Stormrider with offset LDC

[subscriber]

Why do you need the grooves in the steel bolts?

Because the groovy bolt acts as a cutting tap, rather than a cold forming tap.  The latter takes a lot more force to use and might break something, if there is a lot of interfering plastic.

Here are two M10 x 1.5 taps.  One is for cutting; the other cold forms threads.  Cold forming threads takes a lot of force and the starting hold is much larger, because material is pushed out of the way, rather than removed:

https://www.mcmaster.com/8305A2/
https://www.mcmaster.com/2534A113/







I like using thread forming taps on aluminum, but not on steel.  They can work well with plastic, but then you should start with an unthreaded hole of the correct diameter.   Someone can try form taps on printed plastic, but I am a bit concerned about rupturing the part at the layer lines due to the pressure required to form a strong thread.

For mildly tight threads on a printed LDCs, just use the barrel stud to finish form the thread...

[naptemp]

For mildly tight threads on a printed LDCs, just use the barrel stud to finish form the thread...

I have been doing that for a long time

[subscriber]

I have been doing that for a long time

Bob's your uncle!

https://en.wikipedia.org/wiki/Bob%27s_your_uncle

[TorqueMaster]

Glad to hear that design works, Bob.  It does have fairly generous volume.  It also has only five chambers in a 6" long moderator.  Many would ask for more baffles.  Sometimes less is more

Any comment on group size and POI shift?

I set up outside briefly (winds variable around 10 mph and heat index pushing 100)  to test group size and POI.  The moderator has no negative effect that I could determine.  I won't embarrass myself posting images -- the gun is quite capable but my rushed efforts were not.  I forgot how annoying that flappy thumbscrew on the bottom of the rifle stock is -- sometimes it catches the bench surface, and sometimes it doesn't -- I'm pretty sure it was the partial cause of two separate ~1/4" ctc groups at 15 yards using the moderator.  Without the mod, the group was a ~5/8" tall, 1/4" wide, overall roughly the same as with the mod.   No significant change in average POI.

Oh, was using .177 RWS Superdomes -- this Diana is the only gun I have that has shown them to be worth keeping around -- and it actually likes them better than the premium domes from  H&N or JSB, gofigure.

I'll  try to remember to do a less rushed comparison when the weather is more cooperative.

[subscriber]

Thank you, Bob

[naptemp]

With the new moderator printed properly (so it's not loose/wobbly) I get some very good groups now at 15-18 yards.
Much better than before, when i had a different and slightly loose moderator.

[subscriber]

Better is better...

[TorqueMaster]

Beautiful weather today.  I got out with the 177 Chaser with the rifle stock attached, PISTOL BARREL, svbony AO3-9x32 scope (at 9x), with JSB Schak 8.0 grain wadcutters, shooting at the GTA  casual match 50 foot targets from a benchrest/sandbags.  With and without this big moderator.   I haven't done any tuning, and it has maybe a couple hundred pellets through it.

Shot with the moderator first.  A fresh cart, a few sighters, then got after the bullseyes.  It did amazingly well in my opinion.  I've never used these pellets before, and they did their part -- they are 8.02 grain / 4.50 mm.   I scored it at 178/200 (no x) which I believe is getting close to what I score with a Daisy 853. 

Taking the moderator off, the poi shifted, up, roughly 2-1/2 reticle dots, which I think is 2-1/2 mil, which is the ~1.5 inches of shift I saw.  Previously I did not see much shift with RWS Superdomes, so I'm not sure quite what to make of that.  I loaded up a fresh cart, and shot another 24 Schaks at a fresh target.  The results were less than impressive, much more scattered, some shots  scoring as low as a "3."  Overall score 143/200.

I put the moderator back on and took 3 shots at  the lower left corner of the same target --  about 5/16" ctc. The moderator was helping -- a lot.   Extending out to 100 feet, soupcans were no problem, and  once I figured out the drop, I was pinging smaller targets out there too.  Pretty impressive for a "CO2 pistol."

At some point I want to pull the perma-moderator off the longer rifle barrel, and do this same test with and without this big moderator. 

