30-06 AI - Weird Pressure Spikes

[ImBillT]

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

That’s a shame, but I shouldn’t have anything to do with your inconsistency.

I suspect your occasional pressure issues are either from A) your brass 1) causing wildly varied case capacity, or 2) occasional neck interference, or B) occasional hot charges from your automated thrower.

How many loaded case necks have you measure? Do you know which pieces of brass were the two shots in question? If so, go drop a bullet in it the neck. If you haven’t resized them, and the bullet is touching the neck 360 degrees, then you have a neck clearance problem.

 

[ImBillT]

As far as letting it sit in the barrel, I don’t think that’s too likely to be the issue unless you were shooting quite a bit and pretty quickly. I’ve left a round loaded with RL-15 in the chamber for a minute or more waiting for wind to switch during 20 shot strings. I was .5gr under a charge that would leave ejector marks. Would it print high at 600yds? Yes. Did it cause me any other problems? No. I later started opening the bolt and letting the cartridge sit on the follower if my condition didn’t come back fairly quickly just to avoid having to hold low.

 

[Mtnhunter1]

From experience, check the length of the cases in question. My guess is you will find that they are long in the neck. A few thousands over length will cause them to crimp at the throat with the bolt cam-over. This results in a very tight hold on the bullet and high pressure on firing.

 

[ImBillT]

From experience, check the length of the cases in question. My guess is you will find that they are long in the neck. A few thousands over length will cause them to crimp at the throat with the bolt cam-over. This results in a very tight hold on the bullet and high pressure on firing.

This will absolutely happen, and should probably be checked.

Ackley cartridges usually shrink when fire formed, and if trimmed to trim length before forming, will be quite short. Combine that with the fact that Ackley cartridges don’t usually grow in length very quickly, and this would not be high on my list of guesses. That said, it doesn’t hurt to check, and if that’s happening, the next firing will be even worse.

 

[RevJim]

I've owned/used 2 30-06 AIs. One was a 24" factory '06 set-back-reamed out. One was a 26" Shilen semi-custom. I never got blistering speed from anything in either. The "best" consistency I got was with the 26" rifle and the Sierra 200 SGK. It was very accurate too, but accuracy fell off at around 2675fps or so. Of all the AIs I've played with the '06 was the least rewarding, for me. Now, some guys liked the 150 in theirs and we did not have the Barnes 130 TTSX back then. That would be the one I would try first off. Good luck to you Pard.

 

[Mato]

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.

View attachment 222777

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.

View attachment 222778

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?

Speeds please?

Also, try that 62.4 load again and see if you can duplicate it.

 

[antelopedundee]

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

Even jamming bullets wouldn't ordinarily cause what you saw. Shooting on a 50 degree day and shooting on a 80 degree day is a 30 degree difference. Not a whole lot IMO. Letting a round sit in a hot chamber with brass being an excellent conductor of heat could probably easily raise powder temp close to case wall to over 100 degrees. I'd go with that as your problem.

 

[Brian in Montana]

Speeds please?

Also, try that 62.4 load again and see if you can duplicate it.

I've loaded some, but haven't gotten back to the range yet. I'm also going to shoot a string of the 61gn load as well. Going to give the chamber more time to cool and not let a round cook before firing.

I wasn't using a Chrono when I had the "weird pressure signs". I'm not planning to magnetospeed these because if they don't group I'm not really interested in they're velocity, I'll be moving on to another combo. Judging from the ladder test, 61gn should be around 2790fps and 62.4 in the neighborhood of 2880.

 

[JLS]

The chrono is to tell you if you had some weird aberration happen in your loading process. If one round is 75 fps faster, something in your process went wrong.

Speed is also an indicator of pressure. As previously mentioned, ackley cases are a little tricky to read pressure signs on.

 

[Mato]

You mentioned "weird pressure spikes"......that to me would indicate that you were clocking them.

Bottom line, pressure equals speed and speed equals pressure.

One group proves nada (by and large)

 

[Mato]

One thing I've used over the years in order for me to work had to only shoot on a cool barrel is to take a probe thermometer to the range with me.

While I'm getting things set up I set the gun in the rack and drop the probe therm down the tube. B4 I get to shooting my first group I take a reading, say it comes back at 70* or whatever number. once I'm done with my first group/string I stick the gun back in the rack and put the thermometer back down it. The temp will shoot up, I then wait until it goes back down to the original temp of 70* or whatever it is b4 I start up again.

Note...........don't forget to remove the probe therm b4 you begin your next string!

 

[manitou1]

From experience, check the length of the cases in question. My guess is you will find that they are long in the neck. A few thousands over length will cause them to crimp at the throat with the bolt cam-over. This results in a very tight hold on the bullet and high pressure on firing.

Check this ^^^.
I am working up loads for a custom and man the barrel and chamber are tight. Gave me fits. My chamber is to the EXACT SAAMI spec for brass length and my necks were too long. Might need to trim another thou or two. Actually blew two primers out of the case on different loads.
Was hitting pressure a grain under book max on occasion.
Most of my pea shooters won't show pressure signs until book max is exceeded, sometimes by more than a grain!

