at 1500 rds -sping died[greased with moly] and end of buffer hit and marks on the bolt carrier !so whats life of a recoil spring ?
Depends on the quality of the spring. A standard $5 USGI spring will of course work forever. If the spring does not have enough tension to strip a round off of a full 30rd mag then it is spent.
A good test is to lock the bolt back, insert a 30rd mag and hit the release. Did it strip a round off and properly seat into the chamber? If so, then it is stil good.
I personally do not want to wait to find out when the spring goes down, so I typically change out all the extractor springs and buffer springs at around 3-4K. I also use ISMI CS springs. These springs have a MUCH better life than a standard spring and will noticeably alter felt recoil.
C4
ISMI shot peened, stress relieved, heat treated buffer spring
SS spring after about 8k and a new SS spring and a new ISMI spring
well went to a class-3 dealer show the spring -showed a new one [g.i] opps almost 2.75 shorter .said i shot many more in a 20’’ barrel and never seen this happen -the buffer hits the rear of the tube and marks the buffer nylon part !he send the bolt is working faster so more things will work harder than a 20’’ so an aac -ss buffer kit this is the best way to fix all the troubles you have ,anyboby have the same with recoil spring/buffer like bolt/buffer slamming and groups going wild ??
so is a CMT spring a good quality one? Who is USGI?
Sorry…I had to.
The CMT springs are your standard $5 dollar SS spring. They are what the Military would use. Does that mean it is a quality spring? Yes it does. Is it the best choice out there? No it isn’t.
C4
If it is shorter than the minimum length (in inches), it needs to be replaced. If it’s getting close, it probably needs to be replaced. If the minimum were not good enough, it would not be the minimum.
[This was posted in the tacked extractor/O-ring thread.]
ETA: Grant-How long is the spring with 8K on it which is posted above?
I have never heard of ISMI before.
Most have not. They make springs for 1911’s, Glock’s, mag spring for just about everything. They use the highest grade CS available and then shot peen, stress relieve, heat treat and gurantee their springs for one year!
They are one of the best kept secrets in the industry and I use their products on just about every weapon I own (1911, Glock, AR).
C4
The rule of thumb i have heard (not sure if it’s relevant or not) is once a recoil spring loses two coils in stack height, it ought to be replaced. The only way to verify this is to have a 2nd good spring to compare it to.
Anyone else ever heard this?
Not sure if David Tubbs is selling ISMI springs but I first learned of CS springs from his website and his company. He’s been singing the praises of CS for several years now, both recoil, bolt action firing pin, mag springs, trigger and hammer springs, you name it.
G. David Tubbs wears yellow glasses.
Don’t know if the springs on his web site are made by a different manufacturer, though.
Better than a Rule of Thumb.
Action spring…Free length of spring shall be between 11-3/4 and 13-1/2 inches (29.84
and 34.29 cm) M16A2 ONLY and 10-1/16 and 11-1/4 inches (25.56 and 28.58 cm) M4/M4A1 ONLY.
ARMY TM 9-1005-319-23&P p.3-102 Change 4
ETA: Grant-On the 8K spring above, was it functioning or not at that length?
Yes. God help us if we acknowledge the contribution of a yellow glass shooter.
Tubbs ONLY uses ISMI springs.
C4
Even on his 300 plus Magazines?
No. The spring would not allow the bolt to strip a round off of a 30rd mag.
C4
Any idea how long it was? Or how long either of the others are so we have some idea of it’s length to know if it was out of spec low? Did you withdraw it from service the first time it failed or did you try using it for a while as its function deteriorated?
Thanks. This ought to be added as a sticky at the top of the page for future reference.
A normal ISMI Carbine spring is 11 and change (varies). The carbine spring I pulled out was about 2.5-3 inches shorter than it.
When the problem first reared its ugly head, I believed it was mag related. So I continued to use it for some time after that.
This was more than a year ago and a that time, no one was really ever talking about Springs and proper maintence. This is why I have kind taken it on and want to educate people about spring life.
C4
Customers make better decisions with proper education.
Are ISMI springs Chrome-silicon (Valve) A877 or Chrome-silicon (Commercial) A401?
So, 8000 rounds on a typical USGI spring is probably too much. Since this one was probably 9 inches and change, would you probably have changed it out earlier, at say, 10 1/4 inches if that spec had been in your data bank?
Aubrey posted this elsewhere:
Ok Paul, you asked for it. An enginerd’s spin on gun springs:
Besides the obvious design criteria like spring rate, appropriate material and process selection are important components to ensure that springs remain functional and prevent relaxation or fatigue.
