30-06 AI - Weird Pressure Spikes

[Brian in Montana]

Working on a load for a 30-06 AI. Seems to have a couple of potentials, but I had an odd thing happen yesterday when shooting some test groups. I don't think I've seen something quite like this, and I still consider myself having lots to learn about handloading. So here's what I got:

Trying 165gn Accubonds on top of H4831sc. Fire formed Remington brass with Fed210M primers. The test loads come from flat spots in a ladder test, which showed no particular pressure signs. Same thing about a week ago, I shot a few test groups and had no pressure signs. So, yesterday. One group was loaded with 61gn. I usually just shoot 3 shot strings initially, but I just happened to have one extra casing, so I loaded it with this group. So you'll see from the pic, 3 shots touching and one about an inch to the right. The flier was the 4th shot, kicked noticeably harder, extracted rough and the extractor nicked it good.



My next test group was nothing special, but then I got to 62.5gn. Last week I shot 62.4gn and it grouped about .65", but I thought it might tighten up a tad more with a nudge, so I went .1gn higher. So on 62.5gn, 2 shots were in the same hole, the 3rd was low/right, and like the other flier, it showed pressure signs the other casings didn't.



I'm just not sure what to make of this. The only environmental difference is it was a bit warmer. I believe it was in the 30's when I shot the ladder test, but yesterday was pretty warm, about 60. But if you believe the advertising, H4831 is an "extreme powder" and should not be effected by temp changes.

Thoughts? Ideas?

 

[BackofBeyond]

Any chance at all you missed your charge weight? How about any chance you seated that bullet deeper? What’s the relation between seating depth and your lands?

 

[Brian in Montana]

Starting .02" off the lands. I don't think there could have been a problem with seating depth, but I'm using a Hornady Autocharge which I suppose could have malfunctioned, although I'm always very meticulous about letting it warm up and calibrate it before using. Its never failed me in the past.

 

[Nicoli7153]

Was the barrel allowed to cool between shots? I've heard that putting a round in to a hot chamber can change the volatility of the powder causing the velocity to increase. Think the extreme powders were designed not to decrease velocity in cold weather, e.g. Varget

 

[winmag]

Was the barrel allowed to cool between shots? I've heard that putting a round in to a hot chamber can change the volatility of the powder causing the velocity to increase. Think the extreme powders were designed not to decrease velocity in cold weather, e.g. Varget

That’s where my thought process went as well. Cooking a round in a hot chamber for a while will spike pressure.

Otherwise some error in the loading process. Wrong charge weight, large rifle mag primer instead of large rifle, 180gr projectile instead of 165gr, etc. Not trying to imply you’re a poor handloader here, just brainstorming.

Neck tension wouldn’t do it. If you were closer to the lands I’d believe the hot ones were jammed and the others weren’t.

How did you fire form to AI? Are they all uniform?

 

[BackofBeyond]

Starting .02" off the lands. I don't think there could have been a problem with seating depth, but I'm using a Hornady Autocharge which I suppose could have malfunctioned, although I'm always very meticulous about letting it warm up and calibrate it before using. Its never failed me in the past.

Measuring C.O.A.L or base to ogive? Any chance that there was a meplat off so you ended up with one jammed into the lands?

I don’t know. I’m just tossing spaghetti at the wall seeing what sticks.

 

[p_ham]

At that charge weight you should have a ways to go before you hit pressure.
The rounds that threw fliers, were they at all tight closing the bolt? I've had shoulders not get pushed back far enough and throw false pressure signs along with wild fliers.
I could see too if the necks are too long they could protrude into the throat and act like a super crimp under pressure.
Were you using a chronograph?

 

[Brian in Montana]

Measuring frome the ogive.

