[mustang7]

The DAG ammo out of my M1A at 100 yards shoots dead center. My reloads with 168 gr SMK and 41 grains of IMR 4895 shoots 6 inches to the right. I would think there would be a difference in elevation not windage. Is this common or is it just me?

 

[lefty o]

i wouldnt say its common, but its not just you. it has to do with barrel harmonics. different bullet, different powder burn rate, and different velocity, in the end the muzzle of your rifle is in a different spot when the bullet exits. one of my varmint rifles does this, except the only difference is the bullet which is even the same weight, but one shoots about 3" to the right of the other.

 

[RAMMAC]

The difference in the bullet weight is the cause. The heavier bullet will move farther in the direction of the rifling due to the greater mass.

 

[hammonje]

The difference in the bullet weight is the cause. The heavier bullet will move farther in the direction of the rifling due to the greater mass.

My man with the knowledge!!!!!!DI5

 

[MesaRifle]

Given the asymmetrical nature of the total M1A bbl/receiver, those differences in bbl harmonics lefty-o mentioned really do come into play with this pltform.

Ideally, a bbl & it's attached receiver, plus the bolt, should be one lovely, dimensionally concentric mass, no ports or mag openings cut into it. This is, of course, impossible, but it's exactly why the BR (bench rest) guys use sleeved receivers (they add a tube over a commercial lighter-weight receiver in order to beef it up..), and they use receivers without a magazine opening in the bottom.

Then, they attach it to the biggest, honking-est (GI3 ??) bbl they can legally attach, and then they use a light-weight, small mass bullet in typically small low-bang target cartridges as the 6mm PPC or 6BR/Norma. It's known that the larger, hotter target cartridges like the 6.5-284 or Lord Help Us, the .338 Lapua or O M G... the 30-378Wby, all reduce inherent accuracy exactly because they "shake, rattle & roll" even a big stable BR rifle so much when you touch one off!

Those little plinker BR cartridges do not disturb all that accumulated mass very much, unlike when you touch one off your M1A/.308 rounds, which induces a lot of unwanted bbl wanderings, thither and yon! It's unlikely your bbl is pointing in the same direction at the exact time of muzzle exit, with significantly different loads. Which lefty-o and RAMMAC both mention.

You will likely have to make some re-centering notes on each load. The important thing would be, what's it's group size. You can always dial in some PoI corrections after all! Of course, it is nice when the PoI is at least close with several different loads. This is the sign of a good, consistent and stable rifle, but again, it's usually reserved for BR type guns.

 

[RAMMAC]

Barrel harmonics always has some effect on a bullet's trajectory but I don't believe that it has as much effect as the bullet weight/mass differences at this short of range. A change of a quarter inch or so in POI, at 100 yards, due to Harmonics is a reasonable expectation but not 6". So while I agree that this shift in POI is due to a combination of issues, my opinion is that bullet weight and design differences are the major contributors in this case.

For the benefit of the OP, all bullet trajectories are effected in the vertical and the horizontal by all sorts of things, I am just arguing that one of those things/elements is predominate in this case. There are several good sources of information that you can refer to for detailed studies on this stuff, one of the better ones is Bryan Litz's book "Applied Ballistics For Long-Range Shooting" ( I thank the poster on this forum that led me to it).

This is the nature of the shooting sports, we all have an opinion and things that seem to work best for us, and the poor new guy gets caught in the middle wondering who in the heck is right. SHOCKED2

 

[mustang7]

Thanks for the information guys. Part of the problem I'm sure is me. I was shooting from the prone position with a sling. My form probably leaves alot to be desired. Although I was pretty consistant with the 6 inches. I fired 15 rounds of my 93 DAG to check myself after. I plan on working up to 41.5 grains of IMR4895. That seems to be the magic load from what I've read. Is it possible the barrel harmonics could swing the POI the other way with the increase of powder? If not do shooters generally leave the front post sight as is and move the rear sight for the corrections? My goal is to shoot 150 grainers at the 2 and 300 hundred lines and the 168's at the 600. Im just getting into some semi formal competition and right now I'm happy with every shot just being in the score ring. It will be awhile if ever that I can keep up the AR15 shooters.

 

[Eagle 1]

Gus Fisher has commented that he believes it's the barrel whip........harmonics placing the barrel in a whipping motion such that different weight bullets leave the muzzle at different points in the cycle. My NM has a 3" different POI between 168s @ 2600 fps and 147s at 2750 fps. The difference is mostly vertical but also slightly to the right. Bedding the receiver in a very stiff stock and using a unitized GC will diminish this somewhat. A heavier barrel will also. The heavier bullet has a higher POI.

