View Full Version : Stag bolts - are the MPI tested?
Do you know if a standard bolt on a Stag 2H carbine is pressure tested and MPI? I called the factory. They said they were. However, the bolt is not marked.
I believe that they are MP batch tested.
Robb Jensen
06-05-08, 06:58
Stag uses CMT bolts, if I'm not mistaken they are batch HP and batch MPI tested.
If I owned a factory Stag AR I'd keep a BCM bolt as a spare........
I think that is good advice on the spare parts. Based on what I learned on this board, I had my Stag carrier staked properly. Would you have a spare bolt or would you get an entire BCG?
I called the factory. They said they were.
I have an email from their sales department which indicates they batch test and they only mark the bolts if they are specifically tested. It is interesting they didn't qualify their statement to you. I really feel that some of their reps either don't know about the batch testing or are intentionally not providing that information so as to mislead customers. Either way, it's not good business.
BTW, the comparison chart would have provided that information for you.
The Stag guy on the phone also said their carrier was properly staked and that there was no difference between a blue and a black insert.
I read the chart. I wanted to see what the actual manufacturer claimed. The guys on the phone seem like call center operators with a script.
Do you know if a standard bolt on a Stag 2H carbine is pressure tested and MPI? I called the factory. They said they were. However, the bolt is not marked.
They at best batch MPing and not doing ANY HP testing. Without HP testing, MPing is worthless.
C4
The Stag guy on the phone also said their carrier was properly staked and that there was no difference between a blue and a black insert.
I read the chart. I wanted to see what the actual manufacturer claimed. The guys on the phone seem like call center operators with a script.
This is again wrong. We see Stag gas keys come loose all the time. They DO NOT STAKE THEM PROPERLY!
Yes, there is a difference between black extractor insert and a blue one. The black ones we use from LMT are VERY much different than the blue extractor inserts that Stag uses.
C4
Thanks Grant. I wanted to post what they said. I knew that they were wrong when they were on the phone.
I am curious about the MPI testing. We seem to have conflicting data.
Thanks Grant. I wanted to post what they said. I knew that they were wrong when they were on the phone.
I am curious about the MPI testing. We seem to have conflicting data.
What is conflicting?
C4
Stag said that they pressure test and MPI. I am told by those on the board that they don't. That is the conflict.
I tend to believe the people on this board due to the fact that the Stag rep told me that they stake their bolts properly and that there is no difference between the blue and black inserts.
Stag said that they pressure test and MPI. I am told by those on the board that they don't. That is the conflict.
I tend to believe the people on this board due to the fact that the Stag rep told me that they stake their bolts properly and that there is no difference between the blue and black inserts.
In all the years I have been dealing with Stag, they have NEVER HP tested their bolts. They did for awhile MP test every bolt, but they stopped doing that some time ago.
C4
Had you been in the market for a Pinto, do you think the salesman would have told you about the exploding gas tank porblem and other stuff? No, because that would have killed sales. Sales reps are looking after the interest of company not "nit picky" (please note sarcasm) stuff like extractors and bolts.
In the end it will come down to you absorbing info that is posted here and that of the sales guys and deciding what you think is true. I am pretty sure 99% of us will not BS a member and will give an honest opinion based on experience or observations.
Stag said that they pressure test and MPI. I am told by those on the board that they don't. That is the conflict.
I tend to believe the people on this board due to the fact that the Stag rep told me that they stake their bolts properly and that there is no difference between the blue and black inserts.
As I understand it, Stag/CMT will MPI all bolts if requested by a vendor. As Grant said, however, without the HPT this is kind of pointless. The HPT is done to put stress on the part, and the MPI is done to see if that stress caused and surface failures.
The process should really go (1) Shot Peen to reduce potential metal fatigue, (2) Proof Load (Proof Fire, High Pressure Test, HPT, whatever you want to call it) to put the part under stress, (3) Magnetic Particle Inspect (MPI) to check for cracks caused by the Proof Load. Doing the MPI without the HPT is like putting a condom on AFTER sex.
Kurt Reifert
06-06-08, 06:44
Is there any info available comparing the rate of failure of shot peened/HP tested/MPI bolts to those that have not gone thru this test proceedure?
I think it would be pretty hard to test, Kurt. Only way I could see to do it would be to take a large lot of each, say 1,000 of each, and fire thousands of rounds through rifles with each. Problem is that different barrels, ammo variables, etc. would also all play in.
At the end of the day all you can do is educate yourself and decide for yourself if "good enough" really is.
Robb Jensen
06-06-08, 06:52
Is there any info available comparing the rate of failure of shot peened/HP tested/MPI bolts to those that have not gone thru this test proceedure?
In my experience (unscientific) I find that non-HP/MPI tested bolts 'live' about 1/2 as long as HP/MPI tested bolts.
BUT it all really depends on how one shoots. If you shoot hard/fast/suppressed/SBR/full auto etc a bolt of either type will fail much sooner than say a varmint shooter/high-power service rifle shooter. So it's all really relative.
