Stress on upper?

[Gohring65]

Which is better, bipod closer to the barrel nut or farther on a heavy scopes SPR, I’m thinking the bipod closer to the barrel nut for less strain/leverage on upper where the barrel and rail connects. Is it enough to matter, does barrel nut torque make a difference here?
As the mag empties it changes the weight/strain on the upper. A heavy scope makes things even worse. It might not even make a difference in group size. I need to get out and try it.

 

[gixxer822]

if your barrel is free floated no bipod position will make a negative impact on the rifle.

 

[Gohring65]

if your barrel is free floated no bipod position will make a negative impact on the rifle.

How do you figure that?
The strain is where both rail and barrel are connected. It’s the pinch point for all the weight of the unsupported rifle. Think of a bridge with a long span vs a short span between supports.

 

[JohnCarter17]

You want the bipod as far out as you can go.

FFS

Stress is irrelevant unless you have pot metal barrel nuts and airsoft handguards. It's a weapon not a balsa wood model.

 

[Gohring65]

You want the bipod as far out as you can go.

FFS

Stress is irrelevant unless you have pot metal barrel nuts and airsoft handguards. It's a weapon not a balsa wood model.

Have you tested it, or just saying it because it’s the bolt gun logic so it must be the same?

 

[Gohring65]

I’m not taking about a carbine with a red dot, I’m taking 18-20” barrel 30oz. Scope 20 round mag. Carbine will probably never have that heavy of a scope or have a bipod.

 

[TonyTheTiger]

How hard are you loading your bipod?

 

[Gohring65]

How hard are you loading your bipod?

That will have a effect too, inconsistent pressure from loading. Seems the farther out the bipod the worst this will become.

 

[Gohring65]

Loading the bipod with all the other weight added with scope and mag, ask yourself where the rifle would be trying to buckle, and then ask yourself how much a bolt rifle changes with less stresses on the action and action/barrel junction.

 

[RUTGERS95]

Which is better, bipod closer to the barrel nut or farther on a heavy scopes SPR, I’m thinking the bipod closer to the barrel nut for less strain/leverage on upper where the barrel and rail connects. Is it enough to matter, does barrel nut torque make a difference here?
As the mag empties it changes the weight/strain on the upper. A heavy scope makes things even worse. It might not even make a difference in group size. I need to get out and try it.

why are you even worries about this? We've got about 5.5billion years till the sun burns out, worrying about the sun coming up each day is pointless

 

[Gohring65]

why are you even worries about this? We've got about 5.5billion years till the sun burns out, worrying about the sun coming up each day is pointless

I’ve run out of shit to do in my gun room.
Now I’m down to picking apart 60 year old technology. Lol

 

[JohnCarter17]

Have you tested it, or just saying it because it’s the bolt gun logic so it must be the same?

I say it because the further out the bipod is, the greater the stability. Which has fuck all to do with the action type.

 

[RUTGERS95]

I’ve run out of shit to do in my gun room.
Now I’m down to picking apart 60 year old technology. Lol

lol..I've been there!!!!

 

[Gohring65]

I say it because the further out the bipod is, the greater the stability. Which has fuck all to do with the action type.

You’re not even in the same conversation bud.
You’re talking about stability of the platform, I’m talking about group size from inconsistent pressure introduced on the action, barrel and hand guard area, the barrel nut which is attached to a thin wall aluminum upper. We all know the farther the bipod the better for stability, but is it affecting group size. I say yes it is.

 

[Neurotic]

This is one of the reasons monolithic (or Aero enhanced) uppers exist, to increase the stiffness at the handguard/upper/handguard interface. Then, bipod location and loading doesn't really matter.

 

[Rocketvapor]

On an AR the barrel extension, threaded receiver extension, and barrel nut form a pretty solid metal joint.
Bolt lockup, cartridge support, barrel are tied together through this metal connection.
With one of my heavy AR's, a 5.5 pound 28" bull barrel, is hanging on that joint regardless of bipod position on the float tube.
The full up weight is about 18 pounds (not including bipod).
Supported very close to the receiver and the bipod sees close to 15 pounds, supported at the far end of the float tube the bipod sees about 10 pounds. Any stress/flex in the pinch point would be reversed for each of those conditions. Barrel hanging or rifle sagging. Different but minor load change. You could get a rough estimate of POI change due to upward or downward flex but I don't THINK group size would change because a few pounds difference at the joint. I use a thick walled side charge upper that probably helps with the bending flex some.
A monolithic upper is probably even less effected by a change in vertical load through that joint.