 

[Brian in Montana]

You mentioned "weird pressure spikes"......that to me would indicate that you were clocking them.

Bottom line, pressure equals speed and speed equals pressure.

One group proves nada (by and large)

Pressure signs on the brass.

 

[ImBillT]

I've loaded some, but haven't gotten back to the range yet. I'm also going to shoot a string of the 61gn load as well. Going to give the chamber more time to cool and not let a round cook before firing.

I wasn't using a Chrono when I had the "weird pressure signs". I'm not planning to magnetospeed these because if they don't group I'm not really interested in they're velocity, I'll be moving on to another combo. Judging from the ladder test, 61gn should be around 2790fps and 62.4 in the neighborhood of 2880.

Considering that I’m getting to 2950-2980fps with 190s using IMR-4350 in a 26” barrel, I think you should be able to substantially beat those velocities, AND to get pressure signs at those powder charges suggests that something strange is going on.

Measure case length, and some loaded neck diameters. Unless you had that barrel REALLY HOT I don’t think leaving the cartridge in the chamber a little longer than normal is your issue. Maybe it was, but why not measure some cases first?

 

[Brian in Montana]

I don't believe it was case length, but I thought I'd check that anyway. I'd tossed those 2 casings so I dug them out of the trash. I went ahead and ran them through a FL resizer, so they would have been as long or slightly longer than when I shot them. I measured their length and inside the case mouth, chambered them in the rifle, then measured again to see if there was any difference or anything indication they would crimp around the bullet when chambered. They both came out exactly as they went in. One of them was a little longer than the SAAMI max length, but only by about .002.

I can't think of another way to test that, but that doesn't seem to have been the cause. Could be some other issue with the brass, what I'm using is fire-formed Remington brass. Not the highest quality stuff on the planet.

 

[ImBillT]

I don't believe it was case length, but I thought I'd check that anyway. I'd tossed those 2 casings so I dug them out of the trash. I went ahead and ran them through a FL resizer, so they would have been as long or slightly longer than when I shot them. I measured their length and inside the case mouth, chambered them in the rifle, then measured again to see if there was any difference or anything indication they would crimp around the bullet when chambered. They both came out exactly as they went in. One of them was a little longer than the SAAMI max length, but only by about .002.

I can't think of another way to test that, but that doesn't seem to have been the cause. Could be some other issue with the brass, what I'm using is fire-formed Remington brass. Not the highest quality stuff on the planet.

If you meant to say .002” longer than trim length, then that probably isn’t your problem.

Below is the SAAMI spec for a 30-06. The lengths on an AI chamber setup by most smiths will be shorter. Because smiths often setup AI chambers on cases instead of gauges, your chamber dimensions will actually usually be .002”-.004” shorter than the CASE’S neck/shoulder junction. The SAAMI spec on that would be a minimum of 2.1016. If the case your smiths used to set that up was 2.1016, and he barely touched it, and everything else was SAAMI min, then your case mouth would be at 2.495”. However, he likely set it up to crush by .002”+ so your case mouth could easily be at 2.493” or less.

How does a bullet drop into those fired cases necks? They should drop right in. If there is friction on the bullet, the neck is too thick for the chamber, or, if the friction is only at the very edge of the case mouth, then they could be too long and are getting crimped on the bullet when you chamber them.

^^^ just noticed you resized them. Seat a .308” bullet in them and measure the OD of the necks near the mouth and near the shoulder. Then measure some fired, but not resized, brass from the same rifle. The fired brass should be AT LEAST .001” larger in diameter than the two cases that gave you pressure signs and which now have a bullet seated in them.

If it isn’t case length, or neck thickness, then I’d throw a hundred charges with your Hornady and weight them on a separate scale to see if it occasionally throws something 1gr or more too heavy.

 

[Brian in Montana]

The bullets seat into the casings smoothly, no friction or undue resistance. When I said is was .002 longer, I was talking about max length. The casing was 2.946

They chamber just fine in the rifle too.

 

[ImBillT]

The bullets seat into the casings smoothly, no friction or undue resistance. When I said is was .002 longer, I was talking about max length. The casing was 2.946

They chamber just fine in the rifle too.

They’ll chamber just fine when only .001” of the neck is getting into the throat and being crimped onto the bullet. At 2.496” I think you MIGHT be too long. Setting up for no crush on a case that was near the SAAMI min case(max is pictured and min is .007” shorter) would give you a case mouth in the chamber that ends at 2.495”. Setting up with a few thousandths crush would be shorter.

I just noticed you resized them, and edited my post to have you measure the loaded necks.

When I asked how bullet drops in, I meant by hand, not in a die. The bullet should just fall into a fired case. If there is any friction you’re in the realm of potential problems.

 

[ImBillT]

^^^ Edited that one after you read it too.

 

[Brian in Montana]

I'll try to drop a bullet into a fired casing, especially on one if I get similar fliers like what prompted this thread. I'd think, though, that chambering a resized casing would produce a measurable result if it's butting against the end of the chamber.