Cycling 58g bullets

[Badgersmith]

Planning a P dog trip and want to utilize my ARC. 20 " Proof Reseach SS,Gibbz Upper. Viciuos Precision lock in modification to remove all upper/lower movement.
So far even with max loading we are generating enough to cycle the action,went to a lighter spring and got a mild improvement. We are running a Wilson BCG.  Any suggestions before I start working up 87g loads [I have scads of 58's but 87's  would require search and investment.

Thanks, Badger

[StoneHendge]

Is it safe to assume you are running a fixed gas block or an AGB fully open? What powder are you you using? Your pressure is probably really dropping off by the time it hits that R+2 port if it's a fast powder - or maybe it's slightly misaligned. Or maybe the Proof ARC barrels are really optimized for heavier bullets. 70's might be worth a shot before 87s. I do them just shy of 3k in my 24" 6x45 and they are automatic on P dogs to 400. 3100 should be well within reach for a 20" with a temp stable powder like Benchmark or XBR.

[Badgersmith]

Thanks Stonehenge, getting 3025 avg fps.Adjustable Block wide open, Borescoping confirms perfect port alignment. Using Sprinco's lightest "yellow" spring . I am a Fulltime Gunsmith [Vicious Precision TM] ,have built a few hundred plus serious rifles gas,bolt ,lever etc.. Looking like the wilson BC which is V heavy may be a key here. We'll swap out to lighter BC and test.
btw this rifle shoots MOA at 800 w Hndy Match. We finally got some Lapua and Star Grendel Brass and are forming now. I do a Proprietary Modification on AR's that eliminates the rear pin and it's inherent slop and wear.Not the silly deal with a screw to push upper/Lower apart but actually draws the halves together.Zero movement,ends the wear as well. Easily reversable if you wish to return to the stock pin arrangement.Every one we've done resulted in real improvement,usually half a minute ,often more. It is also High Power legal as is no change to rifle's profile. I digress, sorry. Superformance is powder using right now. Thanks for the input and help, Badgersmith

[riggeek]

I’ve been fighting with a similar problem with a 22 inch barrel with a rifle +2 configurations. I have sent my barrel back to the OEM they can find nothing wrong, as it cycles with the factory ammo but on my reloads using 87 Vmax is with a full load of varget it will not cycle. I can get it to work with 87 and heavier bullets with B3L-c2 and cfe 223. I have been contemplating opening up the Gasport a bit to try to get it to improve. I have tried A mil spec rifle lower using a Sprinco Greenspring, a carbine lower using a normal buffer, and a valtor A5 down to a H0 weight. I have Even tried 2 adjustable and 1 fix gas block. Of the three gas blocks the suplitve worked the best. With the valtor combo working the best.

[r.tenorio671]

....beginning to see more & more reports of cycling/gassing issues as folks build with +gas tubes. FWIW, I personally can't recall the specifics of what the DoD requirement for gas specific technical specs was. For the industry partners of that development program, I'm curious what was the "common" gas system spec they arrived at or determined to meet the DoD's requirement....or what they developed and recommended as a change to DoD's initial spec to improve the reliability/performance/accuracy of the platform.

...despite the "leggo build" nature of the AR15 platform, a change in caliber brings new and unknown factors that deviate from the known aspects of what may or may not work if strictly following the build aspects of a 223/556 gasser platform.

[grayfox]

Been following this, don't know the answers. But one point, if you think about it, a 58gr bullet is not that much different from a 55 in 556, plus the case gives higher powder capacity= higher gas ability, with a slightly larger bore diameter; the +2 must have something to do with it.

[Badgersmith]

I’ve been fighting with a similar problem with a 22 inch barrel with a rifle +2 configurations.  I have sent my barrel back to the OEM they can find nothing wrong, as it cycles with the factory ammo but on my reloads using 87 Vmax is with a full load of varget it will not cycle. I can get it to work with 87 and heavier bullets with B3L-c2 and cfe 223.  I have been contemplating opening  up the Gasport a bit to try to get it to improve.  I have tried A mil spec rifle lower using a Sprinco Greenspring, a carbine  lower using a normal buffer, and a valtor A5 down to a H0 weight. I have Even tried 2 adjustable and 1 fix gas block. Of the three gas blocks the suplitve worked the best. With the valtor combo working the best.

