How does Law Enforcement manage to get by with M&P15s?

[SteyrAUG]

I'm surprised that springs are the example you'd give for cut corners, most folks cite the M&P15 Sport's unshielded hand gaurds or to a lesser extent the 4140 nitrided bbl.

Hand guards are such an easy fix probably nobody would take the time to even mention it. But ARs are loaded with springs (extractor springs, detents everywhere) and they aren't always easy to recognize as a problem or change out like a buffer tube spring.

My last problem with an AR (which was actually a Colt) was a selector with a detent hole drilled just a little too deep. The result was an AR locked up on safe and I had to remove the grip to address the problem. Selector was a Scmidt part and got passed Colt CQ somehow and this is why I function test everything before going to the range, or worse handing it to a prospective buyer.

I should mention this is the second Colt in 40+ years where I experienced a defective part. The other was a Colt HBar purchased in 1989 that was failing to extract. Sent it back to Colt and they fixed it and returned with no issues ever again. On the most recent Colt, a 6933-EPR is removed the ambi selector and replaced it with a standard safety selector and it's been 100%.

[Echo40]

It just strikes me as odd, is all. I mean, not only are the cost savings between springs not that substantial, yet simultaneously are a critical part, so it seems like the worst possible part to cheap out on. Grips, Stocks, and Hand Guards make more sense because not only is it easier to save money that way, but they're parts which are commonly swapped out by the end user anyway, so nobody is likely to complain if they cut costs that way, nor does it diminish the overall value of the rifle.

A barrel is another means to save money since most consumers are ignorant of the differences between 4140 and 4150 Steel, nor the particular value of a chrome-lined bore, and even if they look it up then they're most likely to dismiss it as being of little consequence, so manufacturers can easily get away with using a 4140 barrel with a phosphate finish and no chrome-lining.

[lysander]

I'm familiar with those specs, but I wasn't aware that the M&P15 even met the bare minimum of acceptable conditions as per MIL-DTL-71186A.

I'm surprised that springs are the example you'd give for cut corners, most folks cite the M&P15 Sport's unshielded hand gaurds or to a lesser extent the 4140 nitrided bbl.

Building a rifle that can hold 30 rounds in a 5.6 inch circle at 100 yards and last 6,000 is not all that difficult when you have a well proven design, and 50 years of subcontractors making small parts.

4140 is perfectly adequate or a barrel if you don't go Rambo on the mag-dumps and no full auto.

And last, springs are pretty touchy about poor workmanship, especially one that are weak designs to start with, like the AR extractor spring.

[SteyrAUG]

It just strikes me as odd, is all. I mean, not only are the cost savings between springs not that substantial, yet simultaneously are a critical part, so it seems like the worst possible part to cheap out on. Grips, Stocks, and Hand Guards make more sense because not only is it easier to save money that way, but they're parts which are commonly swapped out by the end user anyway, so nobody is likely to complain if they cut costs that way, nor does it diminish the overall value of the rifle.

A barrel is another means to save money since most consumers are ignorant of the differences between 4140 and 4150 Steel, nor the particular value of a chrome-lined bore, and even if they look it up then they're most likely to dismiss it as being of little consequence, so manufacturers can easily get away with using a 4140 barrel with a phosphate finish and no chrome-lining.

You are correct, it's a terrible place to try and save a dime.

[shadowspirit]

I agree with lysander. The M&Ps aren't terrible carbines.

Now the S&W sport ARs are complete shit. I kid we know had one and at least 4 things went wrong in the first few months. Mag catch broke. Buffer roll pin drifted out, and a couple of other things too. Had he paid for the stuff I fixed on the gun, he'd have been out the money to just get a 6920.

What is different about the S&W Sport ARs from the other ones being referred to in this thread?

[pinzgauer]

I guess I'd rather have an m&p 15 then no carbine, but I'm a bit surprised at some of the responses here.

It's like materials and the "TDP" quantifiable items don't matter anymore.

If S&W ever made a M&P-15 with TDP type alloys I have not seen one been able to find it online.

All the ones that I can find listed are:

- 4140 barrels
- Non-chrome lined
- No mention of bolt alloy, which nearly always means 9310
- no mention of receiver extension alloy which nearly always means 6061

And those are just the things we can quantify, we'd have to look at the fire control group castings, bcg staking, and similar to know if they've cheaped out in another areas.

