AR short stroking

[Ragnarok127]

I have an interesting problem with my 20 IN AR. Rifle length gas system.

I've always used 27 GR CFE223 and a 55 FMJ but with how much praise H335 gets i wanted to try it.

Problem is it short strokes every round! Even 25 gr h335 and a lubed BCG it won't pick up the next round.

Chrony says i'm getting 3100 fps so it's not an underloaded round.

I tried a mag of my CFE load and it runs like a top.

Is CFE being a slower powder really produce that much more gas?

The gas system seems to be in order, the only thing i haven't done is measure the gas port hole.

 

[USK308]

I have an interesting problem with my 20 IN AR. Rifle length gas system.

I've always used 27 GR CFE223 and a 55 FMJ but with how much praise H335 gets i wanted to try it.

Problem is it short strokes every round! Even 25 gr h335 and a lubed BCG it won't pick up the next round.

Chrony says i'm getting 3100 fps so it's not an underloaded round.

I tried a mag of my CFE load and it runs like a top.

Is CFE being a slower powder really produce that much more gas?

The gas system seems to be in order, the only thing i haven't done is measure the gas port hole.

Adjustable gas block or Non-Adjustable?

Buffer Weight?

Extension Tube Length?

Buffer spring length & # coils?

And yes, what is the diameter of the gas port hole?

 

[Ragnarok127]

Non adjustable gas block

Rifle buffer weight and extension
Standard rifle buffer
Don't know diameter of gas port. It's a 20' Faxon Gunner

 

[msgriff]

Look for an over-speed issue where the BCG outruns the mag spring. Load 1 cartridge in the mag and test fire to check for last round bolt hold open function. If it doesn't, try it while pushing hard on the lower part of the bolt catch lever, like you're manually engaging the bolt catch, while firing from a mag loaded with 1 cartridge..

 

[Ragnarok127]

Look for an over-speed issue where the BCG outruns the mag spring. Load 1 cartridge in the mag and test fire to check for last round bolt hold open function. If it doesn't, try it while pushing hard on the lower part of the bolt catch lever, like you're manually engaging the bolt catch, while firing from a mag loaded with 1 cartridge..

It will not lock back on empty mag with the h335 rounds. I have also checked the gas key and rings

 

[LRRPF52]

You’re about 2 grains higher than book max load in Hornady’s data with H335.

Back off to 23.2gr and see what happens.

Hornady’s data shows 26” barrel data doing 3200fps with a 23.2gr of H335 under a 55gr cup and core bullet.

You’re most likely out-running the magazine with excessive carrier velocity due to hitting the port with that much pressure.

 

[Ragnarok127]

Ho

You’re about 2 grains higher than book max load in Hornady’s data with H335.

Back off to 23.2gr and see what happens.

Hornady’s data shows 26” barrel data doing 3200fps with a 23.2gr of H335 under a 55gr cup and core bullet.

You’re most likely out-running the magazine with excessive carrier velocity due to hitting the port with that much pressure.

That's load data for 223 chamber. Hodgdons max is 25.3. I believe hornadys max for a 62 fmj is above 25 for a 5.56 chamber. Bolt travel speed is lower than the cfe loads so I don't think it's outrunning the mag

 

[supercorndogs]

If it runs fine on 27g of CFE223, I would expect it to run on 25g of H335. Go look at multiple bullets. The max charge weight differs a couple grains between different 55g bullets.

I want to say my h335 loads are closer to 26.5 with 55g bullets.

 

[M4orturnate]

Cfe223 is really gassy powder. I dont use it because it way overgasses my rifles. If your gun runs well with cfe its undergassed.

 

[bfoosh006]

FWIW... Sierra data shows a 25.7gr max load for Sierra 55gr FMJ, .223 20" AR, for aprox. 3000fps

 

[LRRPF52]

Ho

That's load data for 223 chamber. Hodgdons max is 25.3. I believe hornadys max for a 62 fmj is above 25 for a 5.56 chamber. Bolt travel speed is lower than the cfe loads so I don't think it's outrunning the mag

Sorry. I checked Hornady’s Service Rifle Load data and it only had 68gr and up. I should have looked at Hodgdon’s data as well as Sierra’s.

Next thing is to check port diameter.

One good thing to do when building an upper is to make a notebook for that build, and record your gas port diameter before installing the gas block.

Keep that data with your rifle log book where you track loads and round count, which will also help set you up for replacing your extractor, ejector, and action springs on a schedule. I need to be better about this myself.

 

[Bantam1]

How often are you replacing extractor and/or ejector springs? I have no idea what the round count should be for decent springs, say stock BCM, JP or Geissele components for example. I had planned to just replace them with Springco when they needed them.