Kurt Reifert
06-06-08, 08:30
I think it would be pretty hard to test, Kurt. Only way I could see to do it would be to take a large lot of each, say 1,000 of each, and fire thousands of rounds through rifles with each. Problem is that different barrels, ammo variables, etc. would also all play in.
At the end of the day all you can do is educate yourself and decide for yourself if "good enough" really is.
Fair enough. I thought that data existed.
Another question would be what is the rate of rejection of bolts that are HP/MPI tested.
That info must be out there somewhere and it should validate the test process.
Kurt Reifert
06-06-08, 08:33
In my experience (unscientific) I find that non-HP/MPI tested bolts 'live' about 1/2 as long as HP/MPI tested bolts.
Based on that, we would probably expect a 50% rejection rate on bolt that go thru the HP/MPI test. :eek:
Fair enough. I thought that data existed.
Another question would be what is the rate of rejection of bolts that are HP/MPI tested.
That info must be out there somewhere and it should validate the test process.
I agree with you, but so far I haven't been able to find out anything.
Is there any info available comparing the rate of failure of shot peened/HP tested/MPI bolts to those that have not gone thru this test proceedure?
I have talked to several manufacturers about this. They tell me that that they typically see about 3 failures for every 5000 bolts tested.
C4
I agree with you, but so far I haven't been able to find out anything.
You are not going to either. The problem is that only about 3-4 manufacturers HPT and MP and they tend to keep this type of info quiet.
C4
Kurt Reifert
06-06-08, 08:49
I have talked to several manufacturers about this. They tell me that that they typically see about 3 failures for every 5000 bolts tested.
C4
That's a pretty slim margin. Certainly worth the effort for use in a rifle that will be going to war or used in the line of duty, but it doesn't seem necessary for the average plinker.
That's a pretty slim margin. Certainly worth the effort for use in a rifle that will be going to war or used in the line of duty, but it doesn't seem necessary for the average plinker.
Most of the quality control and assembly items aren't "necessary" for a plinker. The worst that happens if something goes wrong is you bag up and go home. Personally, I hate wasting my time driving to a range and getting set up only to have the damn gun go TU.
I used to own a 400HP car too. It wasn't "necessary" for my daily commute, but I'd rather have it than a 125 HP ecconobox.
That's a pretty slim margin. Certainly worth the effort for use in a rifle that will be going to war or used in the line of duty, but it doesn't seem necessary for the average plinker.
This info has come from two manufacturers. There are more, but these are the only two the would give some kind of number.
I personally believe that a well built bolt does not need to be HP or MP'd, but you have to ask yourself if it is worth the risk. Since they are all about the same price, I think it is worth spending the extra couple dollars.
C4
I personally believe that a well built bolt does not need to be HP or MP'd, but you have to ask yourself if it is worth the risk. Since they are all about the same price, I think it is worth spending the extra couple dollars.
Once again Grant, you provide sound logic. At a rejection rate of 3:5000, that's not enough to concern the average user, even in most tactical environments. But the observation that the HP/MP test adds neglible cost and decreases the odds of failure, substantiates the reason to utilize a bolt that has been HP/MP tested.
Karl
I also look at it another way.
Generally speaking, if a guy is willing to take a polygraph then he's telling the truth. His confidence in the knowledge that he is telling the truth allows him to easily agree to be tested.
Similarly for bolts, the makers that make a good product and know it are more than willing to be tested. If you know that your product won't be tested, the pressure is off to produce a quality part.
My concern would be that while a quality bolt fails 3/5k, who the hell knows how often a sub-standard bolt would fail?
So, while the HPT and MPI may not be totally required, for me it's the only way I know for sure that I'm getting a quality part.
Once again Grant, you provide sound logic. At a rejection rate of 3:5000, that's not enough to concern the average user, even in most tactical environments. But the observation that the HP/MP test adds neglible cost and decreases the odds of failure, substantiates the reason to utilize a bolt that has been HP/MP tested.
Karl
Thanks. We are going to eventually do a lower priced BCG without any testing done at all for those people that need to save $20 bucks.
C4
I also look at it another way.
Generally speaking, if a guy is willing to take a polygraph then he's telling the truth. His confidence in the knowledge that he is telling the truth allows him to easily agree to be tested.
Similarly for bolts, the makers that make a good product and know it are more than willing to be tested. If you know that your product won't be tested, the pressure is off to produce a quality part.
My concern would be that while a quality bolt fails 3/5k, who the hell knows how often a sub-standard bolt would fail?
So, while the HPT and MPI may not be totally required, for me it's the only way I know for sure that I'm getting a quality part.
I do agree that one of the best ways to gurantee that you are getting a quality made bolt is to make sure that it is HPT/MP'd.
C4
Since we are speaking about bolts I thought I would share this beauty. This bolt was in the weapon of my old T/L on a different contract. It came from a select-fire Bushamster M4gery.
This bolt shattered during a firefight in which he expended about 900 rounds. I had to completely disassemble the weapon in order to get it out of the upper. A small failure rate is definitely acceptable out on the range. but, in the real world it can get you killed.
BTW- I emailed this pic to Bushamster after the incident and tried to get their "techs" to give me some info as to what they thought about it. Needless to say after at least 4 emails they never responded and I gave it up.
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