+ Size Rollers

[JayGeeWentWorth]

Ok, ok, I know the CETME bolt gap issue has been beat to death many times over on these forums, but I still have a question. I understand that the significance of the bolt gap is that it indicates the wear of the internal components of the gun and that the actual gap itself is of little importance. I also understand that century ground some bolt heads down so that the gap was in spec and that this is dangerous because it masks the true wear on the rifle. The thing I don't understand is using +size rollers when the bolt gap goes to zero with standard sized rollers. To me, it seems that using larger rollers is the same as grinding the bolt head in the sense that it gives a bolt gap that may be in spec, but is deceiving about the actual wear of the rifle. Obviously, I'm not an expert by any means regarding the bolt gap, but it seems like +sized rollers don't do anything except trick one into believing the CETME has underfone less wear than it actually has. If one of the experts on bolt gap issues could please explain to me why it is better to use larger rollers than grind the bolt head it would be much appreciated.

[SSwee]

Grinding the back of the bolt head changes nothing but the appearance of having a bolt gap. Same as putting a new paint job on a POS lemon. It changes the appearance but it's still a POS lemon.
On the other hand, the rollers are an integral part of the pieces that give you bolt gap. When you change their size you directly effect the bolt gap. You take up some slack from wear of the other pieces by putting in oversized rollers. Same as putting oversized bearings in a car motor. You're not replacing all the worn parts but the ones necessary to give a little more life to something before a complete overhaul is needed.
SS

[Big Steve]

It's late and I can't explain it completely but when you create more gap with larger rollers the bolt unlocks faster and easyer creating less pressure than if you create fake bolt gap by grinding the bolt. This has to do with where the rollers start out on the locking piece. It is called timing. Think of what the system is called. Roller Locked Delayed Blow Back System. The longer it takes to unlock the bolt the more pressure is created. The more things wear the harder and slower it is to unlock the bolt. All the larger rollers do is replace metal that has worn in the exact same place.
Steve

[hunter_la5]

like they said, the rollers actually adjusts the bolt gap and unlocking timing.

grinding the bolt, however, only changes what size feeler guage you can fit between the bolt and carrier. nothing more.

[rustypirate]

To put it simply, + size rollers compensates for the lost mateial on the other worn parts like bolt head, locking piece, and trunion by increasing the size of the intermediary part.

this is similar to replacing the locking shoulder on a FAL rifle. If the bolt head wears down, you replace the receiver locking shoulder with a slightly larger one to compensate for the worn bolt head.

[JayGeeWentWorth]

K, thanks for the info guys. I think I understand now. Luckily, my CETME still has a healthy bolt gap with the original rollers so it should have a lot of life left, but it's good to know that +size rollers can prolong the life of my rifle when the time comes. :thanks: