Whats the Science behind shooting heavier projectiles? (like .247, .30, .357)

[K.O.]

I am also so close to what is needed for that .217 round except for the twist rate...

I have a rather unique 22lr barrel that it would send it out if it was shorter  and dropped with a .22 drive band...

it has a slightly faster twist than normal at 1:15.75 and is choked to about .218 groove and .212 land...

I do not know where a 1:12 or even 1:14 .22 pellet barrel could be found..? almost all I know of are  1:16 or greater twist...

so yep  so close to what I need but not quite... I could cast a slug with a screw in it and lap it just a touch larger(but may cause out of round) but I would have to knock off the boat tail for the twist to work... and that just would defeat the purpose...

[rsterne]

For the relatively slow twist of most airgun barrels, it is simply not practical to make a boattail.... by the time you shorten the BT and increase the diameter to allow it to use the slow twist rate, you may as well just use a flat-base bullet with a gas-check recess....

Increasing the velocity up into the mid 1000s will still increase the wind drift more than what you get at 900.... Even the 25 yd. Benchrest shooters stay below 900 fps to achieve the minimum possible drift.... .22LR target ammo (subsonic) has significantly less drift than the HV does.... As I said, play with the JBM calculator, select any bullet you want from their dropdown menu, and start putting in velocities between 500-1500 fps and you will get a plot of wind drift similar to the above....

http://www.jbmballistics.com/cgi-bin/jbmtraj_drift-5.1.cgi

The first one I picked, an Aquila .22LR, drifts only 4.1" at 850 fps, but 6.7" at 1400 fps at 100 yards....

Bob

[39M]

Just out of curiosity, I was reading about the Eley TenEx. A lot of the information doesn't apply, such as the ability to remain stable at 1085 fps, since the bullet is a 40 grain solid chunk of lead and not a hollow base lighter weight pellet. But it does have the "football with the ends cut off" shape.
The one similarity to subsonoc air rifles that I found of value was the emphasis on the importance of the shape of the nose. It was very similar to Bob's draft. And the particular feature that they accredited it's accuracy to was the sharp edged cut flat nose that promotes the hollow space of air ahead for the bullet to travel through. The bump in the center is just a result of the cutting the sharp edge, and not a design feature.

But while these bullets are used in competition out to 100 yards, or maybe meters, they claim the design is most effective out to 50 yards.

[rsterne]

Not really a football, the rear shoulder is parallel to the bore, only there for chambering in the cartridge.... The nose shape is a typical Tangent Ogive with Meplat, however, which from everything I have read is the best for subsonic and low transonic velocities.... It actually works well right up to Mach 1, but the Meplat has to shrink in diameter or the drag goes up.... Right at Mach 1, a 30% Meplat is optimum, and by the time you get to Mach 2, that shrinks to 10-20% of the caliber.... The little "nub" on the front is proof of the stagnation zone, it has no effect on the flight or drag as it's in a dead air space travelling with the bullet.... I have seen photos of the TenEx where the size and shape of that nub is inconsistent within one box of ammo.... Disconcerting, but irrelevant apparently.... as they are VERY consistent in weight, one of their claims to fame....

Bob

[K.O.]

hey Bob on the .217 BBT maybe if I get the mold and then sand(cut, whatever)the round to  ~85% meplat then it would be closer to a stable round. In this thread you conclude at .8 Mach the Meplat size had little effect from 20%-80%...

http://www.gatewaytoairguns.org/GTA/index.php?topic=94920.0

"
So what conclusions can we draw so far if we are trying to determine the "best" Meplat size?.... Well, below Mach 0.8 it doesn't matter.... If we cared about the Supersonic range (above Mach 1.2), the 80% Meplat is too big.... For short bullets, we can also eliminate the thinner Meplats, as their drag starts to increase sooner.... In the Transonic range, this leaves us with choosing between Meplats of 20-80%.... It appears that for shorter bullets, a Meplat of 60-80% is optimum (thank you, Elmer Keith!), extending the low drag plateau up to Mach 0.9.... while for longer bullets 20-60% looks like the optimum, again extending the low drag plateau to Mach 0.9.... Are you ready for round two?.... Let's set the Meplat at 60% and vary the nose length and see what happens.... and again with a Meplat of 30%....

"
So in the interest of a round that would work in most current barrels do you think the compromise would work... For me half the reason for going to a cast round is the independence of it

I think it would still outperform most pellets? it would be basically a rebated boat tail semi wad cutter, or do you  think I am overlooking something?

I just wish that there was  more research done with subsonic rebated boatails I really do get the feeling that since the Cg is more forward that it will need les twist than a flat based bullet of the same length...

they say that it also would move the center of pressure forwards so it would need more twist iirc,

but to me that is only true near and past 1150 fps..? My gut says I am right... but it has been known to be wrong more than once..

