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Help with a "727" Project
7/7/2011 10:48:22 PM
I've decided to use two A2 uppers to build a pair of carbines that will at least look like 727s. I'm not trying to fool anybody but myself, but I do need some technical advice. I'm going to use the fiberlite CAR stocks and CAR hanguards from M&A and two identical Bushmaster A2 uppers. I'd like to use Bushmaster barrels too, but I don't know if there will be a compatability issue with the sights. I know a flattop upper needs an "F-marked" front sight base with a 16" barrel; does an A2 uppper also require one or does it need a "standard" (or normal or whatever they're referred to as now)? Sorry if this is a dumb question, Bushmaster's website doesn't offer an option so I want to be sure before I order them. Otherwise I'll go with Del-Ton, they're about the same money and they do offer both FSB options with their 16" barrels. Would 8/3 or 6/3 elevation knobs make the difference in whether to use standard or F marked FSB? I should know this, but I just don't. Anyone?
7/8/2011 12:00:31 AM
Bushmaster barrels have regular height FSBs, not the F height FSB. The F height FSB will work fine with either a flat top upper or an A2 upper (and an A1 upper for that matter).
On an F FSB, the shelf the sight post sits on is only .040" higher than a regular FSB. Prior to the M4, all Colt military carbines used a front sight post that was also approximately 0.040" taller to compensate for the shorter sight radius.
For a fixed carry handle A2 rear sight, use the 8/3. The 6/3 rear sight is for flat top detachable carry handles, and has a different range of adjustment.
So, you'll be just fine with your Bushmaster A2 uppers and Bushmaster M4 barrels.
On an F FSB, the shelf the sight post sits on is only .040" higher than a regular FSB. Prior to the M4, all Colt military carbines used a front sight post that was also approximately 0.040" taller to compensate for the shorter sight radius.
For a fixed carry handle A2 rear sight, use the 8/3. The 6/3 rear sight is for flat top detachable carry handles, and has a different range of adjustment.
So, you'll be just fine with your Bushmaster A2 uppers and Bushmaster M4 barrels.
7/8/2011 1:08:09 PM
So, you'll be just fine with your Bushmaster A2 uppers and Bushmaster M4 barrels.
This.
You might want to build one with a 1-7 twist and one with a 1-9 twist. I do believe the BM 16" 5.56 barrels are only available in 1-9 twist. Friend has their M-4 barrel and it is a shooter. I have the super light weight and it's also a shooter. 1-9 twist limits bullet weight stability. You might also want to change calibers also as it doesn't really cost more to build, just ammo depending on what caliber. Only reason I say this is looking back after various AR carbine builds I almost wish I had done this.
This.
You might want to build one with a 1-7 twist and one with a 1-9 twist. I do believe the BM 16" 5.56 barrels are only available in 1-9 twist. Friend has their M-4 barrel and it is a shooter. I have the super light weight and it's also a shooter. 1-9 twist limits bullet weight stability. You might also want to change calibers also as it doesn't really cost more to build, just ammo depending on what caliber. Only reason I say this is looking back after various AR carbine builds I almost wish I had done this.
7/8/2011 8:55:53 PM
Originally Posted By Cdenmark:
So, you'll be just fine with your Bushmaster A2 uppers and Bushmaster M4 barrels.
This.
You might want to build one with a 1-7 twist and one with a 1-9 twist. I do believe the BM 16" 5.56 barrels are only available in 1-9 twist. Friend has their M-4 barrel and it is a shooter. I have the super light weight and it's also a shooter. 1-9 twist limits bullet weight stability. You might also want to change calibers also as it doesn't really cost more to build, just ammo depending on what caliber. Only reason I say this is looking back after various AR carbine builds I almost wish I had done this.
So, you'll be just fine with your Bushmaster A2 uppers and Bushmaster M4 barrels.
This.