Pics or it didn't happen:

[subscriber]

Thanks for the results, Bob

I may be biased, but I see your results as an endorsement of the moderator

The lower POI would seem mainly due to the weight at the muzzle flexing the barrel down.  But if that does not hold for other pellets, then the shift may be more about harmonics.  As long as the moderator reduces groups for a wide range of pellets, it does not seem to be causing any harmonic clashes.  Which one can argue, is more about luck.  Or one can argue that the muzzle movement on firing would be damped due to the length and weight of the moderator...

The "air stripping" effect of the moderator should also be helping at least a little.

What velocity were you seeing with the 8 grain pellets, and how long is the pistol barrel?

[TorqueMaster]

Absolutely endorsed!  At least with these wadcutters, the improvement is undeniable.   And of course, the quiet.  Had a rabbit 20 feet from me who was giving me the stink eye, but didn't seem to care that I was plinking steel downrange.   Take the moderator off and every critter nearby gets spooked.

The barrel is only 8" long, and quite stout, I feel the poi shift may be due to steering more than droop.  As a very quick test, I just loosened the moderator 180 degrees, and shot offhand at spinners I should never miss -- all shots missed.  And all shots with it tightened up -- hit.  I loosened-tightened a few times, same results.  I'll do something more repeatable next time I have the bench set up. 

I did not do any chronograph tests.  I expect it is getting ~500 ish? fps.   Reviews say 525-560.  I can test the speed with and without the moderator next time too.  Actually, if it is like Crosman CO2 pistols, my barrel-mount chronograph may not read right unless there is a moderator or other tube holding it well forward of the muzzle.  IIRC, I got wild velocity swings otherwise, guessing due to CO2 blast, possibly condensing moisture in the air around the pellet???  Anyway, a "without mod" velocity test may not actually happen.

[subscriber]

Bob,

I see the loose mod test as upsetting barrel harmonics because the coupling between barrel and mod is different and variable.  To test this you may be able to shim the mod so it goes tight 90 or 180 degrees off tight without the shim.

The important thing is that in normal use, the mod acts as you expect and is consistent.

As I recall, there was a .22 version of the mod also.  If steering is involved with the .177 mod, that should be reduced with the .22 version.  It would be a little louder, but it might be interesting to see how much louder and if the POI shift is different from the .177.   Or you can just enjoy what works.

[TorqueMaster]

I did more testing -- with a metal washer between the moderator and front sight, snugged tight, ending up a 1/4 turn off from the no-washer position -- groups were tight and no POI shift.  It must have been the looseness of the moderator causing my misses.

I also did chronograph testing with the moderator-- the weight of the chrony on the end of the moderator did cause a slight downward POI shift.  8.02 grain Schak wadcutters -- started at 514, velocity rose to a max of 552 on shot #6, then slowly lowers to 515 on shot #42.  I haven't run the numbers, but expect the average is 530-535 ish.  ~85F ambient.   HAM got 598 with 7.9 grain and the rifle barrel, so my results seem reasonable.

I had good groups ruined by one shot all day -- I think my oversized front rest was nudging the moderator intermittently.  Overall, at 50 feet, it likes wadcutters -- RWS light and heavy and the JSB Schaks all did well.  RWS superdomes and JSB 8.44 had a decent showing as well. The best group of the day was with H&N Barracuda 10.65 -- 5 shots ~1/4" ctc. 

[subscriber]

Thanks, Bob

Useful info.

[Mzq284]

love the look of ecentric cans...

used one on my P17 micro-carbine build and working on one for my chaser chassis system build

Dan, have you posted pics of your P-17 carbine? If not, would you mind doing a thread on it? Thanks

[Back_Roads]

 Here are a couple of my modded p17's
https://www.gatewaytoairguns.org/GTA/index.php?topic=183700.0

[Mzq284]

Here are a couple of my modded p17's
https://www.gatewaytoairguns.org/GTA/index.php?topic=183700.0

Cool guns, James. I put a 1322 barrel in mine,  cut off at the front of the slide. I've thought about putting a longer barrel and buttstock on it, but too many other projects at the moment