Bolt / carrier group for better accuracy

[Willie Lowman]

Hi, I have a BCM stainless 18" 1/8 twist rifle gas upper on a Colt HBAR II lower with a Geiselle trigger. I am trying to get as much accuracy out of it as I can.

When I put the rifle together the only BCG I had on hand was a Fail Zero.

It shoots 1 MOA to 1.5 MOA at 200 yards with 77 grain SMK's. That's as far as I can shoot without driving an hour to a gun club with a longer rifle range. (I have nearly 3000 rounds of Black Hills that I bought back in 2017 when prices were good)

I am wondering if I could get better performance if I upgraded my bolt.

Is this worth looking into or should I be happy with what I have?

I have seen KE arms offers a National Match chrome plated BCG that "Added surface area in the front of the carrier gives a tighter fit when the bolt is in battery for more consistent lock up"

 

[jetinteriorguy]

Personally, if it shoots that good with that ammo I’d say your doing pretty good. Handloading would be the best way to improve your accuracy, and shooting a lot more.

 

[Nathan]

BCG’s are basically a durability part. You could buy a go gage and determine what your actual headspace is with plastigage or tape. Then buy some bolts in search of a tighter fit. Somebody may make +/- bolts. I just cannot remember who. I’m also not aware of anybody making “tru’d” AR bolts. You might try a BCM bolt just because that is surely what they set the headspace to match.

My guess is your barrel just doesn’t like that ammo or the ergonomics of your gun are disagreeing with you.

I would probably try to get a few boxes of other match ammo in the 65-77gr range and see if any shoot better.

 

[Shadow9mm]

if you see any measureable difference from a bolt, I would be shocked.

things you can do to improve accuracy

free float the rail if you have not already
have the barrel mating surface trued/shimmed for a better fit
put a new higher quality barrel on it.
add on a barrel tuner https://www.shootsmallgroups.com/shop/
get a scope with paralax adjustment (if you don't have one already)
possibly an accu wedge, that would be the cheapest option

 

[imashooter]

BCG’s are basically a durability part. You could buy a go gage and determine what your actual headspace is with plastigage or tape. Then buy some bolts in search of a tighter fit. Somebody may make +/- bolts. I just cannot remember who. I’m also not aware of anybody making “tru’d” AR bolts. You might try a BCM bolt just because that is surely what they set the headspace to match.

My guess is your barrel just doesn’t like that ammo or the ergonomics of your gun are disagreeing with you.

I would probably try to get a few boxes of other match ammo in the 65-77gr range and see if any shoot better.

Sounds to me his barrel is thrilled to death and "ergonomics" just fine to get those groups at 200.

OP, appreciate what you have and don't look back.

 

[Nathan]

I only say that because in my experience and reading that many folks struggle with AR15 accuracy. Usually it is not a barrel or bolt issue. I knew a guy that went so far as to yank the gas tube to settle it down in the bags. I also have and adjustable gas block to tune action cycling impulse.

I did not do that. I focused on a forearm and heavier buttstock that both ride my bags better than some.

I bought a barrel with a headspaced bolt from WOA.

My best group so far is 5 shots at 100 yds into 0.50”. Not bad, I suppose. Hoping to do better when I get back at it with better dies.

 

[Rimfire5]

I have a Les Baer Super Varmint .223 AR with a 1:8 twist which is a very accurate rifle. Guaranteed to shoot 5 round groups of factory ammo under 1/2 inch at 100 yards and it does better than that with factory and even better with my hand loads.
5-round group average at 100 yards with all hand loads and all bullet weights is 0.402 and its top 25 loads average 0.273.
69 grain SMKs average 0.302 with H4895 powder.
77 grain TMKs average .0332 with CFE powder.

After several years of shooting, I explored changing bolt carriers and bolts and tried four different ones and saw no difference in accuracy.
If your bolt is malfunctioning, by all means change it, but I doubt you will see any difference in switching out a bolt and carrier that is functioning normally.

 

[chadio]

OP, appreciate what you have and don't look back.

This

 

[bfoosh006]

Those are good groups. Especially from a BCM SS barrel.

I don't think you'd see improvements , with a "better" BCG... at least not at 200yds.. maybe at longer ranges. 500-600

I would suggest making the upper to lower fit as snug as possible for a more consistent wielding of the AR.

I am hesitant to suggest lapping / truing the upper receiver face ... because it is shooting so well. ( FYI, the Brownells lapping tool fits BCM uppers.... PTG does not. )

Here is a bunch of reading... from a guy that knows AR's
https://www.thefreelibrary.com/Carlos%2c+Joe-a14906