View Full Version : Oscillating Mass
Sparky5019
12-29-12, 10:01
Ok guys,
I'm going to say something that might seem dumb until you put a bit of thought into it.
I started doing the research when I started playing with these rifles a few years ago and came to the conclusion that I didn't want all the extra mass of a FA carrier and a H,H2,H3 etc. buffer because to me it increased the recoil impulse of the gun (16" carbine gas system).
It then came to my attention that the reason everyone was preferring these setups was the need to keep the action closed a bit longer to let the case retract from its expansion at firing.
That said, I thought one could accomplish the same thing with a heavier spring and still have a lower oscillating mass of a standard carbine buffer and maybe even a LIGHTENED carrier. So, I chucked that turd into the mill vise and had at it...one or two destroyed end mills later (them sum bitches are hard!) I had a lighter carrier.
I put it all back together with a Tactical Springs "Enhanced" Blue spring and took it out and ran it. It ran great! The action cycled faster, the buffer did not bottom out on the back of the RE, fed great; I could actually shoot the gun faster!
I have been using a PWS comp (soon to be a BCM or BC) and the gun seemed, subjectively, shoot flatter meaning to me that the rearward moving mass didn't combine with what little muzzle rise there was and create compound effect.
Now the only caveat to this is that I have been shooting only steel case ammo. This gun might cycle too fast for brass ammo; I haven't had the time to try that out to see. Even if it did, to me the theory still holds up and I would install a "Extra Power" Red spring and only resort to increasing the mass as a last option.
All that said, my next build will probably be a 14.5" middy. My thought would be to apply this theory to that configuration. It would seem to me that it SHOULD shoot even softer, given the reputation that the middy has for shooting a bit softer than a carbine anyway.
Now some people say I'm crazy...but this just made sense to me.
Sometimes the voices have good ideas.:haha:
Thoughts?
Sparky
Failure2Stop
12-29-12, 11:58
Lightened carriers and heavier springs introduce some new problems to the system.
1- More ammunition sensitive.
2- More spring wear sensitive. Since inertia will be much more dependant on spring tension, as the spring is used it will lose forward pressure, and therefore become "worn out" far earlier than in the standard system.
3- Increased chance of bolt-bounce failures to fire.
4- Increased sensitivity to magazine spring function.
That being said, there are high end competition rifles that use a very light carrier with rifle length action springs. As said above, they are sensitive to ammunition pressure changes, but the rifle length spring tends to last longer.
How long does it take a brass case to spring back in the chamber? The carrier does not begin to move until after the bullet has uncorked the muzzle.
One way to reduce bolt bounce would be to increase the damping of the buffer.
F2S is correct. The "standard" tuning of the AR gives best performance with a wide variety of ammo. Any changes to the mass of the reciprocating parts, spring rates, port sizes and port location changes what ammo will work reliably.
My first thought was "why machine the carrier when you can lighten the buffer?" Then it occurred to me that if you lighten the buffer weights, it will reduce damping. A lighter carrier and a heavier buffer might be worth looking into to reduce or eliminate carrier bounce
Sparky5019
12-29-12, 13:36
F2S,
Good point, I'll look into a rifle length spring at some point. I have to admit, I'm not shooting this gun as much as y'all are but long term reliability is a very real concern. I assume by carrier bounce, you mean the oscillating mass (carrier and buffer) hitting the rear of the RE. I CAN see that forward carrier bounce could cause some FTF issues as going into battery would be inconsistent. Wouldn't carrier bounce be as big of a concern w/ a SA or FA carrier and a worn/weak spring anyway? Admittedly, I didn't weigh the part before and after but there shouldn't be THAT much difference in the weight.
The original Colt SA carriers are semi circular with a standard top shroud. What I did was cut the bottom the same and bring the top shroud back to about a 1/2 inch long. It wouldn't approach the weight reduction of, say, a JP LM carrier I wouldn't think.
MW,
As far as the brass case retraction time, I don't recall. I know I read it somewhere but can't remember what it was exactly.
I have to admit, these are some very real things to think about! Thanks for the points! I'll try to get some pics at some point and let y'all know how things go.
Thanks.
Sparky
skullworks
12-29-12, 15:09
Thought about coupling the lower mass BCG with an adjustable gas block?
Sparky5019
12-29-12, 15:24
Good thought. Right now it has a LT low pro GB under a LT 9.0 rail. On the middy I'll probably go back to a LT 9.0 rail and a FSB. I'll look into that idea as well!
Thanks.
Sparky
Failure2Stop
12-30-12, 20:42
Bolt bounce is when the bolt carrier rebounds after chambering/locking, causing failure to fire due to insufficient firing pin reach when in such condition. Identified issue with carbine gas systems with carbine buffers. Reduced/eliminated by going with a standard carrier and heavy buffer.
Sparky, you have guts. I'm not much for experimenting.
I was wondering if you could put the advantages into quantitative measurements? I understand the concept of flatter shooting, but I have always run a fairly stock set up (only differences where barrel length and different weights for different rails, etc.).
Are you using this set up for competition?
Specifically I was wondering if you noticed improvements in timed splits, or better times in drills?
Forgive is this is drifting off topic.
In concept, lighter is better. I'd like a race gun with a skeleton titanium BC, small gas port, lighter springs...
In reality we make everything heavy so hopefully it slogs through any gunk in the system and shoots when we need it to shoot.
Tagging this for interest.
I expected that lightening the buffer would reduce recoil, but the A5H4 buffer that I just tried in my gun made recoil more manageable. This is probably because the velocity of the reciprocating mass was reduced. Same or similar force over greater time should make it feel softer.
I want to experiment with that new Syrac gas block and an A5H1.
It's been said a thousand times, but bears repeating- Less mass means more recoil, not less. A lighter buffer actually increases free recoil.
In a practical sense, a couple of ounces either way will not make any discernible difference in free recoil.
A 7.7 lbs rifle firing a 62 gr bullet @ 3000 fps using 25 gr of powder will generate 3.98 ft/lbs of recoil. Reduce rifle weight to 7.5 lbs and recoil is now 4.09 ft/lbs. (1 oz is .062 lbs)
As you can see, a lighter buffer (or even a heavier buffer) doesn't reduce (or increase) recoil enough to speak of. What changing buffer weight, spring rate etc. does is change how recoil feels to the shooter
Recoil calculator used- http://www.shooterscalculator.com/recoil-calculator.php
skullworks
12-31-12, 10:30
One aspect that has been ignored thus far is the fact that low mass systems such as JP Enterprises LMOS usually are combined with at least two out of the following three:
An adjustable gas block so that you can adjust the amount of gas travelling back to the BGC (thus lowering the velocity by which the BCG travels to the rear - and also making it über-sensitive to dirt and weak loads),
A HUGE and ungodly loud muzzle brake to lessen felt recoil (this will most likely have the greatest impact over the LMOS-system itself),
Hand loads.
Since you're desired result is less felt recoil, check out the Vltor A5 system with an A5H3 or A5H4 buffer. It feels like the recoil impluse is "spread out" with the A5, not quite as sharp, so the rifle is more controllable and easier to keep your sights on target. The A5 is a lot more reliable than a lightened reciprocating mass, and you don't need to worry about the ammo you shoot or your gas port size.
If you want to increase dwell time, you can try a LMT Enhanced carrier in your 16" carbine.
Sparky5019
12-31-12, 12:45
All good points! As I stated before, aside from the calculator above, this is all subjective. The gun felt better and cycled faster w/ no carrier bounce on either end of the travel; follow up shots were faster and more accurate (splits were better; one can only press the trigger so fast).
SW makes a point about hand loads; at this point I'm using factory. The action hasn't been "cleaned" in over 1000 rounds on purpose. The comp was on before the action mods.
For the most part, this is academic as feel is subjective anyway.
