Bolt Face Erosion on AR

[Religious Shooter]

I just took a look at my 3 of my used AR bolts (2 DPMS and 1 BM) and all of them have a ring groove around the firing pin hole. The ring is due to the gas leaking between the brass and the primer. My main bolt (DPMS) is showing pitting (2) and buckling around the firing pin hole.

I've been mostly using Scharch brass, 90% FSR and 10% WSR primers, 25.9-26.1 grains of A2230C (book max) with 55's.

I've shot maybe 2000 Wolf and 8000 reloads (w/Scharch brass) through these bolts. Not a lot of rounds.

I'm trying to figure out if it is the reloads or the bolts are just "soft" or it is normal or ????

Are you guys getting the same type of erosion with as little # of rounds?

[GentlemanJim]

I dont know if it has anything to do with this problem....but I have a friend that has shot quite a bit of wolf in his gun...and his bolt eroded out of spec.

On the other hand I have shot 10s of thousands in an M16 (LC nato) with little wear and erosion.

Soft bolt? gas leakage? I just dont know

Sorry I dont have an exact answer

Jim

[No.343]

I had that problem when I was using a specific brand of primer. I was getting pin holes in the primers and the hot gases where cutting into the face of the bolt and the tip of the firing pin. Changed loads, bolt and firing pin and have not seen the problem again.

[kurtm]

It is common for a ring to form on an AR bolt face, usually it is meerly cosmetic, a place where the blueing/parkerizing is staying while the rest gets rubbed off by shooting and the bolt rotating. Sometimes pitting is caused by primer sealer getting deposited on the bolt face durring humid weather. Gas cutting is very sharp and doesn't look like pitting it is usually much deeper and jagged on the edges, but when a bolt only costs $35-45.00 I wouldn't worry about it too much! I have a BM bolt with over 27,000 rounds and it is fine, I have a Colt with a slight groove after only 10,000 or so.

[Derek45]

I bought a used COLT SP-1 years ago.

Here's a pic of the original COLT Chrome Boltface.

[Religious Shooter]

The worst of the DPMS bolts I have has a grooved in ring and only two of those pits. The firing pin hole isn't round anymore and the surface around it isn't smooth. I've been getting the occasional double/triple even after having a new trigger installed. I think the protrusions around the firing pin hole and the fact that I use Federals is causing some/all of the doubles/triples via slam fire.

I had that problem when I was using a specific brand of primer. I was getting pin holes in the primers and the hot gases where cutting into the face of the bolt and the tip of the firing pin. Changed loads, bolt and firing pin and have not seen the problem again.

Which primers were you using? Federals?

[busyhawk]

This does seem to be a reloading/ammo problem even though there is not enough information provided to make a good judgement. The damage to your bolt is not common with that few of rounds. The bolt face will take a beating and should last thousands of rounds before showing signs of real damage. Bolts are somewhat inexpensive but should last longer that what you have described. With our Army M4s shooting green tip ammo all day long our biggest problem is broken locking lugs, mostly the lugs closest to the extractor. I don't believe we have ever replaced a bolt because of an enlarged firing pin hole or erossion on the face of the bolt. Contact the manufacture if you think it is weak or soft metal...they can confirm if it was/is and you can make a informed decision from there. Remember to give a manufacture a chance to fix a problem, then you can either praise them or bad mouth them, but first give them a chance to make it right!

For your double/tripple-ing problem you "should" give the manufacture a call. Even though reloads are not the school book answer to most manufactures, they will work with you to fix this type of problem. Manufactures want to fix that problem since it is a liability issue to that manufacture. A friend of mine had to purchase a lightweight firing pin to fix his problem since he was running a light weight bolt carrier and this makes the bolt and carrier close faster hence the firing pin had more of a tendency to hit the primer with more force. You can also have this problem if you run a lighter that spec buffer too (IE: take the weights out of the buffer and not tune your gas system to match).

Hope this helps,

Scott

[BPiatt]

The picture DEREK45 posted is actual flame cutting. That's from the primer getting holes burned thru them at the edges. Either the primers are soft, possibly small pistol primers, or too high a pressure. One pierced primer will cause one little flame cut. As you can see, they can add up quickly.

Most reloaders will work up a load, check it on a chrono and look closely at the cases. Then load a bunch and never check again. The problem is, if you're loading near max, then the tempurature goes up, so does your pressures (each powder is different. They can also increase as the temp drops) Now you're cutting primers and never know it.

I"ve learned this first hand with working 7mmBR loads at the Masters. I worked the load in the 70 degree mornings but by 1 or 2pm, it was now 85 -90 degrees. Stupid me didn't realize what was happening until the damage was done. After shooting thru a 45 round course in the afternoon and never bothering to check my brass, I now have a bolt that looks similar to Derek45's. I still use the bolt without any problems.

Bruce

[No.343]

The picture DEREK45 posted is actual flame cutting. That's from the primer getting holes burned thru them at the edges. Either the primers are soft, possibly small pistol primers, or too high a pressure. One pierced primer will cause one little flame cut. As you can see, they can add up quickly.

Most reloaders will work up a load, check it on a chrono and look closely at the cases. Then load a bunch and never check again. The problem is, if you're loading near max, then the tempurature goes up, so does your pressures (each powder is different. They can also increase as the temp drops) Now you're cutting primers and never know it.