There is probably a midpoint that balances the hanging barrel and the sagging rifle so the static load though the connection to the receiver walls is neutral. Consistent loading, shot to shot is key here. What is the weight change from full to empty mag?
(I single load from a sled )

 

[Gohring65]

This is one of the reasons monolithic (or Aero enhanced) uppers exist, to increase the stiffness at the handguard/upper/handguard interface. Then, bipod location and loading doesn't really matter.

Isn’t the Colt 6940 built this way?

 

[Gohring65]

On an AR the barrel extension, threaded receiver extension, and barrel nut form a pretty solid metal joint.
Bolt lockup, cartridge support, barrel are tied together through this metal connection.
With one of my heavy AR's, a 5.5 pound 28" bull barrel, is hanging on that joint regardless of bipod position on the float tube.
The full up weight is about 18 pounds (not including bipod).
Supported very close to the receiver and the bipod sees close to 15 pounds, supported at the far end of the float tube the bipod sees about 10 pounds. Any stress/flex in the pinch point would be reversed for each of those conditions. Barrel hanging or rifle sagging. Different but minor load change. You could get a rough estimate of POI change due to upward or downward flex but I don't THINK group size would change because a few pounds difference at the joint. I use a thick walled side charge upper that probably helps with the bending flex some.

There is probably a midpoint that balances the hanging barrel and the sagging rifle so the static load though the connection to the receiver walls is neutral. Consistent loading, shot to shot is key here.

Awesome info/input. And I definitely see your point of sag and overhanging load both affecting the POI.

 

[Rocketvapor]

Imagine BALANCING the upper, less mag, ammo, scope, BCG on the bipod. A one finger balance. Any parts (weight added to the rear of the "pinch point" ) added would tilt the upper but it would still be balanced from the walls to crown. The flex load would go up due to full up weight, but the upper/bipod would be balanced.

 

[Rerun7]

I’ve run out of shit to do in my gun room.
Now I’m down to picking apart 60 year old technology. Lol

Sounds like you need to get out of your gun room and go shoot it with the bipod in both positions and let us know how it works out.

 

[Gohring65]

Sounds like you need to get out of your gun room and go shoot it with the bipod in both positions and let us know how it works out.

That is my plan. I always test it. Just waiting on good weather.

 

[whatsupdoc]

So lets see what do you think the difference is between the two bipods attached
to the forearm attached to the barrel nut. Stress on the nut that is.

Took me 4 hours to draw this quality MoFo.

 

[Rocketvapor]

Like your drawing
While it appears the float tube isolates flex, the weight at the joint will be different.
The barrel and float tube will (to a great extent) act as a single solid member flexing just behind the joint.
The barrel will ALWAYS be a hanging force. The net load at the joint (forward wall of receiver) can be changed with bipod position.
The forward bipod location reduces angular input from the operator.

 

[Gohring65]

I think the one closer to the nut would put less stress on the nut.
When the bipod is moved away from the nut, the upper is getting sag from the weight of the barrel and the hand guard because of the leverage from the extended length.
When it’s closer to the nut, it’s getting more over hang force from the barrel and not as much from the guard because the bipod is supporting the guard, and it’s much lighter anyway. So the forces are definitely not equal in each bipod position. The length and weight of the barrel would change the stress direction too. If it’s long with a can or heavy brake, it could cancel the sag introduced with the bipod way out. It could be influencing it no matter where the bipod is. There will be a point where barrel weight/length will over take the weight of the mag and scope and whatever else is weight down the center of the upper, then you got the constant weight change of the mag getting lighter with each pull of the trigger. Going from what a pound or so with a full mag, to a few ounces when getting low on rounds.

