20" Barrel powder loads for 223 and 308

[WT1]

Most of the load data in my books is for 26" barrels but what about 20" barrels? Should someone decrease the powder charge accordingly by 1 grain, for example, or something like that, so that unburnt powder isn't going out of the front of the barrel?

Does anyone have any technical experience with that?

In other words, I should think it would be more efficient to have the powder burn up right at the end of the barrel for the best flight of the projectile. In a 26" barrel I would think it is still burning until inch 25 or thereabouts and so if you put the same load in a 20" barrel, you'd have extra powder flying out of the front of the barrel for no reason.

Or, what is the actual order of events? Does the powder stop burning midway through the barrel as pressure builds, etceteras?

Thanks.

 

[clcustom1911]

I wouldn't even begin to concern yourself about anything you're asking about. Unless someone has some serious testing equipment, there is no way to say at exactly what point in the barrel the powder stops burning. Use the data in the books. You're only losing a little bit of speed from 26 to 20".

There is, however, a relationship between the powder burn rate and projectile weight for safe operating pressures. For example, in the same barrel length a 55gr projectile in 223 can take advantage of the faster H335 powder, 62gr can take advantage of slightly slower BLC2, but a 77gr projectile is better suited for the even slower burning AA2520.

The powder and bullet companies spend lots of money and time testing various bullet and powder combinations for those books. No need to unnecessarily re-invent, or overly complicate, the wheel

 

[WT1]

I wouldn't even begin to concern yourself about anything you're asking about. Unless someone has some serious testing equipment, there is no way to say at exactly what point in the barrel the powder stops burning. Use the data in the books. You're only losing a little bit of speed from 26 to 20".

There is, however, a relationship between the powder burn rate and projectile weight for safe operating pressures. For example, in the same barrel length a 55gr projectile in 223 can take advantage of the faster H335 powder, 62gr can take advantage of slightly slower BLC2, but a 77gr projectile is better suited for the even slower burning AA2520.

The powder and bullet companies spend lots of money and time testing various bullet and powder combinations for those books. No need to unnecessarily re-invent, or overly complicate, the wheel

Thank you. That is what I figured and have been prescribing to but in the interest of efficiency figured I'd ask. I mean two fewer grains on a 308 load means another few rounds or so per pound of powder, maybe, that type of thing, and then of course efficiency itself.

 

[Steel head]

Thank you. That is what I figured and have been prescribing to but in the interest of efficiency figured I'd ask. I mean two fewer grains on a 308 load means another few rounds or so per pound of powder, maybe, that type of thing, and then of course efficiency itself.

Even if he powders is all burned up the the residual pressure will accelerate the bullet till it’s low enough that friction and any other resistances overcome it.
In a 223 I like powders like TAC and 8208 because you don’t get space issues like varget.

 

[Doom]

Powder burn is not an issue. What does happen is the faster powders reach maximum pressure quicker. The result is faster powders will have lower residual pressure and temperature at the muzzle exit. Hence lower recoil and muzzle flash.

As a RSO, I see a lot of powders shot in many rifle and can testify to this.

While I haven’t seen it tested, I think faster powders will loss less velocity per inch of barrel length than slower powders.

Use the cartridge specific powders, but try and stay towards the faster powders in the recommendations.

 

[TheOfficeT-Rex]

As an academic question, I think there is an argument for faster powders in shorter barrels (within a certain burn speed range) to preclude any burning outside the barrel. It should save some muzzle flash and fouling, although pressure curves are an important consideration in gasser function. I think GRT will calculate powder burnout on the pressure curve, but I haven't gotten around to playing with it myself.

As a practical question... I think it depends more on specific firearm function and performance. If you're penny pinching grains, you'll be making certain compromises.

 

[Barelstroker]

I've used AR 2219 with 130 & 135 grn projectiles in my 20" 308 Win with very good results.
AR 8208 also works very well with the 130 & 135's & with 150 & 168 grn.
8208 is an extremely versatile powder with a huge range of compatibility & very easy to keep in the upper pressure regions of most cartridges of 308 size. 8208 seems to be very stable at extreme pressure regions with the ADI hand loaders guide showing powder charge weights with the highest pressure listings of most of the projectile weights it is suitable for.
ADI's pressure listings tell me that 8208 must be very stable & does not readily enter the exponential gradient transition region from conflagration to detonation.

 

[Doom]

On a similar note, staying on the lighter end of projectile weight helps since by nature the powders tend to be faster.

I normally load my 20” 308 with 168SMK and IMR 4064. The rifle seems happy with it but it also likes 8208XBR which is faster. I tried 2000MR which is slower, and while it is accurate the muzzle blast is ridiculous. Recoil much more noticeable

 

[TheNatural21]

Powder burn is not an issue. What does happen is the faster powders reach maximum pressure quicker. The result is faster powders will have lower residual pressure and temperature at the muzzle exit. Hence lower recoil and muzzle flash.

As a RSO, I see a lot of powders shot in many rifle and can testify to this.

While I haven’t seen it tested, I think faster powders will loss less velocity per inch of barrel length than slower powders.

Use the cartridge specific powders, but try and stay towards the faster powders in the recommendations.

This. In a shorter barrel you should still stick with what is in your load manual. Out of those options try the faster burning powders. They'll burn more completely making it a more efficient use of powder and it will reduce the fireballs.

 

[WT1]

This. In a shorter barrel you should still stick with what is in your load manual. Out of those options try the faster burning powders. They'll burn more completely making it a more efficient use of powder and it will reduce the fireballs.

