.25 cal 51 gr. NOE Bob's Boattails

[dyotat100]

Also I have a LW 24" unchoke barrel here. When I slugged it the first time the bullet came out larger then it was when I put it in by about .0005".  There is a lot lead to move because there is 10 grooves.

[owen]

 I decided to listen to what you were telling me, Doug. If anybody knows this stuff, it's probably going to be you. So early this morning I sized several of these bullets to .255". By the way, the .256" sized bullets measure .25607". I was also displeased with the Johnson Paste Wax as yesterday group size began expanding until I pulled a very tight, brushless, bore-snake through the barrel. Since these .255" sized bullets already had wax on them, I dropped a small drop of Lee Liquid Alox into the bottom of the mason jar that I use to tumble lube with. I also added a very small drop of mineral spirits, put the bullets in the jar, screwed down the lid tightly and began tumbling these under the kitchen faucet while hot water was running. The hot water melted the wax on the bullets and allowed this wax to mix with the LLA and mineral spirits. This lube is known as 45-45-10 lube. After tumbling about 5-mins. I dumped these out on waxed paper to dry. They dried all day and in the afternoon I collected these bullets up and went out to the bench. Here's a picture of the first, and only, 50-yard group that I shot:



The small red dot, by the two holes, is the first shot. Since it wasn't on the big red dot and since the shot was a bad one, in that I closed my eye and couldn't call that shot. I thought that I pulled the shot off course and so I covered it with a piece of tape and marked it with a small red dot for reference and I went back to the bench to start the group over. You can see where the next two shots landed. After shooting this I had to go somewhere and I didn't return until after dark, but this is most certainly encouraging and it appears to be a step in the right direction. Thank you for taking the time to correct some of my misconceptions, sir. I really do appreciate that!

[dyotat100]

If you want to try something else get some imperial sizing wax. Comes in a pellet tin type container. Trying sizing with that only. Then shoot them. I only lube to size and that's it.

If you have the ability to open up a sizer then you can buy a under sized one and open it up to just under bore size.

[K.O.]

It is looking very promising... sub moa at 75 looks very likely to me... 121 a challenge but doable... .


Thanks for sharing the challenge...it looks like killing the Choke paid off well... the barrel being short probably took away enough lever to handle well harmonically at  ~100 fpe... that is a feat...for a  .5" O.D. barrel...

When you lapped I get the impression it might have been a poured lead lap used?

It may be a while still but when the 41g mold is done and I get the hang of casting I will send you a few of them so you can check out how they do.

right now I just have recovered pellets  to melt... but will get some 99% lead soon...

I have a bunch of rosin core  60/40  solder I wonder if that will work for the tin content...

[K.O.]

hey Bob check it out,  not the only persons that thinks a rebated tail is a good idea ...1992 filing check out image #3

https://www.google.com/patents/US5275108

[rsterne]

Interesting use in a subsonic .22LR rimfire cartridge.... Corbin have lots of information on rebated boattails on their website which I found very helpful.... and of course the Lapua subsonic bullet for the Whisper (AAC Blackout) as well.... The only thing I did was to apply it to airguns....

Bob

[owen]

Here's my story. I decided that the wax lubrication was a terrible idea, so last night I boiled all of the bullets that I lubed, about 375 which I hadn't shot, in a pot of boiling water. The wax, and Lee Liquid Alox, floated to the surface. I poured off the wax and water and dumped the bullets out on a towel to dry. I then relubed about 80 of them with Krytox GPL201. A single tiny drop in the bottom of a screw lid pellet tin was more than enough for 80 of them. After swirling these around in the tin for several mins, I then sized these to .255", put them back in the tin and swirled the tin around for about 5-mins to get the newly exposed surfaces, from sizing, lubed as well.
Today the gun shot several .25" groups, at 50 yards. And this it did at an average power of 110.86 fpe. This is far better than I had ever hoped to see from these bullets, in this gun. I'm now looking forward to see what happens at 121 yards (the extent of my range.)
So thank you, very much Bob, for designing this mould for NOE. I'm extremely happy with this mould, now. I thought for certain that I was going to be changing barrels soon, after finding out about the 1-17.22" twist. I'm very glad that I don't have to, now. And a very big thank you to you Doug. If you hadn't stepped up and steered me in the right direction I probably would have never got this gun/bullet combination dialed in.

[Hobbyman2007]

Excellent news. I'm using the same 1:17.22 twist barrel in my BT65. Can't wait to start casting and shooting these new BBTs .

