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Low Reciprocating Mass Build

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Low Reciprocating Mass Build was created by jtallen83

I've been working on an AR-15 build with a lightweight BCG and adjustable gas block. I want a real soft shooter and light weight for the wife and grandkids to shoot. I put it together using an enhanced spring from Taccom (10%weaker) and a buffer with the weight removed. I got to a function test of running rounds by hand to see if they would cycle and found that the bullets would get gouged or jam in the lug recess of the feed ramp. I have used P-mags, steel GI mags, and a Lancer mag with no difference seen. I tried all the combinations of light and standard spring and weight free and standard buffer with no change except the standard spring set the bullets back even further. :(
Before I put the file and buffer to the feed ramps I thought I'd check and see if there are any other suggestions, metal is easy to remove but hard to put back! :pinch:









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Last edit: 5 years 3 months ago by jtallen83.
5 years 6 months ago #47024

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Replied by faawrenchbndr on topic Feed Ramp Issue?????

Do you have a standard weight bolt carrier?
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5 years 6 months ago #47025

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Replied by jtallen83 on topic Feed Ramp Issue?????

Yes, I'll try that tomorrow along with swapping lowers, might even try a rifle length buffer system since I have an A2 set sitting around. I don't think it is a weight issue though, the jams in the picture were created when I let the charging handle forward real slow, doesn't seem to matter if I ride the handle or let it fly the exact same jam occurs, grabs the bullet tip right in the lug opening.
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5 years 6 months ago #47027

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Replied by jtallen83 on topic Feed Ramp Issue?????

Spent a couple hours playing with this build. Broke down all my AR-15's and started looking and swapping. Magazines sit the same in all the lowers. Put the lower on my Sig upper, no issues. Tried to put my Armalite upper on the lower but the barrel nut is too close to the hinge pin or the Matrix hinge is too big so no go there. Put a Spikes lower on the Matrix upper got some rounds hanging up as before but only when I rode the charging handle forward slowly. Tried the Sig lower and got the same.

Got out a magnifying glass and light for a close look at the ramps and changed to a pointed pick, found there are some slight burrs along the edges of the ramp cuts. Got out my needle file set and started filing. I found that the QPQ extension is some hard ass chit, no worry about taking too much in one stroke! It became evident that the edges around the lug cuts and the lower part of the ramp were high spots as they got shiny while the center of the ramp still had copper marks from the bullets. I stopped when the pick quit catching on the edges.

Put things back together and ran through the same combinations of the Matrix upper on my lowers. Progress, I hope.....

The Sig and Spikes lower combinations had no hang-ups. The Matrix lower only hung up twice and that was with the low power spring when riding the charging handle forward slowly. The full power spring in the Matrix worked fine. Looks like I'll invest in a dremel next and do some polishing before any live fire function test.

I'm set on making this low mass combination work, no turning back now!
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5 years 6 months ago #47031

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Replied by faawrenchbndr on topic Feed Ramp Issue?????

Blending my help a good bit. Keep in mind, the nitride treatment is going to eat sanding rolls like nobody's business. Blending is going to be fun.
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5 years 6 months ago #47057

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Replied by jtallen83 on topic Feed Ramp Issue?????


yep, ruined two needle files with just some light strokes on the burrs, already working better though....waiting on a dremel kit.
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5 years 6 months ago #47059

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Replied by faawrenchbndr on topic Feed Ramp Issue?????

Not sure if they make the appropriate size carbide cutter or even a diamond impregnated stone. The normal stuff from the big box stores aren't going to get anywhere
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5 years 6 months ago #47060

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Replied by Akai on topic Feed Ramp Issue?????

JT, MSC has some inexpensive diamond needle files or the diamond impregnated rubber wheels for a dremel. You are on the right track.
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5 years 6 months ago #47099

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Replied by jtallen83 on topic Feed Ramp Issue?????

Finally got this rifle test fired. Once I got the gas adjusted there were no malfunctions with any of my mags. Running the buffer with no weights, the "enhanced" spring that has 15% less strength, 4 clicks open on the SLR gas block, and the d wilson lightweight BCG. A nice soft shooter just like I'd hoped for. The 8 year old granddaughter sent 15 rounds down range and pronounced it a "good gun", made grandpa smile!
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5 years 3 months ago #47425

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Replied by jtallen83 on topic Feed Ramp Issue?????



Finished product, for now anyway.
Matrix receiver set and rail
Ballistic Advantage 14.7 inch pencil barrel
d. wilson lightweight BCG
SLR adjustable gas block
Taccom reduced power spring
Weights removed from a standard carbine buffer
Mech Armor TacOps I charging handle
Strike Industries for all the small parts, grip, and stock
Vortex Strikefire red/green dot
Streamlight TLR1
Weighs in at 6 pounds 8 ounces like you see it in the pictures.
Still waiting for the BUIS I want to be in stock.
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The following user(s) said Thank You: Quentin
Last edit: 5 years 3 months ago by jtallen83.
5 years 3 months ago #47433

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