Ground Bolt and Rollers...

[MicroPilot]

Heres what I have:


CAI Stamped CETME with a bolt measuring 1.824" and rollers with a diameter of .312" (7.94mm).

Bolt gap measures >.028" and there is no gap at the cocking handle.


Will replacing the bolt and rollers be the best route to getting this gun back in specs?

[jfowl31]

well.... those rollers are small for one. 8.0 mm are standard, 8.02 are +2, and 8.04 are + 4

I dont know what you have there.

if you r gap is .028, and your bolt length is 1.824, it means that your bolt is .011 too short (nominal is 1.835), so your true gap is .017, so to answer your question... replacing the ground bolt head and rollers SHOULD get everything current and into spec.

Sometimes the rifles can do funny things when you replace parts, but typically, they dont.

Id say buy a new bolt head, and some standard and +2 and +4 rollers and see what combo gives you the best combination of perfect operation and low recoil.

And maybe remeasure those rollers to see if we can confirm the they are in fact "-6's" as you posted above.

[MicroPilot]

I double checked the rollers and they are 7.94mm

[SSwee]

No gap at the cocking handle is going to throw everything off. I've been through that with mine having a ground carrier from CAI and putting a non ground carrier in it's place trying to get a better bolt gap. If he has a bolt gap of .017" but is hitting the cocking handle the bolt gap may actually be quite a bit less. It would not be easy but may be necessary to pull the cocking handle and piston to check the bolt gap accurately. It will also give a more accurate measurement on the interference with the cocking handle.
SS

[bullseye]

I double checked the rollers and they are 7.94mm

Contact Big Steve about your rollers, sounds like they are undersized and he might have use of them.

[jfowl31]

I didn't see the no cocking tube gap... that needs to be addressed first so you can get an accurate bolt gap measurement.

Even if that measurement is right, and they ARE in fact 7.94 mm... Ive nver heard of rollers that size. -6's are not something Ive ever seen for sale, for any of the Hk series of rifles, though Im sure Perro or M1 will chime in here in a second to enlighten us on what -6's are used for.

So should he just grind the carrier to get some cocking tube gap like Century did? or is there a bter fix that doesnt involve cutting it off and resetting it?

[MicroPilot]

OK,

With the cocking handle assembly removed my bolt gap goes down to .009". Does this mean I just need to remove .020" from the end of the carrier tube? If it would be better to buy a new bolt and rollers, I'm not opposed to doing that instead.

[SSwee]

Is that .009" after subtracting the .010" or .011" for the ground bolt head?
If it's not then your down to no bolt gap. +4 rollers will help but I don't see it fixing your problem. With the .028"+ you were getting before, you have about .020" interference on the cocking tube. If you can get the bolt gap right, the cocking handle gap should be OK. Gear shanty has a bolt carrier assembly for $28.00. He's a righteous guy to deal with. That would be where I would start. There is a chance that you could replace the bolt carrier assembly and still have no bolt gap. In which you may be down to repressing the barrel. If I'm off base let someone speak up.
SS

http://www.gearshanty.com/shooting-1.htm

[MicroPilot]

No, I did not account for missing length of the ground bolt.

I will order a bolt assembly tomorrow. Should I get extra rollers also?

Did Century remove material from the front or rear of the bolt?

[SSwee]

They grind off the back of the bolt head.
I get +rollers from RTG. It don't hurt to have on hand but wether they will be needed will depend on the effect of replacing the bolt carrier assembly. If it gives you a bolt gap of .005" or .006" then the + rollers should be a benefit. If there isn't a bolt gap with the different bolt carrier assembly then the + rollers won't be of much use. My CAI sporter is at .006" bolt gap. It shoots good now but if it looses any more gap I'll be pressing the barrel.
SS

[jfowl31]

So with a gap of .009 and the bolt being .011 short, technically, right now your gap is -.002". Start with a new bolt and LP if you can, and some regular sized rollers. See what that gives you... while youre at it, you might as well buy some +4's as well, just incase you are low, youll save on time and shipping costs.