I have to say, for the speed that the mass is traveling when chambering the round, my thought would be that if the carrier is going to stop because the gun nasty, it's going to stop anyway. That mass is being pushed by whatever spring is chosen. I've seen clean guns w/ FA carriers stop short when my dirty gun kept on going.
Y'all I'm not saying I'm right, I'm just thinking out of the box and this gun may be 1/1 but until it fails (in practice and competition), I'm not sure I'll put a new carrier in it.
Keep the thoughts coming! They're all great thought provokers!
If I have time, I'll try to get some splits and stuff for comparision.
Sparky
skullworks
12-31-12, 12:50
I forgot to mention something I have observed first hand; using the bolt release to feed a round from a fresh and fully loaded magazine in an LMOS system is not as reliable as in a MilSpec system. If you run an LMOS system you do run the risk of having a failure to feed on the first round out of the magazine if you do not use the charging handle (that tiny bit of extra travel does make a difference!)
What you did to your carbine has me interested. Please let us know if the modifications change (shorten) the replacement intervals for springs and other wear and tear items as your round count gets higher.
Sparky5019
01-02-13, 12:22
As promised, here are some pics. As y'll can see, there is not THAT much material that I've removed. I took the top "shroud" down to 1/2" and cut the bottom "shroud" off like the old Colt SA carriers. As I said before, it is nowhere near the reduction of a true LMOS like JP. Enjoy!
http://i675.photobucket.com/albums/vv117/SparkySRNA/Carrier1_zps087c108b.jpg
http://i675.photobucket.com/albums/vv117/SparkySRNA/Carrier2_zps4cd1a821.jpg
http://i675.photobucket.com/albums/vv117/SparkySRNA/Carrier3_zps318cadd6.jpg
Sparky
Have you noticed any unusual wear on the inside of the receiver? It seems that removing that much material might alter the path of the carrier during its cycle.
Sparky5019
01-02-13, 14:28
Not at all. Some of the older SA carrier were cut in this semi-circular pattern anyway but had a longer top "shroud" like the FA carriers. I just thought I'd see what it would do. Works great! Again, not as light as most LMOS systems but a good mid point.
Sparky
Not to reinvent the wheel, but I think experimentation like this is fun. Bonus points for cutting the metal yourself.
I just got the JP LMOS carrier group, and an adjustable gas system. I'm going to play with making a super lightweight rifle, and see if I can get it to stay reliable.
I have a big pile of parts waiting for me when I get home from Afghanistan. It's going to be like Christmas.
It's been said a thousand times, but bears repeating- Less mass means more recoil, not less. A lighter buffer actually increases free recoil.
In a practical sense, a couple of ounces either way will not make any discernible difference in free recoil.
A 7.7 lbs rifle firing a 62 gr bullet @ 3000 fps using 25 gr of powder will generate 3.98 ft/lbs of recoil. Reduce rifle weight to 7.5 lbs and recoil is now 4.09 ft/lbs. (1 oz is .062 lbs)
As you can see, a lighter buffer (or even a heavier buffer) doesn't reduce (or increase) recoil enough to speak of. What changing buffer weight, spring rate etc. does is change how recoil feels to the shooter
Recoil calculator used- http://www.shooterscalculator.com/recoil-calculator.php
Sorry, don't mean to sound harsh here, but you're mistaken. While it is true the *overall* weight of the rifle will absorb and lessen recoil, it is the *reciprocating* mass wherein if you increase it, it increases recoil.
Basically, envision a 10Kg rifle. One has 1Kg of mass in the reciprocating parts, and 9Kg in the non-reciprocating parts. Shouldn't be too bad, right?
Then envision a rifle that has 9Kg of mass in the reciprocating parts, and 1Kg in the non-reciprocating parts. You could probably guess that this wouldn't be fun to shoot at all.
What the OP is chasing here is what competition shooters have been doing for a while, but OP you are missing part of the equation. You want as little energy in the reciprocating parts as possible.
The most important part you're missing is an adjustable gas block. The gas from the gas block is your input energy; if you don't alter the input energy then you're only changing around variables to little effect.
