MAX-11/15 Upper How are they, Reliable? Awkward?

[Deerhurst]

An adjustable gas block can slow down the rate in which gas can flow and pressure can build. The Lage upper has an adjustable gas block.


I run a ~2" long gas tube on one of my rifles. I see no appreciable wear compared to even running FA. Adjustable gas block but it's wide open.

Most of my short barrel stuff, 8" or so, tends to have cycling issues due to not enough gas. The pressure peak with rifle powders tends to be often past 8". I often need a suppressor to keep enough gas volume and pressure to make it cycle.

This was a major problem with the tiny 2" tube. I was/am loading subs to chrono ~1040FPS from an 8" barrel. The problem was most recommended powders tended to burn too long and burned well past the end of the barrel causing not enough pressure and volume to cycle the action. I ended up running a pistol powder which still burns in 8.5" so basically finishes burning in my muzzle device. Cycles now. Barely.


I've never heard of bolts wearing out due to short barrels. I'll have to research it more.

 

[Slowmo]

An adjustable gas block can slow down the rate in which gas can flow and pressure can build. The Lage upper has an adjustable gas block.


I run a ~2" long gas tube on one of my rifles. I see no appreciable wear compared to even running FA. Adjustable gas block but it's wide open.

Most of my short barrel stuff, 8" or so, tends to have cycling issues due to not enough gas. The pressure peak with rifle powders tends to be often past 8". I often need a suppressor to keep enough gas volume and pressure to make it cycle.

This was a major problem with the tiny 2" tube. I was/am loading subs to chrono ~1040FPS from an 8" barrel. The problem was most recommended powders tended to burn too long and burned well past the end of the barrel causing not enough pressure and volume to cycle the action. I ended up running a pistol powder which still burns in 8.5" so basically finishes burning in my muzzle device. Cycles now. Barely.


I've never heard of bolts wearing out due to short barrels. I'll have to research it more.

I think you’ve inferred some type of rule I wasn’t suggesting.

 

[A&S Conversions]

I think it is a matter of force over time. A certain amount of energy is required for function. But there is the issue of how that force is applied. I am not an engineer. But even with a finely tuned gas system a 0.001 increase or decrease in port size in a pistol length gas system can have a big effect in function for a 7.5” 5.56X45. I would caricaturize a 7.5” 5.56X45 upper as violet function. Certainly burn rate has an effect, but my understanding is that the highest pressure is during ignition when the bolt is locked. I understand that the power is still burning. I have found that with rifle caliber uppers with pistol length gas tubes tend to wear gas rings much more quickly because of that additional heat and pressure.

Scott

 

[Deerhurst]

Pressure climbs are the powder burns.

Pressure is a variable of time/burn rate.

I have not found a 0.001" port diameter change to be noticable. If it does everything else is already on the limit and needs some attention. I am also a fan of going a little big and restricting gas by and adjustable gas block. I've built guns with ports ranging from ~0.32" to almost 1/4". Shotguns and low ROF LMGs seem to have huge ports which means more effective force to move the action. A DPM in 7.62x54r has a huge port, something close to 0.200", to run commercial ammo. Pressures are low so it needs that over a large area with free gas flow. Shotguns are low pressure and do similar. A Saiga 20ga (and 12ga) have a giant puck for the gas to push on to move the action.


Pistol length tubes see a longer pressure maximum due to burn rate and port location. this can be seen in my 7.62x25 AR. Gas port is just beyond the tip of the bullet. I tried a very fast powder. 29ksi at ~2.5". Just past the port. I thought it was all just pressure is pressure too. Turns out that spike is too short and does not build enough volume to cycle. Doesn't even manage to get that tiny piece of brass out of the camber. I dropped to a ~14ksi load, different and slower powder, that has a pressure maximum around 6" and due to the continued burn volume is expanding through the gas tube with enough energy to fully cycle the action.

Due to running suppressed and chasing the magic sound barrier velocity (which changes with elevation, temperature and humidity) I like to make my loads burn a little past the gas port so I can have enough powder burning to create enough gas to fill the tube and move the bolt. often I like my pressure peak past the port. If it's too early things tend to not work for obvious reasons of less pressure.


There are too many variables to make a blanket statement.

 

[Deerhurst]

I think you’ve inferred some type of rule I wasn’t suggesting.

I believe the statement was a long the lines of "short barrels wear out bolts" which is simply not true. Too many variables to make a rule or blanket statement of such.


It is a very interesting topic though.

 

[Slowmo]

I believe the statement was a long the lines of "short barrels wear out bolts" which is simply not true. Too many variables to make a rule or blanket statement of such.


It is a very interesting topic though.

That may be what you believe the statement was, but re-read my last three comments, and you’ll see I didn’t actually write that.

So apparently it bears repeating, I think you’ve inferred some type of rule I wasn’t suggesting. I don’t know who you’re arguing against, but it ain’t me. If you want to keep shadow boxing, be my guest.

 

[Novagunner]

I love my max-11/15. I put a dead air 3 port comp on it and it likes to shoot flames and loud as hell indoors. Really love it with the can on it. I still need to tune the gas on it.