Switched AR10 to Carbine buffer with springco, and now I cant get it to lock back?

[gritz55]

So I originally bought a PSA ar10 in 6.5 CM. But it down to 16'" and threw on a seekins buttstock and rifle length buffer tube.

rebarrled to 18" 308 due to ammo issues. And then switched back to a carbine length buffer tube, made more a "battle rifle" instead of a DMR rifle set up it had been in. Tried to lighten her up a bit. Shes still heavy.

Anyways, with the carbine buffer setup, it kicked hard. like, not really fun to shoot. So I got a springco spring designed for AR10 carbine buffer length. MUCH smoother shooting. Made it feel like rifle length again.

However, I had issues adjusting the seeking adj gas block. I cannot get it to lock back on an empty mag no matter how much gas I'm letting in. To the point where I've loosened out the gas to the point where the adjuster screw flies out, and I have dobe this twice now.

I'm assuming that the springco spring is making it softer shooting, but also preventing the bcg from being able to move back far enough to lock back. Its ejecting but then having issues feeding the next round, its not moving far back enough to catch the head of the case.

Any other opinions here? SHould I just switch it back to the regular spring?

Just a little frustrated here.

 

[msgriff]

Will it lock back manually with an empty mag by operating the charging handle?

 

[gritz55]

Yep. It can manually move back and lock. That’s not an issue. It’s weird. It’s just not locking back no matter how much gas I give it.

 

[msgriff]

Measure the distance between the bolt face and the bolt catch at full pull back of the CH. Also, it could be overspeed and not under gassed, weigh the buffer. Next, is the barrel dimpled, if not verify AGB alignment. Did you get the Sprinco orange?
ETA: gas tube length, should end at the center of the cam pin cut-out.

 

[Mocadon]

Or, get the Tubbs spring.

 

[bfoosh006]

What Gen is the PSA ?

Gen I and Gen II had issues with the 308 2.5" carbine buffers ( DPMS pattern ) smacking the lowers buffer tube threads.

Check the lower at the buffer tube threads.
And what buffer weight are you using ? And what length is the buffer ?

 

[RUTGERS95]

So I originally bought a PSA ar10 in 6.5 CM. But it down to 16'" and threw on a seekins buttstock and rifle length buffer tube.

rebarrled to 18" 308 due to ammo issues. And then switched back to a carbine length buffer tube, made more a "battle rifle" instead of a DMR rifle set up it had been in. Tried to lighten her up a bit. Shes still heavy.

Anyways, with the carbine buffer setup, it kicked hard. like, not really fun to shoot. So I got a springco spring designed for AR10 carbine buffer length. MUCH smoother shooting. Made it feel like rifle length again.

However, I had issues adjusting the seeking adj gas block. I cannot get it to lock back on an empty mag no matter how much gas I'm letting in. To the point where I've loosened out the gas to the point where the adjuster screw flies out, and I have dobe this twice now.

I'm assuming that the springco spring is making it softer shooting, but also preventing the bcg from being able to move back far enough to lock back. Its ejecting but then having issues feeding the next round, its not moving far back enough to catch the head of the case.

Any other opinions here? SHould I just switch it back to the regular spring?

Just a little frustrated here.

View attachment 7877667

if you have an adj gas block, why are you fking around with buffer springs etc.? this stuff is not rocket science and the more you mess with a non standardized platform the more you open the door for issues

put a normal 308 carbine heavy buffer (kak sells them), normal 308 carbine spring and use your gas block. dump the springco and all the other shit and keep it simple.

 

[Mike_in_FL]

I cannot get it to lock back on an empty mag no matter how much gas I'm letting in.

You know you're going about this completely ass backwards right? Close the gas off completely and make sure the action won't open. The you start to open it as you shoot. I don't waste time with one click or 1/8 turn at a time. Open it a bit and see if the bolt carrier group starts to move backwards. If you're dumping too much gas into the system it may not lock back.

So either you have too much gas or a mechanical issue with weight of spring, or weight or length of buffer. Is it an 18" barrel with a rifle length gas system or carbine or intermediate?

 

[tucaz]

the only adjustable i had on an ar10 was a superlative. it worked well and i was using vltor a5 buffer tubes and heavier ar15 carbine buffers on a bushmaster barrel, normal rate 308 springs though.

the BA barrels i’m using now are normal gas blocks with the same buffer set up.

