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

[cootertwo]

Nice info there Fuzzy, thanks!

[Lani52]

Great info Fuzzy.

Thanks,

Roachcreek

[FuzzyGrub]

Hammers:

First a restating of the oem hammer specs:

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

- Hammer pin: Drop in pin. 
- Throw tension:  Blind hole on the front of hammer.  A small acetal pin is dropped into the blind hole and the throw adjuster is threaded over it.  If you purchased a hammer from crosman parts, the pin is not included.  A small piece of weed trimmer line will suffice.  If fixing a "loose" throw adjuster, you need to pick the old pin out (patience), before inserting new.

Modifying the oem hammer can be a challenge given it is hardened steel.   While I haven't tried it yet, they can be heated to cherry red, then allowed to cool slowly, to soften the steel.  After machining/modding, heating to cherry red and a quick quench, to re-harden. 

If you are tuning with the BStaley O-ring buffer, keeping the throw from moving can be critical for a stable tune.  Small movements in throw can have significant impact on fps.  A common mod is to thread the front hole for a small set-screw.  A set-screw with small piece of weed eater line, becomes a much better way to keep it from moving.  The hole is 0.135" in diameter.  I believe it was a 4mm tap vs the slightly larger 8-32.  I'll have to research it to be sure.   I was able to tap it, without softening, but you have to go slow and use a new tap.  On the third hole with that tap, I snapped it off.      I was able to break pieces off flush, and still use the hammer.  Anyway, just be careful and go slow.

The other main mod to the oem hammer, is widening and deepening the spring pocket.  This allows for using longer and larger OD springs.  Also, allows room for using twin springs.  The one I have, is 0.435" ID X 0.8" depth.  You can use springs up to 0.420" OD, but also requires End cap and rva adjuster mods.  More on that latter.   The weight is 46g.

MDS hammers are available for the Prod/1720/1701, but currently think only via custom order.  The one shown below has a brass core, striker flush recess, and the larger spring pocket.  Weight is 29g. 

Pictures:
- Left to right: OEM Hammer, Modified OEM Hammer, MDS Hammer

 

[FuzzyGrub]

Hammer Binding:

When going to heavier springs, the effort to cock the gun increases.  What also occurs, the cocking point is at the bolt lug/hammer pin contact point.  Because of this the hammer tries to tilt within the air tube.   The back edge of the hammer "digs" into the air tube.   If you look at used oem hammer, you will see a prominent wear made from the sear, but also at the bottom back edge.   This can get severe, and start damaging the tube.  Honing and smoothing out the air tube can help.  MDS hammers don't dig in.   I have also heard of some thin, stick-on "wear" pads.  I haven't used them, but if others can point me to them, might give them a try.  They could be placed on the back edge, off of the centerline, to stay clear of sear, and maybe on the front top, to minimize tilt. 

This hammer binding can also get worse, if using a breech riser, because it raises the bolt lug/hammer pin contact point.  I have used it in the past, with the longer challenger hammer pin.   Sometimes, you can make the lug a little longer, to lower the point, and this is what crosman did with the slightly higher Fortitude breech.  Doing that with the Prod/1701/1720 may require some relief in the cocking lug channel, to fit the longer lug. 

[moorepower]

Good info there on the larger spring! I use a carbide drill bit to drill out Disco hammers on my lathe to make a captured SSG/FFH, so I am sure it would work on Prod hammer, with no heating.

[FuzzyGrub]

OEM Adjuster:

The OEM adjuster rides on 3/8-24 threads and from min to max has an adjustment range of 0.265".   About 0.04" per turn.  It provides a positive stop against the back of the cap, where the smaller diameter degas threads are, which are 5/16-24.  The spring guide is 0.2" OD X 9/16", with an ID of 0.155". 

Pictures:
- OEM Endcap and Adjuster
- Adjuster at Maximum Compression
- Adjuster at Maximum Retraction

[FuzzyGrub]

For those that have AR type stocks mounted on your prod/1701/1720 you are very limited to making changes to the end cap or adjuster.  The AR stock adapters typically screw in to the degas threads of the end cap, so it can not be modified or used by other hardware.  I know that is a good many of you, and I have two myself.  JSAR made a 1 piece adapter that replaced the whole end cap, which fixed the most common problem with the AR stock adapters, the bolt coming loose.  I don't own one, so will not be able to comment on how easy or hard it would be to modify. 

[SILENT SQUIRREL]

For those that have AR type stocks mounted on your prod/1701/1720 you are very limited to making changes to the end cap or adjuster.  The AR stock adapters typically screw in to the degas threads of the end cap, so it can not be modified or used by other hardware.  I know that is a good many of you, and I have two myself.  JSAR made a 1 piece adapter that replaced the whole end cap, which fixed the most common problem with the AR stock adapters, the bolt coming loose.  I don't own one, so will not be able to comment on how easy or hard it would be to modify.

