AR9s and 147 Grain Ammo

[s4s4u]

Glock mags to replace the Endomags

Well, if you do hit me up if you wanna dump the Endo's. Not sure Glock will feed as well, but you don't know til you try.

[Clint]

Was the FM buffer and 308 spring combo not reliable, or wasn't it tested?

I have been running a 16 inch FM9 upper on an Anderson multi cal loser for several months. Foxtrotmike’s interesting little twist on the AR9 recipe is to recommend a 308 spring which consistently forces the round into the chamber even under imperfect conditions but affects the timing of the gun, then offer a propriety special length 3.75 inch buffer you can only get from them to counteract the timing effect of the 308 spring.

I started with a standard carbine spring and an 8 ounce KAK solid buffer. It ran 115, 124, 147, fmj and jhp with zero failures. The sub 1100 fps ammo they recommend against fed with no problems.

I then switched for piece of mind to a 7.5 ounce Macon armory lead shot buffer to eliminate the already minimal chance of bolt bounce. It’s been the same. A standard 4 inch 7.5 to 8 oz buffer on a carbine spring generally seems like it should run this kind of setup on diverse ammo with no problems. Messing with that sends you running off in various directions. Foxtrotmike’s recommendation of the 308 spring and 3.75 inch 6.5 ounce buffer is not the ideal starting point if you want it to eat everything with zero drama. Just geared to catch the attention of people impressed that it is specifically set up to chew through light easy on the wallet steel case fmj all day without a malfunction.

I have never changed anything else except 8oz solid and then 7.5oz moving weight buffer. Never touched the feed cone. Nearly 1000 rounds of various grades of ammo and not a single failure.

[NQNPIII]

Even if you have bolt bounce it shouldn't be an issue unless you are going full auto.

[eman]

Was the FM buffer and 308 spring combo not reliable, or wasn't it tested?

I bought the upper only. Their proprietary buffers and bcgs were not in stock anywhere when I looked for one as they seem to only do limited parts production runs to their vendors to save the stuff for complete guns. They will send you anything you want if you mail them a check as they’re not set up for credit cards and their paypal was cancelled due to them being in the gun industry.

Rather than deal with that I looked at in stock ready to ship 6-8 ounce buffers to swap into carbine spring on the Anderson lower I put it on.

[JB2000]

I’ve been running the FM buffer with a Tubbs 42 coil flat wire .308 spring. It will run with all ammo weights but I notice the recoil is more harsh with full power 115/124 grain loads than with the standard .308 spring.

When I pick up the brass, some of the brass from these loads have burn marks that extend about half way down the case. It makes me wonder if the bolt is opening prematurely. When I get time, I plan to chronograph these loads with the different buffer springs and see if there are any differences.

[eman]

I’ve been running the FM buffer with a Tubbs 42 coil flat wire .308 spring. It will run with all ammo weights but I notice the recoil is more harsh with full power 115/124 grain loads than with the standard .308 spring.

When I pick up the brass, some of the brass from these loads have burn marks that extend about half way down the case. It makes me wonder if the bolt is opening prematurely. When I get time, I plan to chronograph these loads with the different buffer springs and see if there are any differences.

There is a distinct possibility the 6.5 ounce buffer is at the lower end towards the borderline of what is safe with those loads. My 7.5 and 8 ounce buffers never produced case abnormalities. Also read sometimes powder and load issues can cause the ammo to NOT burn hot enough to get sufficient case expansion to fully seal against the chamber until the bullet leaves the barrel. But I would wager buffer weight on the bottom end of the safe range.

[utahjeepr]

+1 on a heavier buffer. I run a 12oz. in my suppressed SBR 9mm. I run extra heavy to quiet down ejection port noise, but you wanna be up around 8oz. minimum IMHO.

[JB2000]

I’ll have to pick up a heavier buffer to try. FM makes one for their 45 that is extended pistol length and 7.8 ounces. Finding any heavy buffer in stock seems to be a challenge these days.

[Clint]

This one appears to be a good choice, given the specs.

https://www.kakindustry.com/ar15-9mm-buffer-long-heavy

[JB2000]

This one appears to be a good choice, given the specs.

https://www.kakindustry.com/ar15-9mm-buffer-long-heavy

Looks nice! I wonder if the weights are the same size as regular buffer weights. If so, that would be even better because you could adjust the weight.