XS60C PCP Repeater project

[RHytonen]

I got a chance today to make a limited travel spring guide for the Grizzly.... It looks like this....



The 7/32" OD spring guide is threaded both ends to 10-32.... On the front, the single nut is loctited and peened in place and turned down to 0.36" OD (same as the spring) to be a loose fit in the 3/8" hole in the hammer, and tapered to match the bottom of the drilled hole.... The space between that and the rear nuts is the length of the spring plus RVA screw, minus just over 1/2", which results in 7 lbs. of preload in the spring as installed in the photo above.... The two nuts at the back are installed against the shoulder on the rod and locked together.... When they hit the back of the adjusting screw, they stop the guide in its tracks, leaving the hammer to fly forward on its own to open the valve.... I had to drill the hole in the stock deeper to miss the nuts when the gun is cocked.... Moving the RVA screw forward reduces the space between the front of the guide and the hammer, which results in less distance for the hammer to coast before hitting the valve, and also results in compressing the spring further when the gun is cocked, storing more energy in the spring.... Therefore the RVA still works as intended....

The original plan was to use a 3" long, 11 lb/in. spring, with 5 lbs. preload and 15 lbs. force when cocked, but to get that to work I had to run it right up until it touched the hammer.... I ended up with a 13 lb/in. spring, with 7 lbs. of preload.... I think I needed more force because the guide is no longer part of the hammer weight, reducing the weight available to open the valve from 102 gr. to 84 gr.... The end of the guide misses the hammer by 0.12", meaning that the 1" cocking stroke compresses the spring an additional 0.88", giving about 18 lbs. force when cocked.... This is when adjusted for 971 fps average (94 FPE) with the 44.8 gr. JSB, the same as I had previously.... Although the maximum cocking force is only 3 lbs. less than with the previous short, stiff spring (2.5" long with a 24 lb/in. rate), the gun is much nicer to cock, with no tendency to not complete the cocking stroke.... I think this is because the force on the bolt handle is much more constant (7-18 lbs.) instead of increasing so rapidly as you pull the bolt back (0-21 lbs.).... With the sudden increase of force at the end of the bolt travel previously, you had a tendency to not complete cocking the gun, which could lead to double loading pellets....

So, how did it work?.... did it make the gun any more efficient?.... Yes, it did, and there is no longer any audible hammer bounce.... When I first assembled and tested the gun, I got 17 shots with the 44.8 gr. JSBs at just under 94 FPE.... However, with use and wear, the gun has developed an audible hammer bounce, and in addition a leak between the barrel and receiver at the transfer port, and was down to 13-14 shots per fill.... It still leaks, but you can no longer hear any hammer bounce (a very obvious difference in the sound), and the shot count is up to 15 shots before any velocity loss.... It is only down 10 fps at 17 shots, by which time it is down to 2000 psi (the setpoint is 2200).... Basically, by changing from a short, heavy spring (which gave me the previous best efficiency) to a lighter, longer spring with preload and a positive stop that holds it 1/8" clear of the hammer when uncocked, I gained at least a shot or two, putting me back over 2 complete magazines, even with the present leak.... I can say with confidence that using a preloaded spring that is not sitting against the hammer can reduce or eliminate hammer bounce.... We now have one more arrow in our quiver for tuning PCPs....

Bob

Bob, what's the OAL of your spring guide (including the head that goes inside the hammer) in this version?

I'm trying to work out some of my internals so I can source more than I have to fab or have built....

(Just a not-reinventing-the-wheel mania of mine -
"they" make almost everything, if you know what to call it.)

Thanks,
Rod

[rsterne]

You should be able to scale it off that photo.... The spring is 3" long, and compressed about 1/2", so what you see in the photo is about 2.5".... That would make the overall length about 4.2"....

Bob

[RHytonen]

You should be able to scale it off that photo.... The spring is 3" long, and compressed about 1/2", so what you see in the photo is about 2.5".... That would make the overall length about 4.2"....

Bob

Thanks - I guessed four, but that's the longest 1/4" shoulder screw/bolt I could find (and that's minus the threads anyway -  and the low head. Inside my striker will be flat, and I haven't yet decided its depth.)
I wish somebody carried the metrics (6mm) in the longest lengths - 100, 110, 120.

Here's a pic of what I found- 4.5565" OAL... but the shoulder is .25 od. (4.186"L shoulder, Plus ~0.3"+ of 10-32 thread. May need a spacer there for the short unthreaded portion, or to adjust the range. The bolts are also available shorter, of course.)

Hopefully spring (i.d.) selection will compensate for the 1/4"OD without having to
turn down the bolt's shoulder (also a possibility - as is drilling out the 7/8"OD, .5"ID hammer, 
for a larger spring O.D..)

