I have been doing some load developement the last few days, with my chrony and serious bench time (both benches). The rilfe chambering in both cases are a custom 350 Remington Mag, and a factory 338 Winchester in a Remington 700.

I shot a short series with the 350 and a non published load with Varget and new cases using 225 Sierras. These loads ran from 2730-2745. Outdoor temp was probably 75 ish. I used the same cases and the dies were not touched. Same exact load, same can powder, scale not moved, etc. I got 2802, 2807, and 2794 for three today. Morning air temp was about the same.

The 338 Win Mag I used Weatherby cases and RL-22. Another slightly over book load that showed no signs of pressure. I shot a 225 Hornady. New cases averaged 2853 fps. Same cases and loads (once fired) yielded 2925 fps. No blown primers, extractor marks, easy extraction, etc. I am not asking your opinions of my loads or choices to exceed published loads, I am inquiring if this is common, if this is a normal increase and why the increase if anyone can explain?

My only explanation would be an increase of "useable" energy, not being wasted fire forming the new case to the chamber, and being used to force the bullet out????

It is possible that your barrel was at a different temperature. Barrel temperature is an important, and often overlooked, variable in pressure and velocity.

Another is a difference in lighting conditions. In my experience, the chronograph will read about 50 fps lower with clouds, vs. straight sunshine.

I'm sure there are other possibilities, including simple, normal random variation. A three shot string is not very "strong" statistically.

Temps may be similar but "barometric pressures" may be different and that would account for some discrepancy in the data. Been there, done that!!! I try to keep accurate data from all different test sessions and use an "average" of the velocities to figure click charts, etc. I have seen the exact same stuff you are speaking of (75-100fps) from one day to the next using smaller calibers (222Mag, 6x47, 243, 6mm, 25-06, 260, 7mmMag) so I think it has more to do with the prssure than the temp. Doesn't mean the chrony is off!! Just my 2Cents worth!! GHD

I have noticed the same increase in velocity with the same load in fire formed brass as compared to unfired brass in my 300 Win Mag.

My best guess is that the forming of the case lowers the breech pressure enough to produce the slightly lower velocities in new cases.

Regards,
hm

A member of Hunt America did this test last winter and the thread is there. www.huntamerica.com

I have found the same thing.

[ 05-10-2003, 22:14: Message edited by: MePlat ]

I went to the range one day with my Oehler chronograph, set it up, and fired 20 rounds of a new, experimental 200-grain load in my .30/40 No.3 Ruger. I got velocities of over 2800 FPS AVERAGE with this load, and it was very accurate as well!! Suspecting something bizarre, I went home, reloaded the brass with the exact same (weighed) load. The next day, at about the same time in the morning, I went back to the range, and tested this 20 rounds again. They averaged UNDER 2600 FPS!! Same load, same brass, same box of Sierra bullets, same powder out of the same can, same chrono, same lighting conditions, same temp., etc. ???? The only thing that did not change was the accuracy - exactly the same (about .75" for three round groups). Started with a clean, cold barrel each day.

[ 05-11-2003, 00:51: Message edited by: eldeguello ]

Jesse,
I've experienced the same thing. I noticed the same degree of change happens with the same rifle everytime the same make of case is used. Change case brands, change the velocity spread. I tried using fired cases that had been full length resized and the same results occured. I'm of the opinion that the difference is the energy loss in reforming the case to fit the chamber. In my '06, which has a tight chamber, the change in velocity is around an average of 27 fps. In my .308, whose chamber it not as tight, its about 50 fps. From the difference you are getting, your rifle chamber sounds as if it's on the large side. Like the shade tree mechanic, there's not a lot of science in this, just some observations. I hope this is of some help. Good luck.

[ 05-11-2003, 01:42: Message edited by: BigBob ]

This is a common occurrence. Rick Jamison writing in Shooting Times once stated that pressures increased every time you reloaded brass ad infinitum. I think he speculated it was hardening of the brass. Didn't believe him, and I don't like most of what he says so I had a friend with an Oehler model 43 run some tests on this. He verified that pressures DID increase at the first reload after fire forming, but remained the same thereafter. He posted the results in that forum where the question arose. That has been my own experience straight across the board on the first reload after fire forming.

As speculation I've believed the reason is that the slop in the new brass when fireforming, acts as a shock absorber of sorts, using some of the energy to expand the brass and spreading the pressure over a bit longer time frame thereby reducing both velocity and pressure. Since not much forming is done on the second and subsequent reloads, all the pressure and energy is utilized by the projectile which increases the velocity.

