Mk 177 mods ? 800+ fps with 7.9g SUCCESS 831 fps @ 16 pumps now 1024 fps @ 20

[lillysdad621]

KO... not to hijack your thread, but you might know the answer to this. Im building a 1377 with the basic mods and a little longer barrel. I am getting 552 fps with 10.5 gr pellets at 10 pumps, but it only does it when you pump it fast and hard. If you pump it slow (kinda holding it before it slaps back against the air tube), it only shoots 381 fps. and it is repeatable. fast and hard... mid 500s. slow and quiet... 380s... i never had any pumper do that... what is your opinion on this?

[K.O.]

I have seen it for two reasons and can think of more...

one is that the cup has taken a set and does not parachute out to seal well unless pumped quickly... can try warming up with a hair dryer and pump to see what happens...

the other I had recently was with my Daisy the exhaust poppet was not closing fully at first unless I pumped quick due to a weak spring...

So what sort of spring is in your valve on this one if you leave the bolt open you can listen for air leaking...

more later need a shower have fiberglass insulation on me from helping a neighbor...

[lillysdad621]

it has a softer spring in the valve... before it needed to be cocked to take the first pump, but after i changed a couple of things now it does not needed. Ill replace the cup... got some spares. Thanks, i'll report back later on.

[K.O.]

ok this is for Matt15

I taped 4 tin cans together and shot them at a distance of 5 feet

with Crosman 7.4g points it at 10 pumps went thru 2 cans  dented and cracked the  first layer of the third... tried twice same results...

at 16 pumps it went thru three cans and  first wall dented on forth  and became pretty much flat...

I then tried a Winnie 9.75g pointed which did pretty much the same but came out almost a round ball... blew slightly bigger holes and left a bigger dent in 4th can

Matt I do not shoot bbs in a rifled barrel so I will not be testing that for you... It was fun after a busy day

From right to left Winnie point 16 pumps, Crosman point 16 pumps, Crosman point 10 pumps

[K.O.]

I think this one does not like being stored with the pump arm closed... I think it makes the cup want to not seal right...

I was about 70 fps low at 16 pumps and it took 23 pumps to get to 801 fps and this is after taking valve volume from about what I had it at (did some actual measurements and math instead of guesstimation)

it was at ~.192 c.i. with an extra half size intake poppet and stock internal volume...

it is now ~.242 c.i. with the unthreaded portion of the exhaust half bored from .4 to .46 and just a half size intake poppet.

It at worst should have caught up at 20 pumps and instead was at 781fps with the 7.9g cphp...



   Pump Tube Diameter            Pump Tube Stroke          Reservoir  Volume         swept volume         
                                          
   0.75                                            3.5                                 0.192                 1.54546875         
                                          
                                          
                                          
                                          
                                          
                                          
PSI Per Stroke         number of strokes      PSI @ 60% Efficiency      PSI @ 70% Efficiency      PSI @ 80% Efficiency
115.1052246            16                         1105.010156         1289.178516         1473.346875
                                          
                                          
                                          
                                          
Atmospheric Pressure      Compression Ratio      PSI @ 65% Efficiency      PSI @ 75% Efficiency      PSI @ 85% Efficiency
   14.3            8.049316406                 1197.094336         1381.262695         1565.431055



___________________________________________________________________________________________________________


Pump Tube Diameter            Pump Tube Stroke          Reservoir  Volume         swept volume         
                                       
0.75                                            3.5                                 0.242                      1.54546875         
                                       
                                       
                                       
                                       
                                       
                                       
PSI Per Stroke      number of strokes      PSI @ 60% Efficiency      PSI @ 70% Efficiency      PSI @ 80% Efficiency
91.32315341            20         1095.877841         1278.524148         1461.170455
                                       
                                       
                                       
