No Bolt-Gap with +4 Rollers?!

[ClockWork]

Ive looked around and haven't found this problem to be addressed here. Forgive me if it has.

My Century CETME had a bolt-gap of .003". "Factory" rollers that came in the rifle measured 8.03mm; +2 rollers. Got some +4 rollers. Now I have no bolt-gap?! I allowed the carrier to "slam-home" and couldnt get any gauge into the gap(started at .004" and on down). Pulled the trigger and obviously got the same result. The bolt-head is the correct length of 1.835". With either set of rollers, there is no play what-so-ever in the charging handle assembly when the rifle is in full battery. Which I am guessing is very telling to the situation.

Is there anything I can do short of having a 'smith re-set the barrel/trunnion? Do I have a parts gun?

Thanks and sorry if there is something obvious here I am ignorant of.

[cimmaronkid]

We just haven't gotten around to this one yet. What is happening is that the stop in the cocking tube is not allowing the bolt assembly into full battery and giving you a "false" bolt gap reading. You can remove metal from the front end of the bolt assembly (the top part above the bolt head where the recoil spring/guide goes) or from the BACK END of the cocking handle support until you have a gap not to exceed .020". Then you can get a true bolt gap. I would also get a locking piece (I think Jorge still has some) as well and you should then be in good shape. We call it the "dime trick" as a dime is close to the .020" gap needed. Go slow as a little goes a long way when removing metal.

[GreenWolf]

What is happening is that the stop in the cocking tube is not allowing the bolt assembly into full battery and giving you a "false" bolt gap reading. You can remove metal from the front end of the bolt assembly (the top part above the bolt head where the recoil spring/guide goes) or from the BACK END of the cocking handle support until you have a gap not to exceed .020". Then you can get a true bolt gap.
+1 to the part about the "false" bolt gap. Keep in mind that after shaving off a bit of metal here or there, you might still have a bolt gap problem. Think the problem through and go easy.

[M1 Tanker]

Whoa hoss, don't be doing anything yet.

If the bolt carrier rest on the cocking tube stop, that will INCREASE your bolt gap reading. While your bolt carrier sitting on the cocking tube stop is a problem and will beat the stop to death...it is NOT the problem.

Before I did anything I would light file just a tad off the bolt carrier so it no longer rest on the stop.

Then you are going to have the problem of bolt gap and from the sounds of it your gun is grossly out of spec. Repressing your barrel maybe the only option and we will get to that.

I just want you to have a clear understading that the necessary gap between the bolt carrier cocking tube stop isn't the cause of low or no bolt gap.

[Big Steve]

I wouldn't take anything off the bolt carrier until you try some new parts (locking piece, bolt head). Because if these parts indeed open up your bolt gap they will be pushing the carrier towards the rear of the gun increasing the gap between your cocking handle support and the bolt carrier. But don't shoot it until you fix it because it now has two problems.
By the way the "dime trick" has nothing to do with removing metal from the bolt carrier. The dime trick is when you have excessive gap between the bolt carrier and the cocking handle support. This condition makes the gun hard as hell to unlock so you can cock it. If you put a dime in the cocking tube before you install the cocking handle and support it takes up some of the gap and makes the gun cock easier. It is NOT safe to do this and is only a way to diagnose a problem and needs to be fixed by other means.
Unless you have very noticeable wear on your locking piece and where the rollers make contact up in the sides of your bolt head you are probably not going to get much of a bolt gap increase by spending money on these parts. You might do better saving it to go towards a barrel re-press.
Good luck!
Steve :machinegun:

[jfowl31]

+1 on Tanker's post. The carrier hitting the stop will increase gap not lower it because it stops the carrier while allowing the bolt head to continue, thus increasing the gap between the 2.

If your new +4's measure out correctly and really are +4's, then Id get a new bolt head and LP, and see what happens. If that still doesnt change things, repressing the barrel is in order. But with .003 and +2's, you MAY be able to replace the bolt and LP, and get back into spec... its worth a try for sure.

[drine]

Has anyone ever got a boltgap less than .004 or so? There seems to be a stopping point at or near that number. I had some really funky readings with new bolt head, LP, +4 rollers. Don't remember them all now.

[jfowl31]

Drine, I think your old readings are still on gunboards... maybe not ALL of them, but there were a bunch if I remember right.

I personally like running mine with a low-ish bolt gap. I have it at .007-.008 right now, and the recoil, and functionality is perfect. It seems to run more efficiently, and is more accurate with the low bolt gap. The recoil is less because more pressure and force is used to unlock the bolt, and therefor the bolt isnt slamming back as fast. I also got an accuracy increase, and my theory is that because the bolt's staying locked longer, maybe the bullet gets a better burn or something, or maybe its just because of the lower recoil, I can focus more on the aiming and firing. No REAL clue, just speculating.

[drine]

Sounds like the guy above has some of the same funky readings I had. I know that with a new bolt head, LP, and plus four rollers, I got .014 I think. Plus 4's only with the old parts gave me .007 and I started out at .004. That's why I think that .004 is the lowest you can go. You have to be setting on the trunnion at some point. I had the barrel out and got a .004!

[jfowl31]

I imagine some trunnions are tighter than others... and maybe on some trunnions, they won allow the rollers to push out far enough to let the gap get below .004. But with the rest of the rifles that that is not the case... ZERO bolt gap is measured quite often.

[texlurch]

Mine was at .004 with std rollers. Added a new LP and no change. Added +4 rollers and went to zero - .001 gap. Thru all this it wouldn't unlock correctly to eject, and kicked like a bolt action. Bolt measured 1.834.
Swapped the entire assembly for the one out of my parts kit, and now have .007 gap, and it runs correctly. Still plan to press the barrel and replace with the new one from the parts kit.

[M1 Tanker]

Mine read .003 for awhile.

[ClockWork]

Thanks for the info, all. I guess my next step is to get a parts kit and swap some bolt parts. If that doesnt work, I dont know what Im going to do. Will keep up-to-date.

Thanks again.
Jake

[drine]

Jorge in Spain(vanLoos is his gunbroker name) has a lot of CETME stuff and RTG has G-3 stuff as in rollers, etc. that will work, just check the cross reference for things that you CAN"T swap between the two.