[25ACP]

The lowest tin/lead alloy I could find at Roto was 2.5 percent, but I also have pure lead. Should I try alloying the 2.5 percent to 1.5 using the pure lead, or just use it like it is?

[dyotat100]

Buy some of the pure tin pellets they sell. They are .6 ounce ea so it's easy to add to your lead. I mix my lead at 1% and that's what I use.

[rsterne]

I buy the "popcorn tin" from Rotometals, it's easy to weigh and you don't have to cut it, just break off what you need.... I have been using 1% tin, in their pure lead, but seem to be gradually increasing my tin content.... I think next time I will buy the 40:1 (2.5% tin) and try that....

Bob

[nielsenammo]

I buy 40 to 1 just the simplicity and it flows well.

[owen]

On Monday afternoon, early this week, I sized some of these bullets with the .254" die. These measured .25385", approximately. I didn't expect much from these "undersize" projectiles, because the bore diameter of the gun's Lothar Walther barrel measures .255". I only shoot 3-shot groups, so many won't find my findings very useful. The very first group that I shot with these .25385" dia. bullets landed in the middle of the 50 yard target's 5/8" dot and ctc the variation was about 1/8"... a ragged single hole. Thinking that this just had to be a fluke, I shot several more groups, but they were all very tight like the first with the largest about 3/8". I was/am, extremely pleased with the way these bullets were/are shooting, now. So Tuesday and Wednesday evenings were dedicated to sitting on a hillside, overlooking the garden, waiting for woodchucks to appear. I killed two woodchucks. This evening, Friday, I decided to shoot at the 50 yard target. I shot 3-shots and walked out to the target. A single hole the diameter of a single bullet is what I was looking at. Sub 1/16" ctc, probably. I have no idea how to actually measure something like this. Again, Doug wrote recently that he slugged his LW barrel and that the 10 lands and grooves resized the bullet's diameter into a larger diameter than it was originally. This must be the reason why this is working so well with these .25385" sized bullets. I still haven't had a chance to shoot these at my 121 yard target. I'm hoping to get to this weekend, though.

[dyotat100]

Glad to see you are getting good results.

 

[rsterne]

These are great results, and certainly show the merit to at least trying bullets that are slightly undersize.... I would like to thank Doug for letting us in on this little secret, and to Owen for proving it can work.... You can bet I will be trying this in my guns as well, particularly those where I am having trouble getting good groups....

Bob

[Hobbyman2007]

Looks like I'll have to get myself a sizing die or two from NOE. Great results .any idea how fast you're pushing the slugs . Sorry if I missed it .

[owen]

Looks like I'll have to get myself a sizing die or two from NOE. Great results .any idea how fast you're pushing the slugs . Sorry if I missed it .

972.5 fps. 9 of these bullets averaged 52.77777778 grains each. Average energy was 110.86 fpe. However, over the weekend I made a new valve-stem. I chronographed these BBT 51gr bullets, using the same settings as the previous valve-stem, but the new one only achieved 959.9 fps average. Because this is basically the same output as what the previous valve-stem gave, I bored the old valve-stem out to a .234" bore (it was .221".) Since it was dark when I did this, I put the chronograph under an incandescent light bulb, as a light source, and the first shot gave a reading of 1027fps. I'll have to wait until I shoot across the cronograph in sunlight to be certain that this is correct though.

[owen]

Well 1027 fps over the chronograph under an incandescent light bulb equals 960.3 fps in daylight. I knew that there was a reason that I didn't use the chronograph indoors, but I couldn't remember why. I do remember that a 100 watt LED bulb gives the same type of error, too. Maybe fluorescent bulbs work?

[rsterne]

If you are using lights indoors, you need two, one over each diffuser.... A single light source, centered over the Chrony, will give a high velocity reading, and the lower the light, or the higher above the Chrony the pellet path, the greater the error.... This is because the light travels in a straight line from bulb to sensor, and from a single source, those lines are converging towards the light bulb.... reducing the distance the velocity of the pellet is measured over....

You want two incandescent bulbs, one above each diffuser.... Do NOT use fluorescent, the flickering messes with the readings as well.... Battery powered LEDs are OK, some AC powered units also flicker (but some don't)....

Bob

[owen]

Thanks a whole lot, Bob. I'll try to rig something like that up. It would be great to have it work indoors.
I am wondering now if I've reached the power limit (approx. 110 fpe) with the 16.25" barrel length. I hardly think that it's worth buying a 24" LW barrel to turn down and cut the muzzle end back to 19.25" (the maximum barrel length that I would put in this particular airgun.)