I let the barrel cool between groups, but not individual shots. One thing I've noticed about that H4831, it certainly heats up the chamber and barrel on any rifle I've used it in. I'm inclined to think it could've been that. Especially on the 61gn group, if memory serves, I chambered it right after 3 shots and sat for a minute while I let a gust of wind settle, so it could've sat in there and got the powder pretty warm. Still, Ive not seen that effect before, and I've used H4831 a lot in .270, .280 Rem, and .280 AI, just not in 30-06 AI. Also, about 60gn is about as high as I usually go, and with relatively light bullets.

 

[cahunter805]

Are you measuring shoulder bump when sizing? I also agree it could be the round heating up in the chamber or it could just be a few bad cases. I’d throw those 2 cases away also.
Id load another test group at each charge and see what happens.

 

[WyoDoug]

Sounds to me you had a few rounds loaded slightly hotter than you realize. Powder loads need to be carefully measured with as much precision as you can get with very little deviation between cartridges. Otherwise you will get stuff like this.

 

[ImBillT]

Working on a load for a 30-06 AI. Seems to have a couple of potentials, but I had an odd thing happen yesterday when shooting some test groups. I don't think I've seen something quite like this, and I still consider myself having lots to learn about handloading. So here's what I got:

Trying 165gn Accubonds on top of H4831sc. Fire formed Remington brass with Fed210M primers.

Throw all Remington brass in the trash (except perhaps Remington BR brass that was made for forming the original 6BR).

I’m shooting 61gr of a slightly faster powder behind 190gr VLDs in my 30-06AI, so I don’t think you should be getting pressure signs behind a 165 with 4831SC.

 

[ImBillT]

I believe it was in the 30's when I shot the ladder test, but yesterday was pretty warm, about 60. But if you believe the advertising, H4831 is an "extreme powder" and should not be effected by temp changes.

Thoughts? Ideas?

Hodgedon Extreme powders are less temperature sensitive than most powders from their era and before. LESS TEMPERATURE SENSITIVE does not equal NOT EFFECTED BY TEMP. Many newer powders have similar temperature sensitivity, and some have inverse sensitivity(RL-23). Nonetheless, you’re only talking about 30deg difference. I don’t think powder is your problem. I would look at your brass first.

I have no experience with the Hornady auto scale, but that could be a problem.

A 30-06AI is obviously a wildcat, so that does bring chamber specs into question. Measure the neck diameter of a fired case, and then measure a BUNCH of loaded rounds(AND THE TWO CASES WERE HOT WITH A BULLET SEATED IN THEM) If any are within .001” of the diameter of a fired case neck, you could have a neck clearance issue.

Going from jumping to jammed can cause pressure spikes, so if you were just looking at mild pressure signs, I would consider your seating depth to be an issue. .002” off the lands is great if you have legit March grade bullets or if you sort them by BTO. Pulling Hornady’s out of the box won’t work though(even their match bullets which shoot very well). They are going to have more than .002” variation in that box. If you set them .010”-.015” off the lands, they would almost certainly all jump. At .002” off the lands you will almost certainly have the occasional bullet be slightly jammed. That will cause a pressure spike, and often cause a flier. That said, I would not expect a noticeable difference in felt recoil. The difference in felt recoil makes me thing of something more like a significant increase in powder charge or lack of neck clearance on the chamber.

 

[cowboy]

The Ackley cartridges have a tendency to not show indications of gradual pressure increases like more conventional shoulders - when you hit the high end of pressure threshhold they can have a drastic spike. This can be caused by lots of different reasons.

With that said I will assume that all your reloading procedures and components were in order, were correct and were the same.

If you fire formed brass - it takes at least 2 firings to fully form your brass to your chamber. I’ve seen 3rd time reloads be considerable faster than the first 2 reloads.

How many rounds down your barrel? Some barrels I’ve seen have gotten close to a 100 fps increase after somewhere in the 100 round mark down the tube after break in.

How clean was your barrel? Any chance you have enough rounds down it that you have a carbon ring forming? This is one of the first things I’d look at if you feel all reloads were the same.

