Buffer weights, bolts and ammo. How do they play well together?

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gun'sRgood

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What is the relationship between buffer weights, bolts and ammo? Or is that too simplistic? AR 15's lite to heavy take a 2.1 - 5 oz, an AAR 10 with a 3.7 - 5.8 and then a 9 takes a 5.4 - 7.4. This data from Odin Works Adjustable buffer weight system. Watching a gun show and they were discussing how certain combinations were incompatible as a monster 40 oz weight would be required. I don't recall the premises. Open -v closed bolt? Which is? To further impregnate this, JP has a short stroke 9mm bolt. Is this for faster operation or used in full auto? Would a short stroke 9mm bolt take less weight?
 
For Direct Gas Impingement rifles... ( gas tubes in Typical AR's ) you need to add gas port size, recoil spring strength , and how smoothly the various parts cycle to your "buffer, bolts, and ammo"

Gas ports being the most important... I have seen massive gas port sizes ( WAY bigger than desired ) and smaller sizes ( limiting gas flow for suppressors )
So a huge gas port will need a different heavier buffer weight v. a small gas port needing a lighter buffer weight.

Oops... the powder used ( 300BK pistol powder ) will also dictate buffer weights and springs.

Open v. Closed 9MM Bolt ....
https://www.youtube.com/watch?v=Ga4uoWmfEt4
However the CMMG delayed 9MM bolt is a worthwhile design.

Short stroke 9MM bolts are mostly because the travel needed by a 9MM PCC bolt... the 9MM is much shorter then a typical 5.56 sized AR.

Because most 9MM PCC's are blowback operated , IMHO... you "want" a heavy reciprocating mass to reduce out of battery firing. IE to fast a cyclic speed, and the firing cartridge can become no longer fully supported by the chamber... and resulting in possible case ruptures. And bolt bounce in a 9MM blowback action is a real thing.... ( more possible out of battery discharge )

A heavy reciprocating mass will slow the action... but can also increase possible bullet setback, if the ammo doesn't feed readily.

Also... a blowback 9MM really needs to have its chamber kept fairly clean... easy chambering will lessen possible out of battery firing.

Ironically.... I have even seen the shooters body mass have impact on smooth function.

If you have a specific setup you are trying to tune... please describe it in detail.

If this is a curiosity thing.... then more power to you for trying to learn !
 
Yeah, I do have a particular issue but the whole thing is very interesting. So, first, thx! On the AR 15. I thought that the larger gas port was for the FA set ups? And as such, the semi auto's tend to be over gassed? Do barrel mfg's port for FA and expect you to put on an adjustable gas block? Right now I'm trying to get a 9 to work. It has a heavy buffer weight and a short stroke JP bolt. It looks like there is not enough time to get the fired round out before it's trying to load the next round. Am I off base to think that the short stroke bolt would need less buffer weight mass?
 
Large gas ports "allow" the use of underpowered 5.56 / .223 ammo... Wolf, Tula ,PMC Bronze, with their weaker powders used ( those brands tend to use as low cost of powders available ) .. a large gas port will also help force function under crappy conditions... filthy rifle , cold weather, etc.

However a large gas port can batter parts faster with full power 5.56 ammo.

FWIW... the AR15 carbine length gas system has been used for decades, successfully. And it draws gas at a fairly high PSI point in the barrel as opposed to a rifle length gas system and its lower gas port pressure point.

FWIW, the huge gas port size I mentioned earlier was WAY oversized, and was actually breaking the owners hammer pins ! WAY to much BCG speed.

What are your 9MM build details ? Brand, pattern ( Colt or Glock ? )

And sometimes the cyclic speed can be to fast, not allowing the various parts "time" to keep up.

Using a suppressor will even increase cyclic speed, over working the system.

My Colt pattern 9MM PCC 16" barrel runs best with a Tubbs 308 flatwire recoil spring, a 7.5oz buffer weight, and a typical 9MM AR bolt.
I tried danged near every buffer weight and recoil spring weight I could get my hands on... all the way up to a 10oz buffer and a Sprinco Red recoil spring ( WAY to heavy a setup.. it would function, but the muzzle would dip everytime it went into battery .

