Revisiting Prod/1701P/1720T Hammer, Springs, and Adjustment

[FuzzyGrub]

It has been quite a while since I've done much with tuning these guns.  For the most part, mine are either regulated or tuned with an O-ring buffer.  Experimenting recently for my 2501P build, with the latter, had me coming back to the limitations of space within these guns.  I thought I'd post some of the info for other owners here.  I'll cover what options are available, from increasing difficulty, and side effects to consider. 

From a cocking perspective, the Prod, 1720T, and 1701P all share the same components.  Hammer, striker, spring, adjuster, and end cap.  All of these air tubes have the same dimensions in this area.   The Fortitude has the same air tube dimensions, but uses different components.   I'll discuss the stock components and limitations.

Hammer Travel: From sear latch to poppet contact, there is only 1/2" of travel.  That is with the throw adjustment at maximum (full CCW).   That compares to 0.9" of a Mrod, if memory serves.  This short distance in itself, is a significant limitation.  It complicates power mods, and efficiency mods such as SSG and dual spring configurations. 

Below, you will see a piece of a Prod tube, left over from a double tube build.  Along the hammer pin slot you will see two long indicator marks.  The rear most mark is the pin location at sear latch and the one ahead of it, the pin location on poppet contact.  You will also notice there is 3/8" from poppet contact to where the hammer pin would contact the end of the slot.   The poppet stem only extends out of the valve 1/4", so the pin will not contact the air tube.  The hammer will hit the back of the valve first.   That normally would never happen in normal use, except if shooting the gun down to zero psi. 

[FuzzyGrub]

Hammer: 

Dimensions: 1.3" L X 0.738" Max OD

Spring Pocket: 0.488" Depth X 0.312" ID

Weight: The stock hammer weighs 54g and a total of 58g with the oem striker.  That compares to 73g (78g w/striker + hammer pin) of a Mrod hammer.  The Mrod hammer is considered "heavy" though. 

Throw Adjustment: Greater than the 1/2".  You could adjust it such that you would have no throw!  Not that has any real value.   

[FuzzyGrub]

Hammer Spring and Adjuster:

The hammer spring is 0.312" OD X 1.5" L X 0.035" wire.  Please note that I believe newer guns, within the last 3 years, have a different spring.  I need to remove and check the one in my most recent purchase.   I believe the wire size was increased to 0.042", but same length.   I'll post an update when I have that.

Update: Current production stock spring: 0.282" OD X 1.85" L X 0.035" wire

Spring Adjuster:  The adjuster has 6.5 turns of adjustment from full CCW stop to falling out of the threads, for about 0.27" of travel.  The spring is under slight pre-load at the full CCW stop.  About 0.1" of preload.  So the total amount of preload is limited to 0.37".   In stock form, you can not adjust it for zero preload or negative (gap), which is done to prevent hammer bounce and improve efficiency. 

With current production spring, there is 0.43" of preload plus the 0.37" of adjustment for 0.60" of total preload available.

[AKM]

What has more affect on de-tuning (less power) for indoor range use, turning the hammer spring CCW or turning the stroke CW?

Is one better then the other or should both be adjusted equally for lower power?

[Tonycalves]

Fuzzy amount of tremendous info thanks Bro!
Got the brass tube you linked. It's a snug fit can't wait to affix it to the probe. Thanks

AKM Theres a few ways to do that. You can order a smaller TP from Crosman.  You can cut the length of the poppet a little.  Adding a B Staley oring mod.

[AKM]

I asked because a friend has a 12yard indoor range and wants to shoot the P-rod.

I don't want to do anything permanent as this gun is used for pesting.

Guess I'll turn the hammer spring all the way out CCW, turn the stroke in CW and see what happens.

Thanks.

[JBinCO]

Little off topic I guess.... where can you get hammer springs....I am looking for the Gauntlet (think it is the same as you have on picture but need to confirm that with some caliber work.   What I have has a kink and is hanging up or binding some (Haj put in with a JSAR super tune kit......I have a PM in to Haj but he is very busy and if I can get it on my own he can keep making videos for us!) after 5000 rounds or so

[FuzzyGrub]

What has more affect on de-tuning (less power) for indoor range use, turning the hammer spring CCW or turning the stroke CW?

Is one better then the other or should both be adjusted equally for lower power?

You can think of the hammer spring as the course adjustment and throw as the fine.   In your case, you will be trying to move your shot string to a lower pressure, which also reduces the shot power.  Let’s say that your current shot string is centered on 2400 psi, try lowering it to around 2000.  If that doesn’t lower it enough, it may take extra measures, like was mentioned above.

[FuzzyGrub]

Little off topic I guess.... where can you get hammer springs....I am looking for the Gauntlet (think it is the same as you have on picture but need to confirm that with some caliber work.   What I have has a kink and is hanging up or binding some (Haj put in with a JSAR super tune kit......I have a PM in to Haj but he is very busy and if I can get it on my own he can keep making videos for us!) after 5000 rounds or so

I don’t know Gauntlet spring dimensions or rate.  McMaster-Carr was my go to spring supply, but their selection has dwindled over the last few years.  There are many other online sources, and can have them custom made to your specs.  Lee springs is one you should check out.    Recently looking on Zoro.  They seem to have a decent selection in the range I want, but the layout makes it harder to find the specific one you want.   Prices look to be around $15 for 10 springs. 

