Benjamin Franklin 317 RestoMod

[USAFANG6799]

Made a few more parts over the weekend

Amazing the goodies that are going into this 317.
When you try it out I don't think it will recognize itself 

[Tack Driver 10]

Put the gun together without incident.
Ran it over the chrony to get a base line.

With 7.9 CPHPs

3 pumps 435 FPS
5 pumps 601 FPS
7 pumps 644 FPS (dumped all the air)

Respectful numbers but, I have only just begun to mod....LOL

The bolt leaks and there's a blast of air when the gun is fired even when adjusted.
The stock bolt not only leaks but the probe tip is 1/8" and cocking the gun is rough.
Best described as dragging a bag of rocks down a cobblestone drive.
One of the problems is the breech is very short and the bolt hangs out the back usually scraping against the tube when cocked.
The heavy hammer spring compounds the matter.

When the going gets tough, the tough get going and make a new bolt....LOL
Made a prototype brass bolt with an o-ring seal and .070" probe tip.
The elongated back will sit on a Delrin saddle resulting in a buttery smooth cocking experience.
The saddle is set in a counter bore in the PA.
Might have to make a new, slightly longer PA to accommodate the saddle.

[USAFANG6799]

644 FPS - Respectful numbers for sure given how long it's been in a coma 
I'd say those first few words are pretty encouraging.

Loose bolt probe, no oring, blast of air, scraping against the tube when cocked with the sense of dragging rocks down a cobblestone drive..........sounds pretty normal from what I remember.
Amazing it shot the FPS's you just reported as well as it did.

Many thanks for the encouraging update with the best is yet to come news.

[Tack Driver 10]

The lug on the bolt requires a 5-40 thread so I have a tap in the mail.
Should be in around the end of the week.

In the meantime since I have some spare rods I made an experimental piston.
It's made from Delrin with a 80 duro polyurethane seal.
Same poly I used for the bumper.
Instead of a slot I drilled 8 holes equally spaced around the edge.
The holes will allow a certain crush factor and expand with pressure as the gun is pumped.
Plus I think it looks kind of cool....LOL

[avator]

You definitely have my attention Ron. As you know I have a 312 here. I wonder if you would consider putting together a kit that would include some of these upgrades as a drop in? If so, please PM me.

[USAFANG6799]

Instead of a slot I drilled 8 holes equally spaced around the edge.
The holes will allow a certain crush factor and expand with pressure as the gun is pumped.

Very imaginative!
Talk about boldly going where no one has gone before!
Braking new grounds with this idea or have you see it used somewhere else?

[StockClassDD68]

Nice rehab. Can't wait to see the finished re-finished product!

[Tack Driver 10]

Instead of a slot I drilled 8 holes equally spaced around the edge.
The holes will allow a certain crush factor and expand with pressure as the gun is pumped.

Very imaginative!
Talk about boldly going where no one has gone before!
Braking new grounds with this idea or have you see it used somewhere else?

Something I came up with instead of a groove in the seal, patent pending....LOL
I like this version better, easier to make and can vary the hole size, depth and spacing.
 
I stated there were 8 holes but there are actually 12 spaced 30 degrees apart.
Once the bolt is finished I'll run another chrony test with the stock piston then with this one.

[avator]

You definitely have my attention Ron. As you know I have a 312 here. I wonder if you would consider putting together a kit that would include some of these upgrades as a drop in? If so, please PM me.

Ron...
Well, I guess we can forget about this...
As I'm sure you know, a deal is in the works for this gun to be headed your way then on it's way to a new owner... pretty sure you'll find that it won't need much mechanical improvement.

[Tack Driver 10]

You definitely have my attention Ron. As you know I have a 312 here. I wonder if you would consider putting together a kit that would include some of these upgrades as a drop in? If so, please PM me.

Ron...
Well, I guess we can forget about this...
As I'm sure you know, a deal is in the works for this gun to be headed your way then on it's way to a new owner... pretty sure you'll find that it won't need much mechanical improvement.

