5.56 Barrel, Tightbore Question

[PBWalsh]

Hi,

Did a little searching but couldn’t specifically find an answer.

Has anyone used a barrel in an AR15 with a tighter bore? Example would be a .222 bore shooting .223/5.56x45. Wondering if there is any validation to a thought experiment I’m going through as far as “gaining back” velocity with a shorter barrel.

Question 1B: Does a tighter bore need to be just used with a single projectile or could you still run a duty (Mk262) and plinking (M193) load in the same tighter barrel with no undue effects?

Basically, I’m wondering how close a 12-13” premium (CLE Bartlien or the like) could get to 16” barrel velocities. All of course being able to work within the same parameters.

 

[TonyTheTiger]

It seems like I've seen @Frank Green posting about bore dimensions more than anyone else here. He might know a thing or two.

 

[bigjake83]

Hi,

Did a little searching but couldn’t specifically find an answer.

Has anyone used a barrel in an AR15 with a tighter bore? Example would be a .222 bore shooting .223/5.56x45. Wondering if there is any validation to a thought experiment I’m going through as far as “gaining back” velocity with a shorter barrel.

Question 1B: Does a tighter bore need to be just used with a single projectile or could you still run a duty (Mk262) and plinking (M193) load in the same tighter barrel with no undue effects?

Basically, I’m wondering how close a 12-13” premium (CLE Bartlien or the like) could get to 16” barrel velocities. All of course being able to work within the same parameters.

I would send @Frank Green a message.

 

[bigjake83]

It seems like I've seen @Frank Green posting about bore dimensions more than anyone else here. He might know a thing or two.

Jinx motherfucker...lol

 

[Frank Green]

So lets make sure we are all on the same page. Don't use the term bore size in general.... you have to talk bore size and groove size. They are two different things but most call them the bore etc...

To the OP's questions and I'll answer the best I can...

Has anyone used a barrel in an AR15 with a tighter bore? Example would be a .222 bore shooting .223/5.56x45. Wondering if there is any validation to a thought experiment I’m going through as far as “gaining back” velocity with a shorter barrel. .222" I'm going to assume you are asking about the groove size here correct? Standard specs for a 223 Remington barrel or a 5.56Nato barrel has a .2190" bore x .2240" groove size.
We've made and as far as I know Krieger still makes they're AR15 barrels with a .218" bore and a standard .224" groove size. So this would be a tight bore barrel but not a tight groove barrel.
A tight bore/tight groove barrel by reducing the total surface area of the bore with everything else being equal normally drives up pressures.... and I'll say in most cases it will drive up velocities. Keep in mind there are a lot of variables and not just the bore/groove size.
Question 1B: Does a tighter bore need to be just used with a single projectile or could you still run a duty (Mk262) and plinking (M193) load in the same tighter barrel with no undue effects? Are you loading the ammo or buying box ammo? Either way.... you what you have here is another variable. In years past I've run ball ammo and handloads with match bullets thru the same gun. Keep in mind ball ammo is machinegun ammo basically. Bullet quality isn't the greatest and ammo quality overall isn't the same as box match ammo or handloads. So running ball ammo... it is what it is. In terms of accuracy and you want to run ball ammo run a slower twist rate. A 55gr ball bullet will stabilize just fine in a 12 or 13 twist barrel etc... and that can actually help the accuracy. Running that 55gr ball ammo thru a 7 twist barrel.... I've actually seen the bullets go thru the target sideways at a 100 yards. It has happened to me. This is due to the quality of the ammo/bullet. I shot handloaded 52gr Hornady boattail hollow point match bullets thru the same gun on the same day and thru a rack grade Colt 1-7 twist barrel it would hold 3/4moa. Same accuracy as the 69gr SMK's where giving me.
You want a jack of all trades... run a 1-9 twist barrel. It will handle up to a 70gr bullet and help with shooting the lighter weight bullets as well.