[Hawkeye51]

Fuzzy

Timely post for me since I just got a bargan on a new P-rod. Looking at tunes, parts, springs etc. Thanks for posting the info. Amazon has a few choices in .042-.047 springs but I was unsure of the length needed for a tiny bit of free flight. I'm assuming a power adjuster would give me a little more fudge factor.

Anyone wanting to suggest tip, tricks and links, for P-rod tunes would be greatly appreciated by me.  I know it's all been done before & your experience would save me time & money. Looking for best power at about 3 mags. I have one set at max power, but limited shot count. I love the platform.

[FuzzyGrub]

I am planning to cover the minor mods next.  Springs, RVA, and hammer travel.  I was not planning to cover specific tuning how-to here, outside of mentioning what may be beneficial or appropriate for conventional, BStaley (O-ring), SSG, Short stiff springs, type tuning.   My favorite for Prods, over the years, is still the BStaley.  Try doing a search on that, here and maybe on the marauder forum.  There was a whole guide that was written on it. 

[RDB]

Which ones wear regulators, and how are they tuned?

[Blutroop]

Watching.

[FuzzyGrub]

Which ones wear regulators, and how are they tuned?

Using a regulator, usually means optimizing for a lower pressure.  A lighter hammer and spring change, SSG, dual springs, or SSS (short stiff spring) are candidates.  Working within the tight confines is the challenge. 

In my particular case, all three of my "long" tube rifles are regulated.  The 25 uses a zero preload spring, the 22 a twin spring set-up, and don't remember what is in the 177, but likely a MDS lighter hammer. 

[SILENT SQUIRREL]

I am planning to cover the minor mods next.  Springs, RVA, and hammer travel.  I was not planning to cover specific tuning how-to here, outside of mentioning what may be beneficial or appropriate for conventional, BStaley (O-ring), SSG, Short stiff springs, type tuning.   My favorite for Prods, over the years, is still the BStaley.  Try doing a search on that, here and maybe on the marauder forum.  There was a whole guide that was written on it.

Following you John
It's good for the shot curve & the learning curve

Ed

[FuzzyGrub]

There are a couple of ways to increase the hammer travel.  Not a big increase, but will provide some additional force on hammer impact. 

Shortening the valve poppet stem will provide some additional travel.   The stem extends out of the valve by a 1/4".  You need around 1/8" of travel for use, and would add some buffer.   If going this route, would only remove about 0.080" or close.   Crosman valve poppets are inexpensive, around $1.70, if you mess up.  You do need to grind a slight taper in the end to prevent mushrooming.  If it mushrooms and you try to remove it, can jam and/or damage the valve.  I would also recommend extending the hammer slot, the same amount as removed from poppet stem to prevent hammer pin from hitting the end.   I expect that modding the hammer slot, and requiring a de-gas to mod poppet, will keep most people away from this one.

The much more common way is to shorten the striker.  A 1/4"-28  set-screw in  3/8" - 1/2" length, with the head ground flat can do the job.  With set-screw set flush, you will gain 0.080" of travel.   If you recess the set-screw, you could get a little more.  Like the poppet stem mod, you need to be concerned about the hammer pin hitting the end of the slot.   In this case, there is an easier way to protect it.  Installing a single -113 O-ring, against the back of the valve, will prevent the pin contact and from the hammer contacting valve using dry fire degas method.  Many will have these size O-rings, as it the size used within the prod/1701/1720.   A -113 X-ring would hold in place better, and if using only as a bumper, 90D will last longer.

The set-screw striker, is not a complete free lunch.   Without the striker head, you do not have a positive stop to reference for tuning.  Using this, it generally becomes stationary.  That is not an issue for most tuning, as many airguns out there do not have a throw adjustment to begin with.  While it can be used with the BStaley O-ring buffer, it would only allow for two O-rings and you have to carefully track how many turns are on the set-screw.  I don't recommend it for tuning with that method.  You also lose 3g of weight by going to set-screw, but it is inconsequential. 

I will mention here, but discuss further in the thread, that some aftermarket and custom hammers allow for the striker to be recessed flat to the hammer.  That will provide 0.080" additional travel with a positive stop for the striker. 

Theoretically, you could do both mods to gain 0.160" of travel.  In which case, you definitely need to extend the hammer slot to prevent the pin from impacting.

Pictures:
1 - Poppet showing the bevel to prevent mushrooming
2 - OEM hammer, striker, and set-screw striker
3 - Set-screw striker installed flush
4 - Tube showing the 0.080" travel increase with set-screw striker

[TF89]

Thanks for the awesome details and the time you are putting into sharing this information.  It takes a lot of time to put this type of presentation together.

[moorepower]

Fuzzy, you are the P master. The only things I can add, is that the Square Orings stay put much much better than the round ones. If I recall your using an Xring?? A word of caution to all of those that throw in a heavier spring, make sure the bolt is pulled all the way back, because if your not deliberate you WILL double load. I have a .045 spring in my Prod, if I remember and I am going down to a .042 to try to get easier cocking. "If" JSAR ever produces the balanced valve again, it might be worth getting one just for the reduced cocking effort. I need to tear in to the 1720 and tweak it a bit to get the shot count up. "If" I could only have two airguns the Prod would for sure be one of them. It's the only airgun I own that I will take the pump with me not the tank, if I am just hunting.

[SwampHunter]

Following! I have a prod that was modified before I got it, so I didn't get the chance to go through the learning curve on them, lots of help here!

[FuzzyGrub]

Thx, Guys.  Glad someone has found the info helpful.

Busy on other stuff, but hope to post about hammers by sometime tomorrow.   Followed by RVA's, and then springs to tie it all together.