.25 cal 51 gr. NOE Bob's Boattails

Yesterday I received my mould for my new Bob's Boattail Airgun Bullets from NOE.... It is a 2-cavity aluminum mould with a Lyman style HollowPoint pin in one cavity.... I am absolutely delighted with the quality of the mould, and the bullets it produces.... First, some pics of the mould....

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I conditioned it according to the enclosed instructions, used a film of Sprue lube, preheated it to about 400*F, and with my lead at just over 720*F I started casting.... I was using pure lead with about a 1.5% tin content (I had mixed roughly equal parts of 1% and 2% that I had lying around).... I discarded the first 10 bullets, and once the quality settled down I cast about 20 more.... The HPs were not filling out well, with a few wrinkles and rounded edges on the base, but the FN bullets were good for the most part, just a few with rounded corners on the base.... I dropped those bullets back into the pot, and increased the temperature to just over 760*F, and the FN bullets were then perfect, but about half of the HP still had rounded corners on the base.... You could observe this after cutting the sprue and before you opened the mould, as a slight line between the bullet and mould.... By this time I had found a tempo and method that was working well, but I still needed more heat.... I gradually increased the temperature until every bullet showed a completely filled base with a square corner, and found that required just over 800*F for the HP bullets.... The FN bullets were still casting perfectly, so that is what I found works for me.... The temperature was measured with an Infrared Digital thermometer, my dial thermometer, which I know to be out by 100*F, said just over 900*F.... I did find that overfilling the sprue on the HP moulds was necessary to get perfect corners every time.... I ended up with a sprue puddle nearly dime-sized on the HP side, but just larger than the sprue countersink on the FN worked fine....

When I sorted and examined the bullets, I ended up discarding about 30 of HP bullets, presumably the ones first cast where the temperature was not high enough.... I ended up with 115 FN and about 90 HP bullets that are virtually perfect in every way.... I then weighed and measured them and got the following results....

The FN bullets weighed an average of 50.8 gr., varying over 20 bullets from 50.6 to 51.1 gr.... The nose diameter was 0.2515", the midbody was 0.2415", and the driving band was 0.2535", with all bullets being within 0.0005" of those dimensions.... This places them 0.0015" over the design size, just about perfect to allow for sizing, IMO....

The HP bullets weighed an average of 47.8 gr., varying over 20 bullets from 47.7 to 48.1 gr.... The diameters averaged 0.0002" less than the FN bullets, so still 0.0012" over design.... I am delighted with these results.... Here is a photo of the bullets....

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I am very pleased with the results of this casting session.... and look forward to seeing how they fit the magazines and barrels, and whether they need sizing.... and of course how they shoot....

Bob

I checked these new NOE BBTs in both my Hatsan AT-44 and my Disco Double (with .25 cal MRod magazine).... They fit both magazines fine and function perfectly.... That, of course was one of the design parameters, that the overall length fit the Hatsan mags.... and they are spot on .... Remember that I got the smaller NOE mould for these bullets, with a 0.250" nose and 0.252" driving band, but I don't think the larger ones will have any problem fitting the mags....

In the Hatsan I can feel a slight resistance on closing the lever, but they will feed fine into a stock Hatsan chamber without sizing.... I chambered one bullet and then pushed it back out, and the rifling marks are clear, and appear the same depth all the way to the rear of the driving band, so I would say the chamber has little or no tapered leade.... There were absolutely no marks on the 0.2535" driving band between the rifling marks, indicating the groove diameter of the Hatsan barrel is larger than that.... It is possible that for the best accuracy in a Hatsan, the larger (0.253/0.255") NOE mould may be the better choice, but could require cutting a longer, tapered chamber to reduce chambering force.... If you don't want to do any barrel work, the smaller (0.250/0.252") NOE mould, like I got, may be the better choice....The Hatsan was tuned for 70 FPE with JSB King 34.2 gr. Heavies, and shot 75 FPE with the 50.8 gr. FN BBTs (815 fps).... I did not try increasing the hammer spring preload as that is not the gun I bought them for.... I have the 41 gr. BBT mould with the larger 0.253" nose / 0.255" driving band coming for the Hatsan.... and I now know I will likely have to cut a tapered leade for them....

In the .25 ACP liner by TJ's in my Disco Double, there was a fair amount of resistance closing the bolt, indicating they are slightly large for the chamber I have.... Once sized, they fed easier than the unsized ones in the Hatsan, basically no more resistance than chambering a JSB King Mk2 Heavy, and easier than the original King Heavy pellets with the oversize skirts.... I maxed out the hammer spring preload in the Disco Double, and tethered at 2900 psi they screamed over the Chrony at 1007 fps (114 FPE).... I backed the preload out 2.5 turns, and got the following average velocities for 5 shots....

50.8 gr. FN BBT unsized - 940 fps (100 FPE)
50.8 gr. FN BBT sized - 960 fps (104 FPE)
47.8 gr. HP BBT unsized - 965 fps (99 FPE)
47.8 gr. HP BBT sized - 985 fps (103 FPE)

Note that the velocity increased 20 fps with sizing the bullets, a good indication they are a bit tight as cast.... All four 5-shot groups that I fired through the Chrony were ragged holes in the backstop at 20 feet.... They all shot tighter during Chrony testing than the .25 cal 51 gr. BBTs I cast from my LBT mould, and a lot tighter than the 52.7 gr. RN Lyman 57902, or its HP version which was 46.4 gr.... I never found a setup that grouped with the Lymans.... It may be some time before I can get to try the new NOEs at long range, unfortunately....

