Modern Sporter - Build Discussions

bukwild said:
Folks I can not get my rifle to cycle the next round or catch the bolt on the last round. Gas block has been installed using the TNA dimpling jig and I have adjusted both the gas block and buffer through all increments. I'm wondering if the length of the carbine buffer system is the issue and I may need a rifle length system. When I charge the bolt it travels past the bolt catch about 3/16 - 1/4". I also have an upper in 6.5 Grendel which cycles but does not hold open (I did switch parts between uppers with the same results.) Any ideas? My parts are as follows:

MRA Match Stainless Barrels 18.6" in .223, (6.5 is 20")
Superlative Arms, Adjustable Bleed-Off Gas Block,
Strike Industries Enhanced Receiver Extension,
Strike Industries Optimus Modular Weight Buffer,
Strike Industries, Flat Wire Carbine Spring,
Brownells M16 5.56 lightweight BCG,
Hiperfire EDT Designated Marksman trigger
rifle length gas system?
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I'd just double check the gas port size on the barrel itself. I had to open mine up, but it was actually undersized.
 
Some tips and tricks I found on my F/A Sporter build:

1) Standard Geissele handguard modification as discussed previously (I utilized a fibreglass grinding wheel and a dremel, cut like butter). CAREFUL.
2) F/A Installation I had to go through 2 forward assist assemblies (Mil-spec) to find one that fit, no idea why.
3) Strike Industries enhanced dust cover is only one that worked on my Upper that wouldn't have needed cutting of standard dust cover rod (Shortening)
4) Required a shorter bolt to install my Ergo grip. Bolt that came with it was too long and bottomed out.
5) TNA Reaction Rod used for majority of build. Lifesaver
6) Buy good quality roll pin punches and use lots of grease/oil

uc
 
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bukwild said:
What should the diameter be?
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Not sure if there is a specific size for 18.6" barrels, but the recommendation for 20" barrels is 0.0935" or drill size #42.

I actually went #41 which is 0.096".

My barrel was undersized from the maker though, I can't recall the exact size of the gas port, but I want to say it was around 0.080"
 
ssapach said:
Not sure if there is a specific size for 18.6" barrels, but the recommendation for 20" barrels is 0.0935" or drill size #42.

I actually went #41 which is 0.096".

My barrel was undersized from the maker though, I can't recall the exact size of the gas port, but I want to say it was around 0.080"
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That fits with what I have been able to find in the google machine .09 up to about .123 for 18" will work. I will start at .09 when I get back in a few weeks.
 
How far should the FA protrude into the chamber?

I swapped the pawl and spring on a Strike Industries FA with some from a mil-spec Colt FA assembly, and the pawl looks like it now sticks out further into the chamber than with the stock SI FA. Should it be flush or completely inside the recess to avoid hanging on the bolt?
 
J.L.C. said:
How far should the FA protrude into the chamber?

I swapped the pawl and spring on a Strike Industries FA with some from a mil-spec Colt FA assembly, and the pawl looks like it now sticks out further into the chamber than with the stock SI FA. Should it be flush or completely inside the recess to avoid hanging on the bolt?
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I had to file mine down. Took it down probably a good 3/16th. Still functions like it should.
 
Anyone know if a 12.25” Daniel Defense RIS II handguard would fit on the upper receiver? Even if it does fit, would it look weird on a rifle length 18.6 inch barrel? Has anyone used a RIS II on their reciever yet?
 
TopShelf97 said:
Anyone know if a 12.25” Daniel Defense RIS II handguard would fit on the upper receiver? Even if it does fit, would it look weird on a rifle length 18.6 inch barrel? Has anyone used a RIS II on their reciever yet?
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You will have to modify the mounting bracket to fit the upper receiver. Yes, it will look slightly off with the gas block/tube exposed.
 
Dohhunter said:
Some tips and tricks I found on my F/A Sporter build:

1) Standard Geissele handguard modification as discussed previously (I utilized a fibreglass grinding wheel and a dremel, cut like butter). CAREFUL.
2) F/A Installation I had to go through 2 forward assist assemblies (Mil-spec) to find one that fit, no idea why.
3) Strike Industries enhanced dust cover is only one that worked on my Upper that wouldn't have needed cutting of standard dust cover rod (Shortening)
4) Required a shorter bolt to install my Ergo grip. Bolt that came with it was too long and bottomed out.
5) TNA Reaction Rod used for majority of build. Lifesaver
6) Buy good quality roll pin punches and use lots of grease/oil

uc
Click to expand...

Nice looking guns!!! (and grass too LOL!!!) :)
 
No, if it sticks out, and can touch the bolt under recoil it will jam the FA into the pin and lock up the rifle. Trust me, happened my first trip out with my sporter. I used my stag as a guide as to where it should be, then I went a bit more, and I lengthened the slot for the pin too. Still works great. It doesn’t need to be even close to the BCG, once the pin disengages the cam it drops right in there.
 
I've now tried the SI FA, and they Colt FA in their stock configurations and modified by swapping prawls and springs. The carrier binds in every configuration.

Would that suggest the upper is out of spec?
 
You also will have to modify the fasteners. The upper 2 cap screws need to have the heads ground down in order to reduce the radius enough to clear the upper and washers will need to be used. Side locking screws will not fit so you have to just go with 4 instead of the 6.
 
Anyone here build a 6.8spc .....been thinking about building one ..... what twist rate barrel ...what make ....bolt....
Anyone have any suggestions....I’d like to here them ....trigger gesissle ......hmmm Gen 3 magpul adjustable rear stock......front stock ...black label ....
But ...bcg???jp???......barrel ....muzzle break...
Any suggestions people .....and thanks for your opinion
 
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