After briefly looking at the JP short stroke system... it appears to be a setup designed for a 9MM PCC, again for its shorter bolt travel.
My Colt pattern has a "short stroke system" as well, simply because its bolt doesn't need to travel as far as a typical 5.56 / .223 bolt would ( 9MM is shorter then the 5.56 OAL )
I guess you could call a Large Frame AR in .308 a long stroke system. ( Again longer cartridge )
 
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just like tuning the recoil springs in a semi automatic pistol, all you are doing is changing the speed of the bolt. larger gas ports or ammo that results in higher port pressure imparts more force and speed on the bolt. Heavier reciprocating mass or heavier springs slows down the bolt speed. If your ejecting brass 10 feet, ripping the rims off cases, or generally experiencing harsh recoil, then the bolt is going too fast. If you are having stove pipes, failure to lock back on an empty mag, or generally weak ejection, then the bolt is not traveling fast enough.

The purpose of the sliding weights in the buffer is to help prevent bolt bounce on full auto. The little weights in the buffer hit the back of the bolt a moment after the bolt closes, which cancels out the bounce. Several of my rifles have adjustable gas blocks to tune the bolt speed and no buffer weights at all. Just an empty buffer housing, which is probably an ounce or ounce and a half. I like the smooth feel of the reduced reciprocating weight and I have no issues at all.
 
bfoosh006 said:
Large gas ports "allow" the use of underpowered 5.56 / .223 ammo... Wolf, Tula ,PMC Bronze, with their weaker powders used ( those brands tend to use as low cost of powders available ) .. a large gas port will also help force function under crappy conditions... filthy rifle , cold weather, etc.

However a large gas port can batter parts faster with full power 5.56 ammo.

FWIW... the AR15 carbine length gas system has been used for decades, successfully. And it draws gas at a fairly high PSI point in the barrel as opposed to a rifle length gas system and its lower gas port pressure point.

FWIW, the huge gas port size I mentioned earlier was WAY oversized, and was actually breaking the owners hammer pins ! WAY to much BCG speed.

What are your 9MM build details ? Brand, pattern ( Colt or Glock ? )

And sometimes the cyclic speed can be to fast, not allowing the various parts "time" to keep up.

Using a suppressor will even increase cyclic speed, over working the system.

My Colt pattern 9MM PCC 16" barrel runs best with a Tubbs 308 flatwire recoil spring, a 7.5oz buffer weight, and a typical 9MM AR bolt.
I tried danged near every buffer weight and recoil spring weight I could get my hands on... all the way up to a 10oz buffer and a Sprinco Red recoil spring ( WAY to heavy a setup.. it would function, but the muzzle would dip everytime it went into battery .

After briefly looking at the JP short stroke system... it appears to be a setup designed for a 9MM PCC, again for its shorter bolt travel.
My Colt pattern has a "short stroke system" as well, simply because its bolt doesn't need to travel as far as a typical 5.56 / .223 bolt would ( 9MM is shorter then the 5.56 OAL )
I guess you could call a Large Frame AR in .308 a long stroke system. ( Again longer cartridge )
Click to expand...
This 9 is a Glock with Rainier Arms barrel. Both the JP and Stern Defense are having problems extracting the spent round. Or, changing the bolt and buffer weights in any combination have the same result. I have a fancy titanium muzzle brake that threads into a suppressor. Can I have a extraction issue with what is screwed onto the end of the barrel? I will try any of the combinations I can think of, I just would like to know what math problem I'm trying to solve. Thanks for your time and thoughts. I'll get a few pics up in a bit.
 
someguy2800 said:
just like tuning the recoil springs in a semi automatic pistol, all you are doing is changing the speed of the bolt. larger gas ports or ammo that results in higher port pressure imparts more force and speed on the bolt. Heavier reciprocating mass or heavier springs slows down the bolt speed. If your ejecting brass 10 feet, ripping the rims off cases, or generally experiencing harsh recoil, then the bolt is going too fast. If you are having stove pipes, failure to lock back on an empty mag, or generally weak ejection, then the bolt is not traveling fast enough.

The purpose of the sliding weights in the buffer is to help prevent bolt bounce on full auto. The little weights in the buffer hit the back of the bolt a moment after the bolt closes, which cancels out the bounce. Several of my rifles have adjustable gas blocks to tune the bolt speed and no buffer weights at all. Just an empty buffer housing, which is probably an ounce or ounce and a half. I like the smooth feel of the reduced reciprocating weight and I have no issues at all.
Click to expand...
That's really interesting. Thx. I think I'm up against an ejection issue. Be it the Stern Defense or Ranier Arms bolt and with any weight, the end results seem the same. I don't get that as to me the bolt "has" to have the ejector engaged to have fired the first round?
 
