I picked up a LH bolt a couple weeks back and noticed the same thing. They must have taken a look at the BoreBuddy pin and decided to add a radius to the front shoulder. :bthumb: The rear looks like it was not an intentional radius, just the limits of the tooling. I've never seen a pin broken back there anyway, so it's probably unnecessary.

 

I totally agree about the back shoulder. I know we discussed this here and on ARCOM before. And I did send them an email back then about it. I never heard a response from CMMG but it's good to see that they did address the front radius.

And I just got one of your update kits with the solid weight today in the mail. I'm just waiting on my handguard and ambi charging handle to complete the build.

 

I totally agree about the back shoulder. I know we discussed this here and on ARCOM before. And I did send them an email back then about it. I never heard a response from CMMG but it's good to see that they did address the front radius.

And I just got one of your update kits with the solid weight today in the mail. I'm just waiting on my handguard and ambi charging handle to complete the build.

12B & CH: I have experienced at least a half-dozen broken CMMG pins in as many years (I have four or five of their conversion bolts in as many uppers), but none very recently. As CH stated, the CMMG pins that have failed always break at the front end, and that was the case with all of mine as well. On at least one of the pins, the rebound spring was broken into two pieces as well. Perhaps the larger radius CMMG is now using at this point will stop, or at least decrease, this breakage problem. Like many, I always have a spare pin with me during a range session "just in case". I know, I should have purchased a BoreBuddy pin and been done with it. I will say, however, that CMMG has been VERY good about replacing the broken pins under "warranty", and very quickly as well. I have been MORE than satisfied with their excellent customer service.

For CH-- I recently used my heavy-barreled upper in a 40 shot, 200 yd prone match, with your stainless "adjustable" weight installed. The upper ran perfectly (Taylor "blue" hammer spring, BMA/S&W mags), zero malfunctions, using ELEY "Semi-Auto Benchrest Precision" ammo. No, I didn't win the match...but came in 3rd, though, against a bunch of bolt guns (Rem 40X, Kimber 82, H&R 12, etc.). I noticed my lower is running MUCH cleaner with the weight installed, far less powder/debris being deposited in the trigger group area. I can only surmise the weight is delaying the bolt opening just enough, such that the powder charge is more fully burned before the bolt fully opens. This, and no bolt bounce, are two VERY good things for an AR-22.

 

Triggershoe. We had a long in depth discussion about the CMMG firing pins on ARFCOM about the same time that the discussion about the 17m2 barrels started. And yes the firing pins breaking at the front shoulder was definitely due to not having any type of shoulder cut into it.

We actually had this conversation before the Bore Buddy firing pins were actually released for sale IIRC.


CH being an engineer and myself being a tool and die maker, we understand this very well.

 

I have wandered for a long time why they did not try something..Has to be expensive to keep replacing them all the time for people..

I have a Bore Buddy pin that was a proto they sent me for free..It has long outlasted my CMMG ones and is still going strong..

I am still not sure if that will be enough yo save their pins though..Hopefully they revisited the material and hardening process also..

 

I have a Bore Buddy pin that was a proto they sent me for free..It has long outlasted my CMMG ones and is still going strong..

That's rather impressive -- I heat treated that pin with a propane torch using visual cues to judge temperature on both the quench and the temper. A faaaaaaaar cry from a professional HT. The production ones are done at a high end HT shop.

We've got a new version in the works as well, but we're dealing with the supply chain issues that are plaguing everyone and slowing down release.

I am still not sure if that will be enough yo save their pins though..Hopefully they revisited the material and hardening process also..

The material appears to be the same as the older ones on the new one I have on hand. It's some type of soft-ish magnetic stainless -- I can easily scratch it with 440 stainless cheap pocketknife. I don't think it has any heat treat on it unless they removed the oxide layer afterwards (which is unnecessary so I doubt they did so)

Time will tell...could be the radius takes care of the problem and we've been wasting money on high end material and heat treatment.

 

I have made various Fring pins for obsolete stuff I have "restored" over the years, using air hard steel and a propane torch..Always worked out well..These were not firearms that see the round counts like my M16A2 clone that your pin is in..But they held up fine..

 

This upper shot a ten-shot group last week that measured slightly less than 2.5" @ 200 yards. This was shot with the aforementioned Eley "semi-auto" ammo.
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Jaia needs to know about this. My best group I ever measured at 100 was half that; using the half/third rule yours is a .8 to .9 group at 100. That's amazing.

Zuk-- That group my friend shot WAS pretty amazing for an AR-22 platform semi-auto, it certainly was better than anything that I was getting that day @200. I was having a bit of trouble with vertical dispersion of MY groups, not sure exactly why (technique?). Now, that group could be a "one-off" (we quit shooting after that group), or perhaps (more likely) my friend's bench technique is just THAT much better than mine! That scenario is a bit sobering for me, but I'll be sure get to him back behind the rifle at the next opportunity. I'm MORE than OK with it if he's a better "bench" shooter than me, technique is everything. We DO go back and forth a lot (in terms of on-target results) on who is the better OFFHAND shooter, though... All in good fun for sure!

I know that Jaia has tested this ammo @200 (Eley "Semi-Auto Benchrest Precision") and was impressed by the results he obtained. It's too bad I didn't have the chrono set up to see what my particular lot of this stuff was actually doing. But hey, that's an excuse for another range trip.

