GTA
Airguns by Make and Model => AirForce Airguns => Topic started by: rsterne on December 12, 2018, 04:11:53 PM
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First of all, I would like to thank everyone for participating in the Polls for all 4 calibers of the Texan to inquire about your preferred weight of bullet.... The results are visible in each Poll, in the form of a bar graph, showing how many votes each weight received.... I have converted the weights to the Sectional Density, and the results of the polling are shown below....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Other%20Bullets/Texan%20Sectional%20Density_zpsjgyrvcf5.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Other%20Bullets/Texan%20Sectional%20Density_zpsjgyrvcf5.jpg.html)
As expected, the most popular bullet weights occur within a narrow range of SD, in this case the curves peaking between 0.17 and 0.19.... This range agrees quite well with what could be expected for a fill pressure of 3000 psi and a barrel length of 34".... For those of you unfamiliar with SD, it amounts to the "weight per unit area" of the bullet, so bullets with similar SD will offer the same resistance to acceleration in the barrel, and so will have the same velocity potential for a given combination of air pressure and barrel length.... They will also have a similar ability to carry their momentum through both the air and tissue, although the shape will have some affect as well.... Here is a graph of bullet weight vs. SD for the 4 calibers available in the Texan....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Other%20Bullets/Texan%20Bullet%20Weight_zpsnuwtjvse.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Other%20Bullets/Texan%20Bullet%20Weight_zpsnuwtjvse.jpg.html)
The two vertical dotted lines are at SD values of 0.17 and 0.19, so the range between those reflects the most popular bullet weights in each caliber.... Based on that data I have come up with four bullet designs, with the intention of both the solid FN version and a HP version of the same bullet lying within that range.... The .357 cal Poll, for some reason, showed a bias towards the lighter end of the SD range, so I have favoured that in my choices, and the HP version has an SD of just under 0.17 for that reason....
I have not discussed these results with Al at NOE yet, I wanted to post them here, along with my proposed designs, for further comment.... Note that bullets with similar SD will also have similar overall lengths, as these do.... This makes smaller caliber bullets slimmer in appearance, with a better Form Factor, and since the Ballistics Coefficient is found from BC = SD / FF, should also give them a better BC.... The designs will follow in the next post....
Bob
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Here are my four bullet designs which meet the criteria above, one for each Texan caliber.... I used a conventional "Gas Check" base, as those are the most popular for airgun use.... and separate any damage from cutting off the sprue from the release point of the bullet with the crown (the back of the driving band), which tends to contribute to better accuracy.... Since all the bullets had a similar LOA, I used a 0.300" deep HollowPoint on all of them....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Other%20Bullets/257%20Texan_zpsj49ghghe.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Other%20Bullets/257%20Texan_zpsj49ghghe.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Other%20Bullets/308%20Texan_zpsdsac4t7i.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Other%20Bullets/308%20Texan_zpsdsac4t7i.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Other%20Bullets/357%20Texan_zpsxh7zjeyy.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Other%20Bullets/357%20Texan_zpsxh7zjeyy.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Other%20Bullets/457%20Texan_zps1uupcdnu.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Other%20Bullets/457%20Texan_zps1uupcdnu.jpg.html)
Note that in each case, the nose band is only 0.002" over the nominal land diameter of the barrel, based on the information I have received.... I sized and tested bullets to that size, and they could be pushed into the muzzle of barrels by hand, with some resistance, so I feel they should chamber OK when pushed by hand into the Texan's short chamber.... The driving band at the rear is 0.001" larger than the groove diameter, to allow for sizing if required.... The twist rates specified are the slowest twist that should provide stability and are not to be considered the "optimum" for the bullet, but only a minimum.... The vertical dotted line in the nose represents the approximate point where the nose will first engage the nominal land diameter, and the dimension from there to the back of the driving band is the length engaged with the rifling, and hence supporting the bullet in the bore....
If you have any comments about these proposed bullet designs, please post them in this thread....
Bob
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I'd still love to see a HP on the lighter side for the SS models. Especially the .45 SS if it was possible from an engineering standpoint (I understand that lightening up one too much may make it unsuitably short). I think the stock .45 SS is really straining the limits of what the SS platform can do in terms of delivering a projectile at an optimal velocity. Notwithstanding the fact that the .45 SS seems to shoot heavy bullets very well in terms of accuracy. I think the SS market is important because the shorter guns seem more accessibly and practical and I suspect the platform will grow in popularity over time.
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Bullfrog, I see the HP version only weighs 255 and based on my success with the 280/300 gr range in a regular Texan and how a shooting buddy with a SS has done well with a 252gr SWC I think it will work better than you think.
I will sure be buying both the .45 and .35 molds
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My SS is running 217 and 220 grain bullets between 810 and 820fps. Anything heavier is getting into the 700s. I don't necessarily doubt the accuracy. 290 grain NSAs at only 720fps are extremely accurate out of my SS at 50 yards. I would just prefer something that could hit the mid 800s or even low 900s. Right now the only projectiles I have that can do that out of the .45 SS are the button bullets and .457 Hornady roundball.