                                       
Atmospheric Pressure     Compression Ratio   PSI @ 65% Efficiency      PSI @ 75% Efficiency      PSI @ 85% Efficiency
14.3              6.386234504         1187.200994         1369.847301         1552.493608       


so

knowing what I show above  I looked at the shot waveform and check for retained air and both check out fine...

so I figure it is most likely the pump cup or I some how introduced headspace that was not there before...

it is cold out (I chrony indoors anyways though) so I have the oil filled heaters going...

so I opened the pump arm and sat it on the top of one pump side down... (with no air in the valve)

sure enough  1024, 1011 and 1017 fps at 19-20 pumps (each with just the smallest puff of retained air)


and then it went back to were it was being behind I guess the cup cooled...

[K.O.]

well the tables did not copy well from excel starter... but I think you can see how it was and make sense of it...

[Matt15]

Thanks Kurby I think on ten pumps my crosman 2100 is shoting 740-750. Big Bore Bary is making me a delrin t port so I should gain a few more fps there. I am going to try to make a little more volume in the valve by rounding the exhaust stem seal because at 15-20 pumps there does not seem to be much gain. WoW 1000 FPS 

[K.O.]

yep I was surprised and wish I had another pump cup for it. because  it is back down around 800...

 I looked at the wave forms of the shots to make sure they were accurate so I am pretty sure of my #s

In the other thread the 13xx pump cup was about 80% efficient at about 1500 psi and 75% at 1750 psi, so at 20 pumps

and using that as a model it should  be .242 ci @ around  1500 psi that got me  there...

Man I wish I had a copy of a certain spreadsheet...  I would look at the relative efficiencies  of  832 fps with  .192 c.i.  at 16 pumps (1500 psi) and the above...

what is cool about it is it is with the 16.75" Mk 177 barrel and 7.9 pellets not 7.4...

Now it is getting hard to wait on the 24" .22 barrel and parts to turn this into a 1322WT... and a couple spare pump cups...

it is starting to look like 875-900 fps and 24+ fpe with 14.3 pellets is a good possibility with a 20"-22" barrel...

[Rivers3Plinker]

well I did not take any pics and other than the bolt probe it looks like a stock MK 177  but I offer the below as proof of life...

the bolt probe

first with the MK still together I  marked the plastic part of the probe at the point it enters the breech (scratched with a razor knife)

when I had it apart I then took the barrel and the bolt and  pulled the probe out until it looked like it would seat the pellet past the port (looking though the port)

I then checked with a pellet and had gone  about .1 to far so I push it back in that bit and checked again... perfect...

so I then measured how far it extended out of the plastic portion...   about .175  I also made sure it would clear the clip at this time...

I then found a nail that was just a bit larger around than the stock magnet/probe and chucked it up in my Dremel and turned it down to the same

diameter as the stock probe  I then cut it to length with a cutting disk.   Then I turned down the part that is not seated in the bolt.

This is a great idea and relatively easy so long as you never plan to shoot bb's with the gun, which I don't.

Took me a couple tries but I fabricated a cool, tapered, wire probe style tip and have it installed in the bolt. Seems to work fine but no chrony numbers and haven't even sighted the gun yet. I also did the zip tie trick with the barrel to the pump tube near the adapter. Tried a 2200 hammer spring but it was a bit too short and didn't seem any stronger in comparison to stock anyway. Didn't have a quick, easy way to shim it with a spacer or anything so I just tried it. After testing, it started holding air at 9 pumps and sounded weird with it so I swapped back stock hammer spring and it's dumping 12 no problem now. I pined the piston cup and reduced the shim a bit too. It's only a mildly modded gun now. I want to try a softer valve spring and stronger hammer spring next and that's it.

Just wanted to say thanks for your tips and insight KO!

Looking forward to seeing a post on your MK1322 project.
I have a couple 14" barrels, a trigger frame assby and other parts in my bin so I'll be watching closely!

[K.O.]