The other thing I would love to figure out is why the Marlin barrels seem to do ok with the 60g subs while they tumble out of other 1:16 .22 barrels?

Long winded but shoots a little past 8 min in... 

and this I am pretty sure is a Marlin 980v... 

[39M]

I think some older Marlins had 12 grooves and then switched to 16 grooves, botg 1 in 16 twist. Don't know if the number of grooves makes any difference on stabilizing heavier bullets or not.

[39M]

Pretty sure that's a Savage Mark II FV in that video.

[K.O.]

Pretty sure that's a Savage Mark II FV in that video.

Hmmm with a closer look It looks like you are right...

So what Voodoo  is keeping the 60g round from tumbling..?

[K.O.]

I think some older Marlins had 12 grooves and then switched to 16 grooves, botg 1 in 16 twist. Don't know if the number of grooves makes any difference on stabilizing heavier bullets or not.

I am using a Marlin 883N .22 Mag barrel for my .224 project they have 20 lands and grooves...

I used a used Glenfield model 60(same as Marlin 60) to practice turning it down to 9/16 first... just finished turning the .22mag down...

[39M]

Now I'm going to have to get out my magnifying glas and count some grooves.

By the way, I've been a long time admirer of your long tube 13xx builds. I plan on having one in .22 in a few months.
The 1377 standard tube carbine is up first though. It'll be a rear cocker.

[rsterne]

The size of the Meplat has little to do with the twist rate, some, but nothing compared to the diameter of the boattail base.... The easiest thing you could do to make the 43 gr. work in a slower twist would be to machine off the back of the mold to shorten the boattail and increase the diameter.... I can make that calculation for you.... It will also lighten the bullet, which seems to be what you want....

Bob

[Schmeddz1]

https://www.augustana.ualberta.ca/~hackw/mp480/exhibit/ballisticsMP480.pdf

Here's an actual published paper on ballistics. I thought it was funny that "Serving the Darkside" was in the title!

REAL science!!!

[rsterne]

K.O., here is the skinny on the .224 cal 43 gr.... As it stands, in a 14" twist barrel, it has the following Stability Factors (less than 1.0 is unstable, 1.5 is recommended, but generally 1.3 works just fine)....

Mach 1.... 0.8
1000 fps.... 1.0
900 fps.... 1.1
800 fps.... 1.2
700 fps.... 1.3

So the stock 43 gr. should be fine at 700 fps and less, and should get more stable as it goes downrange because the forward velocity decays faster than the RPM.... If you shorten the back of the bullet by just 0.030", that increases the diameter of the boattail base by only 0.008", but that, plus shortening the bullet, increases the stability to the following....

Mach 1.... 1.0
1000 fps.... 1.25
900 fps.... 1.4
800 fps.... 1.5

Now you could push the bullet to at least 950 fps without an issue.... Just imagine, that big a difference from less than 1/32" removed from the base of the bullet.... 
Incidently, it would only reduce the weight by about 2.6 gr, to about 40 gr....

Bob

[K.O.]

thanks Bob I had to go take care of a slight emergency for a friend and just got home... need to go get cleaned up and will be reading a bit more carefully...but the quick scan is reading well...

slight misunderstanding on the last because of me thinking I was being clear and wasn't (Concentration probs strike again)

[K.O.]

The size of the Meplat has little to do with the twist rate, some, but nothing compared to the diameter of the boattail base.... The easiest thing you could do to make the 43 gr. work in a slower twist would be to machine off the back of the mold to shorten the boattail and increase the diameter.... I can make that calculation for you.... It will also lighten the bullet, which seems to be what you want....

Bob

what I meant about

"
hey Bob on the .217 BBT maybe if I get the mold and then sand(cut, whatever)the round to  ~85% meplat then it would be closer to a stable round. In this thread you conclude at .8 Mach the Meplat size had little effect from 20%-80%...
"

was to shorten the nose after casting until it was stable with a 1:16 twist  and that would increase the meplat size...

the price paid would be a touch more drag generated at the nose..?  If I understand correctly shortening the boat tail would have a bit larger effect on drag...

but decking the mold and shortening the boatail would be less work to get a stable round in the end...for currently available barrels...

edited for clarity (reread and my occasional concentration probs are showing)**

[K.O.]

K.O., here is the skinny on the .224 cal 43 gr.... As it stands, in a 14" twist barrel, it has the following Stability Factors (less than 1.0 is unstable, 1.5 is recommended, but generally 1.3 works just fine)....

Mach 1.... 0.8
1000 fps.... 1.0
900 fps.... 1.1
800 fps.... 1.2
700 fps.... 1.3

So the stock 43 gr. should be fine at 700 fps and less, and should get more stable as it goes downrange because the forward velocity decays faster than the RPM.... If you shorten the back of the bullet by just 0.030", that increases the diameter of the boattail base by only 0.008", but that, plus shortening the bullet, increases the stability to the following....