But you know me.
I practically insist on standard replaceable parts where possible.
(And still don't have a lathe or mill.
Working on reconditioning the W-T DP this weekend)

Photo is the best I could do - VERY tricky shot with the reflective scale...

Rod

[rsterne]

I made my spring guide from a length of drill rod, threaded both ends.... The front cone is a nut screwed on, the end peened over (with Loctite for good measure) and then turned to the shape I wanted to match the bottom of the drilled hole in the hammer....

Bob

[avator]

A couple of months ago Stalwart contacted me and asked if I would mind testing a couple of his modified XS-60c trigger groups. He asked Betty Lou and I to each shoot 500 shots with them and report our findings. Needless to say, I jumped at the chance. Eric has done his magic on 2 of our Beeman P-17 pistols in the past and he knows our trigger pull prefernces. Betty Lou a long pull for her smallish hands and surprisingly enough, she also likes her's a bit heavy. I like mine to snap right at the top. Break like glass with very little first stage. This is exacly how he set these 2 trigger groups up. We made zero adjustment to them. Betty Lou loved her's right out of the gate. She may be a little less critical than you and I.... cuz she's a girl.... I felt a whisp of a sticky spot in mine for the first 20 or so shots that soon developed into an easy touch of a first stage and a crisp snap. I have about 250 shots on mine now and it seems to just get better. A month or so prior Eric sent me one of his teflon coated hammers which is also in this gun. Along with the b-staley o-ring mod and set for low count/high power this .22 is my goto 50yd. de-nutter. When we are out plinking it always sits at the ready right next to the shooting bench waiting for Alvin and the crows. Eric has genoerously made a Birthday gift of Betty Lou's trigger group but, mine will be sent back to him so he can study how the improvments have held up. I'm going to miss it... Now I know what you're thinking.. I thought about it too but.... she puts it under her mattress at night.
Guys... contact Eric at StalwartArms.com or right here on the good ole GTA and get the skinny on these trigger groups... I'm sure there will be one in my future.
Stalwart... please jump in here and give us a little rundown on what you did to these things.

[rokitman60]

I'm going to miss it... Now I know what you're thinking.. I thought about it too but.... she puts it under her mattress at night.

Bill,

I've got one of Eric's trigger groups sitting here on the shelf waiting for the rest of the gun to be finished, and knowing what I know about it...

I think if I was you, I'd chance it!!!

[avator]

Plotting as we type...

[RHytonen]

( .oO  ...hope there's still one in "my box")

[stalwart]

Plotting as we type...

Bill, let us know when you are transferred from the ER to the ICU, so we can send flowers? Also, let us know if you still have teeth, and we'll send some appropriate snacks.

I'm going to miss it... Now I know what you're thinking.. I thought about it too but.... she puts it under her mattress at night.

Bill,

I've got one of Eric's trigger groups sitting here on the shelf waiting for the rest of the gun to be finished, and knowing what I know about it...

I think if I was you, I'd chance it!!!

Guys, you are going to like the touches Butch has done to his 60.

( .oO  ...hope there's still one in "my box")

Oh, yeah. It's in there.

These triggers are stout, but not very refined. It takes a while, but squaring off the sears, and putting just a touch more engagement angle in, does wonders for them. As they are nice and wide, a good safe engagement is still there without a lot of overlap. The metal is good enough to take (and keep) a fairly sharp edge, so they can be tuned for a very crisp release.

I ship them set for hunting, but after some use, they can be tuned to be decent target triggers (top screw, sets amount of overlap), too. My experience, backed by Bill and others, is that within 100 rounds, the faces mate nicely... for a smooth release.

I can polish them to eliminate a break in, but this takes time (spelled $$$), and if overdone, will take away some of the precise squaring I do. I'm doing these precisely the way I do my own triggers... and I like the results enough that I don't bother going back for the last adjustment unless the gun is purely for target use. I'm not, technically, a "trigger nazi", but I do like to bring a design up to the designer's intended quality. With the 60s/Fusions it's straightforward, and effective.

[Bob K]

Stalwart,
I am new here and I just "cleaned up" my trigger. (Gen 1 )
400,600,1000 and some molly grease really helped ( a lot)
But, when you said  that you slightly change the engagement angle,
well, not being an expert I was very careful not to change any angles.
I would very much appreciate a picture , written or visual, of just where
and how much ( indeed, and how little)  you change that engagement angle.
you spoke of.
Thank you.
Bob K

[avator]

I finished off the tin of 500 pellets this afternoon and the trigger is buttery smooth and predictable. I can really focus all my attention on the shot instead of trying to anticipate break. If I were not sending this trigger back to be analyzed I would take a little more first stage out of it. Everything else feels right for my taste.