Basically, I’m wondering how close a 12-13” premium (CLE Bartlien or the like) could get to 16” barrel velocities. All of course being able to work within the same parameters. You don't get to eat your cake and keep it too and this is a prime example. You cut barrel length and you will cough up velocity. No way around it. We did a while back make some AR15 barrels for a special forces unit (I'm using that term loosely as I'm not going to say who exactly). This unit was going to be deployed back to the same area they were at before in Afghanistan. The fighting they did in this one town/province area... that once they ran out of the ammo for the 308 guns and all they had left was the AR15/M4 type guns they coughed up so much velocity with the 14.5" factory barrels didn't make the guns as effective etc...so they asked us to make them a 12" barrel (going totally off of memory with out looking up the order/emails etc..) and they wanted to still make 3000fps. I said no matter what we do that isn't happening. I'd stick with the 14.5" barrels and we made them .218" bores if I recall correctly and we put in 223 Wylde chambers vs a Nato chamber spec. We actually made the blanks and rough turned them and I had Paul at Craddock Precision finish them up. They told me the velocity was coming in at 2995fps if I recall correctly. The guns shot great accuracy wise (which was almost a given vs the factory mil spec barrels) and it helped them deal with the bad guys at extended ranges.

So that is the other thing you have to consider.... and that is the chamber spec. The actual chamber can have an effect on pressures and velocities as well and not just the bore and groove size.

I'm not a overall fan of tight bore barrels and running box ammo. You can have pressure issues and you might not have pressure issues. Just too many variables. Also the tight bore barrel will not guarantee better accuracy or longer barrel life. It might help accuracy if the bullet diameter that you have with your bullets are undersize but that's all I'll say. I use to run .218" bore barrels here and when I was at Krieger but it can create pressure issues. I would tell you not a great idea if your running box ammo. Handloads is one thing but box ammo is another thing.

I've got two reg. SBR's built. Both are 11.5" barrels. Why... because I'm running Surefire Suppressors on them and wanted a shorter barrel length. I'm running standard .219" bore and .224" groove size. 5R rifling and both have 223 Wylde chambers in them. Accuracy is great and the velocity is good but it's not going to be like a 16" or 20" barrel. If I recall correctly box Hornady 75gr match ammo was only giving me 2400-2500fps. I don't shoot light bullets at all on a regular basis. Maybe once in a blue moon. If I'm down to ball ammo.... it's going to be because.... it's an emergency.

Later, Frank

 

[camocorvette]

And there's the best answer you could literally get. I love this place haha Thanks Frank!

 

[PBWalsh]

So lets make sure we are all on the same page. Don't use the term bore size in general.... you have to talk bore size and groove size. They are two different things but most call them the bore etc...

To the OP's questions and I'll answer the best I can...

Has anyone used a barrel in an AR15 with a tighter bore? Example would be a .222 bore shooting .223/5.56x45. Wondering if there is any validation to a thought experiment I’m going through as far as “gaining back” velocity with a shorter barrel. .222" I'm going to assume you are asking about the groove size here correct? Standard specs for a 223 Remington barrel or a 5.56Nato barrel has a .2190" bore x .2240" groove size.
We've made and as far as I know Krieger still makes they're AR15 barrels with a .218" bore and a standard .224" groove size. So this would be a tight bore barrel but not a tight groove barrel.
A tight bore/tight groove barrel by reducing the total surface area of the bore with everything else being equal normally drives up pressures.... and I'll say in most cases it will drive up velocities. Keep in mind there are a lot of variables and not just the bore/groove size.
Question 1B: Does a tighter bore need to be just used with a single projectile or could you still run a duty (Mk262) and plinking (M193) load in the same tighter barrel with no undue effects? Are you loading the ammo or buying box ammo? Either way.... you what you have here is another variable. In years past I've run ball ammo and handloads with match bullets thru the same gun. Keep in mind ball ammo is machinegun ammo basically. Bullet quality isn't the greatest and ammo quality overall isn't the same as box match ammo or handloads. So running ball ammo... it is what it is. In terms of accuracy and you want to run ball ammo run a slower twist rate. A 55gr ball bullet will stabilize just fine in a 12 or 13 twist barrel etc... and that can actually help the accuracy. Running that 55gr ball ammo thru a 7 twist barrel.... I've actually seen the bullets go thru the target sideways at a 100 yards. It has happened to me. This is due to the quality of the ammo/bullet. I shot handloaded 52gr Hornady boattail hollow point match bullets thru the same gun on the same day and thru a rack grade Colt 1-7 twist barrel it would hold 3/4moa. Same accuracy as the 69gr SMK's where giving me.
You want a jack of all trades... run a 1-9 twist barrel. It will handle up to a 70gr bullet and help with shooting the lighter weight bullets as well.

