Improving accuracy on my deer rifle

My deer gun came from my grandpa.  A Winchester model 100 semi-auto in 308 (post '64 rifle, not carbine).  They were a very popular gun back in the day but haven't necessarily been known for their accuracy.  I have shot 1" groups at 100 yards but usually they're closer to 1.5-2".  I'm starting to work towards reloading my ammo so that I can "tune" it in even better (thread here).  But back to the point of this thread.  What steps should I take to ensure the gun is as accurate as it can be?

I have a Leupold scope on it already with the style of rings that let you see the open sights underneath.  I don't need that feature so I could get standard rings if that is likely to make a difference.  All the fasteners are tight, both on the scope and those holding the action to the wood.  This model has a front swivel sling mount that connects to the barrel, unlike a bolt action that (I believe) doesn't have any connection between the fore end of the stock and the barrel.

I did get the firing pin recall issue taken care of.  A semi-professional gun guy I know looked at the barrel and said it was in very good shape.

I've seen some videos about glass bedding a stock but I'm not sure you can do that with a model 100 with the arduous way it has to be maneuvered into and out of the stock and the swivel mount.

Any steps I can take to ensure this gun is as accurate as it can be?

Mike Haasl wrote: I have shot 1" groups at 100 yards but usually they're closer to 1.5-2".

What is your goal you wish to accomplish with this rifle? I think this is very accurate for hunting purposes. To me it means you can make a humane kill shot on the first shot. This may not be accurate enough for competition long range shooting where a prize and shiny trophy is offered to the winner.

My goal is to be able to hit a grapefruit at 300 yards.  

I neglected to say that I tried about 8 brands/styles of lead ammo when I first got the gun to find the one that grouped the best.  But now I've switched to copper bullets and I'm back to crappier groups.  I've only tried two brands but the selection and availability is pretty poor so I haven't been able to acquire more.  Now I'm shooting around 2.5" at 100 yards.

I would personally love to be able to shoot 1" groups at 100 yards from a stable bench.  Then I know that with a bit of wind and nerves I can still be accurate enough to humanely make a one shot kill across a field.

The first thing I always do is run a piece of paper between the stock and barrel.  I have found any wood touching anything other than the bolt mount will cause some deviation.  I also use the shortest scope mounts that will fit and has a natural line to your eye.  Anytime you have to adjust your head it will put a small tweak on the alignment of the scope and target.  The shorter mounts also make the scope much more rigid adding to a better group.  All guns I have dialed in seem to have a sweet spot with a given bullet.  Some barrel twists are slightly different and like to have a different bullet speed other than factory loading. Most of the time when I slow it down a bit it gets more accurate. Good luck.

Right. Those high scope rings are not optimal for accuracy.

I dunno man, I wouldn't touch anything on the rifle until you get your ammo sorted out, Reloads will go a long way towards your goal. Since you know there is a load that can do 1 or even 1.5 inch groups then that means all you have to do is find it. Then you got 3-4.5 inches at 300 yards and a dead grapefruit.

If you do go the upgrade route you can bead your own rifle with JB Weld and floor wax. I did it and it worked nicely.

Thanks gents!  So it sounds like I'd be in better shape if I just get better scope rings and then do the reloading work.  Only after that should I consider other work on the rifle...

Unless your rifle is damaged or worn out I suggest concentrating on the ammo. Getting the ammo length exactly right is super critical for each individual chamber. Once you get that dialed in & everything else consistent your shot groups will probably be reduced to 1/4 or less their current size. Using a very stable mount for the testing will eliminate the human error factor with aim. Take a shot. Adjust the cross hairs onto where it hit. Done.

Mike Haasl wrote:My goal is to be able to hit a grapefruit at 300 yards.   I would personally love to be able to shoot 1" groups at 100 yards from a stable bench.  

When you are taking groupings, are you letting the barrel cool down completely between each shot?  It can take a while for a barrel to cool completely.  If not, the non-uniform mass of the barrel will creep as it is heated.  You won't get tight groupings comparing a hot barrel to a cold barrel.  That being said, 1.5 groups are very acceptable for hunting.  One can get sub minute arc quality rifles, but the cost does not justify the precision.  Besides, a harvest will mean that much more from a gun that was passed down to you; than an expensive tack driver or 'range queen'.  

If you want to know how the gun will perform, take one shot, the first shot.  Where does it hit the target.  In a hunting situation, you are only going to get one placed shot.  Practice the same at the bench.  Forget about groups.  Also edit to add, you have a lot of good advice already.  better rings and consistent ammo is the first steps to consistency.  

What shape are your groups?  Round?  Strung vertically or diagonally?  

Gobs of match grade 308 ammo can be purchased during normal times.  No guarantee, but it might return smaller groups.  If your get into handloading for absolute accuracy, the variables are endless.  Bullet selection (brand and weight), powder selection, charge selection, brass selection, primer selection.  Then you get into things like seating depth, neck runout, primer pocket and flash hole uniforming, neck tension, amount of crimp...   The list is endless!