Youll still need to mess with that carrier even once you set your gap though. Right now, youre charging mech is holding you bolt open by .019 since it was .028 before and .009 after. So your carrier is .019 too long right now. Once you get a new bolt and all that, your carrier still could be too long... say you get your bolt gap up to .014... your carrier will still be .005 too long... Then, even if you just grind off htat much, as soon as your gap falls, youll be resting on the charging mech again. So if you get your gap to .014 hypothetically, youll want to have at least .014" of cocking tube gap so that even as you gap falls, youll never rest on the charging mech.

thats a sorry explanation of how it works, but hopefully you got the point. If not, just get the stuff to fix the bolt gap, and then we'll walk you through fixing the cocking tube gap... you dont want to make the gap too big, or the thing will be a bitch to cock.

[M1 Tanker]

You have multiple problems:

1. Your bolt carrier is resting on the cocking handle stop, this is bad and you must file a tad off the end of the bolt carrier so there is a ever so small gap in there. You should be able to start to pull the charging handle out, before the carrier moves to the rear.

2. I have never heard of -6 rollers, so they are Century specials or just worn out. You need to realize they ground the bolthead in the first place because something was out of spec. A new bolt head might bring your bolt gap to zero, and maybe more with new rollers. You need to get an accurate measurement once you remove some material from the bolt carrier and its not resting on the cocking tube stop and giving you a false gap.

[MicroPilot]

You have multiple problems:

....You need to get an accurate measurement once you remove some material from the bolt carrier and its not resting on the cocking tube stop and giving you a false gap.

Are you saying to remove material from the bolt carrier with the current parts?
Isn't the gap measured with the cocking handle removed the accurate bolt gap (allowing for the modified bolt)? Wouldn't it be better to get proper sized parts and then work from there?

I am concerned that something else was out of spec which caused Century to grind the bolt head.

[M1 Tanker]

Micro, sure you can wait until you get the new bolt carrier, which will probably be even longer then the one you currently have.

I'm not sure how you checked bolt gap with no charging handle. Part of the procedure to to let the bolt fly home and lock up, then pull the trigger. How did you do that with no charging handle? I don't think you will have a true idea as to what you have until you get the carrier off the stop.

[MicroPilot]

...
I'm not sure how you checked bolt gap with no charging handle. Part of the procedure to to let the bolt fly home and lock up, then pull the trigger. How did you do that with no charging handle? I don't think you will have a true idea as to what you have until you get the carrier off the stop.

I removed the charging handle assembly, re-assembled the rifle, and then used a large steel punch to cock it (through the cokcing tube slot) and then let it slam home. Pulled the trigger, and then measured.

What problems might make Century grind the bolt? It's starting to sound like I'm going to have to repress the barrel.

[M1 Tanker]

Micro, when century built these rifles, they used barreled trunnions and numated internals. In many cases they parts were just so worn they had zero bolt gap. So, their "repair" was to grind material off the bolt had to give it gap...but the parts are still worn out. Instead of replacing parts or pressing the barrels, they chose to destroy rifles instead. You won't really know what you have until you get new parts and see how they fit.

[MicroPilot]

I ordered a complete bolt carrier. This is the bolt carrier, bolt head, rollers, locking piece and firing pin.

I finally received these parts today. After dis-assembling the new parts and measuring to make sure the bolt head and rollers were the proper spec I re-assembled and installed them into my rifle WITHOUT the cocking handle assembly and measured the bolt gap at .016". I then assembled the rifle with the cocking handle assembly and again measured a gap of .016". There is also now a very small amount of play in the cocking handle assembly when the rifle is in battery. I then took it all apart and lubed everything up and then went out on the front porch and and fired off a few rounds. It works great!

My guess is Century used the undersized rollers which threw everything out of whack and to compensate they ground the bolt off.

I noticed a few things about my new parts.

1.) My old firing pin was in 2 pieces, broken right where the cone in the rear stops tapering.

2.) The new carrier doesn't have the groove milled all the way through. I've read that the slot being milled all the way through is a compliance feature so that the carrier can not be used in a FA configuration. Will this cause me problems if the ATF ever visits?

