Seekins SP-10 gas block mounting question

[rmiked]

I’m new to ARs, don’t own one yet. I like the Seekins SP-10. I contacted Seekins after watching a video they created to show how to adjust the gas block to get ideal spent cartridge ejection patterns. I noticed one of the 2 set screws which attach the block to the barrel, was sticking out further than the other. I suspected only one of the set screws was dimpled into the barrel. Seekins confirmed that is the case. Is this an issue for securely mounting the gas block? I can’t imagine a set screw butting directly into the side of a round barrel, creating appreciable retaining force? The contact area would be infinitesimal because the barrel is round and the set screw end has to be flat. The intersection of a flat plane with a cylinder is a line at best. For people that build ARs here, are the set screws normally both dimpled into the barrel ? I don’t see how a non-dimpled set screw could work. I appreciate any experience here as I am new to ARs. I was ready to buy the SP-10 in 6.5 CM until this design feature bugged me. And then these rifles have become scarce with the store I was ordering from. Back order only right now.

 

[MSTN]

Barrels typically have one dimple opposite the gas port. For the longest time, gas blocks just had one set screw. It was sufficient, too.

The better gas blocks nowadays typically have two set screws. But, the spacing is unfortunately not standardized. Unless provisions are made for the precise spacing of dimples for these screws, the forward set screw in the gas block doesn't get its very own dimple. So, this set screw will be "proud" compared to the one behind it. Use a thread locker and 25 inch-pounds and you won't have the first problem.

 

[346ci]

MSTN covered the set screw part, there are a metric ton of gas gun barrels running fine with one dimple.

If your dealer has an Lipsey's account, they have 2 of the battle worn od green in stock. A Hide vendor may have one also but I'm not sure where the vendor list is, you could ask in this section; https://www.snipershide.com/shooting/forums/sniper-s-hide-px-commercial-sales/

 

[rmiked]

Thanks to both of you for your responses. I will proceed to acquire an SP-10 in 6.5 CM.

 

[bfoosh006]

You can add another dimple if you want.
Just remember, after you have dimpled the other hole, you are kinda stuck with the set screw hole width.

 

[rmiked]

That’s a very good point. Perhaps why Seekins only uses one dimple. Gives user options. I’m assuming it’s not good to drill thru barrel into rifling area. Don’t see much guidance on barrel thicknesses and using a depth limiter for drilling dimples. You could always measure OD of barrel (using dial caliper) at gas block axial location. Subtract caliber dimension (eg, 0.308 for 308), then divide by 2. That will give you thickness at drilling location. Then decide how close to rifling area you want to go. Mark your drill bit with tape or some better method. Stop drilling before hitting that mark. Measure twice, cut (drill) once. I‘m feeling good about the thought process Seekins is using. Just not obvious to someone new to ARs.

 

[bfoosh006]

That’s a very good point. Perhaps why Seekins only uses one dimple. Gives user options. I’m assuming it’s not good to drill thru barrel into rifling area. Don’t see much guidance on barrel thicknesses and using a depth limiter for drilling dimples. You could always measure OD of barrel (using dial caliper) at gas block axial location. Subtract caliber dimension (eg, 0.308 for 308), then divide by 2. That will give you thickness at drilling location. Then decide how close to rifling area you want to go. Mark your drill bit with tape or some better method. Stop drilling before hitting that mark. Measure twice, cut (drill) once. I‘m feeling good about the thought process Seekins is using. Just not obvious to someone new to ARs.

When in doubt.. I just setup the jig at the single factory dimple, insert the drill bit, and then mark the depth with a masking tape flag.

 

[rmiked]

Pretty smart.

 

[rmiked]

I just ordered the Seekins SP10 in 6.5 CM, battle worn OD Green. Look forward to it arriving and running it thru its paces.

 

[TonyTheTiger]

The Hide welcomes it's newest overthinker.

Dimple or no dimple, the grub screw or serrated grub screw that gas blocks come with find a way to bite sufficiently into the round barrel. Is a dimple or two dimples better? In theory absolutely, especially if you have an exposed gas block or GB/front sight post that can catch on things. That said, I've got 4 un dimpled barrels in my dead barrel pile that never once had a gas block move.
You can see this one had two different gas blocks, with different screw spacing. Hence the reason many dimpled barrels are only dimpled at the rear.

 

[rmiked]

Very good explanation. I am a retired Structural Engineer. Forgive my over-thinking. I can see the mechanical engagement of the 2nd screw

 

[Joeg26er]

On a side note: Anyone know the gas block journal size of the stock SP10?