Lightweight bolt carriers

[Brian46]

Looking for literature (or real world knowledge) on how to select a buffer and buffer spring when going to a lightweight carrier on my stag 10 to maintain proper operation.

I don't want to be one of those guys who keeps throwing parts at a gun that never seems to work right other than on internet message boards (we all know these guys)

I will be doing the same on a big bore AR15, so any knowledge there is much appreciated as well.

 

[TRG-42]

Did a pair of Stag-10 in 6.5CM with JP LMOS carrier

JP recommends their H1 Silent Capture Spring ( they have selector chart which shows this )

Just for comparison, the other one i went with a Armaspec Stealh Recoil Spring ( same idea as SCS but bit less expensive ) . I emailed Armaspec and they responded ( within the hr ! ) to go with the H1 ( 3.8 oz ) SRS

Keep in mind this is with a adjustable gas block . which is highly recommended with these setups

Hard to tell the difference since one gun is significantly heavier than the other

Bottom line, both manufacturers recommend only a H1 weight for 308 and 6.5 CM with adjustable gas block and LOMOS carrier

Total different if you didn't have the JP LMOS

So far , don't think there is any issue of not having the inertia to strip a round of mag

 

[JungerJager]

Odin Works has an Adjustable line of buffers now, for exactly this purpose, and they have one specifically for AR10's. I'm waiting on one of their Low Mass BCG's for an AR I'm building and will be using one of their adjustable gas blocks and buffers.

 

[Brian46]

Odin Works has an Adjustable line of buffers now, for exactly this purpose, and they have one specifically for AR10's. I'm waiting on one of their Low Mass BCG's for an AR I'm building and will be using one of their adjustable gas blocks and buffers.

Thanks for the info. Odin doesn't appear to do a low mass carrier for the ar10 or a "lite" buffer like they do for the ar15 with a low mass carrier. The buffer spring chosen with said buffer will also effect operation and I didn't see anything about how to select one.

Ideally I would want to get the rifle shooting as soft as possible via the buffer, buffer spring and size of gas port selection. Then I would add an adj gas port to compensate for different ammo types. If I add the adj gas block into the mix right away, it will add another level of complication in to initial setup.

I'm surprised there isn't more information on the topic from parts manufacturers on what buffer and spring combo to use on their carrier for said caliber for even a baseline to start with.

 

[Blastattack]

Thanks for the info. Odin doesn't appear to do a low mass carrier for the ar10 or a "lite" buffer like they do for the ar15 with a low mass carrier. The buffer spring chosen with said buffer will also effect operation and I didn't see anything about how to select one.

Ideally I would want to get the rifle shooting as soft as possible via the buffer, buffer spring and size of gas port selection. Then I would add an adj gas port to compensate for different ammo types. If I add the adj gas block into the mix right away, it will add another level of complication in to initial setup.

I'm surprised there isn't more information on the topic from parts manufacturers on what buffer and spring combo to use on their carrier for said caliber for even a baseline to start with.

Not sure why that’s surprising. They have no idea what kind of gun you’re using it in. Installing a lightweight BCG in an AR with an adjustable gas block means you can use any buffer you want, theoretically. Conversely in a fixed gas system it depends on your barrel length, gas length and gas hole size. Essentially any variation or combination of different sizes would mean a different buffer. It’s the same reason that scopes don’t come with rings, they don’t know what it’s going to be used on, and if the first set doesn’t work, try another!

As for adjustable gas blocks, they simplify everything immensely. Start with the thing closed and open it up one increment every shot (magazines loaded with 1 round). When the gun cycles and locks back on a given setting, open up one or two more increments and you’re golden. You’ve now successfully set it as soft as it can go for that ammo and bolt/buffer setup.

 

[Brian46]

Not sure why that’s surprising. They have no idea what kind of gun you’re using it in. Installing a lightweight BCG in an AR with an adjustable gas block means you can use any buffer you want, theoretically. Conversely in a fixed gas system it depends on your barrel length, gas length and gas hole size. Essentially any variation or combination of different sizes would mean a different buffer. It’s the same reason that scopes don’t come with rings, they don’t know what it’s going to be used on, and if the first set doesn’t work, try another!

