Opening AR15 bolt face?

[lar45]

Hello everybody. I'm trying to work on a locked bolt 9mm AR15. The closest bolt I can find is the 6.8, but it is a little on the large side. I tried to open a 5.56 bolt on the lathe, but didn't get much accomplished. I used a high speed steel lathe bit. Should I try Carbide? or are they just too hard to work on?
TIA
Glenn.

[country gent]

I have reworked AR-15 bolts to 6ppc (.441-2?) I used ground and honed carbide tooling. The interrupted cut is a small issue with cutting them. Keep the cutting relief angles to around 5* and relieve so bottom of cutter dosnt rub.

I thought 223 bolt would be close enough to work with 9mm

[SSGOldfart]

Humm isn't the 223 bolt the same as the 9mm bolt???

[lar45]

The 9mm rim is .389"
The 223 rim is .375"
I can not get a 9mm case to go in a 223 bolt.
I'll try the carbide boring bar. I'll get it as short and stiff as possible.

[SiliconeSword]

Sounds interesting, bolt action or somehow gas operated?

I was reading about some guy's bolt action 9mm and he used a 5.45x39 bolt directly. They're $75 plus shipping though, so I think it may be worth trying to grind the face out if carbide doesn't do it for you. I think that if you mounted a Dremel as a tool post grinder you'd get it done, of course changing stones when necessary
https://vtsupply-com.3dcartstores.co...15_p_7375.html

[lar45]

Gas operated

[Rapier]

The coating is ceramic so a HSS cutter will be eaten up, carbide is needed. You just need to open the outside, do not deepen the face. Then modify the extractor to fit.

[country gent]

You can buy a short carbide bar or grind one on a 3/8 square cemented carbide bit. dont leave a sharp point stone a small radius on it a small radius in the corner will make the reworked bolt much stronger. The small radius will also help with the interrupted cut

[405grain]

I doubt that a 9mm pistol cartridge is going to generate sufficient gas volume to operate an AR style action. This is probably why there are so many blow back operated bolt carrier assembly's available over the counter for the AR platform. This begs the question; why reinvent the wheel when you can select from several better choices right off the shelf? If you want a locked bolt action, I can understand desiring something unique. But it seems to me that you would get very similar performance from a blow back carrier group.

[lar45]

I just want to see if I can make it work. A locked breach will be lighter and won't need to use the standard buffer spring and weight.

[M-Tecs]

If you have a lathe the easiest most cost-effective way to do this likely is using Dremel as a small tool post grinder. Most of the bolts will be 9310 or Carpenter 158 case hardened. Some are made of S7 tool steel. S7 is not case hardened and normally are in the mid-40's RC. Depending on the type of case hardening and carbide may or may not cut it. All carbide is not created equal even in the claimed same grade. I have little faith based on first hand experience with the Chinese import carbide for anything moderately hard. For things like aluminum or soft steel it tends to have less operating life but since the cost is significantly less the cost per part may be less also.

If you have the correct wheels for grinding carbide that may or may not work depending on the grade of carbide, type of material and what type of base material. I've never opened an AR boltface but I have reworked some nitrate parts that the case was about .003" deep. It ate the Chinese carbide like popcorn, however my Kenametal carbide had zero issues.

The spindle bearing on a Dremel are not good enough for high precision work but they work well for things like this.

[SiliconeSword]

Interested to hear how this goes, will follow suit if it works out. I like my AR9 a lot but not particularly fond of the 40oz reciprocating mass to smooth out the recoil. I imagine the price of a 9mm Banshee setup was a turn off for you

[Barry54]

https://castboolits.gunloads.com/sho...ck-rifle/page3

See post #53 above. Moleman- has built direct impingement 9mm ar’s.

[Plate plinker]

Where is moleman? I believe he has posted about his adventures in 9mm AR platform. IIRC he has done 9mm gas guns.

[deltaenterprizes]

Sounds interesting, bolt action or somehow gas operated?

I was reading about some guy's bolt action 9mm and he used a 5.45x39 bolt directly. They're $75 plus shipping though, so I think it may be worth trying to grind the face out if carbide doesn't do it for you. I think that if you mounted a Dremel as a tool post grinder you'd get it done, of course changing stones when necessary
https://vtsupply-com.3dcartstores.co...15_p_7375.html

I had the same idea!

[lar45]

I used a diamond grinding drum for the dremmel and it opened it up just fine. Now to work on the other parts.

[Moleman-]

missed this thread as I've been up north. I'd cleaned up my picture storeage and deleted a bunch of pics with the 9mmDI being some of them. Here's the main picture from the thread Barry54 linked. Assembled 20" upper with steel straight tube gas block, 16" barrel (cut it to 11" yesterday) and aluminum straight gas block, and barrel extenions mods. The bolts on mine I just opened up 223 bolts with a braised carbide bit ground to clear and ID cut and plunged it in while turning it as fast as the little 9x20 lathe would go to keep the carbide from chipping from the interupted cut and less than ridged lathe. The pitcher mouthed 9mm cases are what the barrel extensions were doing to the brass before the addition of the ejector rail. A roll pin drilled into the barrel for retension works just fine for the rail as well.