Could you supply the exact size of your gasport measured with a plug gauge if you have that
available? Can you verify alignment via borescope too? My own specs will be gathered soonest
for comparison. The weight of your complete BCG is important to.

Here's to solving the mystery..   Badger

[StoneHendge]

Superformance is way too slow of a powder for ARC, even for heavier bullets. I'm surprised it works at all. You really need to be with one of the fast powders you see in the Hornady data. H322 would be my first try given its temp insensitivity, but finding it isn't easy. I've never tried LT 30 or 32 but they were made for light benchrest bullets and might be worth a try and they have been on the shelves.

[riggeek]

I’ve been fighting with a similar problem with a 22 inch barrel with a rifle +2 configurations.  I have sent my barrel back to the OEM they can find nothing wrong, as it cycles with the factory ammo but on my reloads using 87 Vmax is with a full load of varget it will not cycle. I can get it to work with 87 and heavier bullets with B3L-c2 and cfe 223.  I have been contemplating opening  up the Gasport a bit to try to get it to improve.  I have tried A mil spec rifle lower using a Sprinco Greenspring, a carbine  lower using a normal buffer, and a valtor A5 down to a H0 weight. I have Even tried 2 adjustable and 1 fix gas block. Of the three gas blocks the suplitve worked the best. With the valtor combo working the best.

Could you supply the exact size of your gasport measured with a plug gauge if you have that
available? Can you verify alignment via borescope too? My own specs will be gathered soonest
for comparison. The weight of your complete BCG is important to.

Here's to solving the mystery..   Badger

I do not have a bore scope, but was able to see the shadow on the barrel was centered when pulled the gas block off. I do not have any pin gauges at this point, but have been thinking about getting some. I should have the barrel back in my hands from shipping on 3-17.

[r.tenorio671]

I’ve been fighting with a similar problem with a 22 inch barrel with a rifle +2 configurations.  I have sent my barrel back to the OEM they can find nothing wrong, as it cycles with the factory ammo but on my reloads using 87 Vmax is with a full load of varget it will not cycle. I can get it to work with 87 and heavier bullets with B3L-c2 and cfe 223.  I have been contemplating opening  up the Gasport a bit to try to get it to improve.  I have tried A mil spec rifle lower using a Sprinco Greenspring, a carbine  lower using a normal buffer, and a valtor A5 down to a H0 weight. I have Even tried 2 adjustable and 1 fix gas block. Of the three gas blocks the suplitve worked the best. With the valtor combo working the best.

Could you supply the exact size of your gasport measured with a plug gauge if you have that
available? Can you verify alignment via borescope too? My own specs will be gathered soonest
for comparison. The weight of your complete BCG is important to.

Here's to solving the mystery..   Badger

I do not have a bore scope, but was able to see the shadow on the barrel was centered when pulled the gas block off. I do not have any pin gauges at this point, but have been thinking about getting some. I should have the barrel back in my hands from shipping on 3-17.

...as an expedient measure, you can use drill bits in place of "pin gauges", just try fitting them in the gas port until you find one that drops down into the hole.

[riggeek]

Spoke with my wife’s great uncle, he is a retired machinist. He has a full set of drill bits covering that size range to use a gauges. Checked the BCG weight. 13.7 oz and it is a PSA.

[StoneHendge]

riggeek, before you start drilling, have you tried a powder faster than Varget which is probably a tad too slow? There lots of A2460 around these days.

