View Full Version : Gas system and upper building questions.
I currently own a M&P15 (I bought it in 2008 before I understood much about ARs) with the 1/9 twist. I've been thinking about upgrading the barrel to something with a 1/7 twist, and was looking for some input.
Is going to a mid-length gas system a big enough deal to justify the extra parts needed? I'm set on my next AR being a mid-length 16" gun from BCM or DD. Do mid-length guns really run that much smoother? Anyone own both a carbine and a mid-length system?
The other thing I'm wondering is if any of the M&P15 upper is suitable for using as part of a new build. Would it be feasible to install a new barrel on the M&P upper receiver, or am I wasting time buying anything less than a complete upper?
Thanks.
polymorpheous
06-05-13, 08:14
First, let's get the obvious question out of the way...
Do you have the tools and knowledge to perform a barrel swap?
If you don't already have the tools, you are better off just buying a complete upper.
Middy vs carbine was thoroughly hashed out awhile back and a search should turn those threads. In a nutshell, both systems work well when properly tuned. Middy fans claim recoil impulse of the longer system is softer, carbine fans claim it makes no difference. Some have found the combination of the middy length with a 14.5" bartel makes for a rifle that's finicky about ammo.
As long as your current barrel is not having accuracy or reliability problems, there's little practical reason of incurring the cost of replacement. That said, if I had a good stash of ammo and the funds available to do so, I'd replace the barrel with a 16" lightweight or lighter weight profile middy. I would also just replace the barrel & gas tube and reuse the upper as I have the necessary tools to do so.
Searching and reading will give you more details about the pros & cons about both gas systems and the pros & cons about rifling twist. Molon has a good thread about accuracy and twist rate
What is your current barrel NOT doing for you?
I see this "I want to dump my 1/9" all the time by guys who have not actually had their barrel fall short.
I cite this example all the time... but we shoot Pappabear's nominal 1/9 out to 1000 yards with both 77 grain and 80 grain SMKs.
If your barrel is failing to perform for your needs, by all means... but if you're just basing this desire on what Idiots parrot on the gun forums, slow down and try the barrel.
Don't discredit 1/9 twist barrels. My buddy has a Savage BVSS bolt action with a 1/9 26" barrel. It shot .9" 5-shot groups at 105 yards with 75gr Wolf Gold Match (BTJHP made by Prvi Partizan, boxed for Wolf). The only ammo that would do better in that barrel is 69gr Federal Gold Medal Match and that was getting about .6". Both of those are supposedly "heavier" than what a 1/9 barrel can shoot.
Try a various assortment of ammunition through your barrel before deciding you need a different twist rate. Just my .02
It isn't really that my current set-up dissapoints, but rather would mid-length be all that better? I intend to wear the thing right out by shooting it till it's done for. It currently shoots under 1" at 50 yards with an Aimpoint, can't complain there.
I personally think the weapon is probably overgassed, but I also haven't, except for a single bad magazine, had malfuntions using proper ammo, though sub-par ammo doesn't always cycle the action since I added a Blue Sprinco action spring and a H2 buffer. I guess I'm not expecting the S&W upper to have the longest life.
What I wanted to know is if switching to a mid-length barrel was that big a deal. If it was, going with a 1/7 twist seems like a good idea, especially if a new BCM barrel is gassed correctly. Sounds like the the right course of action is to shoot the barrel out and replace it with a new upper?
I guess I'm not expecting the S&W upper to have the longest life.
Not sure why you think that. S&W makes a decent gun.
I'd build a complete additional upper if you want to mess with the middy. Then you could switch back and forth.
Shoot it until the practical accuracy drops off then replace the barrel assembly.
As to whether or not switching to a middy is worth it, only you can decide that. Search for the carbine vs middy threads for more information
...doesn't S&W use melonite barrels on some of their rifles.?...and idk if they were treating their barrels this way in 2008. But if your rifle does have a melonite barrel, then you definitely do not have to worry about shooting it out any time soon. And as far as carbine vs middy goes, that is entirely subjective; you may not notice that much of a difference at all.
Not what you asked but since it seems to be working for you, i'd keep it and put the money towards an SBR.
Carbine v middy? Been done repeatedly. Here's a good link that links to several good links...
http://m4carbine.net/showthread.php?t=51748&highlight=carbine+length
I read up on this subject until it was coming out my ears; my takeaway was this: buy from a high quality builder and the carbine v middy debate ultimately won't amount to much.
I like the middys better as over the years I have had both, A quality manufacture makes both carbines and middys reliable enough. Keep the S@W as is and save up for a BCM,Daniel defense etc. Everyone needs at least 2 ARs.
I like the two AR approach too. Get a BCM midlength upper now to swap with your S&W upper then build up a quality lower for the BCM upper so you can marry back the S&W receivers.
I currently own a M&P15 (I bought it in 2008 before I understood much about ARs) with the 1/9 twist. I've been thinking about upgrading the barrel to something with a 1/7 twist, and was looking for some input.
Is going to a mid-length gas system a big enough deal to justify the extra parts needed? I'm set on my next AR being a mid-length 16" gun from BCM or DD. Do mid-length guns really run that much smoother? Anyone own both a carbine and a mid-length system?
The other thing I'm wondering is if any of the M&P15 upper is suitable for using as part of a new build. Would it be feasible to install a new barrel on the M&P upper receiver, or am I wasting time buying anything less than a complete upper?
Thanks.
I don't think either the 1:7 twist or the mid-length gas system offer any significant advantage over what you already have. Mid-lengths don't run any smoother. They extend the recoil impulse a little bit, but 5.56 isn't exactly a punishing round, and as a percentage of the total the difference isn't much, and in practical terms barely noticeable, if at all.
As to the twist rate..are you finding accuracy problems with 77-grain bullets?
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.