A 4140 melonite barrel certainly will shoot, and will likely serve them. Similarly, 9310 bolts.

But thats not the core question, which is why do we recommend 6920s and similar? Or is the m&p " just as good as". Just those items listed alone could justify the $100-200 price difference.

They may certainly be "good enough" for LEO on a budget. Most likely will be carried a lot and shot little.

But it's a far leap to say that they're just as good as a properly tdp'ish carbine.

[markm]

What is different about the S&W Sport ARs from the other ones being referred to in this thread?

No idea. It's Smith's designation. But it CLEARLY illustrates that they tossed the TDP out the window and said "how cheaply can we build this turd?"

The fact that Smith gave it its own designation, AND lowered the price tells me they knew it was substandard. Shit was going wrong on that gun, that I'd never even thought about.

I mean... who thinks their mag catch will break mid shoot?

[pinzgauer]

One review I read describe the main difference between the m&p sport and the patrol carbine was upgraded furniture.

I did find a S&W listing for the patrol (LEO only) carbine and it's still a 4140 melanite barrel and no other materials specifications listed.

[lysander]

I guess I'd rather have an m&p 15 then no carbine, but I'm a bit surprised at some of the responses here.

It's like materials and the "TDP" quantifiable items don't matter anymore.

If S&W ever made a M&P-15 with TDP type alloys I have not seen one been able to find it online.

All the ones that I can find listed are:

- 4140 barrels
- Non-chrome lined
- No mention of bolt alloy, which nearly always means 9310
- no mention of receiver extension alloy which nearly always means 6061

And those are just the things we can quantify, we'd have to look at the fire control group castings, bcg staking, and similar to know if they've cheaped out in another areas.

A 4140 melonite barrel certainly will shoot, and will likely serve them. Similarly, 9310 bolts.

But thats not the core question, which is why do we recommend 6920s and similar? Or is the m&p " just as good as". Just those items listed alone could justify the $100-200 price difference.

They may certainly be "good enough" for LEO on a budget. Most likely will be carried a lot and shot little.

But it's a far leap to say that they're just as good as a properly tdp'ish carbine.

For a LEO, the first most important question is, "Will it shoot when I need it to shoot?" He is not going to go over the confidence course with it, he is not going to jump in and out of his Bradley IFV on a regular basis, he is not going to live in the jungle for three or four weeks at a time with it. A LEO is going to keep it in his trunk, or in a rack in the passenger seat of his car. He will never be an hour or two away from his logistical support. And, if he is a good officer, he will clean and inspect the carbine on a regular basis.

4140 barrels won't cause sudden malfunctions.
A non-chromium plated barrel will not cause sudden malfunctions.
A 6061-T851 receiver extension will not cause sudden malfunctions.

As to 9310 bolts . . .

What applications was Carpenter 158 designed for? What applications was 9310 designed for?

Carp 158 is a die steel, optimized for cold working dies, die rollers, and other similar things. Massive parts that pressed or impacted with other massive parts.

9310 was optimized as a gear steel, designed for good case hardening properties and fatigue resistance in gear teeth exposed to substantial bending stress.

If Carpenter 158 was the best stuff out there what are only AR and AR clone bolts made from it?

M249 loves 9310, most of the operating parts are 9310. M60, same thing, operating rod and bolt 9310. H&K MR556 bolt is made from 14 NiCr 18, basically a DIN equivalent of 9310, Haenel uses the same stuff. The FAL bolt is 3310, basically 9310 with the molybdenum removed and more chromium added. 9310 is considered excellent for shock loading, and fatigue life.

Ever wonder why Carpenter 158 was chosen for the AR bolt? Armalite did not have an on-staff metallurgist, so they did what everyone does when they don't have their own expert, they call the steel foundry and ask to talk to their steel expert and ask what steel alloy he would recommend for this particular application. Carpenter's metallurgist had two choices, he could recommend 9310 as it is very good for this application as we have seen above, and available everywhere, or he could suggest Carpenter 158 which is very similar to 9310, but only available from his company, Carpenter Technologies®.

Steel qualities aside, a 9310 bolt will not make a carbine suddenly malfunction.

