M4 RAS foregrip barrel flex and bolt wear?

[ta0117]

This is something I think I read before, but can't find the article anymore. Essentially, it says that some of the problems contributing to bolts breaking in early M4s with non-free float RAS handguards is the foregrip. When operator grips the broom handle foregrip and pulls it towards the body to control recoil and what not, the slight flex in the barrel means that some lugs experience more stress than others, especially if the foregrip is pulled tightly. I can't find where I read this, but I wonder if this is another one of those urban myths. And if so, wouldn't compensators also have this problem, since they push the muzzle down from the venting gasses?

[markm]

If the barrel flexed, it would leave the extension squared and not be a problem. I.E. the barrel would curve along its length.

Now receiver flex is a real issue. VLTOR did some laser measuring on receiver flex during the MUR upper development. This could present the problem you bring up.

To me... not worth worrying. The RAS has some spring to it in the Delta ring, but you you're a guy who really pulls on the fore grip, a FF with a MUR upper would be good.

[rpoL98]

the upper half of the KAC RAS uses a screw-clamp to lock on to the barrel nut. If you get the UK/SAS lower-half KAC RAS, it also uses a screw-clamp to lock on to the barrel nut. with top and bottom screw-clamp lock-on, that's a pretty solid hook-up to the barrel nut.

[lysander]

This is something I think I read before, but can't find the article anymore. Essentially, it says that some of the problems contributing to bolts breaking in early M4s with non-free float RAS handguards is the foregrip. When operator grips the broom handle foregrip and pulls it towards the body to control recoil and what not, the slight flex in the barrel means that some lugs experience more stress than others, especially if the foregrip is pulled tightly. I can't find where I read this, but I wonder if this is another one of those urban myths. And if so, wouldn't compensators also have this problem, since they push the muzzle down from the venting gasses?
No.

The maximum diameter of the bolt carrier is 0.9955". The bearing length is 2.536".

The minimum diameter of the hole in the upper is 1.000"

That gives a clearance of 0.0045".

That gives an allowable tilt of the bolt carrier of 0.100 degree, not even accounting for the additional tilt of the bolt inside the carrier.

You are not going to bend anything a tenth of a degree, let alone more to cause trouble. You might twist the upper quite a bit, but you are going to get the first three inches of an upper to deflect that much while installed on a lower.

Besides, lug failure was a very well understood issue.