If you lighten the carrier without changing the input energy (gas block), then since the carrier is being moved with the same amount of energy, its velocity will increase. The velocity increase will cause it to hit the back of the buffer tube more violently, and in doing so, in many cases will *increase* felt recoil compared to a heavier carrier.
In a balls out attempt to reduce the energy in the reciprocating mass, reliability be damned, you need to change these parts:
* Buffer spring (to a lighter value)
* Adjustable gas block
* Lightened Carrier
* Lightnened Buffer
The extent to which you alter any of these parts will affect reliability in its own way, determined by its role in the whole mechanism. So it's a tradeoff between reliability and recoil reduction.
- Hygienist
Primary recoil is created when the bullet "pushes off" the barrel. At this point, the carrier hasn't even started to move.
That being said, Mistwolf is correct.
Yes, but another form of recoil is experienced with the reciprocating mass.
The initial recoil from firing the bullet will be absorbed by the overall weight of the gun (incl the reciprocating parts that haven't moved yet), but then the movement of the reciprocating mass afterwards is going to also create its own recoil movement.
Sparky5019
01-03-13, 22:00
- Hygienist
Primary recoil is created when the bullet "pushes off" the barrel. At this point, the carrier hasn't even started to move.
That being said, Mistwolf is correct.
Exactly. Now my intent here was to let the muzzle device take care of this to the extent that it does.
Past that, my intent was to see if a SLIGHTLY lighter carrier would decrease the action impuls and make it cycle just a bit faster without bounce on either end and and without going to a sensitive LMOS.
It was for nothing more than shits and giggles. I'll compare again with a FA carrier when I get the new carrier for the middy just to see.
All I know is I was able to shoot the gun faster consitently on target AFTER doing this than others on the same course who shoot these guns way better than I do. Just sayin'. There's SOMETHING there, at least for me; how much? That's what we're going to find out over time! But hanks for the thoughts and reading y'all.
I'll post updates as I have them along with some splits and if I can get some vids I'll get those as well; that might be a bit though.
Sparky
Sorry, don't mean to sound harsh here, but you're mistaken...
The recoil energy generated by a fired cartridge is the same whether it's fired in a 7 lbs self loading rifle or a 7 lbs bolt action. What you're talking about is felt recoil and that is an entirely different animal
The point I'd just like to make is this.
What we're going for here is to improve our shot times by reducing the muzzle rise/movement of the rifle after each shot.
One way we can do that, and the method shown in this topic, is to decrease the mass in the reciprocating components (assuming you adjust other components of the action)
Now, decreasing the mass in the reciprocating components means less overall mass, and thus less overall mass to absorb the free recoil of the rifle after firing.
However, the movement of the reciprocating mass back and forth in the rifle has its own effect on muzzle rise/movement. If your reciprocating mass is 1Kg moving at 100 Ft/s (totally made up numbers), then versus an action that is 0.1Kg moving at 100 Ft/s (note in both instances the velocities are equal), then the latter rifle is going to have much less muzzle rise/movement induced by action cycling, not considering differences in reliability.
Now, in the latter rifle example, you have less mass to absorb the free recoil and thus increasing muzzle rise/movement. However, you also have less muzzle rise/movement from the action cycling as a result. Now the question is, does this result in a net increase or decrease of muzzle rise/movement?
In competition, it's been shown pretty definitively that it's a net decrease in muzzle movement. Competition gunners go to rather extensive trouble of tuning the cycling to make sure they're moving as little mass as possible with as little energy (gas) as possible. It does have tangible consequences for reliability, so therefore you wouldn't see people using it unless it actually did help reduce muzzle movement, which it does.
Sparky5019
01-04-13, 06:55
Y'all are both right from different perspectives...
I'll put this in other terms...