 

[Gohring65]

Now I’m thinking the best approach might be a front heavy barrel the overtakes any sag forces no matter the weight in the center. It just seems that the barrel overhang would be more consistent, heavy and long enough not to be influenced by any bipod force, position or any weight from the scope and mag.
Much easier to map and load for than constant changes in bipod force. I guess that’s why Varmint uppers tend to be more accurate overall. But then again we got our fat faces and hands hanging and pressing down also! shit! I need to get out of the house.

 

[Neurotic]

Isn’t the Colt 6940 built this way?

Yeah, and there are a few monolithic or functionally similar upper/handguards out there.

I think some are:
- Larue
- LMT
- Aero enhanced
- Colt
- LWRC

I see most are implying this is a non-issue, but with the torques applied I could see receiver flex as an issue. Aside from the aforementioned receiver types, a thermal fit (or well bedded) barrel should also mitigate the issue.

 

[Neurotic]

Now I’m thinking the best approach might be a front heavy barrel the overtakes any sag forces no matter the weight in the center. It just seems that the barrel overhang would be more consistent, heavy and long enough not to be influenced by any bipod force or position.
Much easier to map and load for than constant changes in bipod force. I guess that’s why Varmint uppers tend to be more accurate overall. But then again we got our fat faces and hands hanging and pressing down also! shit! I need to get out of the house.

The best solution is to increased the stiffness of the receiver around the barrel extension. A slight interference fit between the barrel and receiver could suffice. But I like the other, albeit proprietary receiver designs.

 

[Trigger Monkey]

I haven't found that it really matters where the bipod or support is located when engaging practically sized targets (poppers and mini poppers to 300, 10"-12" circles or BC targets to 600) from various shooting positions. If there's any correlation between degradation in accuracy and the location of the support along the rail it's likely to get lost in the noise compared to the stability of the position and wind.

This is based on my experience shooting DMR and multi-gun matches with guns using standard forged uppers with 16" and 18" SPR contour barrels, a BCM upper with 16" SPR barrel, and a thick walled Vltor upper with an 18" SPR barrel.

 

[Gohring65]

The best solution is to increased the stiffness of the receiver around the barrel extension. A slight interference fit between the barrel and receiver could suffice. But I like the other, albeit proprietary receiver designs.

Maybe a more solid gas tube design that would be rigid, acting as a support strap mitigating some of the sag behind the gas block, keeping the upper and barrel contact interface out of the barrel sag equation.

 

[Neurotic]

Maybe a more solid gas tube design that would be rigid, acting as a support strap mitigating some of the sag behind the gas block.

You really want the gas tube to float. Otherwise it compromises the barrel's free floatedness...

 

[Gohring65]

You really want the gas tube to float. Otherwise it compromises the barrel's free floatedness...

I agree, but is the lack of free float in that area worse or better than the sag and stress on the action/barrel?
Maybe it’s been tested early in the development of the system. I haven’t dug that far into it. Lol

 

[Rocketvapor]

Some really off the wall ideas are popping up
I brought up the heavy/long barrel AR and it really is a different animal than the original question.
Trying to improve my F-class scores and X count (1/2 MOA X ring @ 600).
IF accuracy is impacted by bipod placement I agree it is likely buried in the noise.
My goal is of course, to reduce the Noise.
Especially wind reading.
Until I can shoot tiny little groups, I won't see tiny little impacts to accuracy.
My avatar is a 600 yard Clean Cold Bore X. I want more of these
Shot with a NO-Gas AR.


While the proprietary uppers are much stronger where strength matters, the heavy walled uppers should control flex, both under static and firing loads better than light weight uppers.

Uppers fail when abused where the threaded nose joins the forward receiver wall. Not in the threaded joint.
Properly faced, bedded and torqued, the joint itself is almost SOLID METAL. Aligning forces in a straight line through the joint and into the upper receiver might help.
Things like light/heavy, long /short, whip/harmonics with different barrels might have an impact on straight line force and action alignment when fired. Static force alignment, if it even matters is a balance issue.

Even though this has gone little off track, there still doesn't seem to be a good solid answer.

