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Posted: 8/31/2025 8:05:30 PM EDT
[Last Edit: 308Sako][Edited]
 This home built/assembled pistol has been reliable for over 4,000 rounds. It's an Aero upper, CMMG .22 LR 4.5" barrel with a BCM handguard and a Tion Minuteman suppressor underneath. Lower is a polymer New Frontier Armory with a Geissele HI Speed match trigger. Generally, only use the Blackdog 15 round magazines. The problem: Failure to feed Cci HS solids and Aguila Hi Speed solids also. Twice in the last 100 rounds I have had a cartridge fire prematurely before fully chambered. Exciting times needless to say. My thoughts: Perhaps the mainspring has gotten weak so the bolts forward motion is insufficient to complete the cycle. However, the cartridge feeding is about halfway into the chamber when presenting a jam. About the same for the explosions. Or is it the magazine springs have become weaker, and the cartridge isn't fully positioned when the bolt makes initial contact. So what experiences have you had that can help me solve this? Thanks Sako Well hell it appears the problem comes from the New Frontier Polymer lower which cracked at 12 o'clock where the receiver extension would normally be found. Put the upper on one of my SBR's and it ran great for 250 rounds before yet another deep cleaning. Vascar, thanks for the memories, I worked one of the toggle devices in the 1970's LOL. Sako So, I decided to try the lower once again and what troubled me was the upper on it's own seemed to move smoothly, but when on the lower there was a hitch when crossing over the bolt catch, a standard AR15 one. So having a spare part or 3 (LOL) I ground down the clearance until there was smooth travel. I found that the CMMG appeared to drag over that. I more importantly think that the crack wasn't really the issue. So off to the range I went. 30 Remington "Golden Bullets" and 70 Winchester Suppressed load, no problems at all. |
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Going to have to try a few things until it works. Like you said, springs. They have a life expectancy. Lubrication or a dirty chamber? When rimfires act up they can be frustrating |
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First do the cheap fixes. Clean the heck out of the BCG along with the feed ramp and chamber collar, then the chamber, inside and out. Don’t forget the extractor and extractor groove on the chamber sides and make sure the firing pin is ok and it is clean along with the FP channel. Clean that BCG until it looks like new, inside and out. Next try a different magazine that has not seen much use. Then try replacing the recoil spring on the BCG. Have you dry fired a lot? If so, make sure the chamber has not been peened on the edge. My money is on a good and complete cleaning and newer mag will clear things up. |
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When the above issues presented themselves, the pistol was spotlessly clean. Including the chamber and the firing pin channel. I should also mention the magazines had been disassembled and cleaned as well. Thanks for the above replies. |
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Try putting a little bit of oil on the feed ramp. I suggest putting some oil on a Q-Tip, then rubbing it on the feed ramp. This often helps the nose of a 22LR round feed just a tiny bit easier, and can actually make a big difference in reliability. I know someone above said to clean the feed ramp, but this takes it one step further. HighSpeedSteel |
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You mention you are using a polymer lower and a Geissele trigger. At higher velocity ammo could be affecting the cycle timing where the hammer is snagging on the underside of the bolt. Inspect the hammer and underside of the bolt for unusual wear. There could be tolerance stacking between the lower, FCG and bolt. It is a relatively common problem with 22 LR AR-15’s to have issues with some hammers and CMMG pattern bolt. Any snagging can zap bolt recoil momentum contributing to stoppages. You might try the upper on a different lower and see if the symptoms persist. If there is any slack for the 22 LR bolt assembly to move inside the upper this can zap recoil energy. You could try to fill any void by cutting down a pressure plug like sold by Borebuddy or Right to Bear. You might be able to squeeze a couple quarters between the bolt end plate and the receiver plug. Since you are running a suppressor the higher velocity ammo with the added back pressure of the suppressor might be inducing the malfunctions. Using Borebuddy weighted bolt system lets you configure the bolt for optimum cycle without cutting springs. I would try the upper with the trouble some ammo without the suppressor attached. If the rifle cycles without the suppressor that would indicate a bolt speed timing issue which could be mitigated by the borebuddy weight system. The easiest solution might be to run ammo that functions reliably, maybe standard velocity or weaker bulk ammo like Federal Auto Match. It sure can’t hurt to polish the chamber which improves reliability with semi auto rimfires. I use a short cleaning rod with a barrel mop attached with Flitz polishing compound. I use a hand drill to polish the chamber with the barrel mop and Flitz. CMMG recommends buzzing the chamber with a brass bore brush soaked in oil spun by a hand drill. I’d suggest you use lube on the bolt and I use Breakfree CLP but Hornady 1 Shot gets very good reviews as do some other dry lubricants. Link to borebuddy adjustable weight system. https://borebuddy.com/product/22lr-bolt-weight/ |
| You could be experiencing bolt bounce. I hear its an issue with short barrel and suppressor. Try the Bore Buddy bolt weight. They have adjustable and solid bolt weights. The weight just clips into the back of the bolt and acts like a dead blow. I have one in mine and it runs fine with standard and high velocity ammo. |
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What's different about these two ammos that is giving you issues? Does everything else you run feed/extract reliably? Borebuddy offers a bolt spring kit. Light, medium, and heavy springs. That might be good to try out. Also, the bolt weight is helpful with bolt bounce, but I only see bolt bounce being an issue when you're pulling the trigger extremely fast. It could be that you're dropping the hammer when the bolt is on the rebound and carrying the live cartridge with it. It could be this chamber just doesn't like that profile bullet. There's a procedure we refer to as "buzzing the chamber". With a brass brush and some cleaner on an electric drill. There's a sticky post that describes this. 2 malfunctions in 100 is not too terribly bad but if you weren't having this issue before (with the same ammo) then something has changed. Need to get back there. |
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I have heard of polymer lowers cracking in the rear of the receiver where the buffer tube threads into the lower. I never heard of a polymer lower cracking with just an end cap. I always heard blow back actions were harder on FCG pins and hammers. I thought the failures with the polymer lowers might have been because of the added weight of the buffer, tube, spring and stock. I guess that is just an inherent weak point of the polymer AR-15 lowers. Thanks for the update on your 22 build. I’m glad to hear you got it sorted out! As to the Clicky thing, did you have an older one with computer under the seat and used a stop watch for calibration? I only used the Plus version, I really liked it and it was a versatile tool. |
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Originally Posted By VASCAR2:As to the Clicky thing, did you have an older one with computer under the seat and used a stop watch for calibration? I only used the Plus version, I really liked it and it was a versatile tool. 1975/1976 vintage I just can't remember much of those fun times. The lower actually had a seam in the casting/or however it was formed. Thinking some crazy glue :-) |
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