New AR-15 Upper Build - Barrel Bedding and Gas Block Questions

[Stevie Boy]

Looking to pick the MDS brain trust again. I feel more comfortable asking here than arfcom but I may also pose this to the SOTAR facebook page.

Later this summer, I have it in my head to start a new build for a “more accurate” AR 15. Not necessarily match grade mind you but better components (primarily barrel) to improve accuracy. So, my plan is to combine a BCM upper with a Criterion barrel and a Geissele gas block as the primary components of the upper. My questions are as follows.

With respect to bedding the barrel, I’m prepared to lap the upper. Given what I hear about BCM uppers being tight fits, I’m expecting to have to do a thermal fit of the barrel. Just so I’m clear, if going that route, no Loctite 620, Rockset, etc. is needed. Correct? I also expect that I may well need to heat the upper to get the lapping tool to fit. Anything else I need to watch out for? Or, am I off base?

Regarding the gas block, when Chad posted those videos from Criterion about accurizing the AR, Criterion clearly said that they don’t recommend pinning the gas block. Pretty sure I’ve seen/read elsewhere that the Geissele gas blocks are relatively straightforward to pin without special tools even though they’re set up for set screws. I think they call it “bomb proofing”. So, to pin or not to pin? That is the question. If pin, has anyone on here done it with the Geissele GB? Usually you can find youtube videos for just about anything but my searches have come up empty.

Fwiw, this will be my first upper build. Done a number of lowers but always steered clear of building my own upper. But, in retirement, I’m looking to try something new.

 

[outrider58]

I've never had to do a thermal fit, so I won't comment.
Pinning gas blocks don't take any special tools, except a carbon steel drill bit. Dimpling barrels, depending on the type, oftentimes reqire a jig. The main thing you'll need to do is make sure you have the block perfectly aligned with the gas port first. If you don't have access to a bore scope, you can use the spaghetti trick. A little piece of noodle inside the gas block port. Once it aligns with the gas port on the barrel, the noodle drops through, into the barrel. I'm more of a linguini man myself so I use toothpick. Just gotta make sure it isn't too long.

I've kinda gotten away from pinning and rely more on dimpling or clampon. The latter for precision barrels.

 

[DutchV]

Yes, you'll probably have to heat the upper to get the lapping tool to fit. An extra set of hands would be useful here. I'd still use Loctite 620 to bed the barrel, even if it's a thermal fit. It'll fill any gaps.

The Geiselle so-called "bombproof installation" uses a roll pin, which is not that great compared to a solid pin. Since this is a precision rig, I'd use Rocksett on the screws and skip pinning the gas block.

 

[calicojack]

If you want to have a bedded barrel and hand lapped upper receiver, might as well polish the feed ramps while you are at it. Want to do all of that in one day? Take the SOTAR build class. Look in the IP section https://www.mdshooters.com/forumdisplay.php?f=227

Well, well, worth the money.

[EDIT] Wait - you are in Naples??

 

[3paul10]

I use a heat gun to blow hot air on the bcm uppers, works well for me.....I also still bed with loctite 620.....

 

[3paul10]

Reading more of your question....I use alot of the Geissele super gas blocks and pin them....I love them. If you're doing a more precision rig then pinning not the best option as I does effect ballistics....

 

[mvee]

I’ve used my wheeler upper receiver lapping tool in several BCM uppers. It fits inside fine. There is enough clearance to fit at room temperature

 

[calicojack]

I also still bed with loctite 620.....

Yes. I can say from experience this makes a difference.

 

[calicojack]

I've kinda gotten away from pinning and rely more on dimpling or clampon. The latter for precision barrels.

I have been told that pinning a gas block MIGHT impact accuracy due to stressing the barrel; but I don't have before and after data to prove that. Even so, I think this makes sense.

 

[calicojack]

I wished I lived in Naples. I could put together a retro AR w/o the need for an HBAR barrel. I could have an SBR PCC under 29" OAL. I could buy a FAL. I could order standard capacity magazines. I could own a Min- 14 with a folder.

