Velocity and primers

[bulls n bucks]

I am wondering if any knows how much different brands of primers can affect velocity. I worked up a load for my Winchester m70 in 30-06 from the hornady 9th edition for 165gr the same barrel length the same case the same everything except I used cci 200 and the book called for federal primers. The book velocity was 2900fps and mi e was 2760fps. Can a primer affect velocity that much or are the books that far off?

[USSR]

Short answer: No, your difference in velocity is not a result of using a different primer. Velocities in reloading manuals are simply the result they got with a particular firearm on a particular day. Barrel quality and barrel length are the more determinate factor. As an example: I have 2 .30-06's both with 26" barrels. One is a stock Winchester Target rifle, and the other is a match rifle with a Krieger barrel. With the very same load, the match rifle does 2950fps, while the Winchester Target rifle does 2875fps. Hope that helps.

Don

[Unclenick]

It's possible the primer is to blame, but unlikely. I have seen documented velocity change with small rifle primers in a small case (.223 Rem) of about 5%, but that was going from a Federal standard SRP (lowest velocity) to a hot magnum primer (forgotten whose). I've never seen large rifle primers make that much difference, though trying a magnum primer would be a reasonable step for you to take in the .30-06 as there is a fair amount of room in there. Just see which primer produces the lowest velocity SD, and it is giving you the most consistent ignition.

USSR is correct that difference in chamber size, exact bore diameter and firing conditions like outside temperature are common causes of this sort of velocity difference. Another factor in this case, however, is the style of manual Hornady publishes. They throw all their 165 to 168-grain bullets together and give them all the same velocities with the same loads. That won't be what actually happens. They will have stopped working that load up with the highest pressure-producing bullet in the bunch. That is likely to be the GMX solid. I don't know which bullet you have, but if it isn't that one I would not be not surprised it comes out somewhat slower owing to having lower start resistance for the burning powder to build pressure against.

[bulls n bucks]

Ok so my next question is how would I start to get a load at least up to factory ammo velocities? I would think that it shouldn't be a problem to get 2800fps out 30-06 with a 24 inche barrel with 165 grain bullets.

[sako2]

use a different powder

[old roper]

Hornady loads are first shot, pressure gun SAAMI Spec barrel/chamber, then shot model 70 for velocity. I got Hornady new manual and the list WLR primers for 30-06.

[hounddawg]

15 LRP's tested, 35 FPS extreme spread

http://www.targetshooter.co.uk/?p=1471

[USSR]

use a different powder

Yep.

Don

[Unclenick]

Old roper,

It's the other way around. They worked up the load in the model 70 watching for pressure signs and then pressure tested ten rounds of the hottest load they developed with a powder to make sure none of them goes over the SAAMI MAP. If one does, they drop back to the next velocity step. Sierra does the same thing. Hornady's print manual (9 or 10) thanked other companies for the loan of test barrels to make that manual possible. They probably only own pressure barrels for the chamberings they manufacture ammunition for. The conformal piezo transducer test barrels are expensive and have limited life, like any barrel, so firing all the loads for each chambering would probably cost them an average of around $3K-5K per chambering, making their manual impractically expensive to produce.

Originally Posted by bulls n buck's

k so my next question is how would I start to get a load at least up to factory ammo velocities? I would think that it shouldn't be a problem to get 2800fps out 30-06 with a 24 inche barrel with 165 grain bullets.

Since you haven't told us what specific bullet or powder you are using we can't really address that question very well. I can only suggest that when you look at the Hodgdon site you will see both IMR and H 4350 get to over 2930 fps with a 24" barrel and Superformance gets to 2972 fps. These are with a Sierra SPBT bullet, which may be close to the bullet you are using (I don't know unless you tell us), suggesting you should be able to work up to 2800 fps just fine with a cup and core construction bullet and one of those powders.

Hodgdon also has data for the Hornady GMX and it does, indeed, hit its pressure limit with several grains less 4350 than the Sierra bullet does, indicating a charge acceptable for it will not produce maximum safe velocity with the standard construction bullet. This is the problem I was trying to explain with the multiple-bullet-per-load type of manual.

[old roper]

Nick, page 85/86 from Hornady manual #10 .

When possible, loading data was fired in a special firearm designed to measure pressure. There is a description of a pressure gun in the illustrated Glossary in of the Hornady Handbook. The barrel and chamber dimensions are carefully produced to exact SAAMI specifications. Data is generated until maximum pressure, determined by SAAMI,is reached. These various loads are then tested fired in a commercially available firearms for (VELOCITY). The powder charge and velocity chart in Hornady Handbook were derived from those test firings.

In some calibers and for some cartridges, pressure barrels were not available. We developed and tested loads in these situations by employing a factory or custom firearm and examining the brass case and fired case extracted from chamber. The brass case will show several indications of increasing pressure. One is case head expansion as measure by good micrometer and compared to fired, factory loaded cartridge. Other pressure signs of significance were crated or flattened primers, brass flow into ejector slots, case head separations, as well as difficult case extraction.

We employed the procedures above only when we have no other options. The vast majority of the data in this book was derived from use of strain gauges.

All testing of this reloading data was done at 70 degree Fahrenheit. Higher temperatures usually increased pressure and velocity. Lower temperature generally lower pressure and velocity.

