View Full Version : Convert Commercial stock setup to Mil-Spec setup (Bushmaster)
WinSomeLoseNone
02-12-10, 23:59
Basically I am tired being last to get access to new stocks (Magpul ACS) because I have a commercial tube diameter. I don't know if there are any benefits to converting to mil-spec other than the convenience of availability but I am interested in doing it. Is it as simple as buying a new buffer tube or do I need a new buffer, buffer tube, recoil spring, lock plate and nut. To convert to mil-spec and a nice precision buffer tube what parts do i need to order.
Thanks, and advice on precise buffer tubes is appreciated.
You will only need a tube and the stock of your choice.
WinSomeLoseNone
02-13-10, 01:43
Thanks.... soon learned after posting.
I'm going down the list and fixing my bushmaster....
so far..
bought a BCM BCG
H Buffer
buying Mil-Spec buffer tube
staking my buffer roll pin
staking rec end plate after new stock install...
hopefully when I will have a quality rifle that can offer me a LONG lifespan
ChicagoTex
02-13-10, 07:29
I don't know if there are any benefits to converting to mil-spec other than the convenience of availability
Mil-spec diameter tubes are threaded differently. I don't really understand it (as I've never had the chance to compare both types side by side) but supposedly the mil-spec threading style is slightly more durable.
Mil-spec buffer tubes are also sometimes made from harder aluminum.
As I don't swap stocks, I'm perfectly content with my commercial tube/Magpul CTR combo on my upgraded BM that I got for about half of what a milspec tube/CTR combo would cost.
I changed out the buffer tube on my BM. Putting on the mil-spec tube was easy. I changed out the locking plate and nut because I staked the castle nut properly before I learned about the difference between the Commercial buffer tube and the mil-spec tube. Dont worry its easy just be careful not to lose the buffer detent, its under pressure and will shoot out if your not careful:D
Milspec and commercial tubes have the same thread dimensions, but they way the threads are made is different. Commercial tubes feature cut threads, milspec tubes feature rolled threads. Rolling alters the crystalline structure of the metal, and makes it stronger through work hardening. The rolling process also leaves rounded contours instead of the sharp contours of cut threads. Sharp contours act as stress concentration risers, and are more likely to be the origin of fatigue failures. Milspec tubes have a smaller diameter because the material in the threads actually flows during rolling and the volume of material that is displaced by the forming die pressing into the part flows out to form the top of the threads. Commercial tubes start life with a larger outside diameter, and material is removed to make the threads.
It's an easy operation. Just keep track of your buffer retaining pin and spring, and takedown pin detent and spring. Replace the end plate with a quality unit, as this part should have been originally staked, and if it wasn't the manufacturer may not have staked it because the material was too brittle for proper staking. It's a cheap part for a little peace of mind.
WinSomeLoseNone
02-13-10, 15:44
Milspec and commercial tubes have the same thread dimensions, but they way the threads are made is different. Commercial tubes feature cut threads, milspec tubes feature rolled threads. Rolling alters the crystalline structure of the metal, and makes it stronger through work hardening. The rolling process also leaves rounded contours instead of the sharp contours of cut threads. Sharp contours act as stress concentration risers, and are more likely to be the origin of fatigue failures. Milspec tubes have a smaller diameter because the material in the threads actually flows during rolling and the volume of material that is displaced by the forming die pressing into the part flows out to form the top of the threads. Commercial tubes start life with a larger outside diameter, and material is removed to make the threads.
It's an easy operation. Just keep track of your buffer retaining pin and spring, and takedown pin detent and spring. Replace the end plate with a quality unit, as this part should have been originally staked, and if it wasn't the manufacturer may not have staked it because the material was too brittle for proper staking. It's a cheap part for a little peace of mind.
Great info, thanks. I'll be swapping everything out shortly, already have the new mil-spec tube, H buffer and stock on the way. Just need to find a new end plate.
One problem with the commercial tubes is they usually have about a 1.170 max thread diameter. The threads are flat topped and provide about a 70% thread engagement in the lower.