A-Square did some research on this, and their take on it is that the brass is work hardening.
A-Square says the problem is in the case neck.
I have found this to be true.
My own custom 338 Ultra is a good example of this.
The chamber was cut tight on a no go gauge( I think I have that right) and is a crush fit on factory brass. The brass doesn't blow out very much at all so the case body effect should be minimized.
First firing 225 X at 3005 fps std dev 4 fps.
Second firing 225X at 3050 fps std dev. 3 fps.
The third fing doesn't change much.
You will notice at 4 or 5 firings that velocity can go wild on you.
Aneal the cases and start all over again if it is a concern.

Chrono your loads again and check it out.
Remember 2 feet per second for every degree F.
Measure the temp. and do the math.
RL-22 is a little unstable in the .338 Win with regard to pressure and therefore velocity (ask Alliant on this). RL-22 has worked well in every .338 Win I've tried it in that said.
Measure your chrono to muzzel spacing an keep it the same.
good luck

Jamie

Good tips and advice from everyone. I generally half ass most of the stuff, not figuring much variance would come from it. Doubt I'll get serious enough to measure chrony to muzzle diference or barometric pressures, but can comprehend how they'd affect velocities. Just din't figure they'd more the fps that much. As I said, temp were about the same, plus or minus 5 degrees. Distance looked about the same to the chrony. As for annealing, not even interested. I need to shoot more and reload less. I have a 6.5 WSM that is a huge pain in the ass and is absolutely no fun to shoot. The chamber is too tight, the 'smith won't fix it and for $1000 or just work, my extreme spreads are still in the 40's. Accuracy blows as well.

One question on the 338. Steve's pages doesn't list velocities, but his best load for 225 bullets and the 338 Win Mag was a healthy dose of RL-25. I'd of figured this way to slow for the 338 as 4350 is usually recommended in most books as optimum. I guess that goes as well for the 6.5 WSM. I have been using RL-25 and Retumbo, but Lazzeroni uses H4350 in his with like 140 grainers. This is a big difference in burn rates, what's up???

I've been through about a dozen 338's of my own plus several others for which I've loaded. With but one exception the best performance in both 225g and 250g bullets has been with RL22. The one exception is one I have now that does real well with N160 behind 225's. Each gun will be different. Velocity just isn't there along with accuracy with any 4350 I've ever tried as much as I'd love to use the Hodgdon Extreme. Great accuracy with IMR4831 but way slower than RL22. Since there isn't much difference in burn rate between RL25 and RL22 I'm sure some rifles would respond real well to RL25. With the universal success with RL22 I've just not done much with the other and the little that I've done sends me back to RL22.

Great thoughts and info there Bob. Do you find velocity over or at 2900 to be rare in your guns??? Most writers admit that the 338 is underloaded and can be leaned on a bit. I was not really looking to push the envelope for max speed, but the fast RL-22 load is pretty accurate, less than 1 inch, versus a one hole group for H4350 at a pokey 2745 fps

Also were you not the guy that was building a 338 WSM a year ago? I have no desire for one as the 350 Remington is cruising at 2800 with 225's, but I am interested in the progress and velocities.

Right on all counts.

The WSM was about 2 years ago. That rifle has scored 3 elk and one mule deer since then, one elk a 368" gross. Velocity is way less than a 338 Win Mag though quite adequate. I'm building another right now on a Montana Rifles action. Without checking my records I believe the best velocity I got from 225g bullets was 2820fps, mostly near 2800. If you do a Search at HuntAmerica, the story behind that one is there, including load development.

Re the Win Mag, the N160 behind a 225g Nosler gives 2920fps measured on an Oehler 35P. A couple of others went at near 2900fps and the others varied from there down to 2800, so yes, 2900 or more is rare and that is absolute max. If I could get one hole groups even down to 2700fps I'd sure take them in preference to larger groups at 2900, particularly with H4350. You lose quite a bit of velocity to the cold with most propellants, but not the Extreme line. At zero temps I'd bet the velocity of the H4350 load you have would at least equal most other propellants. I think that RL22 and the Win Mag are a perfect marriage in moderate temperatures. I've never had one fail to shoot with that propellant.

I know from calculating power transistor temperature that thermal conductivity is a function of surface area and contact pressure.

My thought is that once fired brass has more contact area and more contact force than unfired brass.

That would make the powder temperature asymptotically approach the chamber pressure faster in formed brass.

Ammo in a hot chamber has velocities rising as a function of time in the chamber. The formed ammo has a faster rise rate than the unformed.

