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Old 03-15-2017, 12:31 AM
growr growr is offline
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Default .308 loading

Quote:
Originally Posted by BB57 View Post
A few thoughts:

1) A lot depends on the how far you want to shoot.

The 168 gr SMK for example is an excellent bullet at the 600 yard line, however in the rather under powered M852 loading (2550 fps) it goes subsonic around 825 yards and it's transonic around 750 yards. Unfortunately, due to the angle of the boat tail on the 168 gr SMK, it does not transition to sub sonic flight all that well, and the resulting instability as it transitions has a negative impact on accuracy beyond 800 yards.

That's where the 175 gr SMK and some of the more modern VLD bullets come into their own. These slicker designs also start out slower but retain more velocity down range, so despite the extra weight it's still a win-win in for a .308.

For ranges under 750-800 yards the 168 gr SMK is fine, even at M852 velocities. And if you have a 26" barrel you can get 2700 fps out of it. You can also get 2650 fps out of a 22-24" barrel, and that extra 100 fps makes a significant difference. At 2650 fps it will stay supersonic out to 1050 yards.

I have from time to time bought Mil-spec's copies of the M852 and M118 (173 gr BTFMJ) projectiles, but I do so knowing what I'm getting into. Sierra 168 gr SMKs will vary maybe .1 grain from 168 grains from bullet to bullet, while the Milspec bullets, will vary by .5 or .6 grain from bullet to bullet, and will vary from the advertised weight by as much as 2 grains.

That's basically what I saw with issued M118 ammo after Lake City's tooling for the 173 gr BTFMJ got worn.

So you can save a little (and sometimes a lot) of money with them, but you'll have to hand sort them by weight and then adjust the loads to get the target velocity for each weight range, and keep them separated if you want optimum accuracy. Mostly it isn't worth the trouble unless SMKs are in short supply.

2) Consistency in velocity matters.

Standard deviation in velocity isn't a big deal at short ranges (400 yards or less), but it starts to be a major factor at long ranges. For my long range .308 loads I shoot for an SD of 10 fps and while I'll live with an accurate load with an SD of 15, I'll reject any old with an SD higher than 15 fps.

In short, 67% of the bullet fired will have velocities +/- 1 SD, so if the average velocity is 2600 fps and the SD is 10 fps, it means 67 out of 100 rounds will have a velocity between 2590 and 2610 fps. 95% of the rounds will fall between +/-2 SD, so in other words 13 or 14 out of 100 rounds will have velocities between 2610 and 2620 fps and 13 or 14 out of 100 rounds will have a velocity between 2580 and 2590 fps. For all practical purposes all the rounds will fall within +/- 3 SD, so int his example you'll end up with 2-3 rounds with velocities of 2570-2580 fps and 2 or 3 more with velocities that fall between 2620 and 2630 fps.

So that 10 fps SD creates an extreme spread of about 60 fps. That means if your SD is 20, your extreme spread is now 120 fps, and with an SD of 30 it's now 180 fps. I've seen shooters who find a very accurate load that shoots wonderfully sub MOA groups at 100 yards but don't realize the impact of an SD of 45 fps - leading to an extreme spread of 270 fps and the effects it has on both horizontal and vertical dispersion at long range.

The moral here is to get a chronograph, learn how to use it, and then test you precision loads not just for group size but also for consistency in velocity.

3) A chronograph also does some other nifty things for you.

- It will allow you to see if the results you are actually getting are close to the results you expect to get based on the load data.

- It will give you accurate numbers to put in a ballistic app or Whiz Wheel, which will help you develop the ability to have a higher percentage of first shot hits at long range, rather than walking rounds on to a steel plate when shooting at long ranges.

- It will help you learn over time, the effects that temperature actually has on the velocity of your load in your rifle.

- It will let you see the actual differences that occur due to changing primer brand or type and the effects of things like uniforming flash holes, or neck sizing or partial resizing versus full length resizing.

- It will let you load for an actual velocity rather than just saying 42 grains of IMR 4895, and ignoring the fact that even canister grade IMR 4895 varies from lot to lot.

- It will let you identify the velocity in your rifle that produces the best barrel harmonics for maximum accuracy, and then develop a load that achieves this velocity.

4) Some people say you can't load precision ammo on a Dillon - they are right and wrong, as it depends.

Part of it depends on your definition of "precision" and what level of accuracy you are ok with. Personally, I'm happy with a 1 MOA load (as measured by 10 shot groups at 200 yards) that has an SD of 10 fps. Sure, a half MOA load is nice, and a 1/4 MOA load is really nice, but in the real world where wind estimation is still "estimation", that extra 1/2 or 3/4 MOA is not the limiting factor.