 

[Stevie Boy]

I've never had to do a thermal fit, so I won't comment.
Pinning gas blocks don't take any special tools, except a carbon steel drill bit. Dimpling barrels, depending on the type, oftentimes reqire a jig. The main thing you'll need to do is make sure you have the block perfectly aligned with the gas port first. If you don't have access to a bore scope, you can use the spaghetti trick. A little piece of noodle inside the gas block port. Once it aligns with the gas port on the barrel, the noodle drops through, into the barrel. I'm more of a linguini man myself so I use toothpick. Just gotta make sure it isn't too long.

I've kinda gotten away from pinning and rely more on dimpling or clampon. The latter for precision barrels.

Thanks. Barrel comes with a dimple already so good to go there.

 

[Stevie Boy]

If you want to have a bedded barrel and hand lapped upper receiver, might as well polish the feed ramps while you are at it. Want to do all of that in one day? Take the SOTAR build class. Look in the IP section https://www.mdshooters.com/forumdisplay.php?f=227

Well, well, worth the money.

[EDIT] Wait - you are in Naples??

Yes, the class is on my "bucket list". I'll be back in Maryland for the summer but would probably have to rely on a cancellation to work it in.

Had not considered the feed ramps so I guess I'll use my isolation to research that now.

 

[Stevie Boy]

I wished I lived in Naples. I could put together a retro AR w/o the need for an HBAR barrel. I could have an SBR PCC under 29" OAL. I could buy a FAL. I could order standard capacity magazines. I could own a Min- 14 with a folder.

Yes, this will be a Florida gun when the time comes. Will hopefully do the upper work in MD this summer but lowers are "scheduled" for the fall down here. My pre-2013 firearm will stay in Maryland.

 

[outrider58]

Yes, the class is on my "bucket list". I'll be back in Maryland for the summer but would probably have to rely on a cancellation to work it in.

Had not considered the feed ramps so I guess I'll use my isolation to research that now.

Very important. Instead of a ball point pen for inspecting feed ramps, I use an x-acto knife. If it doesn't hang up, then all I need to do is make sure the ramps line up(or cut them so that they do), and then polish them for snag free feeding.

 

[Stevie Boy]

Very important. Instead of a ball point pen for inspecting feed ramps, I use an x-acto knife. If it doesn't hang up, then all I need to do is make sure the ramps line up(or cut them so that they do), and then polish them for snag free feeding.

After watching some videos and reading up, I think I'm ready to take this on. Got some Mothers and Flitz and a few dremel felt tips. "Practiced" on my 9mm handgun barrel and that looks pretty good. Next up is my AR barrel. I was uncertain as to felt tip size for the feed ramp but looks like I'm going to use a bullet shape tip in 6mm. I used a 10mm tip for the 9mm barrel.

 

[outrider58]

After watching some videos and reading up, I think I'm ready to take this on. Got some Mothers and Flitz and a few dremel felt tips. "Practiced" on my 9mm handgun barrel and that looks pretty good. Next up is my AR barrel. I was uncertain as to felt tip size for the feed ramp but looks like I'm going to use a bullet shape tip in 6mm. I used a 10mm tip for the 9mm barrel.

May be repetitive, but make sure the feed ramps are worked on while not inside the upper. You don't want to remove any of the anodizing from the aluminum upper.

 

[Stevie Boy]

May be repetitive, but make sure the feed ramps are worked on while not inside the upper. You don't want to remove any of the anodizing from the aluminum upper.

Got it. Barrel not mounted yet. Been watching videos, reading all the posts on SOTAR, etc. My remaining concern is whether I'll have to remove the barrel after mounting if there an issue with the feed ramps lining up particularly since I'm expecting to have to do a thermal fit as I mentioned previously. But, I've come this far, so gonna try to do it right. Hopefully it works out. Trying to go outside my comfort zone somewhat and hopefully learn a new skill so I'm willing to put in the effort.

 

[rbird7282]

Yes, you'll probably have to heat the upper to get the lapping tool to fit. An extra set of hands would be useful here. I'd still use Loctite 620 to bed the barrel, even if it's a thermal fit. It'll fill any gaps.

The Geiselle so-called "bombproof installation" uses a roll pin, which is not that great compared to a solid pin. Since this is a precision rig, I'd use Rocksett on the screws and skip pinning the gas block.

This. Good advice here.


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[Stevie Boy]

This. Good advice here.


Sent from my iPhone using Tapatalk

Yes, this is now the plan. There's been lots of good advice. I'm very appreciative. Hopefully, this old dog can learn some new tricks.