Bolt Jam

Guns & Gear Guns
1

Has anyone experienced this before? You’re casually firing semi-auto, a case is extracted and the bolt flies home, stripping the next round from the magazine and then “click” :scream::scream::scream:

I’ve been here before, it happens, but this one was new to me. The round had chambered, mostly, but the bolt head had stopped just short of being fully seated, right in the middle of the feed ramps. It was stuck. Bad. Obviously the gun didn’t go off because the firing pin didn’t properly strike the primer. I tried to rerack it, either to properly seat the round, or just 86 it and use the next one. The bolt wouldn’t budge. It was in there pretty good. Tried the charging handle, even the forward assist… lol. Ended up having to mortar it.

Then I kept shooting. Got through the rest of the mag just fine. Next I tried a different mag, with a different grain weight. Same thing happened once more. Had to mortar it again.

Hmmm… The first 60ish rounds through this new build didn’t have an issue. The next 30 had these two bolt jams totally kill the cycle. Not sure what to make of it. Couldn’t be cleaning related, the things brand new, right? Sure it doesn’t sparkle, but under a hundred rounds and two jams kill the gun with two different grain weights??

The build is a Palmetto standard “pistol” lower. Grid Defense 10.5, 300 BLK upper. Nothing remarkable about it, buffer weight standard, typical pistol length DI gassed, titanium nitrite BCG from Brownells.

I’ve been trying to check if anything was out of spec, as the action isn’t exactly as smooth as, say, a Daniel Defense. It didn’t appear to have issues when I manually racked snap caps through it. Only 2 out of about 90 rounds had the issue. Was using 300 BLK mags as is only proper.

Any thoughts? How does a bolt get stuck in the feed ramps like that?

2

Check the feed ramps, the ammo, and headspace, the mag, and check that the barrel is on straight. One other possibility that I can think of is the gas tube. @craig will likely have good advice for you.

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3

Had that exact same problem with an AR 5.56. In my case it was the ammo. some of my ammo was of a different manufacture, ( european ) and it was slightly out of spec at the base. The base of the cartridge was .001 over spec, and my brand new tight chamber got them stuck just a fraction before the bolt was closed, and, they were VERY stuck. My other 5.56 fired all of the rounds without a hint of trouble. The bolt felt frozen in place right along with the cartridge.

I would check chamber dimensions against spec and the ammo against spec as well.

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4

Internet medicine is just about as much fun as internet gun plumbing :confounded:

At first read I thought mebby you had a case head separation and half the brass was in the chamber. When you say “mortar” it does that mean you slammed the but on the ground while pulling the charging handle or did you drive the round out with a cleaning rod or some such?

Did you recover the offending round?

Are you using 300BO ammo or 223/5.56 blown out to make 300BO?

If the gun is nominally working with two instances I would lean more to the fault of the ammo rather than the gun.

That said it is always a good time to take your bolt apart and scrubby it. Grit, grime or brass “could” lock up the bolt but that is pretty thin as far as it goes.

Check your ammo dim’s.

Cheers,

Craig6

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5

P.S. The reason they got stuck so badly was that the cartridge was a nearly identical, but ductile, gradual cone shape, being jammed into another gradual cone shaped hole, and so the “sticking” surface area was a lot greater than might be imagined. Also, the bolt on my AR held on to the rounds so firmly, that unless the round was kicked out by the ejector, it would not budge. The extractor claws had a VERY effective grip on the cartridge head.

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6

By “mortar” I mean hit stock on ground while pulling charging handle. I think I just reloaded and fired both rounds at some point. By blown out 5.56/.223, do you mean reloaded? If so it wasn’t me, I bought them as 300 BLK from Cabelas.

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7

I’ll check spec at some point. To check chamber spec what should I use?

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8

Gauges are your friend. As you built it, did you use a set of go/no go gauges to check/set headspace?

And do you have a case checker gauge? Those are good to check ammo to possibly eliminate one variable.

Also, not sure about cabelas ammo. Is it new or reman?

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9

New. One was a lightweight budget round. The other was a heavier grain match round. Point is, it’s not a supersonic vs subsonic issue, nor a cheap vs expensive issue.

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10

And the gauges? Have you checked the headspace with go/no go gauges when you built it?

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11

Most of the gun was pre built. The upper was complete minus a BCG and charging handle. The lower was also complete. Grind Defense, a small shop in Flordia who built the upper, says they test fire every upper they build before shipping it, according to their website.

