View Full Version : Swapping out stocks on old Bushmaster lower
I have an older Bushmaster lower (2003) which was purchased as a complete 20" vmatch rifle with an A2 stock.
Bought a BCM 18" SS 410 upper to replace the old upper.
Bought this
http://www.bravocompanyusa.com/Milspec-Receiver-Extension-Buffer-Tube-p/bcm-milspec-re.htm
BCM Milspec Carbine Receiver Extension (Buffer Tube) 6 Position
For your AR15, M16, M4. Carbine receiver extension (buffer tube) machined from 7075T6 and manufactured to Mil-Spec dimensions and specifications. Mil-Spec receiver extensions have a slightly smaller dimension where the stock slides on.
Hard Coat Anodized per Mil-A-8625F, Type III, Class 2
These tubes should be used with stocks such as USGI, BCM, Colt, LMT, SOPMOD, VLTOR, Stag Arms, Magpul CTR (Milspec), and others that a made to the Mil-Spec size.
Can I just replace the original buffer tube with this and use the same spring and buffer assembly? Do I need a shorter assembly? Stiffer springs?
Any help would be appreciated.
No. You need a carbine length spring and buffer for that receiver extension. I would start with an H buffer.
If you haven't installed the new tube this would be the perfect opportunity to go with the A5 setup.
If you are going to go this route, I suggest an H3 buffer and a blue Sprinco spring.
I have an older Bushmaster lower (2003) which was purchased as a complete 20" vmatch rifle with an A2 stock.
Bought a BCM 18" SS 410 upper to replace the old upper.
Bought this
http://www.bravocompanyusa.com/Milspec-Receiver-Extension-Buffer-Tube-p/bcm-milspec-re.htm
BCM Milspec Carbine Receiver Extension (Buffer Tube) 6 Position
For your AR15, M16, M4. Carbine receiver extension (buffer tube) machined from 7075T6 and manufactured to Mil-Spec dimensions and specifications. Mil-Spec receiver extensions have a slightly smaller dimension where the stock slides on.
Hard Coat Anodized per Mil-A-8625F, Type III, Class 2
These tubes should be used with stocks such as USGI, BCM, Colt, LMT, SOPMOD, VLTOR, Stag Arms, Magpul CTR (Milspec), and others that a made to the Mil-Spec size.
Can I just replace the original buffer tube with this and use the same spring and buffer assembly? Do I need a shorter assembly? Stiffer springs?
Any help would be appreciated.
Thanks!!!! I'll either stop by the local shop and pick up the carbine length spring and H buffer or look deeper into an A5 setup.
Not an H, an H3 buffer.
Thanks!!!! I'll either stop by the local shop and pick up the carbine length spring and H buffer or look deeper into an A5 setup.
Leaveammoforme
03-28-16, 19:21
If you are going to go this route, I suggest an H3 buffer and a blue Sprinco spring.
That sounds awfully heavily sprung for a rifle length gas system.
What do you know that you're not saying? To make up the missing weight of a semi-auto carrier?
That depends on if the OP is using the semi auto carrier from his original rifle upper. The new upper wouldn't have ever had a semi auto carrier. He swapped it for an 18" BCM.
I have no idea what you are asking or what a semi-auto or full-auto carrier has to do with this.
That sounds awfully heavily sprung for a rifle length gas system.
What do you know that you're not saying? To make up the missing weight of a semi-auto carrier?
Leaveammoforme
03-28-16, 21:34
I have no idea what you are asking or what a semi-auto or full-auto carrier has to do with this.
It'll be a soft shooter, that's for sure.
For your enjoyment.
Rifle buffer- 5.1-5.3 oz.
H3 Carbine- 5.3- 5.5 oz.
U.S Army H6 Buffer- 5.15 oz.
titsonritz
03-28-16, 22:20
For your enjoyment.
Rifle buffer- 5.1-5.3 oz.
H3 Carbine- 5.3- 5.5 oz.
U.S Army H6 Buffer- 5.15 oz.
VLTOR A5H2 buffer- 5.33 oz.
Not mentioning it because it doesn't seem that he is going to go that route.
VLTOR A5H2 buffer- 5.33 oz.
Did a little more checking. The 18" BCM upper is all original, very recent, and included a full BCM bolt carrier group as an ordered option, so I believe that is a rifle length system as has been noted.
Looking on some sites right now. I see an H-heavy, H2-heavy and a standard carbine buffer. I've seen somewhere that H2 or H3 would be the recommended buffer for this setup and it also looks like the A5 kit would also work for more money.
So, H2 or H3 and a carbine action spring should do the trick- right? Is the A5 system really all that much better?
Again, thanks for the help. I do make sure to let BCM know that I learned about them on this site when I place an order. I was informed about this company by an older thread I started about old Bushmasters. Trying to get one or two of these up to snuff!
It were me, I would go with the Vltor A5 set up. I don't own a standard receiver extension except for demonstration purposes.
Did a little more checking. The 18" BCM upper is all original, very recent, and included a full BCM bolt carrier group as an ordered option, so I believe that is a rifle length system as has been noted.
Looking on some sites right now. I see an H-heavy, H2-heavy and a standard carbine buffer. I've seen somewhere that H2 or H3 would be the recommended buffer for this setup and it also looks like the A5 kit would also work for more money.
