roval
Member
Would there be an improvement in accuracy shooting for groups with an m1a fired single shot? As in having the gas valve turned off.
Is an m1a more accurate if fired single shot?
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Steel Horse Rider
Member
My take would be that it is more accurate when fired deliberately than when spray and praying.......
rbernie
Contributing Member
It's not an irrational question - the rifle actually should be more accurate by my reckoning without the cycling of the action and the associated harmonics....
roval
Member
When our main range was undergoing renovation we were relegated to the side range and without a shooting screen I would turn off the gas port so as not to have to pick up the.brass from far away.
Last time I used it I forgot to turn the spindle back to the on position after cleaning and my first 2 shots were overlapping holes but the 3rd was off after I turned the spindle on and my subsequent groups never had overlapping holes. But it may just have been me also.
Last time I used it I forgot to turn the spindle back to the on position after cleaning and my first 2 shots were overlapping holes but the 3rd was off after I turned the spindle on and my subsequent groups never had overlapping holes. But it may just have been me also.
Curator
Member
My M1A ("loaded") is somewhat more accurate when fired with the gas system turned off. I suspect this is due to the action beginning to function before the bullet is out of the barrel. Using the same load with 168 grain Sierra Match King HPBT bullets, 100 yard, 5-shot groups with the gas system off average .85 to 1.0, but this opens up to 1.25- 1.50" with the gas system turned on. Another advantage of turning the gas system off is not having to crawl through the weeds to find your cases.
roval
Member
Agree about not wanting to go looking for the brass if no screen is available. I only had a few bullets left when I went last time so I was shooting for 3 shots at a time. 1st 2 were single shot third was with the port open.
Was wondering if it means with the gas port closed was I getting slightly faster velocity (which I can duplicate with a bump in the charge) or was it harmonics or luck. The other 3 shot groups were probably 1.3 moa. This was at 100 yes with a scope.
Was wondering if it means with the gas port closed was I getting slightly faster velocity (which I can duplicate with a bump in the charge) or was it harmonics or luck. The other 3 shot groups were probably 1.3 moa. This was at 100 yes with a scope.
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Possibly.
My personal and completely unscientific opinion is that you would be engaging in an exercise of diminishing returns.
Interested in your results if you decide to put the theory into action.
Nature Boy
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I've heard that it does positively affect accuracy. I'm going to try it my next time to the range. I'll post my results here
rbernie
Contributing Member
The Garand and all derivative designs (M14/M1A/Mini) have an offset reciprocating op rod, which is commonly blamed for making the action harmonics less controlled than, say, an AR.
My initial comment questioned the practical purpose of turning off the gas.
Match tuned M1As shoot 1/2 minute in semi mode. My scoped M1A Loaded factory version was a 3/4 MOA shooter with Federal Match. How does one improve that?
I guess you wouldn't lose anything if you tried it. Good luck.
M
Match tuned M1As shoot 1/2 minute in semi mode. My scoped M1A Loaded factory version was a 3/4 MOA shooter with Federal Match. How does one improve that?
I guess you wouldn't lose anything if you tried it. Good luck.
M
M14/M1A rifle's bullets are 3 to 4 feet out their muzzles when their op rod starts to move. M1's bullets are 5 to 6 feet out their barrels when their op rods start to move.
Theory says these semi autos should shoot equally accurate when single round loaded. All parts going into battery equally and repeatable from shot to shot. Both will have repeatable center of mass this way and bore axis at bullet exit will be repeatable. The more rounds outside the chamber will add mass below the recoil axis which causes different bore axis angles relative to the LOS when a round fires. The frequencies barrels vibrate at is the same for all rounds fired but it's amplitude their muzzle axis swings through is greater with heavier loads.
M14 style magazines don't all fit a given rifle the same. Top ranked marksmen will observe a half MOA or more zero shift across several magazines with the most accurate ammo and rifles.
Theory says these semi autos should shoot equally accurate when single round loaded. All parts going into battery equally and repeatable from shot to shot. Both will have repeatable center of mass this way and bore axis at bullet exit will be repeatable. The more rounds outside the chamber will add mass below the recoil axis which causes different bore axis angles relative to the LOS when a round fires. The frequencies barrels vibrate at is the same for all rounds fired but it's amplitude their muzzle axis swings through is greater with heavier loads.
M14 style magazines don't all fit a given rifle the same. Top ranked marksmen will observe a half MOA or more zero shift across several magazines with the most accurate ammo and rifles.
roval
Member
Like nature boy maybe I'll try it once I load a few more of the rounds for the next range visit.5 shot groups with single action vs semi. But it sounds like it shouldn't be a factor from Bart b's post.
Sunray
Member
Shutting the gas off only means it doesn't reload itself. Same rifle otherwise.
"...without the cycling of the action and the associated harmonics..." Like Bart says, the cycling starts after the bullet has left the barrel. Pressure has to drop first or all kinds of horrible things will happen.
More rounds outside the chamber will add mass below the recoil axis with said mass changing with every shot.
"...without the cycling of the action and the associated harmonics..." Like Bart says, the cycling starts after the bullet has left the barrel. Pressure has to drop first or all kinds of horrible things will happen.
More rounds outside the chamber will add mass below the recoil axis with said mass changing with every shot.
I don't know if it's more accurate, but I have shot mine like that to ease in brass collection. An added benefit should be longer case life as well, but I haven't specifically tested for it. The M1A/M14 can be rough on brass, in particular casehead separations.
rbernie
Contributing Member
I always assumed that it wasn't harmonics *during* bullet travel that was being blamed but the harmonics of the rifle shifting it slightly in the bedding in non-repeatable ways. I certainly don't know the specifics - only the lore.
I'm not sure that I understand this.
Steel Horse Rider
Member
No matter the reality of the physics involved I am sure that my 61 year old body and eyes do not retain the ability to see a measurable difference shooting offhand whether my M1A is cycling itself or whether I am manually cycling it between shots. Otherwise everything I shoot from my 03's would be in one hole........
briansmithwins
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Another factor is people shooting differently because they know the gas has been turned off.
That might easily be a bigger contributer than actually turning the gas off. But I'm in the 'doesn't make a significant difference' camp.
BSW
That might easily be a bigger contributer than actually turning the gas off. But I'm in the 'doesn't make a significant difference' camp.
BSW
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