Max Chamber Pressure

[English Rifleman]

I have noticed that Hornady state the maximum chamber pressure for Bolt Guns is 62,000psi and GasGuns 52,000Psi

This makes me ask the question
1. what pressure is Hornadys Factory loads loaded at.

2. Does Hornady state why the gasguns handle less pressure.
(is this a gas system issue or a Bolt / Battery issue)

[grayfox]

It is a bolt thrust issue, this 52 ksi is the same limit as its parent, the 6.5 grendel.
Both have a lower max due to greater surface area of the 0.441 cartridge base, meaning more thrust onto the bolt and lugs during the shot and before unlock.
Bolt action guns don't have that limitation of course.

[English Rifleman]

Thank you for that great explannation.

[Fmuguira]

Since Hornady can’t control what type of action/firearm their leaders axed 6 ARC gets used in it would be my guess it’s the 52K pressure limit. I know their factory ammo runs 100-120 fps under their advertised velocity when ishoot it through my 22” bolt gun.

Your asking the same question/s I ve wondered !

[762nato]

Most likely test with a 24" barrel, that would account for reduced velocity with shorter tube( 40 - 60 fps in this velocity range per inch). First time I have seen 2 sets of data(other than 45 70), usually platform does not change data. Thinking higher pressure bolt gun loads will effect brass life.... Usually if it sounds to good to be true it is. We shall see.

[GRH]

The bolt face diameter for 5.56 is .384 which leaves adequate wall thickness for the locking lugs to handle 62K of pressure.

To fit a larger diameter case into the same action, the bolt face diameter is increased to .445 All other things remaining the same, that equates to removing .06 of very high strength steel supporting the locking lugs from breaking/shearing off.

As for Hornady factory ammo not a clue, neither of my barrels have seen a factory made round.

Never tried the stuff myself, but my guess would be LeverRevolution or some proprietary derivative. On paper at least, it should give about 100fps more before hitting top pressure again.

[English Rifleman]

Different question / same subject.
i would assume that at 52000 or just over pressure will not show signs in the brass / primer etc as the pressure is relitivlty low
So how do we know we have passed the 52K limit.
we cant just use generic load data for assumed limits as there setups will be very differnt from mine?

Any thoughts

[grayfox]

Velocity and pressure are closely related. You don't get one without the other.
For a given powder, bullet, and barrel length, if you are getting lots more MV than the book value for the same barrel length, powder and bullet, then good bet you are over pressure.
The 6Arc, like the Grendel, is a moderate pressure round, not a hot rod.

Alternative if you want more MV is to get a longer barrel and make it bolt action as well, so you can go up to 62 ksi. But even so it will not out-perform a 6mm creedmoor, nor will a grendel outperform a 6.5 Creed. You are getting a very effective long-range cartridge at modest powder loads in a compact, AR15 frame. Well suited for some jobs, not so well suited for others.

This last point: means you have to buy another rifle in different caliber... o my!!!
You can thank me later.

[English Rifleman]

i was asking how we find out our own pressure,
because i cant find data thats even close to my barrel / powder / bullet / case.
trying to find my first load for new rifle. so have no Mv as a guide.
so what Mv are you saying stay away from

for info
22" heavy barrel / RS52 / 107 SMK /Lapau Caase
Ooh  And NO GAS SYSTEM

[CZ527 Guy]

So are we to understand you are working with a 22" bolt action rifle?

Barrel length will have little or no effect on max pressure as upper pressure is realized in the first few inches of bullet travel down the barrel.

If you are working with a bolt action as i think, I understand. Primer protrusion & flatness would offer some strong hints. Resistance on bolt lift would indicate you have likely exceeded pressure limits.

Not sure if anyone on this side of the pond has had any exposure to RS52. See they list load data for .24 nosler with up to 100 grain bullets. Looks like burn rate may be close to IMR 4320 / Varget. for the most part I feel you are on your own with this propellant.

Would contacting Reloader swiss be a option in terms of seeking a start point?


My limited knowledge on this propellant is giving me the impression that you will not be likely able, to fit enough powder under the 107 SMK to get to max pressure for a bolt gun.

So I would reach out to the distributer & share the water capacity of your cartridge & see if they may be able to offer some insight as they likely have more experience in this matter than most if not all of us here.

Keep us posted!

[GRH]

i was asking how we find out our own pressure,
because i cant find data thats even close to my barrel / powder / bullet / case.
trying to find my first load for new rifle. so have no Mv as a guide.
so what Mv are you saying stay away from

for info
22" heavy barrel / RS52 / 107 SMK /Lapau Caase
Ooh  And NO GAS SYSTEM

 Please do not use this as good to use, it is a simulation based on my brass capacity, database bullet numbers and user compiled powder model. I took MY model, changed the barrel length, bullet and powder.

That said, the database powder model is very well represented, which means many many user submissions have been compiled together to get a very accurate powder model. Since the visual color indicator is only one step away from being 100% "green" I'd say it's a very popular powder.

Obviously, start low and work up bla bla bla... but this might help give you an idea of place to get going.    

[English Rifleman]

So are we to understand you are working with a 22" bolt action rifle?