So, H2 or H3 and a carbine action spring should do the trick- right? Is the A5 system really all that much better?
Again, thanks for the help. I do make sure to let BCM know that I learned about them on this site when I place an order. I was informed about this company by an older thread I started about old Bushmasters. Trying to get one or two of these up to snuff!
If you've already bought the RE the rifle will run fine with it, and the right spring and buffer.
If you're still shopping for the RE/Spring/Buffer, there is zero reason not to go with an A5 system. It really is that much better. I own rifles with both, but I've already bought spare A5 REs for future builds, and if I decide to replace the standard carbine REs.
You will also need a reciever end plate and castle nut to install your reciever extension. The rifle reciever extension uses neither. My apologies if this was already understood.
titsonritz
03-29-16, 13:10
If you've already bought the RE the rifle will run fine with it, and the right spring and buffer.
If you're still shopping for the RE/Spring/Buffer, there is zero reason not to go with an A5 system. It really is that much better. I own rifles with both, but I've already bought spare A5 REs for future builds, and if I decide to replace the standard carbine REs.
This. No reason to buy an A5 if you already have a carbine RE but if you haven't there is no reason not to get an A5.
I've got the receiver extension but no castle nut or receiver endplate (or proper spring and correctly sized buffer as has been noted). I think I'll return the RE and just go with the A5 system, which sounds like it will work with most any setup. Thanks again everyone for the info. I had forgotten to order the castle nut and end plate.
It looks like the BCM Stock should fit right on the A5 intermediate extension. Any reason why it would not?
I've got the receiver extension but no castle nut or receiver endplate (or proper spring and correctly sized buffer as has been noted). I think I'll return the RE and just go with the A5 system, which sounds like it will work with most any setup.
I don't know of a setup where the A5 would not be an improvement over the standard system.
BCM has a "BCM Intermediate Buffer System (A5) Mounting Kit" (sorry, no link, but Google will find it) that has everything included except a stock. It will save a little coin over ordering what you need seperately. Yes, any stock which fits a milspec carbine extension should fit an A-5 receiver extension.
titsonritz
03-29-16, 20:17
It looks like the BCM Stock should fit right on the A5 intermediate extension. Any reason why it would not?
It will work. I'd suggest picking up a BCM A5 RE (http://www.bravocompanyusa.com/BCM-Intermediate-Receiver-Extension-A5-Buffer-Tub-p/bcm-intermediate-re.htm), a castle nut (http://www.bravocompanyusa.com/Receiver-Extension-Nut-Castle-Nut-p/nut%20receiver%20extension.htm) and a A5H2 buffer (http://www.bravocompanyusa.com/VLTOR-A5-Buffer-p/vltor-a5-buffer.htm), then a Sprinco Green Spring (http://www.sprinco.com/tactical.html). You could get an end plate from BCM but check out the ones from IWC and MI, I like them for the one piece construction and limited rotation.
I see that, AndyLate. Looks like its in stock and looks like a relatively affordable upgrade compared to fleshing out my Carbine length receiver extension and experimenting with Buffers. I think that's the way that I'll go and I'll report back here with results if I can finally get this thing constituted and on the range.
titsonritz
03-29-16, 21:27
You do not want the BCM kit, it comes with a A5H0 buffer and the Vltor kits have been scarce lately. I mentioned in another thread it is highly unlikely I'll ever buy another A5 "kit" because I want the green spring and a QD endplate, plus the buffer of my choice. The cost may be a little more but I want what I want, otherwise if cost is the factor may as well stick with a standard carbine RE & buffer.
Do you think the 3.8 oz. A5H0 buffer will be an issue for this rifle length system? I can get an A5H2, "Standard" buffer for another 40 dollars but the A5 kit is on its way. At this point, I just want to get a mix of ingredients likely to succeed.
It won't be an issue. I ran my BCM 18" upper on a lower with the same kit until I finished the lower with a rifle RE and PRS. Ran just fine.
As an update, BCM says it's good to go. They got back me extremely quickly on this so I am very happy with their customer service.
For anyone trying to make a similar decision, here is their answer regarding function of the A5 system with A5H0 buffer on their own 18" SS rifle-length upper.
My upper = BCM-URG-18-SS410-KMR-A-13
Hi, XXXXXXXXX
If you choose to hop over to the intermediate buffer system you would want to use the included A5H0 buffer which is the same weight but designed for that system. Function between the two is nearly identical but the intermediate system offers a longer length of pull and a total of 8 adjustment positions.
Personal preference really dominates this choice.
Now all I have to do is put the system and stock on, figure out which optic to use, attach it, head to the range and actually put some rounds on paper. I'll probably get it all done in a couple months!
I think that your build is going to be a very nice rifle! BCM was very responsive to questions I had as well, and an all around good buying expirience.
It won't be an issue. I ran my BCM 18" upper on a lower with the same kit until I finished the lower with a rifle RE and PRS. Ran just fine.
This is very helpful input!
I think that your build is going to be a very nice rifle! BCM was very responsive to questions I had as well, and an all around good buying expirience.
I was just thinking this exact thing! Had a gunsmith put a G2S trigger into it and I'm realizing that this should be quite a rifle.
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