Receiver extensions

#1
I’ve been enjoying the SOTAR videos on YouTube so I figured I would pose the question here. I’m selecting parts for a lower I have and given all the reputable manufacturers offering extension are some better than others? I’m an A5 koolaid guy - is there a difference between the BCM intermediate extension and the VLTOR? It stands to reason VLTOR makes both. Geissele is making carbine extensions these days - what about the magpul extensions? Differentiation is becoming difficult.
 
#2
I've used the BCM when I couldn't find the Vltor A5 extension and it works just fine. BCM has Eric Kincel so I would hope they'd have the capacity to do an A5 tube right.

I attempted to use an LMT MWS for the A5, but it is a too short and doesn't have the bolt travel space of the above...
 

Pearce

Amateur
Network Support I
#3
I've used the BCM when I couldn't find the Vltor A5 extension and it works just fine. BCM has Eric Kincel so I would hope they'd have the capacity to do an A5 tube right.

I attempted to use an LMT MWS for the A5, but it is a too short and doesn't have the bolt travel space of the above...
Just to confirm, you tried the 3/4in longer LMT .308 receiver extension and it didn't work with the A5 buffer?
 
#4
Just to confirm, you tried the 3/4in longer LMT .308 receiver extension and it didn't work with the A5 buffer?
Yes, the LMT 308 that's +3/4" (that's used on the MWS).
This extension measures and has slightly different specs than either a Vltor or BCM A5 tube.

I should amend my statement above...it may theoretically cycle. I was not confident in testing it much less use it long term.

When I assembled my (5.56) gun as I would with an A5, it did not feel right on the function check. It felt like the bolt throw was too short. When attempting to lock the bolt to the rear, there was only enough travel left in the operating system to barely release tension on the bolt catch...no additional rearward movement in the bolt/buffer.

In visual comparison to another gun with A5, when drawn all the way to the rear as far as possible, the the bolt sits back just a bit from the ejection port (Vltor buffer w/ Green Springco). On other milspec stuff (Milspec tube, Colt H1 and milspec spring), about 1/8" of the bolt is visible...so there's some difference there anyways. With the LMT 308 buffer tube, the bolt group bottoms out with about 3/8+" of the bolt visible in the port (as it would when you lock the action open).

Upon disassembly, I took some measurements of the LMT tube and externally, it was a little over 1/16" and visibly shorter than a Vltor or BCM and internally, it was over 1/8" of an inch shorter.

Some Arfcomer may say it's GTG, but I'm not cool with that 1/4+" loss of bolt travel
 
#6
@pointblank4445 any experience using an A5 setup with a 14.5 mid gas?
I have 2x Hodge 14.5" barrels with the 0.075" gas ports running on A5H2 buffers and Green Springco Springs currently. They run anything I got, but I don't run cheap stuff. Probably the "softest" I've tried is either Black Hills 77gr .223 reman or the 55gr .223 reman and done the "limp wrist pistol" test. They both run like a champ.

Also throwing together a DD 14.5" middy (supposed to be 0.076 gas port) as a truck gun currently and will run the same A5 combo as above.

I have a 3rd Hodge barreled gun that just flat would not run an A5. Just happens I never checked the port diameter in that one (might be "reduced" if there is such a thing in the 14.5") and it flat would not cycle even hot Mk262. Ended up going with the "original recipe" on that one of a milspec extension (H1 buffer and milspec carbine spring). I'm sure I could have gotten it to run with either an H1 or H0 A5 buffer and a regular powered spring but I didn't feel like dicking with it any further.
 

SmElly

Regular Member
#7
Any perceivable benefit using an A5+Hodge setup? Or is it just the cool factor of "my rifle is more mechanically efficient"?
 
#8
Any perceivable benefit using an A5+Hodge setup? Or is it just the cool factor of "my rifle is more mechanically efficient"?
The guns with the A5 are lighter guns and shoot hotter ammo, but shoot as soft or softer than the other gun. If I can cheat and get better recoil management by having slightly milder recoil as apposed to adding an annoying muzzle device and/or use anemic ammo...so much the better. Be it splits on the gun set up for CQB or tracking hits/misses on the DMR at extended range, every little bit helps. And in the case of the later, that little bit of extra LOP doesn't hurt with my long-ass arms on my 6'5" frame.

That said, I was heavy into A5 parts coming fresh off of over-gassed 16" middy's and 14.5 Colt M4's. I've had the "A5+Hodge" guns out in some very cold (single digit F) conditions and I've not had them seem sluggish; they've also been shot hot and dry too. I remember my old Mk12 w/ and A5H2 would begin to short-stroke in the cold every now and again...so I'm not pushing too far into over-springing and too heavy of a buffer.
 

SmElly

Regular Member
#9
The guns with the A5 are lighter guns and shoot hotter ammo, but shoot as soft or softer than the other gun. If I can cheat and get better recoil management by having slightly milder recoil as apposed to adding an annoying muzzle device and/or use anemic ammo...so much the better. Be it splits on the gun set up for CQB or tracking hits/misses on the DMR at extended range, every little bit helps. And in the case of the later, that little bit of extra LOP doesn't hurt with my long-ass arms on my 6'5" frame.

That said, I was heavy into A5 parts coming fresh off of over-gassed 16" middy's and 14.5 Colt M4's. I've had the "A5+Hodge" guns out in some very cold (single digit F) conditions and I've not had them seem sluggish; they've also been shot hot and dry too. I remember my old Mk12 w/ and A5H2 would begin to short-stroke in the cold every now and again...so I'm not pushing too far into over-springing and too heavy of a buffer.
Sounds like a 14.5 bcm+A5H2 should do well. Many thanks!
 

Pearce

Amateur
Network Support I
#10
Yes, the LMT 308 that's +3/4" (that's used on the MWS).
This extension measures and has slightly different specs than either a Vltor or BCM A5 tube.

I should amend my statement above...it may theoretically cycle. I was not confident in testing it much less use it long term.

When I assembled my (5.56) gun as I would with an A5, it did not feel right on the function check. It felt like the bolt throw was too short. When attempting to lock the bolt to the rear, there was only enough travel left in the operating system to barely release tension on the bolt catch...no additional rearward movement in the bolt/buffer.

In visual comparison to another gun with A5, when drawn all the way to the rear as far as possible, the the bolt sits back just a bit from the ejection port (Vltor buffer w/ Green Springco). On other milspec stuff (Milspec tube, Colt H1 and milspec spring), about 1/8" of the bolt is visible...so there's some difference there anyways. With the LMT 308 buffer tube, the bolt group bottoms out with about 3/8+" of the bolt visible in the port (as it would when you lock the action open).

Upon disassembly, I took some measurements of the LMT tube and externally, it was a little over 1/16" and visibly shorter than a Vltor or BCM and internally, it was over 1/8" of an inch shorter.

Some Arfcomer may say it's GTG, but I'm not cool with that 1/4+" loss of bolt travel
Welp, it looks like a BCM Intermediate Receiver Extension is in my future. Thanks for the detailed respose, I really appreciate it.