 

[Runnineh]

Heavy spring, then heavier buffer. Also, make sure you have an ar10 buffer tube. They are longer than a 15's

 

[pmclaine]

I have two LMTs MWS and MRP.

Made the mistake of mounting MRP tube on MWS.

Caused the exact condition you mention.

There is a difference between .223 tubes and .308 tubes in regards to allowing bolt travel,

Sounds like you have a short tube that won’t allow full travel.

 

[RUTGERS95]

Heavy spring, then heavier buffer. Also, make sure you have an ar10 buffer tube. They are longer than a 15's

huh? buffer tubes are universal to both platforms

op simply needs a heavy carbine buffer, standard buffer tube and standard carbine spring.

this is NOT rocket science

 

[RUTGERS95]

I have two LMTs MWS and MRP.

Made the mistake of mounting MRP tube on MWS.

Caused the exact condition you mention.

There is a difference between .223 tubes and .308 tubes in regards to allowing bolt travel,

Sounds like you have a short tube that won’t allow full travel.

no not true. buffer tubes work for both platforms and are universal to both

JHC where do you people come up with this stuff

the buffers are different, tubes are universal

 

[pmclaine]

no not true. buffer tubes work for both platforms and are universal to both

JHC where do you people come up with this stuff

the buffers are different, tubes are universal

Nope.

Not in an LMT anyway.

You can even count the holes 5 position vs 4.

JHC…. “You people”

Edit add, my bad looks like both LMT tubes are 6 position - Genius!

 

[RUTGERS95]

Nope.

Not in an LMT anyway.

You can even count the holes 5 position vs 4.

JHC…. “You people”

I have 2 mws including a veneuzalean on top of 3 in 5.56, I think i know the platform. and OP is talking a home build not a platform that has non standard parts. 'you people'

that said, buffers are different, buffer tubes are interchangable.

no one cares about LMT in this thread, read better

 

[pmclaine]

I have 2 mws including a veneuzalean on top of 3 in 5.56, I think i know the platform. and OP is talking a home build not a platform that has non standard parts. 'you people'

that said, buffers are different, buffer tubes are interchangable.

no one cares about LMT in this thread, read better

Nope you are wrong.

Gene at LMT will back me up on it.

Do a test. Flip your tubes and come back to apologize.

 

[pmclaine]

Read the description….

.308 Extension Tube - LMT Defense

LMP259C

lmtdefense.com

I know you are familiar with 3/4 of an inch.

 

[TheOE800]

Rutgers is a moron, block him.

 

[Runnineh]

Believe what you want @RUTGERS95 , I had the same issue with my home build. A fellow member asked which buffer tube I had, and I had the wrong one. I would post a picture of the two, but I'm not taking my shit apart to prove you wrong. OP, I had the same issues, and what I posted earlier is what fixed mine. Hope it works out for you.

 

[MPD142]

So I originally bought a PSA ar10 in 6.5 CM. But it down to 16'" and threw on a seekins buttstock and rifle length buffer tube.

rebarrled to 18" 308 due to ammo issues. And then switched back to a carbine length buffer tube, made more a "battle rifle" instead of a DMR rifle set up it had been in. Tried to lighten her up a bit. Shes still heavy.

Anyways, with the carbine buffer setup, it kicked hard. like, not really fun to shoot. So I got a springco spring designed for AR10 carbine buffer length. MUCH smoother shooting. Made it feel like rifle length again.

However, I had issues adjusting the seeking adj gas block. I cannot get it to lock back on an empty mag no matter how much gas I'm letting in. To the point where I've loosened out the gas to the point where the adjuster screw flies out, and I have dobe this twice now.

I'm assuming that the springco spring is making it softer shooting, but also preventing the bcg from being able to move back far enough to lock back. Its ejecting but then having issues feeding the next round, its not moving far back enough to catch the head of the case.

Any other opinions here? SHould I just switch it back to the regular spring?

Just a little frustrated here.

View attachment 7877667

Which receiver extension (buffer tube) did you use? Is it a Standard AR-15 length or longer AR-10/SR-25/A5 length extension. Which buffer are you using the shorter AR308 buffer of the longer AR-15. Could be an issue of an AR-10 length spring in an AR-15 extension and yiu are getting coil bind. Lots of parts incompatibility issues of you are not careful.

Make sure all the parts at the back end of the rifle are compatible with your platform.

After that I would attempt to adjust the gas block starting off at close to fully closed to make sure it’s not so overgassed it’s not able to lock back and then open it a few clicks at a time.