 

The material appears to be the same as the older ones on the new one I have on hand. It's some type of soft-ish magnetic stainless -- I can easily scratch it with 440 stainless cheap pocketknife. I don't think it has any heat treat on it unless they removed the oxide layer afterwards (which is unnecessary so I doubt they did so)

Time will tell...could be the radius takes care of the problem and we've been wasting money on high end material and heat treatment.

I doubt that CMMG is heat treating their firing pins either. If I was still working, I would take the pin in and put it on the hardness tester. But if it scratches easily then it is not heat treated. I'll run the new CMMG version before putting the Bore Buddy pin in and see.

Wouldn't hardening just make a pin more brittle and more prone to snapping? I'm not an engineer; maybe a lawyer is exactly the opposite of an engineer...so maybe I just don't understand how hardening helps with the stresses a pin sees.

Hardening by itself will make things brittle. That is why it is important to temper the steal after heat treating it.

 

my thoughts on radius of the strike end... from an experience with my AR9 for PCC and OEM pin breakage at about 1000 rounds... I rounded the strike end of a Colt pin so that the hammer would hit closer to the center line and not transmit any side stress on the pin... the modified pin is over 7000 rounds without a problem

prior to getting a Bore Buddy for my CMMG conversion, I stuck the factory pin in a cordless drill, reversed direction, and used a Dremel with sanding drum to cut a cone taper on the pin similar to the Bore Buddy... I think it was a worthwhile modification... regards

 

Tooling and stress risers

The improvement is two fold for CMMG
-Large radius carbide inserts can be pushed harder and last longer than fine tip "finishing" inserts.
-The large radius will reduce the stress riser at the sharp corner where the pin cracks from hardening (see: Metal Fatigue) They may still break but the service life will likely double if not triple over the old design

 

The improvement is two fold for CMMG
-Large radius carbide inserts can be pushed harder and last longer than fine tip "finishing" inserts.
-The large radius will reduce the stress riser at the sharp corner where the pin cracks from hardening (see: Metal Fatigue) They may still break but the service life will likely double if not triple over the old design

Absolutely correct. Anytime you have a square shoulder on a pin or shaft of any size, it introduces a weak spot. It doesn't matter if it is something small like the CMMG firing pin or a larger 24" steel roller.

And yes I have had to replace 24" steel rollers due to the manufacturer failing to cut a radius at the shoulder and the shaft breaking right there.

 

I do not know whether CMMG even makes the .22LR firing pins that they sell. What is being observed may well be variations from different suppliers that CMMG might change from time to time based on cost, availability, payment terms, and the like.

Disclaimer: I have no affiliation with or financial interest in any vendor or manufacturer; and I am not a competitive shooter or a blogger who receives any form of compensation for endorsements or favorable public or private comments. Use of vendor and/or product brand names, if any, is for informational purposes only.

Best of luck.
MHO, YMMV, etc. Be well.

 

That could be what is happening. But CMMG does have big shop in Booneville, Mo. And the firing pins have been the same for a very long time with the square shoulders. I know myself and others have sent emails to CMMG about machining a radius at the shoulders to keep them from breaking. Maybe they finally listened.

 

somewhat of a thread drift... the novelty I appreciate with the Bore Buddy pin, in addition to the radius at the step down, and cone machining to center the hammer strike, is the actual location of the strike on the cartridge... unlike a chisel end strike that must deform the radius of brass at the rim edge, and thus expending impact force, the circular strike just below the rim edge, coupled with the diameter of the strike impact really seems to be a good solution... especially for someone like me that typically does not buy match grade ammunition...... regards

 

I notice that my S&W 617 uses their standard CF firing pin instead of the chisel tip, too. Have yet to have a F-to-F due to that FP.

 

CMMG Rimfire Firing Pins

Dittos on the non-radiused FP breakages. I made the suggestion to CMMG about 5 or 6 years ago to add the radii when I had two break at the front step. Glad to see that they made the change(s). I have at least one spare radiused FP for each CMMG upper I own, but have yet to have a breakage on the new pins.

Also, CMMG has a lifetime warranty on their parts, so notify them and they will send you a replacement (probably 2).

Another modification I do is to carefully grind the FP tip so it is ever so slightly thinner (take 0.005" off both sides) so it hits the rims a bit harder (same force across a smaller impact area). This reduced failures-to-fire on the cheaper ammo that otherwise needed to be hit twice. Gotta also remember that the CMMG FP has a return spring that the hammer force has to overcome as well.

 

Firing pin & pressure plug

When I bought my RTB 16" upper a few months ago, I had occasional misfires/light strikes with CCI Tactical. After a few posts I was advised to get the BoreBuddy firing pin & pressure plug. Not sure which one fixed it, but I'd have gladly paid the few extra bucks for a better pin & pressure plug.

 

When I bought my RTB 16" upper a few months ago, I had occasional misfires/light strikes with CCI Tactical. After a few posts I was advised to get the BoreBuddy firing pin & pressure plug. Not sure which one fixed it, but I'd have gladly paid the few extra bucks for a better pin & pressure plug.

It all depends on your particular upper and if it is on the large side of the allowed tolerances if the pressure plug was the fix or not.

If you have a bolt that the overall length is at the minimum of the allowed tolerances and an upper that is at the maximum, then that combo will definitely benefit from a pressure plug. This is known as tolerance stacking. And it gets worse when you use parts from multiple manufacturers.

I have some AR22's that the bolt is a tight fit when closing the receivers while others need a pressure plug.

If your bolt is at the minimum length and upper is at the maximum, then the bolt can move which can cause light primer strikes.