Looked like a nice gun.
Thanks for the update.

[avator]

Not a safe queen but a solid shooter with lots of cosmetic potential. I was proud to be it's care taker while I owned it.

[jackssmirkingrevenge]

Instead of a slot I drilled 8 holes equally spaced around the edge.

Don't the holes create dead volume that effectively limits the maximum pressure that can be reached?

[USAFANG6799]

Not a safe queen but a solid shooter with lots of cosmetic potential. I was proud to be it's care taker while I owned it.

How many owners before you Bill? Or is it too late to ask 

[USAFANG6799]

Instead of a slot I drilled 8 holes equally spaced around the edge.

Don't the holes create dead volume that effectively limits the maximum pressure that can be reached?

Thinking on the same line. Thinking that it's being offset by the holes expanding the cup which make a tighter seal as the compresses the air ahead of it.
The advantage I see to this design as the seal gets used over time the seal is still able to expand to help overcome the wear that's overcome by the conventional seal design.
I'm sure Ron will fill us in though.

[Tack Driver 10]

Instead of a slot I drilled 8 holes equally spaced around the edge.

Don't the holes create dead volume that effectively limits the maximum pressure that can be reached?

Exactly, these guns are not built for high performance.
The long stroke brass/bronze wall tube is only about .055" thick and will bend when pushed hard.
Could also jeopardize the solder joint between the tube and barrel.
Leaving some air will limit max pressure but provide some spring back for the return pump.
A man's got to realize the limitation of the gun and leave a little safety margin.

I tried a FT o-ring piston on the last gun and the return was heavy with a strong gasp at the top.
Even the long stroke Crosman tubes made of steel and .060" thick walls will bend to a lesser degree.
To me an ideal stroke length is between 4"-5".

I have a 13xx gun with a modified 766 pump link and have pumped it to over 3400 psi.
The short 3 1/2" stroke and tube make for a very stiff pump engine.

[avator]

Not a safe queen but a solid shooter with lots of cosmetic potential. I was proud to be it's care taker while I owned it.

How many owners before you Bill? Or is it too late to ask 

Sorry, I don't know the answer to that.... Matter of fact... I have so many that I lost track and can't even tell you who I got it from...

[avator]

Matt.... sent you another PM.

[USAFANG6799]

Ron -

I have a 13xx gun with a modified 766 pump link and have pumped it to over 3400 psi.
The short 3 1/2" stroke and tube make for a very stiff pump engine.

When is it going to make it's day-view in the Classifieds? 

[Tack Driver 10]

Received the 5-40 tap for the lug on the bolt and got that done.

Ran it over the chrony with the original piston using 7.9 CPHPs.

Piston is adjusted at 7.375" the max without hitting.
3 pumps 556 FPS 05.42 FPE
5 pumps 662 FPS 07.69 FPE
7 pumps 694 FPS 08.45 FPE

Next installed the Holy Grail piston adjusted at 7.375".
3 pumps 508 FPS 04.53 FPE
5 pumps 648 FPS 07.36 FPE
7 pumps 750 FPS 09.87 FPE
8 pumps 763 FPS 10.21 FPE

Adjusted the Holy Grail piston to just over 7 7/16"
This allowed a slight cam over and the piston just cleared the breather hole in the tube.
For the 8 pump test I oiled the piston to see if the gun would beat 800 FPS.

3 pumps 544 FPS 05.19 FPE
5 pumps 727 FPS 09.27 FPE
7 pumps 773 FPS 10.48 FPE
8 pumps 826 FPS 11.97 FPE (full dump)

Interesting that there was still a slight puff of air coming from the breech area.
I dry fired the gun and figured the air is the result of the hammer pushing forward as the puff was still present.

Food for thought:
Generally a 17 cal will perform about 150 FPS faster than a 22 cal gun of equal design.
That means a modded 312 should produce about 675 FPS 14.35 FPE.

[jackssmirkingrevenge]

Impressive results considering the original would be hovering around 500 fps at 5 pumps from what I've read.