GTA
Airguns by Make and Model => AirForce Airguns => Topic started by: Steelhead on March 15, 2019, 07:25:31 PM
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I had the most successful shooting session yet with the .308 Texan. I got amazing results with side-by-side comparisons. Some I expected, some exceeded expectations, and others performed below expectations.
My best 4 shot groups were 1" at 100 yards and 1 7/8" at 200 yards.
The bullets I used were NOE 134 BBT flat nose (sized .309 and .308), NOE 154 BBT flat nose (sized .308 and .309), Lee's 113 flat nose gas check (sized .309), and Lee's 150 flat nose gas check (.309 and .308).
The 134 BBT is hands down the cream of the crop. Super tight groups at all ranges and just a great performing bullet. 1" at 100 yards and 2" to 3" at 200 yards. It's absolutely my number one go-to for all things accuracy and hunting related. The surprise for a very close second place is the Lee's 150 fngc. That bullet is a tack driver and hundred yard groups were in the 1" range. At 200 yards it started to open up a bit to around 4" average for four shots.
I had slightly better groups with .309 sized bullets vs. .308 but not a marked difference.
The surprise was the lack of performance from the 154 BBT's. Based on the 134's you'd think that the big brother would work well, but the Lee's 150 was consistently tighter and more accurate. The Lee's 113's were shotgunning and I'm not really into forcing them to work so that mould is going on the shelf.
I did not bother with the chronometer since I was switching back and forth between 100 and 200 yards and didn't want to keep moving it. I've pretty much narrowed that down anyway (920's with 134's and 880's with 150's) Power setting was on full and at 3000 psi reg'd.
I don't think that it's a coincidence that sorting bullets makes a difference. Until I can get to the stage where I'm casting at very consistent weights I'm going to have to keep doing it. I kept everything between 133.6 and 134.5 and 152.6 to 153.5, and tossed the rest (almost half) back into the pot. I sorted the 113's too, but it didn't matter. They just didn't group well at all.
I'm just happy that I have two bullets (with moulds) that perform exceptionally well. It's been a long journey to find real consistency with all of the choices of .30 cal ammo available.
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Did you get the 134 with HP option? Curious if the HP's are just as accurate as the solid nose.
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I wanted it, but they (NOE) are out of stock and have no current plans to make more HP versions of that mould.
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I understand that the .308 Texan is a 14" twist.... Here are the Kolbe Twist and Stability graphs for both BBTs....
Optimum Twist for 134 gr. for SF = 1.5
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/135%20BBT_zpsgpx1kcif.png) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/135%20BBT_zpsgpx1kcif.png.html)
Stability Factor for 134 gr. in 14" twist
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/135%20BBT%2014in_zpsbdkoaklj.png) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/135%20BBT%2014in_zpsbdkoaklj.png.html)
Optimum Twist for 154 gr. for SF = 1.5
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/154%20BBT_zpsptaqbydn.png) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/154%20BBT_zpsptaqbydn.png.html)
Stability Factor for 154 gr. in 14" Twist
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/154%20BBT%2014in_zpslkzbpnsh.png) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/154%20BBT%2014in_zpslkzbpnsh.png.html)
The 134 gr. BBT has an optimum twist of 14" at 900 fps, and in a 14" twist the SF = 1.3 at about 1030 fps.... a great match for the Texan....
The 154 gr. BBT has an optimum twist of 12" at 900 fps, and in a 14" twist the SF = 1.1 (marginal) at 850 fps, and unstable above 950 fps....
So it's not too surprising that the longer BBT doesn't work in your Texan....
Based on approximate measurements of the Lee 150 F taken from my screen.... The Kolbe Twist calculator says the optimum twist is about 15", so a 14" would be no problem for that.... On the other hand, the 115 gr. Lee would prefer a 22" twist....
Bob
PS, NOE still have one 2-cavity mould with a HP in 1 cavity, in brass only, for the 135 gr. BBT....
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That's awesome, Bob. When it comes to the science I'm completely behind the curve. However, seeing someone take the reality that the paper is showing and apply the science to confirm it is amazing. Thank you for doing that and reaffirming that what I'm seeing on the paper is making sense.
I know there are guys here like you who are much better marksman and tuners than myself. That being said, I like posting my progress like this so that maybe it helps someone new just getting into it. Saving someone else the headaches, money, lost time, money, confusing of who to believe, money, etc. would be anice way ofgiving back for the info I've received. I'm the prototype for the typical yahoo wanting to get into big bore and if I can get satisfactory results, anyone can.
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Kevin
You found the right slugs for the 308 Texan.
Sounds like your ready for turkeys this sprimg season.