As for adjustable gas blocks, they simplify everything immensely. Start with the thing closed and open it up one increment every shot (magazines loaded with 1 round). When the gun cycles and locks back on a given setting, open up one or two more increments and you’re golden. You’ve now successfully set it as soft as it can go for that ammo and bolt/buffer setup.

I understand the theory, but that is assuming the gas port was drilled larger than required and you use the adj block to reduce the amount of gas until the rifle barely cycles.

You could do the same with changing buffer spring rates and weights until you have a soft shooting rifle

Obviously people manufacturing rifles have a formula to figure out how to get a soft shooting rifle without an adj gas block or every ar would come with one from factory. Or do you believe they do the trail and error method and keep trying barrels with different gas port sizes, buffer weights and buffer spring rates until they find a combo that works?

 

[Brian46]

I'm leaning towards the cobalt kinetics pro buffer system, anyone have experience good or bad with it?

 

[Blastattack]

I understand the theory, but that is assuming the gas port was drilled larger than required and you use the adj block to reduce the amount of gas until the rifle barely cycles.

You could do the same with changing buffer spring rates and weights until you have a soft shooting rifle

Obviously people manufacturing rifles have a formula to figure out how to get a soft shooting rifle without an adj gas block or every ar would come with one from factory. Or do you believe they do the trail and error method and keep trying barrels with different gas port sizes, buffer weights and buffer spring rates until they find a combo that works?

Pretty sure the vast majority of commercial AR builders go with “size the port and buffer so that the barrel will wear out before the gun stops working”. Unless you buy a top end rifle, every gun will be over gassed to ensure very long term reliability.

 

[Brian46]

Pretty sure the vast majority of commercial AR builders go with “size the port and buffer so that the barrel will wear out before the gun stops working”. Unless you buy a top end rifle, every gun will be over gassed to ensure very long term reliability.

Sure, but they must have a formula for a starting point.

If you go with a heavier buffer and/or spring to get proper operation vs just bleeding more gas to compensate, you end up with a softer shooting rifle.

To me, ideally, the adj gas block is only used to compensate for variations in ammunition, not compensate for an inadequate buffer system

 

[Brian46]

Odin Works has an Adjustable line of buffers now, for exactly this purpose, and they have one specifically for AR10's. I'm waiting on one of their Low Mass BCG's for an AR I'm building and will be using one of their adjustable gas blocks and buffers.

I actually emailed odin about the buffers and spring they suggest to use. Interestingly enough, they said as a rule of thumb, low mass or lightweight carriers should not be used in a high pressure situation and sighted the creedmore and valkyrie as examples

 

[mileageman]

Not sure why that’s surprising. They have no idea what kind of gun you’re using it in. Installing a lightweight BCG in an AR with an adjustable gas block means you can use any buffer you want, theoretically. Conversely in a fixed gas system it depends on your barrel length, gas length and gas hole size. Essentially any variation or combination of different sizes would mean a different buffer. It’s the same reason that scopes don’t come with rings, they don’t know what it’s going to be used on, and if the first set doesn’t work, try another!

As for adjustable gas blocks, they simplify everything immensely. Start with the thing closed and open it up one increment every shot (magazines loaded with 1 round). When the gun cycles and locks back on a given setting, open up one or two more increments and you’re golden. You’ve now successfully set it as soft as it can go for that ammo and bolt/buffer setup.

What he said^^^^^^

Why do you want to run a lightweight carrier?

There is no 'simple formula' to do a calculation. If you aren't going to run an adjustable gas block, whatever weight you save on the bolt carrier, just add that to the buffer to get you in the ball park area

Manufacturers would size their gas port to function in the cold, with a dirty gun, with frozen lube and the weakest ammo available. That is why most factory guns are over gassed.

Just save yourself the aggravation and buy an adjustable gas block from the beginning.

 

[Brian46]

What he said^^^^^^

Why do you want to run a lightweight carrier?

There is no 'simple formula' to do a calculation. If you aren't going to run an adjustable gas block, whatever weight you save on the bolt carrier, just add that to the buffer to get you in the ball park area

Manufacturers would size their gas port to function in the cold, with a dirty gun, with frozen lube and the weakest ammo available. That is why most factory guns are over gassed.

Just save yourself the aggravation and buy an adjustable gas block from the beginning.

The idea is to have a lighter rifle overall, but even moving weight rearward (out of carrier and into buffer) makes sense

It is also not a 556 cal rifle. I may even go with a master of arms carrier that incorporates a deadblow system for added dampening of the big bore caliber.