Eagle 1

 

[MesaRifle]

OK then; he may be right. Then again.....

For the benefit of the OP, all bullet trajectories are effected in the vertical and the horizontal by all sorts of things, I am just arguing that one of those things/elements is predominate in this case.

This is the nature of the shooting sports, we all have an opinion and things that seem to work best for us, and the poor new guy gets caught in the middle wondering who in the heck is right. SHOCKED2

I sure hope he doesn't feel that way, RAM ["caught in the middle" I mean!]. It's just us girlz telling our tales of glory and sorrow is all! We all basically agree, and if we don't... why, we just tell the offender to leave! GI1

No worries, RAM: I agree with you. I WAS wrong once though; back in, what was it? 1967? Now, I'm only occasionally just slightly off-center..... a mental PoI shift, my wife would prob'ly say.....

Thanks for the information guys. Part of the problem I'm sure is me. I was shooting from the prone position with a sling. My form probably leaves alot to be desired. Although I was pretty consistant with the 6 inches. I fired 15 rounds of my 93 DAG to check myself after. I plan on working up to 41.5 grains of IMR4895. That seems to be the magic load from what I've read.

Is it possible the barrel harmonics could swing the POI the other way with the increase of powder? If not do shooters generally leave the front post sight as is and move the rear sight for the corrections? My goal is to shoot 150 grainers at the 2 and 300 hundred lines and the 168's at the 600. Im just getting into some semi formal competition and right now I'm happy with every shot just being in the score ring. It will be awhile if ever that I can keep up the AR15 shooters.

Oh! A sling hold? Can have BIG diffs in PoI for sure!! Even with moderately good form, which for high accuracy level, has to be remarkably consistent!

I'd suggest (others please chime in here, please!) the obvious; if you are going to a match, you need to find, develop and pick a load you then set your specific rifle up with, and with your notes in order. Also, don't ignore checking your rifle out in all sorts of climatologic conditions (incl. different humidities if you have a wood stock...). Far different game, but my BPCR (Blk Pwdr Crt Rifles) Sharps & High-Wall are certainly affected by temps. And those are very hefty, target-specific models with less design compromise than the M1A.

As for those AR mousie-girl gunners (Oh. GI3 Ahem.... sorry to all youz men out there who play around with one-them twinkly-liddle 5.5mm thangs... plink, plink, plink...); don't worry. If one of them guyz ever comes after you with such a projectile (it'll just be right there, under the skin... like a sliver...), just find it and chew and spit it aside, and then take aim on their hidey-hole out @ 5 - 750 yds, and then take their tonsils out!

Gus Fisher has commented that he believes it's the barrel whip........harmonics placing the barrel in a whipping motion such that different weight bullets leave the muzzle at different points in the cycle. My NM has a 3" different POI between 168s @ 2600 fps and 147s at 2750 fps. The difference is mostly vertical but also slightly to the right. Bedding the receiver in a very stiff stock and using a unitized GC will diminish this somewhat. A heavier barrel will also. The heavier bullet has a higher POI.

Eagle 1

I do love what is called a "heavy barrel" in M1A land. So it goes with my new SAI NM rifle. What I call a Heavy Bbl would be one with a muzzle diam of, let's say, 1" or more! A nice 1.5 inch'r would be desirable for sure! Now THAT would stabilize an M1A.

Has anyone ever screwed a real man's bbl onto one of these things? If not, why not?

 

[MesaRifle]

Thick-headed barrels?

Thinking about this issue a bit further, I wonder what a different, somewhat heavier, and/or longer, flash hider/brake might do to reduce or stabilize bbl harmonics?

I mean, my experiences were that when I "sweated" one of those QUE adjustable MBs onto my pet long range hunter rifle's 26" Douglas bbl (it's a 6.5-06 Ackley) that alone improved accuracy by about 0.5 MoA without any other adjustment. (You can see that clubby looking brake in my album of rifles, on the grey thumbhole...) That one certainly does not have what could be described as a heavy bbl! Sure helped though....

 

[mustang7]

This is for service rifle matches. Muzzle brakes wouldn't be allowed. I've been using my Garand with 1967 HXP and actually shooting that better than my M1A with the match sites. Non hooded. I just need alot more trigger time.