Sighting in a .308 rifle...

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Sighting in a .308 rifle...

Post by Neptune Glory » Fri May 29, 2015 2:11 pm

Hi everyone,

I recently purchased a Smith & Wesson M&P 10 rifle, which shoots .308 Winchester. It didn't come with it's own sights, so I also purchased (and just had mounted today) Magpul's Back Up Sight (MBUS for short) flip-up sights.

I read the instructions on how to sight them in, and watched a couple of Youtube videos about how to do it properly. My question for the Squad is: What range would you recommend sighting this rifle in at? 100 yards? 50 yards? 200 yards?

It's purpose at the moment is for target shooting, putting down a rabid (insert critter here) before it can hurt me or my family, and if the fit hits the shan in other ways (better imagined than described). Eventually, I intend to build it into a reasonable "Designated Marksman Rifle", at which point I'll primarily use the optic and the MBUS sights will just be there for back-up.

Thanks for the advice!
-Neptune
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Re: Sighting in a .308 rifle...

Post by 91Eunozs » Fri May 29, 2015 2:18 pm

Depends on how far you plan to typically shoot... For me here, I almost never take a shot past 150-200 yards due to brush, etc. so I typically sight in for a 100 yard zero with my preferred round and hold over as required (depending on the ammo I'm using at the time of course) for longer shots.

Sounds like a 100 yard zero would work for you as well... Especially if you're only using "iron" sights.
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Re: Sighting in a .308 rifle...

Post by Paladin1 » Fri May 29, 2015 3:56 pm

When I ran .308 I zero'd at 100yds. Little short for a round that is reliable out to 800yds-but in my anticipated use in SD scenario it would be extremely unlikely to take any shot over 200yds. IMO.

You can see from the chart below, that a 100yd zero could still put you on a man sized target out to 300yds.

This is from SniperCentral and may help guide your decision.

"The polymer tipped bullets are designed to expand rapidly, and lend themselves well to situations where over penetration is a concern, which for Law Enforcement can be quite often. We have included a HSM load using the Hornady 155gr Amax bullet which will deliver high energy with a bit less penetration which may work in these scenarios. Of course, extensive testing of any load should be conducted before adopting it as an agency standard.

F-168gr : Federal Gold Medal Match .308 Win 168gr HPBT (2600fps)
F-TBBC : Federal Premium .308 165gr Trophy Bonded Bear Claw (2700fps)
HSM Amax : HSM 308-12 308 Win 155gr AMAX Match (2875fps)
Bullet Drop (Inches)

50y(46m) 100y(91m) 200y(183m) 300y(275m)
F-168gr -0.1 Zero -4.5 -15.9
F-TBBC -0.1 Zero -4.3 -15.9
HSM Amax -0.2 Zero -3.4 -12.6"

Of course there are many, many loads out there and you may find a load your rifle likes best. But a 100-150yd zero would cover just about any situation your likely to encounter. YMMV.
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Re: Sighting in a .308 rifle...

Post by Doctorr Fabulous » Fri May 29, 2015 4:03 pm

Off the top of my head, your rifle will likely tend toward the 165-180gr stuff, but you may do just fine with the lighter bullets. For precision, zero where you're going to shoot. In general, I'd zero for maximum-point-blank.
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Re: Sighting in a .308 rifle...

Post by Hollis » Fri May 29, 2015 5:40 pm

What are you looking for? Target competition? Hunting? Kill those evil dirt clogs?

What ranges are you thinking about. Evil dirt clogs out at XXXXX Meters?
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Re: Sighting in a .308 rifle...

Post by Neptune Glory » Fri May 29, 2015 8:22 pm

Hollis wrote:What are you looking for? Target competition? Hunting? Kill those evil dirt clogs?

What ranges are you thinking about. Evil dirt clogs out at XXXXX Meters?
I'm mainly going to be target shooting with this thing. The free, unmanned outdoor range I go to now has a range of about 100 yards max, but I may upgrade to a better range one day.

If I'm shooting at something other than a target with this rifle, something is seriously wrong... but if that happens, it would be for a rabid dog or something, probably 100 yards maximum.
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Re: Sighting in a .308 rifle...

Post by Stercutus » Fri May 29, 2015 9:12 pm

In case the above posts were not clear the ammo selection is critical for the task and purpose of the rifle. Each specific type and weight will vary within it's tolerances and different types and weights will vary a lot, even at 100 yards. There could be as much as 8" difference with POI, especially with a gas gun.

The first thing you need to do is figure out what type of ammo you want to shoot based upon the roles you want it to fill.

Dogs can be pretty tough compared to a lot of game animals but most .308 rounds will take them with ease.
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Re: Sighting in a .308 rifle...

Post by Halfapint » Fri May 29, 2015 11:59 pm

I have the same irons (as I'm sure about everyone on here has) on my 5.56. They are as described "back up", I'd get a decent RDS. Even my cheap RDS I got off amazon (Bushnell something or other) at 100 yards I can hit within a paper plate on a man size target. I actually MUCH prefer the RDS over the MBUS (fun fact I keep deploy the front MBUS while using the Bushnell because it keeps me centered). But using the MBUS I can hit a man size target but not as accurately as I'd like, I counted 22 of 30 rds hitting the target at 100yrds where with the RDS I had 29 of 30 and the one stray was my own mistake because I coughed.