Basically, I’m wondering how close a 12-13” premium (CLE Bartlien or the like) could get to 16” barrel velocities. All of course being able to work within the same parameters. You don't get to eat your cake and keep it too and this is a prime example. You cut barrel length and you will cough up velocity. No way around it. We did a while back make some AR15 barrels for a special forces unit (I'm using that term loosely as I'm not going to say who exactly). This unit was going to be deployed back to the same area they were at before in Afghanistan. The fighting they did in this one town/province area... that once they ran out of the ammo for the 308 guns and all they had left was the AR15/M4 type guns they coughed up so much velocity with the 14.5" factory barrels didn't make the guns as effective etc...so they asked us to make them a 12" barrel (going totally off of memory with out looking up the order/emails etc..) and they wanted to still make 3000fps. I said no matter what we do that isn't happening. I'd stick with the 14.5" barrels and we made them .218" bores if I recall correctly and we put in 223 Wylde chambers vs a Nato chamber spec. We actually made the blanks and rough turned them and I had Paul at Craddock Precision finish them up. They told me the velocity was coming in at 2995fps if I recall correctly. The guns shot great accuracy wise (which was almost a given vs the factory mil spec barrels) and it helped them deal with the bad guys at extended ranges.

So that is the other thing you have to consider.... and that is the chamber spec. The actual chamber can have an effect on pressures and velocities as well and not just the bore and groove size.

I'm not a overall fan of tight bore barrels and running box ammo. You can have pressure issues and you might not have pressure issues. Just too many variables. Also the tight bore barrel will not guarantee better accuracy or longer barrel life. It might help accuracy if the bullet diameter that you have with your bullets are undersize but that's all I'll say. I use to run .218" bore barrels here and when I was at Krieger but it can create pressure issues. I would tell you not a great idea if your running box ammo. Handloads is one thing but box ammo is another thing.

I've got two reg. SBR's built. Both are 11.5" barrels. Why... because I'm running Surefire Suppressors on them and wanted a shorter barrel length. I'm running standard .219" bore and .224" groove size. 5R rifling and both have 223 Wylde chambers in them. Accuracy is great and the velocity is good but it's not going to be like a 16" or 20" barrel. If I recall correctly box Hornady 75gr match ammo was only giving me 2400-2500fps. I don't shoot light bullets at all on a regular basis. Maybe once in a blue moon. If I'm down to ball ammo.... it's going to be because.... it's an emergency.

Later, Frank

Thank you for that Frank, thats the exact answer I was fishing for. I shoot factory as reloading is not very time efficient for me. Mostly shoot Mk262 or similar. Sounds like I need to just figure out how important an extra 9% velocity difference means to me.

I appreciate the response a ton!

 

[Frank Green]

Thank you for that Frank, thats the exact answer I was fishing for. I shoot factory as reloading is not very time efficient for me. Mostly shoot Mk262 or similar. Sounds like I need to just figure out how important an extra 9% velocity difference means to me.

I appreciate the response a ton!

Your welcome!

Just remember your shooting a gas gun here and not a bolt gun. The gas gun is going to show you problems a lot faster than a bolt gun will.