My primary competitive sport is high level Cowboy Action Shooting. I custom build 1873 rifles for this sport. There is no part of the '73 action that I don't address and that will not have an impact on the shot splits and the shootability of the rifle. Winchester advertised the 1873 rifle as "2 shots a second"; personally I can get 5-8 shots a second, depending on target size, distance, etc. That would not be possible without optimizing every action component as well as the technique to power the gun as it is a repeating rifle. A guy who shoots 10 funds in 5 seconds can't and won't appreciate the difference that one of my rifles can make where a guy who shoots 10 rounds in 1.7 seconds will.
This is the same concept applied to a self loading rifle; is it not completely balls out MIL-SPEC save for a trigger? No. Is still reliable? Absolutely.
Everyone has plenty of opinion here, I can tell. I would not advocate making any change that would compromise the reliability of a battle rifle for battle; at this point we are not in battle so I'm exploring some options to make the action cycle a bit faster. So far, it works.
Let y'all know more as it develops!:haha::agree:
Sparky
Sparky, I want to be clear that I understand you are talking about tweaking your competition rifle. All I'm doing is clarifying that by reducing reciprocating mass, we are talking about managing recoil (how it feels) to better control muzzle disturbance, not reducing recoil. To reduce recoil, we must do one or more of four things: increase weapon mass, reduce ejecta mass, reduce ejecta velocity, redirect the vector of the exiting gases
...the movement of the reciprocating mass back and forth in the rifle has its own effect on muzzle rise/movement...
You are correct and I never claimed otherwise. You are also correct that the greater the mass of the reciprocating parts, the greater affect it can have on muzzle disturbance during recoil & cycling.
What I am trying to get folks to understand is that by changing the reciprocating mass, changing spring rate or changing the amount of gas used to cycle the rifle does not reduce or increase the amount of recoil energy generated with the shot. It only changes how the recoil feels by changing acceleration, duration, peak, dissipation and vector, all factors that can and do affect muzzle disturbance.
For example, a bolt action rifle has no reciprocating mass. The shooter gets all the recoil as it's happening with only the recoil pad to slow down the acceleration forces. It's like driving a car with solid tires and no suspension. Hit a speed bump at 40 miles and hour and your gonna really feel it!
The self loading rifle is like a car with springs. The action spring is, of course, like the springs of a car's suspension. The BCG/buffer is like the unsprung weight (mass) of a car, the axle and other parts that move as the springs deflect. The rifle itself is the sprung weight which is like the chassis of the car. The springs and the moving of the unsprung mass slows down the transfer of energy
The greater the mass of the unsprung components (BCG/buffer) compared to the sprung mass (the rifle) means the unsprung mass will have a greater amount of disturbance to the sprung mass when in motion.
In all cases, the amount energy transferred to the car from hitting the bump, whether is has no suspension, a suspension with little unsprung mass or lots of it, is the same. What suspension type and tuning does is change how that energy feels
Sparky5019
01-04-13, 09:36
You are correct and we are fine.:agree:
Absolutely, energy put into the system by any given will be constant; that EVERYONE HERE should understand up front.
The area in which I am tweaking is in the cycle speed and feel of the impulse generated by the reciprocating parts.
Your analogy to the car is a good one. Mitigating THAT disturbance, however slight, is for me an interesting endeavor for carbine gas system.
Thanks for the clarification!
Sparky
The self loading rifle is like a car with springs. The action spring is, of course, like the springs of a car's suspension. The BCG/buffer is like the unsprung weight (mass) of a car, the axle and other parts that move as the springs deflect. The rifle itself is the sprung weight which is like the chassis of the car. The springs and the moving of the unsprung mass slows down the transfer of energy
Your analogy is backwards. BCG-Buffer is the sprung weight, as this is the part that moves in relationship to the rifle. The rest of the rifle is the unsprung weight, as it makes contact with the shoulder of the shooter, and at the two grip points, hand grip and fore end of the rifle.
Never seen so much over thinking in a thread. Impulse created by the BCG-Buffer moving rearward can either be snappy, thus quick, or dull with a longer duration, if the only variable is the mass of the BCG-Buffer.
Also, muzzle rise is due to the forces occurring not being in line with the center of mass of the rifle, thus a torquing action.
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