Mind you this is without a rest, I'm standing, crouching or generally not resting the gun on anything, except my extremities. I did all my testing as if I needed to use it in an offensive type scenario.
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Re: Sighting in a .308 rifle...

Post by Frank » Sat May 30, 2015 4:31 am

Rear MBUS only adjust for windage, not elevation. And I'll second that they are only useful as back ups for a primary optic.
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Re: Sighting in a .308 rifle...

Post by Stercutus » Sat May 30, 2015 7:21 am

Frank wrote:Rear MBUS only adjust for windage, not elevation. And I'll second that they are only useful as back ups for a primary optic.
That really depends upon the kind you have. Some adjust for elevation, some for range as well as windage. I prefer the type that adjust for range myself.
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Re: Sighting in a .308 rifle...

Post by Frank » Sat May 30, 2015 1:20 pm

Stercutus wrote:
Frank wrote:Rear MBUS only adjust for windage, not elevation. And I'll second that they are only useful as back ups for a primary optic.
That really depends upon the kind you have. Some adjust for elevation, some for range as well as windage. I prefer the type that adjust for range myself.
I was taking in regards to the Magpul backup sights (MBUS)
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Re: Sighting in a .308 rifle...

Post by Neptune Glory » Sun May 31, 2015 11:25 am

Frank wrote:Rear MBUS only adjust for windage, not elevation. And I'll second that they are only useful as back ups for a primary optic.
The two that I got, the front sight can be adjusted up and down for elevation, and the rear sight can be adjusted left to right. I agree than an optic would be much, much better than the MBUS system... but at the moment, I have other things that need the financial attention. With these, at least I can aim coarsely!
"When it comes to justifiable use of deadly force, you should seek to avoid confrontation, unless you have no choice and your life is on the line. This is easier to say than to do because it requires that you be calm and peace-loving throughout your life, but ready to use deadly force at any moment."

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Re: Sighting in a .308 rifle...

Post by Frank » Sun May 31, 2015 11:29 am

Neptune Glory wrote:
Frank wrote:Rear MBUS only adjust for windage, not elevation. And I'll second that they are only useful as back ups for a primary optic.
The two that I got, the front sight can be adjusted up and down for elevation, and the rear sight can be adjusted left to right. I agree than an optic would be much, much better than the MBUS system... but at the moment, I have other things that need the financial attention. With these, at least I can aim coarsely!
Sorry, I assumed that you had a front sight post for some reason :oops:

I have no experience with the magpul front sight
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Re: Sighting in a .308 rifle...

Post by RickOShea » Sun May 31, 2015 12:33 pm

Neptune Glory wrote:Hi everyone,

I recently purchased a Smith & Wesson M&P 10 rifle, which shoots .308 Winchester. It didn't come with it's own sights, so I also purchased (and just had mounted today) Magpul's Back Up Sight (MBUS for short) flip-up sights.
Did you get the metal or plastic Magpul front sight?
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Re: Sighting in a .308 rifle...

Post by Neptune Glory » Sun May 31, 2015 1:01 pm

RickOShea wrote:Did you get the metal or plastic Magpul front sight?
It's a plastic housing, but the post itself is metal. I didn't spring for the all-metal front sight. It came with a little tool that can be used to raise or lower the post of the Magpul front sight.
"When it comes to justifiable use of deadly force, you should seek to avoid confrontation, unless you have no choice and your life is on the line. This is easier to say than to do because it requires that you be calm and peace-loving throughout your life, but ready to use deadly force at any moment."

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Re: Sighting in a .308 rifle...

Post by RickOShea » Sun May 31, 2015 1:21 pm

Neptune Glory wrote:
RickOShea wrote:Did you get the metal or plastic Magpul front sight?
It's a plastic housing, but the post itself is metal. I didn't spring for the all-metal front sight. It came with a little tool that can be used to raise or lower the post of the Magpul front sight.
Well, keep an eye on it as you're shooting. The gas block on the rifle gets pretty hot......and Magpul doesn't recommend their plastic sight be mounted to the gas block.
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Re: Sighting in a .308 rifle...

Post by Neptune Glory » Sun May 31, 2015 1:41 pm

RickOShea wrote:
Neptune Glory wrote:
RickOShea wrote:Did you get the metal or plastic Magpul front sight?
It's a plastic housing, but the post itself is metal. I didn't spring for the all-metal front sight. It came with a little tool that can be used to raise or lower the post of the Magpul front sight.
Well, keep an eye on it as you're shooting. The gas block on the rifle gets pretty hot......and Magpul doesn't recommend their plastic sight be mounted to the gas block.
Will do, thanks!
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Re: Sighting in a .308 rifle...