My main concern is this…. You go to a tight bore and or a tight bore/tight groove barrel it will drive up pressures and like I said you might see a velocity increase. As much as you want… that will be a guess as to how much you gain vs the barrel length lost etc… but my main concern is with the pressure increase… piercing / popping primers with box ammo. If this happens and depending on the ammo you’re using could be an issue. A primer pops out during firing and falls down into the trigger area of the lower and the gun will hang up.

If you wanted to try a tight bore here would be my recommendation. .218” bore but not tight groove. 223 wylde chamber. It’s the best of both worlds of the standard 223 Rem and a 5.56 nato. Don’t run a 223 REM. chamber. It’s a tighter shorter throat and will only amplify any problems. I’ll say most of the time but not all the time you could run box ammo with out popping primers but no guarantees.

Ammo quality and brand can and will be a factor. I’d only stick with brand name/quality ammo.

I’ve never tried running/making a standard .219” bore barrel and say a tight groove barrel like a .2235” groove size. That’s a question I should put towards one of the ammo makers and suggest we make an ammunition pressure test barrel and see what happens in regards to pressures and velocities.

Like I said though…anytime you start changing the overall surface area of the bore…you do effect pressures.

 

[PBWalsh]

Your welcome!

Just remember your shooting a gas gun here and not a bolt gun. The gas gun is going to show you problems a lot faster than a bolt gun will.

My main concern is this…. You go to a tight bore and or a tight bore/tight groove barrel it will drive up pressures and like I said you might see a velocity increase. As much as you want… that will be a guess as to how much you gain vs the barrel length lost etc… but my main concern is with the pressure increase… piercing / popping primers with box ammo. If this happens and depending on the ammo you’re using could be an issue. A primer pops out during firing and falls down into the trigger area of the lower and the gun will hang up.

If you wanted to try a tight bore here would be my recommendation. .218” bore but not tight groove. 223 wylde chamber. It’s the best of both worlds of the standard 223 Rem and a 5.56 nato. Don’t run a 223 REM. chamber. It’s a tighter shorter throat and will only amplify any problems. I’ll say most of the time but not all the time you could run box ammo with out popping primers but no guarantees.

Ammo quality and brand can and will be a factor. I’d only stick with brand name/quality ammo.

I’ve never tried running/making a standard .219” bore barrel and say a tight groove barrel like a .2235” groove size. That’s a question I should put towards one of the ammo makers and suggest we make an ammunition pressure test barrel and see what happens in regards to pressures and velocities.

Like I said though…anytime you start changing the overall surface area of the bore…you do effect pressures.

No, you’ve definitely talked me out if the idea! I mainly stick to IMI 77 SMK, or reloads from Badlands Ammo (75gr Hornady BTHP). But I use random mixed M193 for closer stuff and stages in competition. I’m not blasting 75/77s at 20 yards.

So with my use, its sounding way more practical to use standard interior dimentions with a 223W, or even 556 Nato chambering. My current barrel, a 16” Black River Tactical, is chrome lined and still prints around 1.5 MOA.

The autistic nerd in me wants to try out one of your barrels just to see how far I can push a “practical” 12.5-13” barrel.

Looking at an estimated 13” velocity and comparing it to my current 16” data, there is roughly a 10% difference in velocity translating to a 21% difference in kinetic energy out to 600 yards. Thats not an insignificant amount.

As with most, I’m looking for that special cake that I can have, and also eat.

 

[Naaman]

So lets make sure we are all on the same page. Don't use the term bore size in general.... you have to talk bore size and groove size. They are two different things but most call them the bore etc...

To the OP's questions and I'll answer the best I can...

