Air Gun Home :: View topic - DPH1377RAP - What a stupid freakin' name for a gun. . . .

vAgRaNt · Member

But it's still my favoritest and most accurate gun. . . . .

I promised something "interesting", so let's try this:

When I first got back into airgunning a couple of years ago, I came to the internet seeking the knowledge on how to make my new 1377 shoot through cinder block walls. . . . . . . . Well, maybe not quite that powerfull, but I did want to find out how to wind it up a bit. I read all the tutorials about increasing/decreasing spring rates, valve porting and volume modifications, transfer port hogging, and pumping 40 times per shot.

That last part got kinda old, really, really fast; and as I do 80% of my shooting in my basement, and even when outdoors, the only thing I need to "shoot through" are carefully tee'd up paintballs, I decided that I didn't really need a bazillion FPS, and instead, would be quite happy with ~500, but in the fewest pump strokes possible.

I'd seen on the Green Forum a real neat setup, that claimed some pretty impressive numbers for .22 velocity on comparitively low pumpstroke figures. If it could work in .22, I figured it might work even better in .177, and proceeded to research the build, and amass the parts and pieces required.

Despite there being pictures and results posted on the Green, there was comparitively little information(pics) on what had physically been done to the gun, to achieve the final result. At the time I didn't even have a Flat Top Piston(FTP) installed in the chassis yet, and already, I was trying to figure out how I was gonna sink the manometer into the side of the mostly virgin valve. I wanted to do the guage before I did the piston, cause I wanted to quantify the benefits of an FTP from a pressure standpoint, not just a velocity result point of view.

I found that the FTP did increase the efficiency over the stock pump by several orders of magnitude, and would develop pressures in 20 pumps that a stock plastic plunger couldn't do 60 or more = Great Start! The whole concept behind RAP (Retained Air Pumper), was that you'd "precharge" the gun with "X" number of pumpstrokes, and the initial shot would only use a small portion of the stored air, which would allow you to either add a "few" more pumpstrokes for each subsequent shots, or allow a small number of followup shots without pumping at all. My goal was to be able to maintain ~500 fps shots with the fewest number of strokes between them.

The early iteration of the gun looked much like this, the grips however, did come a little later:
1377RAP

At this point, it was working pretty much as planned, other than one alarming glitch. 15 pumps precharged the valve to approximately 1300psi (indicated), and it would deliver reasonably stable ~500fps velocities with 3 recharge pumps for several shots, and then without warning, BOOM, it would loose a shot at well over the target figure, and blow much of the retained air out of the valve. I was leaning towards buying a "debouncer", as when it did the BOOM thing, I could hear the multiple hammer hits as the valve exhausted it's charge. A knowledgable member(Ustilago) over at the CAF (Canadian Airgun Forum) suggested that what I needed was a "lighter" hammer, which in his opinion would be more tuneable for strike delivery, and almost certainly "debounce" its self due to it's lower mass. He conveniently offered his sevices to "turn one up", and I challenged him to do it one better. . . . .

I opined that if there were to be a "lighter" hammer manufactured, why couldn't it also be a Dual Power Hammer (DPH)? As this gun was capable of storing more energy than it could use in a single shot, it might be nice for those really rare occasions when I need to "reach out and touch something" farther away, to have the ability to easily "select" a higher power setting. He said he'd "look into it" and went to work. . . . .

A few weeks later, I was the proud owner of the first ever working prototype of his design:
DPH

It's a rear pull cocking design, that allows the easy selection of one of the two tactile and audible power settings, with an infinitely adjustable hammer spring tensioner for fine tuning. A stunningly beautiful piece of knurled brass and hardened steel - a wonder to behold! Would it work?

The now DPH1377RAP:

Oooooh Yeaaaa! I dialed in ~500fps by shooting half a dozen shots over the chrony, and then shot a string of ~50 shots where the standard deviation was less than 15fps, with the exception of the one shot where I inadvertantly clicked it into "high" power (I did say that it was to be "easily" selectable). This was easily the flattest shot string the gun had ever shot; previous strings were more like 25-40 fps deviation, and then as I had mentioned the occassional unexpected BOOM!

In the past year or so I've put about 5-6000 pellets through this gun and it has worked completely flawlessly for all that time. The "Low" setting gives 500fps with 3 strokes for recharge, and the "Kill" setting sends pellets whizzing just over 7's requiring 7/8 strokes for recharge. The standard deviation is a wee bit taller on the high setting(~35fps), but as I use that option so infrequently, I've never really looked at trying to settle it down. It hit's anything I can reasonably see over the 0x magnification of the RDot, or open sights.

It's time to tear the gun down a little bit to re-adjust the pump linkage, and in general give it a fall tune-up in preparation for winter "matches". I'm hoping to participate in the online matches here, once I get a few things off my plate, and can assign the time.

