Installing Mag Pull furniture

[Mike G 0351]

Today I finally got around to installing my Mag pull furniture.
The stock MAG 347, I thought would be the easiest to replace wound up being the hardest, Man this thing was tight, It's almost impossible to slide....
Has anyone else had this problem..?

 

[MichiganScott]

Are you trying to put a mil-spec stock on a commercial tube?

 

[Rastoff]

Take a look at this pic:

See that little step in the buffer tube just to the left of the threads? That's the easiest way to distinguish a civilian spec tube. All the civilian spec tubes I've seen have this step. All the military spec tubes I've seen do not have this.

I think most of the M&P15s have Mil-Spec buffer tubes though.

 

[WR Moore]

I would expect the guys above have hit the nail on the head. You're trying to put a mil-sec stock on a commercial receiver extension.

My former employer bought a slew of M&P15s. They all had commercial receiver extensions/buffer tubes. It may vary by production runs.

Flirting with the edge of the rabbit hole.....the mil-spec tube uses a 7000 series aluminum and reduces the tube diameter down where the stock slides to save weight. [The threads are allegedly "full diameter" but measuring 20 tubes, I only found one full thread diameter.] The commercial tube is most often made from a 6000 series aluminum and the tube walls are thicker-so the outside diameter is larger. Looking at the mechanical specs for the aluminum alloys, the relative strengths are a wash for this application. The 6000 series is easier to machine.

Rastoff, the commercial tubes I've seen don't have the step you show. Maybe the variation by one particular maker. I don't believe I've ever seen the angled rear of the tube shown on the drawing above.

 

[Mike G 0351]

I checked the box the stock came in and it read Mil spec.
I was told on this forum S&W MP 15 2 was Mil spec
I'll have to take it off to check to make sure.

 

[Rastoff]

Rastoff, the commercial tubes I've seen don't have the step you show. Maybe the variation by one particular maker. I don't believe I've ever seen the angled rear of the tube shown on the drawing above.

Obviously it's possible to eliminate the step. However, the civilian spec has to have the step somewhere.

If it's going to thread into a normal receiver, which they all do, then the threads must be the Mil-Spec diameter. If the step is right at the threads, it would look like it doesn't have a step.

This is why just seeing the step isn't enough. The right way is to measure the diameter.

 

[Mike G 0351]

Okay,I'm confused now.
My buffer tube is squared at the end, But it is solid with a small hole.
I don not have a caliper to measure with, Butt the diameter is 1 1/8"
So I called Brownells back, To late to stop shipment, So I have to stocks on the way. One Milspec and one commercial....

 

[WR Moore]

Obviously it's possible to eliminate the step. However, the civilian spec has to have the step somewhere.

Ah, no. The thread spec for the receiver is 1.185 (i 3/16") x 16 tpi. This is greater than the OD of the commercial tube, however, the OD of the commercial tube is still within the accepted machining tolerances for the threads. There is a step down on the mil-spec tube just behind the threads. See the top drawing above.

I just double checked the tube on my RRA. Commercial diameter, no step, no angle at the rear of the tube. Maybe once upon a time by someone somewhere. I expect the extra machining step was eliminated to save money. And, there will be a hole at the end of all buffer tubes to prevent compression of air and allow moisture to be expelled during operation.

Which is is why just seeing the step isn't enough. The right way is to measure the diameter.

YEP!

 

[Rastoff]

Good note on the thread diameter. I stand corrected.

 

[SavageMessiah]

Did the OP not mean he had a hard time getting the retention pin(s) pulled down in order to slide the stock from the end into the outermost notch on the tube? For newbs (such as myself), if I were to do the install again I would use mechanic's gloves as the pins are under quite a bit of tension and the squeezing and pulling does hurt. Or even better, use ChannelLocks with a small cloth. Muzzle into carpet, hold rifle with knees, squeeze and pull the pins outward whilst pushing stock down onto tube with free hand. A proper work area with vise would make this easier, but that's my poor man's method.

 

[Brian in Oregon]

I just installed Magpul furniture on my new MP15 Sport II. The buttstock is Milspec, not Commercial.

Measured the buffer tube and it is 1.1475", close enough to the specified 1.148" for Milspec.

It's also flat on the end, not sloped.

 

[Mark S.]

Did the OP not mean he had a hard time getting the retention pin(s) pulled down in order to slide the stock from the end into the outermost notch on the tube? For newbs (such as myself), if I were to do the install again I would use mechanic's gloves as the pins are under quite a bit of tension and the squeezing and pulling does hurt. Or even better, use ChannelLocks with a small cloth. Muzzle into carpet, hold rifle with knees, squeeze and pull the pins outward whilst pushing stock down onto tube with free hand. A proper work area with vise would make this easier, but that's my poor man's method.

Yep. Unfortunately that is sometimes the only way to make it happen.


Sent from my iPad using Tapatalk

 

[Mike G 0351]

The retention pins were no problem, Used a small roll pin punch to pull down on them....
I received the Full stock in Milspec, It went on fine, The collapsible one would not, Who knows why, Miss marked, Wrong one put in box....

 

[Rastoff]

Could have been a manufacturing defect too. Those things are injection molded and some extra material could have been left on the inside.