Lockhart raven questions for the ar15 and raven building experts gas system questions

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soheipp

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Hey,

I finally received my raven the other day. I've been piling up parts yo customize it and I've been slowly putting it together. Have a few questions regarding the gas system and buffers.

I started with a bone stock platinum model. Came with mid length gas system.

I'm trying to build it to represent an A2 style AR.

I've made the following changes:

Swapped stock, buffer tube, recoil spring and buffer with a Surplus milspec solid stock, mil spec buffer tube, recoil spring and buffer.

Swapped barrel with aero precision 20" barrel with FSB gas block. This is a rifle length gas system. Swapped gas tube with a rifle length gas tube.


So the main take aways here are the following:

- started with a stock mid length gas system rifle
- changed carbine length buffer tube/spring/buffer to a rifle length tube/spring/buffer
- changed gas system from mid length to rifle length


So my questions are:

1) with these changes, would you change anything before test firing? Would you say the buffer weight will be adequate or should I go heavier or lighter before test firing? Is there a specific weight in ounces I should be aiming for?

2) will there be any possibility of the bolt carrier over traveling?

3) for anyone that has done something similar, did you have to modify the gas port size or was a standard gas port adequate?

4) being that the bolt carrier is skeletonized and thus lighter than a typical mil spec ar bolt carrier, would the rifle be over gassed as it is currently set up?
 
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soheipp said:
I've made the following changes:

Swapped stock, buffer tube, recoil spring and buffer with a Surplus milspec solid stock, mil spec buffer tube, recoil spring and buffer.

Swapped barrel with aero precision 20" barrel with FSB gas block. This is a rifle length gas system. Swapped gas tube with a rifle length gas tube.


So the main take aways here are the following:

- started with a stock mid length gas system rifle
- changed carbine length buffer tube/spring/buffer either a rifle length tube/spring/buffer
- changed gas system from mid length to rifle length


So my questions are:

1) with these changes, would you change anything before test firing? Would you say the buffer weight will be adequate or should I go heavier or lighter before test firing? Is there a specific weight in ounces I should be aiming for?

2) will there be any possibility of the bolt carrier over traveling?

3) for anyone that has done something similar, did you have to modify the gas port size or was a standard gas port adequate?

4) being that the bolt carrier is skeletonized and thus lighter than a typical mil spec ar bolt carrier, would the rifle be over gassed as it is currently set up?
Click to expand...

A. You seem to not understand what "mil spec" means with respect to the buffer tube. Mil spec refers to the outer diameter of the buffer tube. The civilian buffer tubes have a different outer diameter. This is only relevant to how the carbine stocks fit the carbine buffer tubes. What you really did (I think) was to switch from a carbine buffer tube to a rifle buffer tube. This is a difference in buffer tube length, which requires a rifle length buffer.

1. The only way to know is to shoot the thing. I am not aware of different weight rifle buffers. The AR gas system is self regulating, so it can use many different weight buffers and work just fine.

2. You can figure this out prior to shooting the rifle. Remove the upper. Take the BCG and by hand, push it into the buffer tube. You will be able to feel it bottom out. The gas key should not hit the back end of the lower receiver.

3. As port size cannot be made smaller, you should leave it alone until you have exhausted all buffer and spring weight combinations.

4. That carrier is longer, which is likely why it needs to be skeletonized to bring it back within the normal weight range of an AR BCG. The best way to know if the BCG/spring combination is working properly with the gas port size is to shoot the thing and see where it is ejecting the cases.

https://www.wideners.com/blog/ar-15-ejection-patterns/

AR-15-Ejection-Patterns-Web.jpg
 
Ok. I'll check the over travel and report back. If it's good, then maybe I'll just buy an adjustable buffer weight and take with me to the range and work with the chart you shared. Thanks for your assistance.
 
Over travel isn't an issue. The carrier travels good. So I guess it's time to test. I'll report back when I have a chance to get out to the range.
 
There is "prepared" and then there is "contingency exhaustion". You are tending towards over-preparation and are waaayyyy over-thinking the problem. Just shoot the damned thing already, and adjust according to ejection pattern as discussed. Easy-peasey.

The Bolt-Carrier is skeletonized because it is longer than a standard AR15 Carrier. It maintains the same approximate weight as an AR15 Carrier, and is therefore not something that you need to worry yourself about.