When I size these bullets, there is just a hint of contact with the sizing die on the nose, enough to polish it all the way around, and the driving band is definitely smaller (now the same size as the nose, of course), but slides easily through my 0.250" sizing die.... When chambered in my Disco Double, which has a tapered leade of 2* per side, the nose is evenly, but not deeply marked by the rifling, as is the driving band.... I would say that sizing to 0.250" is just about perfect in the TJ's barrel.... I plan to size all my bullets prior to any further testing....

One other thing, I tried chambering these bullets in a .25 cal Lothar Walther barrel I bought many years ago from Mountain Air.... This barrel was chambered for pellets, and I am sure could benefit from having a longer chamber and tapered leade cut for use with bullets.... I could barely chamber an unsized bullet, but sized to 0.250" it chambered smoothly until it came up against the rifling (obviously no, or very little, taper in the leade), and the last 1/8" you had to give the bolt a firm shove to chamber it.... I understand the earlier LW barrels (which mine is) are smaller than the current production, which is listed on the LW website as 0.248" land and 0.254" groove.... If the specs on the website are correct, I think the larger size NOE mould (0.253" nose / 0.255" driving band) would be the better choice....

Now what we need are more readily available sizing dies in airgun calibers.... Al, are you listening?.... ???

Bob

I did some penetration testing today in my standard media, which is clear "Melt and Pour" Soap, cast into blocks.... This material will stop a HV .22LR RN bullet in less than 11", and shows expansion of HollowPoint bullets well enough to photograph the cavity, and allow the bullet to be recovered.... It is harder than Ballistics Gel, but the wound cavity retains its shape after impact, and it's nowhere near as hard as Paraffin Wax or Phonebooks.... Here is the comparision between the 50.8 gr. FN and the 47.8 gr. HP, both shot at 100 FPE....

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The FN bullet penetrated 155 mm (6.1") and the HP penetrated only 85 mm (3.3") but created a much wider wound channel.... Here is the cavity created by the HP bullet, which broke into 6 pieces....

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and here are the recovered bullets.... The FN expanded to larger than bore size.... The HP expanded well, with the nose portion coming apart....

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Although the HP cavity is only 1/8" in diameter and about 3/16" deep, it certainly does its job.... I am very pleased with how these bullets performed....

Bob

I got a chance to do some velocity testing at 50 yards today, so I was able to calculate the Ballistics Coefficient for the new NOE Bob's Boattails.... I tested five bullets, the RN and HP version of the Lyman 57902 bullet for .25 ACPs, the BBT I designed for LBT Moulds, and the new BBT I designed for NOE.... I also tested the JSB King pellets.... I used two (calibrated) chronographs, at 1 yard and 51 yards from the muzzle, and then calculated the BC, corrected for the pressure, temperature, and altitude of the tests, to NPT conditions.... Here are the results....

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The difference in the BC with the boattail bullets is significant.... about 30-33% improvement compared to the flat based .25 ACP bullet from the Lyman mould.... The new NOE bullets had an 11% better BC than the almost identical BBT I cast using the LBT moulds, which have a smaller Meplat.... This confirms that there is no disadvantage to having a Meplat as large as 70% on relative short bullets, as proven many years ago by Elmer Keith.... It is interesting what happened with the 25 gr. JSB King pellets.... The way my Disco Double was tuned for the testing today, it blasted the Kings out at over 1200 fps.... What was astounding is that they arrived at 50 yards going only a bit faster than the bullets.... This confirms two things.... 1. That pellets have a poor BC.... and 2. that Supersonic velocities cause pellets to slow down at an extreme rate.... At 50 yards, the Bob's Boattails still had about 78 FPE of energy, but the Kings were down to just 43 FPE....

I then proceeded out to the ranch where I do my Varmint hunting.... I wanted to see how the 47.8 gr. NOE HP Bob's Boattail performed.... All I can say is, that headshots are no longer required, in fact the recovery rate is greater with a shot to the chest.... Not only do you have a much bigger target, but the bullet does a huge amount of damage as it passed through the quarry.... accompanied by a large spray of blood, clearly visible in the scope, and a loud WHACK! as the bullet hits.... Photos of the exit wounds on a Marmot and a Ground Squirrel, both taken at about 50 yards, will be in the hunting gate....

Bob

Preliminary testing by Nick at Nielsen Specialty Ammo, using a Sumatra and a Cricket, were disappointing.... At 50 yards, some bullets from the Sumatra (20" twist) were showing tumbling and even missing the target paper.... The Cricket (17.7" twist) shot OK, but not great, and at 100 yards some showed signs of yaw....

The design twist for this bullet was 14", although calculations show that below 1000 fps they should be fine in a 16" twist.... I guess we should not be too surprised that they are not working well in slower twist rates.... All data is important in these early stages, so I wanted to pass this along....

Bob