1st shot low with 308 ammo in m14

[Grizzlypeg]

Never experienced this before, but I thought I would check my m14's point of impact with Federal blue box 308's, just in case I wanted to use the rifle out hunting. After shooting a couple of mags of 7.62 milsurp ammo and zeroing the scope at 1 1/2" high at 100 yards, I reloaded with 3 rounds of Federal Blue box 308 150 grain. First shot came in 5" low. So I fire the last two rounds, and they impact right up there with the group at 1.5" high. Wondering if that first low shot was a fluke, I load 3 more rounds into the mag. First shot, once again, 5" low from the previous group. Next two shots, right up there in the group. Next test, I reload the mag with 7.62 fmj and fire a couple shots, all of them right where they were supposed to be, 1.5" high.

Couple of years ago I hunted with the Federal ammo, and it was not doing that. I've also shot my best 5 shot groups at the range with that brand of ammo. What could have changed, and why is the first shot so low?

 

[Grizz Axxemann]

are you shooting that first round from a cold, clean barrel? That's the only thing I can possibly think of.

Mind you, 5"@100 should still be minute of deer.

 

[Grizzlypeg]

I shot a box of 20 rounds of 7.62 fmj to sight in the rifle. Then around 3 days later I shot some more to make sure it was where I wanted it, 1.5" high at 100 yards. So then immediately after shooting 5 rounds of 7.62 fmj, I switched to the Federal Hunting ammo and fired two set of 3 shots. Each time the first shot hit 5" lower than the others. And then when I switched back to 7.62 fmj, the problem wasn't there. First shot right back into the 1.5" mark and all subsequent shots. Something wacky is going on here. What could move a gun that groups decently, that low, and only on first shots with a particular ammo? Deer hunting is over for me for this season, but that result bothers me and I'm really itching to know what is the cause. Never seen it do that before. With that Federal ammo it usually shoots a great pattern, and doesn't have a consistent tendancy to shoot the first one low, especially that far below the rest.

 

[Lazerus2000]

How are you racking the op rod??

Are you pulling it back, letting go, and letting it fly forward on its own??

Try to get the first MANUAL feed from the magazine as close to the rest done by the gas operation.

LAZ 1

 

[Grizzlypeg]

Lazerus, I pull back the op rod to uncatch the whatchamacazlit, and let the bolt slam home. I could have kept repeating the experiment until I ran out of ammo, but the pattern of twice in a row having the first one go that wildly low, really threw me for a loop. I get around 1.5" groups out of this gun, and never wild one's with that Federal Ammo. Milsurp, I might get a wild one, but it would be more like a wild group, say 3-4" random, not a nice group on subsequent shots and those first two low one's grouping together an inch apart.

 

[Grizzlypeg]

I could try a little experiment like racking the op rod and instead of firing that cartridge, take it out and compare it to the others and see if it is in some way altered by the first load process. Maybe the bullet gets mangled or pushed into the case? I think the soft lead tip gets a little wedge like nick, but that should happen to all of them (rounds 1-5), I would think.

 

[cancer]

I'm not a fan of that ammo. i find it very inconsistent.

 

[Grizzlypeg]

I'm not a fan of that ammo. i find it very inconsistent.

It worked pretty well for me in the past and was probably the most accurate ammo I have shot in this gun. I just grabbed a box from my old stash and figured I'd double check the vertical point of impact, just in case I had the urge to take it on a walk for whitetail.

Some day I need to get brave and shoot some of my handloads in this rifle. I don't know what I'm missing, good or bad.

 

[chemo]

my handloads have not provided an incredible update in group size, mind you i have never shot surplus, only factory hunting ammo and my handloads

 

[maynard]

Try 3 FMJ and 2 Federals from the same mag. Then try 1 FMJ and 4 Federals from the same mag, just to see if the pattern is the same.

 

[Ganderite]

If this was my rifle I would look at a bedding issue. The vibration of shooting is making the barrel and action settle down somewhere different than where the barrel settles after handling and loading.

To test this theory, I would wedge some ammo box cardbaord in a couble of places, to change the bedding presures to see if the problem changed.

 

[Grizzlypeg]

Ganderite, the action was bedded into the glass stock with epoxy, and I haven't broken it loose yet. The front barrel band is tig welded to the gas piston cylinder, and there is good tension between the barrel band and stock ferule, which I polished and greased. But yeah I agree, unless its a problem with the optics / mount, something is shifting.

As an aside, there sure is a lot of brass dust in the chamber / action area for having shot off only around 40 rounds.

 

[chopper 1]

Something else to try

I presume gas piston and cylinder is normal and clean, flash hider not over torqued or loose etc..

Military shooters at Camp Perry label there most accurate mags for 1000 yds, less accurate mags for the lesser distances - because -

M14 and especially mini14 mags shift while shooting , changing harmonics.

Try single loading with no mag. As long as your firing pin is clean and does not stick it wont slam fire.

I do all my accuracy M14 testing with no mags - never had a slam fire in 43 years.

The test would eliminate the mag squirm as a cause.

If it still happens its a bedding issue - break the action and look inside and trim any epoxy over flow. Reassemble - check ferrule lip pressure {grease the lip} and test again.

This may be a harmonics issue or a pressure issue which some ammo may be more sensitive to.

 

[Grizzlypeg]

Chopper, I'm going to look into this. The mag I brought out with me, because it was a hunting trip, was a shorty. Its is a SOB to get in and out. Possibly some epoxy overflow has tightened the mag well area of the stock. I will have to look at that, as I don't remember the mag being that difficult to remove before.

 

[Ganderite]

Only 40 rounds since new??

If it has more than that, make sure you have cleaned out the carbon from the gas piston. match shooters do this each day (about every 100 rounds) As it carbons up, the group opens due to funny harmonics.

I don't know if this would cause the first shot low, though.

 

[Grizzlypeg]

No, 40 rounds since last cleaning. The rifle has seen approx 800 rounds.

 

[howasan]

This has only happened twice? I would try a couple of times more to see if it was a fluke. Then maybe mix and match ammo as Maynard says. Then get serious about the other stuff. The kicker is the first round occurence. Solutions that don't explain that don't need to be pursued.

 

[Grizzlypeg]

I'll add that when this was occuring, I was using a 5 round short mag. Such a pain to remove in the cold, that I did all my reloads by stuffing them in from the top of the open action.