You have an adjustable Gas Block that allows you to regulate the amount of energy that in turn, determines your Bolt-Carrier's velocity and thus the ejection pattern. Adjust the Gas Regulator and that will adjust the ejection pattern until you get it where you want it. Ensure that the Bolt locks back behind the Bolt Catch on a reliable basis after the last round is fired. Add 2 more clicks of extra Gas (turning out the Gas Screw) for good measure. You are done.
 
Bartok5 said:
There is "prepared" and then there is "contingency exhaustion". You are tending towards over-preparation and are waaayyyy over-thinking the problem. Just shoot the damned thing already, and adjust according to ejection pattern as discussed. Easy-peasey.

The Bolt-Carrier is skeletonized because it is longer than a standard AR15 Carrier. It maintains the same approximate weight as an AR15 Carrier, and is therefore not something that you need to worry yourself about.

You have an adjustable Gas Block that allows you to regulate the amount of energy that in turn, determines your Bolt-Carrier's velocity and thus the ejection pattern. Adjust the Gas Regulator and that will adjust the ejection pattern until you get it where you want it. Ensure that the Bolt locks back behind the Bolt Catch on a reliable basis after the last round is fired. Add 2 more clicks of extra Gas (turning out the Gas Screw) for good measure. You are done.
Click to expand...

Non adjustable gas block. It's a front sight base gas block. Think of a Vietnam Era m16. That's what I was trying to copy but with a round handguard.
 
soheipp said:
Non adjustable gas block. It's a front sight base gas block. Think of a Vietnam Era m16. That's what I was trying to copy but with a round handguard.
Click to expand...

With a fixed Gas Port size, your Buffer and (to a lesser extent) the Operating Spring selection will give you some adjustment capability. The heavier the Buffer, the slower it will run, giving more time for the casing to eject clear of the action. It is when you have inadequate adjustment with Buffers and a fixed Gas Block that you may have to potentially increase your Gas Port diameter (If gas is inadequate) by drilling it out on the Barrel and Gas Block.

I run a Geissele H2 Buffer on a Braided "Super 42" Operating Spring in my Raven and it functions perfectly with the Gas set at around 17 clicks. Your results are going to be different with a fixed Gas Block. If anything, you are likely to be over-gassed, in which case a heavier Buffer may be necessary to try to slow the cyclic rate (Bolt velocity) down until you get the ideal 4 o'clock ejection pattern with positive empty lock-back.
 
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Just run it with the mods, there was no reason to change the buffer tube lengths when changing the gas system.

As a rule of thumb, you want enough gas to cycle the action, but not so much gas that its slamming the carrier back. but not so little that it wont cycle reliably.
The heavier your buffer weight, the slower your bolt moves backwards, too heavy of a buffer will cause short cycling, too light will increase felt recoil
You can achieve results in various ways, changing gas tube lengths, buffer weights, or adjustable gas blocks.

In your case i would test it first, pick what needs to be tuned and then decide what method you will adopt to accomplish that.
Is it under gassed or short cycling? reduce buffer weight
Is it over gassed? increase buffer weight.
Don't want to change buffer weights and would just like that perfect smooth action, buy an adjustable gas block, then fine tune it without changing anything else.
My ATRS was tuned to cycle flawlessly with 55 grain XM193 with zero felt recoil, captured springs, adjustable buffer and adjustable gas block, carbine length buffer spring with rifle length gas tube. Rested on the bipod with no bracing anywhere else, it could shoot unsupported and moved back maybe 2mm per shot, and even that could be reduced but then it wouldn't cycle reliably with varying brands.

with these changes, would you change anything before test firing? Would you say the buffer weight will be adequate or should I go heavier or lighter before test firing? Is there a specific weight in ounces I should be aiming for?
Nothing, whatever parts you have and test them, change them if needed.

will there be any possibility of the bolt carrier over traveling?
Not really, your spring will prevent that, but if its too violent for recoil then its over gassed and underweight on the buffer.

for anyone that has done something similar, did you have to modify the gas port size or was a standard gas port adequate?
Don't modify your barrel or block, its not worth the effort, get an adjustable gas block if all other methods to tune fail

being that the bolt carrier is skeletonized and thus lighter than a typical mil spec ar bolt carrier, would the rifle be over gassed as it is currently set up
May not be over gassed but might increase felt recoil due to travel speed, buffer weights will help compensate, but may not be needed. skeletonized BCGs are primarily used to reduce total build weight.
 
