Zero Bolt Gap roller question

[bladeworks123]

Drine is on the right track here, but I guess I would suggest double checking the length of your bolt head and the overall length of your carrier. How much cocking tube gap do you have with the standard 8mm rollers in? Could be that you had zero gap and a ground bolt head, with a shortened carrier to get CT gap on the ground head. Best to get measurements of everything so that you can get the big picture of what is going on. Especially on a Century gun.

See if you can get your hands on a pair of calipers to measure the bolt head, bolt windows and CT gap, You can use a ruler to get the overall length of the carrier. Get the following measurements and report back....

Bolt head length
Carrier length
CT gap on the standard 8mm rollers
Bolt head window width

[bladeworks123]

Can someone sticky this thread or at least add the information to the first post in the delayed roller blowback sticky with the bolt gaps?
My bolt gap is zero and I just got around to measuring the rollers. They are -2s from century. If I had gotten +8s it would probably be too high, .0196 which isn't max I guess. Should I go +8 or +6? +6 will give me .0157

My bolt carrier also has two spot welds on the end of it (on the cocking tube end), wat.

Same goes for your rifle. It's easy to assume that everything is right, but one wrong assumption throws everything off. -2 rollers is a sign of barrel not pressed deep enough. That would also explain the two dabs of weld on the end of your carrier, put there to increase the length of your carrier to match the shallow barrel press. But, you need to do the same on your rifle as sevensixtytwo. It's easy to assume that everything is right, but one wrong assumption can throw everything off. Remember the abbreviated rules..

Fix bolt gap first
Verify bolt gap is not artificial, (ground bolt head, carrier at rest on cocking tube stop, etc.)
fix CT gap.

On yours, you may very well be able to put in standard rollers and then get your carrier down to the correct length. But make sure everything is in spec before you start.
The chart of roller sizes vs gap is good to go in situations where you have all in spec parts, it is an excellent tool for getting an idea of what you need to do for rollers, but is not always absolute gospel, depending on what might be worn in the rifle, but it won't vary by much in my experience unless you have badly worn windows or if you have one window or roller, or both, that are worn more on one side than the other. Example, I recently worked on a gun that gapped .008 that had one window badly worn on the left side and the window on the right side was fairly good. It had an 8mm roller in the bad side and a +4 in the good side that only measured 8.03,,,,, Put in new plus four rollers and a good bolt head and the gap went to .013, the carrier was the right length but I had to shim inside the cocking handle support to compensate for the CT gap being too large.

[TheOnlyDoor]

Yeah Im going to have to buy a caliper I guess.....just the cheapest ones are like 40 bucks.
I went ahead anyways and ordered a new (unused) bolt head and carrier from apex, the ones on this page...https://www.apexgunparts.com/index.php/cPath/23
Now I also ordered a set of +4's.
So now I'll have the unmarked century's rollers, a set of 4's and a set of 8's.
When I installed the 8's I went from .000 to .015 BG, but coudlnt charge the handle(yes the handle opened just fine it just wouldnt unlock the bolt)
So do you think Ill be fine just installing the new bolt and carrier?

[bladeworks123]

....When I installed the 8's I went from .000 to .015 BG, but coudlnt charge the handle(yes the handle opened just fine it just wouldnt unlock the bolt)
So do you think Ill be fine just installing the new bolt and carrier?

Possibly,,,,By putting in parts that you know are in spec., you have eliminated the need for checking your old bolt head and carrier right away. You will just have to start over with the new bolt carrier assembly and go from there. If it were me I would start out with the plus 4's and see where that gets you, you may find that on a new bolt head, you will not get the +8's to pass through the roller windows. Do yourself a favor and check the overall length of your old bolt carrier against the length of a new one,,, that will pretty much tell you if you might have trouble with the new one bottoming out on the cocking tube stop,,, A new carrier is right at 277 mm (10 1/16") long. If your old one is short, that gives you a heads up for when you put in your new carrier assembly and lock it in, you can make sure that you have CT gap so you are not getting a false reading, and prior to letting it fall under pressure of the recoil spring the first time and whacking the beejeezus out of your cocking tube stop.

[TheOnlyDoor]

It'll be a week before i get the parts in . I also found a digital caliper on Amazon for 25 bucks, so Ill measure the old and new parts and attempt a reinstall a couple of ways......otherwise I'll be back for sure to pick your brain again....

Thanks for the help!

[TheOnlyDoor]

Ok I got the NEW parts in from apex, still waiting on the caliper from amazon , so hers what ended up working...mabey you math nuts can figure it out and tell me what ultimatly was wrong.
Original situation:1) Century Arms Cetme: used bolt head/carrier, unmarked rollers....Charging handle operates just fine...ZERO bolt gap.
2) ordered +8 rollers(same bolt head/carrier)...now .015" bolt gap...Charging handle will open but NOT unlock bolt.
So I bought a NEW Bolt head and NEW Carrier from apex....
1)New bolt head/New carrier, unmarked rollers..now .006" bolt gap..charging handle opens and pulls back with no resistance...have to shake rifle downwards to have assembly fall back in place...
2)New bolt head/OLD carrier and +8 rollers........012" bolt gap..charging handle opens and operates flawlessly... yay!!!!!
So what do you guys think the problem was based on the info I gave?.........BTW if you notice the +8 rollers went in the NEW bolt head just fine(just had to work them a bit).

[bladeworks123]

Your new bolt carrier is missing the recoil spring guide bushing from inside the recoil barrel. I would suspect that most of your problem was bolt head window but not all of it. You will Oprobably find what I suggested before,,,that your bolt head had been ground and the carrier was modified to compensate. If you are getting more bolt gap with the old carrier, I would check to make sure that you are not getting false bolt gap with it in there. Some of the new bolt carriers do not have the bushing in them. Look inside the recoil barrel on both carriers and you will see what I am talking about. If you need a bushing for your new carrier, and Apex doesn't have them, I have some here in my shop.

[TheOnlyDoor]

I tried to send you a PM but not sure it went through,
I look inside both carriers and did see what looked like a choke in the old carrier that was absent from the new carrier.
I also checked both apex and RTG and didnt see anything labeled carrier bushing...so If you have extra that would be great.
It'll be a few weeks before I have the cash again, just let me know how much and how I can pay you.
By the way how do you get/secure it in the recoil barrel?
Thanx again for your help.

[bladeworks123]

I apologize, I just noticed in my previous post that I called it the recoil spring guide bushing,,,It is actually the recoil spring carrier bushing. The recoil spring guide bushing is the small bushing at the end of your recoil spring guide on the back plate.
The recoil spring carrier bushing is what the recoil spring guide bushing operates against. It is a spring steel split bushing, and it can either be pressed in or carefully driven in from the rear. There is a shoulder at the front of the carrier barrel that it presses against that keeps it from passing through. Some of the NOS bolt carriers come with them and some don't. Trying to get the old one out of your old carrier is a struggle sometimes. It's a lot easier task just to put a new one in. Apex doesn't show them on their site, but you might give them a call and ask them if they have any, I'm pretty sure they are aware of the absence of them in some carriers. Like I said, if they don't, I do, but maybe they will send you one no charge if they have any, or exchange your carrier for one that is truly complete. They are pretty good folks.

[Splinter]

Been following this post since I got my CETME a few weeks ago. First, I had spec but false bolt gap with the ground bolt head and zero CT gap. Ordered a new complete bolt from Apex and now have zero bolt gap and zero CT gap! My bolt carrier is 277mm. I have the standard rollers in. Will replacing the rollers fix my problem or is this a "parts" gun? Thanks!