Gamo Urban with 30gr BBTs

[EdinGa]

It's starting to look like there's a .22 conversion for one of my BSAs in the future. The Scorpion SE carbine would make a nice and compact gun and I have two barrels to choose from ... although the parts bin gun has a regulator and long air tube ... what velocity are you guys getting at around 2000 psi?

I'm still 640+ at 2000 psi but it drops off rapidly around that point. The gauge on the Urban is hard to read so I never shoot down that far if I'm shooting groups. I cut it off around 2200.

[Wayne52]

I did a video showing the weights of the hollow points with my Gemini scale.

[rkr]

RKR , you should be good for close to 50 FPE at 2000.

I don't think that's doable with 15" barrel and 2000 psi, something in mid 30s fpe could be reachable.

[Hobbyman2007]

https://www.gatewaytoairguns.org/GTA/index.php?topic=46011.0

It’s a lofty goal . And there’s no way it would be efficient at that power but 50fpe might be doable at 2000 psi and a 15” barrel .

[EdinGa]

Back to 60 yards today. One bad apple.

[rsterne]

Denis, my "lofty goal" formula for a 15" long .22 cal barrel at 2000 psi would be as follows....

(.22 x .22 x PI/4) x 2000 x (15 / 24) = 47.5 FPE.... That would be with a 23.7 gr. pellet @ 950 fps.... However, I have never achieved my "lofty goal" numbers, I usually fall short by about 10%, even with a gun with full bore-area porting throughout.... Most of the time anyone approaches my "lofty goal" it is by using a much heavier bullet, so that it is a larger percentage of the total mass, and then of course the velocity is lower.... The lofty goal prediction is, of course, for a single shot at maximum power, not something usable....

Bob

[rkr]

In my case I would be limited by 4mm barrel port and probe nose. In addition I would have small regulator plenum designed for 30 fpe guns. Those things combined would make mid 30s fpe a realistic goal.

[rsterne]

Agreed, the 4 mm port will limit you to the mid 30s at 2000 psi....

Bob

[K.O.]

I failed to mention that I switched lubes after I started casting with pure lead. These were all tumbled in RBCS Case Slick spray.

Looked up the msds...< 92% hexane and unspecified fatty acids and polymers...

Do not have much to add have been moving dirt (~10 yard³) bout 40 yards with a wheelbarrow... building a back porch...
need to get it done soon before I have to have superglue(medical)injected in a AVM that feeds my pancreas... which may be a couple weeks to a couple months away...they have to mesh schedules... if all goes right will not even notice...but if goes wrong may have to open me up... so want to get the porch built quick as I can... little worn out so have not done any casting and testing...

I do think That Harry pope had it right...We need the bases to be very consistent and clean... that one group at 60 yards of mine was picked for the crisp bases with no slight rounding at all...in my 35 and 45 yard groups was letting some less than perfect bases thru... good enough for hunting at that distance...

so yeah at 740* with the 1.5% tin mix did get some bases with very slight rounding around about 1/3 of the base... I think that was enough to cause a slight imbalance and a slight drag imbalance... those even if it does not cause a large amount of precession will steer the round of in a random direction a bit...

so say a 20 twist barrel at 30 yards it has done 54 revolutions 60 yards 108 and 90 yards 162... so yeah the further out the more it precesses and steers off course... so what does not show up at 30-40 yards does by 60-90 yards...

I also think if the round is doing much precessing it will ride more nose up on the downward leg of its flight... may even start nutation.... and at 30 fpe it is falling pretty good from about 35 yards on...

So yep will be trying about the same tin mix next casting session but will up the pour temp back up about 20* to 760 to see if I get less less than perfect bases...

though I have some years of listening/learning from casters... and spent time working in an aluminum foundry... still a bit of a neophyte with lead and these little pills... 

will also try the pressure pour and am betting that will help get those nice crisp bases... I do think it is what is most important with these cast rounds...

the larger base of the 225-37 NOE was very easy to get crisp bases...  just a large sprue puddle to keep the plate hot works...

With the BBT 40g it needed a smaller sprue hole to get nice crisp bases... Al sent a .22 sprue plate for it and they come out very crisp now...

so yep when I get back to it that is what I think I can improve upon... 

[EdinGa]

I failed to mention that I switched lubes after I started casting with pure lead. These were all tumbled in RBCS Case Slick spray.

Looked up the msds...< 92% hexane and unspecified fatty acids and polymers...

Do not have much to add have been moving dirt (~10 yard³) bout 40 yards with a wheelbarrow... building a back porch...
need to get it done soon before I have to have superglue(medical)injected in a AVM that feeds my pancreas... which may be a couple weeks to a couple months away...they have to mesh schedules... if all goes right will not even notice...but if goes wrong may have to open me up... so want to get the porch built quick as I can... little worn out so have not done any casting and testing...

I do think That Harry pope had it right...We need the bases to be very consistent and clean... that one group at 60 yards of mine was picked for the crisp bases with no slight rounding at all...in my 35 and 45 yard groups was letting some less than perfect bases thru... good enough for hunting at that distance...

so yeah at 740* with the 1.5% tin mix did get some bases with very slight rounding around about 1/3 of the base... I think that was enough to cause a slight imbalance and a slight drag imbalance... those even if it does not cause a large amount of precession will steer the round of in a random direction a bit...

so say a 20 twist barrel at 30 yards it has done 54 revolutions 60 yards 108 and 90 yards 162... so yeah the further out the more it precesses and steers off course... so what does not show up at 30-40 yards does by 60-90 yards...

I also think if the round is doing much precessing it will ride more nose up on the downward leg of its flight... may even start nutation.... and at 30 fpe it is falling pretty good from about 35 yards on...

So yep will be trying about the same tin mix next casting session but will up the pour temp back up about 20* to 760 to see if I get less less than perfect bases...

though I have some years of listening/learning from casters... and spent time working in an aluminum foundry... still a bit of a neophyte with lead and these little pills... 

will also try the pressure pour and am betting that will help get those nice crisp bases... I do think it is what is most important with these cast rounds...

the larger base of the 225-37 NOE was very easy to get crisp bases...  just a large sprue puddle to keep the plate hot works...

With the BBT 40g it needed a smaller sprue hole to get nice crisp bases... Al sent a .22 sprue plate for it and they come out very crisp now...

so yep when I get back to it that is what I think I can improve upon...

I hope the procedure goes well and that you don't notice. I prefer to be busy, and don't do well with being sidelined. Something tells me that you are the same. 😊

I'm a complete novice when it comes to casting and I'm afraid my equipment is rudimentary at best. That said, I did try the pressure pour method last night, and I can report an almost perfect run of clean, crisp bases. I will inspect them closer this afternoon. I also incorporated the "sinking boat" method that Back_Roads described to fill my bottom pour ladle. I'm hoping that the two changes will give me more consistency in weight and uniformity. We shall see.