Why is F.P.S. so much different than Reloading Data

[Crapshoooter2]

Hi Crapshoooter2 again with a reloading question. I'm new to reloading but have gone thru all the reloading steps for the last three months. Decided to do my first reloads using Lyman 50th year manual. I have a bolt action, 26 inch Krieger bull barrel 1:12 twist. I decide to start with a Sierra 55 gr and a Sierra 52 gr. All cases are trimmed to 1.750, full sized and loaded with Benchmark powder. I started at the suggested starting grain per the load data for each bullet 52 gr bullet 23.1 grains of powder, 55 gr bullet 22.7gr. Bullets set so that O.A.L. was to data spec. 2.250 and 2.260 respectfully. No problems chambering or extracting, cases were new. I used two scales, one digital and one balance beam, calibrated and trickler to check each load to a pretty accurate like charges for each round They all fired fine with nice groups. I did not use a chronograph because of range conditions, so I don't know the F.P.S.

Yesterday I load 5 rounds of the 52 and 55 with 24.6 gr of powder. Why? Because I just wanted to see how the two bullets compared using the same amount of powder. This was still well below the Max Load as stated in the load data which was 25.7gr for 52 bullet and 25.3gr for the 55 bullet. Went to the range and used chronograph to check the loads. Also took 5 rounds of Hornady 55 gr SP manufactured ammo.

Fired the rounds and recorded the F.P.S. Went I got home and compared the recorded speeds to the load data speeds, I was some what surprised.

The load data said that the 52 gr bullet at max powder load 25.7gr would be around 3251 F.P.S. and the 55 gr bullet at max powder load of 25.3 would be 3137 F.P.S.

My reading at 24.6 grs were 3390 F.P.S. for the 52 bullet with a Standard Dev. of 40 and 3333 F.P.S. for the 55 bullet with a Std Dev of 36.The Hornady manufactured rounds of 55gr SP stated 3240 f.p.s. on the box and registered 3194.


My question is: Any ideas as to why 24.6 grs of powder was generating such faster speeds than the MAX LOAD SPEEDS listed in the load data? Yes I re checked both scales.

Thank You

[Rimfire5]

I normally expect that my chronograph readings and the projected readings from load manuals will be different. The test set up used - particularly barrel length, primers, temperature, etc. will effect muzzle velocity.

My first thought is that the 26-inch barrel you are using is probably at least 2 inches longer, maybe even 4 inches longer, than the test barrel length used to create the load data that you were referencing. A 24-inch barrel would drop the estimated mv for a 52 grain SMK bullet from about 3300 to about 3250 fps. A 22-inch test barrel would yield a mv of 3190 fps. That is right in the ball park of the differences you are seeing.

My second thought is that your chronograph might be reading slightly high. It might do that if it was set up too close to the barrel and is triggering on the pressure wave instead of the bullet. There is also the possibility that the unit just reads a bit higher. Manufacturer don't precisely calibrate chronographs since the position of the chronograph from the muzzle is dependent on where the shooter sets up the unit. They get within an acceptable spec range.

My third thought is that the batch of powder might be a bit hotter than the norm for Benchmark.
Powder batches can vary as much as 10% (although they normally don't vary as much as 5%, in my experience.)

I used QuickLOAD to see what mv it projected.
There is only one 52 grain Sierra bullet (SMK HPBT # 1410) but there are 9 different 55 grain Sierra bullets in .224. I used the 52 SMK because the 55 grain bullet all may have different shapes, BCs, the amount of bullet body that touches the rifling, etc. Any of those variations can change the mv, but not as much as 100 fps.
Since you didn't specify the specific 55 gr bullet you used, it is hard to give you projections based on weight alone.

A variance of 0.010 in seating depth for that powder with a 52 grain bullet should change fps by only about 5 fps.

A temperature change of 20 degrees with Benchmark can change the mv fps by 32 fps for the 52 grain bullet. Cold drops the velocity and heat increases it. You need to know the testing temperature and the shooting temperature before you can compare predictions and results.