 

[1911hombre]

Take the reloads out of the equation. Get some M193 or M855 ammo and load one round in a mag and see if it locks back with both or either. If not, tune accordingly with springs and /or buffers.
Then and only then worry about your reloading recipes.
ON EDIT: I see in OP the gun is a known runner. Use H335 for something else. Done.

 

[FredHammer]

I suspect your gas port is too small. It worked for the CFE223 "gassy" powder, but not for others. You can buy a numbered drill bit kit from Harbor Freight and use the smooth ends as pin gauges. Measure the pin gauge with a caliper when you find one that fits snug in the gas port hole. You can report that size back here, or just pick a size larger and drill the port out. Put a dowel rod in the barrel so the drill bit has something to stop it from hitting other side of the barrel when it punches through. Absolutely would rather have a slightly over gassed gun than a no working under gassed. Obviously.

 

[DeathBeforeDismount]

First thing I would do is look at the gas block. Depending on the way its mounted, it could have slipped or turned, starving the gun of gas. This would explain why you aren't losing velocity.

Take it apart, clean it and put it back together.

Is this a new gun or one that just started showing issues? If it ran before now it doesnt, its not the gas port. If its always been this way, thats a possibility. Lots of cuplripts with mixmaster AR's using budget parts like faxon.

 

[FredHammer]

Just thought about this. Borescope the gas block hole as you set the gas block. Not all gas blocks have their holes in the same spot.

 

[Ragnarok127]

Sorry. I checked Hornady’s Service Rifle Load data and it only had 68gr and up. I should have looked at Hodgdon’s data as well as Sierra’s.

Next thing is to check port diameter.

One good thing to do when building an upper is to make a notebook for that build, and record your gas port diameter before installing the gas block.

Keep that data with your rifle log book where you track loads and round count, which will also help set you up for replacing your extractor, ejector, and action springs on a schedule. I need to be better about this myself.

This is good advice, i need to take the gas block and measure the port hole.

 

[Ragnarok127]

First thing I would do is look at the gas block. Depending on the way its mounted, it could have slipped or turned, starving the gun of gas. This would explain why you aren't losing velocity.

Take it apart, clean it and put it back together.

Is this a new gun or one that just started showing issues? If it ran before now it doesnt, its not the gas port. If its always been this way, thats a possibility. Lots of cuplripts with mixmaster AR's using budget parts like faxon.

The gas block is pinned in position so it is possible it is not pinned in the perfect spot.

 

[Ragnarok127]

How often are you replacing extractor and/or ejector springs? I have no idea what the round count should be for decent springs, say stock BCM, JP or Geissele components for example. I had planned to just replace them with Springco when they needed them.

I've tried a few different BCG's. So i'm thinking the gas port is too small

 

[Ragnarok127]

I suspect your gas port is too small. It worked for the CFE223 "gassy" powder, but not for others. You can buy a numbered drill bit kit from Harbor Freight and use the smooth ends as pin gauges. Measure the pin gauge with a caliper when you find one that fits snug in the gas port hole. You can report that size back here, or just pick a size larger and drill the port out. Put a dowel rod in the barrel so the drill bit has something to stop it from hitting other side of the barrel when it punches through. Absolutely would rather have a slightly over gassed gun than a no working under gassed. Obviously.

Do you know what the spec for a 20" rifle gas port size is supposed to be? Google tells me about .093

 

[FredHammer]

Do you know what the spec for a 20" rifle gas port size is supposed to be? Google tells me about .093

Yup. .93-.96 on a .750" GB journal.

 

[msgriff]

Do you know what the spec for a 20" rifle gas port size is supposed to be? Google tells me about .093

With a 0.625" gas journal, you can drop a size, so 0.089" should run.

 

[FredHammer]

With a 0.625" gas journal, you can drop a size, so 0.089" should run.

Yassir, reduce the distance the gas must travel upwards and the diameter should be smaller. An inversely proportional relationship.

 

[cas6969]

Back off to 23.2gr and see what happens.

You have nothing to lose trying this. You could have some odd stars align, timing/dwell issue going on hindered extraction, slowing things down.

 

[Ragnarok127]

Well went to the range today and had no luck with the h335 loads. Tried everything from 23-26 in half grain increments but it was still a single shot gun..

What's weird is i loaded some 50 grain frangibles with 24 grain cfe223 and it would run perfect, 3-4 o clock ejection pattern and lock back on every mag.

I guess this is just a CFE223 gun

 

[FredHammer]

Well went to the range today and had no luck with the h335 loads. Tried everything from 23-26 in half grain increments but it was still a single shot gun..

What's weird is i loaded some 50 grain frangibles with 24 grain cfe223 and it would run perfect, 3-4 o clock ejection pattern and lock back on every mag.

I guess this is just a CFE223 gun

Sometimes a dude just gotta say "fuck it!" and go with what ya got!