From everything I have read and researched so far it will need to be a 5+oz buffer and heavy spring.

Yes, factory rifles come overgassed, not what I want. I also don't want to compensate for the wrong buffer with an adj block. You have a better operating rifle with smoother recoil impulse if you get the buffer and buffer spring correct.

It is not as simple as adding the weight difference in the carrier to the buffer because we are dealing with different buffer spring rates as well.

Here is the basics dumbed down

The rule of thumb to follow is that you want the heaviest that will allow your rifle to fully cycle, extract and eject the spent casing, and load a new round in the chamber.

For most builds, a standard carbine buffer is the way to go. A lot of times however, you may find that the gas port on barrel may have a slightly oversized gas port.

This can often lead to your BCG travel too fast, violent extraction, etc. Barrel makers do this so their rifles will still cycle when people use cheaper, underpowered ammo. You can also tell if your system is overgassed by making a note of how the spent casings are ejected. Ideal ejection will throw spent casings in the 3-4 o’clock direction. If it’s throwing the casings ahead of the shooter, the system is overgassed.

Going heavier in this instance will slow down the BCG and lead to better operation, as well as allowing more of the excess gas and carbon to exit the rifle and give you cleaner operation overall.

 

[greg olmstead]

My 6.5 creedmoor stag 10 was so over gassed that using the lantac e bcg (18.2 oz) and the jp scs h2 with their heaviest spring still didnt get it to where I wanted it I had to use a adj gas block. I could add one more tungsten weight (h3) and it would still be over gassed. using a light weight bcg without a adj gas block you are going to run into over gassed problems unless you start with a rifle length +2 gas system and smaller than normal gas port. That would be the way to get it gassed right is to start extra small with the gas port and slowly open up the gas port until you get the rifle to cycle reliably. The 6.5 has such a high case volume to bore capacity ratio that I dont think a person would be able to get it gassed right without messing with the gas port.

Just my experience with the 6.5 creedmoor.

 

[Brian46]

My 6.5 creedmoor stag 10 was so over gassed that using the lantac e bcg (18.2 oz) and the jp scs h2 with their heaviest spring still didnt get it to where I wanted it I had to use a adj gas block. I could add one more tungsten weight (h3) and it would still be over gassed. using a light weight bcg without a adj gas block you are going to run into over gassed problems unless you start with a rifle length +2 gas system and smaller than normal gas port. That would be the way to get it gassed right is to start extra small with the gas port and slowly open up the gas port until you get the rifle to cycle reliably. The 6.5 has such a high case volume to bore capacity ratio that I dont think a person would be able to get it gassed right without messing with the gas port.

Just my experience with the 6.5 creedmoor.

There is a HSS – 6.5oz and a XH – 8.5oz for ar15, nothing similar for AR10?

 

[cr5]

The whole point of a low mass carrier is to reduce reciprocating mass and to reduce the secondary recoil impulse caused by the BCG for a smoother rifle and faster follow up shots.
If you're doing it to make the rifle lighter your doing it wrong and adding more buffer weight to compensate for the low mass carrier is defeating the whole point of spending the money on the lightweight BCG.
You need to run an adjustable gas block with a low mass BCG to get the benefit it was designed to give you.
A standard carbine spring and buffer with an adjustable gas block is what you need.
An adjustable gas block isn't expensive, and it will make your rifle run better without having to buy a bunch of buffers and springs trying to find the right combination.

Since you're not dealing with a 223 you've moved away from the gas pulse the action was designed to use. Your comments in post 12 are 100% correct if you were running a 223 with 55-75 grain projectiles but by going to something like 30AR you are going to need to control the gas pulse better, especially if you're going to run lightweight parts.
The two cartridges make similar pressure from what I've read but there's more to it than that. Think of a Garand, same 30-06 cartridge loaded with two different powders making similar muzzle velocity but one will function perfectly while the other breaks the op rod. This is an extreme example but just showing that there's more to pressure than the number.

When running calibers other than 223 an adjustable gas block is not a solution to a problem that never existed.
My 6.5 Grendel barrel came with a matching BCG and an adjustable gas block, they know that different cartridges adapted to the AR-15 deliver pressure differently than the 223 and it needs to be managed differently.