As to the sacred "Holy TDP" that is above all and shall remain immutable for all eternity.* There are two types of specifications:

1) Performance specifications
2) Detailed specifications

Performance specifications are a list if things that must be accomplished, it must be reliable, it must be durable, it must be accurate. The you must define what is reliable; X malfunctions and Y parts breakage in Z thousand rounds, define durable; Not break when dropped from the height of a truck bed, still work after being dropped out of a car going 35 mph, etc, define accurate; 10 shot group of W diameter at 100 yards, and so on. Patrol cars are purchased on performance specifications, “How fast does it accelerate?” “How safe is it?” “How easy is it to remove puke smell from the rear passenger area?”

The Army’s specification for the M110 is a performance specification and is why they could change vendors half-way through the program.

Detailed specification throws an extra layer of administrative overhead, instructing not only what performance you have to achieve, but how you will make it and who will make it. Generally, all it does is make things more expensive. There are some benefits, but they really aren’t relevant here.

For example: I could detail spec an engine block to be a A356 casting. This limits not only “what”, but “how” and to a certain extent “who” (you are now limited to companies capable of casting aluminum). What if you can machine a similar block from a billet of 6061? Would this be “per the TDP”?

No, but it could be the same, or may be even better. What if I plan on derating the engine 30 horsepower for a more economic-minded market, could I use A319 aluminum instead? It would not be “per the TDP”, but it could be perfectly adequate to the performance required.

As the various law enforcement agencies are consumers of your tax dollars, I would expect chiefs and sheriffs to exercise a little realism in in their requirements. How would you feel if you found out your taxes were going up because the city police chief decided to issue all his officers $4,500 customized Glocks, he could truthfully argue that they were much better that the run of the mill stock Glock.

_ _ _ _ _ _ _ _
* Except it doesn't, the TDP changes all the time. More and more parts are now authorized MIM manufacture.

[pinzgauer]

For a LEO, the first most important question is, "Will it shoot when I need it to shoot?" He is not going to go over the confidence course with it, he is not going to jump in and out of his Bradley IFV on a regular basis, he is not going to live in the jungle for three or four weeks at a time with it.

I am mostly with you on most of your points, and 100% with you on the bolt alloy.

But that was not my point, which this is really a false equivalence or comparison.

It's not an "as good as" comparison, it's a "good enough for people who won't use it much" positioning.

Because I'm pretty sure you wouldn't say that 4140 is a better steel for m4 barrels then 4150CMV. It might be sufficient, certainly worked in earlier weapons and works in a lot of ARs now.

Same for 6061 receiver extensions versus a forged 7075. Most of us have been around or seen receiver extensions fail. Usually from misuse like mortaring or similar.

I'm pretty sure you're not saying cast/extruded 6061 is better than 7075 forged in a receiver extension application.

Bolts are a different issue and there are a lot of arguments to be made that c158 is an anomaly and probably not the best choice for AR bolts.

I've had personal conversations with Bill Alexander on this, and as he explains c158 is a wonderful alloy for some purposes but it was never intended for parts as small as an AR bolt. And it's extremely difficult to get consistent heat treating, which is what led to the requirement for HPT and MPI.

So I would accept the argument that a well-made 9310 bolt is probably acceptable even if technically not per TDP. Somewhat argue it might well be better.

Sounds like we are saying the S&W is good enough, if (acceptably) compromised with lower quality/expense parts.

So does that mean Ruger, Core 15, DPMS, ArmaLite, etc etc are also okay?

Granted, S&W's support infrastructure for LEO is probably stronger and they have a historical relationship.

I personally am not a TDP bigot, And I've always rejected some of the M4 players other than colt acting like they had some secret knowledge about the TDP.

But that said, there are some quantitative/qualitative items associated with the TDP and OG Colt mfg'd M4s that I want.

I've had beautiful billet 6061 receivers, and they didn't fail. But now I want a quality 7075 with a proper hardcoat.

Same for forged 7075 receiver extension, and 4150CMV chrome lined barrel. Unless I'm chasing accuracy in which case a good stainless barrel. Or it's a DD/Steyr/FN CHF barrel.

So to me, carbines like the SW are false economy. I'd rather have the better materials for the small increase in price. But LEO purchasing is an unusual thing. In some things they demand premium, and others they try to buy commodity.

I'm watching local agencies spend $10000-15000 per officer on extremely complex radios. That might have some slight advantages, but also some compromises.

So I have a harder time rationalizing buying lower spec rifles due to budget issues. Same for cars and lights.