[stalwart]

I finished off the tin of 500 pellets this afternoon and the trigger is buttery smooth and predictable. I can really focus all my attention on the shot instead of trying to anticipate break. If I were not sending this trigger back to be analyzed I would take a little more first stage out of it. Everything else feels right for my taste.

Got the trigger back, and have to thank you for shooting the heck out of it (would have taken me forever to accumulate that many shots with it). I agree with your assessment of it. It's going in one of my demos... 

Stalwart,
I am new here and I just "cleaned up" my trigger. (Gen 1 )
400,600,1000 and some molly grease really helped ( a lot)
But, when you said  that you slightly change the engagement angle,
well, not being an expert I was very careful not to change any angles.
I would very much appreciate a picture , written or visual, of just where
and how much ( indeed, and how little)  you change that engagement angle.
you spoke of.
Thank you.
Bob K

Bob, if your sear needs lube to function, the last thing you need is more engagement angle. I would suggest setting up something that absolutely squares the faces, and then go for lighter spring pressure to get that feel you want. A good trigger job should never need lube on the sear faces.

As supplied, most triggers I have seen in AGs do what is called "rolling off", where the last tiny bit of overlap is actually overcome without more input. This is caused by the tiny bit of roundness at the sear's edge, allowing the striker spring (not you) to finish the action. You cannot get a crisp and predictable trigger without eliminating as much roll off as possible, with a square and sharp edge.

[avator]

LMBO..... My friend... anytime you need any of your amazing works of art tested/demoed, I'm your huckleberry. I completely enjoyed the trigger. It was a great advantage to have another gun with a stock trigger in it to compare side by side. It was also interesting to have another one of your triggers in Betty Lou's gun with the different pull setup. (3 guns total) Thank you for the opportunity.

[stalwart]

Bill, there is more to come. That, I can promise... but, as everyone knows by now, I cannot promise when.

Just plugging away here... it'll all happen, eventually.

[stalwart]

Guys, although I had intended to go for 4.5K, or nothing on these... I am contemplating doing some 2K (almost thru-tube, as seen in my earlier prototyping) setups, in response to the tube problems in some FDPCPs. This would vastly increase the safety margin, and could have internal fill cap threading, if desired.

It would eliminate the tube seal as well. I would include a Teflon striker, and if you polish the striker's channel, it would still be pretty slick... but, without some of the costs associated with machining the full TT (4.5K) rigs.

Please LMK if this sounds like a viable option? These things are a ton of fun at 2K, and this option would make the best of that pressure, at a more affordable price.

Also, any prices quoted to date will be good until Nov 1.

[StevenG]

Sounds neat. I take it you mean burst at 6k?
No way could I pump to 4.5k anyway.

[stalwart]

The weakest part will be the fill cap retaining nut, as always with a well fitted tube. QVT's finite analysis (posted here, earlier) shows that clearly... that's why I'm thinking internal threads for the cap.

If there is interest, I'll proto one, and submit it to Our Beloved Safety Officer for some hard numbers.

[stalwart]

Here's some prelim numbers on the new design... I'm pretty happy with them!

"The safety margin for the bearing load would be about 2:1.... compared to about 1.2:1 now.... For my money, that’s good enough, I mean they aren’t crushing the reciever now, at over 2000 psi, and you are nearly doubling the thickness by adding steel.... If you drill the rear hole through to the head diameter of the screw, and use a full depth head, plus the stock installation on the front screw, that goes to about 3.5:1.... overkill, IMO.... I don’t mind if the bearing load is “only” 2:1.... You do need to use better screws, though.... minimum 120K tensile.... "

There is a minor twist to this design, that makes all the difference in the strength. More soon...

[rsterne]

Two 5mm screws, used in the current manner (shank in shear) would have a 3:1 safety margin at 2000 psi if the screws used are 120K tensile strength.... The increased thickness of the tube plus receiver increases the bearing load safety factor to an acceptable level.... because of the "twist" that Eric mentions, quite clever I might add.... The big bonus is that leaks should be a thing of the past, due to the tube extending past the valve.... No weak point where the tube threads into the front of the receiver, either.... and it won't matter if your receiver is worn or out of tolerance.... 

Bob

[StevenG]

That makes me feel a lot more comfortable to hear. I still shoot my gen1, but I do keep it in a rack pointed at a concrete basement wall.

I defer to the combined wisdom of the fine folks here, but 3:1 makes me feel better than 2:1, which of course makes me feel a lot better than 1.2:1.