There have been times I've put in the time (and money) at the reloading bench turning a 1 MOA load into a 1/4 MOA load by uniforming flash holes, sorting case by volume, inside and outside turning necks for perfect concentricity, indexing the case from the chamber through the entire loading process, hand weighing powder and bullet, etc.

But mostly I put in less time at the bench loading more 1 MOA ammo so I can spend more time actually shooting. There is a point of diminishing returns in precision reloading and you need to find a point you are comfortable with.

There are some great third party tools for the Dillon 550B and I use billet tool heads and a clamp kit on all my rifle caliber tool heads, and I use a floating tool head for my precision calibers.

I also use a 3/4" powder measure adapter and a BR-30 powder measure on my precision rifle loads. Depending on the end use I may also hand weigh the charges, which doesn't take long on a 550B if you've got a electronic scale, a powder trickler and a funnel.

I will uniform the flash holes on new or once fired brass when I receive it, and trim it to minimum length, but I don't waste time cleaning primer pockets because my chronograph data has shown in makes absolutely zero differences in consistency. If it adds nothing, don't waste your time on it - but don't tell that to the companies that market "case prep centers" or the people that wasted money on them.

5) Powders and primers

Bench rest primers are nice, but whether you need to spend the extra money depends on whether you need it to get an acceptably small SD with a load.

IMR-4064 is my preferred .308 powder but that dates back to my M14/M1A Service rifle competition days.

IMR 4895 also works great and if you're shooting it in a .308 Garand it's a lot easier on the operating rod.

RL-15 is another excellent .308 powder, particularly with a 175 gr bullet.

6) Cleaning and barrel break in.

Not all barrels are the same. Hammer forged barrels have very smooth and very durable bore surfaces, but they must be perfectly stress relieved to prevent them from changing the point of impact as they heat up. Broach rifled barrels are also stressed in the process and must be properly stress relieved. They are also much rougher and benefit most from being hand lapped. Cut rifling induces the least stress but still benefits from hand lapping. In all cases, hand lapping can be used to create some "choke" near the muzzle which generally improves accuracy by helping the bullet exit more consistently.

The crown of the muzzle is also vital as any damage or un-evenness in the crown will cause gas to exit asymmetrically around the bullet at exit. That will induce yaw, and the resulting yaw in a spinning bullet create precession that take the bullet off its line of flight.

Similarly, you want to be kind to the throat in the chamber and avoid any asymmetric wear on the throat and the start of the rifling. It's throat erosion that eventually spells the doom of an accurate barrel and poor cleaning can accelerate the process.

On the other hand, you also want to break in a barrel to help iron out the rough spots and reduce the tendency of the barrel to accumulate copper fouling. That's a post all by itself. Do some internet research and you'll find a number of methods and opinions. But in general it will involve a process of shooting a small (and usually increasing) number of rounds and then cleaning for a specified protocol before you're done. And once done, you don't want to over clean the barrel, nor do to want to let copper fouling build up until accuracy falls off, so again it's a balancing act.

As a result you should clean from the breach whenever possible and you should use a bore guide. This helps ensure the cleaning rod is centered in the bore as it enters the throat to eliminate asymmetric wear, and it keeps cleaning solvents from dripping into the action and on to the bedding in the action.

If you've got a rifle that has been bedded, take it out of the action only as needed and for most rifles that means maybe once or twice a year - unless you've gotten it wet, etc. The more you take the action in and out of the stock the more wear you inflict on the bedding.

You also want to use a quality one piece cleaning rod that is close to the ore diameter. If the rod is too small it will flex and wear on the bore. If the rod has joints, those joints will wear on the rifling.

There is some debate about coated rods versus stainless steel rods. The "coated" advocates cite the soft coating won't harm the bore. The uncoated stainless rod folks point out that the rubber plastic coating on a coated rod can hold grit that can abrade the barrel.

Personally I like one piece stainless rods. If you use a coated rod, be sure to wipe it down with a clean cloth after each pass.

No precision shooter advocates aluminum or brass rods. They are too flexible and they are soft enough to hold grit so they have the worst traits of both coated and stainless rods. If you have an aluminum cleaning rod, just put the rifle down and walk away.

I put bore snakes in the same category. The have their uses, but those uses are strictly related to cleaning a barrel quickly in the field to remove sand, dirt, or other foreign matter that may have gotten there. They are probably not going to do much harm on a chrome bored 3 or 4 MOA service rifle, they have no real purpose with a precision rifle.

Great information from a fellow service rifle competitor! Are you a High Master? Distinguished? etc....

Randy

PS...I have worn out 4 barrels on my M1A (2 Douglas, 1 Krieger and the original which I think was also a Douglas) and am on my 5th which is an Obermeyer 5R SS and what an incredible performer it is! It even surpasses the Krieger....

Last edited by growr; 03-15-2017 at 12:42 AM. Reason: spelling
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