 

[Gohring65]

Some really off the wall ideas are popping up
I brought up the heavy/long barrel AR and it really is a different animal than the original question.
Trying to improve my F-class scores and X count (1/2 MOA X ring @ 600).
IF accuracy is impacted by bipod placement I agree it is likely buried in the noise.
My goal is of course, to reduce the Noise
Especially wind reading.
Until I can shoot tiny little groups, I won't see tiny little impacts to accuracy.

While the proprietary uppers are much stronger where strength matters, the heavy walled uppers should control flex, both under static and firing loads better than light weight uppers.

Uppers fail when abused where the threaded nose joins the forward receiver wall. Not in the threaded joint.
View attachment 7763428

Properly faced, bedded and torqued, the joint itself is almost SOLID metal. Aligning forces in a straight line through the joint and into the upper receiver might help.
Things like light/heavy, long /short, whip/harmonics with different barrels might have an impact on straight line force and action alignment when fired.

Even though this has gone little off track, there still doesn't seem to be a good solid answer.

It’s great input on the subject as a whole. And definitely adds to the discussion.

 

[JohnCarter17]

You’re not even in the same conversation bud.
You’re talking about stability of the platform, I’m talking about group size from inconsistent pressure introduced on the action, barrel and hand guard area, the barrel nut which is attached to a thin wall aluminum upper. We all know the farther the bipod the better for stability, but is it affecting group size. I say yes it is.

FFS

You asked about what I posted. I gave you the answer to that.

Your "not in the same conversation bud" is flippant and facetious. You asked, I answered, that was the conversation no matter how you want to misrepresent it. You also forgot to capitalize "bud".

As per your original post, I think you are mountaining really hard about a molehill.

But, since you asked nicely, an experiment

Rifle is ~11.6 lbs. Magpul bipod is 11.9 oz (w/ DEFY lever). I will round to 12 for ease of math.

The weight of the cat is irrelevant and I won't know if it actually weighs anything until I measure it.

With the bipod at the furthest point, there is 6 lbs 7.6 oz of weight. Minus bipod is 5 lbs 11.6 oz.

With the bipod closest in, there is 8 lbs 2 oz of weight. Minus bipod is 7 lbs 6 oz.

I equate that weight to what will be transmitted via the rail to the barrel nut.

Oops. It goes up when you bring the rail in. Probably because you are getting closer to the center of mass of the rifle as you move the bipod in.

In any case, at least in my example, its less than 2 lbs. I am not including leverage in my calculations, despite what Archimedes said, that effect for this weight over ~ 12 inches is a rounding error.

If you think that is going to impact your barrel at its thickest point, I think you have some basics you need to revisit.

 

[Gohring65]

FFS

You asked about what I posted. I gave you the answer to that.

Your "not in the same conversation bud" is flippant and facetious. You asked, I answered, that was the conversation no matter how you want to misrepresent it. You also forgot to capitalize "bud".

As per your original post, I think you are mountaining really hard about a molehill.

But, since you asked nicely, an experiment

Rifle is ~11.6 lbs. Magpul bipod is 11.9 oz (w/ DEFY lever). I will round to 12 for ease of math.

The weight of the cat is irrelevant and I won't know if it actually weighs anything until I measure it.

View attachment 7764217View attachment 7764218


With the bipod at the furthest point, there is 6 lbs 7.6 oz of weight. Minus bipod is 5 lbs 11.6 oz.

With the bipod closest in, there is 8 lbs 2 oz of weight. Minus bipod is 7 lbs 6 oz.

View attachment 7764219
View attachment 7764220

I equate that weight to what will be transmitted via the rail to the barrel nut.

Oops. It goes up when you bring the rail in. Probably because you are getting closer to the center of mass of the rifle as you move the bipod in.

In any case, at least in my example, its less than 2 lbs. I am not including leverage in my calculations, despite what Archimedes said, that effect for this weight over ~ 12 inches is a rounding error.

If you think that is going to impact your barrel at its thickest point, I think you have some basics you need to revisit.