3.) The old carrier also has "wings" on the bottom where the slots on the bottom of the new piece go all the way back. I've never noticed the "wings" difference in the carriers before. I'll post a pic later on tonight when the camera is finished charging.

[jfowl31]

You probably should mill the slot in the carrier just to be safe. the other featureson the trigger pack make it non-FA, but as Perro will state, it does specify that for HK type weapons, the groove needs to be machined to be compliant.

Youre firing pin shouldnt have been in 2 pieces....

You seem to have totally fixed the sucker up... how does she shoot???

Keep an eye on the cocking handle and make sure that it maintains gap there or youll start to self-destruct the gun. Basically evey time you check the gap, check the cocking handle for gap as well to make sure the gap hasnt shrunk enough to start to rest on the handle.

Congrats on getting her fixed up though! Most peopledon't even ever get to see their rifle sit up there at .016 so thats a major plus. Youve got thousands of rounds ahead of you til the rifle drops below spec, so sit back and enjoy!

btw, did you just use standard rollers?

[MicroPilot]

The new rollers are standard size.

Here is a pic of the old carrier:

http://www.users.kih.net/~micropilot/PostedPics/2007-04-23 066 small.jpg

And the new one:

http://www.users.kih.net/~micropilot/PostedPics/2007-04-23 067 new small.jpg

[Reloader_26D]

Micropilot,
From whom did you order the complete bolt carrier assy? I've read the thread, and I'm experienceing the same issues. I want to get non-modified parts, and start clean. Thanks!

[jfowl31]

thats a funny looking bolt... Is that a Modelo A or B bolt--- directed at the resident Cetme Gurus... Ive read that the B's had lightened bolts to shoot 7.62 CETME ammo... that seems to be what I'm seeing there.

Maybe the B bolts are shorter????? and that ones not ground at all?????

[hunter_la5]

I'm pretty sure that the "old bolt carrier" that you have is the model B bolt carrier. It's the same one I have in my gun

[rustypirate]

The top pic is a Model B bolt carrier with the lightening cuts on the sides, but they were quite often used in Model C rifles.

The bottom one is a Model C bolt carrier without the semi auto modification cut.

[SteelCore]

Could. Needat dremel it out at least.

Old carrier was definitely a Mod B.

[jfowl31]

so was his B model bolt in fact ground or is it shorter from the factory?

[rustypirate]

Jfowl31,

What are you referring to, the bolt head? I cannot see enough of it to determine if it is shorter thanthe other one, or if it is ground.

If Micropilot were to give us a shot of the two complete bolt heads we could probably tell.

The bolt carriers should be dimensially identical with the exception of the missing material on the sides of the Model B one

[jfowl31]

sorry, I wasn't very clear, but you answered my question regardless... I didn't know if the B bolts were dimensionally different than the C ones. I figured since he had a B carrier that he had a B bolt head too, and he's already told us it was shorter than normal. I didnt know if the BH's were all dimensionally the same, or if his was shorter simply because it was a B bolt... But if they are the same part and the only difference between is the carrier, then, I guess the old ground bolt head is basically trash right?

[rustypirate]

I would keep it as an emergency spare, but it is basically worn out.

[kevin]

do you still have the small rollers? i could use some that are undersized

[MicroPilot]

Yea, but I think I'll hold onto them. Sorry.

[texlurch]

Good job on getting it fixed, AND recognizing the ground bolt and it's issues.

[Big Steve]

Glad you got your gun back in shape! I believe I heard that HK 21's started with -6 rollers and went all the way up to + 6's. As they wore quickly as belt fed full auto's. Don't know if + or - 6's are safe in a G3,91 or a Cetme.
Steve

[Tom Doniphon]

I don't think those are -6 rollers, just worn out. Both Apex and RTG had complete new bolt and carrier assembies for sale. I think Apex is out. I know where they got them and I don't think we will see new ones for sale again anytime soon. Rusty we need to make a sticky showing the different ways to fix the short cocking tube problem.

[tanstaafl4y]

Congrats another rifle fixed by <font=strikethu> cetmerifles.com </a> er umm militaryfirearm.com

Don't forget another member/vendor
http://www.gearshanty.com