I wouldn’t trust any powder today from any manufacturer without working up slowly. A reloading manual, the internet, or any friends advise is only as good as the lot number of powder that they used compared to what you are using. Any different rifle I work on, any change in powder lot numbers I always use a chronograph to see what the reloading combination gives me.

I have shot a 280AI for many years using H4831sc pushing a 168 gr bullet. I had one lot of powder that I had to reduce by 1.6 gr to get to my original desired velocity. The 280AI is nothing more than a ’06 case necked down to .284.

In summary:
- Double check your component procedure and check your powder thrower. Weigh the same charge a half dozen times and see what your scale is telling you.
- Be aware of how many times your brass has been reloaded
- Are you over 100 rounds down this barrel or there about and did the pressure happen in that area.
- You have a higher than average chance that you might have some copper or carbon build up in your barrel.
- I wish I knew what your velocity was - it’d be a much better indication of where you’re at on the high end rather than using a gr. of powder amount. Do you have a chronograph or access to one?

By the way - is your barrel a factory or custom barrel? If it’s a custom barrel, or a factory barrel that was reamed out, I’d be talking to your gunsmith. The 30-06AI is not a SAAMI cartridge and there are a lot of variations in reamers for non SAAMI cartridges. You could have a tighter than normal throat.

 

[Brian in Montana]

I'm thinking the most likely cause is the chamber cooking them before shooting. I do remember I had both those shots in a hot chamber longer than I usually would.

So about that, educate me a bit on Hodgdon Extreme powders. Is it design more that it won't be effected in cold, but heating it up might different?

 

[Brian in Montana]

Also, this rifle does have a very little free bore.

 

[winmag]

So about that, educate me a bit on Hodgdon Extreme powders. Is it design more that it won't be effected in cold, but heating it up might different?

Most powders increase in pressure and velocity when fired at hotter temperatures (temperature of the powder itself, pre-ignition, within the loaded cartridge). Some powders, specifically older ball powders, may approach sensitivity as high as 2fps per degree Fahrenheit.

Temperature stable powders such as the Hodgdon extreme line may only change in velocity by 0.1 or 0.2fps per degree Fahrenheit. You can see how this aids in long range accuracy in temperature extremes and would be beneficial for a hunting rifle that gets used in different climates.

Usually velocity/pressure increases with temperature, however some powders actually show the inverse, gaining velocity/pressure as the temperature decreases.

 

[cahunter805]

Also, this rifle does have a very little free bore.

Is the freebore shorter than SAAMI? 62.5gr is book max for a 30-06ai according to Nosler.

 

[brocksw]

Sorry, if i missed it, but how are you measuring your COAL? The Hornady OAL gauge? Sharpie Marker? Removing firing pin from bolt?

 

[ImBillT]

I'm thinking the most likely cause is the chamber cooking them before shooting. I do remember I had both those shots in a hot chamber longer than I usually would.

So about that, educate me a bit on Hodgdon Extreme powders. Is it design more that it won't be effected in cold, but heating it up might different?

Hodgedon Extreme powders are less temperature sensitive than most other Hodgedon powders. Most powders will show increased velocity and chamber pressures as temperature increases. Some powders do this quite drastically. RL-17 and RL-22 were known for that for a while, as were most spherical powders. RL-15 didn’t have as large of pressure increases as most other powders. The Hodgedon Extreme line all features a specific additive that reduces the amount of pressure increase as temperature increases. Some of the newest powder additives actually cause pressure and velocity to increase as temperature DROPS, but with all of these powders, the amount of pressure change vs temperature change is much lower than with older powders.

You will still see pressure increase as temperature increases with Hodgedon Extreme powders. It just won’t be as large an increase as with most of the powders that are not in their Extreme line.

 

[ImBillT]

Is the freebore shorter than SAAMI? 62.5gr is book max for a 30-06ai according to Nosler.

Nosler’s data for the 30-06AI is quite possibly the worst batch of loading data I’ve ever seen. I started with it, and boy was it NOT EVEN CLOSE for three different powders.