If a person was to take a .75" barrel with an existing .75" front sight base pinned and cut (turn on a lathe) the area of the barrel in between the front and rear portions of the sight base where taper pins go in down to .625" and in front of the FSB to .625 will that sudden cut cause a weak spot and potential problem due to normal barrel whip.

To me, it's not much different than the M203 cut on an m4 barrel except that it supporting the front sight base?

Has anyone ever shot a barrel like this or made one?

Like this?
Attached File

Yes taking the top barrel and cutting around the front sight base on a lathe to create the bottom barrel but still using the same front sight base from the top but have the identical appearance of the bottom one.

Yes to make an a Hbar look like a A1 barrel but still use the original pinned front sight base. instead of fitting an A1 .625" FSB cut around the .75" FSB so it looks like a .625" FSB but is not .625

RRA does this with their light weight profile barrels:

http://christianarmoryworks.com/images/RRA_Barrels.gif


Though my new favorite is the FAXON GUNNER profile.

DTI

DTI

Like this to capture the true appearance of a A1 barrel skinny barrel including the area between the FSB portions that are pinned yet use the .75" FSB

Don't see why it wouldn't work.  Maybe try to round out the corners at the base a little for strength I suppose; but in truth I've not done anything like that, so can't say I speak from a position of authority on this.  It is interesting that pretty much nobody anywhere does this....  My guess is the weight reduction for such a small spot is pretty trivial.  And structurally, since there are things going on there, There might be some benefit to haveing a little mass at that spot.  If the goal is weight savings, there isn't going to be very much.  If the goal is aesthetics, you kind of can't really tell it's thick there in a RRA LW cut; unless you are really looking for it.  And unless you cut it perfectly, it might look a little strange with this approach as well.

Me - I'd probably just go all skinny and just a skinny gas block. Or just keep it full thick at that spot like everyone else does.  This seems like a lot of effort to avoid just buying the skinny FSB.

Why though, when .625 blocks exist and are inexpensive?  

Unless you machine to perfect tolerance, you will see the "ring" left behind on the barrel next to the gb...

I don't think the juice is worth the squeeze.  Are .625" barrels that hard to find?

Once thought of this trick, but never actually tried it.

I’m no mechanical engineer, but I wouldn’t have much heartburn over the the corners you indicate acting as stress risers — the barrel in between is stiffened by the FSB.  If anything the forward step-down might concern me more.

More generally though, I’d hesitate to do this to a barrel that’s a good shooter, just because taking a lot of meat off the exterior can change the bore dimensions.  I wonder what people’s experiences have been with reprofiling from .750 to .625 ?

Also, don’t know whether it matters to you, but you will have to keep the .750 handguard retainer....

Actually, true .625 barrels are hard to find some companies like the RRA and DTI even with some of their skinny barrels are using .75" front sight bases as noted in some of the posts above. .625" blocks are not that hard to find but if you have a barrel that has a front sight base factory pinned and it's just a boring ole Hbar and you want to build a low budget GUA5 or XM177E2 clone finding that exact profile is not in stock and even so, do tend to cost more.

Taking a 16" Hbar with factory front pinned FSP and making it into an XM177E2 clone. Front sight pinning is not all that hard to do but it does take some precision to make sure the FSB is not canted then drilling and reaming it's a lot of extra work and unnecessary IF a .75" can be used to achieve the same results without damaging the barrel.  .75" FSB are a dime a dozen where a .625" will typically have to be purchased new.

Going from HBAR to this