Is it a safe assumption, as much a it's a PITA, that one could remove the AR stock from the degas thread, make adjustments; & then restore the stock?

Soakin' the info up  like a sponge!

Thanks
Ed

[FuzzyGrub]

About four year ago, Bob (rsterne) led one of the most collaborative efforts I have ever seen on an airgun forum.  Design and development of the SSG : https://www.gatewaytoairguns.org/GTA/index.php?topic=102095.0   It was just amazing to see so many people come together, brainstorm, and implement so many different solutions.     I haven't seen anything that even begins to eclipse that, since. 

Back then, I looked to make one for prod/1720T:  https://www.gatewaytoairguns.org/GTA/index.php?topic=103054.msg983994;topicseen#msg983994  where I used the adjuster from the Crosman Challenger.   

That adjuster threads into the degas threads in the endcap, and provides a much larger range of adjustment.   Actually more range than any typical spring will have available.   It is a non-destructive change.   If you still want to use the degas tool, it can be removed, degassed and re-installed. 

More to come on this:

On the challenger adjuster, you get 3/8" of additional space in the back of the adjuster.  That allows for longer springs.  The springs should be 0.3" OD such that they don't rub against the threads.  It also can compress further than the oem adjuster.  About 1/8" of additional compression, if your spring is capable. 

Another interesting thing with the challenger adjuster is that it has internal threads.  The 10-32 threads allow for the possibility of a twin spring, albeit limited selection of springs that can fit with the 0.3 OD ones.  But, there is a number of 0.187" OD ones to look at.  If you are making an external SSG with this, those threads need to be drilled out.


Pictures:
- Challenger Adjuster installed w/jam nut
- Maximum Retraction
- Maximum Compression
- With 10-32 bolt screwed in

[FuzzyGrub]

For those that have AR type stocks mounted on your prod/1701/1720 you are very limited to making changes to the end cap or adjuster.  The AR stock adapters typically screw in to the degas threads of the end cap, so it can not be modified or used by other hardware.  I know that is a good many of you, and I have two myself.  JSAR made a 1 piece adapter that replaced the whole end cap, which fixed the most common problem with the AR stock adapters, the bolt coming loose.  I don't own one, so will not be able to comment on how easy or hard it would be to modify.

Is it a safe assumption, as much a it's a PITA, that one could remove the AR stock from the degas thread, make adjustments; & then restore the stock?

Soakin' the info up  like a sponge!

Thanks
Ed

Yes, that is how it is done if you have one of those stock adapters.  Back when I was actively tuning mine, I just reinstalled the crosman skeleton stock, and when complete, reinstalled the AR stock and adapter. 

[SILENT SQUIRREL]

For those that have AR type stocks mounted on your prod/1701/1720 you are very limited to making changes to the end cap or adjuster.  The AR stock adapters typically screw in to the degas threads of the end cap, so it can not be modified or used by other hardware.  I know that is a good many of you, and I have two myself.  JSAR made a 1 piece adapter that replaced the whole end cap, which fixed the most common problem with the AR stock adapters, the bolt coming loose.  I don't own one, so will not be able to comment on how easy or hard it would be to modify.

Is it a safe assumption, as much a it's a PITA, that one could remove the AR stock from the degas thread, make adjustments; & then restore the stock?

Soakin' the info up  like a sponge!

Thanks
Ed

Yes, that is how it is done if you have one of those stock adapters.  Back when I was actively tuning mine, I just reinstalled the crosman skeleton stock, and when complete, reinstalled the AR stock and adapter.

Thanks

[FuzzyGrub]

While the challenger adjuster allows for allot of adjustment, some will not like having the additional hardware extending out the back.  You can get close to the adjustment range by modifying the end cap.  It is a permanent change, but one of the main reasons I like modifying crosman guns, is the easy availability of parts at a reasonable cost. 

To get the additional adjustment, need to drill out the degasser threads and tap the threads out the back to the larger diameter oem adjuster.   You will gain about the same as the challenger for maximum extension, and able to use longer springs.  There is no additional compressive adjustment, though.  One advantage of this mod, using 0.3" OD springs, they can be changed without gun dis-assembly.  You might need a pick to pull them through the threads though.

The correct drill for aluminum is a "Q" size drill, for a 3/8-24 tap.  Once drilled out, tap from the inside to align with the existing threads.  The key is to hold the end cap securely without messing up the finish.  Not hard for the drilling, but more of a challenge with the tapping part.  I ran some short SHCS into the two 4-40 and one 8-32 holes.  I then used a bench drill vise, clamping on the SHCS heads.   Use a good tap, and back up often to clear chips. 

