Author Topic: Two new .308 cal Bob's Boattails (Read 7051 times))

rsterne · « **on:** July 29, 2014, 05:52:07 PM »

I have received some interest in heavier bullets in .308 cal, so I have submitted the following two rebated boattail designs to Tom at Accurate Molds for him to include in his online catalogue....

The 95 gr. is a stretched version of the 79 gr.... while the 111 gr. design uses a longer 1.5 R Ogive.... All three share the same boattail design....

The designed twist rate is shown, but of course a faster twist is OK.... The LW barrel is a 450 mm (17.7") twist, so they would be fine in that, providing you get the one that is 0.300" land and 0.308" groove diameter.... These two bullets, plus the existing 79 gr. (#31-079A) give the shooter the choice of three weights which should cover their needs for any PCP up to at least 3000 psi.... including rifles like the DAQ Exile....

I will let you know when the designs are in Tom's catalogue and the molds are available to be ordered through Accurate....

Bob

rsterne · « **Reply #1 on:** July 30, 2014, 04:00:11 PM »

These are now in Tom's catalogue as #31-095A and #31-110A....

http://accuratemolds.com/bullet_detail.php?bullet=31-095A-D.png

http://accuratemolds.com/bullet_detail.php?bullet=31-110A-D.png

Bob

sixshootertexan · « **Reply #2 on:** August 20, 2014, 12:01:03 AM »

How would you go about ordering a LW barrel with the .308 groove?

rsterne · « **Reply #3 on:** August 20, 2014, 12:45:45 AM »

Contact LW and ask them what they have.... The one I got a couple of years ago was 0.308" groove.... but I have heard they now have a smaller one.... Only asking them directly would clarify....

Bob

sixshootertexan · « **Reply #4 on:** August 20, 2014, 01:07:03 AM »

Their website says it's .298/.306. If I order the 111gr bullet mold can I just get it in .306 to match that barrel?

rsterne · « **Reply #5 on:** August 20, 2014, 02:46:09 AM »

Yes, absolutely.... I would wait until you get the barrel and slug it first to check it....

Bob

sixshootertexan · « **Reply #6 on:** August 20, 2014, 10:12:42 PM »

Will definitely get the barrel first. If the barrel is .306 what size should i get the mold .306, .307 or .305?

Thanks

Tommy · « **Reply #7 on:** August 20, 2014, 10:20:07 PM »

Will there be a boattail in .22
Tommy

rsterne · « **Reply #8 on:** August 20, 2014, 10:28:09 PM »

I would likely get it at 0.306" and hope I don't have to size it.... Some guys would get 0.307" and a custom sizing die at 0.306"....

Tommy, I already have a drawing for a 41 gr. in .224 cal, basically a skinny version of the .25 cal 52 gr.... The problem is that you will need a 12" or faster twist for it....

Bob

sixshootertexan · « **Reply #9 on:** August 29, 2014, 10:58:59 PM »

What's the fastest twist rate the 110gr can handle?

rsterne · « **Reply #10 on:** August 30, 2014, 12:26:50 AM »

Faster twist is not generally an issue, certainly a 16" twist is not a problem at all.... It would probably shoot fine in a PB barrel with a 10-12" twist, providing you did a good job of casting with no wrinkles or voids.... The faster you spin a bullet, the more it will emphasize any imperfections.... I've used 100 gr. jacketed bullets in a .308 Winchester PB (10" twist) at low (subsonic) velocity for Grouse loads and got sub-2" groups at 100 yards....

Bob

sixshootertexan · « **Reply #11 on:** August 30, 2014, 12:41:53 AM »

If I got the calculator right it says for a 12" twist the stability factor is 3.4 @1000fps and 4 @ around 800fps. I don't know how far off the 1.5 you can go before it's to unstable.

I'm looking at the Green Mountain barrel for $100.

http://www.gmriflebarrel.com/308-caliber-1-12-twist-chrome-moly-barrel-blank/

rsterne · « **Reply #12 on:** August 30, 2014, 01:16:39 AM »

Anything over 3.5 to 4.0 can produce an increase in group size due to an out of balance bullet starting to wobble.... the Military use an SF of 1.5 - 2.5 and that covers the "best" range.... If the bullets are near perfect, a 12" twist should work, but I would prefer a faster one.... TJ's have liners in 10", 20", and 26".... and may have something in between, you would have to call Mike to ask....

Bob

dyotat100 · « **Reply #13 on:** August 30, 2014, 09:53:26 AM »

TJ's has the 1-14 the I had made. Works good for me and I shoot 116-158 gr. 990's for the the 116 gr and 890's for the 158 gr.

PakProtector · « **Reply #14 on:** August 30, 2014, 09:59:44 AM »

Quote from: dyotat100 on August 30, 2014, 09:53:26 AM

TJ's has the 1-14 the I had made. Works good for me and I shoot 116-158 gr. 990's for the the 116 gr and 890's for the 158 gr.

Sounds like a plan Doug; the next build I undertake will be a 30 cal and almost certainly run that barrel...

cheers,
Douglas

sixshootertexan · « **Reply #15 on:** August 30, 2014, 12:45:01 PM »

Ok for now the barrel options that I have found for the 110gr is the LW (.306- 1:16 twist) and TJ liner (.308- 1:14 twist).

rsterne · « **Reply #16 on:** August 30, 2014, 01:35:21 PM »

The 16" twist has an SF of about 1.6 at Mach 1, 2.0 at ~950 fps, and 2.5 at ~500 fps.... With a 14" twist that becomes 2.1 at Mach 1, 2.6 at 950, and 3.3 at 500.... Based solely on twist rate I would choose the LW barrel, but the 0.308" TJ's will allow you to use many different .308 cal bullets without getting a custom sizing die made for the 0.306" LW.... For flat based bullets, an even slower twist (eg. 1 in 20) would be better.... In a 20" twist, the 111 gr. BBT has a theoretical SF of 1.0 (unstable) at Mach 1, 1.3 at ~950 fps (just fine), and 1.6 at ~ 500 fps.... so the 20" TJ's would work fine up to about 1000 fps.... and be a great barrel for flat based, 0.308" cal bullets.... Unless you have a real powerhouse, I would consider the 1 in 20" TJ's....

Bob

sixshootertexan · « **Reply #17 on:** August 30, 2014, 04:32:58 PM »

Ok so the TJ 1:20 barrel is a third option. My target is 800-1000fps with the 110gr. I'm leaning more to TJ because of the off the shelf sizing dies and being able to choose a more wide variety of cast bullets.

Thanks Bob for you help.

rsterne · « **Reply #18 on:** August 30, 2014, 04:43:25 PM »

My DAQ shot about 185 FPE at 3000 psi with 118 gr. bullets (835 fps), so pushing the 111 gr. fast enough to go unstable in a 20" barrel will require a pretty stout PCP.... likely over a 24" barrel and/or over 3000 psi.... With that in mind, the 20" twist may well be ideal for you....

Bob

Fur-n-dirt · « **Reply #19 on:** September 27, 2014, 01:48:29 PM »

Bob, I'm going to seriously consider this for the extreme!

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Two new .308 cal Bob's Boattails

Author Topic: Two new .308 cal Bob's Boattails (Read 7051 times))