I have an SLR GB-7 low-pro gas block and a Daniel Defense barrel that DD no longer sells (16" mid-length S2W). The gas block comes with a roll pin, but I’d like to use a taper pin instead. Is there a go-to gunsmith that the M4C hive mind recommends? Need the barrel drilled for both the set screw and the pin, and the gas block has a starter hole where the roll pin goes but needs to be drilled as well (which is why I’m assuming I can convert this to a taper pin).
Thanks.
(Also, if I’m wrong about preferring a taper pin please educate me.)
IMO… I would be comfortable with just the set screw. There are no forces trying to rotate the GB. To me the adjustable GB is more of a liability than the set screw mount. I am assuming the barrel is new and not drilled.
I’m on the other side of the fence. I have set screw GB’s but prefer pinned.
Contact Marvin Pitts. He pins GB’s for $45. It sure if your requirements would impact that or not. He’s an awesome barrel guy. He’s an awesome guy.
My correspondence with Criterion Barrels Tech Support told me that they do not recommend using taper or roll pins, just set screws, and the taper pins displace barrel material and both can affect harmonics. Here is a quote from them…
"From: CBI Customer Service
Sent: Monday, May 14, 2018 1:10 PM
To: ‘John’
Subject: RE: Enquiry John
John,
I think that you would be very well pleased with one of our chrome lined barrels. In my opinion they are the finest chrome lined barrels available anywhere and our record speaks for itself. We hold numerous National Match titles and world records that were shot with our chrome lined barrels. Head-spacing is essential to obtain optimal timing, function, and performance. An improperly head-spaced barrel/bolt combination results in inconsistent chamber pressures which leads to premature wear on internal components like the extractor and the chamber walls. Inconsistent chamber pressures result in accuracy issues. Head-spacing directly relates to consistent seating depths which aids in accuracy and consistency. Lastly, I do not recommend pinning of the gas block, ever… When you drill a hole through the barrel and the gas block and then drive a taper pin through it, material is displaced. This frequently causes crimping of the bore, harmonics issues, etc. Although this practice has been used by the military for decades, it is something that they are moving away from in order to improve upon their 4 MOA accuracy requirements. As an example here is a recent article about a contract put out by the Marine Corps. Take note of the fourth bullet point under “Required Characteristics”, it specifically stated that gas blocks are not to be pinned.
Working with a number of firearms manufacturers, I have seen issues occur time and time again as a result of this process. I recommend installing your low profile gas blocks with a small amount of thread locker in conjunction with our set screw dimple. If you snug the screws down (being careful not to over torque) to the barrel your gas block will not move until you want to remove it. I have tested this method under sustained full auto fire and have never had a gas block walk off on me… the only thing separating a hobbyist and a professional is knowledge, skill, and experience (something I work on obtaining every day). Let me know if you have any other questions.
I think gas blocks should be pinned rather than relying just on a set screw and some glue (LocTite). It’s cheap and easy, even if you don’t do it yourself. I’ve had gas blocks pinned at Ranier, ADCO, from a local gunsmith, and I did one myself with my good old Sears drill press, all with excellent results. It’s a very straightforward process and doesn’t require much in the way of sophisticated tooling.
OP,
I had that same barrel pinned by ADCO a few years back. I had two smiths turn down the job. They said the barrel was too hard. I don’t know how true that is, ADCO had no problem with it
This isn’t the first time I’ve heard/read this. White Oak said this to Pappabear too if I remember right. The BEST pin jobs are reamed to where just half of the ream hole is in the barrel. COLT, BCM, etc. I’ve seen shit manufacturers where the pin hole is completely in the barrel. WTF?
(Also, I have an ADCO custom cruiser. Their work is American Mediocrity epitomized. Looks like a high school shop student did it)
I remember that old Bushmaster of Maine used to have the taper pin holes completely through the barrels, though I never had any issues with their accuracy. And just recently (maybe not surprisingly) I received a brand new Windham Weaponry 20" A2 profile barrel and I was miffed to see that the taper pin holes were completely through the barrel. Despite this, I believe their barrels are the best of the commercial grade manufacture’s barrels. I just wish they would correct this in future runs of barrels because they’ve corrected a few things since they were Bushmaster.
My preferred barrels are from Colt and Daniel Defense.
I built a GAU-5A using a Criterion was going to pin because I was a little worried about smacking the end of the tube when putting it together but after talking with them I didn’t pin.
The old ones I had the FSBs off of were more or less the same, sometimes one of the two pins would be about 80% into the barrel and the other was 100% into the barrel. I also believe that this made the taper pins more of a b!tch to remove than the ones drilled more evenly to be about 50% into the barrel
