i just built an ar15, 80% lower with a used upper. started out with cycling issues, and i saw the day i purchased it that the gas key and gas tube had hit several times and were beat up. so i replaced the key the tube and the gas block (only did the gas block to get rid of the a2 block/sight). now it cycles better but when shooting 556 i have a stove pipe or spent brass spun 180 in the chamber (like to bolt is moving way to fast) now i pulled the buffer out and weighed it and it was only 2.8oz.. it also has weights inside it, now can i change the weight inside it and how do i tell what weight buffer i need, it cycled 30 223 fine but just doesnt handle the 556 with higher psi??
new ar15 build question??
- Thread starter gunnie61
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One specific difference should be obvious, the parts used are optimized for civilian lower pressure ammo. When firing milspec ammo, the gas is a lot higher, and the bolt carrier speed is higher, too.
Not only do we want to know what barrel and gas length, but who's barrel, to discern what the gas port size is. Milspec is about .061, but the makers sometimes put in ports up to .080 to get it to function with the economy bulk ammo sold in white boxes.
The gas system in the AR15 has to be ported and tuned to match the gas pressure of the ammo used. If milspec, then all of it needs to be set up that way, right down to the buffer, as you checked. If low powered civilian ammo is used, then the range of gas pressure becomes much wider, and things start operating out of the optimum window.
If everything is all found to be one spec or the other, then a compromise will be needed. Only use one kind of ammo, or install an adjustable gas block to accommodate them all.
That isn't a bad idea, as that is exactly what shotgun makers have been doing for a long time with semi autos. They have to allow for a light bird load, up to magnum goose, and it has to cycle correctly regardless. The use compensating gas check mechanisms to meter the right amount no matter what. The gun reviewers then deliberately load alternating light and heavy shells just to see how well they did.
That option doesn't exist for the AR15 - it was originally designed for full power tactical loads, and the Army only issued one or two different ones, both designed with the same gas pressure level to make it work on the battlefield no matter what. White box plinker and cheap import isn't the standard, but these days, sometimes a maker tries to fit it in, and you get the results described.
Not only do we want to know what barrel and gas length, but who's barrel, to discern what the gas port size is. Milspec is about .061, but the makers sometimes put in ports up to .080 to get it to function with the economy bulk ammo sold in white boxes.
The gas system in the AR15 has to be ported and tuned to match the gas pressure of the ammo used. If milspec, then all of it needs to be set up that way, right down to the buffer, as you checked. If low powered civilian ammo is used, then the range of gas pressure becomes much wider, and things start operating out of the optimum window.
If everything is all found to be one spec or the other, then a compromise will be needed. Only use one kind of ammo, or install an adjustable gas block to accommodate them all.
That isn't a bad idea, as that is exactly what shotgun makers have been doing for a long time with semi autos. They have to allow for a light bird load, up to magnum goose, and it has to cycle correctly regardless. The use compensating gas check mechanisms to meter the right amount no matter what. The gun reviewers then deliberately load alternating light and heavy shells just to see how well they did.
That option doesn't exist for the AR15 - it was originally designed for full power tactical loads, and the Army only issued one or two different ones, both designed with the same gas pressure level to make it work on the battlefield no matter what. White box plinker and cheap import isn't the standard, but these days, sometimes a maker tries to fit it in, and you get the results described.
all i know about the upper is that its a dsa 556 1/9 twist cromoly barrel. its a 16" upper with flash hider, and has a carbine length gas system (9 3/4" gas tube). i just put on a new gas key, gas tube and low pro gas block. but when shooting american eagle 556 green box (i think 62gr) the bolt is moving so fast its not ejecting the spent shell but spinning it 180* in the chamber and feeding the spent shell backwards in the chamber jamming up. the 223 cycled normal (only shot 15rds slow fire) and they all ejected perfect in the 1 oclock position 4-5' in front of me. so i did a little research and they were syaing i should have a 3.5-4oz buffer so i pulled mine to weigh it and its only 2.8oz. i am more of a newbie on ar platform....it seems basic as far as gas blowback system but this has me boggled..... i swapped lowers with a friend (his was a bushmaster lower) and it still did the same thing. now i do not know what his gas system is or his buffer weight is.....i just dont want to spend $50 on a buffer and have it not work... all help is welcomed!! thank you
If you decide to try a heavier buffer, you could get the heaviest (stamped H3). If it is too heavy, you could swap out weights with your existing buffer.
There are three weights in the buffer and they can be of two different weight materials. When you shake the buffer, the rattle you hear is the weights moving around.
If you swap out the weights, the the stamping on the buffer will not be correct unless you change it.
Hope this helps.
The brass doesn't spin around in the action because the carrier speed is too high, it does so because the brass isn't being ejected properly. Three faults can cause your Failure To Eject- Bad ejector or ejector spring, short stroking or the extractor isn't holding the case.
Bad ejector could be from a sticking, worn or damaged ejector and/or ejector spring. You can test this by pulling the BCG out of the rifle, placing a case in the bolt under the extractor, pressing the case against the ejector and letting it fly. If it shoots across the room, it should be good. If it sorta dribbles out, something is wrong.
Short stroking is from either using weak ammo and/or a leak in the gas system. As you had to replace the gas key, I'd start there. It's possible the mating surfaces are not flat and leaking gas. Other possible leaks are at the gas block and the gas rings.
