AR 7.62x39 FTF

[quig]

I already posted this on another thread, but I thought I might get a different look here.

I just built a 7.62 AR upper and first took it to the range today. "A little update/range report:

I got the last piece of my build today, the brake. I then went right to the range, indoor only, but good enough for a function test.

I had Golden Tiger and Tula(Wolf) with me today. Since the range allowed these rounds, I didn't bring any Yugo because I didn't want to mess with the corrosion clean-up . . . yet.

I was a little skeptical because I have some low-power JP yellow springs and wasn't sure if they were strong enough for the hard 7.62x39 primers. I've read reports of these sorts. My first mag was with the Golden Tiger. All 10 hits without a discharge. Damn!

However, I came prepared, and switched out the springs to the stock set.

Back to GT, still no fires. Switched to Tula, first round fires. I sure did like the feel of the 7.62 out of an AR. But then, back to FTF. They still appeared to have decent strikes. The GT never fired, and the Tula was only a little better with ~%15 of them going off.

I wish that I had brought some Yugo, but I would like to still have consistency with Wolf ammo like out of my Saiga. Does anyone have this experience? Should I be looking into stronger springs, different hammer, different pin?

Looks like I still need to do some tweaking, but I like the set-up regardless of the hiccups."

UPDATE: GOOGLED IT. My bolt was ordered from Model1, and people reported the same problem. Apparently, Model1 has a specific (not listed) 7.62x39 firing pin which penetrates the primer deeper without puncturing it. Looks like I have to wait for one more item.

[CRTguns]

I have just built 2 7.62 AR rifles-

Wolf makes an extra powered hammer spring that HELPS. You can keep a nice trigger spring in. You may have to grind the hell out of the hammer to get it's mass down to generate the speed needed to pop russian primers. I had to cut hammer on 1- just needed the +P hammer on the other. The horn can be removed completely- and the excess width can be removed. You should be able to take about 40% off.

You can also grind (with great care and precision and caution) about .020" of the tail if the bolt to allow more firing pin protrusion.

[quig]

Thanks for your help.

I am going to start with the firing pin, then work my way down the list. I am hesitant to mess with the hammer just yet. Currently, I am using the same lower with my .556. My next step will be the dedicated 762 lower.

I'll report back,

Thanks.

[CRTguns]

Thanks for your help.

I am going to start with the firing pin, then work my way down the list. I am hesitant to mess with the hammer just yet. Currently, I am using the same lower with my .556. My next step will be the dedicated 762 lower.

I'll report back,

Thanks.

That's the thing- you can't use the nicely tuned light trigger lower with the 7.62 upper- gotta have adedicated heavytrigger.

+P+ hammer spring, lightened hammer, + firing pin protrusion.

[captbilly]

This is very interesting because JARD does the opposite.

I have just built 2 7.62 AR rifles-

Wolf makes an extra powered hammer spring that HELPS. You can keep a nice trigger spring in. You may have to grind the hell out of the hammer to get it's mass down to generate the speed needed to pop russian primers. I had to cut hammer on 1- just needed the +P hammer on the other. The horn can be removed completely- and the excess width can be removed. You should be able to take about 40% off.

You can also grind (with great care and precision and caution) about .020" of the tail if the bolt to allow more firing pin protrusion.

When you use a JARD trigger on a .308 they recommend a heavier hammer (which they make) rather than their standard hammer for hard to ignite primers (military ammo). It would seem that they believe a heavier hammer hits harder. I posted some time ago about the physics of a hammer hitting a firing pin. In the post I contend that according to my mathematical analysis of the physics, what you need is for the hammer to be matched to the firing pin. Not necessarily heavier or lighter, but the properly matched mass. Ideally the mass of the firing pin needs to be the same as the rotational inertia of the hammer (the hammer rotates so simply matching the mass off the hammer to the firing pin would not yield the desired result). In some cases this might mean that lightening the hammer would give better energy transfer to the firing pin while in other cases you might need a heavier hammer. I even wonder if the issue with .308 hammers needing to be heavier might be due to the fact that .308 firing pins are longer and therefor heavier, so the hammer needs to heavier to match.