At what point do you trust a new part?

[grantoga]

I have an SBR with a 10.5" PSA premium upper. I have found that I like the recoil impulse the best with an old style 9mm buffer (havnt tried an H3 buffer). It ejects consistently and locks back on an empty mag of PMC, Wolf and Tula. The buffer length is identical to my other carbine buffers, so overtravel isnt an issue. I recently completed a 400 round carbine coarse with zero malfunctions with the 9mm buffer. Would you guys now trust this weapon in an HD role with a 9mm buffer? The same question goes for other "function" parts. After you guys switch out a part, at what point do you trust that you have not compromised the reliability of the weapon?

[wigbones]

My simple answer is that unless I have had an issue with a part I tend to trust it after I've put some rounds on it. I'd say with over 400 rounds unless you've experienced any issues you can give it the benefit of the doubt.

[firefighter37]

I have an SBR with a 10.5" PSA premium upper. I have found that I like the recoil impulse the best with an old style 9mm buffer (havnt tried an H3 buffer). It ejects consistently and locks back on an empty mag of PMC, Wolf and Tula. The buffer length is identical to my other carbine buffers, so overtravel isnt an issue. I recently completed a 400 round carbine coarse with zero malfunctions with the 9mm buffer. Would you guys now trust this weapon in an HD role with a 9mm buffer? The same question goes for other "function" parts. After you guys switch out a part, at what point do you trust that you have not compromised the reliability of the weapon?

Never, which is why I always try to have a backup. Anything mechanical can fail. It can fail on the first round, the 101 round or the 1,000,001 round. You never know when something will fail, but you can count on it failing at the worst possible time. If you are running parts that are from known, reputable manufacturer I'd say a solid run of 1000 rounds fired would be a good sign of function. It's all subjective. I say 1000, some will say 100. Ultimately it's up to you to decide where YOU feel comfortable.

[tom12.7]

I wouldn't say never or always. Reliability is a function of many things. If one considers MRBS and/or MRBF, then in reference to what? For most of us it would be compared to the issue M4 in general, but that may not be the case to others. An issue 10.5" MK18 may be a better reference for the OP. Another issue to consider is what are the test priorities or what test is considered a priority over the others for the end use?
Reliability sounds simple, but it can be very involving.

[Microadventure]

when I can no longer remember when I installed it.

[tom12.7]

What about times when some shooters add or substitute components that they "feel" are beneficial at the time, but do not realize the unintended consequences of that use over a wider span? Sometimes it can lead to failures, other times to just stoppages. When things are altered without giving merit to the system as a whole, many things can happen. Without knowing or looking how those interactions can alter things is short sighted. A broader view of things would be to look at the system as a whole first, then make forward steps to enhance the system without degrading some things that are needed for others without an unneeded gain for the sacrifice of another. Some components can work well, others do not.

[sevenhelmet]

Short answer, it depends. I trust firearms/parts as long as they function. If they stop functioning as they should, I investigate the problem and make changes until they do. For a gun with new or altered parts, I won't place it in a role where I am depending on its function until I've fired several hundred rounds through it with no problems. It helps me get proficient with it as well, reducing operator error. I typically feel closest to "one with the gun" after 300-500 rounds over several range sessions without a long hiatus in between.

I've found problems on new guns that surfaced within the first 100-200 rounds (such as the dreaded Marlin lever double feed, or feed ramp jamming on a new XD), which are easily corrected, allowing the gun to be reliable once more. So 300-400 rounds of trouble-free shooting is fine by me for a gun I may have to depend on in an emergency.

[WS6]

It depends. Let's say I break a bolt-catch. I replace it with a quality bolt-catch. Will I need thousands of rounds to trust the replacement? No. I won't.

Now, let's say that I buy a new upper. I may need several thousand rounds before I trust it. Some malfunctions reliably happen every 5-600 rounds, and it's hard to know if 1 of them is "random" or if it's a trend. I've had carbines that would malfunction at about that rate, and it took me a few thousand rounds to figure out that the gun had issues. 2 carbine courses, to be exact. About 3500 rounds + range time on my own.

[Boba Fett v2]

I have an SBR with a 10.5" PSA premium upper. I have found that I like the recoil impulse the best with an old style 9mm buffer (havnt tried an H3 buffer). It ejects consistently and locks back on an empty mag of PMC, Wolf and Tula. The buffer length is identical to my other carbine buffers, so overtravel isnt an issue. I recently completed a 400 round carbine coarse with zero malfunctions with the 9mm buffer. Would you guys now trust this weapon in an HD role with a 9mm buffer? The same question goes for other "function" parts. After you guys switch out a part, at what point do you trust that you have not compromised the reliability of the weapon?

If it got you through a carbine course and it's still ticking then I'd say go ahead and run with it. After running over 1K through my A5H2 equipped SBR w/o a single failure or any noticeable adverse effects I'm confident that it's GTG and would feel confident installing it in a similar set-up in the future. My general rule of thumb is that if it's registering miles and it's running strong (and not an ammo or magazine issue), then chances are it'll keep going. Always good to have a back-up system, but so far I haven't had to resort to that as a result of catastrophic failure in either of my heavily run carbines. If failure does occur at some point, I'd try my best to just isolate the component and go from there.

[Tzook]

It depends on the part for sure. I would say, your buffer is good to go. It isn't ever going to weigh any less or any more and prevent anything from cycling or change a recoil impulse. With something like that, you're going to find out within a magazine if it's going to work for you or not.

Also keep in mind what your needs are. I think the "good to go for home defense" can be way, way overthought. That's basically going to consist of you picking the rifle up, which is probably reasonably clean and using it in your house. You don't need to put 70,000 rounds through a rifle before you know it's going to go bang when it's clean in basically an ideal environment. Is it smart to never shoot a brand new gun and stick it beside your bed? Of course not. Buy known quality, run it for a couple hundred rounds and make sure that the manufacturer didn't screw something up and rock it.