, I’d be interested in hearing your results.

-Ed

I opened and inspected the valve return spring on my P1 and was supprised how slim and light it is, so I don't think I should try lighten my valve return spring. My DIY gun is from a local manufacturer and I have all the measurements if your're interested.

So the hammer is 24gr, spring is kinda the same with P1 but is much shorter around 50mm, 1.5mm wire.
Valve propet 8.5mm in diameter, valve stem 2.5mm
Throat diameter 6.5mm, Transfer port has the same dimension as fx double transfer port. It's using pin probe of 5.5mm & 1.5mm pin.
This design has been really efficient and reliable and the gun shoots great. Just curious if I can change a thing or two to make my P1 to perform as good as my DIY gun. Picture below (20inch superior heavy barrel, 0.5L tank, shooting .22 27gr slugs at 925fps.

 

[Vetmx]

I have a box of parts from my two previous RTI standard valve guns at home. I took weight off hammers, tried different springs on both ends, played with poppet angles, materials and diameters. Interesting enough, what they put in the gun was a balance of what worked best. I commented on it years ago. After cleaning up some porting I felt my Priest ll was still a little behind a Prophet. Until I discovered that Prophets come with a 600mm instead of a 510mm. The second I made a 600mm FX barrel for my Priest, instant Prophet performance.

 

[Vetmx]

I have never used a lighter valve return spring in anything. Over the last 10 years while refining various guns, there was always the guy who posted a power gain when he lightened the spring in his gun. At first I jumped right on board and tried it. The results may have been true but there were always side effects I didn’t like. I’m a 600mm and under barrel guy. What manufacturers put in guns coupled with reg pressures is usually adequate. But I always test more tension. I try to clean up that last bit of dirty air. Because you end up going back to more hammer spring when performing the balancing act, a bolt gun got more difficult to cock. Nowadays with lever cocking, no big deal.

 

[lbc_PSI]

Isn’t there a part in the receiver of the P1 that acts as a “transfer port reducer”? Usually installed on the .177 and .22 versions?