Was that too much to play along and have a conversation about it?
You sure were quick to dismiss the whole conversation because of your ego and superiority complex or something. I like technical conversations, you’re probably going to get triggered over a lot of shit I post. If someone wants to troll and rattle my cage I can troll back. I’m here to gather data and troll douche bags. If you want to have adult conversations, I can do that too.
And thanks for that data it was helpful and definitely adds to convo.

 

[Steve_In_29]

FFS

You asked about what I posted. I gave you the answer to that.

Your "not in the same conversation bud" is flippant and facetious. You asked, I answered, that was the conversation no matter how you want to misrepresent it. You also forgot to capitalize "bud".

As per your original post, I think you are mountaining really hard about a molehill.

But, since you asked nicely, an experiment

Rifle is ~11.6 lbs. Magpul bipod is 11.9 oz (w/ DEFY lever). I will round to 12 for ease of math.

The weight of the cat is irrelevant and I won't know if it actually weighs anything until I measure it.

View attachment 7764217View attachment 7764218


With the bipod at the furthest point, there is 6 lbs 7.6 oz of weight. Minus bipod is 5 lbs 11.6 oz.

With the bipod closest in, there is 8 lbs 2 oz of weight. Minus bipod is 7 lbs 6 oz.

View attachment 7764219
View attachment 7764220

I equate that weight to what will be transmitted via the rail to the barrel nut.

Oops. It goes up when you bring the rail in. Probably because you are getting closer to the center of mass of the rifle as you move the bipod in.

In any case, at least in my example, its less than 2 lbs. I am not including leverage in my calculations, despite what Archimedes said, that effect for this weight over ~ 12 inches is a rounding error.

If you think that is going to impact your barrel at its thickest point, I think you have some basics you need to revisit.

So is the cat alive or dead?

 

[JohnCarter17]

So is the cat alive or dead?

Its alive now, but if it keeps sleeping on the wrong part of the downstairs floor at night, that might accidentally change.

 

[Gohring65]

Are we dismissing it because of those weight test. Or is a paper test in order?

 

[Rocketvapor]

Receivers DO flex when fired (saw it on Youtube ). Some uppers are pretty flimsy behind the barrel joint
Static balance MIGHT make a tiny difference.
The load line through the barrel nut into the front of the receiver could be similar to not lining behind the rifle (in prone).
You can hold it still before you fire but the force is higher when fired.
Now, can you actually see this on steel or paper? Probably not.
If static balance causes degraded accuracy it's likely going to be in the small fraction of an MOA zone.
Just for conversation say 1/8 MOA. If you normally shoot .2s and .3s your groups might be a little better.
If you are a MOA shooter it's going to be in the NOISE (if it exists).
Maybe see a POI shift.
I think someone that can CLEAN an F-class target should test this idea
Above my skill level.
Benchrest shooters experiment with both forward rest and rear bag positions. Seems to matter to them.
Steel shooters, probably not.

 

[Gohring65]

Receivers DO flex when fired (saw it on Youtube ). Static balance MIGHT make a tiny difference.
The load line through the barrel nut into the front of the receiver could be similar to not lining behind the rifle (in prone).
You can hold it still before you fire but the force is higher when fired.
Now, can you actually see this? Probably not.
If static balance causes degraded accuracy it's likely going to be in the small fraction of an MOA zone.
Just for conversation say 1/8 MOA. If you normally shoot .2s and .3s your groups might be a little better.
If you are a MOA shooter it's going to be in the NOISE (if it exists).
Maybe see a POI shift.
I think someone that can CLEAN an F-class target should test this idea
Above my skill level.

I agree, it’s obvious it’s going to flex, I’m just not sure why some think it won’t. I’m not sure if my rifle is capable of the groups needed to get out of the noise.

 

[Gohring65]

I also think barrel nut diameter and length can have negative and positive impacts on the junction, I’m still thinking about all the factors involved. I’m thinking bigger diameter nuts might help bring more stress on the barrel extension upper interface especially the farther out the bipod. Longer nuts could do the same.
(Think bigger tires on the same size axle. The axle in this case is the upper receiver threads.) But this was a quick thought and I haven’t thought about it thoroughly. I’m sure I’m missing some physics but maybe not.
My thought is a skinny short nut would put less influence from the rail and bipod on the interface. Just speculation at this point.