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12

My $0.02
Next time it happens go into serious diagnostic mode.
Inspect the round.
Where is it dented,
where are the shiny spots,
Scratches on the side of the case
is the round still concentric to the brass,
Ever see new rounds come out of the can dented
How do the dimensions of the failed brass compare to fire formed brass
is there evidence on the locking lugs,
Is there evidence in the carbon/phosphate on th e feed ramp,
how many rounds are you loading in what capacity magazine
Is it always the first round in a fully packed mag
What if you load one less
Are the mags preloaded with an opportunity to collect dust, dirt, pocket fuzz on the top round
Get in the habit of ‘seating’ the rounds against the back wall of the magazine by giving the mag a firm tap on the table or the heel of your boot once fully loaded. I even do it again before inserting it in the mag well if circumstances permit.
Etc
Etc

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13

Yup, I always use process of elimination and will continue to do so. I know it’s not how I seat the magazine or how many rounds are in it. I regularly tap the bottom, and never put in a full 30.

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14

If all you have is dial calipers, you can go to the books, or on line, and get cartridge dimensions. The poor man’s way to check the chamber is to have a round with dimensions you have checked ( the exact area of the cartridge that caused the problem in mine had been the area just forward of the extractor grove, to about a third of the way to the neck, the base of the cartridge was just a little fat on the bottom third of it ),and then chamber the round by hand checking for the fit. Upper, and lower separated , bolt out, etc. The round should drop in with no resistance until it hits bottom, and then pull back out, also with no resistance. I found that a lot of the better quality ammo I had was just a little under spec in the dimensions, and the cheaper stuff from europe was just a little over. The event you described sounded almost exactly the same to mine, right down to having to either strike the charging handle to get the round out, or, use a cleaning rod.

Let me know what your’s turns out to be, I’d be very interested.

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15

I agree with @DS-1 in checking the problem child rounds but to get a pretty accurate dim of your chamber measure some of the fired cases. If there are/were case variations they will also show up in the fired cases. The largest measurements you find will be most representative of your actual chamber size. Brass when fired actually expands to fit the chamber then reduces all in the instant before the bolt/extractor yanks it out of the chamber. This is also one of the easiest ways to check if you are over pressuring an AR. Look at the face of the brass base, if there are circumferential scratches on the face you are over pressuring the round because the case is still stuck to the chamber as the bolt is rotating to unlock.

Since the ammo was made as 300 BO they “should” be pretty consistent but as noted above mebby not.

Cheers,

Craig6

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16

I knew you had a lot of experience with rifles and would probably know what was wrong. I’m just a pistol guy, but read about most things firearm-related - armament, laws, self-defense, etc. I try to be informed, even if I lack personal experience in the subject matter, I still need to know, as I am frequently asked questions being known as the “gun guy” in my milieu. Also, being here, with people like you, with many years of experience with hardware I don’t use, helps keep me informed.

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17

I would still get some headspace go/no go gauges. You mentioned it shipped minus the BCG, which you added. The bolt assembly/bolt face is a critical part of headspace. So if it was not shipped with a bolt assembly/bolt face matched to the barrel and chamber, it is still something definitely worth checking.

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18

Go/ no go gauges is the next step i would take. Different manufacturers have different quality control so tolerance stacking becomes an issue

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19

The 10 round mags I purchased for my 5.56 pistol build jam every time when I load 10 cartridges, with 9, all functions well, guess mag springs need to break in. My 30 round mags all work fine with full 30 cartridge load

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20

Random question but is the Rifle Cerakoted? I got my wife a rifle that is fully cerakoted and she tried shooting it and had a few jams at the start. She came home from the range and told me, I asked if she cleaned the rifle and she said “it is brand new, you don’t need to clean it”… I laughed and broke down the rifle ( I noticed it was a bit stiffer than just your average new gun, this was also the first cerakoted weapon we have gotten). I did a full clean and lube just like you would do in the military. I then went back to the range and had no issues the next day shooting it.
Others may have different experiences but when I get a new gun, I clean it and lube it before I shoot it just in case. It helps the breaking in period and I have had nearly 0 jams on any new weapon doing it this way vrs just pulling it out of the box and shooting where I have more jams during break in.
-outside of this, I would use gauges to check the pressure

  • if you built it, possible disassemble and re assemble and make sure nothing was done wrong?
  • if it, continues to happen, contact who ever made it and see if they can assist
  • what type of barrel is it? .223 rem, 5.56 nato or .223 wylde? What ammo are you using?
  • Inspect the ammo prior on the next course of shooting just incase you had bad luck with ammo.
  • if all else fails, find a local gunsmith with more experience and see if he could help you without costing an arm and a leg.
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