The call out for the milspec tube I have seen requires 1.185 diameter across the threads with "fully formed threads". This may seem like a small difference but the spec thinks it is important enough to call it out. As previously mentioned, the milspec threads are rolled not cut. This provides a stronger thread.
The best after market mil sized (not spec) tubes I have found are the VLTOR. They are on the high side of the milspec diameter tolerance and usually fit milspec sized stocks with less "wiggle".
Added: I have found the BCM end plates and nuts to among the best.
WinSomeLoseNone
02-13-10, 23:43
One problem with the commercial tubes is they usually have about a 1.170 max thread diameter. The threads are flat topped and provide about a 70% thread engagement in the lower.
The call out for the milspec tube I have seen requires 1.185 diameter across the threads with "fully formed threads". This may seem like a small difference but the spec thinks it is important enough to call it out. As previously mentioned, the milspec threads are rolled not cut. This provides a stronger thread.
The best after market mil sized (not spec) tubes I have found are the VLTOR. They are on the high side of the milspec diameter tolerance and usually fit milspec sized stocks with less "wiggle".
Added: I have found the BCM end plates and nuts to among the best.
Shit, I bought a BCM mil-spec tube yesterday. I am obsessed with getting a tight fitting lightweight collapsible stock. I chose the ACS because of the friction lock. Should I return it for the VLTOR or what? I HATE stock wobble.
The friction lock on the ACS will take care of stock wobble on the BCM tube. The tight-fitting VLTOR tube is handy on stocks without friction locks, like their Modstock/EMod/iMod.
There is one other issue I encountered with collapsible stocks. I wear a beard (I'm a "civilian"). If the receiver extension tube is not a close fit to the stock I get "hair pinch" at the front of the stock. While not fatal it is very annoying and it happens even with the locking stocks. Using the tighter fitting VLTOR tubes that issue disappeared.
One problem with the commercial tubes is they usually have about a 1.170 max thread diameter. The threads are flat topped and provide about a 70% thread engagement in the lower.
The call out for the milspec tube I have seen requires 1.185 diameter across the threads with "fully formed threads". This may seem like a small difference but the spec thinks it is important enough to call it out. As previously mentioned, the milspec threads are rolled not cut. This provides a stronger thread.
Perfectly on point.
On a side note and without any intent to undermine the importance of milspec over comm but I took out my caliper and measured a comm tube I have lying around and the threads strangely measured exactly 1.185". Got lucky with that one I suppose... It came with a comm CTR kit I got off a friend. Not sure as to how it threaded though or even who manufactured it.
The best after market mil sized (not spec) tubes I have found are the VLTOR. They are on the high side of the milspec diameter tolerance and usually fit milspec sized stocks with less "wiggle".
As for Vltor, what isnt milspec about their tubes? Ive been particularly interested in their tubes lately as I find them to be as smooth as the comm one I mentioned above--A feature I was hoping to find, but did not, on the milspec tube I replaced it with.
WinSomeLoseNone
02-14-10, 23:37
All valid points, I think I'm going to return the BCM tube and get the VLTOR with an EMOD stock. I wanted an emod but was opting for the ACS strictly due to the friction lock. If I can get an EMOD without any wiggle I will go for it.
The emod will wiggle some. Almost none when fully collapsed, and progressively more as you extend it further. I run mine only one position out so there isn't much, but there is a small amount of play.
WinSomeLoseNone
02-14-10, 23:50
The emod will wiggle some. Almost none when fully collapsed, and progressively more as you extend it further. I run mine only one position out so there isn't much, but there is a small amount of play.
Ahh, makes it such a difficult choice. I could go with the EMOD and deal with a bit of wiggle ( I prefer its looks), or get an ACS and not ave to worry about wiggle at all.
I rigged up a fixture on my work bench and did some pretty unscientific measuring.