The oem adjuster does not have internal threads like the challenger adjuster.  It does look like it may have enough material to be drilled and taped for 10-32.  ie to try to do a version of twin springs. 

[FuzzyGrub]

To use larger than 0.3” OD springs, will require a larger OD adjuster.  The largest possible is the ½-20, which is the same as the Mrod adjuster.  This will allow for springs upto 0.42” OD.   In this case you want to drill and tap from the outside in.  Use a 29/64” drill for ½-20 threads.  Do not drill all the way through the end cap.  Stop 5/16” from the bottom.  This is the part that inserts into the air tube.  We don’t want to break into the 4-40 breech screw holes and have enough threads for the trigger assy screw.   This section should be back drilled with a 7/16” drill.   For the ½-20 threads, will need a normal tapered tap, followed by a bottoming tap.  The trigger assy screw will just need a thin washer.
 
The Mrod adjuster spring guide will need to be turned down from 3/8” OD to about 0.30” to 0.305” for common 0.42” OD springs.  It can also be threaded on the inside for an inner adjuster for doing a twin spring.  In the pictures below you will see one that has been threaded for ¼” -28, and using a hammer striker. 

Another option is drilling and tapping for 7/16 – 20, and making your own adjuster from a set-screw.  Like the hammer, it may require getting it red hot and slow cooling to soften the set-screw for drilling and taping.  In this case, no need to re-harden it. 

Pictures:
- Modified Mrod End Cap, Mrod Adj, and Modified Prod End cap
- Modified prod End cap w/adj and 1/2 and 3/8 set-screws
- Modified Prod End cap with jam nut

[FuzzyGrub]

Twin Springs:

You have heard me mention “Twin Springs” a number of times.  Twin springs discussion came out on GTA right after SSGs.  Travis drove allot of development in this solution, and like Bob, shared allot of that here.  Another good GTA collaborative effort.   What I found with twin springs, you could use a heavy spring adjusted with a gap and a lighter spring in preload, to get good efficiency, like the SSG, but had less erratic Es. Some of that erratic Es in SSG’s was admittedly component and fitment driven.  Twin springs, were easier to tune for me.  They also could be configured for higher loads.  Two springs working in parallel, the forces are additive.

Travis also has developed both Prod and Mrod versions of the Twin Spring set-up.   I don’t believe the Prod one is available anymore, though.  While I have some of these, I did not go take apart those guns to study or copy.  I believe these adjuster mods are different, and probably not as good or refined as his designs.   It is mainly to spark ideas for other DIYers, vs trying to copy any production solution.   

Next up, within a couple of days. is figuring out spring selection, starting with single springs.  Connecting the hammers and adjusters together. 

[Blutroop]

Hey John, I really like the platform but have been looking for ways to improve. I’m thinking about doing my own aluminum air tube.
If you could design in a little more length would you give more room for hammer travel, spring, or both? With hammer travel only being 1/2” seems like 1/4 or another 1/2 could make a big difference?

[Buldawg76]

Subscribed as well.

[FuzzyGrub]

Hey John, I really like the platform but have been looking for ways to improve. I’m thinking about doing my own aluminum air tube.
If you could design in a little more length would you give more room for hammer travel, spring, or both? With hammer travel only being 1/2” seems like 1/4 or another 1/2 could make a big difference?

While I think there would be improvement for power tunes by adding 1/4" from sear latch to poppet impact, the amount of other mods that would have to change will start questioning "Is it worth it?".   I'll leave all the material change questions aside, and assume it is the same steel tube.  The first thing that jumps out at me is moving the front trigger assy screw back that 1/4 -1/2" and a custom breech to handle the longer cocking effort.  I think it will snowball from there and almost everything will change. 

[TF89]

The twin spring is a great idea. The hard part is getting reverse springs so the two don't bind and get tangle during use.  I really wanted to try that idea in both my disco and p-rod.  Ended up using the x-ring bstaley  tune, which works, just thinking the springs would be a better for lo,g term use.

[FuzzyGrub]

The twin spring is a great idea. The hard part is getting reverse springs so the two don't bind and get tangle during use.  I really wanted to try that idea in both my disco and p-rod.  Ended up using the x-ring bstaley  tune, which works, just thinking the springs would be a better for lo,g term use.

You are correct, finding springs that are left and right wound is hard.  Most places don't indicate winding direction at all.   I have not had any intertwining issues when using springs wound in the same direction.  I believe it is because the spacing of the coils is different between them.