And by faster burning powders, is it signified by faster speeds in fps? Or what am I looking for?

 

[WT1]

At this point the powders I've used which seem to have been effective are Varget, of course, IMR 4064 and 3031, as well as Winchester 748. They all seem to be fairly accurate with 748 seeming to have more recoil. Barrels are 308 1 in 12 and 1 in 10, and 223 1 in 9. Projectiles are various 168's and 69 grain SMK's in 223 or 55 grain varmint tipped type bullets.

 

[Barelstroker]

And by faster burning powders, is it signified by faster speeds in fps? Or what am I looking for?

Can be but if the powder is on the upper limit for the projectile weight, velocities are usually decreased when compared to a more optimum burn rate powder.

 

[TheNatural21]

And by faster burning powders, is it signified by faster speeds in fps? Or what am I looking for?

If you do a Google search for powder burn rate chart you'll find info published by the powder manufacturers. It's usually just a list with the fastest at the top and slowest at the bottom. So go down the list until you see one that your loading manual says is good for the cartridge/bullet combo you want to use.

 

[WT1]

If you do a Google search for powder burn rate chart you'll find info published by the powder manufacturers. It's usually just a list with the fastest at the top and slowest at the bottom. So go down the list until you see one that your loading manual says is good for the cartridge/bullet combo you want to use.

Thank you. Looks like 3031 is the fastest powder I've been using while Varget, 4064, and 748 are all about the same.

 

[Barelstroker]

You can easily tell what the comparative burn rate is when looking at the load recipes in any of the manuals ; i.e. Hodgdon, Sierra, Hornady, ADI etc. The powder load listings will generally run from fastest to slowest or vice versa & you'll notice the powder charges decreasing or increasing with the burn rate.
In general, the faster the burn rate of the powder, the lower the charge weight recommendation because the faster burn rate has a faster pressure rise time &, the projectile takes time to accelerate so, if the powder burn rise time is too fast for the projectile weight, the projectile acceleration rate is too low which creates a situation similar to a plugged barrel however, it's not as straight forward as this & it is not linear either.
This is why it is VERY important to stick very closely to book recommendations because the burn rate of powders is NOT constant & changes with varying conditions, temperatures & pressures & is not a linear function.

 

[Barelstroker]

One very important safety condition to keep in mind is the charge weight to case volume ratio.
Regardless of the book recommendations, it as always best to choose a powder weight recommendation which fills the case to at least 70 -75% of the case volume. This is important for two reasons.
The 1st & by far the most important reason is that by choosing a powder weight which fills the case to 70 -75% will ensure that you do not accidentally double charge the case without making a mess & the double charge will be noticed immediately.
The 2nd reason is that in most situations, a low case volume of powder does not generally perform well.

 

[bobke]

AR Comp. Most weights in 223, lighter weights in 308 ie 155’s. Also works very well in 6.5 Grendel and lighter weights-120/130gr in Creedmoor. Told will work in 22-250, and have done some limited testing in a 35 REM 14” Thompson Contender barrel. Temp stable and low burn temp relative to its competitors with similar burn rate. Pretty broadly usable.

 

[TheOfficeT-Rex]

The 2nd reason is that in most situations, a low case volume of powder does not generally perform well.

The phrase you're looking for is detonation or secondary explosion effect.

 

[WT1]

I have always charged within published ranges. Just wondering if there is some formula based on barrel length or some adjustment that can be made to increase performance and efficiency. I.E., shorter barrel length, less powder by perhaps one grain per inch of barrel, that type of thing. Doesn't sound like such a computation exists, though.

Thanks for all the input.

 

[Barelstroker]

I have always charged within published ranges. Just wondering if there is some formula based on barrel length or some adjustment that can be made to increase performance and efficiency. I.E., shorter barrel length, less powder by perhaps one grain per inch of barrel, that type of thing. Doesn't sound like such a computation exists, though.

Thanks for all the input.

Well I'm not aware of anything like you've described.
It's basically the choice of faster or slower powder burn rates.
If you think about it, a faster burn rate which burns at 100% or close to 100% makes more sense than a slower less efficient powder which only offers a minimal increase in velocity.
The other aspect is that the listed velocities are for the particular barrel length listed.
For example, I achieved higher velocities with 150 grn projectiles using BM 8208 than with AR 2208 in my 20" barrel however, the book lists higher velocities with 2208 than 8208 through a 24" barrel.

 

[r.tenorio671]

...OP, might want to read up in the CMP forums what folks in the "Service Rifle" class use for powders, at least for the .223 as they typically use 20" bbls. I don't know enough about those comps to say if they are using M110's, but there is alot of load data available for the M14's in 7.62.

 

[Doom]

For an understanding of burn rate and pressure behavior it can help to read up on reloading for the M1 and to some extent the M14/M1A as these are rifles that have gas ports where pressure is critical as too much at the gas port can wreck the operating rod. Also a good place for a beginning reloader to learn about rifle powder behavior is "Hatcher's Notebook" which can be found online. While written during the M1903 and M1 era much of the information is still worthwhile.

 

[Alaska]

308 Win Bolt Guns
IMR 8208 most excellent with 130/155 weights
IMR 4895 / Norma 202 very good with 150/155
Benchmark good with lighter bullets
H322 another good powder with lighter bullets
RL 15/ 4064 / Varget/ Norma 203B / N140 good with 165/180