3447 f/s out of a .300 win mag

[canadianloader]

I am loading .300 win mag for a H.S precision rifle I am useing 74 gr of H4350 fed. 215 primers and rem. brass and a 168 gr barnes xxx bullet speers manual#13 showes a max charge of 75 gr @3174 f/s and barnes manual #3 showes a max of 73 gr @3152 f/s as of yet I see no signs of high pressure but velocity is alot higher than listed averege of 3447 for a 10 shot string. Any comments as to why the increased speed help put my mind at ease.

 

[Third_Rail]

What barrel length was the test gun (should be in there with the load data) and what barrel length is your gun?

 

[R.W.Dale]

How far away is your chronograph, It needs to be at least 20 feet away or it'll read part of the muzzle blast and give you errornious readings.

 

[canadianloader]

barrel length on my rifle is 26'' test barrel is 24'' chrony was @ 15' away

 

[lonniemike]

I'd think that you going really fast. I don't know what kind of accuracy your getting with that loading but if I were still looking for a a more accurate load, I'd probably work down. How are the primer pockets holding up? How many times have you reloaded the brass at 3400+fps?best-o-luck

 

[Stinger]

You are using one grain less of powder, and getting 300fps more velocity.

I don't care what the brass, primers, bullets, or your mother, looks like.

STOP!!!

Something is wrong. Check your chronograph for accuracy with a known weapon. If it is correct, you are WAY over max, and risking serious consequences with every shot.

However, I bet your chronograph is off somehow, and the load is safe.

You did climb the ladder and work this up, didn't you?

 

[Ol` Joe]

Velocity and pressure are related!

The fact you are finding velocities almost 300 fps higher then the manuals should tell you the pressures your rifle produces with the components you are useing is much higher then the manual writers found in theirs. I don`t know how much higher yours are but I would bet next weeks check they are more then most would want to subject their rifle to repetitivly. The added barrel lenght might add 100 fps to the load but I would guess it is more likely about 50-75 fps if you cut it and recorded the result. The crony position isn`t going to make much difference either, 20 fps maybe. I`d drop back a few grains to where the velocities matched the book a bit closer and stay at that point.
Keep in mind the books are only reports of what someone else found with their components, in their rifles, and in their test conditions. These are "suggestions" and not cut in stone. The rifle, component lots, test conditions, ect, you are useing are definatly different then theirs. Powders can vary by up to 10% between lots of the same powders. bullets change geometry over time, case volume varies. This is the reason all books tell you to work up your loads and stop at signs of pressure. Extra velocity is a sign of of pressure! Keep it safe, an extra 1-200 fps never made a lick of difference in how a load performed on game, and the trajectory improvment isn`t more then an inch at 300 yds, if that, I`d guess.

 

[canadianloader]

I have worked up to this load in half grain increments starting with 70 grains of H4350 velocity is usually higher by 150-170 f/s than what the manuals show.My last 5 shot group measured in at just over .5''.What is usually the first sign of to high of pressure?

 

[lonniemike]

Non-linear response to added powder with either higher or lower vel that expected.
Primer pockets opening up
Any measurable casehead expansion
Being 300fps over the 'book' top velocity
Hard to open bolt
Flow marks in the case head

Did none of your other loadings(like say the ones around 3000-3100fps or even a little lower) have no accuraccy potenial?

As others mentioned, are yor sure your chrono is giving good reads?
best-o-luck

 

[ID_shooting]

back it off a touch if nothing else then to save your barrel. That much flame forced down a .308 sized hole will wear down the throught much faster than normal.

 

[canadianloader]

Chrono is a range supplyed device so I'm assuming i't good. Every load I have put through my H.S is so far is under 1'' bolt has been easy to open on all loads the highest case exp. is under .004'' primer pockets are still tight after 5 reloads. brass shows no shiny spots and still geting black residue at the case neck.

 

[Ol` Joe]

A tight custom chamber won`t show pressure like a factory one will. The early signs are as listed above, bright marks on the case head, cratering / primer leakage, sticky extraction, poor case life, and faster then normal velocity. Pressures don`t usually show these signs until they are above 70K PSI in most rifles (factory) according to what I have been told.

I have a RSI Pressure Trace http://www.shootingsoftware.com/pressure.htm That I have been playing with lately. Every time I exceed the BOOKS velocity by any notable amount the pressures are above what they were when I ran FACTORY ammo through my rifle. I don`t count the readings my unit gives as PSI I look at them as pressure "units" and try a couple of factory loads to get a idea of what SAAMI psi looks like in MY rifles. I then try to stay at or below this number.

I have had loads that read about 6% pressure units over factory in my 25-06 and gave velocties of 3500 fps with a 100 gr bullet in a 24" barrel. These loads didn`t show ANY pressure signs except primes were starting to flatten. The case ejected fine, no bright spot on the head, ect. They were too hot though! I only fired two of them and have tore down the rest of the cartridges I had. The load was 54gr of R22 with a Sierra bullet. Not a max load according to the books. The book max velocity was 3400 FPS for this bullet under 55.8 gr of powder (max) and from a 26" barrel. My load should have ran ~3300 fps with 2" more barrel then I have and the 54gr of powder I used.