You will note from the source material cited below that not all spring wire alloys are the same. “Commercial” grade spring wire may be adequate for some applications, but it does not have the same properties that “valve” grade exhibits. The processing necessary and quality control necessary to achieve the consistent surface finish necessary for high-fatigue applications certainly adds to cost. Additional processing like shot peening and stress relief will also provide improved properties at additional cost.
Many of the firearms springs that we are concerned with are not exposed to high temperatures, so better-quality music wire springs may be quite appropriate. Depending upon where in the gun’s mechanism a spring resides and the conditions it is exposed to due to the combustion process or environment (e.g., saltwater), corrosion resistance may or may not be of particular concern. Shooters who swim with their carbines may have different material requirements than those who never leave the high desert.
From the Century Spring Technical FAQ
http://www.centuryspring.com/pdfs/techfaqs.pdfWhat material is best for high temperature applications?
As temperature resistance increases, the material and processing cost typically increases significantly. Therefore, it is usually wise to select a material that provides resistance for the intended temperature range with minimal excess capability. The table below lists a variety of spring materials and their maximum service temperatures.Wire Type / Max Temp.
Music Wire 250°F
Hard Drawn Carbon 250°F
Oil Tempered Carbon 300°F
Chrome Vanadium 425°F
Chrome silicon 475°F
302 Stainless 500°F
17-7 PH 600°F
NiCr A286 950°F
Inconel 600 700°F
Inconel X750 1100°FMost spring materials are defined in ASTM specifications. …A list of popular material types and the corresponding ASTM specification is given below.
Wire Type / ASTM Spec
Oil Tempered Carbon (Commercial) A229
Oil Tempered Carbon (Valve) A230
Chrome-silicon (Commercial) A401
Chrome-silicon (Valve) A877
Chrome-Vanadium (Commercial) A231
Chrome-Vanadium (Valve) A232
Hard Drawn Carbon A227, A764
High Tensile Hard Drawn Carbon A679
Music Wire A228
Stainless Steel A313Fatigue Applications:
Since spring wire is primarily subjected to torsional stresses, maximum stress levels occur at the wire surface. As a result, material surface defects (i.e. seams, laps, pits, etc.) can dramatically reduce a spring’s fatigue life. Knowing this, wire manufacturers have developed surface preparation methods to restrict the size of wire surface defects as it leaves the mill. Wire produced with these methods is rated for fatigue applications and is often referred to as “valve spring quality”. Since these methods often involve costly processes, fatigue-rated spring wire is often significantly more expensive than its commercial grade counterpart. The two most popular materials for fatigue applications today are Music Wire (ASTM A228) and Chrome-silicon Valve Spring Quality (ASTM A877). At wire sizes below approximately 0.080" (2.0 mm), Music Wire offers higher tensile strength; however, Music Wire’s maximum service temperature is less than that of Chrome-silicon.Corrosion Resistance:
Once again, the actual operating environment plays a significant role. Many coatings are available that can provide adequate corrosion resistance for wire types that would not themselves resist corrosion. These include powder coating, phosphating with an oil dip or spray, and plating in some cases. Generally speaking, a coated spring produced from a traditional spring material will involve less cost than producing a spring from stainless steel. When the application is such that coated spring wire will not meet the requirements of the application, the focus turns to stainless steel wire. Type 302 stainless steel is generally the first choice. This wire can yield very corrosion-resistant springs for most environments. When the application calls for high operating temperatures as well, 17-7 PH wire will also likely be considered.From the SAE (Society of Automotive Engineers) Manual on Design and Application of Helical and Spiral Springs, SAE HS-795
Shot Peening— This surface treatment has done more to increase the life of springs than any alloy steel or other process ever employed.
Relaxation or Load Loss in Helical Springs at Elevated Temperatures
If a helical spring is compressed by a given amount between parallel plates at elevated temperature, it will be found that the load exerted by the spring will gradually relax or drop off with time. The amount of this relaxation, or set, generally increases as the stress and/or temperature increases. Normally, the set is greater for long periods of time than for short ones.Common Causes of Spring Failure:
- Surface Imperfections
- Corrosion–Corrosion is the major environmental factor which will promote spring breakage. It destroys and removes metal from the surface of the spring by chemical or electrochemical methods in an irregular fashion which causes an overall reduction in the spring stock size, compounded by localized areas of intensive metal removal. These effects seriously reduce both the static strength and the fatigue strength of the spring.
- Improper Heat Treatment