ar bolt skipping over the top of bullets in magazine

[Doug H.]

Party pooper.

[gondo]

@Doug H. - I can't argue with you're experience, but you may be confusing short stroking with a bolt over base malfunction. Lets face it, Winchester Q3131 isn't known to be a high quality ammunition. Unless you have some chrono data, the 223 (whose) may have been supplying more gas than you think. What in the name of Baby Jesus were you doing with Crapchester ammunition at Nationals?

@openclassterror - There is so much wrong with your post I'm not sure where to start, so I won't.

Given a properly built rifle, except for a gas port that is excessively large, and a serviceable magazine, the bolt group can't out run the ammunition stack, period, full stop. 99% of the time, intermittent malfunctions are the result of poor quality parts (read out of spec), junk ammunition, inadequate lubrication or some combination thereof. Our first clue in the OP's case is his opening statement, "this is a new build". His failure to give specifics as to the make of the parts comprising his new amalgamation is the second clue. He'll never be able to solve his problem until, through methodical diagnosis, he uncovers what the problem is...

period full stop lmao... good one

[gondo]

op if it is a new build quit worrying about it until you have lubed the piss out of it and shot a couple hundred rounds, it is amazing what happens after they get broke in...

[naim]

Maybe you guys can clarify. I just don't see how a bolt can outrun the magazine on an ar style rifle. If the magazine and rifle are in good working order, the magazine is putting positive upward pressure on the ammo. The bolt travels completely through its cycle. I can't see how it would not pick up a round regardless of bolt speed. I usually rack this type of malfunction up as short stroking. Just trying to understand what's going on (with the gun not the pissing match)

[billdozer]

Here are rifle specs:

Quentin defense billet upper/lower

Hiperfire trigger

Adjustable gas block(don't remember name)

Saturn barrel, 1-8 twist, rifle gas

Taccom ulw buffer system

Rubber city armory low mass bolt

Lancer carbon fiber furniture

And as always the mags are pmag

The rifle is tuned to lock back on last round, there is no usual drag when manually cycling the system, it's properly lubed. The ammo is the same load I shoot in my other comp rifle without any problems. I may not have decades of experience assembling ar's, but this is the first time I've had any trouble getting them to run. Anymore info I need to give?

[Mark Gale]

It's an adjustable gas block, it's adjusted to lock back, just barely

First I'd open the gas block up a few turns and see what happens. Second, your action spring could be contributing to the problem especially if it's an extra power variant. I'd also meticulously check every leg of the gas system for leaks from the gas block to the bolt rings. If more gas doesn't turn out to cure the the issue, it's likely one of the parts or a combination thereof.

Doug H.'s experience illustrates a lack of understanding not of the gas system but gas itself. Switching from low pressure 223 to high pressure 556 doesn't necessarily equal a faster bolt group speed. It likely had the opposite affect. He could have tested this by opening his gas block a turn or so at which I point I'm certain his malfunction would have evaporated. Gas pressure and volume are inversely proportional to each other. Always has been and always will be.

[Shooter115]

It's an adjustable gas block, it's adjusted to lock back, just barely

Are you absolutely certain the bolt catch is locking back on the bolt face and not the bolt carrier. In a slightly under gassed rifle when firing a single shot it will eject the round and lock the bolt back, it's just not locking all the way back.

[Stlhead]

Over and under gas issues can be tricky. I am not a doctor and did not stay in a holiday inn express last night, but I would go through the exercise of resetting the gas adjustment with each kind of ammo that you would like to use and make note of the highest gas setting required to lock the bolt back then add a full turn. At that point I would start testing again in earnest.

The plastic buffer has no pin to snag, you can't seem to feel any drag on the bolt, a gas leak would be compensated for by opening the gas block more, I just don't see anything other than a gas issue that is likely the cause. I have nothing else to offer and wish you well.

[billdozer]

I have not checked to see if it's locking back on the bolt and not the catch. I will check that tonight. Good call, thanks.

