Custom Bottle Mrod .25 build started

[Rdsail]

I'm getting better at drawing with Autodesk fusion 360!

Once I get it all I have to do is thread for the 4-40 screws.

[Rdsail]

I got the barrel band back. Here is a picture after smoothing and spray painted enamel flat back. it fits perfect

[Tomg]

Nice, what material did they print it in?

[Rdsail]

it ended up being Nylon-11

[Rdsail]

Finally got to get the whole setup. I shot from 50 yards.  So fart the only casts that shot well are Bob's BBT 51s. This was a quick test because I only had 18 bullets. This meant that in 18 shots I had to get the speed to around 880 and somewhat zero the gun.

I was tethered to my scuba tank at 2450 psi. I took a total of 14 shots. Once I to the power were I wanted ( It took 5 shots) I was shooting 880 with a spread of 8fps. But most shots where 1 to 2 fpe from 880. Also at the same time I was adjusting the zero.
51g at 880 is 87.7fpe 2.5 turns of preload

I do have to say I have to get used to the recoil and action movement.




First shot was the bottom lonely one. I adjusted elevation 2 time. the higher groups where the first adjustment and the middle group was the final adjustment. This was a total of 9 shots. The middle set is about ½ in. I did not measure it.

I'm very happy with the outcome.

now some other pictures.








This is what I was shooting and 2 shots will rip through it.




The hole to the left is 3 shots. The big hole is the 9 shots.


Hopefully soon I will have 60g BBTs and I will be testing them. The sad part is that i'm out of BBTs so no more shooting for a while. I do have to thank bob for sending me a sampling of them a while back!

[Geoff]

looking good

[Tomg]

Looks good Daniel!!!

So that's the CF 1/2" barrel (now 0.625" od) ?

[Rdsail]

correct

[Rdsail]

Update:

Today I receive samples from Tom Buchanan of Bob's BBT's in .25 and 58.4g. He sent me two sizes .251 and .250 to test out. I can't wait to test them on my Mrod. I'm looking to shot them around 840fps which will give me 91.5 fpe.

[sixshootertexan]

Hope they work for you Dan.

[Rdsail]

I tested today the .251 and .250.

I did not adjust the power on the gun. I shot tethers at 2350 psi. This what giving me 815fps with the 58.4g slugs. That's 86fpe. and I only have 2 turns in with the power adjuster.

No I shot from 40 yards:

8 shots with .250. There are 4 shots in the bottom group




5 shots with .251



One thing to notice. I have to get used to holding the gun. It has a bit of recoil from the hammer. I bet I can do better with both groups. I'm just wondering what size to order from Tom. The .250 shot a little faster but they opened up a bit.

[sixshootertexan]

Not bad Dan. I would order the mold in .251 and get a sizer if you need it.

[oldpro]

Would you mind sharing your 3D prints? I have 2 top end 3D printers here at the shop.

[Rdsail]

If anyone is interested in my SST you can order them from Shapeways.

load from the left:
http://shpws.me/IZSa

load from the right
http://shpws.me/IZS8

I made a little money on them so I can pay for prototyping.

As far as the barrel/bottle band. This is specific for WAR bottle Kit and ½ barrel with carbon sleeve. It will only work in that configuration.

[ironmule]

hey glad to see that they are working out for you
let me know what the final results are
mule

[Rdsail]

Today I measured the ballistic coefficient of the BBT .251 58.4 grain.

I took 5 shots at each distance.

Gun filled to 2600psi

At the muzzle: 838 fps avg - 91.1fpe

27 yards away: 825 fps avg - 88.2 fpe

the BC came out to be. .2308

I have no idea if this is right or not. I use used chairgun to calculate it. It Seams a bit high but does are the number.

[PakProtector]

It does seem a bit high...from the NOE description of a 55 gr, .224 small flat point its estimated BC is .181. That is probably super-sonic and a 40 gr running at 1070 is about .094. I recall a discussion of number crunching and a very small difference in the velocity gave a very different BC.

So, IOW, I have no idear why the number is so high...
cheers,
Douglas

[Rdsail]

Thinking about it my chrome way tilted some I wonder if that had to do anything with it. The front was a little lower that the back. That is the only thing I can think of that my give a different reading. I'll try tomorrow again.

[Rdsail]

I did some playing around with numbers and just a couple fps difference and the numbers will change drastically.

I think I need to increase the distance and do and average of 10 shots each. I wish I had two Chronis. Also get the sensor close to parallel to the tragectory.

I hope this would help

[rsterne]

Although 25 yards will work well with pellets to measure the BC, bullets lose velocity at a much slower rate, and so 50 yards would give you more accurate measurements.... A small difference in the velocity will, as you say, make a big difference in the calculated BC.... Also, you must input the correct atmospheric measurements to correct the BC to NTP conditions.... In addition, make sure you are using the G1 Model to calculate the drag....

Having said that, you are right in the sweet spot for the BC, it won't yet be on the Transonic upslope for drag, and the boattail is very efficient in reducing the drag in Subsonic flight.... BC's tend to be higher if you measure them Subsonic than Transonic or Supersonic, so a value of 0.23 would not be out of the question....

Bob