Stock: VLTOR eMod
Buffer tube: VLTOR (came with eMod)
Play measured at toe of stock (stock body rotating on buffer tube):
Position 1: .080"
Position 3: .105"
Position 6: .125"
Perceived difference in parallelism between the stock body and buffer tube (trying to "bend" the stock):
Position 1-2: no play
Position 3: play just barely perceptible
Pushing/Pulling on stock body:
All positions: ~ .050"
With the stock in position 2 (its normal position for me), mounted to my shoulder with clothes on, I can only feel wobble in the stock if I intentionally wiggle the gun looking for it, and then it is only just barely perceptible.
Not very scientific, I know. But, maybe it will help you make a decision you'll be happy with.
spamsammich
02-15-10, 02:47
Ahh, makes it such a difficult choice. I could go with the EMOD and deal with a bit of wiggle ( I prefer its looks), or get an ACS and not ave to worry about wiggle at all.
Do you really think you'll notice the stock wiggling when you have the weapon properly shouldered and slung in place with good cheek weld? I don't notice it on ANY AR when I'm actually shooting it, only when I'm finger banging the gun.
WinSomeLoseNone
02-15-10, 12:35
Do you really think you'll notice the stock wiggling when you have the weapon properly shouldered and slung in place with good cheek weld? I don't notice it on ANY AR when I'm actually shooting it, only when I'm finger banging the gun.
Well, when properly finessing a rifle your grip on the weapon should be relatively loose and neutral while maintaining control at the same time. So yes, a very slight wiggle will absolutely affect accuracy. Mostly at the 200+ range.
spamsammich
02-15-10, 14:26
Well, when properly finessing a rifle your grip on the weapon should be relatively loose and neutral while maintaining control at the same time. So yes, a very slight wiggle will absolutely affect accuracy. Mostly at the 200+ range.
My experience has differed, any time I have shot those distances has been from bench rest or prone and did not notice wobble with even a standard m4 collapsible buttstock. Same goes for shooting shorter distances using a squared up carbine stance. I've owned an EMOD, ACS, MOE, CTR, and several M4ish stocks and never really noticed wobble unless I was inspecting for it. My concentration switches to other "problems" when I'm behind the sights, YMMV. I can see where it would be an issue if you were shooting 200+ off hand or kneeling.
Seeing that youre changing up from the basic stock that came with your Bushy, I think you'll come to find even the Emod, without the friction lock, to be very stable...
spamsammich
02-15-10, 17:49
Seeing that youre changing up from the basic stock that came with your Bushy, I think you'll come to find even the Emod, without the friction lock, to be very stable...
I agree, especially if you use something like an LMT tube, I find they fit tighter than Vltor tubes by just a hair.
WinSomeLoseNone
02-15-10, 18:12
You all make valid points. I practice mostly standing and kneeling positions because you rarely have a bench rest when SHTF, ha. At my range when shooting 300yds standing my factory commercial stock is SO sloppy that controlling recoil and reacquiring target picture after firing a round is more difficult.
I think I may go with the EMOD. I love the look of it and have friends that swear by it for a duty stock. If the wiggle is very minor on a VLTOR or LMT buffer tube I suppose I can live with it. Now I just need to decide between the two.
Col Crocs:
It is my understanding that the VLTOR tubes are either machined extrusions with welded ends or machined from bar stock, may or may not be 7075 T6 aluminum and have cut threads.
I believe the true milspec extensions are specified as 7075 T6 aluminum, forged with rolled threads.
Someone please correct me if this is in error.
Thanks for coming back to respond. I was under the impression it was forged and that the threads were rolled on as they appeared to be when I looked at a friends Vltor tube. That, on top of the fact that I found the surface smooth, was the selling point for me because they appeared to be superbly done. Thanks again!
I believe (voted with my $) the VLTOR is more than adequate and I am very satisfied with my choice.
WinSomeLoseNone
02-15-10, 23:06
I believe (voted with my $) the VLTOR is more than adequate and I am very satisfied with my choice.
I'm curious to know if LMT is created with.....
you know what, I'm over thinking this whole buffer tube dilemma. I'm just gonna buy the whole VLTOR kit and be done with it. Buffer, spring, tube, stock.....simple enough
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