By the numbers my SS is running a bit slower than the factory specs by about 30fps. However, note that all of my guns have been running about 30fps slower and my chrony is suspect, especially where a guest's gun also got a low reading and my brother's gun got a low reading here and a hotter reading at his home on his chrony. Let's say my 217s and 220s are actually doing 840 or 850fps. I'd prefer to not shoot any slower than that.
If and when the .45 Hunter pellets come out, that may be what I need for my SS to get it where I want it.
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Put me on the list for the .308. Thank you Bob for your hard work.
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I can understand that the Texan SS versions, with their shorter barrel, could benefit from lighter bullets.... There are two possibilities.... Either the Gas Check shank could be removed by making a shallower mould (producing two versions, if Al can be convinced the market is there)…. or at some point in the future, and again if the demand is there, I could design a lighter bullet.... My concern is that, particularly in the case of the .45 cal, if the weight of a roundball is the appropriate weight for the SS, it would be difficult to make a bullet short enough....
Omitting the GC shank would lighten the bullet by 7 gr. in .257 cal, 11 gr. in .308 cal, 17 gr. in .357 cal and 29 gr. in .457 cal.... That would give the following weights....
.257 cal.... 76 gr. FN and 72 gr. HP
.308 cal.... 113 gr. FN and 106 gr. HP
.357 cal.... 147 gr. FN and 133 gr. HP
.457 cal.... 247 gr. FN and 226 gr. HP
If the Texan SS owners could comment on those weights, I will talk to Al about this possibility, to see what he thinks.... I know that finding room in their extensive Inventory storage is always an issue.... Remember, a .45 cal roundball is only about 143 gr., and a .357 only 68 gr.... so these are still a LONG ways off those weights.... The new NOE Hunter pellets may be a better solution if you need bullets just a bit heavier than roundball…. The .35 cal are now in the NOE Store.... http://noebulletmolds.com/NV/index.php?cPath=35_586 (http://noebulletmolds.com/NV/index.php?cPath=35_586)
Bob
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I think the .45 Hunter pellet will probably be the answer. I already have the NOE .45 Bob’s Boattail mold in 220 hp (I’m getting about 217 grains) and they are shooting decently for whitetail hunting purposes at 50 yards out of my SS. A different design might yeld better chambering and accuracy results, but it terms of speed that niche is already filled I think.
I’ll anxiously await the pellet mold.
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In terms of the .308 SS, the current NOE 105 grain mold, which is giving me 97 grains in HP, is already perfect. So I wouldn’t recommend changing anything to your plans just for the SS model. 3 good shots over 900fps in the same hole at 50 yards is just fine.
Its really just the .45 that seems to be straining with the shorter design of the SS platform and is in need of some light projectile options. Even the .357 SS, which I haven’t shot yet, has some light options in the JSB and Polymag commercial pellets that should take good advantage of the platform. I am aware there are some .45 JSBs being offered but they are very expensive and also too heavy in my opinion.
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Thanks for your comments, Travis.... The .45 cal Magnum Hunter pellets can be cast at 166-190 gr, depending on the base pin chosen.... so will fill in the gap between roundball and the lightest bullets, IMO.... I really think that for now we should just go with the four designs shown in Reply #1 above....
Unless I hear some screaming objections soon, I will be talking with Al to firm up the designs.... 8)
Bob
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A little late posting but I've been busy...
Bob, I have no idea why but GC shanks really seem more accurate than flat or BT bases. But it does not have to be a full length shank, it can be shortened about 50% and still seems to do whatever it does well so it could be shortened for lighter weight but still leave a nub of shank, maybe?
I have experienced this in several molds that were cut down shorter, then shortened again and the second time when they became a flat base and the shank was fully removed they were just a tiny bit less accurate in the same benchrest rifle as before. (A Remington 40x, 7mmBR with a bull barrel and sleeved action in a 22 lb weighted stock). Went from .2 center to center to .42 CtoC at 100 yards. This was also true with some otherwise identical molds that were either plain base or GC shank and the GC were always better.
Of course, that's assuming there is carryover from PB to PCP...
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IMHO that .45 bullet is not going to work in the full length texan. Its to short needs to be longer. 1:40 twist? Texan is 1:20 and it likes longer bullets. I've tested lots and the longer bullets in the 340-380gr seem to be best at range. If NOE would get some RD GC molds made I'd order that. I already have the non GC mold and it dropped a deer less than 15yds with a 53yd shot. I'm sending a 330gr lyman to Eric to have the HP enlarged. It is the best hand cast bullet still in my Texan. And since I have 2 of the mold might as well try a larger pin.
You asked for opinions there is mine. I think the .257 and .308 bullet will shoot well. The .357 may also.