My last thought is that SD results of 36 or 40 fps is quite high for a set of identical loads using a chronograph.
That would mean your extreme difference from highest to lowest velocity would be around 100 fps.
Variations of that magnitude usually indicate that the chronograph is being effected by varying light or shadows, or triggering on the pressure wave.
It could also indicate that your loads are not as precise as you might think. There could be variations in neck tension of some of the loads, for example, and that will change the velocity.

When I am doing every thing right, I expect a SD of about 7 fps or less.
When I have variations, the SD climbs to around 13 to 15 fps. That is what I would expect from factory match ammo.

[Mobuck]

Every rifle barrel is different. Some may be "faster" than others.
There can be some variance in powder burn. Some may be "faster" than others.
Bullet production runs can vary in consistency. Some runs may be harder or softer than others.
You're shooting these loads from a slick 26" bore so it should be expected that velocities will be higher than from a shorter production run type bore. (this is the most likely cause).

[old roper]

Is this your rifle

https://thefiringline.com/forums/att...1&d=1551810387

pretty nice rifle

I would said difference is in the barrel. My 223 Has Krieger barrel @ 24" and you might want to get QL for that rifle.

[Crapshoooter2]

Thanks Rimfire5. As I said not having a lot of experience in reloading or using a chronograph your comments will head me in the right direction. The Lyman data states that a 20 inch barrel was used for AR-15 and a 24 inch universal receiver for non-AR type rifle. Unfortunately, now that I look at the information, they do not say which length the data published was based on. I have noticed in other reload data, the author will state "bolt" or "AR. I will watch closer at data information. The 55gr I used was a Sierra #1360 and the 52 was #1410

The Chronograph information stated to place 10 feet in front. I did not measure distance and will review instructions. I had used the graph 2 other times with no problems at a different range under good conditions, however this time I got 3 or 4 error readings indicating that either the front or back pick up did not read which was unusual. Also due to a heavy snow fall this winter, the shooting range had a snow bank (3' high which we had to shoot over) about 5 feet in front of the shooting station and the graph was a few feet passed the bank. This may have effected the graph some how. In addition the shooting stations are enclosed on 3 sides and are all hard surfaces that create one hell of sound bounce. Finally it was a very bright sunny winter morning, air temp 45. Therefore your comments about chronograph environment may be correct, have caused poor readings and will be reviewed.

Load accuracy. I must admit I was surprised to see the manufactured Hornady 55gr SP to have a better S.D. (20) than my re-loads. I will have to review my procedures to improve my level of accuracy in all areas of loading and measuring powder charges. As I said at the start, I'm new and still developing my knowledge and skill level. My accuracy might be sloppy to a skilled re-loader, therefore all of the above could have added to the load readings.

That's why forums are so helpful in pointing out a direction to look at.


Thanks Again
Crapshoooter2

[Crapshoooter2]

Yes it is my 223. Have a 204 also in similar configuration but is yellow

[Crapshoooter2]

Old Roper

is QL a barrel? Not familiar with what QL means.

Thanks
Crapshoooter3

[std7mag]

QL= Quick Load. A software program designed to compute data for reloaders.
Will compute pressures, case fill, fps, % bunrt, % of effiency and other info.
Large bullet/powder data base.
And you can tweek case volume, desired pressure, seating depth, barrel length, and more.

Most data in manuals is taken with a 24"barrel. Some are 26" (Sierra is known for this).
The closest manuals to actual velocities for me has been Hodgdon's annual updates ( magazine format usually found at gun shops, Barnes & Noble for $8.95) and Hornady.

Nosler has been likened to wishful engineering. (Only manual i've seen using a 26" barrel for 7mm-08).

[buck460XVR]

My question is: Any ideas as to why 24.6 grs of powder was generating such faster speeds than the MAX LOAD SPEEDS listed in the load data? Yes I re checked both scales.

Thank You

Lotsa ideas. Hard to prove any of them from behind the keyboard. The fact that your factory ammo registered fairly close to posted velocities tells me your chrono is probably giving you good readings. Unless you are using the exact components(including cases) and test platform as the manual, I would expect some deviation from their listed velocities. As for the "MAX LOAD SPEEDS", listed velocities in load manuals are not a max....but what they obtained using said components and powder charge. If your ammo extracted easily when using the bolt and the cases showed no signs of over pressure, I wouldn't be concerned with the velocity at all, but the accuracy. Only time a difference of velocity like what you experienced would matter to me, would be if it was substantially different from what the bullet itself was designed for.