Post by Jeriah » Tue Jun 02, 2015 9:57 am

As I understand it, and someone please correct me if I'm right, but 100 yards is approximately the apogee or whatever, the highest point on the ballistic arc of the .308 round. So, by zeroing at 100 yards, you know that you will always hold high, the question is just by how much. And the answer depends on how far away the target is. But basically I think (again, please correct me if I'm wrong), for practical purposes you can treat it as point of aim = point of impact from the muzzle out to 100 yards (for practical purposes, don't forget your sight offset if using a barrier!), and from 100 yards out you start holding high.
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Re: Sighting in a .308 rifle...

Post by Doctorr Fabulous » Tue Jun 02, 2015 10:48 am

Jeriah wrote:As I understand it, and someone please correct me if I'm right, but 100 yards is approximately the apogee or whatever, the highest point on the ballistic arc of the .308 round. So, by zeroing at 100 yards, you know that you will always hold high, the question is just by how much. And the answer depends on how far away the target is. But basically I think (again, please correct me if I'm wrong), for practical purposes you can treat it as point of aim = point of impact from the muzzle out to 100 yards (for practical purposes, don't forget your sight offset if using a barrier!), and from 100 yards out you start holding high.
The apogee depends on how you zero it. If you zero at the muzzle, dead-horizontal then the apogee is at the muzzle and there will be no "rise" just drop. The rize comes from canting the muzzle up slightly so that the bullet is fired upward in an arc to cross the axis of the sight/scope at the desired range. If you play with your zero distance, you can figure out what zero range gives you the flattest trajectory based on your load. Using Hornady's ballistic calculator and a 165gr SST, I got the following results:

100 Yard Zero
RANGE (YARDS) VELOCITY (FPS) ENERGY (FT.-LB.) TRAJECTORY (IN)
Muzzle 2840 2955 -1.5
100 2636 2545 0
200 2440 2182 -3.5
300 2253 1860 -12.9

200 Yard Zero
Muzzle 2840 2955 -1.5
100 2636 2545 1.8
200 2440 2182 0
300 2253 1860 -7.6

The 300 yard zero was four inches high at 100 and five inches high at 200, but only six inches low at 500. Not the best for precision, but a very flat trajectory overall. 50/200 is a pretty flat compromise if you can't zero at two, but you'll be about three-quarter inches high at fifty.

Of course, all this depends on the barrel length and projectile. I used Hornady's load data, which uses a 24" test barrel. OP's 18" barrel won't get quite as much oomph, and the arcs will change somewhat.
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Re: Sighting in a .308 rifle...

Post by hornetguy » Wed Jun 03, 2015 3:16 pm

If memory serves, most "deer-rifle" caliber rifles will be well served being sighted in about 3" high at 100 yards. This will give a maximum point-blank range of about 300 to 315 yards.
In other words, from zero to 315 yards, your bullet will not be outside (high or low) of an approximate 8" circle (kill zone). If your target has a larger kill zone, say 12" or so, then you can change your sight in point, and increase your MPBR.
This works on most standard calibers... 270, 308, 30-06, 280.... If you get into the super-zappers with flatter trajectories, it will change the sight in point somewhat.

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Re: Sighting in a .308 rifle...

Post by hornetguy » Wed Jun 03, 2015 3:27 pm

A fired bullet starts dropping as soon as it leaves the barrel. Gravity works.

DocFab is pretty much right on... the apogee is wherever YOU set it. You decide where you want it to be. It's best to look at it in the maximum point-blank range method. You decide what size your kill zone is, and you zero to keep the bullet inside that kill zone as far out as you can. As I stated earlier, with most standard deer rifle calibers, the kill zone is considered to be 8".... so by sighting in approximately 3" high at 100, you will be inside that 8" circle out to about 315 yrds or so. Using this setting, your apogee would probably be somewhere around 125 yds or so, just guessing. But, knowing the apogee is not important at all, if you know the MPBR.

Also keep in mind that if you shoot at something really close, like 10-15 ft away, you will likely be about 1 1/2" higher than you think, because your scope is about 1 1/2" above the bore line. As you get out to 25yds or so, the angle of the bullet will bring it up more to dead on, and continue climbing out to about 125yds or so, where it starts the journey back down, dropping to about 4" below line of sight at about 315yds.

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Re: Sighting in a .308 rifle...

Post by Neptune Glory » Wed Aug 19, 2015 8:50 am

I had to get a recoil reduction shoulder pad (OUCH!) but should get the back up sights zero'd in at 25 yards soon. After that, will get an inexpensive scope (found some for around $200 that can reach 4x to about 11x) and zero that in for 100 yards.

That's the latest!
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Re: Sighting in a .308 rifle...

Post by Doctorr Fabulous » Wed Aug 19, 2015 12:40 pm

Just remember that you absolutely get what you pay for in optics/mounts.
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Re: Sighting in a .308 rifle...

Post by Mej1947 » Fri Aug 21, 2015 11:46 pm

I'm old school so I'd say with open sights go for 25 yards. That was the standard military distance for the M14, 7.62x 51 NATO [308.] We sited in 1 inch high at 25 yards which put you back at 1 inch high at 250 yards. You didn't start dropping below point of aim until you were out at 300 yds. Of course wind drift and elevation affects point of aim but that's always going to be a problem.

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