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Carl, I made the GC shanks to the shortest lengths that NOE use.... there are much longer ones but I saw no need.... I used the proper GC shank diameters as well, for each caliber, to keep them consistent with what we know works....
Tim, thanks for your comments.... I designed the bullet that was the most popular in the Poll, between 250-300 gr. (5 requests each).... The length is what you get with a bullet of that weight.... I have no idea why Air Force chose such a fast twist rate, which appears to be a mismatch with the FPE of the gun, but I have no control over that.... If enough guys are interested, I could design a longer heavier bullet and forward it to Al in addition to the one above.... A 350 gr. bullet has an SD of 0.24, which in a 3000 psi gun really hurts the velocity.... and only 3 guys were interested in anything that heavy, and nobody wanted anything heavier....
Even a 500 gr. bullet such as this one.... http://noebulletmolds.com/NV/product_info.php?cPath=42_577&products_id=5474 (http://noebulletmolds.com/NV/product_info.php?cPath=42_577&products_id=5474) …. only needs a 26" twist.... ::)
Bob
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The four bullet designs above have been submitted to Al at NOE.... I will let you know when the moulds go into production....
Bob
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Sitting on edge of chair for .257!
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I'd be interested in the .257 and .357 molds!
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Not exactly Texan related, but I would be interested in the 257 scaled to .224. I doubt there would be enough interest in it but it doesn't hurt to throw it out there
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The 83 gr. .257 would be about 55 gr. if scaled down to .224 cal.... I would suggest you look at this bullet which is in Last Call at NOE right now....
http://noebulletmolds.com/smf/index.php/topic,2452.0.html (http://noebulletmolds.com/smf/index.php/topic,2452.0.html)
Bob
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Will this is going to be fun!
Ive already got the BBT .357, 152gr mold that is shooting very well (under an inch at 100 yards) in four test rifles { http://noebulletmolds.com/NV/product_info.php?cPath=35_578&products_id=5488 (http://noebulletmolds.com/NV/product_info.php?cPath=35_578&products_id=5488) }
And now I am going to have to buy this Bob's Gas Check (BGC?, Bob's Straight Shank? BSS?) one so I can do a side by side comparison! ;D ;D ;D
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Just call them the NOE Texan bullets.... 8)
Bob
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Bob, some bullets are just {hate to say it!} too sexy and that .257 is one. I don't currently have a .257 because I think it's too small a calibur.... And .308 is too big.... So when I get my perfect calibur rifle, the 7mm/.284 you have to design the bullet like that for me. I was going to get a .308 Texan and rebarrel it but since I've got a Slayer coming I'm going to ask Tom if he would make me a spare barrel in 7mm. Then I'll need a mold! Basically the same criteria you used to do the others.
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Carl, to keep the same SD, which governs the velocity at a given pressure, a 7mm/.284 would end up between the .257 and .308 bullets, and weigh just over 100 gr.... If I scale the 83 gr. FN .257 up to .284, it ends up at 112 gr., nearly what the .308 bullet weighs, and the SD increases from 0.180 to 0.198.... That would require a 10% or more increase in pressure to get the same velocity....
I designed a .284 BBT, and the mould was made by Veral Smith at LBT.... It works out at 96.5 gr. in FN (SD = 0.170) and 91.0 gr. in HP.... There is also a 7mm mould designed for airguns available from Arsenal, the .284 "Bowman" which is a scaled up Lyman 257420, and weighs 96 gr.... However, if you have your heart set on a 112 gr. version of the .257 above in .284 cal I can certainly draw it up for you.... You already know the deal on custom moulds from NOE.... they charge $300 for the tooling up front....
Bob
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Although I am not really interested in the other Cal's here, the .257 seems to start at what is considered the all time greatest .257 bullet. The Lyman 257420, which is 74 gr's in solid, and .70 gr's in HP version when cast with 20-1 Lead/Tin.
Nice!
Knife
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..... You already know the deal on custom moulds from NOE.... they charge $300 for the tooling up front....
Bob
Yah, I'm going to give Al a call this week and arrange to pay him the cherry fee on another .357 mold.
If I have Accurate make the mold and hollowpointservices do the HP work I've already got $250 invested for a one off mold. By getting the cherry made I can get multiple copies (if I damaged it or wear or something) or other people can buy/try it too if he lists it.
I'll check out those other 7mm molds, thanks for the tip... But it will be at least June before that project kicks off so there's time.
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Although I am not really interested in the other Cal's here, the .257 seems to start at what is considered the all time greatest .257 bullet. The Lyman 257420, which is 74 gr's in solid, and .70 gr's in HP version when cast with 20-1 Lead/Tin.
Nice!
Knife
Question Knife, I notice you quote 1:20 tin/lead, did you experiment with different alloys? How did you decide on that ratio? Was it just accuracy or were you also looking for any expansion?
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I received the final designs for the 4 calibers of Texan bullets from Al today and reviewed them.... Al apologizes for the delay and said they would be added to the lineup for the mill when they ramp up production again in a couple of weeks....
Bob