[r.tenorio671]

...a couple of ways to check gas block alignment using calipers:

1. Measure the distance from the back edge of the gas block to the rear edge of the port hole inside gas block. Take measurement from stepped edge of barrel gas journal to rear edge of gas port on barrel, compare the two. This will identify if you can abut the gas block up against the stepped edge or have to have a gap. This "gap" is to typically to accommodate older handguards/front sights that had the handguard retaining plate, ala older M16 and current MIL M4's using the triangular front sight. If you need the "gap", some heavy paper stock or business card can be used as a shim spacer when you reattach your gas block. You can also use feeler gauges if you have them.

2. Measure the diameter of the gas port hole in the gas block, measure the diameter of the gas port hole in the barrel, compare the two. Some brands of gas blocks drill a larger, "oversized" gas port in the gas block so it would overlap the barrels gas port and allow some "wiggle room" on the alignment of the two.

Good luck!

[Dino11]

Which receiver extension are you using, carbine or rifle?

And which buffer are you using?

The reason I ask is I might have the fix for you, I went through the same issue with an Odin +2 barrel.
I would try not to drill the gas port larger, if you have a problem with the barrel and try to warranty it drilling it will void the warranty.

[grayfox]

As a note to others, you can get a set of "wire gauge" drill bits which has a huge number of diameters, which allows the drill bit method to give you a pretty close value of port hole size. Simply using the 1/16, 3/32, etc set doesn't have the same level of precision.

[riggeek]

Which receiver extension are you using, carbine or rifle?

And which buffer are you using?

The reason I ask is I might have the fix for you, I went through the same issue with an Odin +2 barrel.
I would try not to drill the gas port larger, if you have a problem with the barrel and try to warranty it drilling it will void the warranty.

I have tried all 3 types of lowers, with a valtor A5 with a H0 working the best. All of these lower function with no issues on my other 2 rifles running 556.

[Dino11]

Try lightening the buffer some more by replacing the steel weights with aluminum ones. I made my own from some 1/2" aluminum bar stock I got at the hardware store. I lightened a rifle buffer and used a 10% reduced power RE spring and had to almost close my gas block off. It is barely open and the the rifle is a very soft shooter that only throws the brass a couple feet away from the bench. My gas port on that rifle is .101, it is rather large but it is a rifle +2" on an 18" barrel, not much real estate between the gas port and the muzzle. And the rifle runs a lot cleaner having almost no gasses going to the BCG and the bolt stays locked longer.

[riggeek]

Try lightening the buffer some more by replacing the steel weights with aluminum ones. I made my own from some 1/2" aluminum bar stock I got at the hardware store. I lightened a rifle buffer and used a 10% reduced power RE spring and had to almost close my gas block off. It is barely open and the  the rifle is a very soft shooter that only throws the brass a couple feet away from the bench. My gas port on that rifle is .101, it is rather large but it is a  rifle +2" on an 18" barrel, not much real estate between the gas port and the muzzle. And the rifle runs a lot cleaner having almost no gasses going to the BCG and the bolt stays locked longer.

What weight  did your rifle buffer end up at? And as you reduce power Spring a wolf one?

[r.tenorio671]

.... you might want to look at the KAK configurable buffer kits. Comes with everything you need to work up a buffer configuration of your choice/needs. You can also purchase the individual weights if you prefer that route. Scroll thru the page to see the options.

https://www.kakindustry.com/ar-15-parts/...-and-parts

[Dino11]

Try lightening the buffer some more by replacing the steel weights with aluminum ones. I made my own from some 1/2" aluminum bar stock I got at the hardware store. I lightened a rifle buffer and used a 10% reduced power RE spring and had to almost close my gas block off. It is barely open and the  the rifle is a very soft shooter that only throws the brass a couple feet away from the bench. My gas port on that rifle is .101, it is rather large but it is a  rifle +2" on an 18" barrel, not much real estate between the gas port and the muzzle. And the rifle runs a lot cleaner having almost no gasses going to the BCG and the bolt stays locked longer.

What weight  did your rifle buffer end up at? And as you reduce power Spring a wolf one?

Yes it was a Wolff spring and I replaced 4 of the 5 steel weights with aluminum and reduced it from 5.4 down to 3.8 oz. It cost me about $5 and about a 1/2 hour of time to modify it.