20" 1:10 barrel in 308. Heaviest reasonable bullet=???

[willcombs]

I'm trying to get an idea of what's the heaviest bullet I can load.

I have a 10FCP in 308win with a 20" fluted barrel, 1:10 twist.

Shooting factory stuff was.. eh, I dunno. On good days, I've shot .25-MOA groups at 100yds with Federal Gold Medal Match 175s, so I know it's definitely a very capable rifle.
I've learned that it doesn't like anything less than 168 though. Just kinda projectile-vomits them downrange, and precision on target is anybody's guess. The 147gr M80 milsurp stuff is good for blowing up watermelons, that's it. That stuff shoots a lot better through my M1A than my Savage. And the 150/155gr zone isn't much better. Things start to come together at 168, (seem to) flourish at 175, but I've never shot any factory ammo heavier than 175gr.

I just got into reloading a couple months ago and I started out with my first batch being Sierra 175gr MatchKing BTHP's. They worked great, and if that was the heaviest I should go then I'll be plenty satisfied with that. But I'm trying to get a better idea of how far I can (safely) go.

In my Lyman reloading manual, in the 308Win data section, the heaviest bullet listed is the Sierra 200gr MatchKing.
I've combed through the bullet offerings from some of the major bullet manufacturers and the heaviest 30cal bullet I can find is the Seirra 240gr MatchKing. My guess is that this is for rounds like .300WM or .300RUM, but I was wondering if anybody knew approximately where to draw the line for a 20" 1:10 barrel. I've found some rough-idea information, but there was never consideration for barrel length. The very few places where I did find information, either (a) had NO data on what barrel length was used for testing, or (b) used a barrel way longer than mine like 26" for example.

Any help is appreciated! Thanks yall :)

[LoneWolf]

Depends on how far your shooting and how much velocity you need to be efficient at what you're trying to do. A lot of guys use the 220gr and heavier bullets for subsonic loads, but if you need to reach out with a 308 the 175-185 class is pretty stellar with a 20" barrel. I haven't shot anything heavier then 175-178gr stuff through my 26" barrel, so I'm only speaking of what I've read from others here. What are you trying to accomplish?

[willcombs]

This is my target/precision rifle.
What I need it to do is perform out to 600yds, since that's the furthest range I know of in the area. On my M1A with irons, 600 feels kinda far, but this one with optics, 600 is not extraordinary.
What I want it to do is perform out to 1000. Further, should the opportunity present itself.
The bullet doesn't need to deliver lethal energy that far out, just put a hole in some paper or make a thump on steel.
Sorry for not saying so right up front. Should've been able to anticipate that query.

[LoneWolf]

For 600yds the 168gr is real nice, I find they start to get a little more sporatic around 700 though, the 175's have been my cup of tea for both long range steel and 1000yds F-Class. I also picked up some 178gr OTM's to play with, but I'm still deployed so haven't been shooting for a few months. When I get back I'll have an 18" barrel to play with along with the 26". Only thing you lose with a 20" barrel is velocity which will require a larger adjustment for windage down range, so pushing the 308 out passed 1000 is much trickier than other calibers. I would probably run 175's and no heavier than 185's. You're going to be down in the 2400-2500 range in velocity at that point unless you're pushing a hot load. I get 2700 FPS out of a 26" 10 twist using 175SMK's with 44gr of IMR 4064 and a CCI #200 primer out of Lake City brass.

[willcombs]

I don't wanna have to develop loads for multiple bullets unless it's necessary, so I just went with 175's out of the gate. Never bothered with the 168's.

I figured my short-ish barrel length would limit me to some extent with how heavy I could go. I don't expect that I've got enough barrel to stabilize the 200gr SMK's even with a 1:10 twist, but I was thinking about maybe trying the 190gr SMK's. You think maybe not even those would be wise with a 20" bbl though huh? Interesting. I was interested in going as heavy as possible to see if higher BC's could offset the lower velocities, but now that I take a closer look at it, the velocities drop a lot faster than the BC's rise, so the optimal solution has got to be in the middleground somewhere. But you're telling me I'm basically limited to 185....