 

[Rocketvapor]

Look at the METAL in the normal barrel nut joint.
Now look at the first inch or so BEHIND the joint.
KABOOMS usually leave the barrel nut intact.

Anyone have a JUNK upper? Assemble the joint with a shot out barrel and sit on it, breaking the upper.

 

[Gohring65]

Look at the METAL in the normal barrel nut joint.
Now look at the first inch or so BEHIND the joint.
KABOOMS usually leave the barrel nut intact.

Anyone have a JUNK upper? Assemble the joint with a shot out barrel and sit on it, breaking the upper.

Good point, maybe the pivot should be moved to that area, now we have the bolt being influenced more there. It’s easier to bend a channel than a pipe. And….there’s the mag spring pushing up on the bolt with less and less pressure as the mag empties. Upper quality will definitely make a difference.

 

[Tx_Aggie]

Are we dismissing it because of those weight test. Or is a paper test in order?

I have an AR in 6mm ARC (quality upper, quality rail, 18" proof SS barrel) that would show a significant vertical POI shift between prone with a bipod and supported with a gamechanger bag on a barricade.

Initially I thought this was due to an issue with my fundamentals (though I don't have the same problem with my bolt guns), but after a little experiment with a laser bore sight and a 100 yard paper target, it was clear there was something mechanical going on with the upper. Swapping the barrel into an Aero Enhanced upper and rail, where there is no contact between the handguard and barrel nut, eliminated the POI shift completely.

 

[Gohring65]

I have an AR in 6mm ARC (quality upper, quality rail, 18" proof SS barrel) that would show a significant vertical POI shift between prone with a bipod and supported with a gamechanger bag on a barricade.

Initially I thought this was due to an issue with my fundamentals (though I don't have the same problem with my bolt guns), but after a little experiment with a laser bore sight and a 100 yard paper target, it was clear there was something mechanical going on with the upper. Swapping the barrel into an Aero Enhanced upper and rail, where there is no contact between the handguard and barrel, eliminated the POI shift completely.

This is exactly the results I would expect. You proved there’s definitely a influence.

 

[Steve_In_29]

Demonstrates that receivers do flex, even with free floated hand guards.

Upper Receiver Flex Testing - Part One

This is the test that I originally posted on another forum, but was asked to remove. I had to split it up in two sections as the forum only allows ten pictures per post. More tests, comments and some follow up stuff are in the second part of the post... wherever it is. THIS IS NOT A TEST OF...

www.m4carbine.net

Upper Receiver Flex Testing - Part Two

Here is the rest... work continues on this, see the comments at the bottom. ------------------------------------ Test Two -- This was a duplication of the first test, this time with the upper receiver supported by "pinning" into a fixture that represents a lower receiver. Conventional...

www.m4carbine.net

 

[Gohring65]

Demonstrates that receivers do flex, even with free floated hand guards.

Upper Receiver Flex Testing - Part One

This is the test that I originally posted on another forum, but was asked to remove. I had to split it up in two sections as the forum only allows ten pictures per post. More tests, comments and some follow up stuff are in the second part of the post... wherever it is. THIS IS NOT A TEST OF...

www.m4carbine.net

Upper Receiver Flex Testing - Part Two

Here is the rest... work continues on this, see the comments at the bottom. ------------------------------------ Test Two -- This was a duplication of the first test, this time with the upper receiver supported by "pinning" into a fixture that represents a lower receiver. Conventional...

www.m4carbine.net

Nice!!
Thanks for that, lots of good info.

 

[carbonbased]

What are you doing with this rifle?

 

[Gohring65]

What are you doing with this rifle?

I shoot for fun, it’s not even about a particular rifle. I don’t even have one in mind. It’s all about the physics, theories and solutions. More brain food for me.
Trying to come up with what could be the stiffest platform with the best possible barrel/upper connection steered towards accuracy and precision.

 

[carbonbased]

Ok, fair enough. If it was me, I’d optimize and buy a bolt-action for accuracy and use my semi for faster shooting fun, but you’re not me.

Let us know what you find out. I’m assuming you’re going to test different setups.