Mega arms 16". .308 problem

[mic2377]

I have a Mega 18", and some teething issues as well. The combination of lower, RE, and buffer I had allowed the bolt to move too far back, striking the RE and lower in the corner similar to yours. I ended up shimming the buffer spring until the bolt travel was correct. No more contact was observed. If this is incorrect, it lead to a broken bolt catch.

Also mine was WAY overgassed and required an adjustable gas block to achieve 100% reliability.

[kgj1119]

How did u shim the spring?

[mic2377]

Washers or (don't laugh) a quarter or two work great. The face of the bolt should end up 1/8", maybe 3/16", behind the bolt catch. On mine, it was greater than 3/8". It allowed the bolt corners of the bolt to actually strike the lower, and after 100 rds the force of the bolt slamming forward so far broke the bolt catch.

You will need to verify that it will still lock open on the last round.

If you search my previous posts, there is one detailing the other minor tweaks I did that has mine running with 100% reliability.

[kgj1119]

Thanks for the info you gave me on my post a few days ago. Can you tell what the ar10 buffer should weight. And how long it is? The one I have is 3.73 oz. and is 2.5 in long

[domestique]

Thanks for the info you gave me on my post a few days ago. Can you tell what the ar10 buffer should weight. And how long it is? The one I have is 3.73 oz. and is 2.5 in long

I use a carbine buffer (XH) at 8.5 oz (but I'm also running suppressed). I would at the very least start with an H2 buffer at around 4.6 oz.

[kgj1119]

I use a carbine buffer (XH) at 8.5 oz (but I'm also running suppressed). I would at the very least start with an H2 buffer at around 4.6 oz.

Wouldn't the length of the h2 buffer be too long? It's significantly longer then the ar10 carbine I'm running now

[domestique]

Wouldn't the length of the h2 buffer be too long? It's significantly longer then the ar10 carbine I'm running now

It really depends on your buffer tube length.


Here is a good article to see different options.

loadoutroom.com/10826/tuning-308-ar-part-two-carbine/

I would give Slash at Heavy Buffers a call/email. Provide him with your specs (buffer tube length, suppressed or not, ammo information etc. )

There are too many variables, and he is the expert in all things buffers..... for example MY LMT extension tube is 7 3/4", which is longer then the basic 7" AR15 buffer tube.

[mic2377]

I have actually experimented will virtually all of the possible 308 AR buffer setups.

1. Standard AR-15 buffer tube, DPMS 308 shorty buffer, DPMS 308 carbine spring.
This is the really stubby one. Even with the gas tuned correctly, reliability was never quite as good with this setup. Spring rate is very high and I believe the rifle ends up under-buffered no matter what.

2. AR-10/VLTOR A5 buffer tube, H3 buffer (standard AR-15), and AR-10 carbine spring.
This provides good buffer weight (5.4? oz), and longer spring with better spring rate. This is the optimal setup for a collapsible stock 308. 100% reliable, and what I believe is the optimal buffer weight for most AR-10's.

3. Complete A2 308 buffer tube, buffer, and spring.
This is the best set up of all, similar buffer weight to the A3, with a longer spring and more constant rate.

I don't know if the super heavy buffers are really necessary. If you need an 8.5 oz buffer, I think it ends up being a bandaid for incorrect gas settings or spring rate. Plus they are $$$, I question the utility to $$$ ratio. After my experimentation, I saw zero reason to spend $100+ on a buffer alone. I have a suppressor and experienced no issues shooting mine with or without can with the above setups.

[domestique]

I have actually experimented will virtually all of the possible 308 AR buffer setups.

1. Standard AR-15 buffer tube, DPMS 308 shorty buffer, DPMS 308 carbine spring.
This is the really stubby one. Even with the gas tuned correctly, reliability was never quite as good with this setup. Spring rate is very high and I believe the rifle ends up under-buffered no matter what.

2. AR-10/VLTOR A5 buffer tube, H3 buffer (standard AR-15), and AR-10 carbine spring.
This provides good buffer weight (5.4? oz), and longer spring with better spring rate. This is the optimal setup for a collapsible stock 308. 100% reliable, and what I believe is the optimal buffer weight for most AR-10's.

3. Complete A2 308 buffer tube, buffer, and spring.
This is the best set up of all, similar buffer weight to the A3, with a longer spring and more constant rate.

I don't know if the super heavy buffers are really necessary. If you need an 8.5 oz buffer, I think it ends up being a bandaid for incorrect gas settings or spring rate. Plus they are $$$, I question the utility to $$$ ratio. After my experimentation, I saw zero reason to spend $100+ on a buffer alone. I have a suppressor and experienced no issues shooting mine with or without can with the above setups.

For most people I would agree with you, but not every rifle will work under the same formula.


A lot of factors come into play. The most important being that the LMT (in my case) was built as a battle rifle used for functioning in harsh conditions around the globe. A downside to this is they are notoriously over gassed. A different gas system isn't possible, nor would I want to change what the engineers that designed the system to function 100% all the time, because the gas port is drilled at a 45 degree angle... I do believe Wilson Combat does sell a 45 degree gas port, but LMT press fits the gas block on, making it virtually impossible to get off without factory tools, or THOR's hammer.

It also depends on the suppressor. A buddies AAC provided a lot of extra back pressure in comparison to my Surefire. It needed the extra weight buffer to tame down the extraction (bringing the 5:30 extraction back to factory 3:30. LMT actually ships their rifles with H2 buffers, but I prefer the added shoot ability the recoil pattern of the XH buffer provides. After dropping 2.5k+ on a rifle, the extra cost of a buffer that will prolong to use of the rifle, and make it more enjoyable to shoot is money well spent IMHO..... but every case is different, and I'm all for saving money if possible.

I really think kgj's 3.7 oz buffer is too light, and would benefit from talking to Slash.

Kgj, if you could borrow an H2, or H3 buffer from a buddy that would make for a cheap test.

[kgj1119]

I have an h2 and h3 buffer laying around from ar15 builds. Isn't that buffer too long though for the ar10?