At the velocities I'll be seeing, the 175 SMK's and the 180 SMK's have the same BCs, and their SDs don't even matter in my application so the 180 loses that advantage. The 175 holds its BC for longer than the 180 so it doesn't start losing performance until after the 180.
Looks like maybe where I started is where I should stay, huh? lol. I guess I'll just play with charge weights and find a good velocity then. I also use IMR-4064 and CCI primers, but Hornady brass. My LC brass gets saved for M1A use.

Stay safe out there man. Well, "safe" is relative, and nobody signs up with safety very high up on the list of priorities, but you get the point. :-P I got out of the Marines in 2011 and never even got deployed. Kinda bummed/kinda glad I never got sent. Mixed feelings on it. But yeah ok back on topic...

I use a 1-4X optic on this rifle and it works just fine out to about 600yds. 700 is doable in good light, but beyond 700, the dot in my reticle covers up a lot of the target and precision degrades rapidly. What kind of magnification would you, as a 1000yd shooter, recommend?

[BoilerUP]

1:10?

230 Hybrids, if ya wanted to.

I'd give 208 Amax or HPBT a try, but would think 185 Juggernauts would work great.

[LoneWolf]

I run a Fixed 12XSWFA SS. 10X is perfect though for most cases.

[LoneWolf]

When your velocity is as low as it'd be with those heavy bullet it starts to defeat the purpose of the high BC bullet. velocity does effect the BC rating of a bullet.

[willcombs]

That's about what I expected, it's consistent with the other stuff I've heard from other 1000yd shooters. I figured I'd probably upgrade my glass to the fixed 10x SS before deciding whether or not to drop some major coin for a super-mega-deluxe-ultra-premium-type scope.

[LoneWolf]

That's what I have done in the last year. Go with one of the Mil/Mil versions. it's a very solid scope line in that price range.

[willcombs]

That's the plan 8-)

[darkker]

As BoilerUp said, shoot anything you want to.

Here is some physics for you, regarding your question.

Bullet WEIGHT is essentially irrelevant when it comes to stability. Stability is determined by rotational stabilization, which is a fancy term for RPM. The important thing for stability based upon RPM is the bullet LENGTH.
MV * 720 / twist = RPM
Here is a link to JBM's stability calc, use the list on the left to look-up the bullet length, and fill in the blanks. It will give you an IDEA of whether or not the bullet will be stable at launch:
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

The bullet will "gain" stability the farther it travels, as velocity decays VERY quickly(drag), whereas rotational decay happens very slowly. Another thing to consider is the BC numbers. They change with velocity, that is why Sierra lists stepped numbers. People that don't list the multiple numbers, typically only calculate, or average the number; which isn't all that helpful for dialing your dope. Consider a GOOD ballistic calc for use on the range, or to *see* what the different bullets will do over the course of flight. I personally use "Shooter" by Sean Kennedy, but am sure there are other decent ones out there. For super-sonic flight I have shooter use the G7 ratings on my SMK's, but if I'm crossing, the G1 proves to be more accurate. Litz himself admits G7 is not very good if you cross.

The next trick shouldn't apply to you at that distance, BUT your atmosphere will determine that. Trans-sonic survival. The old 168gr SMK was infamous for causing people problems at Camp Perry a very long time ago.
This came from 2 primary reasons.
#1) Tail angle. It had a stupid 13 degree tail angle, that angle gave it a very sexy high BC(G1)number, but ensured that it wouldn't cross trans-sonic, and go subsonic and stay point forward. Dr. Robert McCoy did some VERY good work on trans-sonic survival, and found the happy compromise between great BC, and survival was approx. 9 degree tail angle.
#2) CP/CG. Basically the center of Pressure(the tip of the bullet) and the center of Gravity was too far apart. With it's very long beak, in relation to where it's mass was, as the trans-sonic point came and the turbulance hit, it caused the over-turning momentum to cause the bullet to tumble.

Out of that problem with the 168 SMK, is precisely where the 175gr SMK came from. Sierra worked VERY closely with the military and did a boatload of testing to prove reliable crossing over and over. In the 30-cals, I have had some(now older) Bergers that would not cross safely. This only matters to you, *IF* you are trying to cross into Sub-sonic; at any distance.