Barrel length will have little or no effect on max pressure as upper pressure is realized in the first few inches of bullet travel down the barrel.

If you are working with a bolt action as i think, I understand. Primer protrusion & flatness would offer some strong hints. Resistance on bolt lift would indicate you have likely exceeded pressure limits.

Not sure if anyone on this side of the pond has had any exposure to RS52. See they list load data for .24 nosler with up to 100 grain bullets. Looks like burn rate may be close to IMR 4320 / Varget. for the most part I feel you are on your own with this propellant.

Would contacting Reloader swiss be a option in terms of seeking a start point?


My limited knowledge on this propellant is giving me the impression that you will not be likely able, to fit enough powder under the 107 SMK  to get to max pressure for a bolt gun.

So I would reach out to the distributer & share the water capacity of your cartridge & see if they may be able to offer some insight as they likely have more experience in this matter than most if not all of us here.

Keep us posted!

As Bizar as it might sound, No i Have an ar15 Platform. UK do not allow Semi-auto In centerfire rifles. ( In The general. although there are exeptions)

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i was asking how we find out our own pressure,
because i cant find data thats even close to my barrel / powder / bullet / case.
trying to find my first load for new rifle. so have no Mv as a guide.
so what Mv are you saying stay away from

for info
22" heavy barrel / RS52 / 107 SMK /Lapau Caase
Ooh  And NO GAS SYSTEM

 Please do not use this as good to use, it is a simulation based on my brass capacity, database bullet numbers and user compiled powder model. I took MY model, changed the barrel length, bullet and powder.

That said, the database powder model is very well represented, which means many many user submissions have been compiled together to get a very accurate powder model. Since the visual color indicator is only one step away from being 100% "green" I'd say it's a very popular powder.

Obviously, start low and work up bla bla bla... but this might help give you an idea of place to get going.

Thank you. That should really help.
At least i have a Mv Cieling now.

Many Thanks

i will post up Results once i can get time to do a load and a range visit.

[BluntForceTrauma]

Would the Reloading Data Center on Hodgdon Powder's website help? They have 6mm ARC load data with pressures listed.

[grayfox]

Sort of like GRH post, I ran a sim with some of my data, on my 22" bolt action (with press kept below 52 ksi), which could show something similar to your case. Couple of posts on Accurate shooter on RS52 powder ( another UK question) for 6mm dasher says your powder is similar to varget but has possibly more temperature sensitivity 68-90 *F. My results (disclaimers about you have to work up in your gun), showed 22" results with 107 smk of ~50ksi and 2650 fps. You will want to make sure that you don't run an over-compressed load, as results get dicey.

Having an AR frame but no gas line will perform much like a bolt action but you're still limited to 52 ksi to avoid excess stress on the unlocking lugs.

Primer flattening can be a sign of overpressure but imo not a good one to place a LOT of confidence in, since a little bit of excess headspace can also flatten primers during the shot. I can't see the MV GRH's plot is showing, but my run yields 2650 fps approx.

Mind your bolt lift... although for an "AR" style it could be stiff for lots of shots. I have 1 kali-key which turns an AR into your style (although there is a little gas bleed off) and it seems to be "stiff" - more like sticky due to some fouling - for most every shot I took (it was an 18" 300 ham'r barrel). So ymmv. i didn't particularly enjoy the 300 hamr/kalikey combo by the way.

One final thought, Hornady has a chart of MV vs barrel length, for its 108-110 gr bullets/ barrel lengths. That would tell you how much extra MV yo might see for a 22 vs 18" gas-type gun, which you could add to that page for any powder on there (gas gun is 18" data). Those extra 4" give you a boost for sure.

[English Rifleman]

Sort of like GRH post, I ran a sim with some of my data, on my 22" bolt action (with press kept below 52 ksi), which could show something similar to your case.  Couple of posts on Accurate shooter on RS52 powder ( another UK question) for 6mm dasher says your powder is similar to varget but has possibly more temperature sensitivity 68-90 *F.  My results (disclaimers about you have to work up in your gun), showed 22" results with 107 smk of ~50ksi and 2650 fps.  You will want to make sure that you don't run an over-compressed load, as results get dicey.

Having an AR frame but no gas line will perform much like a bolt action but you're still limited to 52 ksi to avoid excess stress on the unlocking lugs.

Primer flattening can be a sign of overpressure but imo not a good one to place a LOT of confidence in, since a little bit of excess headspace can also flatten primers during the shot.  I can't see the MV GRH's plot is showing, but my run yields 2650 fps approx. 

Mind your bolt lift... although for an "AR" style it could be stiff for lots of shots.  I have 1 kali-key which turns an AR into your style (although there is a little gas bleed off) and it seems to be "stiff" - more like sticky due to some fouling - for most every shot I took (it was an 18" 300 ham'r barrel).  So ymmv.  i didn't particularly enjoy the 300 hamr/kalikey combo by the way.

One final thought, Hornady has a chart of MV vs barrel length, for its 108-110 gr bullets/ barrel lengths.  That would tell you how much extra MV yo might see for a 22 vs 18" gas-type gun, which you could add to that page for any powder on there (gas gun is 18" data).  Those extra 4" give you a boost for sure.

