Tubb 42 coil spring in 5.56 guns and why it runs almost everything

[lysander]

Thank you for the correction. I know it takes time to post something like that, and I'm in your debt.

Do you think it's fair to say they that the effect of higher preload on bolt timing is largely inconsequential? Because even if we tripled bolt closed force, it's still a trifle compared to the piston power acting inside the BCG? (What is the technical name for that expansion chamber?)

The time from ignition to unlocking is largely independent of the spring due to the large difference in forces. This time is mainly governed by the mass, gas port size, length of gas tube, and how leaky the system is.

As to the spring, there is no sharp demarcation between the elastic region and the plastic region on the stress-strain diagram, they bleed into one another. Continued strain at the upper end of the "elastic range" will result in plastic behavior over time. That is the reason for the rule-of-thumb to keep the working length of a spring at 50% of the free length. Continued compression of the spring beyond about 50% leads to accelerated compression set and reduced spring life due to shortening and loss of spring rate. And this can happen while keeping the stress below the fatigue limit. In general, firearm recoil and magazine springs are over-compressed (working beyond 50% length) to begin with. This is due to the limited space available, and the required movement distances, and why these spring in guns need replacing at regular intervals, measured in thousands of cycles, where as isolation springs under machinery can last for several decades with lives measured in millions of cycles.

I am just very leery of stuffing more spring in a space that didn't have enough room to begin with.

[Hohn]

I'm aware of the fuzzy area between elastic and plastic region which is why the offset (often 0.2%) convention was adopted. And you are of course correct that fatigue can set in before one would consider a stress to be "yield" at the macro level.

I've decided that I'm going to run the carbine lower as long as I can with this spring and just see how long it lasts. If the 42 coil holds up in the carbine tube, it will obviously fare better in the A5 and better still in a Rifle extension. A friend is running the same spring in two separate lowers (one rifle, the other carbine) and likewise having very good luck with it thus far.

Fatigue and potential durability concerns aside, the spring does seem to increase the performance envelope and make the gun really smooth. Time will tell if it's a pyrrhic victory or not.

[DG23]

Fatigue and potential durability concerns aside, the spring does seem to increase the performance envelope and make the gun really smooth. Time will tell if it's a pyrrhic victory or not.

LOL!

No matter how many guys try to explain to you how what you did was not an 'upgrade' you continue to believe it was.

[Leonardo]

LOL!

No matter how many guys try to explain to you how what you did was not an 'upgrade' you continue to believe it was.

Ok,.....your opinion unless you have data to prove otherwise.

Convince me otherwise.

[TomMcC]

I'm going to try a 36 coil. See if I can discern any difference.

[Hohn]

LOL!

No matter how many guys try to explain to you how what you did was not an 'upgrade' you continue to believe it was.

Just so I’m sure I understand, is it your contention that I should fully discount my firsthand experience with a rifle I built in favor of the assessment of internet strangers who have never fired the gun? And I should also discount the successful use in an otherwise factory DDM4? And the successful use by several others in my immediate acquaintance whose rifles I have seen and often shot?


I’m sorry I might have misled you into thinking I was soliciting input on whether this was a good idea or not. Not at all. Rather I was observing that it works, works very well, and inviting discussion on the reasoning why it might work so well.

Do you have meaningful round count experience with this spring in a similar rifle in carbine or A5 extensions? I apologize if I missed your sharing the result of such. The only open question is durability and if your experience sheds light on that, please share it.

[Hohn]

I'm going to try a 36 coil. See if I can discern any difference.

I’m looking forward to your assessment.

I’d be surprised if you found anything more than a subtle difference with the shorter 36 coil version. My internet “research” mostly showed people liking the reduced “sproing” for similar function and reliability with possibly a bit smoother impulse.

I tried the 42 coil because it can be shortened to 36, whereas a 36 cannot be extended to 42. I ended up never shortening any of mine so I have no experience with 36 coil versions and can only convey the internet hearsay of others.

[TomMcC]

I shot my 3gun rifle at the range Thursday. I shot 5 with the flat wound and then 5 with stock round coil spring. I did that a couple of times. Got to watch that ammo. The load was my own, Hornaday 62 gr FMJ-BT over 24 grs. of H335. I did shoot some more, maybe, 30-40 rounds with the flat wound. No malfunction. My impression, and that's all it is, is that the flat wound spring is ever so slightly smoother in operation. It is very subtle, but I could tell the difference. I liked it, and am looking to improve my rifles in even small relatively inexpensive ways. I'll buy a couple more. It also mitigated that sproing sound quite a bit, if it matters.

[tommyrott]

I've used the 42 coil for about 12-13 years starting with a carbine RE then to a A1 rifle stock, RE and finally the A5 RE, and H2 buffer for the last 9-10 years. have never had any issues with any of the combos with multiple uppers from a overgassed 16" upper to 1 dedicated suppressed 11.5 upper with a microtune GB with a .049 port insert and finally a P/W 14.5 BCM EWL and BCM GB. most of my ammo has been hand loads for the last 10 years, but I inherited a small cache of lake city 85 55 gr that was very juicy gas wise but my present configuration ran with out a hiccup at a recent match with little difficulty getting the obligatory double tap on several runs. this is also my original spring for the last 13 years just did a bcg check to see if it was bottoming out, still have the proper 2 quarters gap. I have parts accumulating for a service rifle optic rig so definitely get a fresh one to try the 36 coil trick

[sinister]

I am not an engineer, but I am an inveterate tinkerer.

All things being the same, my experience with (16-inch carbines and 20-inch) USAMU "National Match" M16s and AR-10s, heavy (XH and H3) buffers and Tubb springs give me less perceived recoil, less movement off-target (faster recovery for rapid-fire strings), and abuses my brass a whole lot less with moderate and top-end pressure precision loads.