Looks like I’ll be picking up a M&P10 today. I know from experience on previous rifles that I will be wanting a fixed rifle stock on this – probably the Magpul MOE rifle stock. I’ve done some reading and run some searches, but haven’t found a definite answer to what buffer and spring will work with the A2 receiver. It appears that S&W’s “there, fixed it” solution is to stick a solid aluminum spacer in the A2 RE to give it the same depth as their collapsible stock RE, and just use the same buffer and spring as the collapsible models. I would really rather not do it this way… if I’m going to be installing the longer RE, I want to at least get the benefits of a longer/heavier buffer, and pass on the dead weight of the spacer.
I have read accounts of at least a few people who installed an A2 receiver extension and .308 rifle buffer (like the Armalites and DPMS’ use) with the original S&W spring who say it works… but I haven’t heard about reliability results after any significant kind of round count.
I am fine with embarking down new roads and doing a little experimenting, but I figure there is no need to re-invent the wheel if some of y’all have already tried this. I would be very interested to hear from some of you who are running the A2 buffer tube, .308 rifle buffer, and factory S&W spring to see how it has worked out for you… or what else you had to do to make it work. I hate getting cheek weld on a carbine tube, at least with a scope, so it would be greatly appreciated!
I got the M&P today, and noticed a couple things when comparing it to my LR-308 – the bolt carriers appear to be the exact same length – as do the upper receivers. The two bolt carriers feel like they are very similar in weight as well. I see no reason why the same receiver extension/buffer/spring combo that works on a LR-308 wouldn’t work on this rifle… but then again I haven’t tried it… that’s why I’m asking y’all.
I put an Armalite Xtra heavy buffer from heavybuffers.com in mine (M&P 10) before I ever fired a shot. I have put about 120 rounds through it and have had a lot of trouble with the bolt not locking open on the last round and sometimes not cycling all the way back to grab the next round from the magazine. I believe that the buffer may be too heavy for the Lake City ammo I’m running and the bolt not being broke in (small amount of metal wore where the bolt touches the receiver to make it glide easier). I am going to try it with the factory carbine buffer, this weekend, and see if that remedies the issue. I use it for 3 gun and am trying to make it as soft recoil as I can.
I put on a rifle length buffer tube, rifle length (A2) spring, and the Xtra heavy buffer is rifle as well. I also put on the Magpul MOE rifle stock over the tube. Sorry, I didn’t clarify.
OK, that is helpful info… it suggests to me that the M&P isn’t so overgassed that it needs a heavy rifle buffer, but that a regular .308 rifle buffer might work. Thanks.
It’s what mine came shipped with as well. There are reports on the Smith & Wesson website that the gas port of the M&P-10 is small. A couple have been measured at .068". I tried running an H buffer but the rifle short strokes with NATO pressure ammo. I tried a lock back test with commercial ammo which the rifle passed, but that was only a single round. When I get caught up with my finances, I plan to test the Big Smith more extensively with commercial ammo. With the carbine buffer in place, it still occasionally has issues with short stroking.
The rifle buffer, if I recall, is a bit over 5 oz making it about 2 oz heavier than the factory carbine buffer. It’s very possible that the rifle will short stroke using a rifle RE and a rifle weight buffer
I’ve seen you mention that in the past. I’m wondering if there’s variations between some of the guns. Mine has locked back on an H2 but not 100% reliably. I primarily ran an H after that but there’s a new load that I started testing that occasionally failed to lock. I’ve never had an issue with the carbine buffer (NATO or Commercial).
Sometime soon, I plan to swap handguards. I’ll try to remember to measure the gas port. Now you’ve got me curious…
Unrelated but mine is compatible with the 7.62 Gunfighter CH & many others report that theirs is not. Supporting the idea that perhaps not all 10’s are created equal??
A little update… I ordered an A2 receiver extension, AR-10 rifle buffer, and a JP rifle spring (supposed to be 7% stiffer than the factory one – Brownell’s didn’t have factory springs in stock when I ordered), and a Magpul rifle stock. got all the parts installed, and was able to get the Big Smith out to the range yesterday. I was shooting Lake City M80 ball. I had persistent failure to feed… rounds were getting stuck coming up from the magazine into the chamber. I was using DPMS LR-308 20 round mags. I switched out the JP buffer spring for the factory S&W one (which appeared to be nearly identical in length and stiffness), and continued to have the problem. It never had any trouble locking back on empty mags, however, and never short stroked. i went through maybe 60-70 rounds and had perhaps 5 failure to feed malfs.
Another disheartening discovery was that the Big Smith’s mag well does not accept C Products mags, which worked fine in my LR-308. This means half of my .308 mags won’t work in this rifle. I suppose the next step is to reinstall the factory buffer tube, spring, and buffer and see how it works. If problems are still experienced, possibly try some different mags (like Magpul). I will keep y’all posted.
I would get some Magpul mags, and your feeding issues should go away. My M&P 10 came with the Magpul mag, and I have 5 others. I have yet to have any issues through about 200 rounds of mixed .308 hunting ammo as well as NATO pressure ball.
I will also mention that my rifle is running an H2 buffer during those rounds.
I don’t know man… I have never had a failure to feed with these DPMS mags in my other .308. I’m thinking it may be short-stroking after all – it looked like I was getting “bolt-over” failure to feeds… where the bolt wasn’t engaging the base of the cartridge, but was instead dragging across the top, sticking the cartridge in the chamber at an angle and bending it at the neck. I have re-installed the factory collapsible RE and buffer, and will try it out at the range today.
I did some more testing over the weekend… the M&P does not lock back on empty after all, with either the A2 stock or the factory carbine stock. I got more bolt-over malfs too. My money is on either a misaligned gas block or an undersized gas port. We will see when I pull the GB.
