Author Topic: .25 cal 51 gr. NOE Bob's Boattails (Read 43043 times))

rsterne · « **Reply #160 on:** August 31, 2016, 01:13:44 AM »

If you plot velocity vs. power setting, you will eventually find a plateau for any given pressure and barrel length.... Trying to get more (what I call operating on the plateau) only wastes air, basically because you still have the valve open after the bullet has left the muzzle.... If you back off only a few percent on velocity from that plateau, you can literally save half the air without any significant drop in performance.... When the valve closes with the bullet only half way down the barrel, velocity has usually only dropped by about 3%.... while shot count has doubled....

Bob

customcutter · « **Reply #161 on:** August 31, 2016, 11:47:56 AM »

Quote from: Hobbyman2007 on August 21, 2016, 10:32:50 AM

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 .

Does this mean that the "stock" barrel on the BT65 .25 cal is a 1:17.22 twist? Is it the same bore as Owen's barrel? Mine is a QE model, so I'm assuming it's a choked barrel. What does that do to the accuracy/energy? How many shots would the BT65 get when tuned to approx 100fpe? Very interested in this mold.

thanks,
Ken

Hobbyman2007 · « **Reply #162 on:** August 31, 2016, 12:02:51 PM »

The Hatsans BT65 and AT44 use the same twist as the Lothar Walter barrels . I have a LW barrel on my BT65 that I have confirmed to be 17.2:1 twist with the choke removed . As far as shot count goes a full mag of 9 shots should be possible . Of course it depends on how you've tuned the rifle . I've found the BT to be more efficient than the AT at stock power levels , I believe that is due to the hammer rebound device design.

rsterne · « **Reply #163 on:** August 31, 2016, 02:10:09 PM »

Using 34 gr. JSB Heavies in my AT44 Long, which has a 230 cc reservoir, I get 12 shots within 4% ES, with the best 9 within 2% ES, and that is at 70 FPE, at an efficiency of 1.15 FPE/CI.... The BT65 has a 280 cc reservoir, but I think you might be hard pressed to keep that efficiency at 100 FPE.... With the larger reservoir, you should be able to get about the same shot count I did at about 85 FPE (with 43 gr. Eunjins, for example).... At 100 FPE with a 51 gr. bullet, I think 9 shots might be difficult, but not impossible.... The ES would be the question over that long a string....

Bob

customcutter · « **Reply #164 on:** August 31, 2016, 10:37:52 PM »

Bob,

There is another thread where someone asked about .25 cal guns able to produce 100fpe+. You had commented in that thread on the bore in my BT65, but have removed the comments. Do you know the diameter of the Hatsan .25 cal barrels bore? Just trying to figure out which mold I need if I decide to go in this direction. I have 100+ lbs of lead and some casting equipment, just never done any real casting yet.

thanks,
Ken

rsterne · « **Reply #165 on:** August 31, 2016, 11:02:58 PM »

I think you will find that the Hatsan barrel is about 0.254" groove, like the LW barrels.... I know that my as cast 51 gr. BBTs, which measures 0.2535" at the drive band, did not get any marks on the drive band from the groove portion of the rifling, although the lands were deeply engraved on a bullet chambered and then pushed back out the breech.... There was "some" resistance to closing the side lever, which led me to believe that if you bought the larger size mould (0.253/0.255") you might have to massage the chamber by tapering the leade or they would be difficult to chamber.... Which size would shoot more accurately, and at what precise diameter, I do not know.... My .25 cal Long isn't tuned for a 51 gr. bullet.... I do have the 41 gr. BBT mould on order, though, in .253/.255 and I hope it will be just the ticket in that gun....

Bob

customcutter · « **Reply #166 on:** September 01, 2016, 12:09:14 AM »

Yes, I saw the mold for the 41gr boolits, but I haven't seen any groups that anyone is shooting with it. I also saw in a thread where you had mentioned milling a few thousandths off of the back of the 51 grain, so that it would throw a 45-48gr boolit. That may be an option for me as well. I don't know if I want to try making a D-reamer to make my own mold. I did make one for casting .22 50gr. slugs for swaging .223 bullets.

thanks,
Ken

owen · « **Reply #167 on:** September 02, 2016, 10:18:13 PM »

A few days ago my airgun's grouping at 50 yards, shooting the 51 FNs sized with the .254" bushing, they measure .25385" approx., opened up to 1.5". I spent the last few evenings trying to get to the bottom of the problem. This evening I used a bronze brush to clear the bore, sized a bunch of bullets with the .255" bushing and the gun now is shooting 1/4" to 3/8" groups, 3-shots at 50 yards, again. All of the bullets that I sized with the .254" bushing were dumped into a can of scrap lead, to be recast at a later time. It did work for a while, but now that is over. As Doug suggested, I may also resize the .254" bushing to size a couple of ten thousands under bore diameter. Also, I worked on my new valve stem some more and with it in the gun the .255" sized, 52.77777778gr 51FN BBTs are now averaging 978fps for an average of 112.12fpe.

Hobbyman2007 · « **Reply #168 on:** September 02, 2016, 10:25:16 PM »

I've got the same barrel measurements as Bob if not slightly over. This is a BT65 stock barrel.

aceflier · « **Reply #169 on:** September 02, 2016, 10:58:35 PM »

Dang Owen that thing is hitting hard!

customcutter · « **Reply #170 on:** September 02, 2016, 11:01:17 PM »

Owen, did you by any chance try the .254's after cleaning the barrel?

rsterne · « **Reply #171 on:** September 03, 2016, 01:02:57 AM »

The 41 gr. molds are not made yet, so it would be difficult to see any shooting results.... I understand the Last Call on that Group Buy is about to end and the are going to go on the Mill....