Does the rifle have a trigger that breaks cleanly and under 4 lbs?  While great accuracy is possible with heavy, creepy triggers, they sure don't help.

You should be aware of parallax error in your scope.  Parallax error occurs when your eye ends up in a slightly different position between shots. Depending on the model, your scope is set to be parallax free a certain range.  Perhaps 150 yards in your Leupold.  If you can't find it online for your model,  a call to Leupold should give you the answer.  At 300 yards the error is likely minimal, maybe a half inch to an inch, but it all counts.  Ideally you would have a scope set for 300 yards, but the next best thing to do is making sure you set your cheek weld the same every time.  This will also help the rifle to recoil the same each time.

Semi-autos, while capable of excellent accuracy, do not tend to be quite as accurate as bolt actions.  Generous chamber tolerances aid feeding.  More moving parts. Even the position of the powder in the case from shot to shot can make a difference, especially when feeding from a magazine.

Your rifle is probably fitted with a thin or medium contour barrel.  As mentioned earlier, heat causes the barrel to move slightly.  A heavy barrel's (like those found on target and varmint rifles) thermal mass helps absorb the heat and mitigate the effects of the heat.  A heavy barrel is also stiffer.  If you watch high speed footage of a rifle being fired, the barrel actually has a wave that moves down it like bullwhip.  

You can go as far down the rabbit hole you want chasing accuracy, do a gut check every now and again to make sure you are still enjoying yourself!

Thanks Gary, the groups are normally ovalish.  

The trigger is definitely a creepy one but I'm pretty good at accommodating the creep and having it fire when I expect.  Unless that's a bad thing...

I'll make sure I don't go too far down the rabbit hole.  I suspect that by hand loading and doing some reasonable amount of load optimization I can get it accurate enough for my needs.

Not saying it is the case with you at all, but in my own experience, I am usually the weakest link.  Good cheek weld, good trigger press, not shooting when tired, stressed, over-caffeinated, or in a hurry are huge for me.  After that, as others have said, using really good ammo makes an enormous difference.

Yup, I completely agree that there is some shooter influence on the group size.  I'm just trying to eliminate variables at the range so I can minimize the overall variables.  I'll have to look into that cheek welding thing you speak of though...

If that rifle is that accurate with factory loads, I would be hard-pressed to do any permanent modifications to the gun itself. I agree with ditching the see-through rings. You might look at the scope bases as a possible area of improvement. A single-piece rail would be preferable, but two piece bases can work well if solidly mounted. Many serious target shooters screw 'n glue them with epoxy, but I don't think I would with a classic old gun like that. A less-permanent glue or even rosin can give them a little extra grip on the receiver.  Some bases are better quality than others, as well as rings and scopes. How stout they are will likely not affect baseline accuracy, but it really comes into play when the scope gets bumped as to whether it loses its zero or not.

There are a few things you can try on the bedding that are reversible. You can cut some small card stock shims to go between the action and stock at the front action screw area to elevate the barrel to not touch the stock. This will not likely make much difference due to the action, but you never know, and it's simple to try. Conversely, you can try a layer of felt in between the barrel and barrel channel to dampen vibrations. It's more likely to work, but I still wouldn't expect huge gains in accuracy.

As for loading ammo, I highly recomment it, but I have a feeling the 1.5-2" groups are near the accuracy limit for the gun. With lots of testing (or lots of luck) 1" may be doable. If you get better than 1" immediately buy a lottery ticket! A word of warning, though: handloading for an autoloading rifle is the second most dangerous form of handloading. Since it is gas operated, you will need to know loads safe for that particular model of gun. I'm afraid I have no experience with that model. Your loads will not only have to have a maximum average safe pressure, but also a port pressure within a certain range for the action to cycle, but not too violently. An old caveat for m-14 style rifles is to never use any powder slower than IMR-4064, but I have no idea about your 100. There are other issues that can pop up when loading for autoloaders as well. If you have other guns to load for first that might be simpler, it might be a good experience to get a little experience with them first. I have extensive experience in handloading, don't be afraid to ask.

Double up on ear protection (plugs and muffs).  

Are you shooting off of sand bags or some other stable and repeable rest?

How many shots to a group?  Not too hard to luck into a decent 3 shot group, thats why gunmakers use that number.  Probably good enough for a hunting rifle.  To statistically verify an accurate load you should be shooting 10 shot groups which will require a barrel cooling procedure.  First shots from a cold clean bore should be thrown out.  As an alternative to throwing out the first shot, I've seen people clean between shots to maintain a consistent barrel condition.

Just me, but I have found that rather than chasing accuracy, I would rather work on my shooting abilities.  For example, if you know your rifle shoots around 2.5" at worst.  Set a target up that would be easy to hit benched, maybe even your 4" grapefruit, at 100 yards.  Then practice shooting at it prone, sitting, kneeling and standing.  Rather than a grapefruit at 300 yards, perhaps a 10-12" steel gong.  Not the machine, but the man, kind of thing...and very useful for hunting in the field.

