M4-style barrel extension with Rifle-type upper

[practical_man]

For those who have actually done it... will a new barrel with the M4 feed ramp extension function properly with an old school rifle-type upper receiver?

Seems like it should work to me, but be a real challenge to keep clean and be damned ugly to boot. Reliability is the main concern for me when I re-barrel this rifle. I am having a tough time finding an in-stock barrel (18 or 20 incher) with a rifle extension on it. Seems M4 is all the rage these days.

Thanks for sharing your thoughts.

-john

[GunCat]

Found on the .net

[Doug H.]

A couple of times I ended up with the OK set up from the picture above. I'd get jams from bullets hitting the back of the upper so I took a small round file and made the M4 ramps in the upper. Only took a few minutes.

Doug

[Jamiethesquid]

 

A couple of times I ended up with the OK set up from the picture above. I'd get jams from bullets hitting the back of the upper so I took a small round file and made the M4 ramps in the upper. Only took a few minutes.

Doug

 

I have done the same, protect the Barrel extension with a layer of electrical tape and carefully file or Dremel the ramps into the aluminum receiver. Go slow and you'll be done in no time.

[StealthyBlagga]

You can modify the upper, but bear in mind that the un-anodized aluminum surface will be very soft and prone to wear if your particular bullet hits it frequently. Personally, I would sell the rifle upper and buy an M4 upper - the cost will be small and you will end up with a more satisfactory end product.

[practical_man]

Found on the .net

Thanks. I had seen these pix years ago and dismissed the idea of mix and match. I didn't forsee that we'd ever see the day when replacement parts would be so hard to get.

[practical_man]

You can modify the upper, but bear in mind that the un-anodized aluminum surface will be very soft and prone to wear if your particular bullet hits it frequently. Personally, I would sell the rifle upper and buy an M4 upper - the cost will be small and you will end up with a more satisfactory end product.

This has been my concern with modifying the aluminum parts. My alternative plan is to do exactly as you describe. The upper I want to rebarrel is modified for Service Rifle competition so it's not quite as cheap as buying another $89 upper from Aero. Oh well, as I tell my lovely and understanding bride, guns are relatively free.... it's the ammo and training that cost real money.

Thanks,

-john

[wgj3]

I like that justification!

[openclassterror]

That is what I tell people when they try to convince me that they need a stainless barrel instead of chrome-moly. "It will last 5k rounds instead of 4k. Is it worth the extra 50 bucks?" Well, over the course of 5,000 rounds at .40 a round, you spent two grand on ammo. 50 bucks one way or the other on the barrel ain't squat! Also, barrel life is relative. How long your barrel "lasts" depends on what your accuracy threshold is before you decide it is too bad to keep using. if you are OK with 3MOA, you might go 20,000 rounds! If you don't clean it but demand 3/4MOA you might get 1,500.

You can always buy a non-m4 extension and have the new barrel retimed and headspaced, but it will probably cost more than a new upper receiver.

[HRider]

You can modify the upper, but bear in mind that the un-anodized aluminum surface will be very soft and prone to wear if your particular bullet hits it frequently. Personally, I would sell the rifle upper and buy an M4 upper - the cost will be small and you will end up with a more satisfactory end product.

This has been my concern with modifying the aluminum parts. My alternative plan is to do exactly as you describe. The upper I want to rebarrel is modified for Service Rifle competition so it's not quite as cheap as buying another $89 upper from Aero. Oh well, as I tell my lovely and understanding bride, guns are relatively free.... it's the ammo and training that cost real money.

Thanks,

-john

If your mag catch is at Spec height, you should not have a problem with an M4 cut barrel in a rifle receiver. My factory JP CTR-02 has the appearance of the bottom right picture in the post above, M4 barrel extension in a rifle receiver, and there is not a mark on the aluminum under the barrel extension. It has ran flawlessly (barring tuning of the gasblock when new) with several different brands of magazines and ammo. If your upper isn't showing signs of bullets rubbing on the aluminum under the barrel extension, you should be good with M4 ramps.

Hurley

[Mark Gale]

You can modify the upper, but bear in mind that the un-anodized aluminum surface will be very soft and prone to wear if your particular bullet hits it frequently. Personally, I would sell the rifle upper and buy an M4 upper - the cost will be small and you will end up with a more satisfactory end product.

Forged 7075-T6 aluminum is harder than a bulls balls. I wouldn't be concerned at all with any wear after modifying an upper receiver.

A couple of times I ended up with the OK set up from the picture above. I'd get jams from bullets hitting the back of the upper so I took a small round file and made the M4 ramps in the upper. Only took a few minutes.

Doug

The tip of the cartridge rarely comes into contact with the upper receiver. If it's happening regularly, check the magazines you are using for serviceability. Try this little exercise:

1. Load a magazine with two or three rounds, lock the bolt group back on your rifle or carbine and insert the magazine.

2. Reach in through the ejection port and slide the on deck cartridge about 1/4 inch forward and observe the tip of the bullet in relationship to the barrel extension.

3. Now move move the on deck cartridge forward to the 3/8 of inch position and again note the position of the tip of the bullet in relationship to the barrel extension.

I think you will find that the tip of the bullet clears the M4 cuts in the upper receiver by a wide margin. By my estimates, the tip of the bullet first hits the barrel extension about 1/3 of the way up the respective feed ramp on the barrel extension.

Edited April 27, 2014 by Mark Gale