[Unclenick]

Old roper,

They've changed procedure, then, from the one described in older manuals. I note their mention of the use of strain gauges to measure pressure. That is not the SAAMI method and I am guessing it is a workaround they came up with to avoid investing in the expensive SAAMI standard conformal piezoelectric transducer pressure and velocity test barrels. It is an even more interesting change than I expected because if only the pressure is tested in their strain gauge-equipped test barrel, the test barrel length does not have to conform to SAAMI standard pressure and velocity test barrel length, either.

I'm going to hazard a guess that what they've done is buy precision barrel blanks with SAAMI standard-compliant bore and rifling dimensions, but cut them up shorter than SAAMI standard to get more pressure test barrels out of each blank. That's what I would do, anyway. They then just need a precision reamer made to SAAMI minimum dimensions to chamber each one. If they complied with SAAMI standard barrel lengths, then they could just take the velocities from them, too, and not need to shoot the factory gun data.

Incidentally, the strain gauge method is very good. Dr. Lloyd Brownell used it in his famous 1965 study of absolute pressures in rifle barrels, and Denton Bramwell showed the method to be statistically more repeatable than either copper crushers or conformal transducers. I would be interested to learn if they are calibrating them hydraulically, like a piezoelectric transducer. Harold Vaughn showed how to do that in his book, Rifle Accuracy Facts.

Bramwell also showed the old case head expansion method to be very unreliable (cartridge case heads are not calibrated, after all, and differ from one make to another) but I can understand it is necessary to rely on that for chamberings for which no pressure standard exists. There are a number of obsolete or formerly obsolete cartridges out there for which there really is none.

Anyway, thanks for correcting my out-of-date statement and alerting me to the changes. I learn something new every day.

Here's a good article on SAAMI from a couple of years ago, and it mentions how the early organization eliminated a lot of old loads and chamberings from the outset. It also states the test barrels, less the transducer, are $1500 each. Neither lasts forever. IIRC, the transducers wear out every 4-5,000 test firings, so it is an expensive process. A strain gauge can be got for about $10, though it takes a bit of skill to apply it and solder leads to it. Gauges with pre-soldered leads and strain-relief and connectors are about $25. You can buy your own strain gauge pressure instrument from RSI. Their product is called Pressure Trace.

Getting back on topic, if you detect a velocity difference due to a primer, a good rule of thumb, because these changes are small, is to divide the square of the higher velocity by the square of the lower velocity, and then square the result. You can figure your peak pressure has changed about that much.

[Reloadron]

I am wondering if any knows how much different brands of primers can affect velocity. I worked up a load for my Winchester m70 in 30-06 from the hornady 9th edition for 165gr the same barrel length the same case the same everything except I used cci 200 and the book called for federal primers. The book velocity was 2900fps and mi e was 2760fps. Can a primer affect velocity that much or are the books that far off?

I can't say much as to brand difference other than there will be a difference in brisance. Here are some interesting images of primer flash test from our friends at 6mm Bench Rest.

A few years back I ran some different primers using identical loads through a built up Remington 700 series action with a 26" barrel. Here is what I ended up with, all of the primers were CCI. I was not as concerned with my groups as getting the shots over the chronograph so the groups are not great. The images are mine and linked to my domain but if anyone wants them, have at it.







Not really much difference on the chronograph and the CCI #41 (magnum priming charge) turned in the slightly higher velocities. The cartridge was 223 Remington.

Ron

[hounddawg]

Nice group on the CCI 41. What did you end up with for a final avg speed for that load ? When you broke 3400 it really tightened up

Oh and for the OP my own limited personal tests have also shown it is minimal but can help with group tuning just like in Rons example

[Reloadron]

Nice group on the CCI 41. What did you end up with for a final avg speed for that load ? When you broke 3400 it really tightened up

That group averaged about 3418 FPS but I wasn't really focused on my groups that day so I can't in all honesty say the CCI #41 primers were responsible for the better group. I also can't honestly say faster was better. Maybe when the nice warm days of summer return I can try some of this again. Next time once the chronograph is planted I can focus on the target.

Ron

[bulls n bucks]

That's a good point my load is 57.0 grain of IMR 4350 with hornady sst 165 grain with hornady brass seated to book recommended col with CCI 200 primers shooting out of a Winchester model 70 with a 24 inch barrel

And how would I find load data for each different bullet?

[Unclenick]

There is load data for different bullets in many places. Each powder brand has load data associated with it and they usually include several brands of bullets. I use Hodgdon's data frequently. Each bullet maker also has load manuals just for their bullets.

[bulls n bucks]

Yeah I looked at hodgdons site and all they had was Sears game king or hornady gmx so could I use the data for the game king with a sst

[Unclenick]

The Sierra GameKing data will be close. The capacious 30-06 case is less sensitive to bullet differences than some others, just as long as the basic construction is the same, and that will be the case for the GameKing and SST data, since both are jacketed lead core bullets. Just start with the bottom load and work up in steps of about 2% of the maximum load while watching for pressure signs. When you find you guns maximum from pressure signs or reach the maximum load without pressure signs, you can mess with tuning the loads to get the smallest groups if you are not satisfied with anything you found along the way.