If the extractor is worn, weak or damaged, it could be letting the case loose before it is extracted far enough to be ejected clear of the ejection port.
These are the common culprits when the rifle suffers from a Failure To Eject. If the extractor and ejector are functioning correctly, you won't get an FTE from hot ammo and fast carrier speeds
Bad ejector could be from a sticking, worn or damaged ejector and/or ejector spring. You can test this by pulling the BCG out of the rifle, placing a case in the bolt under the extractor, pressing the case against the ejector and letting it fly. If it shoots across the room, it should be good. If it sorta dribbles out, something is wrong.
Short stroking is from either using weak ammo and/or a leak in the gas system. As you had to replace the gas key, I'd start there. It's possible the mating surfaces are not flat and leaking gas. Other possible leaks are at the gas block and the gas rings.
If the extractor is worn, weak or damaged, it could be letting the case loose before it is extracted far enough to be ejected clear of the ejection port.
These are the common culprits when the rifle suffers from a Failure To Eject. If the extractor and ejector are functioning correctly, you won't get an FTE from hot ammo and fast carrier speeds
Well in usually stove pipe the ammo, but I noticed a few times the spent she'll just spun in the receiver that's why I said that. I will check the extractor yet again and gas rings. I dot think i have a gas leak as the gas system is functioning fine just not feeding 556!! It will feed 223 (as far as I have tested most I have shot was 15 in a row) just fine! I wish I could post videos on here
To be honest I don't know what a bolt overpass is?? But when shooting 556 the bolt cycles so fast the brass either just falls out of the ejection port or it spins the spent brass in the receiver and when the bolt moves forward it will jam the spent round and the new round in the chamber. And a few times it spun the spent brass 180* in the receiver and tried feeding the spent brass in backwards along with the new shell!!
I tested the extractor and ejector and it would throw the brass about 2-3 feet away. So I installed an prong on the extractor spring (upgrade kit) and now it tosses the brass 5-6 feet away. I'm hoping with that and a heavier buffer (to slow the bolt down) it will cycle better. I know with 223 ammo (only shot 15 in a row 30 in total) it ejected the spent cases 4-5 feet in the 1 o'clock position with no probs cycling. Then tried a different lower (mines an 80% lower build) thinking the buffer system was the prob but with 556 had the same results. The lower I swapped with has a very light buffer as well as mine. Mines only 2.8oz his was 3 oz
3oz is what a typical carbine buffer weighs. It is lighter than optimal for an otherwise properly setup 16" barrel and carbine length gas system, but functions fine on many many rifles using both .223 REM and 5.56x45.
I haven't personally witnessed, and cannot remember reading about, the problems you are having.
If I may ask...why did you decide on a DSA upper/rifle?
I haven't personally witnessed, and cannot remember reading about, the problems you are having.
If I may ask...why did you decide on a DSA upper/rifle?
I went with a dsa as it happened to be in the right place at the right time for the right price!! And as far as I know everything I'm the upper is a dsa even the bcg. When I purchased it the gas key and gas tube were best up (look like they hit at some point) so I replaced the key and the tube. Like I said before gas prob is solved now it cycles awesome just to good lol. And about the buffer I have read you want to run the heaviest buffer possible that will cycle reliably with both calibers. Just what I read on several forums
Cycling "too good" = it isn't solved.
Do you know the gas port size of what you put in?
justice06rr
Member
What I suggest is to borrow a different BCG with an auto/M16 carrier that is of milspec quality i.e. from Colt or BCM from someone and try it on your upper. If it works with both 5.56 and 223 with those, then its your DSA bcg that is the issue.
Another suggestion is to use a H (heavy) buffer. These are the usual combination that is used on quality rifles from Colt and BCM with an auto/M16 carrier.
I have a feeling it is either the BCG or the buffer that is at fault here.
The size of the gas block (.750) will not make a difference.
Another suggestion is to use a H (heavy) buffer. These are the usual combination that is used on quality rifles from Colt and BCM with an auto/M16 carrier.
I have a feeling it is either the BCG or the buffer that is at fault here.
The size of the gas block (.750) will not make a difference.
A "Bolt Over Base" is when the bolt does not catch the rim of the case. Instead, the bolt hits the case and partially pushes the case out of the mag or maybe doesn't push it out at all.
Heh! It would also help to understand your posts if you proof-read them before putting them up
Heh! It would also help to understand your posts if you proof-read them before putting them up
My bad on the terminology.
Gas port diameter is what I meant to ask about.
What is the gas port diameter?
Neither of those BCG's will necessarily be 'good'. The Bushmaster may not even be a full profile. The PSA might.
Gas port diameter is what I meant to ask about.
What is the gas port diameter?
Neither of those BCG's will necessarily be 'good'. The Bushmaster may not even be a full profile. The PSA might.
mdThanatos
Member
Not having funds to buy a new upper, I went with a heavier buffer and extractor upgrade kit from BCM on my DSA upper that was having issues with XM193 55gr from Federal.
H2 Buffer, BCM extractor kit, PSA Full Auto BCG is the combo that I have on my 16" DSArms upper if that helps any.
H2 Buffer, BCM extractor kit, PSA Full Auto BCG is the combo that I have on my 16" DSArms upper if that helps any.
Yeah sorry I fat finger a lot on my phone so I apologize for that. But I should have my buffer back today as my father inlaw is making heavier weights for me to put in it will be 4oz when done and ill test it with the extractor upgrade and the heavier buffer!!
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