Clark-

I am a transplant to NM with a college education. We have the lowest education level in the US. I'll have to reread your post and really think about what just happened!!!! I can figure it out if I think about it. Just busting balls pard! I just reread, you are member number 1, you must be smart.

He said tight brass shoots faster than loose brass! . . . .I think!

Thanks for the attention
Yes, my idea came from an email to me from Bart Bobbit who is a famous
good shot:

> I've noted that in 1K-yard matches, for every 15 seconds over 30
> seconds I leave the round in the hot chamber, I have to come down
> 1/4th MOA on the sights so that shot doesn't go high.
>
> And if I have to wait for more than about 5 minutes to shoot again,
> the chamber temperature has dropped enough that the powder
> temperature will be lower and the next shot will be low if I don't
> come up on the sights to compensate. There's been folks at the
> Nationals who've had perfect scores going but had to cease fire for 5
> to 10 minutes because a boat was in the impact area. When firing
> was resumed, their next shot would be a 9 out the bottom. If the
> delay is over 10 minutes, they usually give competitors one sighting
> shot because of this situation. But one shot won't heat up the
> barrel back where it was and one may have to compensate for this
> situation, too.
>
> Bart

I think that a tight fit of neck sized brass conducts heat faster which
makes the powder heat faster which is more likely to increase peak
pressure which is more likely to increase velocity which is more likely
to have a higher point of impact.

I am suspicious that FL sized ammo being more accurate than neck sized
can be detected only with very careful setups:

1) Groups beyond 100 yards where change in velocity caused dispersion.
2) Expensive stress relieved barrels that warpage is not so big it masks
powder pre heat effects.
3) The shooter, ammo concentricity, scope, etc must be very good.

Or someone with a chrono might see the difference.

Or a temp probe into two cartridges and a scope or Voltmeter and stop
watch to record the rise time of powder temperature

Another of Barts emails confirms he also is of the opinion that full
length sized is best:

>> Why do you think your full re sized handloads more accurate than
>> neck sized?
>
>
>
> They shoot smaller groups.
>
> I've tried every neck-only sizing technique around; none shoot as
> accurate as full-length sizing properly done. And I've typically got
> better accuracy from new cases over neck-only sized fired ones.
>
>> What is the mechanism?
>
>
>
> I don't know why. Except that the shoulder on a rimless bottleneck
> case must not be set back more than two-thousandths of an inch. Case
> diameters must not be sized below fired diameters more than about
> two-thousandths. I don't use expander balls; the die's neck is
> lapped out so they aren't needed. Bolt face must be perpendicular
> with chamber axis, not the bolt axis, so case heads stay square.
>
> Martin J. Hull, Sierra Bullet's longtime ballistic man who did
> virtually all their load development for all their bullets in all
> kinds of rifles (plus one of the best highpower rifle competitors on
> this planet) has this to say. In all the thousands of rounds in all
> calibers he fired testing loads for accuracy, the best results
> occurred when the case fit the chamber like a "turd in a punch bowl."
> That means full-length sizing so the case has a bit of room around
> it. He never got neck-only sizing to shoot as well as full-length.
> But full-length sizing has to be done right and most folks don't do
> it right, so they get better results by neck-only sizing.
>
> But if anybody gets better results by neck-only sizing than they do
> with full-length sizing, that's fine by me.
>
> Best regards,
>
> Bart

Good comptetition shooters don't chamber a round unless they are ready to shoot. If they hold the shot longer than about 10-15 seconds they'll eject and put in a cool round and let the warm one cool down. If you leave it in the chamber too long it will shoot high, the reverse of what your friend says with a cool barrel.

Only question I'd ask is why do you think the BR shooters get those tight groups when they don't even size their cases at all? If you get tighter groups with FL sized groups than neck sized, there's something wrong with the marriage of brass and chamber.

Bob338,
Good point, all I can do is think out loud.

It could be that I a wrong about temperature change rates.
Because of spring back, there is only touching at the shoulder, and most heat conduction must go through the convection air gap between case and chamber.

It could be the accuracy advantage to FL brass is all concentricity and uniformity of the brass.

The benchrest brass is extremely uniform and only stretches over the
spring back distance.

The non benchrest brass expands further [passed yeild], and may expand more in the thin
spots, making the thin spots thinner and leaving the thick spots alone.
The thick and thin spots do not spring back uniformly and create an
eccentric condition internally and externally on the case. FL sizing
reverses this process as the thin spots are easier to compress.