[Doug H.]

It's an adjustable gas block, it's adjusted to lock back, just barely

First I'd open the gas block up a few turns and see what happens. Second, your action spring could be contributing to the problem especially if it's an extra power variant. I'd also meticulously check every leg of the gas system for leaks from the gas block to the bolt rings. If more gas doesn't turn out to cure the the issue, it's likely one of the parts or a combination thereof.

Doug H.'s experience illustrates a lack of understanding not of the gas system but gas itself. Switching from low pressure 223 to high pressure 556 doesn't necessarily equal a faster bolt group speed. It likely had the opposite affect. He could have tested this by opening his gas block a turn or so at which I point I'm certain his malfunction would have evaporated. Gas pressure and volume are inversely proportional to each other. Always has been and always will be.

Boyle's Law I understand as well as hot air.

Doug

[kurtm]

Wow talk about an idiotic over simplification of trying to apply Boyles laws to cartridges. I detect hot air as well! 223 vs 5.56, 5.56 usually has 1-1.5 grains more propellant than 223. If you burn both and capture all the gas from the burn the one with more propellant will have a higher volume....this is also the one that has the higher "copper pressure units". It would all be well and good if it was " just a gas", but it isn't it is a solid under going exothermic expanding which creates a given volume of gas.....the more solid you start with the more gas you get, and if your "bottle" is the same size and you burn more crap the higher the pressure is in the bottle. Someone needs to brush up on their high school physics.......hint ....it ain't Doug!

[openclassterror]

It's an adjustable gas block, it's adjusted to lock back, just barely

First I'd open the gas block up a few turns and see what happens. Second, your action spring could be contributing to the problem especially if it's an extra power variant. I'd also meticulously check every leg of the gas system for leaks from the gas block to the bolt rings. If more gas doesn't turn out to cure the the issue, it's likely one of the parts or a combination thereof.

Doug H.'s experience illustrates a lack of understanding not of the gas system but gas itself. Switching from low pressure 223 to high pressure 556 doesn't necessarily equal a faster bolt group speed. It likely had the opposite affect. He could have tested this by opening his gas block a turn or so at which I point I'm certain his malfunction would have evaporated. Gas pressure and volume are inversely proportional to each other. Always has been and always will be.

Boyle's Law I understand as well as hot air.

Doug

HAHA! Now THAT'S a good word play! The operative part of Boyle's law is that they are inversely proportional IN A CLOSED SYSTEM. The law as stated is " The absolute pressure exerted by A GIVEN MASS of an ideal gas is inversely proportional to the volume it occupies IF THE TEMPERATURE AND AMOUNT OF GAS REMAIN UNCHANGED. " Completely wrong application of the law. The volume of the bore and gas tube is not changed by using 5.56 ammunition. The AMOUNT OF GAS produced by the LARGER AMOUNT combusting powder is increased. Thereby increasing operating pressures, as we see in every reloading manual ever published since the introduction of the 5.56/.223 . Have to side with Kurt and Doug on this one.

[Stlhead]

Realy? What has it come to? What's next the Bernoulli principle? The man is not building a nuclear submarine, it is an AR for love of beer.

[billdozer]

I don't know about all these effects or principals, I do know that I gave it a little more gas and it seems to be working.

[Amerflyer48]

Realy? What has it come to? What's next the Bernoulli principle? The man is not building a nuclear submarine, it is an AR for love of beer.

That post is for after he gets it running and asks the question :

which comp/brake works best ?

"The AR Platform : a whole box of physics, then you start making your own ammo and ballistics tables "

Doug H. a round of cold beers for you.

Edited June 23, 2014 by Amerflyer48

[billdozer]

It was weird because it was locking back properly, but still not working right. Gave it a quarter turn more gas and it's running like a top now.....or some parts just broke in. Potato, patoto, don't care, it works. Thanks for the help, gents.