geissele SD3g trigger and bolt options.

[HawkMoney]

Seems from some of the older stuff i have read, you need an un ramped bolt to reset the trigger reliably? Does anyone know who still makes and un ramped bolt? Or has anyone had any luck with a specific bolt with the sd3g trigger? 

Thanks!

[JonF]

Not sure why that would be, the Geissele triggers are made to operate with traditional mil spec design ramped AR15 bolt carriers that fire centerfire rifle cartridges. PCC is merely a retrofit to this platform. 

I have the SD3G and a traditional ramped bolt in my PCC and operation is 100% fine. Have also used the same trigger in a .223 AR with 100% function.

[HawkMoney]

What bolt are you using? I don't think there is any real spec on the 9mm bolts, they are all a little different and with all the fcg's having different shaped hammers thats why some people are having problems.

[JRM83]

SD3G doesn't run with my KVP bolt. Not even a little.

[JonF]

My PCC isn't blowback, its a DI 9mm upper that uses a normal mil-spec bolt carrier group with a 5.45x39 bolt to clear the 9mm case head. Therefore i dont have any of the ramped/unramped nonsense to deal with.

 

But your original statement of Geissele triggers require non-standard unramped bolts to function isn't accurate. Standard 223/556 mil spec bolt carriers have a natural built in ramp so of course Geissele triggers will be designed with ramping in mind.

The question is whether the 9mm ramping you have is similar to mil-spec ar15 ramping.

[HawkMoney]

Thanks jrm83! Thats exactly the kind of information I'm looking for. JonF what kind of upper do you have and it works with a regular mil spec ar15 lower? Ive been looking for who makes a DI 9mm ar upper but not able to find any information about them.

[JonF]

I have a Ron Williams DI 9mm upper. For all intents and purposes, it looks exactly like any typical DI AR15 system. Bolt carrier group with delay lock bolt, barrel with star receiver extension, gas block with gas tube. Only different parts are short gas tube system, bore/bolt for 9mm diameter, ejection port opened up slightly for better 9mm case ejection, bolt ramp is thinned for glock mag lip clearance.

[HawkMoney]

very cool. do you shoot reloads or factory ammo? I'm in the middle of a build right now and trying to figure out which direction to go in.

[JonF]

It is recommended to reload for this gun for a couple reasons. 1. factory 9mm is generally loaded with very fast burning powder such that the combustion is completed within 1-2" of bullet travel down the barrel. In order to prolong the combustion dwell time and provide sufficient pressure and gas volume to cycle the DI action, slightly slower powders are recommended to prolong the burn to 8-14" of travel (these kinds of things you can work out in QuickLoad). 2. You can tailor the load to the gun to optimize recoil. 3. you can use cleaner burning powders to reduce fouling in the DI system. 4. you can adjust the load OAL for better feeding in the long rifle action.

I have found that factory (or normal minor PF pistol loads) can be used with the system after doing some tuning to the gun. Originally the gun comes with a full weight bolt carrier group and is made to work with a typical carbine recoil spring and buffer. Since it is using standard AR15 DI parts, i tapped into the lightweight parts market and put in a rubber city liteweight bolt carrier with adjustable gas key, taccom delrin buffer and wolff reduced power spring. because if this, i had to dial the gas system back considerably as the custom load i was used to using was now overgassing the system creating excessive and wasteful recoil. One side effect of this is that the lightweight carrier system can be more easily cycled reliably with normal pistol loads. Some experimentation may be necessary to see if it works with your specific load but it works a lot better than the old full weight recoil setup.

[HawkMoney]

Interesting. Thank you for all the information I have slot to think about now. I would ideally try to have a load that would work with both my pistol and Pcc. What type of powder do you use that's slower burning?

[JonF]

I use about 6 grains of Vihta Vuori 3N37. In a 16" barrel with a 124gr FMJ, this produces about 130 PF.

The one thing to consider with using one load for both pistol is that while its convenient, you leave a bit on the table in terms wasted energy. A pistol load will often put up much higher velocities in a 16" rifle than from a short 5" pistol barrel. Just like when switching from FMJ to lead, you can download the powder charge to a much lower level and still produce the power factor you need all while producing less recoil and conserving powder resources. While its not essential, it is an potential optimization that is available to you for your application.

[HawkMoney]

Right now I'm loading 165gr plated with 3 gr titegroup which makes 127 PF out of my cz shadow.  Very curious to see what it would make out of a 16" barrel. Im thinking with a blowback gun i should be able to get the weight of the bolt and buffer down quite a bit.

[Deathray]

My simple po folk plain blowback gun will only reset an SD3G trigger about 1/2 of the time when firing.  It will not catch the disconnector when manually cycling the bolt when the trigger is depressed.

After doing some quick and dirty measuring, it appears that the distance between the top of the gas key and the bottom of the carrier on a regular .223 carrier is about 2mm higher than on my generic ramped 9mm bolt.  I've heard of people zapping a small bead of weld onto the bottom of these things to make them run.  I'll give that a whack and see what happens.

This is the bolt I have: http://www.jsesurplus.com/9mmrampedbottomboltassembly.aspx

Receiver is a CMMG MK9

 

Edited November 12, 2016 by Deathray

[HawkMoney]

Thanks Deathray! keep us posted.