Yes thanks
All good info.
I was talking to another shooter here in UK and hes told me to get "Quicklload" as it seems to cater for the European powders / bullets ETC.
As with GRH post of the Gordons Sim, i can see how this takes most of the guess work out.
I dont know anyone else currently shooting this caliber / platform (In UK), so i am kinda on my own at the moment.
Apart from everyone here ofcoarse.

[English Rifleman]

Quick update
I have seen that on Hornady 105 & 108 Factory Loaded ammo, the box states muzzel velocity is 2750.
So i asked Hornady (Who have allways replied to my questions ) if that is suitable for AR15 and they stated yes all under the 52000 Chamber pressure limit,
i also asked for load data, to which they pointed to the APP, so had a look at the app and for the AR15 there is no load for these bullet wieghts that gets anywhrere near the factory boxes of 2750 Mv.
I have also purchased Quickload, and the is NO comination of 105 /108 (Hornady) & ANY powder thats gets even close to 2650.
So is Hornady letting people shot there Factory Ammo at above Max Chamber Pressure.
I have re-asked Hornady but they will not reply to this question.

[grayfox]

The recorded data I have ( a brief search at 3:30 am...) for my 20" barrels (gas gun ARs) show ~2650 for both the 108 and 105 factory loads. This is in my barrels, but would translate to ~2750 for a 24" barrel, which is probably what they used for testing/benchmarking their factory loads... although I'm not sure, but 24" is the typical standard barrel length, for marketing purposes.
Also, keep in mind that they have access to a non-commercial powder, so whatever pixie dust they use, it's not found in a bottle on the shelves.
So welcome to the world of ammo marketing... yes the factory load is suitable for gas gun, but no, probably not with any powders you can get. After all, why list a 20" speed when the 24 MV is a bigger number, 'cause speed sells...
One possible exception, and I mean possible... is Lever. I've got some data for a 20" that mimics the 2650 factory speed in my 20", and that extrapolates to ~2740 in a 24" barrel... sooooooo maybe Lvr could get you "there" as far as "factory speeds.
Footnote, for several calibers, I don't typically get the 24" posted speed out of factory loads... in some of my Creedmoors I can, but other cals -- nope.

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Edit to add: to always search for the "posted factory" MV is sort of a quixotic search... sure it would be nice but they have commercial test rigs that aren't your barrel... every barrle is different. Different internals, different friction factors, different amounts of wear, different harmonics... and for hunting purposes, an extra 100 fps gets you most times about 50 yds extra distance. I don't try to hunt right at the max distance my bullet/load might be ethical, I always like some margin.
Best thing to do is to find out what speed your barrel is most accurate for, which btw is not always the fastest speed. Might hurt to admit it (and this is an IMO) but if you really need more distance you might have to bring more gun to the firing line. just sayin'.

[English Rifleman]

Thanks Grayfox
Yes you are correct the Tested barrel lenght was 24" (Sorry i thought i had included that detail )
Just so we are clear, I am not looking for silly speeds. 2600 will be enough for what i need, i was just trying to get my head around how Hornady achieve such high Mv ( Safely ), but i guess like you say, i dought there someone stood there with an ar15 shooting over a Cadwell chrono.
I have no dought whatever there test rig, it will be very well clamped down example in a tunnel,

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Hornady did finaly reply.
And as Grayfox suggested this is what they said.

""Are you referring to the 2750 on the box? if so we are capable of achieving that without pressure issues because we have access to powders and blends that reloaders do not so we can get more speed with less pressure


Hornady/SnapSafe Tech team""

Well i cant argue with that..

[alwie]

Thanks Grayfox
Yes you are correct the Tested barrel lenght was 24" (Sorry i thought i had included that detail )
Just so we are clear, I am not looking for silly speeds. 2600 will be enough for what i need, i was just trying to get my head around how Hornady achieve such high Mv ( Safely ), but i guess like you say, i dought there someone stood there with an ar15 shooting over a Cadwell chrono.
I have no dought whatever there test rig, it will be very well clamped down example in a tunnel,

---

Hornady did finaly reply.
And as Grayfox suggested this is what they said.

""Are you referring to the 2750 on the box? if so we are capable of achieving that without pressure issues because we have access to powders and blends that reloaders do not so we can get more speed with less pressure


Hornady/SnapSafe Tech team""

Well i cant argue with that..

Why cant we have the super secret powder??

[grayfox]

Can you get hodgdon's leverevolution over there? or perhaps CFE223? These 2 powders have the longest "legs" for 6Arc heavier bullets.
Also according to several users (I myself use the GRT tool, which is free), QL is difficult to set up for accurate modeling of these shorter, fatter cartridges, like Grendel and 6 Arc.
I find I have to first calibrate the model by trying to duplicate mfr load data, then re-calibrate again when I get some chrono data on my own barrel.
If you do not have a chrony, I would heartily recommend to get one. Personally I like the magnetospeed the best as it is easy to set up and portable, and doesn't require a cold firing line so you can do setup 15-20 ft downrange. Cheaper than the lab-radar outfits. But any chrony you can get will be a help.