[SiliconeSword]

missed this thread as I've been up north. I'd cleaned up my picture storeage and deleted a bunch of pics with the 9mmDI being some of them. Here's the main picture from the thread Barry54 linked. Assembled 20" upper with steel straight tube gas block, 16" barrel (cut it to 11" yesterday) and aluminum straight gas block, and barrel extenions mods. The bolts on mine I just opened up 223 bolts with a braised carbide bit ground to clear and ID cut and plunged it in while turning it as fast as the little 9x20 lathe would go to keep the carbide from chipping from the interupted cut and less than ridged lathe. The pitcher mouthed 9mm cases are what the barrel extensions were doing to the brass before the addition of the ejector rail. A roll pin drilled into the barrel for retension works just fine for the rail as well.

Very good stuff, I recall seeing or hearing mention of this years ago but can't remember from where. Could you tell me where I could read more about this? I'm very interested in putting something together sort of like that. I recall there being more details than the thread mentioned earlier.

I also imagine that's even less than a micro length gas tube, did you modify one or did you make your own entirely? Seeing that there's so much dwell time especially with subsonic ammo do you think I'd be able to get away with like a 5in barrel? Also how difficult was it to chamber/headspace everything with the "barrel extension" and such? I've chambered maybe 6 barrels but all were .22lr and probably far easier to do.
Before I go as far as getting reamers, gauges, parts, and chopping up a barrel blank from the stash would you even recommend the project/say it's worthwhile to do?

[Moleman-]

SiliconeSword, There's been a few threads on it over the years. More detailed initial build is on Weaponsguild https://weaponsguild.com/forum/index.php?topic=16509.0 Lots of the pictures are missing though, When I have time I'll see if I still have them. That thread covers the initial build and the updates a few years later with the ejection rail. There's also one on Gunco https://weaponsguild.com/forum/index.php?topic=16509.0 There was on on Military Firearms before that site went dark, and I suspect I've posted it elsewhere or mentioned it in threads like on here. For gas blocks I've just made inline ones with a .781" barrel-tube spacing and straight tubes about 4"-4.375" but there were made before using the ejection rail so you might be able to go a little further out since it doesn't have to overcome the extra force of the case flipping sideways in the extension. I've had other guys over the years ask me questions for their builds. Some have used standard gas blocks and just bent their short gas tubes to work so that is an option as well. 15-20 years ago there were a bunch of cheap .805" barrel blanks and that's what I used on these two barrels. Having no shoulder to torque the extension on they were treated like a savage barrel and use a lock nut so headspacing was somewhat easier. There is around .020" between my Clymer GO and NO-GO gauge so I made a GO +.005" to use to headspace the barrels as a tighter NO-GO.
AR15 barrels are easy to chamber. Quick and dirty method for most that use a .004"-.005" GO to NO-GO gauge length is to get close enough to measure the barrel extension-shoulder gap with a feeler gauge and deepen the chamber until with the extension on hand tight the bolt will just rotate on the NO-GO. Once the barrel extension is torqued on the headspace will close up .003"-.004" and put you just over GO. Occasionally you may have to touch up the chamber with the reamer but usually not. For drilling the gas ports, I'll usually drill them in a dividing head, then spin the barrel 180 degrees and dimple the opposite side to make locating the gas block easy since most set screw gas blocks use the port hole for the rear set screw hole.

"would you even recommend the project/say it's worthwhile to do" That ones is tougher to answer and depends on the person. If you like tinkering it's a fun project. It's somewhat quieter by ear to me for the same length barrel blowback upper shot through the same suppressor on both barrels. They are much more finichy though compared to a blowback.

I cut the 16" barrel down to 11" and threaded it 5/8-24. Tried shooting it yesterday with standard 115gr FMJ loads (remington and Winchester factory) and it was a case throwing machine. Using a load of 3.2 grains of Prima-V and a 147gr Berrys bullet I was getting short strokes although the same load cycles my blowback SBR. It was extremely quiet though. I don't think I shot this load out of the 16" barrel before chopping it but did shoot lots of tuble lube 124gr bullets over 4.0gr W231. Before the addition of the ejection rail that load would also short stroke, but afterwards would shoot fine although you do get some lead dust on the bolt tail. The most 124TL bullets I've shot at one time was 500 just to see how many it would take before it locked up. They had much more than needed alox on them and I actually think that helped blow excess lead dust out the carrier vent and keep it from sticking to the bolt tail. That made the gun super dirty although it still kept working. I'll see what load it takes to cycle the 11" barrel and may shorten it down further.