I have heard people talk about a downside of set screw gas blocks being that the screw induces a dimple into the barrel that can affect accuracy. I have access to FEA software that I could quantify the dimple size. I thought this board may find the results interesting:
Setup:
0.750" OD
0.224" ID
Force applied to 0.170" Dimple on bottom (Not sure the actual diameter these are drilled, but it should not impact the results much)
Force: 580lbs (8-32 Set Screw at 19in-lbs of dry torque)
The SLR adjustable gas blocks and Black River Tactical’s MicroPin gas block use 10-32 set screws. I have torqued many sets of McMaster Carr knurled cup tip screws into these blocks at 20-25 inch pounds without issue.
I could run the same model with a taper pin. The only issue is I’m not sure how to quantify how much force the pin puts on the barrel. If I had the taper angle and a distance for how far the pin is pressed in I could use that. If anybody has those numbers I’ll run the program.
A taper pin that fits properly engages the whole taper. That would mean it is meeting metal all the way around from one end to the other.
Therefore, pressure would be more or less of an effort to swell the hole from one end to the other on the part of the pin.
Because part of the pin would be across the bottom part of the barrel, there would be some pressure, but it would be spread across the whole area it contacted.
A set screw is direct inward pressure, concentrated in the contacting area of the end of the screw.
I would think the taper pin would apply substantially less pressure, and may not deflect into the bore.
The pressure is not concentrated on the barrel, as it is also pressed into the gas block/sight base at either end of the hole at the same time.
Thank you for doing this trackmagic. Could you run the same thing, but for a 0.625" outside diameter barrel (typical light weight diameter) and 33 inch-lbs of torque (on a 8-32 set screw)?
I know this isn’t an exact science. But I am curious.
I specified steel. In general steel all has the same modulus of elasticity regardless of alloy (29,700,000 psi). The modulus is a measure of how stiff the material is. Here is a data sheet for 4150: 4150
410 Stainless has a modulus of 29,000,000. That is 98% as stiff as steel so they are both going to be pretty close.
Excellent thread. I use no torque with dimples when I can, and secure the block with Red Loc-tite on precision builds. That also seals the gas block to the journal.
The set screw only serves as an index/counter-ratation/counter longitudinal travel device in a worst-case scenario.
