Shortened my hammer spring in P35-177

[JimD]

I have three P35s, I really like them, one in each caliber they are offered in.  The regulator in the P35-25 was making the first shot about 30 fps lower in velocity than the rest when I got it.  After consultation with you guys, I adjusted the hammer spring to make the gun produce the peak velocity it would at the regulator setting.  It was supplied a bit low.  That resolved the issue.  My Avenger accuracy improved when I set it's hammer spring about 1/4 turn higher than the minimum level that gave me the highest velocity.  So now I find the hammer minimum spring setting that gives me peak velocity and then try hammer spring settings a little (like 1/2 turn) above and below this setting to see if it affects accuracy.

But on my P35-177 that was not possible.  It was supplied with the hammer spring turned up as high as it could go - about 3 turns in.  But backing if off until the adjusted was contacting the stock did not change the velocity at all.  I've been shooting it this way since June when I got it and it shoots pretty well but not quite as well as my P35-22.  I thought initially about getting a weaker spring for it but I decided to clip a little off the stock spring first.  All you have to do to get to the hammer spring on this gun is remove the action from the stock and then back off the hammer spring adjuster until it comes out of the action.  So I did this and then clipped off about 1 turn.  I measured the stock spring at 8.5mm diameter with wire 1.12mm in diameter and 54.7mm long.  After my reduction I measured it at 51.2mm long.  So I did not remove much.  I will include a picture of these parts including the little piece I removed.  Then I reassembled the gun and tested to see what velocity I got with the hammer spring backed off as far as it could go.

Before I shortened the spring, I got velocities about 925 with 8.33 grain SPA pellets.  I tested again turning the spring in one turn and it stayed the same.  After shortening, I got velocity of about 890.  Then I turned it up in two stages to get back to the original 925.  It took about 1.25 turns of the hammer spring.  I'm happy with that and left the gun there.  It is rainy here today but when the weather improves I will test accuracy adjusting the hammer spring in 1/4 turn increments up and down to see if it affects accuracy.  If it stays the same, I am OK with that but if it improves a little that would be better, of course.  It reduced the cocking effort slightly already.  Mainly it helped me set the gun up the way I have my others. 

[EdinGa]

I'm glad it worked out for you. I've had to trim a few in spa guns myself. I still don't understand why my reg seems to be set higher than yours, but it worked out good for my slug shooting.

[JimD]

It probably also helped your hammer spring to not be too powerful for the reg setting.  I don't think I'll ever turn mine up, I'm thinking I might want to try hunter field target with it and I get enough penetration with it set the way it is.   

[EdinGa]

It probably also helped your hammer spring to not be too powerful for the reg setting.  I don't think I'll ever turn mine up, I'm thinking I might want to try hunter field target with it and I get enough penetration with it set the way it is.   

I'm enjoying the heavier pellets and slugs, so I'll probably leave mine alone.

[mackeral5]

If you can find a Gen 1 Gauntlet .25 spring it works very well when cut down and used as a short stiff spring in the P15 based guns.  It is thicker wire/higher spring rate and fits perfectly inside the P15 hammer.  I wish I had a source for a few more....

The OEM spring puts way too much preload on the stem, IMO.  You did good by shortening it a bit. 

[JimD]

It finally stopped raining here and I shot a few groups this morning.  I shot 5 round groups at the hammer spring setting I picked yesterday, + 1/4 turn, +1/2 turn, - 1/4 turn, and - 1/2 turn.  Then I shot additional groups at what seemed like the best groups from the initial set.  I found no magic setting for the hammer spring.  My backup groups for what appeared to be the better settings did not repeat.  So I just left it at -1/2 turn, one of the better settings from the initial set.  It came closer to repeating the second time.

Velocity followed the hammer spring setting somewhat but our air temperature was 46 degrees as I was testing so the air chamber was cooling off as I was shooting.  The temperature made my +1/2 turn velocities below my initial HS setting.  But if I look at the settings closer together in time they follow the temperature (for instance the velocity average at +1/4 turn is 2-4 mps (about 6-12 fps) lower than the +1/2 turn.  So I'm pretty sure the gun was behaving as I expected.

I think I got the other benefit I was hoping to get, however.  I noticed early that the velocity was about 25 fps higher when the tank pressure was near maximum than it was when the tank pressure was near minimum.  It was higher from 200-250 bar than it was from 115 to 160 bar.  My other P35s don't do this.  But I wondered if the "too high" hammer spring setting might be affecting this.  I think it was although I haven't rechecked the regulator recently so it might have just settled down as it broke in.  I started testing with the tank pressure a little over 150 bar and aired up to about 230 bar during the tests.  Short strings before and after the refill had averages within 10 fps of each other.  But the difference was still there in two settings I had data both ways.  Still not great but better.  Within a smaller pressure change the velocity strings are within 20 fps so even with 10 fps added for a large range of pressures the regulator is not terrible but it is definitely worse than the one in my P35-22.  About the same as my Avenger.

I'm not sure exactly how much velocity I'm giving up by leaving the hammer spring 1/2 turn lower but it was 862 fps at low tank pressure and 872 at high tank pressure so it is still adequate for what I want to use this gun for.  The highest velocity for 5 shots (average) I measured was 883 right after I took the gun outside.  But the averages at +1/4 and +1/2 HS were several mps lower so I don't think there is really a 20 fps difference for 1/2 turn less hammer spring.  In hot weather I've measured as high as 895 fps with these pellets. 

[190mech]

On my Bullshark XM1, I tried an SSG setup with a longer softer spring, did a few revisions but never could get it to work properly.
Installed the original 8.5 OD 55.5 LGTH 1.25 WIRE Dia. spring and it went back to shooting well..Recently did a Short Stiff Spring mod on a Kral and that did great, might try that next on the XM1 just for educational purposes..

[mackeral5]

On my Bullshark XM1, I tried an SSG setup with a longer softer spring, did a few revisions but never could get it to work properly.
Installed the original 8.5 OD 55.5 LGTH 1.25 WIRE Dia. spring and it went back to shooting well..Recently did a Short Stiff Spring mod on a Kral and that did great, might try that next on the XM1 just for educational purposes..

Similar experience here before converting my p15 to .25.  I bought it as a .22 and was bound and determined to equip it with an SSG.  Ultimately made a functioning SSG, but found that with such a light hammer and short hammer travel it was very finnicky, I would go as far as to call it fickle, lol..........  I was pretty hard harded about it because of the successes of using SSG's in my QB based guns.  Ultimately I learned success was easy with QB's as the platform has an abundance of hammer strike capabability....  Ended up going to a short stiff spring, but still have slight preload, hammer is not in free flight.

As a sidenote, an area not often discussed around reducing required hammer spring tension the P15 based guns is increasing hammer travel.....   A combination of shaving .100-.150 off the face of the hammer, shortening  back side of the valve carrier a bit and then adjusting valve stem protrusion to 6-7mm or so will yield ~.200" more hammer travel than oem. This will result in a significant reduction of required hammer spring tension and/or preload.  Careful examination of the breech and the area around the vent hole will help you identify exactly how much you can safely remove from the hammer/valve/stem...

[190mech]

Do you think the longer hammer travel mod would be worth doing on a .177?

[mackeral5]

Do you think the longer hammer travel mod would be worth doing on a .177?

Worth doing?  That really depends on the individual....by itself probably not.  As part of a system, probably yes.

If reducing both hammer spring preload and hammer
spring tension are important to you,  you have the capability and time, then by all means, IMO i would say it is "worth it".

I

[Back_Roads]

Do you think the longer hammer travel mod would be worth doing on a .177?

Worth doing?  That really depends on the individual....by itself probably not.  As part of a system, probably yes.

If reducing both hammer spring preload and hammer
spring tension are important to you,  you have the capability and time, then by all means, IMO i would say it is "worth it".

I

 Pay off would be being able to push heavier .177 ammo as in slugs.

[mackeral5]

Do you think the longer hammer travel mod would be worth doing on a .177?

Worth doing?  That really depends on the individual....by itself probably not.  As part of a system, probably yes.

If reducing both hammer spring preload and hammer
spring tension are important to you,  you have the capability and time, then by all means, IMO i would say it is "worth it".

I

 Pay off would be being able to push heavier .177 ammo as in slugs.

Increasing hammer travel would indeed help if the goal was to increase energy output.  Again, one component of a system of mods.

To put it in perspective, my p15 is a .25 with 19.5" barrel.  It can easily produce upwards of 50 shots at 45fpe using relatively low regulator pressures around 110-115bar.  No single mod created this tune, but a system of mods did add up to these numbers.  Some contributed more than others.  In hindsight, there are some mods I would likely not include if I were trying to replicate this build starting with a new, unmolested P15 based gun.

IMO, for all P15 based guns there are some basic mods that will help yield tuning results that are desirable to me.  In addition to good ES, which I think we all value, I attempt to tune my guns for very specific characteristics.   At any power level, I want a nice snappy shot cycle.  I hate guns that buzz and/or fart.  As little hammer strike as required is a goal.  Achieving these objectives normally results in an accurate, efficient gun that I enjoy shooting.  Sometimes these goals are elusive and the journey is long, frustrating......Some of these goals may not be heavily weighted by other members of our community.  it takes all types, lol...

I am not going to bore everyone with my unabridged version of "the P15, according to me."  but I will share some basic, foundational mods which IMO are very helpful when pursuing "better than delivered" performance from your P15 based guns.

Reduce necessary hammer spring preload and tension by:
1) Increasing hammer travel as described in my earlier post
2) Reduce Poppet diameter
3) Change poppet material to peek

for 40fpe and greater applications:

1)  Increase plenum size, internally or externally depending on what you can find or want. Internally does not increase the P15's overall length, but sacrifices high pressure storage.  Externally increases length but does not sacrifice high pressure storage.  External plenum extensions are typically much larger than internal. 
2)  Reduce poppet stem diameter to 2mm.  This allows for the OEM valve throat to support full bore porting in .22 and call it 85% of bore porting in .25.
3) pay close attention to the area around the valve seat and where the tube connector/plenum screws into the breech block.  IMO this is the area most commonly missed by many who pursue high powered P15 tunes.  Again, IMO, this is an area that creates extreme turbulence and a choke point when attempting to flow enough air for high powered tunes at lower reg settings and greater efficiency.  Run a bore scope in this area with the poppet/spring/tube connector assembled in the breech block and one will see the challenge air faces in its attempt to quickly make its way to the base of the pellet. 

Anyway, I could go on an on with "the p15 according to me....."  There are many ways to skin a cat so to speak, this is just my preferred method.

[190mech]

Yes, I would like to try all of your tips, Have all the machine tools, Hope for long shot count and accuracy. Want to do a barrel swap too. Always had a .177 and am happy with this caliber..