[T. O'Heir]

Manuals reflect averages using the exact components, firearm(if there was one. Most testing is done using a Universal receiver and not actual firearm at all) and environmental conditions of the day of the test. That includes a different powder lot and usually a different primer. Every manual will be slightly different.
Hodgdon for example, used a 1 in 12 24" barrel when testing their on-line .223 data. That'll give faster velocities than a 20" barrel.
"...so I don't know the F.P.S..." Velocity is not as important as accuracy.

{Moderator edited out uninformed B.S.}

[old roper]

std7mag, thanks for posting.

[Unclenick]

Crapshoooter2,

I'll repeat several things you've already been told and add a few things in.

Barrel length:

The Lyman databook lists under its Test Specifications that Velocity and Pressure are taken from one of two guns, the Universal Receiver with 24" barrel or the AR with 20" barrel. The Universal Receiver and 24" test barrels for copper crushers and piezoelectric conformal transducers provide both velocity and SAAMI standard pressure readings. The AR normally only provides velocity data. So I would expect that all the loads and velocities you see listed by Lyman with no pressure appended came from the AR, while those with pressure information came from one of the 24" test barrels. By way of confirmation of that surmise, note that all the velocities without pressure data are consistently lower than those given with pressure in the book. That's due to the AR barrel being shorter.

In your case, adding two inches is expected to give about 50 to 60 fps added velocity, but you are showing more than that. There are several things that account for this. One is that Lyman buys powder for its testing the same as you or I do. Hodgdon says the burn rate of the Hodgdon Extreme line varies ±3% from lot-to-lot. This can easily account for your higher velocity as the worst case 6% difference works out to your bullet going 3401 fps, and you are within that range.

Additionally, while primer choice doesn't affect larger capacity case velocities a lot, in 2006 Charles Petty had a test in Handloader magazine in which a 223 firing a 55-grain bullet over 24 grains of Reloader 10X saw velocity go from 3150 to 3300 fps just by changing primer brand. So primer choice alone could raise the pressure in the 223 enough to account for your greater-than-expected difference in velocity due to the barrel. So, now you have two possible culprits.

Other factors include exact bore dimensions, how smooth or rough the bore is, and how hard your cases hang onto your bullets, and, of course, the accuracy of your chronograph. An optical chronograph within 20 fps of absolute is considered to be doing pretty reasonably well, but I've seen one instance of two different brands of chronograph (Shooting Chrony and Oehler) disagreeing by 200 fps in late day sun. The Oehler reading was reasonable but in that light condition, the old model Shooting Chrony was not.


Other stuff you should know.

All the velocities you see listed on boxes of ammunition are taken shooting one of the SAAMI standard test barrel lengths over a chronograph whose center between its screens is 15 ft from the muzzle. If you want to copy the SAAMI measurement, that's your distance. My exterior ballistics program says your bullet at your velocity will be going 4.7 fps faster at 10 ft than at 15 ft, if you want to know the effect of the distance difference on average readings.

All SAAMI pressure test barrels for cartridges to be fired in rifles are 24" except:

7.62x39 — 20"
.30 Carbine — 20"
350 Rem. Mag. — 20"
351 Winchester — 20"
44 Rem Mag — 20" (rifle only; pistol test barrels are shorter)

[Marco Califo]

Powder makers have been known to exaggerate FPS for marketing purposes, like when introducing a new powder. What you can do is cross check with bullet makers data, and you may see some differences. I will mention CFE223, but do not have a specific example at my finger tips on my phone. Remember Who is selling What when considering one more truthful than the other.

[Bart B.]

Any ideas as to why 24.6 grs of powder was generating such faster speeds than the MAX LOAD SPEEDS listed in the load data?

Commercial canistered lots of powder can have a 4% spread in charge weight to produce a given velocity in a given barrel.

SAAMI specs for commercial barrel bore and groove diameters have a .0030" spread. Tight bores cause higher pressure and velocities for a given component set. SAAMI specs for test barrels is .0005" spread.

Case necks gripping bullets very tight cause higher velocity and peak pressure than those barely holding the bullet. No standard exists for commercial and hand loaded ammo for force required to push bullets out of case necks. Military ammo has such specs called bullet pull or extraction force.

