New Bolt Issue

AR/M4 AR Technical Discussion
1

Earlier this week I received a new bolt from a company greatly esteemed on M4C.

I like to have an extra bolt held in the pistol grip of all of my main ARs and this bolt was intended for my new Centurion Arms rifle.

This being so, I pulled the BCG from the CA rifle and replaced the bolt with this new one. Note that the BCG already in the CA rifle is from the same company who made this new bolt that I wanted to test.

With the new bolt in place, I attempted to charge the rifle but was only able to pull the charging handle back as far as the bolt extends from the carrier. The bolt seemed to be stuck to the barrel extension. I ran the charging handle forward and used the forward assist to put the carrier back into its forward most position. Again I tried to charge the rifle but had the same result as before. Frustrated, I yanked and yanked on the charging handle with all of my strength and after many attempts it finally dislodged.

At this point I was worried the issue lie with the new CA rifle since I hadn’t yet fired it. So I pulled BCGs from three other rifles (all from manufacturers recommended on M4C) and tried them in the CA rifle. All of them worked perfectly fine, so my suspicion shifted to this new bolt. I put this new bolt into the carriers that I had pulled from other rifles and tried them in the CA rifle and the issue I mentioned above occurred in all cases. I had to mortar the rifle a few times during these tests to dislodge the bolt. I should mention that I used several different BCM charging handles in these tests to ensure the BCM charging handle in the CA rifle wasn’t the issue.

To be thorough, I used this new bolt in 3 BCMs, 2 Colts, 1 CA, 1 LMT, and 1 Daniel Defense. The bolt stuck in 2 BCMs, 1 Colt and 1 CA. Note that in the rifles where the bolt stuck it would be just as difficult to pull the BCG from these rifles’ uppers after said uppers were separated from their respective lowers.

I presented the bolt’s company with my concern and test results and was told this:

“Based on your information, hand cycling of a new bolt assembly can be slightly more difficult than a bolt assembly that has been shot hundreds of times.
This is completely normal. All [of our company’s] Bolt Assemblies and [our company’s] barrels are head spaced prior to being offered for sale.
We would recommend taking your bolt assembly to the range and test firing it.
*
Please let us know your results.”

Bracketed words are mine.

This doesn’t sound right to me. It seems to me that I’m being told that I should expect a break-in period for this company’s products. As I’ve learned over the years on this site, there is no break-in period for a properly constructed AR.

So, should I do as this customer service rep suggests or is his direction unwise?

Many Thanks!

2

Having to mortar the handle is far past “slightly more difficult.”

Was the chamber empty in doing all this, or were you using a dummy, live, or fired case? I’ve only ever had severely stuck cases when a fired empty case accidentally got reloaded into the chamber. That was a minute of frustration mortaring the thing.

If on an empty chamber, I think there is a dimensional issue beyond mere break-in.

3

Is it one of those LMT finishes with 40 grit texture? If not and the finish is relatively smooth, then it sounds like there may be a problem.

Do you have a headspace gauge to check that part of the equation?

4

The sticking happened with an empty chamber.

5

Ha Ha Ha! No, the finish is very smooth.

I don’t have any way to check the head spacing.

Looking at it, I see nothing amiss and the tension of the extractor seems right compared to that of other bolts I have.

6

If the bolt is unfired, I would return it for a replacement or refund. Based on the BS they gave you, I would go for the refund. Headspace is not the issue if the bolt will not close on a clean empty chamber/barrel extension.
Mark

7

As far as I can tell, the bolt does close on the chamber and then it doesn’t want to let go.

I would prefer an exchange from the company as I think this bolt is one of those rare lemons that great companies sometimes put out. However, it seems that I need to justify to customer service why they should give me an exchange. I had thought that all of the testing I had done would have spoken for itself.

Do you have any suggestions as to what I might tell CS?

8

I had a similar but not identical problem with a complete BCG. I tried a BCM complete BCG in the rifle and it was smooth as silk. I tried the binding bolt carrier group without the bolt and no resistance, which of course there shouldn’t be. I also tried many different cam pins and it still was binding up. Mine would also bind up with other bolts installed. I believe the carrier track for the cam pin was machined a tad off location in my case. I guess a bolt could also have it’s cam pin hole machined a little off location to create some binding. Check the upper for excessive cam pin wear.

9

What did you end up doing with this complete BCG?

10

That their original explanation makes no sense, that you would like a refund for your unfired and possibly defective item, and that they are welcome to look up this thread if they want to.

11

Thank you! Sounds good to me.

12

Update:

I took SomeOtherGuy’s tack and this company has graciously (no sarcasm here) agreed to do an exchange for the bolt.

Thank you all for your thoughts and direction.

13

Does the new bolt hand cycle in your bc ok? Hold the bcg in your hand and cycle it…any probs?

14

I’ve no issue doing that. What’s the thought behind your question?

15

Eliminate the rifle as a problem. So you can push and pull the bolt and it feels like your other bolts? Also any differences in bolts during a careful visual?

16

Ah, I see.

Yeah, I spent quite awhile comparing the problematic bolt to others from the same manufacturer and to those of other manufacturers and can not discern any differences.

17

Sounds like the locking lugs on the bolt are too large front to back or less likely too thick side to side. If you have some calipers you could check.

18

Have you checked if the firing pin can move freely in the bolt ? I just a very short similar situation and it appears my bolt was a little tighter which prevented the firing pin from moving freely which prevented the lugs from unlocking .

Sent from my iPhone using Tapatalk

19

It did move freely in all BCGs that used with the bolt.

20

did you use the old cam pin?

I had a problem like this, and i ended up comparing cam pins with my stash, found that the “incumbent” cam pin was maybe a couple thousandths smaller dia, so I put in one that was a little bigger (thousandths). that worked.

however. it seems that the bolt isn’t fully rotating to the unlocked position. that’s why the bigger cam pin helped, because then the bolt rotation tracked the cam slot better. could also be that the old cam pin was slightly worn.

could also be this suggestion is nonsense in your context. FWIW.