Depends on who/where you ask.

Over at arfcom, it's Holy Writ, and all heretics are to be flame-warred at the stake.

There are incantations, rites at midnight, specific molecular weights and configurations, all measured with laser 3d micrometry.

Mind that there are millions of ignorant, hick, AR, working just fine right out the box, with, gasp, "book" configurations.

One of the issues with "lego" rifles is getting knotted up on whether a blue lego is better than a red one.
 
Most, but not all 9mm AR guns use straight blow back. Because it's cheap. It takes a chunky bit of mass to hold the round in battery as it fires. What's the totalweight?
A 5.56 bcg weights about 11oz, imagine the 9mm ones are close to that, but a bit more solid. If your max buffer weight is 5.4oz and say the 9mm bcg weighs 12oz, that's going to leave you a bit light. If your buffer is a std carbine buffer, then you are way too light.
My sten runs straight blow back.
The charging handle, bolt, striker weights nearly 23 ounces. That allows the sten to handle insanely hot 9mm loads that rival 357mag with short barrel length. It runs everything from powder puff silencer loads to unspeakable loads of HS-6 under 147gr bullets.

Might need to try a buffer body made of steel and fill it with tungsten. A steel buffer full of tungsten weights will get you to like 7oz.
I'm assuming you are running a carbine buffer?
 
gun'sRgood said:
That's really interesting. Thx. I think I'm up against an ejection issue. Be it the Stern Defense or Ranier Arms bolt and with any weight, the end results seem the same. I don't get that as to me the bolt "has" to have the ejector engaged to have fired the first round?
Click to expand...

what specifically is happening? Is it just failing to get the spent round out the ejection port?

A blowback gun has a fundamental difference from a gas operated gun. A gas operated gun is powered by a piston so the bolt is actually pulling the round out of the chamber. In a blowback gun the only force available to push the bolt back is the brass case pushing on it, so a blowback gun doesn't even need an extractor to get the case out of the chamber. The job of the extractor in a blowback gun is to hold the spent case in the bolt head until it hits the ejector. If your spent rounds are not making it out the ejection port then often its because the extractor doesn't have enough tension on the spent case to hold it in the bolt head, or the ejector is not hitting the case correctly to propel it out the ejection port, or there is something interfering with the case causing it to not make it out. If may just be that you need an upper with a larger port opening.
 
CapnMac said:
Depends on who/where you ask.

Over at arfcom, it's Holy Writ, and all heretics are to be flame-warred at the stake.

There are incantations, rites at midnight, specific molecular weights and configurations, all measured with laser 3d micrometry.

Mind that there are millions of ignorant, hick, AR, working just fine right out the box, with, gasp, "book" configurations.

One of the issues with "lego" rifles is getting knotted up on whether a blue lego is better than a red one.
Click to expand...
Yeah, gotcha. I really like milspec and then I hate it.
 
N555 said:
Most, but not all 9mm AR guns use straight blow back. Because it's cheap. It takes a chunky bit of mass to hold the round in battery as it fires. What's the totalweight?
A 5.56 bcg weights about 11oz, imagine the 9mm ones are close to that, but a bit more solid. If your max buffer weight is 5.4oz and say the 9mm bcg weighs 12oz, that's going to leave you a bit light. If your buffer is a std carbine buffer, then you are way too light.
My sten runs straight blow back.
The charging handle, bolt, striker weights nearly 23 ounces. That allows the sten to handle insanely hot 9mm loads that rival 357mag with short barrel length. It runs everything from powder puff silencer loads to unspeakable loads of HS-6 under 147gr bullets.

Might need to try a buffer body made of steel and fill it with tungsten. A steel buffer full of tungsten weights will get you to like 7oz.
I'm assuming you are running a carbine buffer?
Click to expand...
Pistol. 7.6oz Stern buffer weight. I shortened the barrel to 6" via Rainier Arms. The stern upper is 7" and runs great. I didn't want the "add-on" Stern conversion kit and went with a dedicated 9mm Glock.
 
someguy2800 said:
what specifically is happening? Is it just failing to get the spent round out the ejection port?