A given rifle and ammo will produce higher velocities held hard into the shoulder than very soft or in free recoil. More noticable with larger cartridges and heavier bullets in lighter rifles.

[RC20]

About fell out of my chair when I saw Bart B post.

I cross checked to be sure it was not an archive that snuck in.

Bart: I am getting better and braver. Doing some 7 and 10 shot strings, under 1/2 MOA.

[Unclenick]

The powder in this instance is Benchmark, which is a Hodgdon Extreme powder. Hodgdon has put in their print manual previously that their Extreme line of powders is held to a burn rate tolerance of ±3% and is temperature compensated. The same manual said their IMR powders are held to ±5%. I don't think anything other than surplus bulk powder varies more than that these days.

10 ft spacing for a chronograph works most of the time, but there was one instance on the board where a fellow working up loads for his 338 Lapua Magnum had to move his chronograph to 18 feet from the muzzle before false triggering stopped. I default to having the center between the the two sky screens at 15 feet which is what SAAMI uses as standard. For a handgun, 10 feet is fine.

When you set a chronograph up over a light surface like snow, you run the risk of the light reflected off the snow causing a glint on the bullet surface that can make the start screen or the stop screen trigger too early. It is best to have a dark surface like grass under it or to have some black plastic trash bags with you that you can place under it.

Check the operating temperature specification for your chronograph. Many are made with consumer grade components that are not guaranteed to operate reliably below the freezing point of water (32°F or 0°C). If you have snow I assume it is at least pretty cool here you are and that might compromise accuracy.

Yes! It's good to see Bart posting again.

[Jim Watson]

You may just have the proverbial "fast barrel." Vagaries of dimensions and surface finish make a lot of difference.

I have a pistol with "fast barrel." I am loading it 6% lighter than for three others of the same caliber for the same Power Factor.

None of my rifles are close enough to what the book uses to tell whether they are performing to spec. I just read the velocity, plug it in, and adjust the scope.

[44 AMP]

Quite literally every different factor you can think of is at work here, and probably some you can't think of.

You get differences in the velocity literally because every thing about your rifle and ammo is or could be different to a degree than the rifle and ammo used in their testing.

Some guns are faster than others. Some are faster with some loads and not with others. Several of the factors have been mentioned, and almost any combination of factors is possible.

I shot a lot of ammo over a chronograph, shot a lot of different stuff from the same guns, shot a lot of the same stuff from different guns. Its ALWAYS different.

If you get exactly what the book says, its serendipity. If you get close, its usual. If you're within 100fps or so, its normal. If you're further outside that, its unusual, but not unknown.

I've see 100fps difference between 3 guns with the same barrel length shooting the same ammo. (and no it wasn't what the book said, either)

Eventually I reached the point where I felt knowing the exact velocity was irrelevant, and I put the chrony away. Haven't even seen it in over a decade.

Ever cook anything where the directions on the box tell you heating times may vary because ovens vary? Guns are kind of like that, too.

[Bart B.]

Originally Posted by Marco Califo

Powder makers have been known to exaggerate FPS for marketing purposes, like when introducing a new powder.

Got any proof of that? Or is it an opinion based on assumptions?

[Unclenick]

I certainly don't believe so. The powder companies normally use SAAMI standard velocity and pressure barrels that have hand-lapped bores that have to meet a minimum cross-sectional area requirement and have chambers cut to the SAAMI minimum size with a tolerance of -0.0000 +0.0005 inches. They are fired using a technique that ensures the powder is back over the primer. These things are done to try to get a worst case high pressure (and velocity), with the expectation all but some custom guns with tight bores or special chambers are going to get lower pressure and velocity. The bottom line is they are simply tighter than most production guns. Bullet makers often use production guns for load development.

Incidentally, if you do have an exceptionally tight gun, even at the same barrel length, you can get higher pressures and velocities than the powder company data. It's not so common, but it happens and has been reported in posts here, on occasion.

[old roper]

The barrel OP has is Match Grade Kreiger and they do offer option on Match Grade.

Like I posted back in March I have Kreger 24".

[Unclenick]

Old Roper,

Not sure what your point is.