 

[mtrmn]

The shorter AR15 buffer tube (with a ~7" internal depth) will work on a 308 but you absolutely HAVE to use a shorter 308 buffer which is 2.5" long. You must also make 100% sure you do not use a standard AR15 carbine spring because it will bind up due to having too many coils. The BCG will not lock back on the last round and it may not even pick up the next round in the mag. You MUST use a dedicated 308 carbine spring.( I use the Sprinco orange) The buffer for a 308 SHOULD weigh about 5.4 ounces to tame the recoil impulse of the 308 round. Many, if not most, 308 carbines come with a buffer that's about 3 ounces. It'll work-most of the time.

The longer (Armalite/Vltor/etc) buffer tube is about 7.75" internal depth and it uses the 3.25" length buffer that's common to the AR15 carbine. You do need to use a dedicated 308 spring and the 5.4 ounce (H3) buffer weight. To simplify matters and insure all the parts are correct and made to work together Armalite sells this kit with all matching parts:

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[r.tenorio671]

Heavy spring, then heavier buffer. Also, make sure you have an ar10 buffer tube. They are longer than a 15's

....actually, it depends on the manufacturer of the tube. Aero uses standard AR15 carbine tubes for both their AR15 and AR10 platforms. The differences between the AR15 and AR10 are the springs and buffer for each platform.

 

[pmclaine]

The shorter AR15 buffer tube (with a ~7" internal depth) will work on a 308 but you absolutely HAVE to use a shorter 308 buffer which is 2.5" long. You must also make 100% sure you do not use a standard AR15 carbine spring because it will bind up due to having too many coils. The BCG will not lock back on the last round and it may not even pick up the next round in the mag. You MUST use a dedicated 308 carbine spring.( I use the Sprinco orange) The buffer for a 308 SHOULD weigh about 5.4 ounces to tame the recoil impulse of the 308 round. Many, if not most, 308 carbines come with a buffer that's about 3 ounces. It'll work-most of the time.

The longer (Armalite/Vltor/etc) buffer tube is about 7.75" internal depth and it uses the 3.25" length buffer that's common to the AR15 carbine. You do need to use a dedicated 308 spring and the 5.4 ounce (H3) buffer weight. To simplify matters and insure all the parts are correct and made to work together Armalite sells this kit with all matching parts:

Login

JHC you people and your continuing to against someone that knows his platform and is always willing to claim how big 3/4" is to the ladies but doesnt recognize its crucial requirement on .308 AR.

That friggen .308 BCG is not the itty bitty BCG a .223 is.

 

[r.tenorio671]

.....here are pix from 2015 when I built my large format AR using these Aero parts. There may be more than one picture of each from different angles to show the detailed measurement. You can see the numbers, make your own interpretations.

...FWIW, with a BA 16" Hanson barrel and SLR Sentry 7 Adjustable Gas Block it has functioned perfectly from it's 1st firing to today using factory M80, FGMM and my handloads w/Hdy 155, 168 & 178 projectiles. Recoil is comparable to my 556's and 6ARC and the same ejection pattern of 3:30-4:00, which I attribute primarily to the SLR AGB and the ability to control the gas at the port. I'm using the Aero "standard weight" phosphated BCG.

 

[Evintos]

You can use an AR15 length carbine receiver extension for an LR308 however you must also use the corresponding AR308 carbine length 2.5" buffer (DPMS carbine length). AR15 carbine length buffer is 3.25" and the Armalite AR10 carbine buffer length was also 3.25" (off the top of my head). The LR308/AR308 is buffer length is not the same as the Armalite AR10 length.

Proper length allows for proper stroke. If you use an AR15 carbine length buffer (no matter what weight) in an carbine receiver extension with AR308 BCG, you'll have a physically limited stroke length. Your BCG simply won't be able to travel far enough rearward to cycle properly.

If the stroke length is too long (example - using AR308 buffer in AR15 receiver extension and AR15 BCG) your BCG gas key will impact your lower receiver. You can technically make it work using an appropriately sized spacer but why bother? Just buy the correct buffer.

Springs -
AR15 Carbine length springs are roughly around 10 1/16" to 11 1/4" long (will shorten after compression cycles). Around 39 coils.
Armalite AR10 Carbine length springs are right around 13 3/4" long (will shorten after compression cycles). Around 34 coils.
DPMS/LR308/AR308 carbine length springs are around 11 3/8" to 11 1/2" and around 29 coils.

