Kinda OT; Having a great time with the 5.7X28.

[22_boomer]

I had problems at first with the FN 5.7X28 round but this has been the most fun I've had in a long time. I got the gas system figured out in the modified AR-15, I got the magazine setup figured out in the AR-15 and now I have a second upper receiver with a different barrel to try. The new barrel is a 17" GM 1:14 twist and I did a shorter gas system to allow for some lighter loads. I still have the original upper with the 18", 1:9 twist barrel but this new one is for shooting stuff like the 30gr berger varmint bullets (I like them).

I still have the FN pistol magazine but I also narrowed a 30 M1 carbine magazine that works really good stuffed inside of an old 20 round AR mag -- that's what shown in the picture. I started out using H110 powder but was directed towards AA#9 but Lil' Gun was also talked about -- so I got some Lil' Gun powder. I can't load much of Lil' Gun in a 5.7X28 cartridge but I wanted this rifle for plinking and stuff so hot loads are not necessary. The gas system has tested just fine with loads of 9.0gr to 9.5gr of Lil' Gun and the brass should last me a nice long time. This has turned out to be a really fun project!

Charlie

[nvreloader]

Charlie,
Here are the QL results for this info,
17" bbl, 30gr Berger bullet,Overall loaded length of 1.494"=
9.0 grs 296= 2520fps @26843psi,
9.5 grs 296= 2677fps @31808psi,

35gr Horn,
9.0 grs 296= 2402fps @26783psi,
9.5 grs 296= 2543fps @31187psi,

Another reloadable RIMFIRE case!
Don

[22_boomer]

Originally Posted by nvreloader

Charlie,
Here are the QL results for this info,
17" bbl, 30gr Berger bullet,Overall loaded length of 1.494"=
9.0 grs 296= 2520fps @26843psi,
9.5 grs 296= 2677fps @31808psi,

35gr Horn,
9.0 grs 296= 2402fps @26783psi,
9.5 grs 296= 2543fps @31187psi,

Another reloadable RIMFIRE case!
Don

Don, you did it again -- those pressures should allow the brass to go on for many reloads and the velocity is more than adaquate for what I want -- like a hot 22 magnum. You gave me some good hot loads for this rifle, if I ever need them, but this light load stuff is too much fun right now!

Thanks,
Charlie

[Vibe]

I'm curious where the bolt came from. I haven't found one available for the 5.7 case head. Does it work with a standard barrel extention? Or is it custom to the bolt? I've been playing around with one of my own designs and it sort of revolves around the AR lockup system.

[22_boomer]

Originally Posted by Vibe

I'm curious where the bolt came from. I haven't found one available for the 5.7 case head. Does it work with a standard barrel extention? Or is it custom to the bolt? I've been playing around with one of my own designs and it sort of revolves around the AR lockup system.

The barrel extension is the standard .223 barrel extension. The feed ramps on the extension work great with the FN factory pistol magazine and my home-made one. The modified AR bolt is what makes it work.

A reducing ring is installed and then cut out at the ejector and extractor areas. The extractor needs a bit of adjustment to be able to get full contact on the cartridge rim. There is some adjustments made to the width of the two lower lugs and the carrier to allow them to flow through the FN FiveSeven pistol magazine -- not shown in the picture. Originally, I didn't have a gas system, I operated the rifle by hand as a straight pull bolt action. I was limited in how hot a load I could use so finally decided to go with a gas operated setup.

[Vibe]

Originally Posted by 22_boomer

Originally, I didn't have a gas system, I operated the rifle by hand as a straight pull bolt action. I was limited in how hot a load I could use so finally decided to go with a gas operated setup.

Was this from "hard bolt lift" operating through the bolt/carrier cam?

[22_boomer]

Originally Posted by Vibe

Was this from "hard bolt lift" operating through the bolt/carrier cam?

I guess that's what you would call it -- the leverage between the carrier and cam pin does not lend itself to hand operation when you start getting up there in pressure. The system works like a champ when gas operated -- in this case a slightly shorter than normal pistol length gas system.

This is the short gas system. Most of the parts I used to build the rifle are left-over parts. I didn't want to pay for a special low profile gas block to fit under the handguards when this one works.

[1moose]

22_Boomer,

A great project - well executed, but which magazine would you recommend to start with - the Five-seveN or a modified carbine?

Thanks,

Mike

[22_boomer]

Originally Posted by 1moose

22_Boomer,

A great project - well executed, but which magazine would you recommend to start with - the Five-seveN or a modified carbine?

Thanks,

Mike

The M1 carbine magazine was the first mag I used because I wasn't sure how this all would work. I've since gone to the factory FN pistol mags with an adapter that surrounds the magazine and allows it to use the AR magazine catch. The adapter can be removed so the magazine can still be used in an FN pistol.

This is a picture of another 5.7 rifle I have.

The FN magazine has a 10 round extension on the factory 20 round magazine. It looks like there might be a company that may be making a couple of versions of this 5.7 AR.

[1moose]

Thanks for the magazine answer. I thought that was the way to go.

Reference a manufacturer making a 5.7 AR upper – I would prefer to do it because I can control the critical aspects such as the chamber (my reamer dimensions and concentricity) and the crown.