JR Carbine & DD AR-15 Lite Rail, sorta. - PICS

geclark

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So, my feeding problems with the .45 JR aside, I've gotten started down the path I was planning to take it with the assumption that it will be made right in the future. Camera phone pics, sorry they're crappy.

The first things I wanted to change was the handguard, while the stock one is ok it leaves what feels like waay too much barrel hanging out there. I also think quad-rail is like cowbell, always need more.

I opted to go with the DD AR-15 Lite Rail 14" - since it was the longest I could find. I was also thinking about going with the Troy 13.8" MRF rail, but somehow managed to mentally justify double the cost for the additional .2" of rail. The DD Lite Rail is just slightly prettier to me, and seems to match the 'square-ish' profile of the JR.

So - the way this is supposed to install, is you put a 'BOLT-UP' plate over the barrel and up against the receiver, install the supplied AR nut on top of that, and then bolt the rail to the bolt up plate via 6 supplied bolts. No problem. Sorta. Errr, well - actually some problems. Getting the barrel nut on with the barrel in was a pain in the butt. It went on nicely when the barrel wasn't installed, but seemed really hard to get on with the barrel installed. Not sure if that's normal - this is my first 'AR'-esque platform. Took a long time, but it went on in the end.

On next to bolting the rail to the bolt up plate. The bottom two bolts go through the rail and towards the bolt up plate and receiver - worked great.

Side side and top bolts go towards the rail away from the receiver. And this is where my problems start. They went in, though on both sides the bolts made contact with the receiver resulting in some new shiny parts. The contact looks worse than it was, but was tight on both sides.


IAMBUBBA.JPG



My real problems began with the top bolts, the holes for which are 75% occluded by the top of the JR receiver. This pic doesn't really illustrate it well - but you get the idea.

JRDD-Top-C.jpg



There's just no way I'm going to be able to get those bolts in without shaving off part of the JR receiver - which probably isn't a good plan. (Or is it? Wait - let me get my feeding / warranty issues handled first).

Now - the rail felt very very solid with only two bolts through it. It's up to four now - and I'm mentally trying to justify keeping this on in it's current state. I've slapped it around a bit, and the rail is staying on nicely, tight and aligned. No firing yet, but I'll test later this weekend and see how it goes. Some pics of the rail as mounted up below.

JRDD-Side.JPG


JRDD-SideClose.JPG


So my questions are:

1) Is it crazy to run this with only 4 bolts?
2) Should an optic be mounted straddling the receiver and forend rails to try and shore up the top?

I really like the feel of the of it in this config, though it's a lot more well balanced towards the front. :)
 
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shoot it a little and pay close attention to it. If it moves then stop shooting and consider getting the other 2 bolts in there. I would think mounting an optic between the reciever and rail would be bad news if it does develop play. There goes your zero and possibly wear to the optic mount. Just my 2 cents. It does look good tho
 
Good point. Last thing I need is to trash my optic & mount - thanks.

I'll keep the sight on the receiver, also I guess I'd rather see it not work if it's going to not work.
 
In the first pic, you had the the lower bolt fastened from the muzzle end and the middle bolt fastened from the receivers end, and hence you scraped it. Can you just fasten the top bolt from the muzzle end similar to the bottom bolt? From the pics it appears you have the room.

With regard to your original question: I"m not going to go into an in depth engineering analyses but it would be beneficial to get the top fastener in from a theoretical perspective. However, these are hardened strengthened steel bolts. Steel is very strong. All your hand guard does is transfer a little bit of force to the receiver to hold it up. The weight of the gun compare to the strength of hardened steel bolts is nothing. If it feels solid in your hands, than its good to go.
 
In the first pic, you had the the lower bolt fastened from the muzzle end and the middle bolt fastened from the receivers end, and hence you scraped it. Can you just fasten the top bolt from the muzzle end similar to the bottom bolt? From the pics it appears you have the room.

So - the "bolt up plate" that the forend comes with is threaded to receive a bolt only on the bottom holes, one on each side. Those of course are no problem.

The top 4 holes in the bolt up plate are not threaded, instead the actual rail itself is threaded giving me only one approach from what is for my setup, the wrong direction.

Thanks also for the metallurgical advice, I hear you on it being better to get the top ones in as well. Going to try and do some shooting tomorrow.
 
What you could do is is drill the treads out of the bolt up plate that attaches to the receiver with the next thread size up. Then enlarge the holds on the hand guard if necessary. Then install bolts from the muzzle. Again based on the pictures, it looks like there is enough meat to enlarge the bolt holes.

Have fun shooting tommorow. I went to the range twice this week for the first time in like 4 months, and had a blast.
 
What you could do is is drill the treads out of the bolt up plate that attaches to the receiver with the next thread size up. Then enlarge the holds on the hand guard if necessary. Then install bolts from the muzzle. Again based on the pictures, it looks like there is enough meat to enlarge the bolt holes.

That is an absolutely fantastic plan. I don't have a tap that size but that would totally solve my problem! Going to shoot it tomorrow and then get together what I need to do the work.

It's permanently modding the rail for this gun, but that's fine by me.

Thanks!
 
In the first pic, you had the the lower bolt fastened from the muzzle end and the middle bolt fastened from the receivers end, and hence you scraped it. Can you just fasten the top bolt from the muzzle end similar to the bottom bolt? From the pics it appears you have the room.

With regard to your original question: I"m not going to go into an in depth engineering analyses but it would be beneficial to get the top fastener in from a theoretical perspective. However, these are hardened strengthened steel bolts. Steel is very strong. All your hand guard does is transfer a little bit of force to the receiver to hold it up. The weight of the gun compare to the strength of hardened steel bolts is nothing. If it feels solid in your hands, than its good to go.

Well thats fine if he's just running around the house with it but when firing there will be all kinds of vibrations running through all the parts especially being a semi. I do like the idea of running the bolts in from the front however. To the OP: I would heli-coil the plate and bore the HG holes for a nice fit around the bolt's threads. That way all the bolts will be the same size and you wont have to buy extras. IMO a much cleaner look, not to mention having the bolt heads alternate between front/rear rather than 1 front/2 rear
 
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