Bob

customcutter · « **Reply #172 on:** September 03, 2016, 09:41:58 AM »

That would definitely explain why not shooting results. LOL! Looking forward to great results!

owen · « **Reply #173 on:** September 04, 2016, 01:00:17 AM »

I finally got around to measuring the .255" sized bullet's drive band. It measures .25480", which is exactly .0002" under my bore diameter and is also what Doug says that he sizes his bullets to. I tried to shoot a 5-shot, 50-yard group, today. The first 4-shots went into a single hole, probably 3/16" ctc as the hole was about 3/8" diameter. The center of the 5th shot's hole was 1/2" to the right of the edge of the first 4-shots. I took a 6th shot and it landed about 3/8" to the left of the first 4-shots and about 1/8" high. So I called it a day. This evening I removed the tank and moderator and thoroughly cleaned the barrel with a bronze bore brush, loaded with Hoppes no.9, then another bronze bore brush loaded with JB compound. Wiped out the JB compound, then bronze brushed with Hoppes no.9, again. Pulled patches until they came out clean, then finally I pulled the brushless bore snake through the bore. Hopefully this restores the accuracy that I enjoyed, before I, probably, leaded up the bore shooting such undersize (.25385") bullets through for a short while.

owen · « **Reply #174 on:** September 08, 2016, 08:36:51 PM »

Bob, I had to rezero with a new set of rings, I broke the rear ring of my other set, so here's an image of the last 3-shots that I shot at the 50 yard target, this evening, not zeroed yet:

This is typical of how the NOE 51-FN BBT's are shooting from this LW 1-17.22" twist barrel, at 965-980 fps. Is it possible that the 1-14" TJ's .25-Auto liner could stabilize a heavier 63-67 grain bullet well, at airgun velocities of 1000-1050 fps? If so, is it possible that you'll design something like that in the future?

nielsenammo · « **Reply #175 on:** September 08, 2016, 08:59:47 PM »

Does anyone have any 100 yard groups with these bullets? 50 yards is OK but many bullets are accurate at 50 but are not at 100. I would really like to see these at 100 yards. I will offer this bullet if it can shown to accurate at longer ranges.

customcutter · « **Reply #176 on:** September 08, 2016, 10:00:35 PM »

Quote from: owen on September 08, 2016, 08:36:51 PM

Bob, I had to rezero with a new set of rings, I broke the rear ring of my other set, so here's an image of the last 3-shots that I shot at the 50 yard target, this evening, not zeroed yet:

This is typical of how the NOE 51-FN BBT's are shooting from this LW 1-17.22" twist barrel, at 965-980 fps. Is it possible that the 1-14" TJ's .25-Auto liner could stabilize a heavier 63-67 grain bullet well, at airgun velocities of 1000-1050 fps? If so, is it possible that you'll design something like that in the future?

Correct me if I am wrong but wouldn't you have to be pushing 140-150fpe to push a cast boolit of that weight at that speed???

Hobbyman2007 · « **Reply #177 on:** September 08, 2016, 10:00:36 PM »

Quote from: owen on September 08, 2016, 08:36:51 PM

Bob, I had to rezero with a new set of rings, I broke the rear ring of my other set, so here's an image of the last 3-shots that I shot at the 50 yard target, this evening, not zeroed yet:

This is typical of how the NOE 51-FN BBT's are shooting from this LW 1-17.22" twist barrel, at 965-980 fps. Is it possible that the 1-14" TJ's .25-Auto liner could stabilize a heavier 63-67 grain bullet well, at airgun velocities of 1000-1050 fps? If so, is it possible that you'll design something like that in the future?

Bloody fantastic shooting. i can't shoot JSB's that tight at fifty even on a good day . I should probably lay off the coffee .

rsterne · « **Reply #178 on:** September 08, 2016, 10:47:27 PM »

I have designed several heavier BBTs, but they are designed for .257 cal barrels, not airgun barrels.... Once you cross the 100 FPE area, and are looking at 65 gr. and heavier bullets, everyone seems to want to go for the .257 cal.... There is a TJ's .257 barrel available with a 14" twist (for the 25-20) and the most popular bullet for it is the Lyman 257420, which drops at about 73 gr. in pure lead.... It is also available from Arsenal Molds as a boattail version at a couple of grains less.... I have several BBT designs at NOE, the 65 gr. and 78 gr. are both in Group Buys at present.... http://noebulletmolds.com/smf/index.php/board,26.0.html .... The 65 gr. is intended for the 14" twist.... My suggestion is that if you are contemplating a heavier bullet and higher FPE that you go for a .257 cal barrel, because of the much wider range of bullets available....

Bob

owen · « **Reply #179 on:** September 09, 2016, 12:39:41 AM »

@customcutter Yes and I figured up to 165 fpe. The Airforce platform, which is what I'm using, has been taken up to, at least, 500 fpe.

@Hobbyman2007 I usually take a cup of coffee with me to the bench, to drink before I begin shooting.

@rsterne Thank you, very much, for taking the time to let me know all of that information. That's probably the way to go, for sure.

Thank you to our advertisers!

.25 cal 51 gr. NOE Bob's Boattails

Author Topic: .25 cal 51 gr. NOE Bob's Boattails (Read 43043 times))