You might want to build one with a 1-7 twist and one with a 1-9 twist. I do believe the BM 16" 5.56 barrels are only available in 1-9 twist. Friend has their M-4 barrel and it is a shooter. I have the super light weight and it's also a shooter. 1-9 twist limits bullet weight stability. You might also want to change calibers also as it doesn't really cost more to build, just ammo depending on what caliber. Only reason I say this is looking back after various AR carbine builds I almost wish I had done this.
Thanks for the tips! I'm pretty sure you're right about Bushmaster not offering a 1-7. I want these two carbines to be identical, they're going to be gifts. I have a Stag with a 1-9 and it's fine. I never shoot anything but 55 grain bullets anyway, so it's not an issue for me.
7/8/2011 9:00:02 PM
Originally Posted By SSeric02:
Bushmaster barrels have regular height FSBs, not the F height FSB. The F height FSB will work fine with either a flat top upper or an A2 upper (and an A1 upper for that matter).
On an F FSB, the shelf the sight post sits on is only .040" higher than a regular FSB. Prior to the M4, all Colt military carbines used a front sight post that was also approximately 0.040" taller to compensate for the shorter sight radius.
For a fixed carry handle A2 rear sight, use the 8/3. The 6/3 rear sight is for flat top detachable carry handles, and has a different range of adjustment.
So, you'll be just fine with your Bushmaster A2 uppers and Bushmaster M4 barrels.
Bushmaster barrels have regular height FSBs, not the F height FSB. The F height FSB will work fine with either a flat top upper or an A2 upper (and an A1 upper for that matter).
On an F FSB, the shelf the sight post sits on is only .040" higher than a regular FSB. Prior to the M4, all Colt military carbines used a front sight post that was also approximately 0.040" taller to compensate for the shorter sight radius.
For a fixed carry handle A2 rear sight, use the 8/3. The 6/3 rear sight is for flat top detachable carry handles, and has a different range of adjustment.
So, you'll be just fine with your Bushmaster A2 uppers and Bushmaster M4 barrels.
That's what I needed to know! Thanks for helping out! I'm really looking forward to getting these two put together. I've never handled a carbine with an A2 upper. I guess they'll feel about the same but I'm looking forward to shooting them with my new son-in-law. My middle daughter is getting married in October. cha-ching!
7/9/2011 12:05:17 AM
I carried a Bushmaster select fire, "M4" with an A2 upper for about a year on a job overseas once. Had a 14.5" 1/9 barrel, and worked great.
9/8/2011 4:01:29 PM
One more thing! Do these Bushmaster barrels have M4 feed ramps or not?
9/8/2011 8:14:43 PM
Yes they do have ext. feed ramps. I recently built my 727ish carbine and was trying to get a Bushmaster barrel but they told me it would be a couple of months before they have them in stock. I went with a Model 1 barrel instead and they also have std. front sight assembly's. I also prefer non-chrome lined so it was a better option. I am totally happy with it. The Model 1 barrel has ext. feed ramps too. My upper doesn't but it's been 100% reliable so far. I will cut them eventually.
9/8/2011 8:35:22 PM
Originally Posted By Rokchukrslave:
Yes they do have ext. feed ramps. I recently built my 727ish carbine and was trying to get a Bushmaster barrel but they told me it would be a couple of months before they have them in stock. I went with a Model 1 barrel instead and they also have std. front sight assembly's. I also prefer non-chrome lined so it was a better option. I am totally happy with it. The Model 1 barrel has ext. feed ramps too. My upper doesn't but it's been 100% reliable so far. I will cut them eventually.
Yes they do have ext. feed ramps. I recently built my 727ish carbine and was trying to get a Bushmaster barrel but they told me it would be a couple of months before they have them in stock. I went with a Model 1 barrel instead and they also have std. front sight assembly's. I also prefer non-chrome lined so it was a better option. I am totally happy with it. The Model 1 barrel has ext. feed ramps too. My upper doesn't but it's been 100% reliable so far. I will cut them eventually.
Hey, thanks! I just ordered two. If it takes a couple of months I can wait. I won't need to finish them before Christmas.