If you mix springs, you'll screw up the stroke length just like if you mixed buffers and BCGs.

Rifle length receiver extensions, rifle buffers and rifle length springs of either AR15, AR308/LR308, or Armalite AR10 will differ as well.

Side note - if you want to get into more advanced tuning, you can play with stroke length by modifying the length of the buffer body to allow for the most stroke length without the gas key impacting the lower receiver.

Yep. It can manually move back and lock. That’s not an issue. It’s weird. It’s just not locking back no matter how much gas I give it.

@gritz55 - You can measure all your parts to double check but since you can manually lock back, it's not likely an issue. Assuming nothing (no part) is mismatched, try turning down the gas flow on your AGB. Start at 50% closed. Note the ejection direction (if any). If it's ejecting forward towards the muzzle, reduce gas further. You want to aim for roughly 3-4 o'clock ejection.

 

[r.tenorio671]

....Evintos makes some good observations, but I do wish to point out that my Aero .308 specific carbine spring doesn't jibe with the "coil count" nor "length" he states. Not that he is in error, if anything it just points out the lack of a "standard" when it comes to the .308 platform. A possible explanation for the differences in coil count and length is what the "spring weight". i.e. the compression rate of the spring material that Aero springs are made of and the distance between coils, which will determine it's overall resting length and fully compressed length under load. This is one reason why, when asked, I recommend using buffer tube, spring and buffer from the same manufacturer....one presumes the manufacturer has engineered those parts to be compatible and work in concert properly.

...the comment about the gas key impacting the receiver ring is real, I have witnessed it in .308 builds that the users had done a "mix & match" of divergent brands...I've seen from light marks to a receiver that cracked.

 

[Evintos]

....Evintos makes some good observations, but I do wish to point out that my Aero .308 specific carbine spring doesn't jibe with the "coil count" nor "length" he states. Not that he is in error, if anything it just points out the lack of a "standard" when it comes to the .308 platform. A possible explanation for the differences in coil count and length is what the "spring weight". i.e. the compression rate of the spring material that Aero springs are made of and the distance between coils, which will determine it's overall resting length and fully compressed length under load. This is one reason why, when asked, I recommend using buffer tube, spring and buffer from the same manufacturer....one presumes the manufacturer has engineered those parts to be compatible and work in concert properly.

...the comment about the gas key impacting the receiver ring is real, I have witnessed it in .308 builds that the users had done a "mix & match" of divergent brands...I've seen from light marks to a receiver that cracked.

I am in error. I copied down the wrong length and coil from my saved chart (wrong column/row). My mistake. Armalite AR10 is the 13 3/4 and around 34 coils.

DPMS/LR308/AR308 is around 11 3/8" to 11 1/2" and around 29 coils.

Went back and edited that post.

For sure the difference in coil count can't be used as a definitive spec. Definitely buying the buffer/spring/extension combo is a good way to avoid issues.

 

[Paradox]

So I originally bought a PSA ar10 in 6.5 CM. But it down to 16'" and threw on a seekins buttstock and rifle length buffer tube.

rebarrled to 18" 308 due to ammo issues. And then switched back to a carbine length buffer tube, made more a "battle rifle" instead of a DMR rifle set up it had been in. Tried to lighten her up a bit. Shes still heavy.

Anyways, with the carbine buffer setup, it kicked hard. like, not really fun to shoot. So I got a springco spring designed for AR10 carbine buffer length. MUCH smoother shooting. Made it feel like rifle length again.

However, I had issues adjusting the seeking adj gas block. I cannot get it to lock back on an empty mag no matter how much gas I'm letting in. To the point where I've loosened out the gas to the point where the adjuster screw flies out, and I have dobe this twice now.

I'm assuming that the springco spring is making it softer shooting, but also preventing the bcg from being able to move back far enough to lock back. Its ejecting but then having issues feeding the next round, its not moving far back enough to catch the head of the case.

Any other opinions here? SHould I just switch it back to the regular spring?

Just a little frustrated here.

View attachment 7877667

Read this and you’ll find the solution, problem is ever mother fucker refused to mill-spec one design so change one thing even a quarter oz amd its fucked theres dozens of buffer and opinions bit this article will help. Where does the round eject , should be 315ish to 430

 

[Paradox]

AR-10/AR 308 Buffer Weights

Building an AR-10 style rifle but not sure what buffer weight to use? We got you!

www.80percentarms.com

 

[Jsp556]

Just use the armalite kit. It eliminates any confusion and costs about $75.

If it’s out of stock, A5tube+armalite ar10 carbine/lmt MWS spring+ H3 buffer is the same thing.

Notice that most of the large frames with a rep for running dependably all use the Armalite carbine set up? Skip the DPMS system.

 

[Paradox]

Just use the armalite kit. It eliminates any confusion and costs about $75.

If it’s out of stock, A5tube+armalite ar10 carbine/lmt MWS spring+ H3 buffer is the same thing.

Notice that most of the large frames with a rep for running dependably all use the Armalite carbine set up? Skip the DPMS system.

Wish the did away with the name all d PMS means today is the angle on the upper in the possible 20% chance one upper might fit a different lower completely stupid but if you do go DPMS like he would with ArmaLite it’s so much easier just to get a matching upper and lower in these guys that try to assemble these parts guns that end up with endless issues

 

[msgriff]

Just use the armalite kit. It eliminates any confusion and costs about $75.

If it’s out of stock, A5tube+armalite ar10 carbine/lmt MWS spring+ H3 buffer is the same thing.

Notice that most of the large frames with a rep for running dependably all use the Armalite carbine set up? Skip the DPMS system.

That's a good kit, when its in stock. Spike's makes a similar spec'd kit (A5 w/ nut & plate, H3, spring) that's about $80. Part# SLAX50R-K, usually in stock at all the usual vendors.

 

[gritz55]

Just use the armalite kit. It eliminates any confusion and costs about $75.

If it’s out of stock, A5tube+armalite ar10 carbine/lmt MWS spring+ H3 buffer is the same thing.

Notice that most of the large frames with a rep for running dependably all use the Armalite carbine set up? Skip the DPMS system.

I might just try this, Its ejecting back around 5 o clock, even with the gas block open, its just weird. I have the shorter buffer. I know where the cases are supposed to be ejecting. I have built several ar's and I know what I'm doing there. I've only ever had an issue with this AR10, and its only since I switched out the carbine spring for a orange springco spring. I'm just going to go A5.

Thanks for the advice guys.

 

[Mike_in_FL]

I might just try this, Its ejecting back around 5 o clock, even with the gas block open, its just weird. I have the shorter buffer. I know where the cases are supposed to be ejecting. I have built several ar's and I know what I'm doing there. I've only ever had an issue with this AR10, and its only since I switched out the carbine spring for a orange springco spring. I'm just going to go A5.

Thanks for the advice guys.

If you like the recoil impulse with that spring, why don't you pull a weight out of the buffer itself and try it? Or all of them and try it?

You never answered what length the gas system is. Rifle length gas systems that get cut down barrels will generally not have enough gas to operate in the range you want unless you lighten the buffer or open the gas port.

 

[Paradox]

So I originally bought a PSA ar10 in 6.5 CM. But it down to 16'" and threw on a seekins buttstock and rifle length buffer tube.

rebarrled to 18" 308 due to ammo issues. And then switched back to a carbine length buffer tube, made more a "battle rifle" instead of a DMR rifle set up it had been in. Tried to lighten her up a bit. Shes still heavy.

Anyways, with the carbine buffer setup, it kicked hard. like, not really fun to shoot. So I got a springco spring designed for AR10 carbine buffer length. MUCH smoother shooting. Made it feel like rifle length again.

However, I had issues adjusting the seeking adj gas block. I cannot get it to lock back on an empty mag no matter how much gas I'm letting in. To the point where I've loosened out the gas to the point where the adjuster screw flies out, and I have dobe this twice now.

I'm assuming that the springco spring is making it softer shooting, but also preventing the bcg from being able to move back far enough to lock back. Its ejecting but then having issues feeding the next round, its not moving far back enough to catch the head of the case.

Any other opinions here? SHould I just switch it back to the regular spring?

Just a little frustrated here.

View attachment 7877667

reason number 10000 why the std milspec buffer/spring are all you'll ever need. and as for recoil? come on man, a gas 308 is a joke, put the stock spring and buffer back in it, and go. other issue that's very common is those things should be drowned in oil. had issues with a brand new dpms and literally was a matter of breaking down the bcg clean soak in oil till you think its too much then oil some more. they do not like dirt , or an lack of lubrication in the 308s

also heres all the buffer info you'll ever need

AR-10/AR 308 Buffer Weights

Building an AR-10 style rifle but not sure what buffer weight to use? We got you!

www.80percentarms.com

below at 18.7 pounds loaded, this is heavy