Without knowing Your air, and aversion to recoil... MOST folks choose a 150-155gr bullet for that distance, OR try and launch it at VERY high velocities to keep it supersonic.

As far as the optics go, that REALLY depends upon your personal goals. CAN you shoot to 700 with a 4X? Sure you can, you will have large groups, but can ring a gong if you do your part.
Here is a thread I did after a visit down south last fall:
http://www.shootersforum.com/rifles-rifle-cartridges/88314-meanwhile-valley-sun.html
I was clanging past 1,000 with a crappy 3-9, and using hold-over. I am a better shooter than most, but those groups wouldn't win any competition.

Painless(my 10fp in 308) that I shoot very long distance(been grouping at a mile) uses a 5-15X. Unlike many scopes, it has a pile of adjustment, and is a true Mil/Mil FFP. I personally HATE MOA, but that is a chocolate/vanilla debate.

[Bach]

The heaviest I've tried in my 1 in 10 has been 208 amax. They shot fine but I settled on Hornady 178BTHPs as my 1000yd bullet. Good BC and with 48.1g of 2000MR it flies at 2824fps with 26" barrel. With 20" you should be able to get 2700-2725fps np.

Second heaviest I've tried was 185 Juggernauts. I really liked those but I havent been able to find them anywhere and they are $20 more per 100 than the Hornady 178s.

[willcombs]

Darkker : wow! Thanks for all that information man. I know that bullet weight isn't the best indicator of stability. I read an article once about how to measure bearing surface and so forth but I don't have the equipment for that. Misguided as it may be, the bullet weight rule of thumb works well enough, so that's what I do. Gets 'er dun.
I'm fine with recoil, as most of it can be dealt with just fine with good fundamentals and positioning.
I prefer mil/mil also but know the math just fine for moa's lol so my 1-4 moa/map scope has worked fine up to this point. Once I upgrade I plan to just transplant this scope onto my M1A since the scope and the rifle have about the same maximum accurate ranges.
Where did you learn all that stuff? I'd like to thumb through some of that literature myself :-)

[darkker]

McCoy's work:
http://www.amazon.com/gp/product/0764307207/ref=as_li_ss_tl?ie=UTF8&tag=bison0b-20&linkCode=as2&camp=217145&creative=399349&creativeASIN=0764307207

Litz:
http://www.amazon.com/Applied-Ballistics-Long-Range-Shooting-Understanding-ebook/dp/B00KRJXVZU/ref=sr_1_1?s=books&ie=UTF8&qid=1403335096&sr=1-1&keywords=Brian+litz

Growing up with a library card in a tiny town has side effects :cool:

[390fe]

I've shot 220 grain smk's from my Model 11's 20 inch 1:10 twist barrel. They were great out to 500 meters, but my range doesn't go further.

[emtrescue6]

The 10FCP in 308 comes with a 24" barrel, no? At least mine did... (or did you swap the out the factory barrel?)

Anyway, my 10FLCP-K (the lefty version) really likes the 168g Nosler Custom Competitions...so far I have seen MOA or better out to 600 with them when I do my job.

[CharlieNC]

I ran many cases through JBM across a wide range of calibers, weights, BC, and velocities. An interesting finding is the Max Supersonic Range = G1BC x Muzzle Velocity! The true answer is affected greatly by altitude, but to just compare different options this tells you which is better as a first pass cut.

[rjtfroggy]

[QUOTE=emtrescue6;268109]The 10FCP in 308 comes with a 24" barrel, no? At least mine did... (or did you swap the out the factory barrel?)

Actually Savage had the 20" bull on the LE models for a while(maybe others).I have three of them a 223,308 & a 7mm rem. mag.
My 308 likes the 150gr. pushed by IMR 4895. It is about a .6-.7 five shot @100 and around .95 @200 never shot any further, the 223 shoots in the .3's some times better and the 7mag stays about an inch @200 and the only powder I have or use is IMR4895.
You can find an accurate load for just about anything Savage.