A blowback gun has a fundamental difference from a gas operated gun. A gas operated gun is powered by a piston so the bolt is actually pulling the round out of the chamber. In a blowback gun the only force available to push the bolt back is the brass case pushing on it, so a blowback gun doesn't even need an extractor to get the case out of the chamber. The job of the extractor in a blowback gun is to hold the spent case in the bolt head until it hits the ejector. If your spent rounds are not making it out the ejection port then often its because the extractor doesn't have enough tension on the spent case to hold it in the bolt head, or the ejector is not hitting the case correctly to propel it out the ejection port, or there is something interfering with the case causing it to not make it out. If may just be that you need an upper with a larger port opening.
Click to expand...
Good thoughts. Really nice parts from well established companies. I'll put up a parts list and some pics. Thanks for your time and knowledge.
 
Here are pics of the bolts. Am I missing something here? 9m.jpg 9m.jpg
 

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gun'sRgood said:
Here are pics of the bolts. Am I missing something here?View attachment 1087699 View attachment 1087699
Click to expand...

Is that a regular mill spec upper receiver? Some builders mill out the ejection port on 9mm builds because 9mm AR's tend to have a harder time getting the spent case out the original port opening. CMMG actually sent me a drawing showing the dimensions that they machine their uppers for 9mm and 40 s&w.

It may solve your issue to just swap your barrel and handguard over to a purpose designed 9mm upper with a bigger ejection port like this.

https://ar15discounts.com/products/nbs-ar-9-billet-upper-receiver-for-9mm-45/
 
spikes reciever set.jpg

I bought this. In ten years or so I should have it paid off. I'm now wondering if I have too much absorption of energy at the muzzle. I know that the 9mm pistols sometimes use that spring loaded gizmo to help with cycling. I guess I'm not at the 100% level of understanding on how if you pull off all the forward energy, heat and expansion, why the force of the discharge is not enough to eject it. I'll start with a bare muzzle and go from there. Sure appreciate you guys sharing your advice. I'd bet there's an algorithm for this. Sure like to see it.
 
bfoosh006 said:
Large gas ports "allow" the use of underpowered 5.56 / .223 ammo... Wolf, Tula ,PMC Bronze, with their weaker powders used ( those brands tend to use as low cost of powders available ) .. a large gas port will also help force function under crappy conditions... filthy rifle , cold weather, etc.

However a large gas port can batter parts faster with full power 5.56 ammo.

FWIW... the AR15 carbine length gas system has been used for decades, successfully. And it draws gas at a fairly high PSI point in the barrel as opposed to a rifle length gas system and its lower gas port pressure point.

FWIW, the huge gas port size I mentioned earlier was WAY oversized, and was actually breaking the owners hammer pins ! WAY to much BCG speed.

What are your 9MM build details ? Brand, pattern ( Colt or Glock ? )

And sometimes the cyclic speed can be to fast, not allowing the various parts "time" to keep up.

Using a suppressor will even increase cyclic speed, over working the system.

My Colt pattern 9MM PCC 16" barrel runs best with a Tubbs 308 flatwire recoil spring, a 7.5oz buffer weight, and a typical 9MM AR bolt.
I tried danged near every buffer weight and recoil spring weight I could get my hands on... all the way up to a 10oz buffer and a Sprinco Red recoil spring ( WAY to heavy a setup.. it would function, but the muzzle would dip everytime it went into battery .

After briefly looking at the JP short stroke system... it appears to be a setup designed for a 9MM PCC, again for its shorter bolt travel.
My Colt pattern has a "short stroke system" as well, simply because its bolt doesn't need to travel as far as a typical 5.56 / .223 bolt would ( 9MM is shorter then the 5.56 OAL )
I guess you could call a Large Frame AR in .308 a long stroke system. ( Again longer cartridge )
Click to expand...
If you get a moment would you look at these and tell me if you think the two are related stove.jpg stove 2.jpg ? Thx
 
Dustbowl said:
That definitely looks like an ejector issue. Case isn’t making contact and being flipped out of the gun.
Click to expand...
Idea of what to try? The pics of two different barrels looks the same. But that's my uneducated eye.
 
The shorter the gas tube length the faster and sooner the bolt opens. The result is that the cartridge may be under pressure hindering retraction. Also the extractor is jerking on it causing possible extractor failure. A heavier buffer has more inertia slowing the bolt and extraction. Some use an adjustable gas block for the same purpose.
 
d2wing said:
The shorter the gas tube length the faster and sooner the bolt opens. The result is that the cartridge may be under pressure hindering retraction. Also the extractor is jerking on it causing possible extractor failure. A heavier buffer has more inertia slowing the bolt and extraction. Some use an adjustable gas block for the same purpose.
Click to expand...

blowback 9mm, there is no gas tube or gas block
 
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