Rifle is fine if it's shooting 1.5-2" at 100 IMO. Most of that is probably you, not the rifle. If that's off the shelf ammo that you can find easily, buy a few boxes of that and you're good to go for the next decade - you don't need to shoot 100's of rounds out of a deer getting gun.

What distance are you shooting deer at? You mentioned wanting to hit a grapefruit at 300m, how does that translate to deer vitals at the distance you are likely to shoot one at?

Again IMO, unless you need to be shooting further than 100m you're probably good to go for an old rifle, no sense in hacking it about for marginal gains. 200m doubles your group size to 4" (assuming excitement and adrenaline doesn't open that size up!). 200m is a long way to shoot something if you're not 110% certain you're going to kill it cleanly.

If you NEED to shoot further, don't mess up the hand me down rifle, you might regret that one day. But a modern bolt action rifle and be amazed how little improvement there is after spending $1000 or more.

Don't make card stock shims - when it's damp they'll swell. If you must make shims make them out of something non porous.

Had to look up that rifle.  Don't think I've ever seen one in person.  Nice looking, almost like a Marlin 60 on steroids.  And as others have said, I wouldn't do anything irreversable to that rifle. Under 2" is pretty dang good for a 308 semi-auto that weights around 7lbs. Not to mention a wood stock that moves with changes in temperature and humidity.

This fellow had the best luck with Hornady 168-grain BTHP match ammo.

https://www.woodsnwater.net/articles/2011/4-apr-2011/2-fun_shooting

Thanks team!  I knew I'd get all kinds of great info from the wonderful permies out there

I won't be modifying the stock at all so thanks for setting me straight on that...

Jordan, I have read that auto loaders have more specific pressure needs for loads, but it seems that every factory load I've used in it works fine.  So as long as I stick in the mid range of reloading guides/charts, shouldn't I be in pretty good shape?

Gray, the range I'm using has solid benches with carpeted stepped rests to use.  For deer season I just put the stock on that and the butt is against my shoulder with my arm on the bench.  For this year's accuracy project I'll add sand bags to the front rest and under the butt.  I usually shoot 5 shot groups for exactly the reason you suggest.  I think I'd rather clean between shots since in the real world I only want to just shoot once at a deer.  Unless the accuracy is the same with a cleaned new barrel for each shot as it is with a dirty barrel.  Ie test it at the range with repeated shots and then make sure I'm sighted in later with a clean barrel?

Hi David, my shot this year was 220 yards, last year was about the same.  I see tons of deer in the 200-250 yard range from my stand.  There's the clear potential for a 280 yard shot and possibility of a 333 yard shot if a deer stands in one distant clearing.  I won't take any of those >220 yard shots with the gun/ammo as it currently shoots.  But if I can get it's innate accuracy down to the grapefruit size, and the wind isn't blowing, I'd feel quite confident out to 300 yards.  I was about to put Grandpa's gun on the shelf and look for a new bolt action rifle when I remembered hand loading was an option.  Since I have most of the gear, I'm one $80 die set away from reloading ammo and maybe making a difference.  But if that fails, I'll get a 308 bolt and be able to do just what I want.  I would just prefer to do it with Grandpa's gun...

Came across this review of a "precision" $2700 rifle this morning in a 2013 issue of American Rifleman.  Even using the ammo the rifle was designed around, they were not able to break an inch. They said it might still need breaking in, but at 200+ rounds, I'd consider it broken in. I also think CAD/CNC manufacturing techniques have improved since 2013, and there are numerous reports of $400 rifles shooting as well or better than this now.  I always try to look for a review by a reputable magazine to get an idea for real world accuracy as individuals tend to refer back to that one lucky 3 shot group they shot that one time.

Just a suggestion... here’s a vid on sighting in your rifle with charts, 308
It’s worth a look, bottom line, zero in at 25yrd, verify at 250yrds? Something to consider

https://www.brighteon.com/9f734c8a-d54e-404a-803e-41e8f3879d33

Thanks Patrick!  I didn't click the link since it looked a bit long and funny sounding.  But based on some factory ammo trajectory charts it seems like if I zero at 200 yards, I'm within 4" of the target at least to 250 yards.  I'm sure as I get into the reloading of ammo I'll be even more aware of my trajectories.

It’s a clean link to a vid discussing ballistics at 100yrd zero vs 25yrd zero for both 223 and 308... mike Adams ‘health ranger’ it’s about a ten minute vid. In that pre-posted vid, if you zero in at 25yrds with 308 168gr Hornady, it should hit the mark at about 240yrds, 4”rise up between And about an 6-8” drop to 300yrds. It’s worth a watch. It’s not spam :) promise
...but here’s a ballistics calculator link, if you want
http://www.shooterscalculator.com/

Please excuse... I tried to edit the 268gr to 168gr. Just wanting to make sure most accurate info comes across.