Bolt head space

ChickenHawk

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If I have a brand new upper and brand new bolt that were bought separately from different manufacturers, should I check head space? I’m still a newb at building ARs, but have the big right now.
 
I wouldn't unless you have problems. Modern machining pretty much eliminates this issue with AR pattern rifles. I have put hundreds of them together over the past 12 years and have never had an issue with it.
 
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If I have a brand new upper and brand new bolt that were bought separately from different manufacturers, should I check head space? I’m still a newb at building ARs, but have the big right now.

Small frame or large AR? If it's a large AR, try to buy a matched bolt with your barrel if possible. If that's not feasible, buy a bolt matched to the barrel extension type. If it's a small frame AR, just buy the appropriate bolt for your barrel's chamber.
 
On a AR15 you have a 99.95% having correct headspace. I've gotten lucky in my earlier years without gages. I have gages now however. I run into more headspace issues with AKs down range however.

CD
 
Small frame or large AR? If it's a large AR, try to buy a matched bolt with your barrel if possible. If that's not feasible, buy a bolt matched to the barrel extension type. If it's a small frame AR, just buy the appropriate bolt for your barrel's chamber.
It is a small frame 5.56 AR.
 
I did receive two 'identical' custom AR barrels, one with 0.012", and the second had 0.004" headspace off of 5 cases of new Lapua brass. I don't have gages, used a piece of Scotch tape on the headstamp, it adds 0.003".
 
Question....

I understand that having the gauges will mean no doubt but....

But am I understanding correctly that if the rifle has already proven to have the correct head space then there is no need to check this? A partner has asked me to take off the A2 style handguard and FSP/GB and replace with cheap Chinese knockoff keymod rail. (I know, I know but he’s one of those that only half listens to what I say but pays rapt attention to the Chinese expert with all the gear for great prices). I have all the tools sans the go/no go gauges. Just getting a gut check before I move out and draw fire. It’s a stock M&P15 with maybe 100 rds fired with no issues.
 
Question....

I understand that having the gauges will mean no doubt but....

But am I understanding correctly that if the rifle has already proven to have the correct head space then there is no need to check this? A partner has asked me to take off the A2 style handguard and FSP/GB and replace with cheap Chinese knockoff keymod rail. (I know, I know but he’s one of those that only half listens to what I say but pays rapt attention to the Chinese expert with all the gear for great prices). I have all the tools sans the go/no go gauges. Just getting a gut check before I move out and draw fire. It’s a stock M&P15 with maybe 100 rds fired with no issues.


The barrel pin and extension are fixed in place. Changing the barrel nut for your handguard swap won't change that geometry of the headspace in any way.
 
I had been wondering this too. I bought a TiN BCG and was wondering how interchangeable they are. Thanks for all the answers.
 
Thanks @ChickenHawk

Next newb question.....

Must you “dimple” the barrel for a low pro gas block?

Depends on your components. Is the barrel dimpled or has taper pins. As just a range toy you may get by just screwing the set screws tight and hoping it holds. I build combat rifles here in Afghanistan. For those barrels that use the low profile gas block, yes barrels are dimpled and loktite 242 is applied to the set screws to keep them from backing out. I have never had to replace those components for backing out. After awhile some carbon from gas seepage will for a seal on the gas block and barrel. Sometimes when rebarreling shot out barrels I would have really smack the gas block to get to go forward off the barrel. Lately just been using a band saw to cut barrel so I can remove the free floated barrel nut. Had a discussion on this recently on ARF.com I use the same log in.

https://www.ar15.com/forums/ar-15/Gas-Block-Set-Screws/118-735752/


CD
 
Thanks @Combat Diver

I’m gonna call to him to see what he wants to do. I’m doing this job at cost so we’ll see if a jig for dimpling is in the works.

I’m catching hell right now trying to get the A2 FSP/GB taper pins to come out. All I’ve got right now are flat punches. Need to order some of those that are concave I think. Gonna put some penetrating oil on them to see if that helps.
 
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Tips to getting taper pins out. If you have a FSB block it helps however I've also just used a block of 2x4 under it or on concrete (you want a firm surface). Make sure your driving the pins out in the right direction. Use the largest hammer and punch you have as it gives more weight to the drive. Set punch on pin and give it a whack, using just once or twice. Once pin is flush with FSB then use smaller punch to drive it out. Easy with the right tools.

For a dimple jig I use a discarded low profile gas block for my use. Align it up (use another 2x4 with a recess for the gas block or in vise) and then drill thru the LPGB to just remove a small amount of metal from the barrel creating the dimple.

IMG_6575.jpg

CD
 
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Thanks @Combat Diver

I’m gonna call to him to see what he wants to do. I’m doing this job at cost so we’ll see if a jig for dimpling is in the works.

I’m catching hell right now trying to get the A2 FSP/GB taper pins to come out. All I’ve got right now are flat punches. Need to order some of those that are concave I think. Gonna put some penetrating oil on them to see if that helps.

You may want to consider using a clamp on "Low Profile Gas Block."
Besides a bit easier to install , I believe they seal much better than the Screw Lock type ( although they work as well).

STEEL ADJUSTABLE Micro 223Rifle Gas Ring Roll Pin .750 HideUnder QuadRail
20 delivered

https://www.ebay.com/itm/STEEL-ADJU...4:g:oLQAAOSwBZBcKaLY:rk:1:pf:1&frcectupt=true

FWIW

Safe Shooting


s-l1600.jpg
 
Well, the tool kinda worked (did get one of the taper pins to break loose).

Thanks to @Combat Diver pic last week I said to my self, “self, that man knows what he’s doing and uses a BFH. Better gitcha one” so I did, and a taper pin is no match for a 3lb mini sledge.

Thanks again guys!!!
 
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