Hi Steve
I ended up finding that the MK striker spring is just a bit stronger (same wire but a bit longer)

My parts got  here but there was a barrel shaped hole in in the box and no barrel just a barrel shaped roll of paper. have to call customer service. Guess shipping a 24" barrel in a 24" box can be a prob...

If it was staying an MK it would need even more sealing the 1000+fps shots blew out the seal despite the zip tie its still on but leaks. I had to add more shims to the pump cup also. but now it is shooting 898 fps with the leak...

Mine will dump 22 pumps but before the leak just about 20...

[K.O.]

Thanks Kurby I think on ten pumps my crosman 2100 is shoting 740-750. Big Bore Bary is making me a delrin t port so I should gain a few more fps there. I am going to try to make a little more volume in the valve by rounding the exhaust stem seal because at 15-20 pumps there does not seem to be much gain. WoW 1000 FPS 

The 2100 valve is pretty small so yep gains are a little hard...  I was able to talk Bart into making a .3 longer valve nose and I minimized the size of the exhaust poppet and halfed and drilled out the back side of the check poppet just a bit. but with a pump cup it got 750fps with 14.3 CPHP. took 16 pumps...
sealing is a pain on these...

You have gone Flat top right? 740 is not bad at all at ten pumps... it is at the higher pumps that the flat tops really shine...

[Matt15]

Thanks Kurby I think on ten pumps my crosman 2100 is shoting 740-750. Big Bore Bary is making me a delrin t port so I should gain a few more fps there. I am going to try to make a little more volume in the valve by rounding the exhaust stem seal because at 15-20 pumps there does not seem to be much gain. WoW 1000 FPS 

The 2100 valve is pretty small so yep gains are a little hard...  I was able to talk Bart into making a .3 longer valve nose and I minimized the size of the exhaust poppet and halfed and drilled out the back side of the check poppet just a bitI drilled that out but have not tested it.. but with a pump cup it got 750fps with 14.3 CPHP. took 16 pumps...
sealing is a pain on these...It is a huge pain

You have gone Flat top right? 740 is not bad at all at ten pumps... it is at the higher pumps that the flat tops really shine... That is why I am going for more volume bacause between 10 and 20 there was not much change in fps.

[rsterne]

I've never seen an MK 177, and I was just about to ask you about the swept volume, but I see above it is 1.545 CI = 25.3 cc.... That means it is a bit larger than the pump on a 2100/2200.... and nearly 50% larger than a 13XX pump swept volume.... Here are some numbers for my Uber-Pumper, with 7.8 gr. JSBs, using that 2200 pump and a stock volume 13XX valve (~ 0.1 CI)....

10 pumps: 790 fps
14 pumps: 856 fps
20 pumps: 912 fps
30 pumps: 950 fps

I also tested it with the extended valve from my .22 cal Uber-Pumper (~0.2 CI) with the following results....

10 pumps: 801 fps
14 pumps: 871 fps
20 pumps: 942 fps
30 pumps: 991 fps

As you can see, there wasn't a lot of difference at 10 pumps, but the increase in velocity with the larger valve was more as the pressure increased.... and in fact the pumping effort was less at the same pump number, of course.... as you were storing the air at a lower pressure....

I'm curious why when your velocity at 16 pumps was 861 fps it jumped to 1020 fps at only 20 pumps.... Any idea why?.... Have those 1000+ fps shots been repeatable?....

Bob

[K.O.]

Bob I am almost mystified myself...

I got three shots past 1000 fps and then had trouble getting even what I had gotten before, I then re shimmed the pump cup and it is shooting just a bit better than before...

I do think they we real numbers

the MK 177 striker spring is stronger than the 2200 spring and it was preloaded, and so the ~.242 ci valve was emptying well...

but I think that it is the valve throat and stem turning that helped the most...

with a large valve volume I think it helped the .140 transfer port (it is seated down in the valve like the 2200 valve) see the whole ( or just MORE) valve volume...

thus achieving much higher charge  speed for that initial pulse.  I did not think the barrel was long enough for that kind of speed though.