Mach 1.... 1.0
1000 fps.... 1.25
900 fps.... 1.4
800 fps.... 1.5

Now you could push the bullet to at least 950 fps without an issue.... Just imagine, that big a difference from less than 1/32" removed from the base of the bullet.... 
Incidently, it would only reduce the weight by about 2.6 gr, to about 40 gr....

Bob

Thanks for the effort Bob I tend to estimate what is needed and my gut was thinking that it would need shortening by about .06 to be stable in a 1:14 barrel but just .03 is a bit of a shocker...

So since I am using a 1:16 which works well with .22lr at 40g rounds it would seem even at shortening by .03 would work even if the Microgroove barrel is not a help in reducing twist needed...

I am interested in lightening the round for sure... I think that .224 boat tail boolits will outperform just about any .25 pellet...By having a round that keeps the fpe requirments near that achievable with a near stock Mrod it just might get enough people interested for us to get some molds made... and then if they prove out then it will build..."Build it and they will come"  ...

I do think that for the lower fpe rifle a 1.75 caliber version would be the optimum...

But then again it is probably not that much of a performance penalty if the tail is shortened  rather than the body(as drawn) and as drawn would be better for those that have fpe to spare... Meaning those already sending cast rounds out...

So yep decking the .224 mold by .030 would be acceptable to me and not muddy the choices even more... I think we will have a hard enough time just getting enough interest in the .224 as it is...

Sort of the chicken or egg thing... people have not done it because the molds are not available for the current barrels but the molds are not available because no one is doing it...

Me I am willing to carve my rounds by hand if I have to...

Heck I bet I could deck the 43g .224 mold and then after casting shorten the nose for even more weight loss and that combined with different hollow points and non hollows get anywhere from about a 34g-40 grain round... some where in there I am sure I would find the round that suited a mild tuned Mrod...

Sorry for taking so long to get back but I had to help my buddy fix a pipe in a muddy crawlspace and then my back tweaked on me a bit...

Thanks for your efforts on trying to move things forwards, I did register on the N.O.E. forum and cast my votes for the 37 grain .217 and 43 grain .224.

[rsterne]

I have just drawn two new, shorter, airgun caliber boattails and sent them to Al.... a 0.217" 29 gr. for a 16" twist, and a 0.250" 40 gr. for a 20" twist....

Bob

[K.O.]

Now I'm going to have to get out my magnifying glas and count some grooves.

By the way, I've been a long time admirer of your long tube 13xx builds. I plan on having one in .22 in a few months.
The 1377 standard tube carbine is up first though. It'll be a rear cocker.

Thanks I had fun finding out what could be done sticking with just the pump cup and pretty much stock parts with some mods.
flat tops would be faster and more efficient but I also wanted low budget...so there is a lot of room for improvement... But they all will hit a quarter at 30 yards very reliably and .5 groups at times so I am happy...

the 1322XLT needs to be a rear cocker I keep breaking and bending the cocking pin...

I have most of the parts for an extended valve Mk13xx that would take 40-45 pumps to hit 1500 psi with a gage it just might make a good ACP.

I wonder what rifling Savage .22lr is currently using is it still 6 unequal and ~ .025 land .090 groove

http://www.pochefamily.org/books/RimfireBullets.htm

[K.O.]

I have just drawn two new, shorter, airgun caliber boattails and sent them to Al.... a 0.217" 29 gr. for a 16" twist, and a 0.250" 40 gr. for a 20" twist....

Bob

Will be watching for them..

[K.O.]

Just out of curiosity, I was reading about the Eley TenEx. A lot of the information doesn't apply, such as the ability to remain stable at 1085 fps, since the bullet is a 40 grain solid chunk of lead and not a hollow base lighter weight pellet. But it does have the "football with the ends cut off" shape.
The one similarity to subsonoc air rifles that I found of value was the emphasis on the importance of the shape of the nose. It was very similar to Bob's draft. And the particular feature that they accredited it's accuracy to was the sharp edged cut flat nose that promotes the hollow space of air ahead for the bullet to travel through. The bump in the center is just a result of the cutting the sharp edge, and not a design feature.

But while these bullets are used in competition out to 100 yards, or maybe meters, they claim the design is most effective out to 50 yards.

I think consistent case rim thickness is also a part of it.. also consistent seating depth in the case...
shows case variance...


this is a lot of talking but it does show length/seating variance in cheaper ammo... 



Have you seen the Paco Kelly fixing the nose kit... me personally I do not want to hammer ammo...

I plan on eventually using a    or something close to it help Blueprint my rounds... maybe just a modded nose punch type thing..?

I wonder if I can make my own .217 sizer..? I know there is some one that is making custom sizers for about $25...