I have seen similar results in my 270 Winchester. If velocities are much over what the book says they should be for a max load with that bullet / powder then I feel very safe believing pressures are well over SAAMI recommended psi too. This isn`t saying the books are wrong in their data. Most of the time they are very close and some loads are even a little on the light side. I take the variations to be from the differences in powder, bullet and case lots I have from what was used by the writers of the book.

Here is a related artical on pressure by Denton Bramwell, I believe from Varmite hunter magazine. Note that in it is the claim Hodgdon figures 0.0005" case head expansion from one fireing is too much and Vernon Speer claimed any measurable expansion is excessive. This is a bit less then your measured 0.004".
http://www.shootingsoftware.com/ftp/dbramwell july 19 04.pdf

 

[Johnny Guest]

Well written, friends!

canadianloader, as I read your initial post, I began mentally composing a reply with all manner of cautions and suggestions. I'm glad I read the entire thread before I started typing, though. The other members have written all I could have said, and more besides. Thanks, guys.

Just to repeat, though - - You have a nice rifle there and there's no earthly reason to use up the barrel any quicker than need be. That last couple of hundred feet per second is bought at a very dear price, in terms of throat wear. If you're getting the same accuracy at, say, 3200 fps, this would probably increase useful barrel life by some large percentage. Sorry, I don't have exact figures, and I won't make 'em up just to stress a point. My estimates and foggy old memory wouldn't be FAR wrong, but I still couldn't give cites. If you take the time to do the research, there are plenty of articles and forum discussions about the effects of increased temperatures and pressure on throat errosion and barrel wear.

We'll be interested in the load you end up choosing for general use.

Best of luck
Johnny

 

[redneck2]

There was an article in Handloader some time back titled "Pressure Guessing". They used a variety of rifles and calibers to verify pressure signs we typically rely on.

Bottom line was that some firearms show absolutely no typical signs until well over SAAMI limits, some showed signs under SAAMI limits. Remember, these were conducted in major laboratories, not by Bubba out at the range.

Depending on velocity isn't 100% accurate, but it's the best you've got unless you get a chrono that has a pressure trace.

Every time you fire a rifle over designed pressure limits, it stresses the metal excessively, kinda like bending a coat hanger. You can do it once, twice, maybe twenty times. On the 21st, it snaps.

Snapping with a .300 WM involves 70,000 psi behind significant sized chucks of steel a few inches from your head.

 

[canadianloader]

Thank you for all the replys I think I will back off a bit keep velocity in and about 3200 f/s maybe a bit less and leave it at that.

 

[canadianloader]

Any idea how many f/s per grain I will drop using this powder in this load anyone?

 

[R.W.Dale]

Instead of guessing you need to back the throttle off by dropping your load by at least 10% and start by chronographing that. With the chrony at least 20' away.

 

[Ol` Joe]

There is no way to know how much velocity you`ll lose per grain without cronographing. I peeked at the newest Speer & Sierra books though and Speer shows a 168 gr bullet with 71-75 gr of H4350 as giveing 2984-3174 fps with a 24" barrel. Sierra lists a 165/168 gr with 65.9-73.8 gr of IMR4350 ( no H4350 listed) as giveing 2900-3300 fps out of 26" barrel. Speers 4 gr of powder seems to give about 47 fps/gr. Sierras 7.9 grs gives about 50 fps / gr. The best guess I can give when looking at these is you`ll need to drop about 4 gr to lose 200 fps. Remember this is just a wild guess I nor anyone else I know can tell you this will follow true with your rifle.

 

[GooseGestapo]

I'm going to deviate from the consensus in saying that you've probably got a number factors contributing to the 'high' readings.

First, I'll venture that the chronograph is giving erroneous readings.
I've seen this with my Chrony brand chronograph and my Savage .300 RUM.
I have to set it out past 30' to get accurate readings. With 100.0gr of Retumbo under a 180gr bullets, there is a LOT of muzzle blast! I know that with nominal loadings of a .22-250 and 40gr bullets that it's "close" on accuacy to over 4,000fps. Just not unless the screens/unit is further away with the "cannon".

Second, you are running high pressures as well, as others have stated. A "fast" barrel usually is accompanied by a "tight" chamber. As with the above mentioned Savage, it has a 26" bbl, and had "issues" due to abuse by previous owner not knowing that the extractor was factory installed backwards and using a steel rod of some description to drive the cases out. I had to polished some nasty gouges out of the chamber, and now have a very smooth chamber that dosen't show the usual pressure marks except for the "burnishing"of the case heads.

This rifle, too, "peaks" on pressures before max loads are reached. The above mentioned load of Retumbo is 1.0gr below the book max loads, but is "OVER MAX" in my rifle. I know, because the chrono still says high 3,300 to 3,400fps which is about 100fps faster than it should be. Everything is "about right" at 98.0gr for 3,200fps which duplicates factory ammo. It sure does shoot good groups with the 100.0gr load though. I plan on rechecking it when the temps cool down, as the above data was derived with temps in the high 80's to mid 90's (in the shade!).

So, do as others have suggested and back it down a bit.

In the last dozen or so years, I've seen more rifles "peak" before listed max's are reached than in the previous 30yrs. The tighter tolerances allowed by latest manufacturing techniques is the reason I believe this is happening.

Tread carefully.