I"ve learned this first hand with working 7mmBR loads at the Masters. I worked the load in the 70 degree mornings but by 1 or 2pm, it was now 85 -90 degrees. Stupid me didn't realize what was happening until the damage was done. After shooting thru a 45 round course in the afternoon and never bothering to check my brass, I now have a bolt that looks similar to Derek45's. I still use the bolt without any problems.

Bruce

I found the cases where the primers had visible holes in them. I did it shooting high-power rifle. I learned to keep my ammo in the shade and that definitely helped. Since then I learned from smarter folks than me that they kept their ammo in a cooler to help remedy this issue.

[Carbon]

I too had to replace a bolt from erosion. The bolt face had a very even trench cut the size of the primer. It was a batch of bad brass that caused it. The rounds were reloaded from a "green" no-lead load that some local Law Enforcement had shot up and I reloaded. Now I only use used military brass.

It never did affect function but it did look bad.

Carl

[wsimpso1]

OK, Derek45's bolt was destroyed by flame cutting from cracked primers, not by leakage between the primer cup and case. That is not news. What is news on this thread is that it has nothing to do with a particular brand of primer, but is due to primer storage, either by the retailer of by the customer. Looking at the cases that have smokey primers with a magnifying glass, you will see a split - a radial crack - in the corner where the metal is bent from the flat to the cylindrical part of the cup. IF you can see this, the whole story is confirmed. If you can not see it, look at some more fired rounds. But looking at the pit shapes, it was splits in the cup...

When the brass is soft (or the pressures are too high), it usually craters around the primer and pierces in the firing pin indent, pitting the firing pin.

Buy a new bolt (lucky it is AR15, they are cheap, it could be from a pre-1964 M70). Dispose of the existing batch of primers that did this. Understand how this happens. Take action to prevent it.

Strain-strengthened copper based alloys develop stress corrosion cracks when exposed to ammonia. Primers and cases for rifles are strain-stengthened (cold worked) and copper based (cartridge brass is 70% Cu, 30% Zn). The British army discovered this fact about brass and ammonia in the Boer War. This was still in the early days of brass cases and primers for everything from pistols to artillery shells. The ammo rode in the holds of ships along with horses, which are a terrific source of ammonia. The ammo failures were spectacular, wrecking field pieces and wiping out gun crews. The British government was deep into punishment of the innocent before the actual source of the problem was discovered. That is one of the reasons why the world has been using sealed ammo cans ever since.

How to prevent this? Well, first of all, the manufacturers are all acutely aware of the potential and do not use ammonia in ammo plants... I have first hand experience with this issue, having been a product engineer for big green when I was younger.

The most likely sources of ammonia are at a retailer whose pets roam the recieving areas or who has storage in a building adjacent to barns, chicken houses, etc. The next most likely culprit is your loading area and the guy in the mirror. We usually reload in or near to our houses. We have things like pets, babies, household cleaning supplies, and various copper solvents in these houses. All of these are sources of ammonia. So, store your primers and cases away from these things or in steel ammo cans. Really, if you have dirty diapers in the same basement, your primers can do this. And good ol' Hoppes will do it too, so you don't want your primers stored anywhere near where you use copper solvents, because they all have ammonia in them (that is how they dissolve copper).

Short form, Guns and diapers and household cleaners are in a different place from where my primers, cases, and loaded ammo resides.

Anytime you have primers that have vented out of a corner, you gotta get rid of the whole carton. You can pitch the primers or take it up with the retailer or the manufacturer. Since they view it as likely your fault that they got ruined by ammonia, they may be less than helpful to you. If you elect to pitch the primers, I recommend a bleach dunking to deactivate the primers before recycling the brass. Yeah, those used primers are brass.

I also recommend firing a few primers from each new batch and examine the primers really closely for pierces before committing to a big ammo load. If you do this the day the new primers arrive, you can justify returning them to the seller, because SCC does take time to occur. Wait two weeks and you may be told that you are on your own...

Billski

Edited December 11, 2007 by wsimpso1

[No.343]

Good info. Thanks

[D.Hayden]

25.9-26.1 grains of A2230C (book max) with 55's.

Can you still get the 2230C powder?

How fast are these chrono'ing at? ~ 3,100fps?

[el pres]

So when you say pets and diapers is that physically on the

primers themselfs or just the fumes in the same area???

Reason I ask is the cat box is stuck in the basement with me

and those guys get it fumeing.....

Edited December 12, 2007 by DIRTY CHAMBER

[Religious Shooter]

Can you still get the 2230C powder?

How fast are these chrono'ing at? ~ 3,100fps?

I don't think you can get it anymore. I bought like 52 lbs and shot most of it through these bolts.

With 26 grains and 55's: I got 3096 fps with a CM 16" w/FSR. 3184 fps with a SS 16/17" w/WSR. With a CM 20" 3213 fps w/WSR and 3130 fps w/FSR.

For some reason I got tighter groups with FSR but faster V with WSR.

[wsimpso1]

It is exposure to ammonia vapor and humidity over time that causes stress-corrosion cracking in brass. Anything that will give a steady dose of ammonia vapor - diapers, cat urine, copper solvents, glass wax.

If the cat box and the loading bench have to be close, think about storing your primers and loaded ammo in metal ammo cans in a place further away and change the kitty litter frequently. I would also think about ventilating the cat box. A little box fan from the computer store, a covered cat box, and laundry drier vent hardware will work very well at getting the ammonia overboard and the house will be more pleasant too.

Billski

[wsimpso1]

I did not want anyone to get wrapped around the axle... If you have never had a primer vent on you, your current situation is probably fine. But if you are seeing split primers, you get after the sources of ammonia. Cool?

Billski