I REALLY want to recreate those numbers before I move on to making it into an MK1322( it does sound better than 1322WT)...

part of the problem is the plastic body is screwed together and taking it apart as many time as I have wears  out the screw holes...

but I am going to make a try or two to get it to seal again...

[K.O.]

I am a little confused on your question and numbers...


OK first it was just in the 830s with 7.9g pellets at 16 pumps with about a .19 C.I. valve...

the 1000+ was with a .242 C.I. valve.

there is more but I have to go for about 45 min...

[rsterne]

Bottom line, if it isn't repeatable, it's a fluke.... Annoying, yes, but could have been bad lighting on the Chrony, a blast of air on the sensor, even combustion of a trace of oil in the skirt of a pellet on firing.... Kind of like a springer dieseling.... Wow!, did I really see that velocity !?!?!

Your current numbers are much more in line with my Uber-Pumper.... with a similar swept volume (and hence air input)....

Bob

[K.O.]

I agree Bob to a certain point...

It was a time of flight chrono( soft chrono) and was accurate I am careful...

on your numbers  for the Uberpumper first was with the full pump stroke and .1 C.I. by notching the back of the vavle and then the second with a shortened pump stroke and extended .6"  .2 ci valve? how much did you have to shorten the pump stroke .3"or .6"?

I thought that valve was about .177 C.I. or  so...

"
 I was able to get a 1400 pump tube and linkage, and I decided that the simplest way to get more volume was to add an extension into the middle of an existing 2289 valve.... I made one from the back half of a valve, which increased the length by 0.60" and increased the volume from ~1.6cc to ~2.9cc.... I tried it with and without the extension, adjusting the piston length to compensate.... At anything but very low pump numbers, the larger volume paid dividends....

"

and you did get 1040 fps with 24 pumps and 7.8g jsbs (140 tube)


And like I said I do agree that it could be a fluke so I am not arguing, just trying to figure it out...

And it was so tantalizing that I will try a few more times...

[K.O.]

I just pulled it apart and it is leaking even at 2 pumps where the transfer port seats in the valve...

I do think part of it was the warm pump cup and tube sealed realy well and I could have achieved 1600-1700 psi rather than about 1500 or so...

but my numbers now with the .04 C. I. larger valve are not doing very much so I do think at least some of the problem is the leak.

[K.O.]

Eh maybe I should just find out by making it a MK1377 first since I have to wait for Crosman to send me another .22 barrel for the one that ups lost...

A lot easier to fix the leaks that way than as a MK177...

[rsterne]

Yes, I shortened the piston 0.6", so the stroke would have been shortened the same amount.... so roughly 21 cc per stroke with the extension.... All I did was add the center section which I borrowed from the .22 cal Uber-Pumper.... Yes, you are correct about the volume of the .177 valve with the extension, it was ~ 2.9 cc (0.177 CI)....

I didn't use the 1400 pump tube on the .177, only on the .22 cal.... The .22 cal also had a bored out valve, the total volume with extension was 3.64 cc (0.222 CI).... I got 902 fps at 22 pumps with 14.3 gr., but by then the gun was retaining air (at 20 pumps it did 894 with a 450 2nd shot).... I never tried it with a Disco hammer spring.... pumping to 20 pumps was nearly impossible and the pump tube was starting to bend.... only the barrel prevented it from failing....

The .177 reached 1000 fps @ 40 pumps (of 21 cc) and by then was retaining air.... I then tried a Disco spring to prevent that, and eventually broke Mach 1 with a 7 gr. pellet at something ridiculous like 60 pumps.... I then removed the extension, left the Disco spring in, put the extension back in the .22 cal and sold it.... I still have the .177 Uber Pumper, and my .22 cal Uber-Carbine.... Both have 2200 pumps....

Bob