Has anyone used a barrel in an AR15 with a tighter bore? Example would be a .222 bore shooting .223/5.56x45. Wondering if there is any validation to a thought experiment I’m going through as far as “gaining back” velocity with a shorter barrel. .222" I'm going to assume you are asking about the groove size here correct? Standard specs for a 223 Remington barrel or a 5.56Nato barrel has a .2190" bore x .2240" groove size.
We've made and as far as I know Krieger still makes they're AR15 barrels with a .218" bore and a standard .224" groove size. So this would be a tight bore barrel but not a tight groove barrel.
A tight bore/tight groove barrel by reducing the total surface area of the bore with everything else being equal normally drives up pressures.... and I'll say in most cases it will drive up velocities. Keep in mind there are a lot of variables and not just the bore/groove size.
Question 1B: Does a tighter bore need to be just used with a single projectile or could you still run a duty (Mk262) and plinking (M193) load in the same tighter barrel with no undue effects? Are you loading the ammo or buying box ammo? Either way.... you what you have here is another variable. In years past I've run ball ammo and handloads with match bullets thru the same gun. Keep in mind ball ammo is machinegun ammo basically. Bullet quality isn't the greatest and ammo quality overall isn't the same as box match ammo or handloads. So running ball ammo... it is what it is. In terms of accuracy and you want to run ball ammo run a slower twist rate. A 55gr ball bullet will stabilize just fine in a 12 or 13 twist barrel etc... and that can actually help the accuracy. Running that 55gr ball ammo thru a 7 twist barrel.... I've actually seen the bullets go thru the target sideways at a 100 yards. It has happened to me. This is due to the quality of the ammo/bullet. I shot handloaded 52gr Hornady boattail hollow point match bullets thru the same gun on the same day and thru a rack grade Colt 1-7 twist barrel it would hold 3/4moa. Same accuracy as the 69gr SMK's where giving me.
You want a jack of all trades... run a 1-9 twist barrel. It will handle up to a 70gr bullet and help with shooting the lighter weight bullets as well.

Basically, I’m wondering how close a 12-13” premium (CLE Bartlien or the like) could get to 16” barrel velocities. All of course being able to work within the same parameters. You don't get to eat your cake and keep it too and this is a prime example. You cut barrel length and you will cough up velocity. No way around it. We did a while back make some AR15 barrels for a special forces unit (I'm using that term loosely as I'm not going to say who exactly). This unit was going to be deployed back to the same area they were at before in Afghanistan. The fighting they did in this one town/province area... that once they ran out of the ammo for the 308 guns and all they had left was the AR15/M4 type guns they coughed up so much velocity with the 14.5" factory barrels didn't make the guns as effective etc...so they asked us to make them a 12" barrel (going totally off of memory with out looking up the order/emails etc..) and they wanted to still make 3000fps. I said no matter what we do that isn't happening. I'd stick with the 14.5" barrels and we made them .218" bores if I recall correctly and we put in 223 Wylde chambers vs a Nato chamber spec. We actually made the blanks and rough turned them and I had Paul at Craddock Precision finish them up. They told me the velocity was coming in at 2995fps if I recall correctly. The guns shot great accuracy wise (which was almost a given vs the factory mil spec barrels) and it helped them deal with the bad guys at extended ranges.

So that is the other thing you have to consider.... and that is the chamber spec. The actual chamber can have an effect on pressures and velocities as well and not just the bore and groove size.

I'm not a overall fan of tight bore barrels and running box ammo. You can have pressure issues and you might not have pressure issues. Just too many variables. Also the tight bore barrel will not guarantee better accuracy or longer barrel life. It might help accuracy if the bullet diameter that you have with your bullets are undersize but that's all I'll say. I use to run .218" bore barrels here and when I was at Krieger but it can create pressure issues. I would tell you not a great idea if your running box ammo. Handloads is one thing but box ammo is another thing.

I've got two reg. SBR's built. Both are 11.5" barrels. Why... because I'm running Surefire Suppressors on them and wanted a shorter barrel length. I'm running standard .219" bore and .224" groove size. 5R rifling and both have 223 Wylde chambers in them. Accuracy is great and the velocity is good but it's not going to be like a 16" or 20" barrel. If I recall correctly box Hornady 75gr match ammo was only giving me 2400-2500fps. I don't shoot light bullets at all on a regular basis. Maybe once in a blue moon. If I'm down to ball ammo.... it's going to be because.... it's an emergency.

Later, Frank

Once again...

Answers to questions I never would have thought to ask reveal that a man doesn't always know what he doesn't know....