Bartok5 said:
There is "prepared" and then there is "contingency exhaustion". You are tending towards over-preparation and are waaayyyy over-thinking the problem. Just shoot the damned thing already, and adjust according to ejection pattern as discussed. Easy-peasey.

The Bolt-Carrier is skeletonized because it is longer than a standard AR15 Carrier. It maintains the same approximate weight as an AR15 Carrier, and is therefore not something that you need to worry yourself about.
Click to expand...

Agreed. People have a tendency to overthink stuff. Firearms are not rocket science.



Bartok5 said:
With a fixed Gas Port size, your Buffer and (to a lesser extent) the Operating Spring selection will give you some adjustment capability. The heavier the Buffer, the slower it will run, giving more time for the casing to eject clear of the action. It is when you have inadequate adjustment with Buffers and a fixed Gas Block that you may have to potentially increase your Gas Port diameter (If gas is inadequate) by drilling it out on the Barrel and Gas Block.

I run a Geissele H2 Buffer on a Braided "Super 42" Operating Spring in my Raven and it functions perfectly with the Gas set at around 17 clicks. Your results are going to be different with a fixed Gas Block. If anything, you are likely to be over-gassed, in which case a heavier Buffer may be necessary to try to slow the cyclic rate (Bolt velocity) down until you get the ideal 4 o'clock ejection pattern with positive empty lock-back.
Click to expand...

It is my understanding that he has gone to a rifle stock, with its longer buffer tube and buffer. I've never seen different weight rifle buffers available.

It would be possible to increase the weight of a rifle buffer by opening it up and replacing the aluminum spacer with an additional carbide weight or possibly two, if there is enough room inside.
 
Enough talk. Time to shoot it, analyze, and adjust from there.

- If no adjustment is needed, then great.

- If adjustment is required and different-weighted buffer(s) are not an option, then you will have to find a FSB-style Gas Block with an adjustable Gas Regulator.
 
I was out to the ranch yesterday and the access road is horrible. We need some decent weather for the muck to dry out. I have a bunch of new targets to get set out and some work to do on the shooting point shack.
 
So I went out and shot the rifle. Its ejecting at 1 O'clock position. It's not sending the carrier far back enough to pick up another round. So where do I start? I'm assuming the only thing that can be changed or adjusted is the buffer weight and recoil spring.

Buffer weight is 146g if that helps.
 
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So the ejection is at 1 o'clock which, going by the ejection chart, says the thing is overgassed. However you also say the carrier is short stroking and not picking up another round, which means it is under gassed.

Your buffer is very heavy, being between H2 and H3 in weight.

Lets ignore the ejection pattern for the moment and focus on getting the thing to cycle properly, pick up rounds from the mag and lock back on an empty mag.

As you currently have just about the heaviest possible buffer, the obvious thing and the least expensive would be to try a standard buffer, which will weigh 85gr. Try that and lets see what happens.
 
I Dont Care About You said:
So the ejection is at 1 o'clock which, going by the ejection chart, says the thing is overgassed. However you also say the carrier is short stroking and not picking up another round, which means it is under gassed.

Your buffer is very heavy, being between H2 and H3 in weight.

Lets ignore the ejection pattern for the moment and focus on getting the thing to cycle properly, pick up rounds from the mag and lock back on an empty mag.

As you currently have just about the heaviest possible buffer, the obvious thing and the least expensive would be to try a standard buffer, which will weigh 85gr. Try that and lets see what happens.
Click to expand...

Ok. I ordered an adjustable buffer that goes from 2.8oz to 5.7oz. I'll hit the range next week and report back. Thanks guys!
 
A word of warning on the builder's kit:

My buffer tube threading was out of spec, as was my bolt carrier geometry / height over the trigger.

I assembled my rifle and spent several days getting it to feed and function, needing to dress the underside of the carrier as my trigger drag was so excessive it was scoring into the bolt body.

My point: Keep your eyes out for abnormal wear on bearing surfaces, as it is plausible that tolerances on your kit may not be assumed to be correct.
 
I Dont Care About You said:
It is my understanding that he has gone to a rifle stock, with its longer buffer tube and buffer. I've never seen different weight rifle buffers available.
Click to expand...
ODIN Works offers adjustable rifle buffers designed specifically for rifle-length buffer tubes in the AR-15 platform. This buffer is constructed from high-quality aluminum and feature adjustable weights to fine-tune the recoil impulse and cycling of your AR-15 rifle.
 
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