If anyone's interested in pics of the "guts"; I plan to take some during the tune-up, as I really didn't do a very good job of documenting during the build, otherwise, I hope I haven't bored everyone completely to sleep, with the 500 word dissertation 3rd post. . . . Mr. Green

Oh yea, and ignore the dates on the photos; my VCR flashes "12:00" all the time too. . . . . .

Alstone · Moderator & Site Supporter

Hi vAgRaNt welcome to AirGunHome.

A very interesting and informative article on the 1377, it appears you have put quite a lot of thought and effort into what you wanted and have finished up with an excellent piece of kit.

We would certainly like to see the “guts” when you get round to it, one thing I can’t quite sort out is how do you select high or low power, is that done by re-tensioning the spring with one of the adjusters on the rear of the reciver Question

Al

vAgRaNt · Member

Alstone · Moderator & Site Supporter

A nice simple but effective arrangement of power adjustment, I like it!.

What you were saying about having a good barrel makes all the difference, I have spent ages on some guns only to come to the conclusion that the barrel was crap, such is life. Smile

Al

BBGun Bob · Veteran Member

As I can see you have put a lot of thought and time into this 1377 Classic pistol.
Its always great to see someone who has both the talent and knowledge to improve a already nice shooting pumper.
Keep up the good work!! And please post some tear down pic's when you get a chance.I'd be very interested to see the internals.
Your machinist deserves a lot of credit,that's some fine machining.

BBGun Bob
SE Mich.

cjs · Member

Any updat on the "gut" photos yet.

Great build!

-Chris
________
WEED BUBBLERS

vAgRaNt · Member

broommaster2000 · Moderator

Hey Vagrant, that's pretty neat and all, but I just want to add: .22 will handle both Air and CO2 better then .177, especially in the conservation of power. Speeds don't mean more power. That's also why a falling Piano, falling at the same speed as a piano sized pillow, will do more damage. Exclamation

That's why it's important to work with Ft/lbs (Fpe, Ftp, etc) and pellets weights in stead of speeds. Speeds can be quite easily achieved by just picking the right (light) pellets.

You could try heavier pellets, and maybe exchange to .22 to try and get it down to 500 fps, however, that also means the so called "piss-arch". At higher achieved speeds in .22 you might be getting something even more satisfying.

In short, if you want power, think bigger, not faster.

Don't get me wrong, darn nice set up for a pumper. Mr. Green

vAgRaNt · Member

G'day Broommaster2000,
I think you may be mis-interpreting my design parameter for this gun. I do understand what you're saying about energy, but I have no real interest in achieving conservation of "pellet energy" (FPE), but instead, conservation of "input energy" or pumpstrokes.

I don't hunt, so my chosen targets (paper, paintballs, the dreaded can, etc) are typically just as "holed" (dead) at 4fpe or 8fpe. This gun does pull some outdoor duties at longer ranges from time to time, but it is mostly setup for indoor 10m olympic pistol type shooting.

Little by little, I've been changing all my guns to .177, as hunting just ain't my thing, and .177 is typically a fair bit cheaper for ammo. If wild game would fall dead, and then butcher and package itself, then I'd be all over it. Mr. Green

I really like the flat trajectory of the smaller caliber; I seem to be slightly better(relative term) at gauging wind than distance, so flat trajectory helps me alot!

The "kill setting" is more of a novelty, just for giggles and grins, and proof of concept. It's application to the 22XX (CO2) Crosmans is in reality a much better fit. Once I get picture posting ability again, I'll show ya's a 22XX rifle that'll pull 100 x .177 shots @ ~500fps from a single CO2 cart. Again, not a hunter, but a real nice, convenient, and inexpensive to operate "can extermination" device. Wink

Regards,
vAgRaNt

broommaster2000 · Moderator

I was wrong, excuse me. Mr. Green

How about turning it into a single stroke? Razz

You know, I once saw a guy who had a Crosman pumper, and he thought that you were supposed to do only one pump. Boy, was he surprised with the power he got when I told him to pump more then one time.

I'm looking forward to that rifle of yours. Hope you make a neat little topic about it. Mr. Green

cjs · Member

Can't wait to see the photos and details on the 22XX rifle also!

**AS A NOTE**
If anyone needs something custom made, I have all of the machines to do so; mills and lathes (CNC and manual), grinders, boring equipment, etc.

I am not looking to make money on anything (just a hobby deal), so let me know if you have ideas or drawings. All I would ask is that you provide the material (or money for material) for 2 of the parts you want made; one part for you and the other for me. That's it.

-Chris
________
William Clay Ford, Jr. Picture

broommaster2000 · Moderator

Chris, I have the feeling you and I are going to become great friends. I'll PM you later. Mr. Green

cjs · Member

Sounds good! That is really all it is about, enjoying the hobby and making friends!

-Chris
________
BMW 803

broommaster2000 · Moderator

That sounds so cheesy it has to be right. Mr. Green

vAgRaNt · Member

Ok, if you jokers are done jackin' my thread, I'll get back to talkin' about the gun with the stupid freakin' name. . . . . . Giant Grin

But first: