Low Mass Carrier Questions

[fishsticks]

I'm getting ready to upgrade my upper, and would like to install a JP LMOS.

My question is around buffer/spring set-up. For a mid gas system with adj gas block would I be better off with the JP captured spring or their rifle legnth lo mass buffer?

The captured spring would allow me to keep my current Magpul CTR adjustable stock, going with the low mass rifle buffer would mean changing the stock.

[midget]

You don't have to mess with the buffer system if you don't want to. Personally I have the captured system and like it more than the standard.

[MarkCO]

I use the low mass carriers in all of my competition ARs. I use a standard carbine buffer and spring. I take apart the buffer and remove some of the weights and refill with plastic spacers. Cheaper and better.

[fishsticks]

I use the low mass carriers in all of my competition ARs. I use a standard carbine buffer and spring. I take apart the buffer and remove some of the weights and refill with plastic spacers. Cheaper and better.

Ok, I like this idea.

Would you be willing to share a starting point (how much weight to remove), and what you are using for spacers?

[wgj3]

Lots of info available about this, but basicslly just drive out the pin. Find weights and buffers inside. Replace some of the weights with something lighter. In rifle buffer, a longer case like 30/06 works. In carbine buffer, may have to get a little more creative.

[MarkCO]

Sure. For mid length gas, the stock 3.1 ounces might be fine. That is still lighter than the JP Low mass buffer. For rifle length, I run at 2.5 ounces. Each weight is about 2/3 ounce and the tube and cap are about 1.2 ounces.

Find a plastics shop and buy some delrin rod. I don't remember the OD, but just measure the OD of the weight. Cut off a section, run a 1/2" drill through the center and replace one or two weights. If you want less, but not a whole weight worth, just drill out the center a bit more.

I shot a few rounds with no weights at all and it was a bit too bouncy, but I know there are a few guys running pretty soft loads who have gone to empty buffers.

[fishsticks]

Sure. For mid length gas, the stock 3.1 ounces might be fine. That is still lighter than the JP Low mass buffer. For rifle length, I run at 2.5 ounces. Each weight is about 2/3 ounce and the tube and cap are about 1.2 ounces.

Find a plastics shop and buy some delrin rod. I don't remember the OD, but just measure the OD of the weight. Cut off a section, run a 1/2" drill through the center and replace one or two weights. If you want less, but not a whole weight worth, just drill out the center a bit more.

I shot a few rounds with no weights at all and it was a bit too bouncy, but I know there are a few guys running pretty soft loads who have gone to empty buffers.

Perfect, thanks!

[MickB]

Mark,

you run the low mass carriers even with a non adjustable gas system? Is the reason to increase cycling speed for faster split times?

Mick

I use the low mass carriers in all of my competition ARs. I use a standard carbine buffer and spring. I take apart the buffer and remove some of the weights and refill with plastic spacers. Cheaper and better.

[Jadeslade]

Everybody does this a little differently. JP LMOS rifle buffer weighs the same as a standard carbine buffer. I don't know why you would want to lighten carbine buffers. Most shooters I know don't reload .223. Too time consuming. You can cut springs to ease up on the bounce. Muzzle breaks make a huge difference, too. JP suggested the carbine buffer to me years ago when they were out of rifle LMOS buffers. Some rifle springs, especially JP's are a little tight and benefit from one or two coils taken off. I have some adjustable gas blocks, but these days I want as much velocity as I can get and rarely use them.They are really helpful when using a silencer. Its a constant process to tune a rifle because of ammo variability. I would love for a chrono and zero range to be available at every match. But they aren't. Task Force Dagger has the best set up I have seen for a major match-you can bring your own chrono if you want, but the zero range is available all the time should you need to check zero. Superstition has a zero range all the time, but it is a pain to use quickly.

[MarkCO]

Mick, yes. The low mass carrier reduces the recoil impulse and keeps the gun flatter. I don't load full pop 55s either, so I am essentially reducing the gas through volume and a smaller gas port as well.

[Obsucrem]

What would the downside to a LMOS be in the realm of reliability? It would seem that a light bolt with increased carrier speed would lead to early extraction problems similar to some cheaper over-gassed factory rifles. I guess I could see that slowing down a bit with lighter pressure ammo or perhaps an adjustable gas block...

[kurtm]

Light carriers have been around since 1999, the first ones were aluminum. Since that time virtually every top 3-gunner runs one. If they were a reliability issue I doubt they would use them. I usually run my light carriers fully gassed and unlike my amigo MarCo I do load my 223 HOT! I have never had reliability problems with them.

[MarkCO]

My 69s are at the top end of the .223 pressures, and I have 77s at 5.56 pressures, so I do run some "HOT" ones too.

[Nathan]

It doesn't sound like many people here have had a lot of issues, or know people who have, but from some of the research I've been doing, you run the risk of FTE's. I started having this issue with my .308 AR, here are links to a couple interesting sites that discuss this topic. YYMV, etc etc.

http://ar15barrels.com/prod/operation.shtml

http://www.majorpandemic.com/2012/06/all-about-adjustable-ar-gas-blocks.html

It seems to me like the cliff-notes version is that for .223, most people will find if they don't tune it down they are just dealing with a bit more recoil (negligible with many of the brakes, etc that are run) but for a few, and more common with the .308 (whether through gas port being too larger or just the higher volume of gas?), it can throw off the timing and your bolt carrier starts running back sooner than it should, damaging brass and/or failing to extract. Of courst the down-side is if you tune too tight trying to walk that line, your chances of "under-gassing" go up.

[mpeltier]

Usually when someone has trouble with a LMOS system it's the loose nut behind the wheel. Properly set up and with good ammo it is very reliable. As reliable as anything else.

[fishsticks]

Quick update with another question -

So I installed the LMOS carrier/JP Bolt in combination with a 16" mid gas barrel with a Surefire MBK556 brake, carbine spring/H2 buffer and Syrac adjustable gas block. Shooting XM193 the bolt locks back and extracts reliably even with the adjustment turned all the way down.

The system shoots smooth, and there is much less muzzle rise than before the upgrade. I'm pleased with the result.

Is there any reason to lighten the buffer??

[Therealkoop]

As a related question, what is the actual weight of a JP low mass versus a standard semi or full auto carrier?

[bagdrag]

Why add weight to the system with an H2 buffer? What was wrong with the standard carbine buffer?

[mpeltier]

As a related question, what is the actual weight of a JP low mass versus a standard semi or full auto carrier?

According to my postal scale:

JP LMOS=6.6 oz

AR15=9.1

M16=9.3

Carriers with key and no bolt group

[fishsticks]

Why add weight to the system with an H2 buffer? What was wrong with the standard carbine buffer?

When I bought the lower build kit from PSA several years ago, that's what came with it and it's the only buffer I have.

That's really the question - what are the pros/cons of reducing the buffer weight?

[MarkCO]

Reducing the buffer weight and the carrier weight both serve to slghtly increase wear and decrease the amount of felt recoil due to increased cycle rates.

[Therealkoop]

As a related question, what is the actual weight of a JP low mass versus a standard semi or full auto carrier?

According to my postal scale:

JP LMOS=6.6 oz

AR15=9.1

M16=9.3

Carriers with key and no bolt group

Thank you sir.

Does the buffer weight and carrier act as one unit? Is there a reason to use a low mass carrier over an ultra light buffer if the combined weight of the buffer and carrier are the same?

[Zmego]

#1 - I run a 18" rifle length system with a non-adjustable gas block, full auto carrier, carbine tube/spring, and a heavy buffer. I feel like my setup shoots pretty flat. How big of a difference in recoil are we talking?

#2 - Can I use a low mass BCG with my spring/tube/buffer set up?

#3 - Thanks

[MarkCO]

#1 - I run a 18" rifle length system with a non-adjustable gas block, full auto carrier, carbine tube/spring, and a heavy buffer. I feel like my setup shoots pretty flat. How big of a difference in recoil are we talking?

#2 - Can I use a low mass BCG with my spring/tube/buffer set up?

#3 - Thanks

#1, go to a low mass carrier and you will not think your rifle is the flat anymore.

#2, you can use a low mass carrier with a heavy buffer, but you will be robbing yourself of some recovery time. Better with a standard carbine buffer.

#3, you are most welcome. If you go faster, you owe me a packet of gun oil, I am almost out.

[Zmego]

Everytime you give me advice, it costs me money! You should work out some sort of commission plan with JP!

Gun oil is in the mail!